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See http://www.archive.org/details/steamengines00newyrich +----------------------------------------------------------+ | Transcriber's note: | | | | Inconsistencies have not been corrected (hyphenated | | vs non-hyphenated or spaced words), except horse-power | | changed to horsepower and cut off to cut-off. | | | | Minor typographical errors have been corrected. | | | | Text in italics is enclosed by underscore characters as | | in _italics_. | | | | Subscripts are indicated by _{...}, as in _{subscript}. | | | | In-line multi-line formulas have been changed to | | single-line formulas, where necessary with the addition | | of brackets to prevent ambiguity. | +----------------------------------------------------------+ Machinery's Reference Series Each Number Is a Unit in a Series on Electrical and Steam Engineering Drawing and Machine Design and Shop Practice NUMBER 70 STEAM ENGINES CONTENTS Action of Steam Engines 3 Rating and General Proportions of Steam Engines 11 Steam Engine Details 15 Steam Engine Economy 30 Types of Steam Engines 36 Steam Engine Testing 41 Copyright, 1911, The Industrial Press, Publishers of MACHINERY, 49-55 Lafayette Street, New York City. CHAPTER I ACTION OF STEAM ENGINES A steam engine is a device by means of which _heat_ is transformed into _work_. Work may be defined as the result produced by a force acting through space, and is commonly measured in foot-pounds; a foot-pound represents the work done in raising 1 pound 1 foot in height. The rate of doing work is called _power_. It has been found by experiment that there is a definite relation between heat and work, in the ratio of 1 thermal unit to 778 foot-pounds of work. The number 778 is commonly called the heat equivalent of work or the mechanical equivalent of heat. Heat may be transformed into mechanical work through the medium of steam, by confining a given amount in a closed chamber, and then allowing it to expand by means of a movable wall (piston) fitted into one side of the chamber. Heat is given up in the process of expansion, as shown by the lowered pressure and temperature of the steam, and work has been done in moving the wall (piston) of the closed chamber against a resisting force or pressure. When the expansion of steam takes place without the loss of heat by radiation or conduction, the relation between the pressure and volume is practically constant; that is, if a given quantity of steam expands to twice its volume in a closed chamber of the kind above described, its final pressure will be one-half that of the initial pressure before expansion took place. A pound of steam at an absolute pressure of 20 pounds per square inch has a volume of practically 20 cubic feet, and a temperature of 228 degrees. If now it be expanded so that its volume is doubled (40 cubic feet), the pressure will drop to approximately 10 pounds per square inch and the temperature will be only about 190 degrees. The drop in temperature is due to the loss of heat which has been transformed into work in the process of expansion and in moving the wall (piston) of the chamber against a resisting force, as already noted. Principle of the Steam Engine The steam engine makes use of a closed chamber with a movable wall in transforming the heat of steam into mechanical work in the manner just described. Fig. 1 shows a longitudinal section through an engine of simple design, and illustrates the principal parts and their relation to one another. The cylinder _A_ is the closed chamber in which expansion takes place, and the piston _B_, the movable wall. The cylinder is of cast iron, accurately bored and finished to a circular cross-section. The piston is carefully fitted to slide easily in the cylinder, being made practically steam tight by means of packing rings. The work generated in moving the piston is transferred to the crank-pin _H_ by means of the piston-rod _C_, and the connecting-rod _F_. The piston-rod passes out of the cylinder through a stuffing box, which prevents the leakage of steam around it. The cross-head _D_ serves to guide the piston-rod in a straight line, and also contains the wrist-pin _E_ which joins the piston-rod and connecting-rod. The cross-head slides upon the guide-plate _G_, which causes it to move in an accurate line, and at the same time takes the downward thrust from the connecting-rod. The crank-pin is connected with the main shaft _I_ by means of a crank arm, which in this case is made in the form of a disk in order to give a better balance. The balance wheel or flywheel _J_ carries the crank past the dead centers at the ends of the stroke, and gives a uniform motion to the shaft. The various parts of the engine are carried on a rigid bed _K_, usually of cast iron, which in turn is bolted to a foundation of brick or concrete. The power developed is taken off by means of a belted pulley attached to the main shaft, or, in certain cases, in the form of electrical energy from a direct-connected dynamo. [Illustration: Fig. 1. Longitudinal Section through the Ames High-speed Engine] When in action, a certain amount of steam (1/4 to 1/3 of the total cylinder volume in simple engines) is admitted to one end of the cylinder, while the other is open to the atmosphere. The steam forces the piston forward a certain distance by its direct action at the boiler pressure. After the supply is shut off, the forward movement of the piston is continued to the end of the stroke by the expansion of the steam. Steam is now admitted to the other end of the cylinder, and the operation repeated on the backward or return stroke. An enlarged section of the cylinder showing the action of the valve for admitting and exhausting the steam is shown in Fig. 2. In this case the piston is shown in its extreme backward position, ready for the forward stroke. The steam chest _L_ is filled with steam at boiler pressure, which is being admitted to the narrow space back of the piston through the valve _N_, as indicated by the arrows. The exhaust port _M_ is in communication with the other end of the cylinder and allows the piston to move forward without resistance, except that due to the piston-rod, which transfers the work done by the expanding steam to the crank-pin. The valve _N_ is operated automatically by a crank or eccentric attached to the main shaft, and opens and closes the supply and exhaust ports at the proper time to secure the results described. Work Diagram Having discussed briefly the general principle upon which an engine operates, the next step is to study more carefully the transformation of heat into work within the cylinder, and to become familiar with the graphical methods of representing it. Work has already been defined as the result of force acting through space, and the unit of work as the foot-pound, which is the work done in raising 1 pound 1 foot in height. For example, it requires 1 × 1 = 1 foot-pound to raise 1 pound 1 foot, or 1 × 10 = 10 foot-pounds to raise 1 pound 10 feet, or 10 × 1 = 10 foot-pounds to raise 10 pounds 1 foot, or 10 × 10 = 100 foot-pounds to raise 10 pounds 10 feet, etc. That is, the product of weight or force acting, times the distance moved through, represents work; and if the force is taken in pounds and the distance in feet, the result will be in foot-pounds. This result may be shown graphically by a figure called a work diagram. [Illustration: Fig. 2. Section of Cylinder, showing Slide Valve] In Fig. 3, let distances on the line _OY_ represent the force acting, and distances on _OX_ represent the space moved through. Suppose the figure to be drawn to such a scale that _OY_ is 5 feet in height, and _OX_ 10 feet long. Let each division on _OY_ represent 1 pound pressure, and each division on _OX_ 1 foot of space moved through. If a pressure of 5 pounds acts through a distance of 10 feet, then an amount of 5 × 10 = 50 foot-pounds of work has been done. Referring to Fig. 3, it is evident that the height _OY_ (the pressure acting), multiplied by the length _OX_ (the distance moved through), gives 5 × 10 = 50 square feet, which is the area of the rectangle _YCXO_; that is, the area of a rectangle may represent work done, if the height represents a force acting, and the length the distance moved through. If the diagram were drawn to a smaller scale so that the divisions were 1 inch in length instead of 1 foot, the area _YCXO_ would still represent the work done, except each square inch would equal 1 foot-pound instead of each square foot, as in the present illustration. [Illustration: Fig. 3. A Simple Work Diagram] In Fig. 4 the diagram, instead of being rectangular in form, takes a different shape on account of different forces acting at different periods over the distance moved through. In the first case (Fig. 3), a uniform force of 5 pounds acts through a distance of 10 feet, and produces 5 × 10 = 50 foot-pounds of work. In the second case (Fig. 4), forces of 5 pounds, 4 pounds, 3 pounds, 2 pounds, and 1 pound, act through distances of 2 feet each, and produce (5 × 2) + (4 × 2) + (3 × 2) + (2 × 2) + (1 × 2) = 30 foot-pounds. This is also the area, in square feet, of the figure _Y54321XO_, which is made up of the areas of the five small rectangles shown by the dotted lines. Another way of finding the total area of the figure shown in Fig. 4, and determining the work done, is to multiply the length by the average of the heights of the small rectangles. The average height is found by adding the several heights and dividing the sum by their number, as follows: 5 + 4 + 3 + 2 + 1 ----------------- = 3, and 3 × 10 = 30 square feet, as before. 5 [Illustration: Fig. 4. Another Form of Work Diagram] This, then, means that the average force acting throughout the stroke is 3 pounds, and the total work done is 3 × 10 = 30 foot-pounds. In Fig. 5 the pressure drops uniformly from 5 pounds at the beginning to 0 at the end of the stroke. In this case also the area and work done are found by multiplying the length of the diagram by the average height, as follows: 5 + 0 ----- × 10 = 25 square feet, 2 or 25 foot-pounds of work done. [Illustration: Fig. 5. Work Diagram when Pressure drops Uniformly] The object of Figs. 3, 4 and 5 is to show how foot-pounds of work may be represented graphically by the areas of diagrams, and also to make it clear that this remains true whatever the form of the diagram. It is also evident that knowing the area, the average height or pressure may be found by dividing by the length, and _vice versa_. Fig. 6 shows the form of work diagram which would be produced by the action of the steam in an engine cylinder, if no heat were lost by conduction and radiation. Starting with the piston in the position shown in Fig. 2, steam is admitted at a pressure represented by the height of the line _OY_. As the piston moves forward, sufficient steam is admitted to maintain the same pressure. At the point _B_ the valve closes and steam is cut off. The work done up to this time is shown by the rectangle _YBbO_. From the point _B_ to the end of the stroke _C_, the piston is moved forward by the expansion of the steam, the pressure falling in proportion to the distance moved through, until at the end of the stroke it is represented by the vertical line _CX_. At the point _C_ the exhaust valve opens and the pressure drops to 0 (atmospheric pressure in this case). As it is always desirable to find the work done by a complete stroke of the engine, it is necessary to find the average or mean pressure acting throughout the stroke. This can only be done by determining the area of the diagram and dividing by the length of the stroke. This gives what is called the mean ordinate, which multiplied by the scale of the drawing, will give the mean or average pressure. For example, if the area of the diagram is found to be 6 square inches, and its length is 3 inches, the mean ordinate will be 6 ÷ 3 = 2 inches. If the diagram is drawn to such a scale that 1 inch on _OY_ represents 10 pounds, then the average or mean pressure will be 2 × 10 = 20 pounds, and this multiplied by the actual length of the piston stroke will give the work done in foot-pounds. The practical application of the above, together with the method of obtaining steam engine indicator diagrams and measuring the areas of the same, will be taken up in detail under the heading of Steam Engine Testing. Definitions Relating to Engine Diagrams Before taking up the construction of an actual engine diagram, it is first necessary to become familiar with certain terms which are used in connection with it. [Illustration: Fig. 6. The Ideal Work Diagram of a Steam Engine] _Cut-off._--The cut-off is the point in the stroke at which the admission valve closes and the expansion of steam begins. _Ratio of Expansion._--This is the reciprocal of the cut-off, that is, if the cut-off is 1/4, the ratio of expansion is 4. In other words, it is the ratio of the final volume of the steam at the end of the stroke to its volume at the point of cut-off. For example, a cylinder takes steam at boiler pressure until the piston has moved one-fourth the length of its stroke; the valve now closes and expansion takes place until the stroke is completed. The one-fourth cylinderful of steam has become a cylinderful, that is, it has expanded to four times its original volume, and the ratio of expansion is said to be 4. _Point of Release._--This is the point in the stroke at which the exhaust valve opens and relieves the pressure acting on the piston. This takes place just before the end of the stroke in order to reduce the shock when the piston changes its direction of travel. _Compression._--This acts in connection with the premature release in order to reduce the shock at the end of the stroke. During the forward stroke of an engine the exhaust valve in front of the piston remains open as shown in Fig. 2. Shortly before the end of the stroke this closes, leaving a certain amount of steam in the cylinder. The continuation of the stroke compresses this steam, and by raising its pressure forms a cushion, which, in connection with the removal of the pressure back of the piston by release, brings the piston to a stop and causes it to reverse its direction without shock. High-speed engines require a greater amount of compression than those running at low speed. _Clearance_.--This is the space between the cylinder head and the piston when the latter is at the end of its stroke; it also includes that portion of the steam port between the valve and the cylinder. Clearance is usually expressed as a percentage of the piston-displacement of the cylinder, and varies in different types of engines. The following table gives approximate values for engines of different design. TABLE I. CLEARANCE OF STEAM ENGINES Type of Engine Per Cent Clearance Corliss 1.5 to 3.5 Moderate-speed 3 to 8 High-speed 4 to 10 A large clearance is evidently objectionable because it represents a space which must be filled with steam at boiler pressure at the beginning of each stroke, and from which but a comparatively small amount of work is obtained. As compression increases, the amount of steam required to fill the clearance space diminishes, but on the other hand, increasing the compression reduces the mean effective pressure. _Initial Pressure._--This is the pressure in the cylinder up to the point of cut-off. It is usually slightly less than boiler pressure owing to "wire-drawing" in the steam pipe and ports. _Terminal Pressure._--This is the pressure in the cylinder at the time release occurs, and depends upon the initial pressure, the ratio of expansion, and the amount of cylinder condensation. _Back Pressure._--This is the pressure in the cylinder when the exhaust port is open, and is that against which the piston is forced during the working stroke. For example, in Fig. 2 the small space at the left of the piston is filled with steam at initial pressure, while the space at the right of the piston is exposed to the back pressure. The working pressure varies throughout the stroke, due to the expansion of the steam, while the back pressure remains constant, except for the effect of compression at the end of the stroke. The theoretical back pressure in a non-condensing engine (one exhausting into the atmosphere) is that of the atmosphere or 14.7 pounds per square inch above a vacuum, but in actual practice it is about 2 pounds above atmospheric pressure, or 17 pounds absolute, due to the resistance of exhaust ports and connecting pipes. In the case of a condensing engine (one exhausting into a condenser) the back pressure depends upon the efficiency of the condenser, averaging about 3 pounds absolute pressure in the best practice. _Effective Pressure._--This is the difference between the pressure on the steam side of the piston and that on the exhaust side, or in other words, the difference between the working pressure and the back pressure. This value varies throughout the stroke with the expansion of the steam. _Mean Effective Pressure._--It has just been stated that the effective pressure varies throughout the stroke. The mean effective pressure (M. E. P.) is the average of all the effective pressures, and this average multiplied by the length of stroke, gives the work done per stroke. _Line of Absolute Vacuum._--In the diagram shown in Fig. 6, the line _OX_ is the line of absolute vacuum; that is, it is assumed that there is no pressure on the exhaust side of the piston. In other words, the engine is exhausting into a perfect vacuum. [Illustration: Fig. 7. Constructing a Steam Engine Work Diagram] _Atmospheric Line._--This is a line drawn parallel to the line of absolute vacuum at such a distance above it as to represent 14.7 pounds pressure per square inch, according to the scale used. Construction of Ideal Diagram One of the first steps in the design of a steam engine is the construction of an ideal diagram, and the engine is planned to produce this as nearly as possible when in operation. First assume the initial pressure, the ratio of expansion, and the percentage of clearance, for the type of engine under consideration. Draw lines _OX_ and _OY_ at right angles as in Fig. 7. Make _OR_ the same percentage of the stroke that the clearance is of the piston displacement; make _RX_ equal to the length of the stroke (on a reduced scale). Erect the perpendicular _RA_ of such a height that it shall represent, to scale, an absolute pressure per square inch equal to 0.95 of the boiler pressure. Draw in the dotted lines _AK_ and _KX_, and the atmospheric line _LH_ at a height above _OX_ to represent 14.7 pounds per square inch. Locate the point of cut-off, _B_, according to the assumed ratio of expansion. Points on the expansion curve _BC_ are found as follows: Divide the distance _BK_ into any number of equal spaces, as shown by _a_, _b_, _c_, _d_, etc., and connect them with the point _O_. Through the points of intersection with _BP_, as _a´_, _b´_, _c´_, _d´_, etc., draw horizontal lines, and through _a_, _b_, _c_, _d_, etc., draw vertical lines. The intersection of corresponding horizontal and vertical lines will be points on the theoretical expansion line. If the engine is to be non-condensing, the theoretical work, or indicator diagram, as it is called, will be bounded by the lines _ABCHG_. The actual diagram will vary somewhat from the theoretical, as shown by the shaded lines. The admission line between _A_ and _B_ will slant downward slightly, and the point of cut-off will be rounded, owing to the slow closing of the valve. The first half of the expansion line will fall below the theoretical, owing to a drop in pressure caused by cylinder condensation, but the actual line will rise above the theoretical in the latter part of the stroke on account of re-evaporation, due to heat given out by the hot cylinder walls to the low-pressure steam. Instead of the pressure dropping abruptly at _C_, release takes place just before the end of the stroke, and the diagram is rounded at _CF_ instead of having sharp corners. The back pressure line _FD_ is drawn slightly above the atmospheric line, a distance to represent about 2 pounds per square inch. At _D_ the exhaust valve closes and compression begins, rounding the bottom of the diagram up to _E_. The area of the actual diagram, as shown by the shaded lines in Fig. 7, will be smaller than the theoretical, in about the following ratio: Large medium-speed engines, 0.90 of theoretical area. Small medium-speed engines, 0.85 of theoretical area. High-speed engines, 0.75 of theoretical area. CHAPTER II RATING AND GENERAL PROPORTIONS OF STEAM ENGINES The capacity or power of a steam engine is rated in horsepower, one horsepower (H. P.) being the equivalent of 33,000 foot-pounds of work done per minute. The horsepower of a given engine may be computed by the formula: _APLN_ H. P. = ------ 33,000 in which _A_ = area of piston, in square inches, _P_ = mean effective pressure per square inch, _L_ = length of stroke, in feet, _N_ = number of strokes per minute = number of revolutions × 2. The derivation of the above formula is easily explained, as follows: The area of the piston, in square inches, multiplied by the mean effective pressure, in pounds per square inch, gives the total force acting on the piston, in pounds. The length of stroke, in feet, times the number of strokes per minute gives the distance the piston moves through, in feet per minute. It has already been shown that the pressure in pounds multiplied by the distance moved through in feet, gives the foot-pounds of work done. Hence, _A_ × _P_ × _L_ × _N_ gives the foot-pounds of work done per minute by a steam engine. If one horsepower is represented by 33,000 foot-pounds per minute, the power or rating of the engine will be obtained by dividing the total foot-pounds of work done per minute by 33,000. For ease in remembering the formula given, it is commonly written _PLAN_ H. P. = ------, 33,000 in which the symbols in the numerator of the second member spell the word "Plan." _Example_:--Find the horsepower of the following engine, working under the conditions stated below: Diameter of cylinder, 12 inches. Length of stroke, 18 inches. Revolutions per minute, 300. Mean effective pressure (M. E. P.), 40 pounds. In this problem, then, _A_ = 113 square inches; _P_ = 40 pounds; _L_ = 1.5 feet; and _N_ = 600 strokes. Substituting in the formula, 40 × 1.5 × 113 × 600 H. P. = -------------------- = 123. 33,000 The mean effective pressure may be found, approximately, for different conditions by means of the factors in the following table of ratios, covering ordinary practice. The rule used is as follows: Multiply the absolute initial pressure by the factor corresponding to the clearance and cut-off as found from Table II, and subtract the absolute back pressure from the result, assuming this to be 17 pounds for non-condensing engines, and 3 pounds for condensing. _Example 1_:--A non-condensing engine having 3 per cent clearance, cuts off at 1/3 stroke; the initial pressure is 90 pounds gage. What is the M. E. P.? The absolute initial pressure is 90 + 15 = 105 pounds. The factor for 3 per cent clearance and 1/3 cut-off, from Table II, is 0.71. Applying the rule we have: (105 × 0.71) - 17 = 57.5 pounds per square inch. _Example 2_:--A condensing engine has a clearance of 5 per cent. It is supplied with steam at 140 pounds gage pressure, and has a ratio of expansion of 6. What is the M. E. P.? The absolute initial pressure is 140 + 15 = 155. The factor for a ratio of expansion of 6 (1/6 cut-off) and 5 per cent clearance is 0.5, which gives (155 × 0.5) - 3 = 74.5 pounds per square inch. The power of an engine computed by the method just explained is called the indicated horsepower (I. H. P.), and gives the total power developed, including that required to overcome the friction of the engine itself. The delivered or brake horsepower (B. H. P.) is that delivered by the engine after deducting from the indicated horsepower the power required to operate the moving parts. The brake horsepower commonly varies from 80 to 90 per cent of the indicated horsepower at full load, depending upon the type and size of engine. In proportioning an engine cylinder for any given horsepower, the designer usually has the following data, either given or assumed, for the special type of engine under consideration: Initial pressure, back pressure, clearance, cut-off, and piston speed. These quantities vary in different types of engines, but in the absence of more specific data the values in Table III will be found useful. The back pressure may be taken as 17 pounds per square inch, absolute, for non-condensing engines, and as 3 pounds for condensing engines as previously stated. TABLE II. FACTORS FOR FINDING MEAN EFFECTIVE PRESSURE +--------------+-----------------------------------------+ | | Point of Cut-off | | Percentage +------+------+------+------+------+------+ | of Clearance | 1/10 | 1/6 | 1/4 | 1/3 | 1/2 | 3/4 | +--------------+------+------+------+------+------+------+ | 1.75 | 0.35 | 0.48 | 0.60 | 0.70 | 0.85 | 0.96 | | 3.00 | 0.37 | 0.49 | 0.61 | 0.71 | 0.85 | 0.96 | | 5.00 | 0.39 | 0.50 | 0.62 | 0.72 | 0.86 | 0.97 | | 7.00 | 0.41 | 0.52 | 0.63 | 0.73 | 0.86 | 0.97 | | 9.00 | 0.43 | 0.54 | 0.64 | 0.73 | 0.86 | 0.97 | +--------------+------+------+------+------+------+------+ The first step in proportioning the cylinder is to compute the approximate mean effective pressure from the assumed initial pressure, clearance, and cut-off, by the method already explained. Next assume the piston speed for the type of engine to be designed, and determine the piston area by the following formula: 33,000 H. P. A = -----------------------. M. E. P. × piston speed This formula usually gives the diameter of the piston in inches and fractions of an inch, while it is desirable to make this dimension an even number of inches. This may be done by taking as the diameter the nearest whole number, and changing the piston speed to correspond. This is done by the use of the following equation. First piston speed × first piston area -------------------------------------- = new piston speed. new piston area In calculating the effective piston area, the area of the piston rod upon one side must be allowed for. The effective or average piston area will then be (2_A_ - _a_)/2, in which _A_ = area of piston, _a_ = area of piston rod. This latter area must be assumed. After assuming a new piston diameter of even inches, its effective or average area must be used in determining the new piston speed. The length of stroke is commonly proportioned to the diameter of cylinder, and the piston speed divided by this will give the number of strokes per minute. _Example_:--Find the diameter of cylinder, length of stroke, and revolutions per minute for a simple high-speed non-condensing engine of 200 I. H. P., with the following assumptions: Initial pressure, 90 pounds gage; clearance, 7 per cent; cut-off, 1/4; piston speed, 700 feet per minute; length of stroke, 1.5 times cylinder diameter. TABLE III. PRESSURE, CLEARANCE, CUT-OFF AND PISTON SPEED OF STEAM ENGINES +---------------------+------------+-----------+-------------+------------+ | | Initial | Clearance,| Cut-off, | Piston | | Type of Engine | Pressure, | Per Cent | Proportion | Speed, Feet| | | (Gage) | | of Stroke | per Minute | +---------------------+------------+-----------+-------------+------------+ |Simple high-speed | 80 to 90 |4 to 10 | 1/4 to 1/3 | 600 to 800 | |Simple medium-speed | 80 to 90 |3 to 8 | 1/4 to 1/3 | 500 to 700 | |Simple Corliss | 80 to 90 |1.5 to 3.5| 1/4 to 1/3 | 400 to 600 | |Compound high-speed | 130 to 140 |4 to 10 | 1/10 to 1/8 | 600 to 800 | |Compound medium-speed| 130 to 140 |3 to 8 | 1/10 to 1/8 | 500 to 700 | |Compound Corliss | 130 to 140 |1.5 to 3.5| 1/10 to 1/8 | 400 to 600 | +---------------------+------------+-----------+-------------+------------+ By using the rules and formulas in the foregoing, we have: M. E. P. = (90 + 15) × 0.63 - 17 = 49 pounds. 33,000 × 200 _A_ = ------------ = 192.4 square inches. 49 × 700 The nearest piston diameter of even inches is 16, which corresponds to an area of 201 square inches. Assume a piston rod diameter of 2-1/2 inches, corresponding to an area of 4.9 square inches, from which the average or effective piston area is found to be ((2 × 201) - 4.9)/2 = 198.5 square inches. Determining now the new piston speed, we have: 700 × 192.4 ----------- = 678.5 feet per minute. 198.5 Assuming the length of stroke to be 1.5 times the diameter of the cylinder, it will be 24 inches, or 2 feet. This will call for 678.5 ÷ 2 = 340 strokes per minute, approximately, or 340 ÷ 2 = 170 revolutions per minute. CHAPTER III STEAM ENGINE DETAILS Some of the most important details of a steam engine are those of its valve gear. The simplest form of valve is that known as the plain slide valve, and as nearly all others are a modification of this, it is essential that the designer should first familiarize himself with this particular type of valve in all its details of operation. After this has been done, a study of other forms of valves will be found a comparatively easy matter. The so called Corliss valve differs radically from the slide valve, but the results to be obtained and the terms used in its design are practically the same. The valve gear of a steam engine is made up of the valve or valves which admit steam to and exhaust it from the cylinder, and of the mechanism which governs the valve movements, the latter usually consisting of one or more eccentrics attached to the main shaft. [Illustration: Fig. 8. Longitudinal Section of Slide Valve with Ports] The Slide Valve Fig. 8 shows a longitudinal section of a slide valve with the ports, bridges, etc. The valve is shown in mid-position in order that certain points relating to it may be more easily understood. The valve, _V_, consists of a hollow casting, with ends projecting beyond the ports as shown; the lower face is smoothly finished and fitted to the valve seat _AB_. In operation it slides back and forth, opening and closing the ports which connect the steam chest with the cylinder. Steam is admitted to the cylinder when either port _CD_ or _DC_ is opened, and is released when the ports are brought into communication with the exhaust port _MN_. This is accomplished by the movement of the valve, which brings one of the cylinder ports and the exhaust port both under the hollow arch _K_. The portions _DM_ and _ND_ of the valve seat are called the bridges. It will be seen by reference to Fig. 8 that the portions _OI_ and _IO_ are wider than the ports which they cover. This extra width is called the _lap_, _OC_ being the outside lap and _DI_ the inside or exhaust lap. The object of outside lap is that the steam may be shut off after the piston has moved forward a certain distance, and be expanded during the remainder of the stroke. If there were no outside lap, steam would be admitted throughout the entire stroke and there would be no expansion. If there were no inside lap, exhaust would take place throughout the whole stroke, and the advantages of premature release and compression would be lost. Hence, outside lap affects the cut-off, and inside lap affects release and compression. A valve has _lead_ when it begins to uncover the steam port before the end of the return stroke of the piston. This is shown in Fig. 9, where the piston _P_ is just ready to start on its forward stroke as indicated by the arrow. The valve has already opened a distance equal to the lead, and the steam has had an opportunity to enter and fill the clearance space before the beginning of the stroke. The lead varies in different engines, being greater in high-speed than in low-speed types. [Illustration: Fig. 9. Illustration showing Lead of Slide Valve] [Illustration: Fig. 10. Diagrammatical View of Eccentric] The Eccentric The slide valve is usually driven by an eccentric attached to the main shaft. A diagram of an eccentric is shown in Fig. 10. An eccentric is, in reality, a short crank with a crank-pin of such size that it surrounds the shaft. The arm of a crank is the distance between the center of the shaft, and the center of the crank-pin. The throw of an eccentric corresponds to this, and is the distance between the center of the shaft and the center of the eccentric disk, as shown at _a_ in Fig. 10. The disk is keyed to the shaft, and as the shaft revolves, the center of the disk rotates about it as shown by the dotted line, and gives a forward and backward movement to the valve rod equal to twice the throw _a_. [Illustration: Fig. 11. Relations of Crank and Eccentric] In Fig. 11 let _A_ represent the center of the main shaft, _B_ the crank-pin to which the connecting-rod is attached (see _H_, Fig. 1), and the dotted circle through _B_ the path of the crank-pin around the shaft. For simplicity, let the eccentric be represented in a similar manner by the crank _Ab_, and its path by the dotted circle through _b_. Fig. 12 shows a similar diagram with the piston _P_ and the valve in the positions corresponding to the positions of the crank and eccentric in Fig. 11, and in the diagram at the right in Fig. 12. The piston is at the extreme left, ready to start on its forward stroke toward the right. The crank-pin _B_ is at its extreme inner position. When the valve is at its mid-position, as in Fig. 8, the eccentric arm _Ab_ will coincide with the line _AC_, Fig. 11. If the eccentric is turned on the shaft sufficiently to bring the left-hand edge _O_, Fig. 8, of the valve in line with the edge _C_ of the port, the arm of the eccentric will have moved from its vertical position to that shown by the line _Ab´_ in Fig. 11. The angle through which the eccentric has been turned from the vertical to bring about this result is called the _angular advance_, and is shown by angle _CAb´_ in Fig. 11. The angular advance evidently depends upon the amount of lap. If the valve is to be given a lead, as indicated in Fig. 12, the eccentric must be turned still further on the shaft to open the valve slightly before the piston starts on its forward movement. This brings the eccentric to the position _Ab_ shown in Fig. 11. The angle through which the eccentric is turned to give the necessary lead opening to the valve is called the _angle of lead_, and is shown by angle _b´Ab_. By reference to Fig. 11, it is seen that the total angle between the crank and the eccentric is 90 degrees, plus the angular advance, plus the angle of lead. This is the total angle of advance. [Illustration: Fig. 12. Piston just beginning Forward Stroke] The relative positions of the piston and valve at different periods of the stroke are illustrated in Figs. 12 to 16. Fig. 12 shows the piston just beginning the forward stroke, the valve having uncovered the admission port an amount equal to the lead. The crank is in a horizontal position, and the eccentric has moved from the vertical an amount sufficient to move the valve toward the right a distance equal to the outside lap plus the lead. The arrows show that steam is entering the left-hand port and is being exhausted through the right-hand port. [Illustration: Fig. 13. Steam Port fully Opened] In Fig. 13 it is seen that the valve has traveled forward sufficiently to open the steam port to its fullest extent, and the piston has moved to the point indicated. The exhaust port is still wide open, and the relative positions of the crank and eccentric are shown in the diagram at the right. In Fig. 14 the eccentric has passed the horizontal position and the valve has started on its backward stroke, while the piston is still moving forward. The admission port is closed, cut-off having taken place, and the steam is expanding. The exhaust port is still partially open. [Illustration: Fig. 14. Valve has started on Backward Stroke] [Illustration: Fig. 15. Both Steam Ports Closed] In Fig. 15 both ports are closed and compression is taking place in front of the piston while expansion continues back of it. Release occurs in Fig. 16 just before the piston reaches the end of its stroke. The eccentric crank is now in a vertical position, pointing downward, and exhaust is just beginning to take place through the left-hand port. This completes the different stages of a single stroke, the same features being repeated upon the return of the piston to its original position. The conditions of lap, lead, angular advance, etc., pertain to practically all valves, whatever their design. [Illustration: Fig. 16. Exhaust Begins] Different Types of Valves In the following are shown some of the valves in common use, being, with the exception of the Corliss, modifications of the plain slide valve, and similar in their action. [Illustration: Fig. 17. Engine with Piston Valve] _Double-Ported Balanced Valve._--A valve of this type has already been shown in Fig. 2. This valve is flat in form, with two finished surfaces, and works between the valve-seat and a plate, the latter being prevented from pressing against the valve by special bearing surfaces which hold it about 0.002 inch away. The construction of the valve is such that when open the steam reaches the port through two openings as indicated by the arrows at the left. The object of this is to reduce the motion of the valve and quicken its action in admitting and cutting off steam. [Illustration: Fig. 18. Section through Cylinder of Engine of the Four-valve Type] [Illustration: Fig. 19. Different Types of Corliss Valves] _Piston Valve._--The piston valve shown in Fig. 17 is identical in its action with the plain slide valve shown in Fig. 8, except that it is circular in section instead of being flat or rectangular. The advantage claimed for this type of valve is the greater ease in fitting cylindrical surfaces as compared with flat ones. The valve slides in special bushings which may be renewed when worn. Piston valves are also made with double ports. [Illustration: Fig. 20. Longitudinal Section through Corliss Engine] [Illustration: Fig. 21. The Gridiron Valve] _Four-Valve Type._--Fig. 18 shows a horizontal section through the cylinder and valves of an engine of the four-valve type. The admission valves are shown at the top of the illustration and the exhaust valves at the bottom, although, in reality, they are at the sides of the cylinder. The advantage of an arrangement of this kind is that the valves may be set independently of each other and the work done by the two ends of the cylinder equalized. The various events, such as cut-off, compression, etc., may be adjusted without regard to each other, and in such a manner as to give the best results, a condition which is not possible with a single valve. _Gridiron Valve._--One of the principal objects sought in the design of a valve is quick action at the points of admission and cut-off. This requires the uncovering of a large port opening with a comparatively small travel of the valve. The gridiron valve shown in Fig. 21 is constructed especially for this purpose. This valve is of the four-valve type, one steam valve and one exhaust valve being shown in the section. Both the valve and its seat contain a number of narrow openings or ports, so that a short movement of the valve will open or close a comparatively large opening. For example, the steam valve in the illustration has 12 openings, so that if they are 1/4 inch in width each, a movement of 1/4 inch of the valve will open a space 12 × 1/4 = 3 inches in length. [Illustration: Fig. 22. The Monarch Engine with Corliss Valve Gear.--A, Rod to Eccentric; B, Governor; C, Reach Rod; D, Radial Arm; E, Steam Valve; F, Bell-crank; G, Wrist Plate; H, Exhaust Valve; K, Dash-pot] _Corliss Valve._--A section through an engine cylinder equipped with Corliss valves is shown in Fig. 20. There are four cylindrical valves in this type of engine, two steam valves at the top and two exhaust valves at the bottom. This arrangement is used to secure proper drainage. The action of the admission and exhaust valves is indicated by the arrows, the upper left-hand and the lower right-hand valve being open and the other two closed. Side and sectional views of different forms of this type of valve are shown in Fig. 19. They are operated by means of short crank-arms which are attached to a wrist-plate by means of radial arms or rods, as shown in Fig. 22. The wrist-plate, in turn, is given a partial backward and forward rotation by means of an eccentric attached to the main shaft and connected to the upper part of the wrist-plate by a rod as indicated. The exhaust valves are both opened and closed by the action of the wrist-plate and connecting rods. The steam valves are opened in this manner, but are closed by the suction of dash pots attached to the drop levers on the valve stems by means of vertical rods, as shown. [Illustration: Figs. 23 to 26. Action of Corliss Valve Gear] The action of the steam or admission valves is best explained by reference to Figs. 23 to 26. Referring to Fig. 23, _A_ is a bell-crank which turns loosely upon the valve stem _V_. The lower left-hand extension of _A_ carries the grab hook _H_, while the upper extension is connected with the wrist-plate as indicated. Ordinarily the hook _H_ is pressed inward by the spring _S_, so that the longer arm of the hook is always pressed against the knock-off cam _C_. The cam _C_ also turns upon the valve stem _V_ and is connected with the governor by means of a reach rod as indicated in Fig. 23 and shown in Fig. 22. The drop lever _B_ is keyed to the valve stem _V_, and is connected with the dash pot by a rod as indicated by the dotted line. This is also shown in Fig. 22. The end of the drop lever carries a steel block (shown shaded in Fig. 23), which engages with the grab hook _H_. When in operation, the bell-crank is rotated in the direction of the arrow by the action of the wrist-plate and connecting-rod. As the bell-crank rotates, the grab hook engages the steel block at the end of the drop lever _B_ and lifts it, thus causing the valve to open, and to remain so until the bell-crank has advanced so far that the longer arm of the grab hook _H_ is pressed outward by the projection on the knock-off cam, as shown in Fig. 24. The drop lever now being released, the valve is quickly closed by the suction of the dash pot, which pulls the lever down to its original position by means of the rod previously mentioned. [Illustration: Fig. 27. Governor for Corliss Engine] The governor operates by changing the point of cut-off through the action of the cam _C_. With the cam in the position shown in Fig. 25, cut-off occurs earlier than in Fig. 24. Should the cam be turned in the opposite direction (clockwise), cut-off would take place later. A detailed view of the complete valve mechanism described is shown assembled in Fig. 26, with each part properly named. A detail of the governor is shown in Fig. 27. An increase in speed causes the revolving balls _BB_ to swing outward, thus raising the weight _W_ and the sleeve _S_. This in turn operates the lever _L_ through rod _R_ and a bell-crank attachment, as shown in the right-hand view. An upward and downward movement of the balls, due to a change in speed of the engine, swings the lever _L_ backward and forward as shown by the full and dotted lines. The ends of this lever are attached by means of reach-rods to the knock-off cams, this being shown more clearly in Fig. 22. The connections between the lever _L_ and cam _C_ are such that a raising of the balls, due to increased speed, will reduce the cut-off and thus slow down the engine. On the other hand, a falling of the balls will lengthen the cut-off through the same mechanism. [Illustration: Fig. 28. Dash-pot for Corliss Engine] [Illustration: Figs. 29 and 30. Plan and Longitudinal Section of Adjustable Piston] Mention has already been made of the dash pot which is used to close the valve suddenly after being released from the grab hook. The dash-pot rod is shown in Fig. 26, and indicated by dotted lines in Figs. 23 to 25. A detailed view of one form of dash pot is shown in Fig. 28. When the valve is opened, the rod attached to lever _B_, Figs. 23 and 24, raises the piston _P_, Fig. 28, and a partial vacuum is formed beneath it which draws the piston and connecting rod down by suction as soon as the lever _B_ is released, and thus closes the valve suddenly and without shock. The strength of the suction and the air cushion for this piston are regulated by the inlet and outlet valves shown on the sides of the dash pot. Engine Details Figs. 29 to 37 show various engine details, and illustrate in a simple way some of the more important principles involved in steam engine design. [Illustration: Fig. 31. A Typical Cross-head] [Illustration: Figs. 32 and 33. Methods Commonly Used for Taking Up Wear in a Connecting-rod] A partial cross-section of an adjustable piston is shown in Fig. 29, and a longitudinal section of the same piston in Fig. 30. The principal feature to be emphasized is the method of automatic expansion employed to take up any wear and keep the piston tight. In setting up the piston a hand adjustment is made of the outer sleeve or ring _R_ by means of the set-screws _AA_. Ring _R_ is made in several sections, so that it may be expanded in the form of a true circle. Further tightness is secured without undue friction by means of the packing ring _P_ which fits in a groove in _R_ and is forced lightly against the walls of the cylinder by a number of coil springs, one of which is shown at _S_. As the cylinder and piston become worn, screws _A_ are adjusted from time to time, and the fine adjustment for tightness is cared for by the packing ring _P_ and the coil springs _S_. The points to be brought out in connection with the cross-head are the methods of alignment and adjustment. A typical cross-head is shown in cross and longitudinal sections in Fig. 31. Alignment in a straight line, longitudinally, is secured by the cylindrical form of the bearing surfaces or shoes, shown at _S_. These are sometimes made V-shaped in order to secure the same result. The wear on a cross-head comes on the surfaces _S_, and is taken up by the use of screw wedges _W_, shown in the longitudinal section. As the sliding surfaces become worn, the wedges are forced in slightly by screwing in the set-screws and clamping them in place by means of the check-nuts. [Illustration: Fig. 34. Outboard Bearing for Corliss Type Engine] [Illustration: Fig. 35. Inner Bearing and Bed of Corliss Engine] The method commonly employed in taking up the wear in a connecting-rod is shown in Figs. 32 and 33. The wear at the wrist-pin is taken by the so called brasses, shown at _B_ in the illustrations. The inner brass, in both cases, fits in a suitable groove, and is held stationary when once in place. The outer brass is adjustable, being forced toward the wrist-pin by a sliding wedge which is operated by one or more set-screws. In Fig. 32 the wedge is held in a vertical position, and is adjusted by two screws as shown. The arrangement made use of in Fig. 33 has the wedge passing through the rod in a horizontal position, and adjusted by means of a single screw, as shown in the lower view. With the arrangements shown, tightening up the brasses shortens the length of the rod. In practice the wedges at each end of the rod are so placed that tightening one shortens the rod, and tightening the other lengthens it, the total effect being to keep the connecting-rod at its original length. A common form of outboard bearing for an engine of the slow-speed or Corliss type is illustrated in Fig. 34. The various adjustments for alignment and for taking up wear are the important points considered in this case. The plate _B_ is fastened to the stone foundation by anchor bolts not shown. Sidewise movement is secured by loosening the bolts _C_, which pass through slots in the bearing, and adjusting by means of the screws _S_. Vertical adjustment is obtained by use of the wedge _W_, which is forced in by the screw _A_, as required. The inner bearing and bed piece of a heavy duty Corliss engine is shown in Fig. 35. The bearing in this case is made up of four sections, so arranged that either horizontal or vertical adjustment may be secured by the use of adjusting screws and check-nuts. Engines of the slide-valve type are usually provided either with a fly-ball throttling governor, or a shaft governor. A common form of throttling governor is shown in Fig. 36. As the speed increases the balls _W_ are thrown outward by the action of the centrifugal force, and being attached to arms hinged above them, any outward movement causes them to rise. This operates the spindle _S_, which, in turn, partially closes the balanced valve in body _B_, thus cutting down the steam supply delivered to the engine. The action of a throttling governor upon the work diagram of an engine is shown in Fig. 38. Let the full line represent the form of the diagram with the engine working at full load. Now, if a part of the load be thrown off, the engine will speed up slightly, causing the governor to act as described, thus bringing the admission and expansion lines into the lower positions, as shown in dotted lines. [Illustration: Fig. 36. Common Form of Throttling Governor] The shaft governor is used almost universally on high-speed engines, and is shown in one form in Fig. 37. It consists, in this case, of two weights _W_, hinged to the spokes of the wheel near the circumference by means of suitable arms. Attached to the arms, as shown, are coil springs _C_. The ends of the arms beyond the weights are connected by means of levers _L_ to the eccentric disk. When the engine speeds up, the weights tend to swing outward toward the rim of the wheel, the amount of the movement being regulated by the tension of the springs _C_. As the arms move outward, the levers at the ends turn the eccentric disk on the shaft, the effect of which is to change the angle of advance and shorten the cut-off. When the speed falls below the normal, the weights move toward the center and the cut-off is lengthened. The effect of this form of governor on the diagram is shown in Fig. 39. The full line represents the diagram at full load, and the dotted line when the engine is under-loaded. [Illustration: Fig. 37. Shaft Governor for High-speed Engine] CHAPTER IV STEAM ENGINE ECONOMY Under the general heading of steam engine economy, such items as cylinder condensation, steam consumption, efficiency, ratio of expansion, under- and over-loading, condensing, etc., are treated. The principal waste of steam in the operation of an engine is due to condensation during the first part of the stroke. This condensation is due to the fact that during expansion and exhaust the cylinder walls and head and the piston are in contact with comparatively cool steam, and, therefore, give up a considerable amount of heat. When fresh steam is admitted at a high temperature, it immediately gives up sufficient heat to raise the cylinder walls to a temperature approximating that of the entering steam. This results in the condensation of a certain amount of steam, the quantity depending upon the time allowed for the transfer of heat, the area of exposed surface, and the temperature of the cylinder walls. During the period of expansion the temperature falls rapidly, and the steam being wet, absorbs a large amount of heat. After the exhaust valve opens, the drop in pressure allows the moisture that has collected on the cylinder walls to evaporate into steam, so that during the exhaust period but little heat is transferred. With the admission of fresh steam at boiler pressure, a mist is condensed on the cylinder walls, which greatly increases the rapidity with which heat is absorbed. The amount of heat lost through cylinder condensation is best shown by a practical illustration. One horsepower is equal to 33,000 foot-pounds of work per minute, or 33,000 × 60 = 1,980,000 foot-pounds per hour. This is equivalent to 1,980,000 ÷ 778 = 2,550 heat units. The latent heat of steam at 90 pounds gage pressure is 881 heat units. Hence, 2,250 ÷ 881 = 2.9 pounds of steam at 90 pounds pressure is required per horsepower, provided there is no loss of steam, and all of the contained heat is changed into useful work. As a matter of fact, from 30 to 35 pounds of steam are required in the average simple non-condensing high-speed engine. There are three remedies which are used to reduce the amount of cylinder condensation. The first to be used was called steam jacketing, and consisted in surrounding the cylinder with a layer of high-pressure steam, the idea being to keep the inner walls up to a temperature nearly equal to that of the incoming steam. This arrangement is but little used at the present time, owing both to the expense of operation and to its ineffectiveness as compared with other methods. The second remedy is the use of superheated steam. It has been stated that the transfer of heat takes place much more rapidly when the interior surfaces are covered with a coating of moisture or mist. Superheated steam has a temperature considerably above the point of saturation at the given pressure; hence, it is possible to cool it a certain amount before condensation begins. This has the effect of reducing the transfer of heat for a short period following admission, and this is the time that condensation takes place most rapidly under ordinary conditions with saturated steam. This, in fact, is the principal advantage derived from the use of superheated steam, although it is also lighter for a given volume, and therefore, a less weight of steam is required, to fill the cylinder up to the point of cut-off. The economical degree of superheating is considered to be that which will prevent the condensation of any steam on the walls of the cylinder up to the point of cut-off, thus keeping them at all times free from moisture. The objections to superheated steam are its cutting effect in the passages through which it flows, and the difficulty experienced in lubricating the valves and cylinder at such a high temperature. The third and most effective remedy for condensation losses is that known as compounding, which will be treated under a separate heading in the following. Multiple Expansion Engines It has been explained that cylinder condensation is due principally to the change in temperature of the interior surfaces of the cylinder, caused by the variation in temperature of the steam at initial and exhaust pressures. Therefore, if the temperature range be divided between two cylinders which are operated in series, the steam condensed in the first or high pressure cylinder will be re-evaporated and passed into the low-pressure cylinder as steam, where it will again be condensed and re-evaporated as it passes into the exhaust pipe. Theoretically, this should reduce the condensation loss by one-half, and if three cylinders are used, the loss should be only one-third of that in a simple engine. In actual practice the saving is not as great as this, but with the proper relation between the cylinders, these results are approximated. Engines in which expansion takes place in two stages are called compound engines. When three stages are employed, they are called triple expansion engines. Compounding adds to the first cost of an engine, and also to the friction, so that in determining the most economical number of cylinders to employ, the actual relation between the condensation loss and the increased cost of the engine and the friction loss, must be considered. In the case of power plant work, it is now the practice to use compound engines for the large sizes, while triple expansion engines are more commonly employed in pumping stations. Many designs of multiple expansion engines are provided with chambers between the cylinders, called receivers. In engines of this type the exhaust is frequently reheated in the receivers by means of brass coils containing live steam. In the case of a cross-compound engine, a receiver is always used. In the tandem design it is often omitted, the piping between the two cylinders being made to answer the purpose. The ratio of cylinder volumes in compound engines varies with different makers. The usual practice is to make the volume of the low-pressure cylinder from 2.5 to 3 times that of the high-pressure. The total ratio of expansion in a multiple expansion engine is the product of the ratios in each cylinder. For example, if the ratio of expansion is 4 in each cylinder in a compound engine, the total ratio will be 4 × 4 = 16. The effect of a triple-expansion engine is sometimes obtained in a measure by making the volume of the low-pressure cylinder of a compound engine 6 or 7 times that of the high-pressure. This arrangement produces a considerable drop in pressure at the end of the high-pressure stroke, with the result of throwing a considerable increase of work on the high-pressure cylinder without increasing its ratio of expansion, and at the same time securing a large total ratio of expansion in the engine. In the case of vertical engines, the low-pressure cylinder is sometimes divided into two parts in order to reduce the size of cylinder and piston. In this arrangement a receiver of larger size than usual is employed, and the low-pressure cranks are often set at an angle with each other. Another advantage gained by compounding is the possibility to expand the steam to a greater extent than can be done in a single cylinder engine, thus utilizing, as useful work, a greater proportion of the heat contained in the steam. This also makes it possible to employ higher initial pressures, in which there is a still further saving, because of the comparatively small amount of fuel required to raise the pressure from that of the common practice of 80 or 90 pounds for simple engines, to 120 to 140 pounds, which is entirely practical in the case of compound engines. With triple expansion, initial pressures of 180 pounds or more may be used to advantage. The gain from compounding may amount to about 15 per cent over simple condensing engines, taking steam at the same initial pressure. When compound condensing engines are compared with simple non-condensing engines, the gain in economy may run from 30 to 40 per cent. TABLE IV. STEAM CONSUMPTION OF ENGINES +-------------------------+--------------------------------+ | | Pounds of Steam per Indicated | | | Horsepower per Hour | | Kind of Engine +----------------+---------------+ | | Non-condensing | Condensing | +-------------------------+----------------+---------------+ | { High-speed | 32 | 24 | | Simple { Medium-speed | 30 | 23 | | { Corliss | 28 | 22 | | | | | | { High-speed | 26 | 20 | | Compound { Medium-speed | 25 | 19 | | { Corliss | 24 | 18 | +-------------------------+----------------+---------------+ Steam Consumption and Ratio of Expansion The steam consumption is commonly called the _water rate_, and is expressed in pounds of dry steam required per indicated horsepower per hour. This quantity varies widely in different types of engines, and also in engines of the same kind working under different conditions. The water rate depends upon the "cylinder losses," which are due principally to condensation, although the effects of clearance, radiation from cylinder and steam chest, and leakage around valves and piston, form a part of the total loss. Table IV gives the average water rate of different types of engines working at full load. The most economical ratio of expansion depends largely upon the type of the engine. In the case of simple engines, the ratio is limited to 4 or 5 on account of excessive cylinder condensation in case of larger ratios. This limits the initial pressure to an average of about 90 pounds for engines of this type. In the case of compound engines, a ratio of from 8 to 10 is commonly employed to advantage, while with triple-expansion engines, ratios of 12 to 15 are found to give good results. [Illustration: Fig. 38. Action of Throttling Governor on Indicator Diagram] [Illustration: Fig. 39. Effect of Shaft Governor on Indicator Diagram] [Illustration: Fig. 40. Increasing Power of Engine by Condensing] [Illustration: Fig. 41. Decreasing Steam Consumption by Condensing] The _thermal efficiency_ of an engine is the ratio of the heat transformed into work to the total heat supplied to the engine. In order to determine this, the _absolute_ temperature of the steam at admission and exhaust pressures must be known. These pressures can be measured by a gage, and the corresponding temperatures taken from a steam table, or better, the temperatures can be measured direct by a thermometer. The absolute temperature is obtained by adding 461 to the reading in degrees Fahrenheit (F.). The formula for thermal efficiency is: _T__{1} - _T__{2} ----------------- _T__{1} in which _T__{1} = absolute temperature of steam at initial pressure. _T__{2} = absolute temperature of steam at exhaust pressure. _Example_:--The temperature of the steam admitted to the cylinder of an engine is 340 degrees F., and that of the exhaust steam 220 degrees F. What is the thermal efficiency of the engine? (340 + 461) - (220 + 461) Thermal efficiency = ------------------------- = 0.15 (340 + 461) The _mechanical efficiency_ is the ratio of the delivered or brake horsepower to the indicated horsepower, and is represented by the equation: B. H. P. Mechanical efficiency = -------- I. H. P. in which B. H. P. = brake horsepower, I. H. P. = indicated horsepower. All engines are designed to give the best economy at a certain developed indicated horsepower called full load. There must, of course, be more or less fluctuation in the load under practical working conditions, especially in certain cases, such as electric railway and rolling mill work. The losses, however, within a certain range on either side of the normal load, are not great in a well designed engine. The effect of increasing the load is to raise the initial pressure or lengthen the cut-off, depending upon the type of governor. This, in turn, raises the terminal pressure at the end of expansion, and allows the exhaust to escape at a higher temperature than before, thus lowering the thermal efficiency. The effect of reducing the load is to lower the mean effective pressure. (See Figs. 38 and 39.) This, in throttling engines, is due to a reduction of initial pressure, and in the automatic engine to a shortening of the cut-off. The result in each case is an increase in cylinder condensation, and as the load becomes lighter, the friction of the engine itself becomes a more important part of the total indicated horsepower; that is, as the load becomes lighter, the mechanical efficiency is reduced. Effect of Condensing So far as the design of the engine itself it concerned, there is no difference between a condensing and a non-condensing engine. The only difference is that in the first case the exhaust pipe from the engine is connected with a condenser instead of discharging into the atmosphere. A condenser is a device for condensing the exhaust steam as fast as it comes from the engine, thus forming a partial vacuum and reducing the back pressure. The attaching of a condenser to an engine may be made to produce two results, as shown by the work diagrams illustrated in Figs. 40 and 41. In the first case the full line represents the diagram of the engine when running non-condensing, and the area of the diagram gives a measure of the work done. The effect of adding a condenser is to reduce the back pressure on an average of 10 to 12 pounds per square inch, which is equivalent to adding the same amount to the mean effective pressure. The effect of this on the diagram, when the cut-off remains the same, is shown by the dotted line in Fig. 40. The power of the engine per stroke is increased by an amount represented by the area enclosed by the dotted line and the bottom of the original diagram. Assuming the reduction in back pressure to be 10 pounds, which is often exceeded in the best practice, the gain in power by running condensing will be proportional to the increase in mean effective pressure under these conditions. For example, if the mean effective pressure is 40 pounds when running non-condensing, it will be increased to 40 + 10 = 50 pounds when running condensing, that is, it is 50/40 = 1.25 times as great as before. Therefore, if the engine develops 100 I. H. P. under the first condition, its final power will be increased to 100 × 1.25 = 125 I. H. P. under the second condition. Fig. 41 shows the effect of adding a condenser and shortening the cut-off to keep the area of the diagram the same as before. The result in this case is a reduction in the quantity of steam required to develop the same indicated horsepower. The theoretical gain in economy under these conditions will run from about 28 to 30 per cent for simple, and from 20 to 22 per cent for compound engines. The actual gain will depend upon the cost and operation of the condenser which varies greatly in different localities. CHAPTER V TYPES OF STEAM ENGINES There are various ways of classifying steam engines according to their construction, the most common, perhaps, being according to speed. If this classification is employed, they may be grouped under three general headings: High-speed, from 300 to 400 revolutions per minute; moderate-speed, from 100 to 200 revolutions; and slow-speed, from 60 to 90 revolutions; all depending, however, upon the length of stroke. This classification is again sub-divided according to valve mechanism, horizontal and vertical, simple and compound, etc. The different forms of engines shown in the following illustrations show representative types in common use for different purposes. The Ball engine, as shown in Fig. 42, is a typical horizontal single valve high-speed engine with a direct-connected dynamo. It is very rigid in design and especially compact for the power developed. The valve is of the double-ported type shown in Fig. 2, having a cover plate for removing the steam pressure from the back of the valve. The piston is hollow with internal ribs similar to that shown in Fig. 29, and is provided with spring packing rings carefully fitted in place. The governor is of the shaft type, having only one weight instead of two, as shown in Fig. 37. [Illustration: Fig. 42. The Ball Engine] The Sturtevant engine shown in Fig. 43 is a vertical high-speed engine of a form especially adapted to electrical work. Engines of this general design are made in a variety of sizes, and are often used on account of the small floor space required. In the matter of detail, such as valves, governors, etc., they do not differ materially from the high-speed horizontal engine. Fig. 44 illustrates a moderate-speed engine of the four-valve type. These engines are built either with flat valves, or with positively driven rotary or Corliss valves, the latter being used in the engine shown. It will be noticed that the drop-lever and dash-pot arrangement is omitted, the valves being both opened and closed by means of the wrist-plate and its connecting rods. This arrangement is used on account of the higher speed at which the engine is run, the regular Corliss valve gear being limited to comparatively low speeds. All engines of this make are provided with an automatic system of lubrication. The oil is pumped through a filter to a central reservoir, seen above the center of the engine, and from here delivered to all bearings by gravity. The pump is attached to the rocker arm, and therefore easily accessible for repairs. The standard Harris Corliss engine shown in Fig. 45, is typical of its class. It is provided with the girder type of frame, and with an outboard bearing mounted upon a stone foundation. The valve gear is of the regular Corliss type, driven by a single eccentric and wrist-plate. The dash pots are mounted on cast-iron plates set in the floor at the side of the engine, where they may be easily inspected. The governor is similar in construction to the one already described, and shown in Fig. 27. The four engines so far described are simple engines, the expansion taking place in a single cylinder. Figs. 46 to 48 show three different types of the compound engine. [Illustration: Fig. 43. The Sturtevant Vertical Engine] The engine shown in Fig. 46 is of a type known as the tandem compound. In this design the cylinders are in line, the low-pressure cylinder in front of the high-pressure, as shown. There is only one piston rod, the high-pressure and low-pressure pistons being mounted on the same rod. The general appearance of an engine of this design is the same as a simple engine, except for the addition of the high-pressure cylinder. The governor is of the shaft type and operates by changing the cut-off in the high-pressure cylinder. The cut-off in the low pressure cylinder is adjusted by hand to divide the load equally between the two cylinders for the normal load which the engine is to carry. [Illustration: Fig. 44. Moderate Speed Engine of the Four-valve Type] The engine shown in Fig. 47 is known as a duplex compound. In this design the high-pressure cylinder is placed directly below the low-pressure cylinder, as indicated, and both piston rods are attached to the same cross-head. The remainder of the engine is practically the same as a simple engine of the same type. [Illustration: Fig. 45. The Harris Corliss Engine] Fig. 48 shows a cross-compound engine of heavy design, built especially for rolling mill work. In this arrangement two complete engines are used, except for the main shaft and flywheel, which are common to both. The engine is so piped that the high-pressure cylinder exhausts into the low-pressure, through a receiver, the connection being under the floor and not shown in the illustration. One of the advantages of the cross-compound engine over other forms is that the cranks may be set 90 degrees apart, so that when one is on a dead center the other is approximately at its position of greatest effort. Selection of an Engine The selection of an engine depends upon a number of conditions which vary to a considerable extent in different cases. Among these may be mentioned first cost, size and character of plant, available space, steam economy, and utilization of the exhaust steam. The question of first cost is usually considered in connection with that of operation, and items such as interest and depreciation are compared with the saving made through the saving in steam with high priced engines. [Illustration: Fig. 46. The Skinner Tandem Engine] [Illustration: Fig. 47. American Ball Duplex Compound Engine] The principal use of the stationary engine is confined to the driving of electric generators and the furnishing of motive power in shops and factories. For the first of these uses, in cases where floor space is limited, as in office buildings, and where the power does not exceed about 100 I. H. P., the simple non-condensing high-speed engine is probably employed more than any other type. For larger installations, a saving may usually be made by the substitution of the moderate-speed four-valve engine. The question of simple and compound engines in this class of work depends largely upon the use made of the exhaust steam. In winter time the exhaust is nearly always utilized in the heating system, hence steam economy is not of great importance, and the simple engine answers all purposes at a smaller first cost. In localities where the heating season is comparatively short and fuel high, there is a decided advantage in using compound engines on account of their greater steam economy when operated within their economical range as regards load. [Illustration: Fig. 48. The Monarch Corliss Engine] In large central plants where low cost of operation is always of first importance, it is common practice to use the best class of compound condensing engines of moderate or low speed. Those equipped with some form of Corliss valve gear are frequently found in this class of work. In the generation of power for shops and factories, where there is plenty of floor space, low-speed engines of the Corliss type are most commonly used. When space is limited, very satisfactory results may be obtained by using the moderate-speed four-valve engine. In deciding upon an engine for any particular case, the problem must be studied from all sides, and one be chosen which best answers the greatest number of requirements. CHAPTER VI STEAM ENGINE TESTING The principal information sought in the usual test of a steam engine is: 1. The indicated horsepower developed under certain standard conditions. 2. The friction of the engine, from which is determined the mechanical efficiency. 3. The steam consumption per indicated horsepower. 4. The general action of the valves. 5. The pressure conditions in the cylinder at different periods of the stroke. The ultimate object of an efficiency test is to determine the foot-pounds of work delivered by the engine per pound of coal burned in the boiler furnaces. The general method of finding the pounds of dry steam evaporated per pound of coal has been treated in MACHINERY'S Reference Series No. 67, "Boilers," under the head of "Boiler Testing." In the present case it is, therefore, only necessary to carry the process a step further and determine the foot-pounds of work developed per pound of steam. The apparatus used in engine testing, in addition to that used in boiler testing, consists of a steam engine _indicator_ and reducing device for taking diagrams, and a _planimeter_ for measuring them afterwards. If the test is made independently of the boiler test, a calorimeter for measuring the amount of moisture in the steam should be added to the outfit. It has already been shown how a diagram may be made to represent graphically the work done in a steam engine cylinder during one stroke of the piston. The diagrams shown thus far have been theoretical or ideal cards constructed from assumed relations of the pressure acting and the distance moved through by the piston. An indicator is a device for making a diagram of what actually takes place in an engine cylinder under working conditions. Such a diagram shows the points of admission, cut-off, and release, and indicates accurately the pressures acting upon both sides of the piston at all points of the stroke. A common form of steam engine indicator is shown in Fig. 49. It consists of a cylinder _C_ which is placed in communication at _E_ with one end of the engine cylinder by a proper pipe connection, provided with a quick opening and closing cock or valve. The cylinder _C_ contains a piston, above which is placed a coil spring of such strength that a given pressure per square inch acting upon the lower side of the piston will compress the spring a definite and known amount. Extending through the cap or head of cylinder _C_ is a stem attached to the piston below, and connected by suitable levers with a pencil point _P_. The arrangement of the levers is such that a certain rise of the piston causes the point _P_ to move upward in a vertical line a proportional amount. The springs used above the piston vary in strength, and are designated as 20-pound, 40-pound, 60-pound, etc. A 20-pound spring is of such strength that a pressure of 20 pounds per square inch, acting beneath the piston in cylinder _C_, will raise the pencil point 1 inch. With a 40-pound spring, a pressure of 40 pounds per square inch will be required to raise the pencil 1 inch, and so on for the other strengths of spring. The hollow drum _D_ rotates back and forth upon a vertical stem at its center, its motion being produced by the string _H_, which is attached by means of a suitable reducing motion to the cross-head of the engine. The return motion to the drum is obtained from a coil spring contained within it and not shown. The paper upon which the diagram is to be drawn is wound around the drum _D_, and held in place by the spring clip _F_. In taking an indicator card, the length of stroke must be reduced to come within the limits of the drum, that is, it must be somewhat less than the circumference of drum _D_. In practice, the diagram is commonly made from 3 to 4 inches in length. There are a number of devices in use for reproducing the stroke of the engine on a smaller scale. The most accurate consists of a series of pulleys over which the cord passes on its way from the cross-head to the indicator drum. The indicator is connected with the engine cylinder by means of special openings tapped close to the heads and either plugged or closed by means of stop-cocks when not in use. In some cases two indicators are used, one being connected to each end of the cylinder, while in others a single indicator is made to answer the purpose by being so piped that it can be connected with either end by means of a three-way cock. After the indicator is connected and the cord adjusted to give the proper motion to the drum, a card is attached, after which the three-way cock is opened and steam allowed to blow through the indicator to warm it up. The cock is now closed and the pencil pressed against the drum to get the so-called atmospheric line. The cock is again opened, and the pencil pressed lightly against the drum during one complete revolution of the engine. The cock is then thrown over to connect the indicator with the other end of the cylinder and the operation is repeated. [Illustration: Fig. 49. Steam Engine Indicator] The indicator card obtained in this way is shown in Fig. 50. It is sometimes preferred to take the diagrams of the two ends on separate cards, but it is simpler to take them both on the same one, and also easier to compare the working of the two ends of the cylinder. The analysis of a card for practical purposes is shown in Fig. 51. Suppose, for example, that the length of the diagram measures 3.6 inches; the distance to the point of cut-off is 1.2 inch; and the distance to the point of release is 3.3 inches. Then, by dividing 1.2 by 3.6, the cut-off is found to occur at 1.2 ÷ 3.6 = 1/3 of the stroke. Release occurs at 3.3 ÷ 3.6 = 0.92 of the stroke. Compression begins at (3.6 - 0.5) ÷ 3.6 = 0.86 of the stroke. The diagrams shown in Figs. 50 and 51 are from non-condensing engines, and the back-pressure line is therefore above the atmospheric line, as indicated. The indicator diagram gives a means of determining the mean effective pressure, from which the power of the engine can be found from the previously given equation _APLN_ I. H. P. = ------. 33,000 The method of determining the mean effective pressure is as follows: First measure the area of the card in square inches, by means of a planimeter (an instrument described later), and divide this area by the length in inches. This gives the mean ordinate; the mean ordinate, in turn, multiplied by the strength of spring used, will give the mean effective pressure in pounds per square inch. For example, suppose that the card shown in Fig. 51 is taken with a 60-pound spring, and that the area, as measured by a planimeter, is found to be 2.6 square inches. Dividing the area by the length gives 2.6 ÷ 3.6 = 0.722 inch as the mean ordinate, and this multiplied by the strength of spring gives a mean effective pressure of 0.722 × 60 = 43.3 pounds per square inch. [Illustration: Fig. 50. A Typical Indicator Diagram] In practice, diagrams taken from the two ends of the cylinder usually vary more or less, due to inequalities in the valve action. Again, the effective area of the piston on the crank end is less than that on the head end, by an amount equal to the area of the piston rod. For these reasons it is customary to compute the mean effective pressure of all the cards separately, and take, for use in the formula, the average of the various computations. The corrected value of the piston area is, as already stated, equal to (2_A_ - _a_)/2, in which _A_ is the area of the piston, and _a_ the area of the piston rod. Substituting these values for _A_ and _P_ in the formula, together with the length of stroke and average number of revolutions per minute, the indicated horsepower is easily computed. In making an ordinary test, diagrams are taken from both ends of the cylinder at 10-minute intervals for several hours, depending upon the accuracy required. The revolutions of the engine are counted for two or three-minute periods each time a pair of cards are taken, or still better, an automatic counter is used for the run, from which the average number of revolutions per minute may be determined. [Illustration: Fig. 51. Diagram for Illustrating Method of Computation] The friction of the engine is determined by taking a pair of cards while "running light," that is, with the belt thrown off, or the engine uncoupled, from the dynamo, if part of a direct-connected outfit. The friction load is then computed in horsepower from the indicator cards, and subtracted from the indicated horsepower when loaded. Thus we obtain the delivered or brake horsepower. The delivered horsepower divided by the indicated horsepower gives the mechanical efficiency. This may be expressed in the form of an equation as follows: I. H. P. - friction loss ------------------------ = mechanical efficiency. I. H. P. Planimeter The planimeter is an instrument for measuring areas in general, and especially for measuring the areas of indicator cards. Some forms give the mean effective pressure directly, without computations, by changing the scale to correspond with the spring used in the indicator. A planimeter of this type is shown in Fig. 52. The method of manipulating this instrument is as follows. Set the arm _BD_ equal to the length of the card _EF_, by means of the thumb screw _S_, and set the wheel at zero on the scale, which must correspond to the spring used in the indicator. Next, place the point _D_ at about the middle of the area to be measured, and set point _C_ so that the arm _CB_ shall be approximately at right angles with _BD_. Then move _D_ to the upper left-hand corner of the diagram, and with the left hand move _C_ either to the right or left until the wheel comes back exactly to the zero point on the scale; then press the point firmly into the paper. Now, go around the outline of the diagram with point _D_ from left to right, finishing exactly at the starting point. The mean effective pressure may now be read from the scale opposite the edge of the wheel. When very accurate results are required, the tracer point _D_ may be passed over the diagram several times, and the reading divided by the number of times it is thus passed around. With short cards, 3 inches and under in length, it is best to make the arm _BD_ twice the length of the card, and go around the diagram twice, taking the reading directly from the scale as in the first case. Determining Steam Consumption When it is desired to determine accurately the water rate of an engine, a boiler test should be carried on simultaneously with the test upon the engine, from which the pounds of dry steam supplied may be determined as described in MACHINERY'S Reference Series No. 67, "Boilers." Knowing the average weight of steam supplied per hour for the run, and the average indicated horsepower developed during the same period, the water rate of the engine is easily computed. Sometimes the average cylinder condensation for a given type and make is known for certain standard conditions. In this case an approximation may be made from an indicator diagram which represents the average operation of the engine during the test. [Illustration: Fig. 52. General Construction of Planimeter] A diagram shows by direct measurement the pressure and volume at any point of the stroke, and the weight of steam per cubic foot for any given pressure may be taken directly from a steam table. The method, then, of finding the weight of steam at any point in the stroke is to find the volume in cubic feet, including the clearance and piston displacement to the given point, which must be taken at cut-off or later, and to multiply this by the weight per cubic foot corresponding to the pressure at the given point measured on the diagram. As this includes the steam used for compression, it must be corrected, as follows, to obtain the actual weight used per stroke. Take some convenient point on the compression curve, as _Q_, in Fig. 53; measure its absolute pressure from the vacuum line _OX_ and compute the weight of steam to this point. Subtract this weight from that computed above for the given point on the expansion line, and the result will be the weight of steam used per stroke. The best point on the expansion line to use for this purpose is just before release, both because the maximum amount of leakage has taken place, and also because of the re-evaporation of a portion of the steam condensed during admission. The actual computation of the steam consumption from an indicator diagram is best shown by a practical illustration. _Example_--Let Fig. 53 represent a diagram taken from the head end of a 16 × 30-inch non-condensing engine, running at a speed of 150 revolutions per minute; the card is taken with a 60-pound spring; the clearance of the engine is 6 per cent; the average cylinder condensation is 20 per cent of the total steam consumption; the diameter of the piston rod is 3 inches. [Illustration: Fig. 53. Diagram for Calculating Steam Consumption] Measuring the card with a planimeter shows the mean effective pressure to be 48.2 pounds. The area of the piston is 201 square inches; the area of the piston rod is 7 square inches; hence, the average piston area = ((2 × 201) - 7)/2 = 198 square inches, approximately. Then 198 × 48.2 × 2.5 × 300 I. H. P. = ---------------------- = 217. 33,000 In Fig. 53, _GH_ is the atmospheric line; _OX_ is the line of vacuum or zero pressure, drawn so that _GO_ = 14.7 pounds on the scale; and _OY_ is the clearance line, so drawn that _ON_ = 0.06 _NX_. The line _PQ_ is drawn from _OX_ to some point on the compression line, as at _Q_. From _C_, a point on the expansion line, just before release, the line _CF_ is drawn perpendicular to _OX_. The following dimensions are now carefully measured from the actual diagram (not the one shown in the illustration), with the results given: _OX_ = 3.71 _OP_ = 0.42 _NX_ = 3.50 _CF_ = 0.81 _OF_ = 3.20 _QP_ = 0.81 On the indicator diagram, being taken with a 60-pound spring, all vertical distances represent pounds per square inch, in the ratio of 60 pounds per inch of height. The stroke of the engine is 30 inches or 2.5 feet. The length of the diagram _NX_ is 3.5 inches; hence, each inch in length represents 2.5/3.5 = 0.71 feet. From the above it is evident that vertical distances in Fig. 53 must be multiplied by 60 to reduce them to pounds pressure per square inch, and that horizontal distances must be multiplied by 0.71 to reduce them to feet. Making these reductions gives: _OX_ = 2.63 feet. _OP_ = 0.30 foot. _NX_ = 2.49 feet. _CF_ = 48.6 pounds. _OF_ = 2.27 feet. _QP_ = 48.6 pounds. As a card from the head end of the cylinder is taken to avoid corrections for the piston rod, the area is 201 square inches or 1.4 square foot. With the above data the volume and weight of the steam in the cylinder can be computed at any point in the stroke. When the piston is at _C_, the volume is 1.4 × 2.27 = 3.18 cubic feet. When the piston is at _Q_, the volume is 1.4 × 0.30 = 0.42 cubic foot. From a steam table the weight of a cubic foot of steam at 48.6 pounds absolute pressure is found to be 0.116 pounds. Therefore, the weight of steam present when the piston is at _C_ is 3.18 × 0.116 = 0.369 pounds. The weight of steam present when the piston is at _Q_ is 0.42 × 0.116 = 0.049 pound. That is the weight of steam in the cylinder at release is 0.369 pound, and the weight kept at exhaust closure for compression is 0.049 pound. The weight exhausted per stroke is therefore 0.369 - 0.049 = 0.32 pound. The number of strokes per hour is 150 × 2 × 60 = 18,000, from which the steam accounted for by the diagram is found to be 18,000 × 0.32 = 5760 pounds, or 5760 ÷ 217 = 26.5 pounds per indicated horsepower per hour. If the cylinder condensation for this type of engine is 20 per cent of the total steam consumption, the water rate will be 26.5 ÷ 0.8 = 33.1 pounds per indicated horsepower per hour. In the present case it has been assumed, for simplicity, that the head- and crank-end diagrams were exactly alike, except for the piston rod. Ordinarily, the above process should be carried out for both head and crank ends, and the results averaged. 
22245	----	----------------------------------------------------------------------- By Sara Ware Bassett The Invention Series Paul and the Printing Press Steve and the Steam Engine ----------------------------------------------------------------------- [Illustration: "It was the conquering of this multitude of defects that gave to the world the intricate, exquisitely made machine."--Frontispiece. See page 103.] ----------------------------------------------------------------------- The Invention Series STEVE AND THE STEAM ENGINE By Sara Ware Bassett With Illustrations By A. O. Scott Boston Little, Brown, And Company 1921 ----------------------------------------------------------------------- Copyright, 1921, By Little, Brown, and Company. All rights reserved Published September, 1921 The Plimpton Press Norwood Mass U S A ----------------------------------------------------------------------- CONTENTS CHAPTER PAGE I An Unpremeditated Folly 1 II A Meeting with an Old Friend 19 III A Second Calamity 34 IV The Story of the First Railroad 51 V Steve Learns a Sad Lesson 67 VI Mr. Tolman's Second Yarn 77 VII A Holiday Journey 94 VIII New York and What Happened There 110 IX An Astounding Calamity 125 X An Evening of Adventure 145 XI The Crossing of the Country 156 XII New Problems 169 XIII Dick Makes His Second Appearance 178 XIV A Steamboat Trip by Rail 192 XV The Romance of the Clipper Ship 205 XVI Again the Magic Door Opens 216 XVII More Steamboating 224 XVIII A Thanksgiving Tragedy 238 XIX The End of the House Party 248 ----------------------------------------------------------------------- LIST OF ILLUSTRATIONS "It was the conquering of this multitude of defects that gave to the world the intricate, exquisitely made machine" Frontispiece "You've got your engine nicely warmed up, youngster," he observed casually 9 "I wish you'd tell me about this queer little old-fashioned boat" 181 He was fighting to prevent himself from being drawn beneath the jagged, crumbling edge of the hole 244 ----------------------------------------------------------------------- STEVE AND THE STEAM ENGINE CHAPTER I AN UNPREMEDITATED FOLLY Steve Tolman had done a wrong thing and he knew it. While his father, mother, and sister Doris had been absent in New York for a week-end visit and Havens, the chauffeur, was ill at the hospital, the boy had taken the big six-cylinder car from the garage without anybody's permission and carried a crowd of his friends to Torrington to a football game. And that was not the worst of it, either. At the foot of the long hill leading into the village the mighty leviathan so unceremoniously borrowed had come to a halt, refusing to move another inch, and Stephen now sat helplessly in it, awaiting the aid his comrades had promised to send back from the town. What an ignominious climax to what had promised to be a royal holiday! Steve scowled with chagrin and disappointment. The catastrophe served him right. Unquestionably he should not have taken the car without asking. He had never run it all by himself before, although many times he had driven it when either his father or Havens had been at his elbow. It had gone all right then. What reason had he to suppose a mishap would befall him when they were not by? It was infernally hard luck! Goodness only knew what was the matter with the thing. Probably something was smashed, something that might require days or even weeks to repair, and would cost a lot of money. Here was a pretty dilemma! How angry his father would be! The family were going to use the automobile Saturday to take Doris back to Northampton for the opening of college and had planned to make quite a holiday of the trip. Now it would all have to be given up and everybody would blame him for the disappointment. A wretched hole he was in! The boys had not given him much sympathy, either. They had been ready enough to egg him on into wrong-doing and had made of the adventure the jolliest lark imaginable; but the moment fun had been transformed into calamity they had deserted him with incredible speed, climbing out of the spacious tonneau and trooping jauntily off on foot to see the town. It was easy enough for them to wash their hands of the affair and leave him to the solitude of the roadside; the automobile was not theirs and when they got home they would not be confronted by irate parents. How persuasively, reflected Stephen, they had urged him on. "Oh, be a sport, Steve!" Jack Curtis had coaxed. "Who's going to be the wiser if you do take the car? Anyhow, you have run it before, haven't you? I don't believe your father will mind." "Take a chance, Stevie," his chum, Bud Taylor, pleaded. "What's the good of being such a boob? Do you think if my father had a car and it was standing idle in the garage when a bunch of kids needed it to go to a school game I would hesitate? You bet I wouldn't!" "It isn't likely your Dad would balk at your using the car if he knew the circumstances," piped another boy. "We have got that match to play off, and now that the electric cars are held up by the strike how are we to get to Torrington? Don't be a ninny, Steve." Thus they had ridiculed, cajoled, and wheedled Steve until his conscience had been overpowered and, yielding to their arguments, he had set forth for the adjoining village with the triumphant throng of tempters. At first all had gone well. The fourteen miles had slipped past with such smoothness and rapidity that Stephen, proudly enthroned at the wheel, had almost forgotten that any shadow rested on the hilarity of the day. He had been dubbed a good fellow, a true sport, a benefactor to the school--every complimentary pseudonym imaginable--and had glowed with pleasure beneath the avalanche of flattery. As the big car with its rollicking occupants had spun along the highway, many a passer-by had caught the merry mood of the cheering group and waved a smiling salutation in response to their shouts. In the meanwhile, exhilarated by the novelty of the escapade, Steve had increased the speed until the red car fairly shot over the level macadam, its blurred outlines lost in the scarlet of the autumn foliage. Then suddenly when the last half-mile was reached and Torrington village, the goal of the pilgrimage, was in sight, quite without warning the panting monster had stopped and all attempts to urge it farther were of no avail. There it stood, its motionless engine sending out odors of hot varnish and little shimmering waves of heat. Immediately a hush had descended upon the boisterous company. There was a momentary pause, followed by a clamor of advice. When, however, it became evident that there was no prospect of restoring the disabled machine to action, one after another of the frightened schoolboys had dropped out over the sides of the car and after loitering an instant or two with a sort of shamefaced indecision, at the suggestion of Bud Taylor they had all set out for the town. "Tough luck, old chap!" Bud had called over his shoulder. "Mighty tough luck! Wish we had time to wait and see what's queered the thing; but the game is called at two-thirty, you know, and we have only about time to make it. We'll try and hunt up a garage and send somebody back to help you. So long!" And away they had trooped without so much as a backward glance, leaving Stephen alone on the country road, worried, mortified, and resentful. There was no excuse for their heartless conduct, he fumed indignantly. They were not all on the eleven. Five of the team had come over in Tim Barclay's Ford, so that several of the fellows Steve had brought were merely to be spectators of the game. At least Bud Taylor, his especial crony, was not playing. He might have remained behind. How selfish people were, and what a fleeting thing was popularity! Why, half an hour ago he had been the idol of the crowd! Then Bud had shouted: "Come ahead, kids, let's hoof it to Torrington!" and in the twinkling of an eye the tide had turned, the mob had shifted its allegiance and gone tagging off at the heels of a new leader. They did not mean to have their pleasure spoiled, not they! Scornfully Stephen watched them mount the hill, their crimson sweaters making a zigzag line of color in the sunshine; even their laughter, care-free as if nothing had happened, floated back to him on the still air, demonstrating how little concern they felt for him and his refractory automobile. Well might they proceed light-heartedly to the village, spend their money on sodas and ice-cream cones, and shout themselves hoarse at the game. No thought of future punishment marred their enjoyment and the program was precisely the one he had outlined for himself before Fate had intervened and raised a prohibitory hand. The fun he had missed was, however, of scant consequence now. All he asked was to get the car safely back to his father's garage before the family returned from New York on the afternoon train. Now that his excitement had cooled into sober second thought, he marveled that he had been led into committing such a monstrous offense. He must have been mad. Often he had begged to do the very thing he had done and his father had always refused to let him, insisting that an expensive touring car was no toy for a boy of his age. Perhaps there had been some truth in the assertion, too, he now admitted. Yet were he to hang for it, he could not see why he had not run the car exactly as his elders were wont to do. Of course he had had a pretty big crowd aboard and the heavy load might have strained the machinery; and possibly--just possibly--he had speeded a bit. He certainly had made phenomenally good time for he did not want the fellows to think he was afraid to let out the engine. Well, whatever the matter was, the harm was done now and he was in a most unenviable plight. No doubt it would cost a small fortune to get the automobile into shape again, more money than he had in the world; certainly far more than he had in his pocket at the present moment. What was he to do? Even suppose the boys did remember to send back help (they probably wouldn't--but suppose they did) how was he to pay a machinist? As he pictured himself being towed to a garage and the car being left there, he felt an uncomfortable sensation in his throat. He certainly was in for it now. It would be ignominious to charge the repairs to his father but that would be the only course left him. Fortunately Mr. Tolman, who was a railroad official, was well known in the locality and therefore there would be no trouble about obtaining credit; but to ask his father to pay the bills for this escapade was anything but a manly and honorable way out and Steve wished with all his heart he had never been persuaded into the wretched affair. If there were only some escape possible, some alternative from being obliged to confess his wrong-doing! But to hope to conceal or make good the disaster was futile. And even if he could cover up what had happened, how contemptible it would be! He detested doing anything underhanded. Only sneaks and cowards resorted to subterfuge and although he had been called many names in his life these two had not been among them. No, he should make a clean breast of what he had done and bear the consequences, and once out of his miserable plight he would take care never again to be a party to such an adventure. He had learned his lesson. So absorbed was he in framing these worthy resolutions that he did not notice a tiny moving speck that appeared above the crest of the hill and now came whirling toward him. In fact the dusty truck and its yet more dusty driver were beside him before he heeded either one. Then the newcomer came to a stop and he heard a pleasant voice: "What's the matter, sonny?" Stephen glanced up, trying bravely to return his questioner's smile. The man who addressed him was white-haired, ruddy, and muscular, and he wore brown denim overalls stained with oil and grease; but although he was middle-aged there was a boyish friendliness in his face and in the frank blue eyes that peered out from under his shaggy brows. "What's the trouble with your machine?" he repeated. "I don't know," returned Stephen. "If I did, you bet I wouldn't be sitting here." The workman laughed. "Suppose you let me have a look at it," said he, climbing off the seat on which he was perched. "I wish you would." "It is a pretty fine car, isn't it?" observed the man, as he approached it. "Is it yours?" "My father's." "He lets you use it, eh?" Stephen did not answer. "Some fathers ain't that generous," went on the man as he began to examine the silent monster. "If I had an outfit like this, I ain't so sure I'd trust it to a chap of your size. Still, if you have your license, I suppose you must know how to run it." [Illustration: "You've got your engine nicely warmed up, youngster," he observed casually. Page 9.] A shiver passed through Stephen's body. A license! What if the stranger should ask to see it? There was a heavy fine, he now remembered, for driving a car unless one were in possession of this precious paper, although what the penalty was he could not at the instant recall; he had entirely forgotten there were any such legal details. Fearfully he eyed the mechanic. The man, however, did not pursue the subject but instead appeared engrossed in carefully inspecting the automobile inside and out. As he poked about, now here, now there, Stephen watched him with constantly increasing nervousness; and after the investigation had proceeded for some little time and no satisfactory result had been reached, the boy's heart sank. Something very serious must be the matter if the trouble were so hard to locate, he reasoned. In imagination he heard his father's indignant reprimands and saw the Northampton trip shrivel into nothingness. The workman in the meantime remained silent, offering no comment to relieve his anxiety. What he was thinking under the shabby visor cap pulled so low over his brows it was impossible to fathom. His hand was now unscrewing the top of the gasoline tank. "You've got your engine nicely warmed up, youngster," observed he casually. "Maybe 'twas just as well you did come to a stop. You must have covered the ground at a pretty good clip." There certainly was something very disconcerting about the stranger's conversation and again Stephen looked at him with suspicion. "Oh, I don't know," he mumbled, trying to assume an off-hand air. "Perhaps we did come along fairly fast." "You weren't alone then." "N--o," was the uncomfortable reply. "The fellows who sent you back from the village were with me." For the first time the workman evinced surprise. "Nobody sent me," he retorted. "I just thought as I was going by that you looked as if you were up against it, and as I happen to know something about engines I pulled up to give you a helping hand. The fix you are in isn't serious, though." He smiled broadly as if something amused him. "What is the matter with the car?" demanded the boy desperately, in a voice that trembled with eagerness and anxiety and defied all efforts to remain under his control. "Why, son, nothing is wrong with your car. You've got no gasoline, that's all." "Gasoline!" repeated the lad blankly. "Sure! You couldn't have had much aboard when you started, I guess. It managed to bring you as far as this, however, and here you came to a stop. The up-grade of the hill tipped the little gas you did have back in the tank so it would not run out, you see. Fill her up again and she'll sprint along as nicely as ever." The relief that came with the information almost bowled Steve over. For a moment he could not speak; then when he had caught his breath he exclaimed excitedly: "How can I get some gasoline?" His rescuer laughed at the fevered question. "Why, I happen to have a can of it here on my truck," he drawled, "and I can let you have part of it if you are so minded." "Oh, I don't want to take yours," objected the boy. "Nonsense! Why not? I am going right past a garage on my way back and can get plenty more. We'll tip enough of mine into your tank to carry you home. It won't take a minute." The suggestion was like water to the thirsty. "All right!" cried Stephen. "If you will let me pay for it I shall be mightily obliged to you. I'm mightily obliged anyway." "Pshaw! I've done nothing," protested the person in the oily jumper. "What are we in the world for if not to do one another a good turn when we can?" As he spoke he extricated from his conglomerate load of lumber, tools, and boxes a battered can, the contents of which he began to transfer into Stephen's empty tank. "There!" ejaculated he presently, as he screwed the metal top on. "That isn't all she'll hold, but it will at least get you home. You are going right back, aren't you?" The boy glanced quickly at the speaker. "Yes." "That's right. I would if I were in your place," urged the man. Furtively Stephen scrutinized the countenance opposite but although the words had contained a mingled caution and rebuke there was not the slightest trace of interest in the face of the speaker, who was imperturbably wiping off the moist nickel cap with a handful of waste from his pocket. "Yes," he repeated half-absently, "I take it that amount of gas will just about carry you back to Coventry; it won't allow for any detours, to be sure, but if you follow the straight road it ought to fetch you up there all right." Stephen started and again an interrogation rose to his lips. Who was this mysterious mechanic and why should he assume with such certainty that Coventry was the abiding place of the car? He longed to ask but a fear of lengthening the interview prevented him from doing so. If he began to ask questions might not the stranger assume the same privilege and wheel upon him with some embarrassing inquiry? No, the sooner he was clear of this wizard in the brown overalls the better. But for the sake of his peace of mind he should like to know whether the man really knew who he was or whether his comments were simply matters of chance. There certainly was something very uncanny and uncomfortable about it all, something that led him to feel that the person in the jumper was fully acquainted with his escapade, disapproved of it, and meant to prevent him from prolonging it. Yet as he took a peep into the kindly blue eyes which he did not trust himself to meet directly he wondered if this assumption were not created by a guilty conscience rather than by fact. Certainly there was nothing accusatory in the other's bearing. His face was frankness itself. In books criminals were always fearing that people suspected them, reflected Steve. The man knew nothing about him at all. It was absurd to think he did. Nevertheless the boy was eager to be gone from the presence of those searching blue eyes and therefore he climbed into his car, murmuring hurriedly: "You've been corking to help me out!" The workman held up a protesting hand. "Don't think of it again," he answered. "I was glad to do it. Good luck to you!" With nervous hands Stephen started the engine and, backing the automobile about, headed it homeward. Now that danger was past his desire to reach Coventry before his father should arrive drove every other thought from his mind, and soon the mysterious hero of the brown jumper was forgotten. Although he made wonderfully good time back over the road it seemed hours before he turned in at his own gate and brought the throbbing motor to rest in the garage. A sigh of thankfulness welled up within him. The great red leviathan that had caused him such anguish of spirit stood there in the stillness as peacefully as if it had never stirred from the spot it occupied. If only it had remained there, how glad the boy would have been. He ventured to look toward the windows fronting the avenue. No one was in sight, it was true; but to flatter himself that he had been unobserved was ridiculous for he saw by the clock that his father, mother, and Doris must already have reached home. Doubtless they were in the house now and fully acquainted with what he had done. If they had not missed the car from the garage they would at least have seen it whirl into the driveway with him at the wheel. Any moment his father might appear at his shoulder. To delay was useless. He had had his fun and now in manly fashion he must face the music and pay for it. How he dreaded the coming storm! Once, twice he braced himself, then moved reluctantly toward the house, climbed the steps, and let himself in at the front door. He could hardly expect any one would come to greet him under the circumstances. An ominous silence pervaded the great dim hall but after the glare of the white ribbon of road on which his eyes had been so intently fixed he found the darkness cool and tranquilizing. At first he could scarcely see; then as he gradually became accustomed to the faint light he espied on the silver card tray a telegram addressed to himself and with a quiver of apprehension tore it open. Telegrams were not such a common occurrence in his life that he had ceased to regard them with misgiving. The message on which his gaze rested, however, contained no ill tidings. On the contrary it merely announced that the family had been detained in New York longer than they had expected and would not return until noon to-morrow. He would have almost another day, therefore, before he would be forced to make confession to his father! The respite was a welcome one and with it his tenseness relaxed. He even gained courage on the strength of his steadier nerves to creep into the kitchen and confront Mary, the cook, whom he knew must have seen him shoot into the driveway and who, having been years in the home, would not hesitate to lecture him roundly for his conduct. But Mary was not there and neither was Julia, the waitress. In the absence of the head of the house the two had evidently ascended to the third story there to forget in sleep the cares of daily life. Stephen smiled at the discovery. It was a coincidence. Unquestionably Fate was with him. It helped his self-respect to feel that at least the servants were in ignorance of what he had done. Nobody knew--nobody at all! With an interval of rest and a dash of cold water upon his face gradually the act he had committed began to sink back into normal perspective and loom less gigantic in his memory. After all was it such a dreadful thing, he asked himself. Of course he should not have done it and he fully intended to confess his fault and accept the blame. But was the folly so terrible? He owned that he regretted it and admitted that he was somewhat troubled over the probable consequences, and every time he awoke in the night a dread of the morrow came upon him. In the morning he rushed off to school, found the team had won the game, and came home feeling even more justified than before. Why, if he had not taken the car, the school might have forfeited that victory! All the afternoon as he sat quietly at his books he tried to keep this consideration uppermost in his mind. Then at dinner time there was a stir in the hall and he knew the moment he feared had arrived. The family were back again! Slowly he stole down over the heavily carpeted stairs. Yes, there they were, just coming in at the door, laughing and chatting gaily with Julia, who had let them in. The next instant his mother had espied him on the landing and had called a greeting. There was a smile on her face that reproached him for having yielded to the temptation to deceive her even for a second. "Such a delightful trip as we have had, Steve!" she called. "We wished a dozen times that you were with us. But some vacation you shall have a holiday in New York with your father to pay for what you have missed this time. You shall not be cheated out of all the fun, dear boy!" "Everything been all right here, son?" inquired his father from the foot of the stairs. "Yes, Dad." "Havens has not showed up yet, I suppose." The boy flushed. "No, sir." "It seems to take him an interminable time to have his tonsils out. If he does not appear pretty soon I shall have to get another man to run the car. We can't be left high and dry like this," fretted the elder man irritably. "Suppose I knew nothing about it, where would we be? I wished to-day you were old enough to have a license and could have come to the station to meet us. I believe with a little more instruction you could manage that automobile all right. Not that I should let you go racing over the country with a lot of boys. But you might be very useful in taking your mother and sister about and helping when we were in a fix like this. I think you would enjoy doing it, too." "I--I'm--sure I should," replied the lad, avoiding his father's eye and studying the toe of his shoe intently. It passed through his mind as he stood there that now was the moment for confession. He had only to say, "_I had the car out yesterday_," and the dreaded ordeal would be over. But somehow he could not utter the words. Instead he descended from the landing and followed the others into the library where the conversation immediately shifted to other topics. In the jumble of narrative his chance to speak was swallowed up nor during the next few days did any suitable opportunity occur for him to make his belated confession. When Mr. Tolman was not at meetings of the railroad board he was at his office or occupied with important affairs, and by and by so many events had intervened that to go back into the past seemed to Stephen idle sentimentality. At length he had lulled his conscience into deciding that in view of the conditions it was quite unnecessary to acquaint his father and mother with his wrong-doing at all. He was safely out of the entanglement and was it not just as well to accept his escape with gratitude and let sleeping dogs lie? All the punishments in the world could not change anything now. What would be the use of telling? CHAPTER II A MEETING WITH AN OLD FRIEND The day of the excursion to Northampton was one of those clear mornings when a light frost turned the maples to vermilion and in a single night transformed the ripening summer foliage to the splendor of autumn. The Tolman family were in the highest spirits; it was not often that Mr. Tolman could be persuaded to leave his business and steal away for a week-end and when he did it was always a cause for great rejoicing. Doris, elated at the prospect of rejoining her college friends, was also in the happiest frame of mind and tripped up and down stairs, collecting her forgotten possessions and jamming them into her already bulging suitcase. As for Steve, the prickings of conscience that had at first tormented him and made him shrink from being left alone with his father had quite vanished. He had argued himself into a state of mental tranquility where further punishment for his misdemeanor seemed superfluous. After his hairbreadth escape from disaster there was no danger, he argued, of his repeating the experiment, and was not this the very lesson all punishments sought to instill? If he had achieved this result without bothering his father about the details, why so much the better. Did not the old adage say that "experience is the best teacher"? Certainly in this case the maxim held true. Having thus excused his under-handedness and stifled the protests of his better nature he felt, or tried to feel, entirely at peace with the world; and as he now sauntered out to greet the new day he did it as jauntily as if he had nothing to conceal. Already the car was at the door with the luggage aboard and its engine humming invitingly. As the boy listened to the sound he could not but rejoice that the purring monster could tell no tales. How disconcerting it would be should the scarlet devil suddenly shout aloud: "Well, Steve, don't you hope we do not get stalled to-day the way we did going to Torrington?" Mercifully there was no danger of that. The engine might puff and purr and snort but at least it could not talk, and his secret was quite safe. This reflection lighted his face with courage and when the family came out to join him no one would have suspected that the slender boy waiting on the doorstep harbored a thought of anything but anticipation in the prospect of the coming holiday. "Is everything in, Steve?" asked his father, approaching with Doris's remaining grip. "I think so, Dad," was the reply. "It certainly seems as if I had piled in almost a dozen suitcases." "Nonsense, Stevie," pouted Doris. "There were only four." "Five, Miss Sophomore!" contradicted her brother. "Five! That one Dad is bringing makes the fifth, and I would be willing to bet that it is yours." "That's where you are wrong, Smartie," the girl laughed good-humoredly, making a mischievous grimace at him from beneath the brim of her saucy little toque of blue velvet. "I am not guilty of the extra suitcase. It's mother's." "Your mother's!" ejaculated Mr. Tolman incredulously. "Mercy on us! I never knew your mother to be starting out on a short trip with such an array of gowns." Then turning toward his wife, he added in bantering fashion: "Aren't you getting a little frivolous, my dear? If it were Doris now--" "But it isn't this time!" interrupted the young lady triumphantly. Her mother exchanged a glance with her and they both laughed. "No, Henry, I am the one to blame," Mrs. Tolman admitted. "You see, if I am to keep pace with my big son and daughter I must look my best; so I have not only brought the extra suitcase but I am going to be tremendously fussy as to where it is put." "I do believe Mater's brought all her jewels with her!" Steve declared wickedly. "Well, she shall have her sunbursts, tiaras, and things where she can keep her eye on them every moment. Suppose I put them down here at your feet, Mother." Without further ado, he started to lift the basket suitcase into the car. "Don't tip it up, son. Don't tip it up!" cautioned his mother. "Your mother is afraid of knocking some of the pearls or emeralds out of their setting," chuckled Mr. Tolman. "Go easy, Steve!" A general laugh arose as the offending piece of baggage was stowed away out of sight. An instant later wraps and rugs were bundled in, everybody was cosily tucked up, and Mr. Tolman placed his hands on the wheel. "Now we're off, Dad!" cried Stephen, as he sprang in beside his father. Mr. Tolman needed no second bidding. There was a whir, a leap forward, and the automobile glided down the long avenue and out into the highway. Steve, studying the road map, was too much interested in tracing out the route they were to follow to notice that after the car had spun along smoothly for several miles its speed lessened, and it was not until it came to a complete standstill that he aroused himself from his preoccupation sufficiently to see that his father was bending forward over the starter. "What's wrong, Henry?" inquired his wife from the back seat. "I can't imagine," was the impatient reply. "Had I not left the tank with gasoline in it, I should say it was empty; but of course that cannot be the case, for I always keep enough in it to carry us to the garage. Otherwise we should be stalled at our own doorstep and not able to get anywhere." Climbing out, he began to unscrew the metal top of the tank while Stephen watched him in consternation. The boy did not need to hear the result of the investigation for already the wretched truth flashed upon him. The tank was empty; of course it was! He knew that without being told. Had not the workman who had replenished it Wednesday said quite plainly that there was only enough gas in it to get him home to Coventry? He should have remembered to stop at the garage and take on an extra supply on the way back as his father always did. How stupid he had been! In his haste to get home he had forgotten every other consideration and the present dilemma was the result of his thoughtlessness. Yet how could he have stopped at the Coventry garage even had he thought of it? All the men there knew him and his father, and if he had gone there or had even driven through the center of the town somebody would have been sure to see him and mention the incident. Why, it was to avoid this very danger that he had returned by the less frequented way. The man in the brown jeans had certainly calculated to a nicety when he measured out that gasoline. He had not meant him to do any more riding that day; that was apparent. What business was it of his, anyway, and why was he so solicitous as to where he went? There was something puzzling about that man. Steve had thought so at the time. Not that it mattered now. All that did matter was that here they were stalled at the side of the road in almost the same spot where he had been stalled the other day; and they were there because he had neglected to procure gasoline. The lad felt the hot blood throb in his cheeks. Again the chance for confession confronted him and again his tongue was tied. In a word he could have explained the whole predicament; but he did not. Instead he sat as if stunned, the heart inside him pounding violently. He saw that his father was not only deeply annoyed but baffled to solve the incident. "The gas is all out; that's the trouble!" he announced. "What are we going to do, Dad?" inquired Doris anxiously. "Oh, we can get more all right, daughter," returned her father reassuringly. "Don't worry, my dear. But what I can't understand is how we come to be in such a plight." "Doesn't gasoline evaporate, Henry?" suggested Mrs. Tolman. "To some extent, yes; but there could be no such shrinkage as this unless there was a leak in the tank. I never dreamed the supply was so low. Well, it is my own fault. I should have made sure everything was right before we started." Steve shifted his position uncomfortably. He was manly enough not to enjoy hearing his father shoulder blame that did not rightfully belong to him. "Now let me think what we had better do," went on Mr. Tolman. "Unfortunately there isn't a house in sight from which we can telephone for help; and we are fully five miles from Torrington. Our only hope is that some one bound for the town may overtake us and allow Steve to ride to the village for aid." "Couldn't I walk it, Dad?" asked the boy, with an impulse to make good the mischief he had done. "Oh, no; I wouldn't do that unless the worst befalls," his father replied kindly. "We should gain nothing. It is a long tramp and would simply be a waste of time. Let us wait like Mr. Micawber, and see if something does not turn up." Wretchedly Stephen settled back into his seat. He would rather have walked to Torrington, done almost anything rather than remain there in the quiet autumn stillness and listen to the accusations of his conscience. What a coward he was! "It is a shame for us to be tied up here!" he heard Doris complain. "I know it, daughter, and I am as sorry as you are," responded her father patiently. "In fact, probably, I am more sorry, since it is through my own carelessness that we are stranded." Again the impulse to blurt out the truth and take the blame that belonged to him took possession of Stephen; but with resolution he forced it back. Nervously he fingered the road map. If he had only spoken at the beginning! It was harder now. He should have made a clean breast of the whole affair when his father got home from New York. Then was the time to have done it. But since he had let that opportunity pass it was awkward, almost absurd, to make confession now. He would much better keep still. In the meanwhile a gradual depression fell upon the occupants of the car. Mrs. Tolman did not speak; Doris subsided into hushed annoyance; and Mr. Tolman began to pace back and forth at the side of the road and anxiously scan the stretch of macadam that narrowed away between the avenue of trees bordering the highway. Presently he uttered an exclamation of relief. "Here comes a truck!" he cried. "We will tip the driver and persuade him to let you ride on to Torrington with him, Steve. This is great luck!" Stepping into the pathway of the approaching car he held up his hand and the passer-by came to a stop beside him. Stephen looked up expectantly; then a thrill of foreboding seized him and he quickly turned his head aside. It needed no second glance to assure him that the man whom his father was addressing was none other than the workman in the brown jeans who had rescued him from his former plight. He bent lower over the road map, trying to conceal his face and decide what to do. In another moment the teamster would probably recognize him, recall the incident of their former meeting, and hailing him as an old acquaintance, relate the entire story. The possibility was appalling, but terrible as it was it did not equal the disquietude he experienced when he heard his father ejaculate with sudden surprise: "Why, if it isn't O'Malley! I did not recognize you, Jake. You are just in time to extricate us from a most inconvenient situation. We are headed for Northampton and find ourselves without gasoline. If you can take my son along to Torrington with you so he can hunt up a garage and ride back with some one on a service car I shall be very grateful to you." "I'd be glad to go myself, sir." "No, no! I shall not allow you to do that," protested Mr. Tolman. "You are on your way to work and I could not think of detaining you. All I ask is that you take my boy along to the village." "I'd really be pleased to go, sir," reiterated O'Malley. "I am in no great rush." "No, I shan't hear to it, Jake," Mr. Tolman repeated. "Nevertheless I appreciate your offer. Take the boy along and that is all I'll ask. Come, Steve, jump aboard! O'Malley, son, is one of our railroad people, whose services we value highly. He is going to be good enough to let you ride over to Torrington with him." Although the introduction compelled Stephen to give the waiting employee a nod of greeting, he did not meet his eye or evince any sign of recognition, and he sensed that the light that had flashed into the man's face at sight of him died out as quickly as it had come. The boy had an uncomfortable realization as he climbed to the seat of the truck and took his place beside its driver that O'Malley must be rating him as a snob. No one but a cad would accept a stranger's kindness and then cut him dead the next time he encountered him. It was better to endure this misjudgment, however, than to acknowledge a previous acquaintance with the mechanic and thereby arouse his father's suspicion and curiosity. Hence, without further parley, he settled himself and in silence the truck started off. For some minutes he waited, expecting that when they were well out of earshot of the family the man at the wheel would turn and with a laugh make some reference to the adventure of the past week. It certainly must have amused him to find the great red car again stalled in the same spot, and what would be more natural than that he should comment on the coincidence and perhaps make a joke of the circumstance? But to the boy's chagrin the teamster did no such thing. Instead he kept his eyes fixed on the road and gave no evidence that he had ever before seen the lad at his elbow. Stephen was aghast. It was not possible the workman had forgotten the happening. He began to feel very uncomfortable. As the landscape slipped past and the car sped on, the distance to Torrington lessened. Still there seemed to be no prospect of the stranger at the wheel breaking his silence. If it had merely been a silence perhaps Steve would not have minded so much; but there was an implied rebuke in the stillness that nettled and stung and left him with a consciousness of being ignored by a superior being. "I say!" he burst out, when he could endure the ignominy of his position no longer, "don't you remember me, Mr. O'Malley?" The man who guided the car did not turn his head but he nodded. "I remember you all right," replied he politely. "I just thought you did not remember me." "Oh, I remembered you right away," declared Steve eagerly. "Did you?" There was a subtle irony in the tone that the lad was not clever enough to detect. "Of course." "Is that so!" came dryly from O'Malley. "Yes, indeed! I remembered you right away," Steve stumbled on. "You are the man who gave me the gasoline when I was stuck here Wednesday." "I am." "I knew you the first minute I saw you," repeated Stephen. "I did not notice any sign that you did," was the terse response. "Oh--well--you see, I couldn't very well speak back there," explained Steve with confusion. "They would all have wanted to know where I--I mean I would have to--it would just have made a lot of talk," concluded he lamely. For the first time the elder man, moving his eyes from the ribbon of gleaming highway, confronted him. "So your father did not know you had the car out the other day?" said he. "N--o." The workman showed no surprise. "I guessed as much," he remarked. "But of course you have told him since." "Not yet," Steve stammered. "I was going to--honest I was; but things kept interrupting until it got to be so late that it seemed silly to rake the matter all up. Besides, I shan't do it again, so what is the use of jawing about it?" He stopped, awaiting a response from the railroad employee; but none came. "Anyhow," he argued with rising irritability, "what good does it do to discuss things that are over and done with? You can't undo them." The man at the wheel vouchsafed no answer. "It is because I forgot to stop for more gas when I went home the other day that we are in this fix now," Steve finally blurted out, finding relief in brutal confession. Still the only reply to his monologue was the chugging of the engine. At last his voice rose to a higher pitch and there was anger in it. "I'm talking to you," he shouted in exasperation. "I am listening." "Well, why don't you say something?" "What is there to say?" "Why--eh--you could tell me what you think." "I guess you know that already." Stephen's face turned scarlet. "I did intend to tell my father," repeated he, instantly on the defensive. "Straight goods, I did." The man shrugged his shoulders. "It was only that it didn't seem to come right. You know how things go sometimes." He saw the workman's lip curl. "You think I ought to have told." "Have I said so?" "No, but I know you do think so." "I wasn't aware I'd expressed any opinion." "No--but--well--hang it all--you think I am a coward for not making a clean breast of the whole thing!" cried Stephen, now thoroughly enraged. "What do you think yourself?" O'Malley suddenly inquired with disconcerting directness. "Oh, I know I've been rotten," admitted the boy. "Still, even now--" He paused. "You mean that even now it isn't too late?" put in the truckman, his face lighting to a smile. "N--o; that wasn't exactly what I was going to say," began the lad, resuming his argumentative tone. "What I mean is that--" A swift frown replaced the elder man's smile. "Here we are at the garage," he broke in. "They will do whatever you want them to." He seemed in a hurry and as Stephen could find no excuse for lingering he climbed reluctantly out of the truck and stood balancing himself on the curb that edged the sidewalk. "I'm much obliged to you for bringing me over," he observed awkwardly. "That's all right." The man in the brown jeans started his engine. "Say, Mr. O'Malley!" called Stephen desperately. "Well?" "You--you--won't tell my father about my taking the car, will you?" he pleaded wretchedly. "_I_ tell him?" Never had he heard so much scorn compressed into three words. "You need have no worries," declared the man over his shoulder, a contemptuous sneer curling his lips. "I confess my own wrong-doing but I do not tattle the sins of other people. Your father will never be the wiser about you so far as I am concerned. Whatever you want him to know you will have to tell him yourself." Baffled, mortified, and stinging with humiliation as if he had been whipped, Stephen watched him disappear round the bend of the road. O'Malley despised him, that he knew; and he did not at all relish being despised. CHAPTER III A SECOND CALAMITY While hunting up the garage and negotiating for gasoline Steve thrust resolutely from his mind his encounter with O'Malley and the galling sense of inferiority it carried with it; but once on the highroad again the smart returned and the sting lingering behind the man's scorn was not to be allayed. It required every excuse his wounded dignity could muster to bolster up his pride and make out for himself the plausible case that had previously comforted him and lulled his conscience to rest. It was now more impossible than ever for him to make any confession, he decided; for having denied in his father's presence O'Malley's acquaintance it would be ridiculous to acknowledge that he had known the truck driver all along. Of course he could not do that. Whatever he might have said or done at the time, it was entirely too late to go back on his conduct now. One event had followed on the heels of another until to slip out a single stone of the structure he had built up would topple over the whole house. If he had spoken in the beginning that would have been quite simple. All he could do now was to let bygones be bygones and in the pleasure of to-day forget the mistakes of yesterday. Consoled by this reflection he managed to recapture such a degree of his self-esteem that by the time he rejoined the family he was once more holding his head in the air and smiling with his wonted lightness of heart. "We shall get you to Northampton now, daughter, without more delay, I hope," Mrs. Tolman affirmed when the car was again skimming along. "We may be a bit behind schedule; nevertheless a late arrival by motor will be pleasanter than to have made the trip by train." "I should say so!" was the fervent ejaculation. "Come, come!" interrupted Mr. Tolman. "I shall not sit back and allow you two people to cry down the railroads. They are not perfect, I will admit, and unquestionably trains do not always go at the hours we wish they did; a touring car is, perhaps, a more comfortable and luxurious method of travel, especially in summer. But just as it is an improvement over the train, so the train was a mighty advance over the stagecoach of olden days." "Oh, I don't know, Dad," Stephen mused. "I am not so sure that I should not have liked stagecoaches better. Think what jolly sport it must have been to drive all over the country!" "In fine weather, yes--that is, if the roads had been as excellent as they are now; but you must remember that in the old coaching days road-building had not reached its present perfection. Traveling by stage over a rough highway in a conveyance that had few springs was not so comfortable an undertaking as it is sometimes pictured. Furthermore you must not forget that it was also perilous, for not only was there danger from accident on these poorly constructed, unlighted thoroughfares but there was in addition the menace from highwaymen in the less populated districts. It took a great while to make a journey of any length, too, and to sleep in a coach where one was cramped, jolted, and either none too warm or miserably hot was not an unalloyed delight, as I am sure you will agree." "I had not thought of any of those things," owned Stephen. "It just seemed on the face of it as if it must have been fun to ride on top of the coach and see the sights as one does from the Fifth Avenue or London buses." "Oh," laughed his father, "a few hours' adventure like that is quite a different affair from making a stagecoach journey. I grant that to ride on a clear morning through the streets of a great city, or bowl along the velvet roads of a picturesque countryside as one frequently does in England is very delightful. To read Dickens' descriptions of journeys up to London is to long to don a greatcoat, wind a muffler about one's neck, and amid the cracking of whips and tooting of horns dash off behind the horses for the fairy city his pen portrays. Who would not have liked, for example, to set out with Mr. Pickwick for the Christmas holidays at Dingley Dell? Why, you cannot even read about it without seeing in your mind's eye the envious throng that crowded the inn yard and watched while the stableboys loosed the heads of the leaders and the steeds galloped away! And those marvelous country taverns he depicts, with their roaring fires, their steaming roasts, their big platters of fowl deluged in gravy, and their hot puddings! Was there ever writer more tantalizing?" "You will have us all hungry in two minutes, Dad, if you keep on," exclaimed Stephen. "And Dickens has us hungry, too," declared Mr. Tolman. "Nevertheless we must not forget that he paints but one side of the picture. He fails to emphasize what such a trip meant when the weather was cold and stormy, and those outside the coach as well as those inside it were often drenched with rain or snow, and well-nigh frozen to death. Moreover, while it is true that many of the inns along the turnpike were clean and furnished excellent fare, there were others that could boast nothing better than chilly rooms, damp beds, and only a very limited hospitality." "I believe you are a realist, Henry," said his wife playfully. Her husband laughed. "Nor must we lose sight of the time consumed by making a trip by coach," he went on. "Business in those days was not such a rushing matter as it is now, of course; yet even when issues of importance were at stake, or crises of life and death were to be met, there was no hurrying things beyond a certain point. Physical impossibility prohibited it. Horses driven at their liveliest pace could cover only a comparatively small number of miles an hour; and at the points where the relays were changed, or the horses fed and rested; the mails deposited or taken aboard; and passengers left or picked up, there were unavoidable delays. In fact, the strongest argument against the stagecoach, and the one that influenced public opinion the most, was this so-called fast-mail service; for in order to make connections with other mail coaches along the route and not forfeit the money paid for doing so, horses were often driven at such a merciless rate of speed that the poor creatures became total wrecks within a very short time. Many a horse fell in its tracks in the inn yards, having been lashed along to make the necessary ten miles an hour and reach a specified town on schedule. Other horses were maimed for life. It is tragic to consider that in England before the advent of the railroad about thirty thousand horses were annually either killed outright or injured so badly that they were of little use afterward." "Great Scott, Dad!" ejaculated Stephen. "And England was no more guilty in this respect than was America, for in the early days of our own country when people were demanding quicker transportation and swifter mail service thousands of noble beasts offered up their last breath in making the required rate of speed." "I suppose nobody thought about the horses," murmured the boy. "I am sure I didn't." "If the public thought at all it was too selfish to care, I am afraid, until threatened by the possibility of the total extermination of these creatures," was his father's reply. "This danger, blended with a humane impulse which rose from the gentler-minded portion of the populace, was the decisive factor in urging men to seek out some other method of travel. Then, too, the world was waking up commercially and it was becoming imperative to find better ways for transporting the ever increasing supplies of merchandise. The quick moving of troops from one point to another was also an issue. Although the canals of England enabled the government to carry quite a large body of men, the method was a slow one. In 1806, for instance, it took exactly a week to shift troops from Liverpool to London, a distance of thirty-four miles." "Why, they could have marched it in less time than that, couldn't they?" questioned Doris derisively. "Yes, the journey might easily have been made on foot in two days," nodded her father. "But in war time a long march which exhausts the soldiers is frequently an unwise policy, for the men are in no condition when they arrive to go into immediate action, as reënforcements often must." "I see," answered Doris. "When the Liverpool and Manchester Railroad was opened in 1830 this thirty-four miles was covered in two hours," continued Mr. Tolman. "Of course the quick transportation of troops was then, as now, of very vital importance. We have had plenty of illustrations of that in our recent war against Germany. Frequently the fate of a battle has hung on large reënforcements being speedily dispatched to a weak point in the line. Moreover, by means of the railroads, vast quantities of food, ammunition and supplies of all sorts can constantly be sent forward to the men in action. During the late war our American engineers laid miles and miles of track under fire, thereby keeping open the route to the front so that there was no danger of the fighters being cut off and left unequipped. It was a service for which they, as well as our nation, won the highest praise. And not only was there a constant flow of supplies but it was by means of these railroads that hospital trains were enabled to carry to dressing stations far behind the lines thousands of wounded men whose lives might otherwise have been lost." "I suppose the slightly wounded could be made more comfortable in this way, too," Mrs. Tolman suggested. "Yes, indeed," was the reply. "Not only were the men better cared for in the roomier hospitals behind the lines, but as there was more space there the peril from contagion, always a menace when large numbers of sick are packed closely together, was greatly lessened; for there is nothing army doctors dread so much as an epidemic of disease when there is not enough room to isolate the patients." "When did England adopt railroads in place of stagecoaches, Dad?" asked Doris presently. At the question her father laughed. "See here!" he protested good-humoredly, "what do you think I am? Just because I happen to be a superintendent do you think me a volume of railroad history, young woman? The topic, I confess, is a fascinating one; but I am off for a vacation to-day." "Oh, tell us, Dad, do!" urged the girl. "Nonsense! What is the use of spoiling a fine morning like this talking business?" objected her father. "But it is not business to us," interrupted Mrs. Tolman. "It is simple a story--a sort of fairy tale." "It is not unlike a fairy tale, that's a fact," reflected her husband gravely. "Imagine yourself back, then, in 1700, before steam power was in use in England. Now you must not suppose that steam had never been heard of, for an ancient Alexandrian record dated 120 B. C. describes a steam turbine, steam fountain, and steam boiler; nevertheless, Hero, the historian who tells us of them, leaves us in doubt as to whether these wonders were actually worked out, or if they were, whether they were anything but miniature models. Still the fact that they are mentioned goes to prove that there were persons in the world who at a very early date vaguely realized the possibilities of steam as a force, whether turned to practical uses or not. For years the subject remained an alluring one which led many a scientist into experiments without number. In various parts of the world men played with the idea and wrote about it; but no one actually produced any practical steam contrivance until 1650, when the second Marquis of Worcester constructed a steam fountain that could force the water from the moat around his castle as high as the top of one of the towers. The feat was looked upon as a marvel and afterward a larger fountain, similar in principle, was constructed at Vauxhall and from that time on the future of steam as a motive power was assured." "Did the Marquis of Worcester go on with his experiments and make other things?" demanded Stephen. "Apparently not," replied his father. "He did, nevertheless, furnish a basis for others to work on. Scientists were encouraged to investigate with redoubled zeal this strange vapor which, when controlled and directed, could carry water to the top of a castle tower. When in 1698 Savery turned Worcester's crude steam fountain to draining mines and carrying a water supply, every vestige of doubt that this mighty power could be applied to practical uses vanished." "Did the steam engine come soon afterward?" queried Doris, who had become interested in the story. "No, not immediately," answered Mr. Tolman, pausing to shift the gear of the car. "Before the steam engine, as we know it, saw the light, there had to be more experimenting and improving of the steam fountain. It was not until 1705 that Thomas Newcomen and his partner, John Calley, invented and patented the first real steam engine. Of course it was not in the least like the engines we use now. Still, it was a steam device with moving parts which would pump water, a tremendous advance over the mechanisms of the past where all the power had been secured by the alternate filling and emptying of a vacuum, or vacant receptacle, attached to the pump. Now, with Newcomen's engine a complete revolution took place. The engine with moving parts, the ancestor of our modern exquisitely constructed machinery, speedily crowded out the primitive steam fountain idea. The new device was very imperfect, there can be no question about that; but just as the steam fountain furnished the inspiration for the engine with moving parts, so this forward step became the working hypothesis for the engines that followed." "What engines did follow?" Doris persisted, "and who did invent our steam engine?" "Silly! And you in college," jeered Steve disdainfully. "I am not taking a course in steam engines there," laughed his sister teasingly. "Anyway, girls are not expected to know who invented all the machines in the world, are they, Dad?" Mr. Tolman waited a moment, then said soothingly: "No, dear. Girls are not usually so much interested in scientific subjects as boys are--although why they should not be I never could quite understand. Nevertheless, I think it might be as well for even a girl to know to whom we are indebted for such a significant invention as the steam engine. "It was James Watt," Stephen asserted triumphantly. "It certainly was," his father agreed. "And since your brother has his information at his tongue's end, suppose we get him to tell us more about this remarkable person." Stephen flushed. "I'm afraid," began he lamely, "that I don't know much more. You see, I studied about him quite a long time ago and I don't remember the details. I should have to look it up. I do recall the name, though--" His father looked amused. "I don't know which of you children is the more blameworthy," remarked he in a bantering tone. "Doris, who never heard of Watt; or Stephen, who has forgotten all about him." Both the boy and the girl chuckled good-humoredly. "At least I knew his name, Dad--give me credit for that," piped Steve. "That was something, certainly," Mrs. Tolman declared, joining in the laugh. "Well, since neither of us can furnish the story, I don't see but that you will have to do it, Dad," Doris said mischievously. "It would be a terrible humiliation if I should discover that I could not do it, wouldn't it?" replied Mr. Tolman with a smile. "In point of fact, there actually is not a great deal more that it is essential for one to know. It was by perfecting the engines of the Newcomen type and adding to them first one and then another valuable device that Watt finally built up the forerunner of our present-day engine. The progression was a gradual one. Now he would better one part, then some other. He surrounded the cylinder, for example, with a jacket, or chamber, which contained steam at the same pressure as that within the boiler, thereby keeping it as hot as the steam that entered it--a very important improvement over the old idea; then he worked out a plan by which the steam could be admitted at each end of the cylinder instead of at one end, as was the case with former engines. The latter innovation resulted in the push and pull of the piston rod. So it went." "How did Watt come to know so much about engines?" asked Stephen. "Oh, Watt was an engineer by trade--or rather he was a maker of mathematical instruments for the University of Glasgow, where he came into touch with a Newcomen engine. He also made surveys of rivers, harbors, and canals. So you see it was quite a consistent thing that a man with such a bent of mind should take up the pastime of experimenting with a toy like the steam engine in his leisure hours." "Did he go so far as to patent it, Henry?" Mrs. Tolman questioned. "Yes, he did. Many of our scientists either had not the wit to do this, alas, or else they were too impractical to appreciate the value of their ideas. In consequence the glory and financial benefit of what they did was often filched from them. But Watt was a Scotchman and canny enough to realize to some extent what his invention was worth. He therefore obtained a patent on it which was good for twenty-five years; and when, in 1800, this right expired he retired from business with both fame and fortune." "It is nice to hear of one inventor who got something out of his toil," Mrs. Tolman observed. "Indeed it is. Think of the many men who have slaved day and night, forfeited health, friends, and money to give to the world an idea, and never lived to receive either gratitude or financial reward, dying unknown or entirely forgotten. There is something tragic about the injustice of it. But Watt, I am glad to say, lived long enough to witness the service he had done mankind and enjoy an honored place among the great of the world." "Is the kind of engine Watt invented now in use?" Doris inquired. "Yes, that is a double-acting or reciprocating engine of a more perfect type," her father returned. "Mechanics and engineers went on improving Watt's engine just as he had improved those that had preceded it. It is interesting, too, to notice that after thousands of years scientists have again worked around to the steam turbine described so long ago in the Alexandrian records. This engine, although it does away with many of the moving parts introduced by Newcomen, preserves the essential principles of that early engine combined with Watt's later improvements. To-day we have a number of different kinds of engines, their variety differing with the purpose to which they are applied. Their cost, weight, and the space they require have been reduced and their power increased, and in addition we have made it possible to run them not only by means of coal or wood but by gasoline, oil, or electricity. We have small, light-weight engines for navigation use; mighty engines to propel our great warships and ocean liners; stationary engines for mills and power plants; to say nothing of the wonderful locomotive engines that can draw the heaviest trains over the highest of mountains. The principle of all these engines is, however, the same and for the brain behind them we must thank James Watt." "Was it Watt who invented the locomotive, too?" ventured Doris. Her father shook his head. "The perfecting of the locomotive, my dear, is, as Kipling says, another story." "Tell it to us." "Not now, daughter," protested Mr. Tolman. "I am far too hungry; and more than that I am eager to enjoy this beautiful country and forget railroads and locomotives." "Did you say you were hungry, Henry?" asked Mrs. Tolman. "I am--starved!" her husband said apologetically. "Isn't it absurd to be hungry so early in the day?" "It is nearly noon, Dad!" said Steve, glancing down at the clock in the front of the car. "Noon! Why, I thought it was still the middle of the morning." "No, indeed! While you have been talking we have come many a mile, and the time has slipped past," his wife said. "If all goes well--" The shot from a bursting tire rent the air. "Which evidently it does not," interrupted Mr. Tolman grimly, bringing the car to a stop. "How aggravating! We were almost into Palmer, where I had planned for us to lunch. Now it may be some little time before we can get anything to eat." "Motorist's luck! Motorist's luck, my dear!" cried Mrs. Tolman gaily. "An automobilist must resign himself to taking cheerfully what comes." "That is all very well," grumbled her husband, as he clambered out of the car. "Nevertheless you must admit that this mishap on the heels of the other one is annoying." Stephen also got out and the two bent to examine the punctured tire. "I should not mind so much if I were not so hungry," murmured Mr. Tolman. "How are you, Steve? Fainting away?" The boy laughed. "Well, I could eat something if I had it," he confessed. "I wish I hadn't mentioned food," went on Mr. Tolman humorously. "It was an unfortunate suggestion." "I'm hungry, too," piped Doris. "There, you see the epidemic you have started, Henry," called Mrs. Tolman accusingly. "Here is Doris vowing she is in the last throes of starvation." Nobody noticed that in the meanwhile the mother had reached down and lifted into her lap the small suitcase hidden in the bottom of the car. She opened the cover and began to remove its contents. At length, when a remark her husband made to her went unheeded, he sensed her preoccupation and came around to the side of the car where she was sitting. Immediately he gave a cry of surprise. "My word!" he exclaimed. "Steve, come here and see what your mother has." Stephen looked. There sat Mrs. Tolman, unpacking with quiet enjoyment sandwiches, eggs, cake, cookies, and olives. A shout of pleasure rose from the famished travelers. "So it was not your jewels, after all, Mater!" cried Stephen. "No, and after the way you have slandered me and my little suitcase, none of you deserve a thing to eat," his mother replied. "However, I am going to be magnanimous if only to shame you. Now climb in and we will have our lunch. You can fix the tire afterward." The men were only too willing to obey. As with brightened faces they took their seats in the car, Stephen smiled with affection at his mother. "Well, Mater, Watt was not the only person who lived to see himself appreciated; and I don't believe people were any more grateful to him for his steam engine than we are to you right now for this luncheon. You are the best mother I ever had." CHAPTER IV THE STORY OF THE FIRST RAILROAD The new tire went on with unexpected ease and early afternoon saw the Tolmans once more bowling along the highway toward Northampton. The valley of the Connecticut was decked with harvest products as for an autumnal pageant. Stacks of corn dotted the fields and pyramids of golden pumpkins and scarlet apples made gay the verandas of the old homesteads or brightened the doorways of the great red barns flanking them. "All that is needed to transform the scene into a giant Hallowe'en festival is to have a witch whisk by on a broomstick, or a ghost bob up from behind a tombstone," declared Mrs. Tolman. "Just think! If we had come by train we would have missed all this beauty." "I see plainly that you do not appreciate the railroads, my dear," returned her husband mischievously. "This is the second time to-day that you have slandered them. You sound like the early American traveler who asserted that it was ridiculous to build railroads which did very uncomfortably in two days what could be done delightfully by coach in eight or ten." "Why, I should have thought people who had never heard of motor-cars would have welcomed the quicker transportation the railroads offered," was Mrs. Tolman's reply. "One would have thought so," answered Mr. Tolman. "Still, when we recall how primitive the first railroads were, the prejudice against them is not to be wondered at." "How did they differ from those we have now, Dad?" Doris asked. "In almost every way," answered her father, with a smile. "You see at the time Stephenson invented his steam locomotive nothing was known of this novel method of travel. As I told you, persons were accustomed to make journeys either by coach or canal. Then the steam engine was invented and immediately the notion that this power might be applied to transportation took possession of the minds of people in different parts of England. As a result, first one and then another made a crude locomotive and tried it out without scruple on the public highway, where it not only frightened horses but terrified the passers-by. Many an amusing story is told of the adventures of these amateur locomotives. A machinist named Murdock, who was one of James Watt's assistants, built a sort of grasshopper engine with very long piston rods and with legs at the back to help push it along; with this odd contrivance he ventured out into the road one night just at twilight. Unfortunately, however, his restless toy started off before he was ready to have it, and turning down an unfrequented lane encountered a timid clergyman who was taking a peaceful stroll and frightened the old gentleman almost out of his wits. The poor man had never seen a locomotive before and when the steaming object with its glowing furnace and its host of moving arms and legs came puffing toward him through the dusk he was overwhelmed with terror and screamed loudly for help." A laugh arose from the listeners. "And that is but one of the many droll experiences of the first locomotive makers," continued Mr. Tolman. "For example Trevithick, another pioneer in the field, also built a small steam locomotive which he took out on the road for a trial trip. It chanced that during the experimental journey he and his fireman came to a tollgate and puffing up to the keeper with the baby steam engine, they asked what the fee would be for it to pass. Now the gate keeper, like the minister, had had no acquaintance with locomotives, and on seeing the panting red object looming like a specter out of the darkness and hearing a man's voice intermingled with its gasps and snorts, he shouted with chattering teeth: "There is nothing to pay, my dear Mr. Devil! Just d-r-i-v-e along as f-a-s-t--as--ever--you--can." His hearers applauded the story. "Who did finally invent the railroad?" inquired Doris after the merriment had subsided. "George Stephenson, an Englishman," replied her father. "For some time he had been experimenting with steam locomotives at the Newcastle coal mines where some agency stronger than mules or horses was needed to carry the products from one place to another. He had no idea of transporting people when he began to work out the suggestion. All he thought of was a coal train which would run on short lengths of track from mine to mine. But the notion assumed unexpected proportions until the Darlington road, the most ambitious of his projects, reached the astonishing distance of thirty-seven miles. When the rails for it were laid the engineer intended it should be used merely for coal transportation, as its predecessors had been; but some of the miners who lived along the route and were daily obliged to go back and forth to work begged that some sort of a conveyance be made that could also run along the track and enable them to ride to work instead of walking. So a little log house not unlike a log cabin, with a table in the middle and some chairs around it, was mounted on a cart that fitted the rails, and a horse was harnessed to the unique vehicle." "And it was this log cabin on wheels that gave Stephenson his inspiration for a railroad train!" gasped Doris. "Yes," nodded her father. "When the engineer saw the crude object the first question that came to him was why could not a steam locomotive propel cars filled with people as well as cars filled with coal. Accordingly he set to work and had several coach bodies mounted on trucks, installing a lever brake at the front of each one beside the coachman's box. In front of the grotesque procession he placed a steam locomotive and when he had fastened the coaches together he had the first passenger train ever seen." "It must have been a funny looking thing!" Steve exclaimed, smiling with amusement at the picture the words suggested. "It certainly was," agreed his father. "If you really wish to know how funny, some time look up the prints of this great-great-grandfather of our present-day Pullman and you will be well repaid for your trouble; the contrast is laughable." "But was this absurd venture a success?" queried Mrs. Tolman incredulously. "Indeed it was!" returned her husband. "In fact, Stephenson, like Watt, was one of the few world benefactors whose gift to humanity was instantly hailed with appreciation. The railroad was, to be sure, a wretched little affair when viewed from our modern standpoint, for there were no gates at the crossings, no signals, springless cars, and every imaginable discomfort. Fortunately, however, our ancestors had not grown up amid the luxuries of this era, and being of rugged stock that was well accustomed to hardships of every variety they pronounced the invention a marvel, which in truth it was. "You've said it!" chuckled Steve in the slang of the day. "In the meantime," went on Mr. Tolman, "conditions all over England were becoming more and more congested, and from every direction a clamor arose for a remedy. You see the invention of steam spinning machinery had greatly increased the output of the Manchester cotton mills until there was no such thing as getting such a vast bulk of merchandise to those who were eager to have it. Bales of goods waiting to be transported to Liverpool not only overflowed the warehouses but were even stacked in the open streets where they were at the mercy of robbers and storms. The canals had all the business they could handle, and as is always the result in such cases their owners became arrogant under their prosperity and raised their prices, making not the slightest attempt to help the public out of its dilemma. Undoubtedly something had to be done and in desperation a committee from Parliament sent for Stephenson that they might discuss with him the feasibility of building a railroad from Manchester to Liverpool. The committee had no great faith in the enterprise. Most of its members did not believe that a railroad of any sort was practical or that it could ever attain speed enough to be of service. However, it was a possibility, and as they did not know which way to turn to quiet the exasperated populace they felt they might as well investigate this remedy. It could do no harm." Mr. Tolman paused as he stooped to change the gear of the car. "So Stephenson came before the board, and one question after another was hurled at him. When, however, he was asked, half in ridicule, whether or not his locomotive could make thirty miles an hour and he answered in the affirmative, a shout of derision arose from the Parliament members. Nobody believed such a miracle possible. Nevertheless, in spite of their sceptical attitude, it was finally decided to build the Liverpool-Manchester road and about a year before its opening a date was set for a contest of locomotives to compete for the five-hundred-pound prize offered by the directors of the road." "I suppose ever so many engines entered the lists," ventured Steve with interest. "There were four," returned his father. "And Stephenson drove one of them?" "Yes." "Oh, I hope it got the prize!" put in Doris eagerly. Her father smiled at her earnestness. "It did," was his reply. "Stephenson's engine was called the 'Rocket' and was a great improvement over the locomotive he had used at the mines, for this one had not only a steam blast but a multi-tubular boiler, a tremendous advance in engine building." "I suppose that the winner of the prize not only got the money the road offered but his engine was the one chosen as a pattern for those to be used on the new railroad," ventured Stephen. "Precisely. So you see a great deal depended on the showing each locomotive made. Unluckily in the excitement a tinder box had been forgotten, and when it came time to start, the spark to light the fires had to be obtained from a reading glass borrowed from one of the spectators. This, of course, caused some delay. But once the fires were blazing and steam up, the engines puffed away to the delight of those looking on." "I am glad Stephenson was the winner," put in Doris. "Yes," agreed her father. "He had worked hard and deserved success. It would not have seemed fair for some one else to have stolen the fruit of his toil and brain. Yet notwithstanding this, his path to fame was not entirely smooth. Few persons win out without surmounting obstacles and Stephenson certainly had his share. Not only was he forced to fight continual opposition, but the opening of the Manchester and Liverpool road, which one might naturally have supposed would be a day of great triumph, was, in spite of its success, attended by a series of catastrophes. It was on September 15, 1830, that the ceremonies took place, and long before the hour set for the gaily decorated trains to pass the route was lined with excited spectators. The cities of Liverpool and Manchester also were thronged with those eager to see the engines start or reach their destination. There were, however, mingled with the crowd many persons who were opposed to the new venture." "Opposed to it?" Steve repeated with surprise. "Yes. It seems odd, doesn't it?" "But why didn't they want a railroad?" persisted the boy. "I thought that was the very thing they were all demanding." "You must not forget the condition of affairs at the time," said his father. "Remember the advent of steam machinery had deprived many of the cotton spinners of their jobs and in consequence they felt bitterly toward all steam inventions. Then in addition there were the stagecoach drivers who foresaw that if the railroads supplanted coaches they would no longer be needed. Moreover innkeepers were afraid that a termination of stage travel would lessen their trade." "Each man had his own axe to grind, eh?" smiled Steve. "I'm afraid so," his father answered. "Human nature is very selfish, and then as now men who worked for the general welfare regardless of their own petty preferences were rare. To the side of the enemies of the infant invention flocked every one with a grievance. The gentry argued that the installation of locomotives would frighten the game out of the country and ruin the shooting. Other opposers contended that the smoke from the engines would not only kill the birds but in time kill the patrons of the railroads as well. Still others protested that the sparks from the funnels might set fire to the fields of grain or to the forests. A swarm of added opponents dwelt on the fact that the passengers would be made ill by the lurching of the trains; that the rapid inrush of air would prevent their breathing; and that every sort of people would be herded together without regard to class,--the latter a very terrible calamity in a land where democracy was unknown. Even such intelligent men as the poet Wordsworth and the famous writer Ruskin came out hotly against the innovation, seeing in it nothing but evil." "Didn't the opening of the Manchester and Liverpool Railroad convince the kickers they were wrong?" asked Steve. "Unfortunately not," was Mr. Tolman's reply. "You see several unlucky incidents marred the complete success of the occasion. As the trains trimmed with bunting and flowers started out the scene seemed gay enough. On one car was a band of music; on another the directors of the road; and on still another rode the Duke of Wellington, who at that time was Prime Minister of England and had come down from London with various other dignitaries to honor the enterprise. Church bells rang, cannon boomed, and horns and whistles raised a din of rejoicing. But everywhere among the throng moved a large group of unemployed laborers who had returned from the Napoleonic wars in a discontented frame of mind and resented the use of steam machinery. They were on edge for trouble and if there were none they were ready to make it. So strong was the resentment of this element against the government that it seemed tempting Providence for the Prime Minister to venture into the manufacturing district of Manchester. At first it was decided that he would better omit the trip altogether; but on second thought it seemed wiser for him not to add fuel to the flames by disappointing the mill workers. The audience was in too ugly a mood to be angered. Therefore Wellington bravely resolved to carry out the program and ride in one of the open cars." "I hope nothing happened to him, Dad!" gasped Doris breathlessly. "Nothing beyond a good many minor insults and indignities," responded her father. "He was, however, in constant peril, and to those who bore the responsibility of the function he was a source of unceasing anxiety. But in spite of the jeers of the mob, their crowding and pushing about his car, he kept a smiling face like the true gentleman he was. Some of the rougher element even went so far as to hurl missiles at him. You can imagine how worried his friends were for his safety and how the directors who had invited him fidgeted. And as if this worry were not enough, by and by a fine rain began to fall and those persons riding in the open coaches, as well as the decorations and the spectators, got well drenched. Then there were delays on the turnouts while one train passed another; and as a climax to these discouragements, Mr. Hickson, a member of Parliament from Liverpool, got in the path of an approaching engine, became confused and was run over; and although Stephenson himself carried him by train to Liverpool he died that evening." "I should call the fête to introduce the steam engine into England a most disastrous and forlorn one," remarked Mrs. Tolman. "Well, in reality it was not such a failure as it sounds," replied her husband, "for only those most closely connected with it sensed the misfortunes that attended it. The greater part of the people along the route were good-humored and pleased; they marveled at the trains as they passed, cheered the Duke and the authorities with him, listened with delight to the band, and made a jest of the rain. A holiday crowd, you know, is usually quite patient. Hence the delays that fretted the guests and the officials of the road did not annoy the multitudes so vitally." "Poor Stephenson really got some satisfaction out of the day then," sighed Mrs. Tolman. "Oh, yes, indeed," said her husband. "Although I fancy the death of Mr. Hickson must have overshadowed his rejoicings. Notwithstanding this, however, the railroad proved itself a practical venture, which was the main thing. Such slight obstacles as the terror of the horses and the fact that the tunnels into Liverpool were so low that the engines had to be detached and the trains hauled into the yards by mules could be remedied." A flicker of humor danced in Mr. Tolman's eyes. "And did England begin to build railroads right away?" Steve inquired. "Yes, and not only England but France also. Frenchmen who crossed the Channel took home glowing accounts of the novel invention and immediately the French Government realized that that country must also have railroads. But just as the conservative element in England had been sceptical and blocked Stephenson's progress--or tried to--so a corresponding faction in France did all it could to cry down the enterprise. Even those who upheld the introduction of the roads advocated them for only short distances out of Paris; a long trunk route they labeled as an absurdity. Iron was too expensive, they argued; furthermore the mountains of the country rendered extensive railroading impossible. France did not need railroads anyway. Nevertheless the little group of seers who favored the invention persisted and there was no stopping the march of which they were the heralds. Railroads had come to stay and they stayed." "It was a fortunate thing they did, wasn't it?" murmured Doris. "A very fortunate thing," returned Mr. Tolman heartily. "Every great invention is usually suggested by a great need and so it was with this one. By 1836 the craze for railroad building swept both hemispheres. In England the construction of lines to most out-of-the-way and undesirable places were proposed, and the wildest schemes for propelling trains suggested; some visionaries even tried sails as a medium of locomotion instead of steam. Rich and poor rushed to invest their savings in railroads and alas, in many cases the misguided enthusiasts lost every shilling of their money in the project. Great business firms failed, banking houses were ruined, and thousands of workmen were thrown out of employment. In consequence a reaction followed and it was years before wary investors could again be induced to finance a railroad. In the interim both engines and coaches underwent improvement, especially the third-class carriage which in the early days was nothing more than an open freight car and exposed its unhappy patrons to snow, rain, and freezing weather." "Great Scott!" cried Steve. "I should say there was room for improvement if that was the case." "There was indeed," echoed his father. "In fact, it was a long time before travel by train became a pleasure. Most of the engines used pitch pine or soft coal as a fuel and as there were no guards on the smokestacks to prevent it, the smoke, soot, and cinders used to blow back from the funnels and shower the passengers. On the first railroad trip from New York to Albany those sitting outside the coaches were compelled to put up umbrellas to protect themselves from these annoyances." "Imagine it!" burst out Doris, with a rippling laugh. "Nor were the umbrellas of any service for long," continued Mr. Tolman, "for the sparks soon burned their coverings until nothing but the steel ribs remained." "I don't wonder the trip was not a pleasure," smiled Mrs. Tolman. "Yet, in spite of its discomfort, it was a novelty and you must not forget that, as I said before, the public of that period was a simple and less exacting one than is the public of to-day. We make a frightful fuss if we are jolted, chilled, crowded, delayed, or made uncomfortable; but our forefathers were a hale and hearty lot--less overworked perhaps, less nervous certainly, less indulged. They had never known anything better than cold houses, draughty and crowded stagecoaches, and stony highways--plenty of obstacles, you see, and few luxuries. Therefore with naïve delight they welcomed one new invention after another, overlooking its defects and considering themselves greatly blessed to have anything as fine. Probably we, who are a thousand per cent better off than they, do more grumbling over the tiny flaws in the mechanism of our lives than they did over the mammoth ones." "Oh, come, Dad!" protested Stephen. "Aren't you putting it rather strong?" "Not a whit too strong, Steve," Mrs. Tolman interrupted. "I believe we are a fussy, pampered, ungrateful generation. It is rather pathetic, too, to think it is we who now reap the benefits of all those perfected ideas which our ancestors enjoyed only in their most primitive beginnings. It seems hardly fair that Stephenson, for example, should never have seen a modern Pullman. "He was spared something, wasn't he, Dad?" chuckled Steve mischievously. But Mr. Tolman did not heed the remark. "He had the vision," returned he softly, "the joy of seeing the marvel for the first time, imperfect as it was. Perhaps that was compensation enough. It is the reward of every inventor. Remember it is no mean privilege to stand upon the peak in Darien which Keats pictures." CHAPTER V STEVE LEARNS A SAD LESSON No more disasters attended the journey and the travelers spun swiftly on to Northampton, arriving at the old New England town late in the afternoon. What a scene of activity the college campus presented! Bevies of girls, hatless and in gay-colored sweaters, drifted hither and thither, their laughter floating through the twilight with musical clearness. Occasionally some newcomer would join a group and a shout of welcome would hail her advent. Although Steve turned away from these gushing greetings with masculine scorn nevertheless he was far more interested in the novel picture than he would have been willing to admit. More than once he caught his eyes following a slender figure in white, across whose hair the sunset slanted, turning its blowing masses to a glory of gold. With what ease and freedom the girl moved! And when, as she passed, some one unceremoniously tossed her a ball and she caught it with swift accuracy, his admiration was completely won. Steve speculated as to whether she would prove to be as pretty at close range as she was at a distance and decided not. Distance always brings a glamor with it. However, pretty or not, there was no disputing that she was a great favorite for every circle of students opened its magic ring at her approach and greeted her with a noisy clamor of affection. That she held herself with quiet reserve and was less demonstrative than those about her did not appear to lessen in the least their regard for her, and as Stephen watched he registered the wager that she was a person of more common sense than most girls. Until recently it had been his habit to condemn the entire sex; but of late he had discovered that exceptions might be made to his rule. There were girls in the world worth noticing, even some worth talking to; and he felt certain that this attractive creature in white was one of them. However, it was an absurdity to be thinking about her now and quite beneath his dignity. But he meant sometime, when he could do so in casual fashion, to find out from Doris who she was. He had a curiosity to know what this person who looked as if she could row a boat, swim, and play tennis well, was called. Doris was always raving about her roommate, Jane Harden. She had said so much about her that he fairly detested the sound of her name. Now if only Jane Harden were a girl like this one, there would be some reason and excuse for being enthusiastic over her. To have this guest brought home to spend the Christmas holidays would be a pleasure to look forward to. How well she would skate and how gracefully; and how pretty she would be, especially if she had her hat off as she had now! It was Doris who interrupted his reverie with the words: "I hate to have you dear people go but I suppose you will have to. But do just wait long enough for me to see if I can't find Jane somewhere. She is crazy to meet my family and will scold me to death if I let you get away." "I am afraid we can't stay but a moment or two, dear," objected Mrs. Tolman. "It is growing late, you know, and we must get to the hotel before it is too dark." "But I won't delay you a second, Mother--truly, I won't. I do want you to meet Jane. I'll ask the girls if they have seen her anywhere." "If you get out into that mob they'll fall all over you and you'll never get back," growled Steve, who was beginning to feel hungry and was none too graciously inclined toward the prospective stranger. "Oh, yes, I will," laughed Doris as she darted away. In spite of this sanguine prediction, however, she did not return as promptly as she had promised, and Mr. Tolman began to fidget uneasily. "We really ought to be starting on," he said at last. "Where is that child?" "I knew she'd stop to admire everybody's new hat and talk over the whole summer," grumbled Steve scornfully. "You are thinking of your dinner, son," his mother put in playfully. "You bet I am! I'm hungry as a bear." A pause followed in which visions of a big beefsteak with crisply fried potatoes blotted out every other picture from Steve's mind. "Perhaps we ought not to have waited," he heard his mother murmur. "But I had not the heart to disappoint Doris. She is so fond of Jane and has talked so much about her! I had no idea it would take her so long to--" "Here she comes!" Mr. Tolman broke in. Stephen glanced up. Yes, there was Doris hurrying across the grass and beside her, walking with the same free and buoyant swing, was the girl of the golden hair,--Jane Harden. With the same reserve and yet without a shadow of self-consciousness she came forward and in acknowledgment of the hurried introductions extended her hand with a grave smile of welcome; but both smile and gesture carried with them a sincerity very appealing. When she greeted Steve he flushed at being addressed as _Mr. Tolman_ and mentally rose six inches in his boots. Yes, she was decidedly pretty, far prettier than she had been in the distance even. In all his life he had never seen a more attractive girl. "I hope, Jane, that you are coming home with Doris for a visit sometime when your own family can spare you," he heard his mother say. "We all should like to have you." "And I should like to come," was the simple and direct answer. "Do plan on it then. Come any time that you can arrange to. We should very much enjoy having you, shouldn't we, Stephen?" Stephen, so suddenly appealed to, turned very red and answered "Yes" in a tone that seemed to come gruffly from way down inside his chest, and then to the sound of hasty farewells the car started and shot out into the village street and the campus with its rainbow-hued occupants was lost to sight. "A charming girl, isn't she?" Mrs. Tolman said to her husband. "So natural and unaffected! Doris says that she is quite the idol of the college and bids fair to be class president. I wish Doris would bring her home for the holidays." Inwardly Steve echoed the sentiment but outwardly he preserved silence. He was too human a boy to dwell long on thoughts of any girl and soon Jane Harden was quite forgotten in the satisfaction of a steaming dinner and a comfortable bed, and the fairy journey of the next day when amid a splendor of crimson and gold the glories of Jacob's Ladder and the Mohawk Trail stretched before his eyes. Within the week the big red car headed for Coventry and without a mishap rolled into the familiar main street of the town which never had seemed dearer than after the interval of absence. As the automobile sped past, friendly faces nodded from the sidewalks and hands were waved in greeting. Presently his mother called from the tonneau: "Isn't that the Taylors' car, Henry, coming toward us? If it is do stop, for I want to speak to them." Mr. Tolman nodded and slowed down the engine, at the same time putting out his hand to bring the on-coming car to a standstill. Yes, there were the Taylors, and on the front seat beside the chauffeur sat "But," the friend who had been most influential in coaxing Stephen into the dilemma of the past fortnight. It was Bud, Steve could not forget, who had been the first to drop out of the car when trouble had befallen and who had led the other boys off on foot with him to Torrington. The memory of his chum's treacherous conduct still rankled in Steve's mind. He had not spoken to him since. But now here the two boys were face to face and unless they were to betray to their parents that something was wrong they must meet with at least a semblance of cordiality. The question was which of them should be the first to make the advance. Twice Bud cleared his throat and appeared to be on the verge of uttering a greeting when he encountered Stephen's scowl and lost courage to call the customary: "Ah, there, Stevie!" And Stephen, feeling that right was on his side and being too proud to open the conversation, could not bring himself to say: "Hi, Bud!" as he always did. As a result the schoolmates simply glared at each other. Fortunately their elders were too much occupied with friendly gossip to notice them and it was not until the talk shifted abruptly into a channel that appalled both boys that their glance met with the sympathy of common danger. It was Bud's mother from whose lips the terrifying words innocently fell. "Havens ill and you in New York Wednesday!" she exclaimed incredulously. "But I certainly thought I saw your car turning into the gate that very afternoon." "I guess not, my dear," asserted Mrs. Tolman tranquilly. "The car has not been out of the garage until now. It must have been somebody else you saw." "But it was your car--I am certain of it," persisted Mrs. Taylor. "Nonsense, Mary!" laughed her husband. "If the car has been in the garage for a week how could it have been. You probably dreamed it. You want a big red car so much yourself that you see them in your sleep." "No, I don't," protested Mrs. Taylor smiling good-humoredly at her husband's banter. "Well, it may have been the Woodworths'," Mrs. Tolman said with soothing inspiration. "They have a car like ours and Mrs. Woodworth came to call while I was away. I'll ask the maid when I get home." "Y-e-s, it may have been the Woodworths'," admitted Mrs. Taylor reluctantly. It was plain, however, that she was unconvinced. "But I could have staked my oath that it was your car and Steve driving it," she added carelessly. "Steve!" Mr. Tolman ejaculated. "Oh, Steve never drives the car," put in Mrs. Tolman quickly. "He is not old enough to have a license yet, you know. That proves absolutely that you were mistaken. But Stephen has run the car now and then when Havens or his father were with him and he does very well at it. Some day he will be driving it alone, won't you, son?" Bending forward she patted the boy's shoulder affectionately. For an instant it seemed to Stephen as if every one in both cars must have heard the _pound_, _pound_, _pound_ of his heart, as if everybody from Coventry to Torrington must have heard it. Helplessly he stared at Bud and Bud stared back. No words were needed to assure the two that once again they were linked together by misdoing as they often had been in the past. Bud looked anxiously toward his chum. He was a mischievous, happy-go-lucky lad but in his homely, freckled face there was a winsome manliness. Whatever the scrapes he got into through sheer love of fun it was characteristic of him that he was always courageous enough to confess to them. This was the first inkling he had had that Stephen had not acquainted his father with the escapade of the previous week and such a course was so at variance with his own frank nature that he was aghast. Even now he waited, expecting his pal would offer the true explanation of the mystery under discussion. He was ready to bear his share of the blame,--bear more than belonged to him if he could lighten Steve's sentence of punishment. But the silence remained unbroken and the words he expected to hear did not come. A wave of surprise swept over his face, surprise followed by a growing scorn. It came to him in a flash that Stephen Tolman, the boy he had looked up to as a sort of idol, was a coward, a coward! He was afraid! It seemed impossible. Why, Steve was always in the thick of the football skirmishes, never shrinking from the roughness of the game; he was a fearless hockey player, a dauntless fighter. Coward was the last name one would have thought of applying to him. And yet here he sat cowering before the just result of his conduct. Bud was disappointed, ashamed; he turned away his head but not before the wretched lad who confronted him had caught in his glance the same contemptuous expression he had seen in O'Malley's face. Again Stephen was despised and knew it. Nevertheless it would not do to betray his secret now. He must not show that he was disconcerted. At every cost he must brazen out the affair. He had gone too far to do otherwise. He wondered as he sat there if any one suspected him; if his father, whose eye was as keen as that of an eagle, had put together any of the threads of evidence. He might be cherishing suspicions this very moment. It seemed impossible that he shouldn't. If only he would speak and have it over! Anything would be better than this suspense and uncertainty. Mr. Tolman, however, maintained unwonted stillness and save for a restless twitching of his fingers on the wheel of the car did not move. If, thought Steve miserably, he could summon the nerve to look up, he would know in a second from his father's face whether he was annoyed or angry. At last the situation became unbearable and come what might he raised his eyes. To his amazement his father was sitting there quite serenely and so was everybody else, and the pause that seemed to him to stretch into hours had glided off as harmlessly and as naturally as other pauses. Apparently nobody was thinking about him, at least nobody but Bud. With a sigh of relief his tense muscles relaxed. He could trust Bud not to betray him. Once again he was safe! CHAPTER VI MR. TOLMAN'S SECOND YARN For a day or two it seemed to Stephen that he would never cease to be haunted by the shame and regret that followed his confiscation of the big red touring car, or forget the good resolutions he made in consequence; but within an incredibly short time both considerations were thrust into the background by the rush of life's busy current. School and athletics kept him occupied so that he had little leisure for thought, and when he was in the house his father and mother smiled on him as affectionately as before, which did much to restore to him his normal poise. Long ago the boys had dropped the motor-car episode from their memories and even Bud Taylor did not refer to it when he and Steve came together to organize the hockey team for the approaching matches. In the meantime the Thanksgiving holidays were drawing near and Mr. Tolman suggested that he and Stephen should run over to New York for a short visit. With the prospect of so much pleasure was it strange the boy ceased to dwell on the unhappiness of the past or the possibility of disaster in the future? The coming journey to New York was, to be sure, no great novelty, for Stephen had often accompanied his father there on business excursions; nevertheless such an outing was a treat to which he looked forward as a sort of Arabian Nights adventure when for a short time he stayed at a large hotel, ate whatever food pleased his fancy, and went sight-seeing and to innumerable "shows" with his father. He was wont to return to Coventry after the holiday with a throng of happy memories and many a tale of marvels with which to entertain the boys. Therefore when he and his father boarded the express Thanksgiving week the lad was in the highest spirits. "Motor-cars are all very well," observed Mr. Tolman, as the porter stowed their luggage away, "but on a cold night like this a Pullman car on a well-laid track is not to be despised. Eh, son?" "I don't believe that I should want to travel to New York in a touring-car at this time of year," agreed Stephen, smiling. "It is getting too late in the season to use an open car, anyway," rejoined his father. "I have delayed putting the car up because I have been hoping we might have a little more warm weather; but I guess the warm days have gone and the winter has come to stay now." "But there is no snow yet, Dad." "No. Still it is too chilly to drive with any comfort. The Taylors shipped their car off last week and when I get home I shall do the same." Stephen looked disappointed. "I don't mind the cold when I'm wrapped up," he ventured. "You are not at the wheel, son," was his father's quick retort. "The man who is has his fingers nipped roundly, I can assure you. It is a pity we have become so soft and shrink so from discomfort. Think what our forbears endured when they went on journeys!" "Neither the English stagecoaches nor Stephenson's railroad could have been very comfortable, to judge from your descriptions of them," laughed Steve. "Oh, don't heap all the blame on the English," his father replied. "Our own modes of travel in the early days were quite as bad as were those on the other side of the water." "I wish you would tell me about the first American railroads," said the boy. "I was wondering about them the other night." Mr. Tolman settled back in his seat thoughtfully. "America," he answered presently, "went through a pioneer period of railroading not unlike England's. Many strange steam inventions were tried in different parts of the country, and many fantastic scientific notions put before the public. Even previous to Watt's steam engine Oliver Evans had astonished the quiet old city of Philadelphia by driving through its peaceful streets in a queer steam vehicle, half carriage and half boat, which he had mounted on wheels. Evans was an ingenious fellow, a born inventor if ever there was one, who worked out quite a few steam devices, some of which Watt later improved and adopted. Then in 1812 John Stevens of New York got interested in the steam idea and urged the commissioners of his state to build a railroad between Lake Erie and Albany, suggesting that a steam engine not unlike the one that propelled the Hudson River ferryboats could be used as power for the trains. He was enthusiastic over the scheme but the New York officials had no faith in the proposition, insisting that a steam locomotive could never be produced that would grip the rails with sufficient tension to keep cars on the track or draw a heavy load." "They'd better have given the plan a showdown," interrupted Steve grimly. "No doubt that is true," admitted his father. "However, it is very easy for us, with our knowledge of science, to look back and laugh at their mistakes. The world was very new in those days and probably had we lived at that time and been equally ignorant of railroads and engines we should have been just as cautious and unbelieving. The railroad was still a young invention, you must remember, and to many persons it seemed a rather mad, uncertain enterprise." "When was the first American railroad built?" inquired the lad. "If by a railroad you mean something which moved along rails like a tram-car, the first such road was built at Quincy, Mass., in 1826; but it was not a steam railroad. It was merely a train of cars drawn by horses along a track that spanned a series of stone ties. Nor was it very extensive in length. In fact, it was only three miles long and probably would not have been built at all if the question had not arisen as to how the heavy blocks of granite necessary for the construction of Bunker Hill monument were to be carried from the quarries to the Neponset River, the point from which they were to be shipped to Charlestown. Bryant, the builder of the road, had heard of Stephenson's successful use of tracks at the Newcastle coal mines and saw no reason why a road of similar pattern could not be laid from the quarries to the ship landing. If such a plan could be worked out, he argued, it would be a great saving of time and labor. Accordingly the railroad was built at a cost of more than ten thousand dollars a mile and it unquestionably performed the service required of it even if it did necessitate the expenditure of a good deal of money. Since the grade sloped toward the river the heavily loaded cars moved down the tracks very easily and as they were empty on their return the ascent was made with equal ease. All the year round this quaint railroad was in constant use, a snowplow being attached to the front car in winter to clear the deep snow from the tracks." "I suppose that was the first railroad snowplow, too," observed Stephen. "I suppose it was," his father agreed. "For some time afterward this old road with its granite ties was the model from which American engineers took their inspiration, it being many years before railroad builders realized that wooden ties were more flexible and made a better, even though less durable roadbed." "Were any more railroads like the Quincy road built in America?" questioned Steve. "Yes, a railroad very much like it was built in the Pennsylvania mining country to transport coal from the mines at Summit down to the Lehigh Valley for shipment. An amusing story is told of this railroad, too. It extended down the mountainside in a series of sharp inclines between which lay long stretches of level ground. Now you know when you coast downhill your speed will give you sufficient impetus to carry you quite a way on a flat road before you come to a stop. So it was with this railroad. But the force the cars gained on the hillside could not carry them entirely across these long levels, and therefore platform cars were built on which a number of mules could be transported and later harnessed to the cars to pull them across the flat stretches. At the end of each level the mules would be taken aboard again and carried down to the next one, where they were once more harnessed to the cars. Now the tale goes that to the chagrin of the railroad people the mules soon grew to enjoy riding so much that they had no mind to get out and walk when the level places were reached and it became almost impossible to make them. All of which proves the theory I advanced before--that too much luxury is not good for any of us and will even spoil a perfectly good mule." Steve chuckled in response. "I'm afraid with railroads like these America did not make much progress," he said. "No very rapid strides," owned his father. "Nevertheless men were constantly hammering away at the railroad idea. In out-of-the-way corners of the country were many persons who had faith that somehow, they knew not how, the railroad would in time become a practical agency of locomotion. When the Rainhill contest of engines took place in England before the opening of the Liverpool-Manchester road, and Stephenson carried off the prize, Horatio Allen, one of the engineers of the Delaware and Hudson Canal Company, was sent over to examine the locomotives competing and if possible buy one for a new railroad they hoped to put into operation. Unluckily none of the engines were for sale but he was able to purchase at Stourbridge a steam locomotive and this he shipped to New York. It reached there in 1829--a ridiculous little engine weighing only seven tons. Before its arrival a track of hemlock rails fastened to hemlock ties had been laid and as the Lackawanna River lay directly in the path of the proposed road a wooden trestle about a hundred feet high had been built across the river. This trestle was of very frail construction and calculated to sustain only a four-ton engine and therefore when the seven-ton locomotive from Stourbridge arrived and was found to weigh nearly double that specification there was great consternation." "Did they tear the trestle down and build another?" asked Steve with much interest. Mr. Tolman did not heed the question. "Now in addition to the disconcerting size of the engine," he continued, "the wooden rails which had been laid during the previous season had warped with the snows and were in anything but desirable condition. So altogether the prospect of trying out the enterprise, on which a good deal of money had already been spent, was not alone disheartening but perilous." "The inspectors or somebody else would have put an end to such a crazy scheme jolly quick if it had been in our day, wouldn't they?" grinned the boy. "Yes, nobody could get very far with anything so unsafe now," his father responded. "But all this happened before the era of inspectors, construction laws, or the _Safety First_ slogan. Hence no one interfered with Horatio Allen. If he chose to break his neck and the necks of many others as well he was free to do so. Therefore, nothing daunted, he got up steam in his baby engine, which was the more absurd for having painted at its front a fierce red lion, and off he started--along his hemlock railroad. The frail bridge swayed and bent as the locomotive rumbled over it but by sheer miracle it did not give way and Allen reached the other side without being plunged to the bottom of the river." Steve drew a long breath of relief. "Did they go on using the railroad after that?" he asked. His father shook his head. "No," he replied. "Although every one agreed that the demonstration was a success the wooden rails were not durable enough to last long and the company was not rich enough to replace them with metal ones. Therefore, in spite of Allen's pleas and his wonderful exhibition of courage, the road fell into disuse, the engine was taken apart, and the enterprise abandoned." "What a pity!" "Yes, it was, for had New York persevered in this undertaking the railroad might have made its advent in the United States much sooner than it did. As it was, once again, like a meteor, the experiment flashed into sight and disappeared with success well within reach." "And who was the next promoter?" "Peter Cooper was the next experimenter of note," Mr. Tolman answered, "and his adventure with railroading was entertaining, too. He lived in Baltimore and being of a commercial trend of mind he decided that if a railroad could be built through the Potomac Valley and across the Alleghany Mountains it might win back for his state the trade that was rapidly being snatched away by the Erie and Pennsylvania Canal. With this idea in mind Cooper built thirteen miles of track and after experimenting with a sort of tram-car and finding it a failure he had a car made that should be propelled by sails." "Sails!" gasped Steve. His father smiled at his astonishment. "Yes, sails!" he repeated. "Into this strangely equipped vehicle he invited some of the editors of the Baltimore papers, and little sensing what was before them the party set forth on its excursion." "Did the car go?" "Oh, it went all right!" chuckled Mr. Tolman. "The trouble was not with its _going_. The difficulty was that as it flew along the rails a cow suddenly loomed in its pathway and as she did not move out of the way of the approaching car she and the railroad pioneers came into collision. With a crash the car toppled over and the editors, together with the enraged Peter Cooper, were thrown out into the mud. Of course the affair caused the public no end of laughter but to Cooper and his guests it proved convincingly that sails were not a desirable substitute for steam power." "I suppose Cooper then went to work to build some other kind of a railroad," mused Steve. "That is exactly what he did," was the rejoinder. "He did not, however, do this deliberately but rather fell into a dilemma that left him no other choice. You see a group of men coaxed him to buy some land through which it was expected the new Baltimore and Ohio Railroad was to pass. These prospectors figured that as the road was already started and a portion of the wooden track laid the railroad was a sure thing, and by selling their land to the railroad authorities they would be enabled to turn quite a fortune for themselves. In all good faith Cooper had joined the company and then, after discovering that the railroad men had apparently abandoned their plan to build, in dastardly fashion, one after another of the promoters wriggled out of the enterprise and left poor Peter Cooper with a large part of his money tied up in a worthless, partially constructed railroad." "What a rotten trick!" cried Steve. "Yes; and yet perhaps Cooper deserved a little chastisement," smiled Mr. Tolman. "Instead of making money out of other people as he had intended--" "He got stung himself!" burst out the boy. "Practically so, yes," was the reply. "Well, at any rate, there he was and if he was ever to get back any of his fortune he must demonstrate that he had profound faith in the partly constructed railroad. Accordingly he bought a small engine weighing about a ton--" "One ton!" "So small that it was christened the 'Tom Thumb.' He now had his wooden rails and his pygmy engine but was confronted by still another perplexity. The railroad must pass a very abrupt curve, it was unavoidable that it should do so--a curve so dangerous that everybody who saw it predicted that to round it without the engine jumping the track and derailing the cars behind would be impossible. Poor Peter Cooper faced a very discouraging problem. There was no gainsaying that the curve was a bad one; moreover, his locomotive was not so perfect a product as he might have wished. It had been built under his direction and consisted of the wee engine he had bought in New York connected with an iron boiler about the size of an ordinary tin wash boiler; and as no iron piping was made in America at this time Cooper had taken some old steel musket barrels as a substitute for tubing. With this crude affair he was determined to convince the public that a steam railroad was a workable proposition." "He had a nerve!" "It took nerve to live and accomplish anything in those days," returned Mr. Tolman. "In the first place few persons had fortunes large enough to back big undertakings; and in addition America was still such a young country that it had not begun to produce the materials needed by inventors for furthering any very extensive projects. In fact the world of progress was, as Kipling says, 'very new and all.' Hence human ingenuity had to make what was at hand answer the required purpose, and as a result Peter Cooper's Tom Thumb engine, with its small iron boiler and its gun-barrel tubing, was set upon the wooden track, and an open car (a sort of box on wheels with seats in it) was fastened to it. Into this primitive conveyance the guests invited for the occasion clambered. Ahead lay the forbidding curve. Stephenson, the English engineer, had already stated mathematically the extreme figure at which a curve could be taken and the locomotive still remain on the track, and Peter Cooper was well aware that the curve he must make was a far worse one. However, it would never do for him to betray that he had any misgivings. Therefore, together with his guests, he set out on his eventful trip which was either to demolish them all, or convince the dignitaries of the railroad company that not only was a steam railroad practical but that the Baltimore and Ohio Road was a property valuable enough to be backed by capital." Steve leaned forward, listening eagerly to the story. "Slowly the little engine started, and nearer and nearer came the terrible curve. The train was now running at fifteen miles an hour, a speed almost unbelievable to the simple souls of that time. Round the curve it went in safety, increasing its velocity to eighteen miles an hour. The railroad officials who were Cooper's guests were frantic with enthusiasm. One man produced paper and pencil and begged those present to write their names, just to prove that it was possible to write even when flying along at such a meteoric rate of speed. Another man jotted down a few sentences to demonstrate that to think and write connected phrases were things that could be done, in spite of the fact that one was dashing through space with this unearthly rapidity." "So the railroad men were converted, were they?" "They were more than converted; they were exultant," said his father. "Of course it was some time after this before the Baltimore and Ohio Railroad became a reality. Capital had to be raised and the project stably launched." "Oh, then this was not the first railroad in the country, after all," observed the boy in a disappointed tone. "No. South Carolina boasts the first regular passenger locomotive propelled by steam," returned Mr. Tolman. "This road ran from Charleston to Hamburg and although a charter was obtained for it in 1827 it took all the first year to lay six miles of track. In fact it was not until 1830 that the railroad began to be operated to any extent. When it was, a locomotive, every part of which had been produced in this country, was employed to draw the trains. This was the first steam locomotive of American make in history. It was dubbed 'The Best Friend' and, like the engines that had preceded it, had a series of interesting adventures. Since it was the only locomotive in the possession of the road and was in use all day any repairs on the hard-worked object had to be made at night." "Humph!" ejaculated Stephen. "Nevertheless 'The Best Friend' might have gone on its way prosperously had it not been for the ignorance of those who ran it. The engineer, to be sure, understood more or less about a steam locomotive although he was none too wise; but the fireman, unfortunately, understood next to nothing, and one day, on being left alone in the cab and seeing the steam escaping from the safety valve, he conceived the notion that a leak was causing unnecessary waste. Therefore he securely screwed up the space through which the steam had been issuing, and to make prevention more certain he himself, a large and heavy man, sat down on the escape valve." "And presto!" exclaimed Steve, rubbing his hands. "Exactly so! Presto, indeed! Figuratively speaking, he blew sky-high and 'The Best Friend' with him," replied Mr. Tolman. "It was an unfortunate happening, too, for people were still ill-informed about the uses of steam and very nervous about its mysterious power and this accident only served to make them more so. For some time afterward many persons refused to patronize the railroad in spite of all the authorities could do to soothe them. In time, however, the public calmed down, although in order to reassure them it was found necessary to put a car heaped with bales of cotton between them and the engine, not only to conceal the monster from their view but also to convince them that it was some distance away. Whether they also had a vague notion that in case they went skyward the cotton might soften their fall when they came down, I do not know." "Railroading certainly had its troubles, didn't it?" Steve commented with amusement. "It certainly had, especially in our own country," was the reply. "In England Stephenson and other experimenters like him had materials at hand which to some extent served their purpose; moreover, thanks to Watt and other inventors, there were definite scientific ideas to work from. But in America the successful railroad which might serve as a model was unknown. Therefore for some time English engines continued to be shipped across the sea, and even then it was a long time before our American engineers understood much about their mechanism. Only by means of repeated experiments, first in one part of the country and then in another, did our American railroads, so marvelous in their construction, come into being." Mr. Tolman paused a moment, yawned, and then rose and beckoned to the porter. "We still have much to perfect in our modern railroad, however," he said with a touch of humor. "The sleeping car, for example, is an abomination, as you are speedily to have proved to you. Here, porter! We'd like these berths made up. I guess we'd better turn in now, son. You have had enough railroading for one day and are tired. You must get a rest and be in the pink of condition to-morrow for, remember, you are going to wake up in New York." "If it will make to-morrow come any quicker I am quite ready to go to bed," retorted Stephen, with a sleepy smile. CHAPTER VII A HOLIDAY JOURNEY The next morning, when Steve woke to the swaying of the train and a drowsy sense of confusion and smoke, he could not for an instant think where he was; but it did not take long for him to open his eyes, recollect the happenings of the previous day, smile with satisfaction, and hurriedly wriggle into his clothes. Already he could hear his father stirring in the berth below and presently the elder man called: "We shall be in New York in half-an-hour, son, so get your traps packed up. How did you sleep?" "Sound as a top!" "That is fine! I was afraid you might not rest very well. As I observed last night, a sleeping car is not all that it might be. The day will come when it will have to be improved. However, since it gets us to New York safely and economizes hours of day travel, it is a blessing for which we should be grateful." As he spoke he moved into the aisle and helped the boy down from his perch; they then sought out a distant seat where they dropped down and watched the rapidly passing landscape. "I have been thinking, as I was dressing, of the story you told me last night about our American railroads," said the lad. "It surprised me a good deal to hear that the South took the lead over the North in the introduction of the steam locomotive." Mr. Tolman smiled into the eager face. "While it is true that South Carolina took the initiative in railroading for a short time the South did not remain long in the ascendency," he answered, "for the third steam locomotive put into actual passenger service was built at Albany. This city, because of its geographical position, was a great stagecoach center, having lines that radiated from it into the interior in almost every direction. And not only was it an important coaching rendezvous but as it was also a leading commercial tributary of New York the Mohawk and Hudson Railroad had built a short track between Albany and Schenectady and supplied it with cars propelled by horse power. Now in 1831 the company decided to transform this road into a steam railroad and to this end ordered a steam locomotive called the 'DeWitt Clinton' to be constructed at West Point with the aim of demonstrating to the northern States the advantages of steam transportation. You can imagine the excitement this announcement caused. Think, if you had never seen a steam engine, how eager you would be to behold the wonder. These olden time New Yorkers felt precisely the same way. Although the route was only sixteen miles long the innovation was such a novel and tremendous one that all along the way crowds of spectators assembled to watch the passing of the magic train. At the starting point near the Hudson there was a dense throng of curious onlookers who gathered to see for the first time in all their lives the steam locomotive and its brigade of coaches,--for in those days people never spoke of a train of cars; a group of railroad carriages was always known as a brigade, and the term _coach_ was, and in many cases still is applied to the cars. This train that created so much interest was practically like Stephenson's English trains, being made up of a small locomotive, a tender, and two carriages constructed by fastening stagecoach bodies on top of railroad trucks. Stout iron chains held these vehicles together--a primitive, and as it subsequently proved, a very impractical method of coupling." "It must have been a funny enough train!" Steve exclaimed. "I doubt if it appeared so to the people of that time," his father returned, "for since the audience of that period had nothing with which to compare it, it probably seemed quite the ordinary thing. Was it not like the railroad trains used in England? How was America to know anything different? Yes, I am sure the 'DeWitt Clinton' was considered a very grand affair indeed, even though it was only a small engine without a cab, and had barely enough platform for the engineer to stand upon while he drove the engine and fed the pitch-pine logs into the furnace." "How many people did the train hold?" inquired Steve, with growing curiosity. "Each coach carried six persons inside and two outside," was Mr. Tolman's reply, "and on this first eventful trip not quite enough adventurous souls could be found to fill the seats. Perhaps could the unwary passengers who did go have foreseen the discomforts ahead of them there would have been fewer yet. But often ignorance is bliss. It certainly was so in this case for in high feather the fortunate ones took their places, the envied of many a beholder." "What happened?" asked the boy eagerly. "Was the trip a success?" "That depends on what you mean by success," laughed his father. "If you are asking whether the passengers arrived safely at Schenectady I can assure you that they did; but if you wish to know whether the journey was a comfortable one, and likely to convert the stranger to steam travel, that is quite another matter. The description of the excursion which history has handed down to us is very naïve. In the first place the pitch-pine fuel sent a smudge of smoke and cinders back over all the passengers and if it did not entirely choke them it at least encrusted them thickly with dirt, particularly the ones who sat outside. The umbrellas they opened to protect themselves were soon demolished, their coverings being blown away or burned up by the sparks. In fact, it was only by continual alertness that the clothing of the venturesome travelers was not ignited. In the meantime those inside the coaches fared little better, for as the coaches were without springs and the track was none too skilfully laid, the jolting of the cars all but sent the heads of the passengers through the roof of the coaches. Added to this the train proceeded in a series of jerks that wrenched the chains and banged one coach into another with such violence that those outside were in danger of being hurled down upon the track, and those inside were tossed hither and thither from seat to seat. You will easily comprehend that the outing was not one of unalloyed pleasure." The boy laughed heartily. "Of course," went on Mr. Tolman, "there was no help for anybody until the first stopping place was reached; but when the engine slowed down and the grimy, almost unrecognizable pilgrims had a chance to catch their breath, something had to be done by way of a remedy. The remedy fortunately was near at hand and consisted of nothing very difficult. Some of the more enterprising of the company leaped out and tore the rails from a near-by fence and after stretching the coupling chains taut, they bound them to the wooden boards. In this way the coaches were kept apart and the silk hats of the dignitaries who had been invited to participate in the opening of the road rescued from total annihilation." "I'll bet everybody was glad to disembark at Schenectady," declared Stephen. "I'll wager they were! They must have been exhausted from being jounced and jostled about. Nevertheless the novelty of the adventure probably brought its own compensations, and they were doubtless diverted from their woes by the sight of the cheering and envious spectators, the terrified horses, and the open-mouthed children that greeted them wherever they went." "But the promoters could hardly expect the public to be very keen for a steam railroad after such an exhibition," reflected Steve. "Fortunately our forefathers were not as critical as you," said his father, "and in consequence the coach line from Albany to Schenectady was speedily supplanted by a steam railroad, as were the various coach lines into the interior of the State. As a result hundreds of broken-down coach horses were turned out to pasture, a merciful thing. Gradually a series of short steam railway lines were constructed from one end of the State to the other, until in 1851 these were joined together to make a continuous route to Lake Erie. Perhaps we have only scant appreciation of the revolution that came with this advance in transportation. It meant the beginning of travel and commerce between the eastern States and those in the interior of the country; it also meant the speedy shipment of eastern products to the West, where they were greatly needed, and the reception of western commodities in the East. But more than all this, it signified a bond of fellowship between the scattered inhabitants of the same vast country who up to this time had been almost total strangers to one another, and was a mighty stride in the direction of national loyalty and sympathy. Therefore it was entirely seemly that Millard Fillmore, then President of the United States, and Daniel Webster, the Secretary of State, should be honored guests at the celebration that attended the opening of the railroad." "Did the road reach no farther than Lake Erie?" asked Stephen. "Not at first," replied his father. "From that point commerce was carried on by means of ships on the Great Lakes. But in time western railroad companies began to build short stretches of track which later on they joined together as the other railroad builders had done." "Did the line go all the way across the country?" "Oh, no, indeed. Our trans-continental railroads were a mighty project in themselves and their story is a romance which I will tell you some other time. Before such stupendous enterprises could be realities, our young, young country had a vast deal of growing to do, and its infant railroads and engineering methods had to be greatly improved. So long as we still built roads where the rails were liable to come up through the floor and injure the passengers, and where the tracks were not strongly enough constructed to resist floods and freshets, our steam locomotion could not expect any universal degree of popularity." "I don't suppose, though, that the cows continued to tip the cars over and turn the passengers out into the dirt as they did in the days of Peter Cooper," mused Steve thoughtfully. "They may not have derailed the trains," his father replied quite seriously, "but they often did delay them. Nor could the passengers be blamed for finding fault with the unheated cars, or the fact that sometimes, when it snowed hard, the engineer ran his engine under cover and refused to go on, leaving those on the train the choice of staying where they were until the storm abated or going on foot to their destination." "Not really!" "Yes, indeed. Such things happened quite frequently. Then there are stories of terrible gales when the snow piled up on the track until the engine had to be dug out, for snow plows did not keep the tracks clear then as they do now; nor was it an uncommon thing for the mud from the spring washouts to submerge the rails, in which case the engines had to be pulled out of the mire by oxen. In fact, at certain seasons of the year some trains carried oxen for this very purpose. For you must remember that the engines of that date were not powerful enough to make progress through mud, snow, or against fierce head winds. Often a strong gale would delay them for hours or bring them to a standstill altogether." "Well, I guess it is no wonder we were not equipped to build a trans-continental road under such conditions," said the lad, with a quiet smile. "Oh, these defects were only a minor part of our railroad tribulations," responded his father. "For example, when Pennsylvania started her first railroad the year after the line between New York and Schenectady was laid, there was a fresh chapter of obstacles. Strangely enough, the locomotive, 'Old Ironsides,' was built by Mr. M. W. Baldwin, whose name has since become celebrated as the founder of the Baldwin Locomotive Works. In 1832, however, the Baldwin locomotive was quite a different product from the present-day magnificently constructed steam engine. This initial attempt at locomotive building was a queer little engine with wheels so light that unless there was plenty of ballast aboard it was impossible to keep it on the track; and besides that, the poor wee thing could not get up steam enough to start itself and in consequence Mr. Baldwin and some of his machinists were obliged to give it a violent push whenever it set out and then leap aboard when it was under way in order to weigh it down and keep it on the track." "Imagine having to hold an engine down!" ejaculated Steve, with amusement. "The story simply goes to prove how much in the making locomotives really were," Mr. Tolman said. "And not only did this toy engine have to be started by a friendly push, but it was too feeble to generate steam fast enough to keep itself going after it was once on its way. Therefore every now and then the power would give out and Mr. Baldwin and his men would be forced to get out and run along beside the train, pushing it as they went that it might keep up its momentum until a supply of steam could again be acquired. Can you ask for anything more primitive than that?" "It certainly makes one realize the progress locomotive builders have made," the boy replied, with gravity. "It certainly does," agreed his father. "Think how Baldwin and his men must have struggled first with one difficulty and then with another; think how they must have experimented and worked to perfect the tiny engine with which they began! It was the conquering of this multitude of defects that gave to the world the intricate, exquisitely made machine which at this very minute is pulling you and me into New York." There was an interval of silence during which Stephen glanced out at the flying panorama framed by the window. "Where was New England all this time?" demanded he, with jealous concern. "Didn't Massachusetts do anything except build the old granite road at Quincy?" "Railroads, for various reasons, were not popular in Massachusetts," returned his father. "As usual New England was conservative and was therefore slow in waking up to the importance of steam transportation. Boston was on the coast, you see, and had its ships as well as the canal boats that connected the city with the manufacturing districts of the Merrimac. Therefore, although the question of building railroads was agitated in 1819 nothing was done about the matter. As was natural the canal company opposed the venture, and there was little enthusiasm elsewhere concerning a project that demanded a great outlay of money with only scant guarantee that any of it would ever come back to the capitalists who advanced it. Moreover, the public in general was sceptical about railroads or else totally uninterested in them. And even had a railroad been built at this time it would not have been a steam road for it was proposed to propel the cars by horse power just as those at Quincy had been." "Oh!" interjected Steve scornfully. "They might at least have tried steam." "People had little faith in it," explained Mr. Tolman. "Those who had the faith lacked the money to back the enterprise, and those who had the money lacked the faith. If a company could have gone ahead and built a steam railroad that was an unquestioned success many persons would undoubtedly have been convinced of its value and been willing to put capital into it; but as matters stood, there was so much antagonism against the undertaking that nobody cared to launch the venture. There were many business men who honestly regarded a steam railroad as a menace to property and so strong was this feeling that in 1824 the town of Dorchester, a village situated a short distance from Boston, actually took legal measures to prevent any railroad from passing through its territory." "They needn't have been so fussed," said Stephen, with a grin. "Railroads weren't plenty enough to worry them!" "Oh, the Quincy road was not the only railroad in Massachusetts," his father asserted quickly, "for in spite of opposition a railroad to Lowell, modeled to some extent after the old granite road, had been built. This railroad was constructed on stone ties, as the one at Quincy had been; for although such construction was much more costly it was thought at the time to be far more durable. Several years afterward, when experience had demonstrated that wood possessed more _give_, and that a hard, unyielding roadbed only creates jar, the granite ties that had cost so much were taken up and replaced by wooden ones." "What a shame!" "Thus do we live and learn," said his father whimsically. "Our blunders are often very expensive. The only redeeming thing about them is that we pass our experience on to others and save them from tumbling into the same pit. Thus it was with the early railroad builders. When the Boston and Providence Road was constructed this mistake was not repeated and a flexible wooden roadbed was laid. In the meantime a short steam railroad line had been built from Boston to Newton, a distance of seven miles, and gradually the road to this suburb was lengthened until it extended first to Natick and afterward to Worcester, a span of forty-four miles. Over this road, during fine weather, three trains ran daily; in winter there were but two. I presume nothing simpler or less pretentious could have been found than this early railroad whose trains were started at the ringing of a bell hung on a near-by tree. Although it took three hours to make a trip now made in one, the journey was considered very speedy, and unquestionably it was if travelers had to cover the distance by stagecoach. When we consider that in 1834 it took freight the best part of a week to get to Boston by wagons a three-hour trip becomes a miracle." "I suppose there was not so much freight in those days anyway," Steve speculated. "Fortunately not. People had less money and less leisure to travel, and therefore there were not so many trunks to be carried; I am not sure, too, but the frugal Americans of that day had fewer clothes to take with them when they did go. Then, as each town or district was of necessity more or less isolated, people knew fewer persons outside of their own communities, did a less extensive business, and had less incentive to go a-visiting. Therefore, although the Boston and Worcester Railroad could boast only two baggage cars (or burthen cars, as they were called), the supply was sufficient, which was fortunate, especially since the freight house in Boston was only large enough to shelter these two." "And out of all this grew the Boston and Albany Railroad?" questioned the boy. "Yes, although it was not until 1841, about eight years later, that the line was extended to New York State. By that time tracks had been laid through the Berkshire hills, opening up the western part of Massachusetts. The story of that first momentous fifteen-hour journey of the Boston officials to the New York capital, where they were welcomed and entertained by the Albany dignitaries, is picturesque reading indeed. One of the party who set out from Boston on that memorable day carried with him some spermaceti candles which on the delegates' arrival were burned with great ceremony at the evening dinner." "I suppose it seemed a wonderful thing to reach Albany in fifteen hours," remarked Steve. "It was like a fairy tale," his father answered. "To estimate the marvel to the full you must think how long it would have taken to drive the distance, or make the journey by water. Therefore the Boston officials burned their spermaceti candles in triumph; and the next day, when the Albany hosts returned to Boston with their guests, they symbolized the onrush of the world's progress by bringing with them a barrel of flour which had been cut, threshed, and ground only two days before, and put into a wooden barrel made from a tree which was cut down, sawed, and put together while the flour was being ground. This does not seem to us anything very astounding but it was a feat to stop the breath in those days." "And what did they do with the flour?" "Oh, that evening when they reached Boston the flour was made into some sort of bread which was served at the dinner the Boston men gave to their visitors." "I wonder what they would have said if somebody had told them then that sometime people would be going from Boston to New York in five hours?" the lad observed. "I presume they would not have believed it," was the reply. "Nor would they have been able to credit tales of the great numbers of persons who would constantly be traveling between these two great cities. At that time so few people made the trip that it was very easy to keep track of them; and that they might be identified in case of accident the company retained a list of those who went on the trains. At first this rule worked very well, the passengers being carefully tabulated, together with their place of residence; but later, when traffic began to increase and employees began to have more to do, those whose duty it was to make out these lists became hurried and careless and in the old railroad annals we read such entries as these: "'_Woman in green bonnet; boy; stranger; man with side whiskers,_' etc." A peal of laughter broke from Stephen. "Railroad officials would have some job to list passengers now, wouldn't they?" he said. "We should all just have to wear identification tags as the men did during the War." His father acquiesced whimsically. "I have sometimes feared we might have to come to that, anyway," he replied. "With the sky populated with aeroplanes and the streets filled with automobiles man stands little chance in these days of preserving either his supremacy or his identity. When we get on Fifth Avenue to-day you see if you do not agree with me," he added, as the train pulled into the big station. CHAPTER VIII NEW YORK AND WHAT HAPPENED THERE It took no very long interval to prove that there was some foundation for Mr. Tolman's last assertion, for within a short time the travelers were standing on Fifth Avenue amid the rush of traffic, and feeling of as little importance as dwarfs in a giant's country. The roar of the mighty city, its bustle and confusion, were both exhilarating and terrifying. They had left their luggage at the hotel and now, while Steve's father went to meet a business appointment, the boy was to take a ride up the Avenue on one of the busses, a diversion of which he never tired. To sit on top and look down on the throng in the streets was always novel and entertaining to one who passed his days in a quiet New England town. Therefore he stopped one of the moving vehicles and in great good humor bade his father good-by; and feeling very self-sufficient to be touring New York by himself, clambered eagerly up to a seat. There were few passengers on the top of the coach for the chill of early morning still lingered in the air; but before they reached Riverside Drive a man with a bright, ruddy countenance and iron-grey hair hailed the bus and climbed up beside the boy. As he took his place he glanced at him kindly and instantly Steve felt a sense of friendliness toward the stranger; and after they had ridden a short distance in silence the man spoke. "What a beautiful river the Hudson is!" he remarked. "Although I am an old New Yorker I never cease to delight in its charm and its fascinating history. It was on this body of water, you know, that the first steamboat was tried out." "I didn't know it," Stephen confessed, with an honest blush. "You will be learning about it some day, I fancy," said the other, with a smile. "An interesting story it is, too. All the beginnings of our great industries and inventions read like romances." "My father has just been telling me about the beginnings of some of our railroads," observed Steve shyly, "and certainly his stories were as good as fairy tales." "Is your father especially interested in railroads?" inquired the New Yorker. "Yes, sir. He is in the railroad business." "Ah, then that accounts for his filling your ears with locomotives instead of steamboats," declared the man, with a twinkle in his eyes. "Now if I were to spin a yarn for you, it would be of steamboats because that happens to be the thing I am interested in; I believe their history to be one of the most alluring tales to which a boy could listen. Sometime you get a person who knows the drama from start to finish to relate to you the whole marvelous adventure of early steamboating, and you see if it does not beat the railroad story all out." He laughed a merry laugh in which Stephen joined. "I wish you would tell it to me yourself," suggested the lad. The man turned with an expression of pleasure on his red-cheeked face. "I should like nothing better, my boy," he said quickly, "but you see it is a long story and I am getting out at the next corner. Sometime, however, we may meet again. Who knows? And if we do you shall hold me to my promise to talk steamboats to you until you cry for mercy." Bending down he took up a leather bag which he had placed between his feet. "I am leaving you here, sonny," he said. "I take it you are in New York for a holiday." "Yes, sir, I am," returned Steve with surprise. "My father and I are staying here just for a few days." "I hope you will have a jolly good time during your visit," the man said, rising. Stephen murmured his thanks and watched the erect figure descend from the coach and disappear into a side street. It was not until the New Yorker was well out of sight and the omnibus on its way that his eye was caught by the red bill book lying on the floor at his feet. None of the few scattered passengers had noticed it and stooping, he picked it up and quietly slipped it into his pocket. What should he do with it? Of course he could hand it over to the driver of the bus and tell him he had found it. But the man might not be honest and instead of turning it in to the company might keep it. There was little doubt in Steve's mind that the pocketbook belonged to the stranger who had just vacated the place and it was likely his address was inside it. If so, what a pleasure it would be to return the lost article to its rightful owner himself. By so doing he would not only be sure the pocketbook reached its destination but he might see the steamboat man again. He longed to open the bill book and investigate its contents. What was in it, he wondered. Well, the top of a Fifth Avenue coach was no place to be looking through pocketbooks, there was no question about that. Let alone the fact that persons might be watching him, there was danger that in the fresh morning breeze something might take wing, sail down to the Hudson, and never be seen again. Therefore he decided to curb his impatience and wait until he reached a more favorable spot to examine his suddenly acquired treasure. Accordingly he tucked the long red wallet farther down into the breast pocket of his ulster, and feeling assured that nothing could be done about it at present, gave himself up to the pleasure and excitement of the drive. It was not until he had rejoined his father at the hotel and the two were sitting at lunch in the great dining room that the thought of it again flashed into his mind. "Gee, Dad!" he suddenly exclaimed, looking up from his plateful of fried chicken with fork suspended in mid-air. "I meant to tell you I found a pocketbook in the bus this morning." "A pocketbook!" "Yes, sir. I think the man who had been sitting beside me must have dropped it when he stooped over to get his bag. At any rate it was lying there after he got out." "What did you do with it?" Mr. Tolman inquired with no great warmth of interest. "Gave it to the conductor, I suppose." The boy shook his head. "No, I didn't," was the answer. "I was afraid he might not turn it in, and as I liked the man who lost it I wanted to be sure he got it, so I brought it back with me." "And where is it now?" demanded Mr. Tolman, now all attention. "I hope you were not so careless as to leave it upstairs in our room." "No. I didn't leave it in the room," returned the lad. "It is out in my coat pocket. I meant to take it out and see what was in it; but so many things happened that I forgot about it until this very minute." "You don't mean that you left it in your ulster pocket and let them hang it out there on the rack?" "Yes." "You checked your coat and left it there?" "Why--yes," came the faltering reply. Mr. Tolman was on his feet. "Wait here until I come back," he said in a sharp tone. "Where are you going?" "Give me your check quickly," went on his father, without heeding the question. "Hurry!" Steve fumbled in his jacket pocket. "Be quick, son, be quick!" commanded Mr. Tolman impatiently. "Don't you know it is never safe to leave anything of value in your coat when you are staying at a large city hotel? Somebody may have taken the pocketbook already." Scarlet with consternation the lad produced the check. "If nothing has happened to that pocketbook you will be very fortunate," asserted the man severely. "Stay here! I will be right back." With beating heart the boy watched him thread his way between the tables and disappear from the dining room into the lobby. Suppose the bill book should be gone! What if there had been valuable papers in it, money--a great deal of money--and now through his carelessness it had all disappeared? How stupid he had been not to remember about it and give it to his father the instant they had met! In fact, he would much better have taken a chance and handed it to the bus conductor than to have done the foolish thing he had. He had meant so well and blundered so grievously! How often his father had cautioned him to be careful of money when he was traveling! Tensely he sat in his chair and waited with miserable anxiety, his eyes fixed on the dining-room door. Then presently, to his great relief, he saw his father returning. "Did you--" he began. "You will have to come yourself, Steve," said the elder man whose brow was wrinkled into a frown of annoyance. "The maid who checked the coats is not there, and the one who is insists that the ulster is not mine, and in spite of the check will not allow me to search the pockets of it." Stephen jumped up. "I suppose she is right, too," went on Mr. Tolman breathlessly, "but the delay is very unfortunate." They made their way into the corridor, where by this time an office clerk and another man had joined the maid who was in charge of the coat rack. Stephen presented his check and without comment the woman handed him his coat. With trembling hand he dived into the deep pocket and from it drew forth the red bill book which he gave to his father. "There it is, Dad, safe and sound!" he gasped. Instantly the clerk was in their path. "I beg pardon, sir," said he with deference, "but does that pocketbook belong to you?" Mr. Tolman wheeled about. "Eh--what did you say?" he inquired. "I asked, sir, if that pocketbook was your property?" repeated the clerk. Mr. Tolman faced his inquisitor. "What business is that of yours?" he demanded curtly. "I am sorry, sir, to appear rude," the hotel employee replied, "but we have been asked to be on the lookout for a young lad who rode this morning on one of the Fifth Avenue busses where a valuable pocketbook was lost. Your son tallies so well with the description that--" "It was I," put in Stephen eagerly, without regard for consequences. "Who wants me?" With a smile of eagerness he turned, expecting to encounter the genial face of his acquaintance of the morning. Then he would smile, hold out the pocketbook, and they would laugh together as he explained the adventure, and perhaps afterward have luncheon in company. Instead no familiar form greeted him. On the contrary the slender man who had been standing beside the clerk came forward. Mr. Tolman sensed the situation in a second. "You mean somebody thinks my son took the pocketbook?" asked he indignantly, as he confronted the clerk and his companion. "It is not my affair, sir, and I am sorry it should happen in our hotel," apologized the clerk. "Perhaps if you will just explain the whole matter to this gentleman--" he broke off, saying in an undertone to the man at his elbow. "This is your boy, Donovan." The tall man came nearer. "You are a detective?" asked Mr. Tolman bluntly. "Well, something of the sort, sir," admitted the man called Donovan. "It is occasionally my business to hunt people up." "And you have been sent to hunt my son up?" Donovan nodded. Stephen turned white and his father put a reassuring hand on his shoulder. "My son and I," he replied, addressing the detective quietly, "can explain this entire affair to you and will do so gladly. The boy did find the pocketbook but he was ignorant of its value because he has not even looked inside it. In fact, that he had the article in his possession did not come into his mind until a few moments ago. If he had known the thing was valuable, do you suppose he would have left it in his ulster pocket and checked the coat in a public place like this?" The detective made no reply. "We both shall be very glad," went on Mr. Tolman firmly, "to go with you to headquarters and straighten the matter out." "There may be no need of that, sir," Donovan responded with a pleasant smile. "If we can just talk the affair over in a satisfactory way--" "Suppose you come upstairs to our room," suggested Mr. Tolman. "That will give us more quiet and privacy. Will that be agreeable to you?" "Perfectly." As the three walked toward the elevator Steve glanced with trepidation at the plain-clothes man. The boy knew he had done nothing wrong; but would he be able to convince the detective of the truth of his story? He was thoroughly frightened and wondered whether his father was also alarmed. If, however, Mr. Tolman was worried he at least did not show it. Instead he courteously led the way from the elevator down the dim corridor and unlocked the door of Number 379. "Come in, Mr. Donovan," he said cordially. "Here is a chair and a cigar. Now, son, tell us the story of this troublesome pocketbook from beginning to end." In a trembling voice Stephen began his tale. He spoke slowly, uncertainly, for he was well scared. Gradually, however, he forgot his agitation and his voice became more positive. He recounted the details of the omnibus ride with great care, adding ingenuously when he came to the termination of the narrative: "And I hoped the man's name would be inside the pocketbook because I liked him very much and wanted to return to him what he had lost." "And wasn't it?" put in Mr. Donovan quickly. "I don't know," was the innocent retort. "Don't you remember I told you that I hadn't looked inside yet?" The detective laughed with satisfaction. "That was a shabby trick of mine, youngster," said he. "It was mean to try to trap you." "Trap me?" repeated Steve vaguely. "There, there, sonny!" went on Donovan kindly. "Don't you worry a minute more about this mix-up. Mr. Ackerman, the gentleman who lost the bill book, did not think for a second that you had taken it. He simply was so sure that he had lost it on the bus that he wanted to locate you and find out whether you knew anything about it or not. His name was not inside the pocketbook, you see, and therefore any one who found it would have no way of tracing its owner. What it contains are valuable papers and a big wad of Liberty Bonds which, as your father knows, could quickly be converted into cash. In consequence Mr. Ackerman decided that the sooner the pocketbook was found the better. The omnibus people denied any knowledge of it and you were the only remaining clue." Mr. Tolman sank back in his chair and a relaxation of his muscles betrayed for the first time that he had been much more disturbed than he had appeared to be. "Well," he said, lighting a fresh cigar, "the bill book is not only located but we can hand it back intact to its owner. If you can inform us where the gentleman lives, my boy and I will call a taxi and go to his house or office with his property." A flush of embarrassment suffused the face of the officer. "Maybe you would like to come with us, Donovan," added Mr. Tolman, who instantly interpreted the man's confusion. "I hate to be dogging your footsteps, sir, in this fashion," Mr. Donovan answered, with obvious sincerity. "Still, I--" "You have your orders, no doubt." "Well, yes, sir," admitted the plain-clothes man with reluctance. "I have." "You were to keep your eye on us until the pocketbook reached its owner." "That's about it, sir. Not that I personally have the least suspicion that a gentleman like you would--" "That is all right, my man. I perfectly understand your position," Mr. Tolman cut in. "After all, you have your duty to do and business is business. We'll just telephone Mr. Ackerman that we are coming so that we shall be sure of catching him, and then we will go right up there." "Very well, sir." Stephen's father started toward the telephone and then, as if struck by a sudden thought, paused and turned. "Steve," he said, "I believe you are the person to communicate with Mr. Ackerman. Call him up and tell him you have found his purse and that you and your father would like to come up to his house, if it will be convenient, and return it." "All right, Dad." "You will find his number on this slip of paper, sonny," the detective added, handing the lad a card. "He is not at his office. He went home to lunch in the hope that he had left the pocketbook there." After some delay Stephen succeeded in getting the number written on the card. A servant answered the summons. "May I speak to Mr. Ackerman, please?" inquired the lad. "He is at luncheon? No, it would not do the least good for me to tell you my name for he would not know who it was. Just tell him that the boy who sat beside him this morning on the Fifth Avenue bus--" there was a little chuckle. "Oh, he will be here directly, will he? I thought perhaps he would." A moment later a cheery voice which Steve at once recognized to be that of the steamboat man came over the wire: "Well, sonny?" "I found your bill book, Mr. Ackerman, and my father and I would like to bring it up to you." "Well, well! that is fine news!" cried the man at the other end of the line. "How did you know who it belonged to?" "Oh, I--we--found out--my father and I," stammered the lad. "May we come up to your house with it now?" "You would much better let me come to you; then only one person will be inconvenienced," the New Yorker returned pleasantly. "Where are you staying?" "At the Manhattan." "You must not think of taking the trouble of coming way up here. Let me join you and your father at your hotel." "Very well, Mr. Ackerman. If you'd rather--" "I certainly should rather!" was the emphatic answer. "I could not think of bringing two people so far out of their way." "There are three of us!" squeaked Stephen. "Three?" "Yes, sir. We have another person--a friend--with us," explained the boy, with quiet enjoyment. How easy it was to laugh now! "All the more reason why I should come to you, then," asserted Mr. Ackerman. "I will be at the Manhattan within half an hour. Perhaps if you and your father and your friend have the afternoon free you would like to go to some sort of a show with me after we conclude our business. Since you are here on a holiday you can't be very busy." Stephen's eyes sparkled with merriment. "I don't know whether our friend can go or not," he replied politely, "but I think perhaps Dad and I could; and if we can we should like to very much." "That will be excellent. I will come right along. Not only shall I be glad to get my pocketbook back again but I shall be glad to see you once more. I told you this morning that I had a feeling we should meet some time. Whom shall I ask for at the hotel?" "Stephen Tolman." With a click the boy hung up the receiver. "Mr. Ackerman is coming right down," said he, addressing his father and the detective with a mischievous smile. "He has invited the three of us to go to the matinee with him." "The three of us!" echoed the plain-clothes man. "Yes," returned the lad. "I told him we had a friend with us and so he said to bring him along." "Good heavens!" Donovan ejaculated. Mr. Tolman laughed heartily. "Not all the thieves you arrest take you to a theater party afterward, do they, Officer?" he asked. "I said from the first you were gentlemen," Mr. Donovan asserted with humor. "But couldn't you go?" inquired Steve, quite seriously. "Bless you, no, sonny!" replied the man. "I am from headquarters, you know, and my work is chasing up crooks--not going to matinees." Nevertheless there was an intonation of gentleness in his voice, as he added, "I am obliged to you just the same, for in spite of my calling I am a human being and I appreciate being treated like one." CHAPTER IX AN ASTOUNDING CALAMITY Mr. Ackerman was as good as his word, for within half an hour he presented himself at the hotel where he found Mr. Tolman, Mr. Donovan and Steve awaiting him in their pleasant upstairs room. As he joined them his eye traveled inquiringly from one to another of the group and lingered with curiosity on the face of the detective. The next instant he was holding out his hand to Stephen. "Well, my boy, I am glad to see you again," said he, a ring of heartiness in his voice. "And I am glad to see you, too, Mr. Ackerman," Steve replied, returning the hand-clasp with fervor. "This is my father, sir; and this"--for a second he hesitated, then continued, "is our friend, Mr. Donovan." With cordiality the New Yorker acknowledged the introductions. "Mr. Donovan," explained Mr. Tolman, scanning Mr. Ackerman's countenance with a keen, half-quizzical expression, "is from headquarters." The steamboat magnate started and shot a quick glance at those present. It was plain he was disconcerted and uncertain as to how to proceed. Mr. Donovan, however, came to his rescue, stepping tactfully into the breach: "I was not needed for anything but to supply your address, sir; but I was able to do that, so between us all we have contrived to return your pocketbook to you as good as before it left your possession." As he spoke Mr. Tolman drew forth the missing bill book and held it toward its owner. "That looks pretty good to me!" Mr. Ackerman exclaimed, as he took the article from Mr. Tolman's outstretched hand and regarded it reflectively. "I don't know when I have ever done anything so careless and stupid. You see I had got part way to the bank before I remembered that I had left my glasses, on which I am absolutely dependent, at home. Therefore, there being no taxi in sight, I hailed a passing bus and climbed up beside this youngster. How the bill book happened to slip out of my pocket I cannot explain. It seemed to me it would be safer to have the securities upon my person than in a bag that might be snatched from me; but apparently my logic was at fault. I was, however, so certain of my wisdom that I never thought to question it until I had reached the sidewalk and the bus had gone. "Your boy, Mr. Tolman, confided while we rode along this morning that he was visiting in New York for a few days; but of course I did not ask his name or address and so when I wanted his help in tracing the missing pocketbook I had no way of locating him beyond assuming that he must be staying at one of the hotels. Therefore when the omnibus company could furnish no clue, I got into touch with an agency whose business it is to hunt people up. If the pocketbook had been dropped on the bus I felt sure your boy, who was almost the only other person on top of the coach, would know about it; if, on the other hand, it had been dropped in the street, my problem would be a different one. In either case the sooner I knew my course of action the better. I hope you will believe, Mr. Tolman, that when I called in the aid of detectives I had no suspicions against your son's honesty." Mr. Tolman waved the final remark aside good-humoredly. "We have not taken the affair as a personal matter at all," he declared. "We fully appreciate your difficulty in finding Stephen, for he was also up against the problem of finding you. New York is a rather large city anyway, and for two people who do not even know one another's names to get together is like hunting a needle in a haystack. Our only recourse to discovering the owner of the pocketbook would be through the advertising columns of the papers and that is the method we should have followed had not Donovan appeared and saved us the trouble." He exchanged a smile with the detective. "The advertising column was my one hope," Mr. Ackerman replied. "I felt sure that any honest person who picked up the purse would advertise it. It was not the honest people I was worrying about. It was the thought that I had dropped the bill book in the street where any Tom-Dick-and-Harry could run away with it that concerned me. Moreover, even if your boy had found it on the bus, he might have turned it in to an employee of the coach line who was not honest enough to give it in turn to his superiors. So I wanted to know where I stood; and now that I do I cannot tell you how grateful I am both to Stephen and to this officer here for the service they have rendered me." Then, turning toward Mr. Tolman, he added in an undertone, "I hope neither you nor your son have suffered any annoyance through this unfortunate incident." "Not in the least," was the prompt response. "I confess we were a trifle disconcerted at first; but Mr. Donovan has performed his duty with such courtesy that we entertain toward him nothing but gratitude." "I am glad of that," Mr. Ackerman replied, "for I should deeply regret placing either you or your boy, even for a moment, in an uncomfortable position, or one where it might appear that I--" But Mr. Tolman cut him short. "You took the quickest, most sensible course, Ackerman," said he. "Too much was at stake for you to risk delay. When a pocketbook filled with negotiable securities disappears one must of necessity act with speed. Neither Stephen nor I cherish the least ill-will about the affair; do we, son?" "No, indeed." Then smiling ingenuously up into the face of the New York man, he said: "Don't you want to look in your pocketbook and see if everything is all right, sir?" The steamboat financier laughed. "You are a prudent young man," declared he. "No, I am quite willing to risk that the property you have so kindly guarded is intact." "It ought to be," the boy said. "I haven't even opened the pocketbook." "A better proof still that everything is safe within it," chuckled Mr. Ackerman. "No, sonny, I am not worrying. I should not worry even if you had ransacked the bill book from one end to the other. I'd take a chance on the honesty of a boy like you." Mr. Tolman, however, who had been listening, now came forward and broke into the conversation: "Stephen's suggestion is a good, businesslike one, Ackerman," he declared. "As a mere matter of form--not as a slam against our morals--I am sure that both he and I would prefer that you examined your property while we are all here together and assure yourself that it is all right." "Pooh! Pooh! Nonsense!" objected the financier. "It is a wise notion, Mr. Ackerman," rejoined Mr. Donovan. "Business is business. None of us questions the honor of Mr. Tolman or his son. They know that. Nevertheless I am sure we should all feel better satisfied if you went through the formality of an investigation." "Very well, just as you say. But I want it understood that I do it at their and your request. I am perfectly satisfied to leave things as they are." Taking the now familiar red pocketbook from his coat he opened it unconcernedly; then the three persons watching him saw a look of consternation banish the smile from his face. "What's wrong, Ackerman?" inquired the plain-clothes man quickly. Without a word the other held the bill book toward him. It was empty. Bonds, securities, money were gone! A gasp of incredulity came from Stephen. "I didn't open it--truly I didn't!" exclaimed he, in a terror-stricken voice. But Mr. Ackerman did not heed the remark. "I am afraid this looks pretty black for us, Ackerman," said Mr. Tolman slowly. "We have nothing to give you but the boy's word." Mr. Donovan, however, who had been studying the group with a hawklike scrutiny now sprang to his feet and caught up his hat. "I don't see how they dared put it over!" he exclaimed excitedly. "But they almost got away with it. Even I was fooled." "You don't mean to insinuate," Mr. Tolman burst out, "that you think we--" "Good heavens, no!" replied the detective with his hand on the door knob. "Don't go getting hot under the collar, Mr. Tolman. Nobody is slamming _you_. I have been pretty stupid about this affair, I'm afraid; but give me credit for recognizing honest people when I see them. No, somebody has tricked you--tricked you all. But the game isn't up yet. If you gentlemen will just wait here--" The sentence was cut short by the banging of the door. The detective was gone. His departure was followed by an awkward silence. Mr. Ackerman's face clouded into a frown of disappointment and anxiety; Mr. Tolman paced the floor and puffed viciously at a cigar; and Steve, his heart cold within him, looked from one to the other, chagrin, mortification and terror in his eyes. "I didn't open the pocketbook, Mr. Ackerman," he reiterated for the twentieth time. "I truly didn't." But the steamboat magnate was too deeply absorbed in his own thoughts and speculations to notice the high-pitched voice with its intonation of distress. At last Mr. Tolman could endure the situation no longer. "This is a most unfortunate happening, Ackerman," he burst out. "I am more concerned about it than I can express. My boy and I are utter strangers to you and we have no way of proving our honesty. All I can say is that we are as much amazed at the turn affairs have taken as yourself, and we regret it with quite as much poignancy--perhaps more since it reflects directly upon us. If there is anything we can do--" He stopped, awaiting a reply from the other man, but none came. "Good heavens, Ackerman," he cried. "You don't mean to say you do not believe my son and me--that you suspect us of double-dealing!" "I don't know what to believe, Tolman," owned Mr. Ackerman with candor. "I want very much to credit your story; in my heart, I do credit it. But head and heart seem to be at variance in this matter. Frankly I am puzzled to know where the contents of that pocketbook have gone. Were the things taken out before the bill book fell into your son's hands or afterward? And if afterward, who took them? Who had the chance? Donovan seems to think he has a clue, but I confess I have none." "Hadn't you looked over the bonds and stuff since you took them home?" "No," Mr. Ackerman admitted. "I got them from the broker yesterday and as it was too late to put them into the safe-deposit vault, I took them home with me instead of putting them in our office safe as I should have done. I thought it would be easier for me to stop at the bank with them this morning on my way to business. It was foolish planning but I aimed to save time." "So the pocketbook was at your house over night?" Mr. Ackerman nodded. "Yes," confessed he. "Nevertheless it did not go out of my possession. I had it in the inner pocket of my coat all the time." "You are sure no one took the things out while you were asleep last night?" "Why--I--I don't see how they could," faltered Mr. Ackerman. "My servants are honest--at least, they always have been. I have had them for years. Moreover, none of them knew I had valuable papers about me. How could they?" was the reply. Once more silence fell upon the room. "Come, Tolman," ejaculated the steamboat man presently, "you are a level-headed person. What is your theory?" "If I did not know my son and myself as well as I do," Mr. Tolman answered with deliberation, "my theory would be precisely what I fancy yours is. I should reason that during the interval between the finding of the purse and its return the contents had been extracted." He saw the New Yorker color. "That, I admit, is my logical theory," Mr. Ackerman owned with a blush, "but it is not my intuitive one. My brain tells me one thing and my heart another; and in spite of the fact that the arguments of my brain seem correct I find myself believing my heart and in consequence cherishing a groundless faith in you and your boy," concluded he, with a faint smile. "That is certainly generous of you, Ackerman!" Mr. Tolman returned, much moved by the other's confidence. "Stephen and I are in a very compromising situation with nothing but your belief between us and a great deal of unpleasantness. We appreciate your attitude of mind more than we can express. The only other explanation I can offer, and in the face of the difficulties it would involve it hardly seems a possible one, is that while the coat was hanging in the lobby--" There was a sound outside and a sharp knock at the door, and an instant later Mr. Donovan entered, his face wreathed in smiles. Following him was the woman who had checked the coats, a much frightened bell boy, and a blue-uniformed policeman. The woman was sobbing. "Indeed, sir," she wailed, approaching Steve, "I never meant to keep the pocketbook and make trouble for you. I have a boy of my own at home, a lad about your age. What is to become of him now? Oh, dear; oh, dear!" She burst into passionate weeping. "Now see here, my good woman, stop all this crying and talk quietly," cut in the policeman in a curt but not unkind tone. "If you will tell us the truth, perhaps we can help you. In any case we must know exactly what happened." "She must understand that anything she says can be used against her," cautioned the detective, who in spite of his eagerness to solve the mystery was determined the culprit should have fair play. "Indeed, I don't care, sir," protested the maid, wiping her eyes on her ridiculously small apron. "I can't be any worse off than I am now with a policeman taking me to the lock-up. I'll tell the gentlemen the truth, I swear I will." With a courtesy he habitually displayed toward all womanhood Mr. Tolman drew forward a chair and she sank gratefully into it. "I spied the bill book in the young gentleman's pocket the minute he took off his coat," began she in a low tone. "It was bright colored and as it was sticking part way out I couldn't help seeing it. Of course, I expected he would take it with him into the dining room but when he didn't I came to the conclusion that there couldn't be anything of value in it. But by and by I had more coats to hang up and one of them, a big, heavy, fur-lined one, brushed against the young gentleman's ulster and knocked the pocketbook out on to the floor so that it lay open under the coat rack. It was then that I saw it was stuffed full of papers and things." She stopped a moment to catch her breath and then went resolutely on: "It seemed to me it was no sort of a plan to put the wallet back into the lad's pocket, for when I wasn't looking somebody might take it. So I decided I much better keep it safe for him, and maybe," she owned with a blush, "get a good-sized tip for doing it. I have a big pocket in my underskirt where I carry my own money and I slipped it right in there, meaning to hand it to the young man when he came out from lunch." The corners of her mouth twitched and her tears began to fall again, but she wiped them away with her apron and proceeded steadily: "But nothing turned out as I planned, for no sooner was the bill book in my pocket than I was called away to help about the wraps at a lady's luncheon upstairs. There were so many people about the hall that I had no chance to restore the bill book to the lad's pocket without some one seeing me and thinking, perhaps, that I was stealing. There was no help but to take it with me, trusting they would not keep me long upstairs and that I would get back to my regular place before the young gentleman came out of the dining room. It was when I got out of the elevator in the upper hall that I spied Dick, one of the bell boys I knew, and I called to him; and after explaining that I couldn't get away to go downstairs I asked him to take the wallet and put it in 47's pocket. He's a good-natured little chap and always ready to do an errand, and more than that he's an honest boy. So I felt quite safe and went to work, supposing the young man had his pocketbook long ago." All eyes were turned upon the unlucky bell boy who hung his head and colored uncomfortably. "So it was the boy who took the contents of the pocketbook!" was Mr. Ackerman's comment. "Speak up, boy," commanded the officer. "The gentleman is talking to you." The lad looked up with a frightened start. He might have been sixteen years of age but he did not look it for he was pale and underfed; nor was there anything in his bearing to indicate the poise and maturity of one who was master of the occasion. On the contrary, he was simply a boy who was frankly distressed and frightened, and as unfeignedly helpless in the present emergency as if he had been six years old and been caught stealing jam from the pantry shelf. It did not take more than a glance to convince the onlookers that he was no hardened criminal. If he had done wrong it had been the result either of impulse or mischief, and the dire result of his deed was a thing he had been too unsophisticated to foresee. The plight in which he now found himself plainly amazed and overwhelmed him and he looked pleadingly at his captors. "Well, my boy, what have you to say for yourself?" repeated Mr. Ackerman more gently. "Nothin'." "Nothing?" "No, sir." "You did take the things out of the pocketbook then." "Yes, sir." "But you are not a boy accustomed to taking what does not belong to you." The culprit shot a glance of gratitude toward the speaker but made no reply. "How did you happen to do it this time?" persisted Mr. Ackerman kindly. "Come, tell me all about it." Perhaps it was the ring of sympathy in the elder man's voice that won the boy's heart. Whatever the charm, it conquered; and he met the eyes that scanned his countenance with a timid smile. "I wanted to see what was in the pocketbook," said he with naïve honesty, "and so I took the things out to look at them. I wasn't goin' to keep 'em. I dodged into one of the little alcoves in the hall and had just pulled the papers out when I heard somebody comin'. So I crammed the whole wad of stuff into my pocket, waiting for a time when I could look it over and put it back. But I got held up just like Mrs. Nolan did," he pointed toward the woman in the chair. "Some man was sick and the clerk sent me to get a bottle of medicine the minute I got downstairs, and all I had the chance to do was to stick the empty wallet in 47's pocket and beat it for the drug store. I thought there would be letters or something among the papers that would give the name of the man they belonged to, and I'd take 'em to the clerk at the desk an' say I found 'em. But no sooner had I got the medicine up to room Number 792 than the policeman nabbed me with the papers an' things on me. That's all there is to it, sir." "Have you the things now?" the officer put in quickly. "Sure! Didn't I just tell you I hadn't had the chance to hand 'em over to the clerk," the boy reiterated, pulling a wad of crumpled Liberty Bonds and documents out of his pocket, and tumbling them upon the table. There was no doubting the lad's story. Truth spoke in every line of his face and in the frankness with which he met the scrutiny of those who listened to him. If one had questioned his uprightness the facts bore out his statements, for once out of the hotel on an errand he might easily have taken to his heels and never returned; or he might have disposed of his booty during his absence. But he had done neither. He had gone to the drug store and come back with every intention of making restitution for the result of his curiosity. That was perfectly evident. "I'm sorry, sir," he declared, when no one spoke. "I know I shouldn't have looked in the pocketbook or touched the papers; but I meant no harm--honest I didn't." "I'll be bound of that, sir," the woman interrupted. "Dick was ever a lad to be trusted. The hotel people will tell you that. He's been here several years and there's never been a thing against him. I blame myself for getting him into this trouble, for without meaning to I put temptation in his way. I know that what he's told you is the living truth, and I pray you'll try and believe him and let him go. If harm was to come to the lad through me I'd never forgive myself. Let the boy go free and put the blame on me, if you must arrest somebody. I'm older and it doesn't so much matter; but it's terrible to start a child of his age in as a criminal. The name will follow him through life. He'll never get rid of it and have a fair chance. Punish me but let the little chap go, I beg of you," pleaded the woman, with streaming eyes. Mr. Ackerman cleared his throat; it was plain that the simple eloquence of the request had touched him deeply. "With your permission, officer, I am going to withdraw my charge," he said, with a tremor in his voice. "You are to let both these persons go scot free. You, my good woman, meant well but acted foolishly. As for the boy, Donovan, I will assume the responsibility for him." "You are willing to stand behind him, Mr. Ackerman?" "I am." The detective turned toward the boy who had risen and was fumbling awkwardly with the brass buttons adorning his uniform. "You hear, Dick Martin, what the gentleman says," began he impressively. "He believes you are a good boy, and as you have handed back the valuables in your possession he is going to take a chance on you and let you go." A wave of crimson swept over the face of the boy and for the first time the tension in the youthful countenance relaxed. "But Mr. Ackerman," Donovan continued, "expects you are going to behave yourself in future and never do such a thing again." "I am going to see your father, Dick," broke in Mr. Ackerman's kindly voice, "and talk with him and--" "I haven't any father," declared the lad. "Your mother then." "I've no mother either." "Who do you live with?" "Mr. Aronson." "Is he a relative?" "Oh, no, sir! I haven't any relatives. There's nobody belongin' to me. Mr. Aronson is the tailor downstairs where I sleep. When I ain't working here I do errands for him and he lets me have a cot in a room with four other boys--newsboys, bell hops and the like. We pay two dollars between us for the room and sometimes when I carry a lot of boxes round for Mr. Aronson he gives me my breakfast." "Nobody else is responsible for you?" "Nop!" returned the boy with emphasis. "No, sir, I mean." "I'll attend to all this, Donovan," murmured Mr. Ackerman in an undertone to the detective. "The lad shall not remain there. I don't know yet just what I'll do with him but I will plan something." Then addressing the lad, he continued, "In the meantime, Dick, you are to consider me your relative. Later I shall hunt you up and we will get better acquainted. Be a good boy, for I expect some day you are going to make me very proud of you." "What!" In sheer astonishment the boy regarded his benefactor. There was something very appealing in the little sharp-featured face which had now lost much of its pallor and softened into friendliness. "Why shouldn't you make me proud of you?" inquired Mr. Ackerman softly. "You can, you know, if you do what is right." "I'm goin' to try to, sir," burst out Dick with earnestness. "I'm goin' to try to with all my might." "That is all any one can ask of you, sonny," replied the steamboat magnate. "Come, shake hands. Remember, I believe in you, and shall trust you to live up to your word. The officer is going to let you go and none of us is going to mention what has happened. I will fix up everything for you and Mrs. Nolan so you can both go back to your work without interference. Now bid Mr. Tolman and his son good-by and run along. Before I leave the hotel I will look you up and you can give me Mr. Aronson's address." Master Richard Martin needed no second bidding. Eager to be gone he awkwardly put out his hand, first to Mr. Tolman and then to Steve; and afterward, with a shy smile to the detective and the policeman and a boyish duck of his head, he shot into the hall and they heard him rushing pell-mell down the corridor. Mrs. Nolan, however, was more self-controlled. She curtsied elaborately to each of the men and called down upon their heads every blessing that the sky could rain, and it was only after her breath had become quite exhausted that she consented to retire from the room and in company with the policeman and the detective proceeded downstairs in the elevator. "Well, Tolman," began the New Yorker when they were at last alone, "you see my heart was my best pilot. I put faith in it and it led me aright. Unfortunately it is now too late for the matinee but may I not renew my invitation and ask you and your son to dine with me this evening and conclude our eventful day by going to the theater afterward?" Mr. Tolman hesitated. "Don't refuse," pleaded the steamboat man. "Our acquaintance has, I confess, had an unfortunate beginning; but a bad beginning makes for a good ending, they say, and I feel sure the old adage will prove true in our case. Accept my invitation and let us try it out." "You are very kind," murmured Mr. Tolman vaguely, "but I--" "Help me to persuade your father to be generous, Stephen," interposed Mr. Ackerman. "We must not let a miserable affair like this break up what might, perhaps, have been a delightful friendship." "I don't need any further persuading, Ackerman," Mr. Tolman spoke quickly. "I accept your invitation with great pleasure." "That's right!" cried Mr. Ackerman, with evident gratification. "Suppose you come to my house at seven o'clock if that will be convenient for you. We will have a pleasant evening together and forget lost pocketbooks, detectives and policemen." Taking out a small card, he hurriedly scrawled an address upon it. "I keep a sort of bachelor's hall out on Riverside Drive," explained he, with a shade of wistfulness. "My butler looks out for me and sees that I do not starve to death. He and his son are really excellent housekeepers and make me very comfortable." He slipped into his overcoat. "At seven, then," he repeated. "Don't fail me for I should be much disappointed. Good-by!" and with a wave of his hand he departed, leaving Stephen and his father to themselves. CHAPTER X AN EVENING OF ADVENTURE That evening Steve and his father took a taxi-cab and drove to the number Mr. Ackerman had given them. It proved to be an imposing apartment house of cream brick overlooking the Hudson; and the view from the fifth floor, where their host lived, was such a fascinating one that the boy could hardly be persuaded to leave the bay window that fronted the shifting panorama before him. "So you like my moving picture, do you, Steve?" inquired the New Yorker merrily. "It is great! If I lived here I shouldn't do a bit of studying," was the lad's answer. "You think the influence of the place bad, then." "It would be for me," Stephen chuckled. Both Mr. Tolman and Mr. Ackerman laughed. "I will own," the latter confessed, "that at first those front windows demoralized me not a little. They had the same lure for me as they have for you. But by and by I gained the strength of mind to turn my back and let the Hudson River traffic look out for itself." "You might try that remedy, son," suggested Steve's father. "No, no, Tolman! Let the boy alone. If he is enjoying the ferries and steamboats so much the better." "But there seem to be plenty of steamboats here in the room to enjoy," was Mr. Tolman's quick retort. "Steamboats?" repeated Steve vaguely, turning and looking about him. Sure enough, there were steamboats galore! Wherever he looked he saw them. Not only were the walls covered with pictures of every imaginable type of steamer, but wherever there was space enough there were tiers of little ship models in glass cases. There were side-wheelers, awkwardly constructed boats with sprawling paddles, screw propellers, and twin-screw craft; ferryboats, tugs, steam yachts, and ocean liners. Every known variety of sea-going contrivance was represented. The large room was like a museum of ships and the boy gave an involuntary exclamation of delight. "Jove!" It was a laconic tribute to the marvels about him but it was uttered with so much vehemence that there was no mistaking its sincerity. Evidently, terse as it was, its ring of fervor satisfied Mr. Ackerman for he smiled to himself. "I never saw so many boats in all my life!" burst out Steve. "I told you I was in the steamboat business," put in Mr. Ackerman mischievously. "I should think you were!" was the lad's comment. "This is a wonderful collection, Ackerman," Mr. Tolman asserted, as he rose and began to walk about the room. "How did you ever get it together? Many of these prints are priceless." "Oh, I have been years doing it," Mr. Ackerman said. "It has been my hobby. I have chosen to sink my money in these toys instead of in an abandoned farm or antique furniture. It is just a matter of taste, you see." "You must have done some scouring of the country to make your collection so complete. I don't see how you ever succeeded in finding these old pictures and models. It is a genuine history lesson." "I do not deserve all the credit, by any means," the capitalist protested with modesty. "My grandfather, who was one of the owners of the first of the Hudson River steamers, began collecting pictures and drawings; and at his death they came to my father who added to them. Afterward, when the collection descended to me, I tried to fill in the gaps in order to make the sequence complete. Of course in many cases I have not been able to find what I wanted, for neither prints nor models of some of the ships I desired were to be had. Either there were no copies of them in existence, or if there were no money could tempt their owners to part with them. Still I have a well enough graded lot to show the progression." "I should think you had!" said Mr. Tolman heartily. "You have arranged them beautifully, too, from the old whalers and early American coasting ships to the clippers. Then come the first steam packets, I see, and then the development of the steamboat through its successive steps up to our present-day floating palace. It tells its own story, doesn't it?" "In certain fashion, yes," Mr. Ackerman agreed. "But the real romance of it will never be fully told, I suppose. What an era of progress through which to have lived!" "And shared in, as your family evidently did," interposed Mr. Tolman quickly. His host nodded. "Yes," he answered, "I am quite proud to think that both my father and my grandfather had their humble part in the story." "And well you may be. They were makers of history." Both men were silent an instant, each occupied with his own thoughts. Mr. Tolman moved reflectively toward the mantelpiece before which Steve was standing, gazing intently at a significant quartette of tiny models under glass. First came a ship of graceful outline, having a miniature figurehead of an angel at its prow and every sail set. Beside this was an ungainly side-wheeler with scarce a line of beauty to commend it. Next in order came an exquisite, up-to-date ocean liner; and the last in the group was a modern battleship with guns, wireless, and every detail cunningly reproduced. Stephen stood speechless before them. "What are you thinking of, son?" his father asked. "Why, I--" the boy hesitated. "Come, tell us! I'd like to know, too," echoed Mr. Ackerman. "Why, to be honest I was wondering how you happened to pick these particular four for your mantel," replied the lad with confusion. The steamboat man smiled kindly. "You think there are handsomer boats in the room than these, do you?" "Certainly there are better looking steamships than this one," Steve returned, pointing with a shrug of his shoulders at the clumsy side-wheeler. "But that rather ugly craft is the most important one of the lot, my boy," Mr. Tolman declared. "I suppose that is true," Mr. Ackerman agreed. "The fate of all the others hung on that ship." "Why?" was the boy's prompt question. "Oh, it is much too long a yarn to tell you now," laughed his host. "Were we to begin that tale we should not get to the theater to-night, say nothing of having any dinner." "I'd like to hear the story," persisted Stephen. "You will be reading it from a book some day." "I'd rather hear you tell it." "If that isn't a spontaneous compliment, Ackerman, I don't know what is," laughed Mr. Tolman. The steamboat man did not reply but he could not quite disguise his pleasure, although he said a bit gruffly: "We shall have to leave the story and go to the show to-night. I've bought the tickets and there is no escape," added he humorously. "But perhaps before you leave New York there will be some other chance for me to spin my yarn for you, and put your father's railroad romances entirely in the shade." The butler announced dinner and they passed into the dining room. If, however, Stephen thought that he was now to leave ships behind him he was mistaken, for the dining room proved to be quite as much of a museum as the library had been. Against the dull blue paper hung pictures of racing yachts, early American fighting ships, and nautical encounters on the high seas. The house was a veritable wonderland, and so distracted was the lad that he could scarcely eat. "Come, come, son," objected Mr. Tolman at last, "you will not be ready in time to go to any show unless you turn your attention to your dinner." "That's right," Mr. Ackerman said. "Fall to and eat your roast beef. We are none too early as it is." Accordingly Stephen fixed his eyes on his plate with resolution and tried his best to think no more of his alluring surroundings. With the coming of the ice-cream he had almost forgotten there were such things as ships, and when he rose from the table he found himself quite as eager to set forth to the theater as any other healthy-minded lad of his age would have been. The "show" Mr. Ackerman had selected had been chosen with much care and was one any boy would have delighted to see. The great stage had, for the time being, been transformed to a western prairie and across it came a group of canvas-covered wagons, or prairie schooners, such as were used in the early days by the first settlers of the West. Women and children were huddled beneath the arched canopy of coarse cloth and inside this shelter they passed the weary days and nights of travel. Through sun and storm the wagons rumbled on; jogging across the rough, uncharted country and jolting over rocks, sagebrush, and sand. There were streams to ford, mountains to climb on the long trip westward, but undaunted by obstacles the heroic little band of settlers who had with such determination left kin and comfort behind them passed on to that new land toward which their faces were set. It was such a company as this that Stephen now saw pictured before him. Perched on the front seat of the wagon driving the horses was the father of the family, rugged, alert, and of the woodsman type characteristic of the New England pioneer. The cavalcade halted. A fire was built and the travelers cooked their supper. Across the valley one could see the fading sunset deepen into twilight. From a little stream near-by the men brought water for the tired horses. Then the women and children clambered into the "ship of the desert" and prepared for a night's rest. In the meantime the men lingered about the dying fire and one of them, a gun in his hand, paced back and forth as if on guard. Then suddenly he turned excitedly to his comrades with his finger on his lips. He had heard a sound, the sound they all dreaded,--the cry of an Indian. Presently over the crest of the hill came stealing a stealthy band of savages. On they came, crouching against the rocks and moving forward with the lithe, gliding motion of serpents. The men sank down behind the brush, weapons in hand, and waited. On came the bloodthirsty Indians. Then, just when the destruction of the travelers seemed certain, onto the stage galloped a company of cowboys. Immediately there was a flashing of rifles and a din of battle. First it seemed as if the heroic rescuers would surely be slaughtered. But they fought bravely and soon the Indians were either killed or captured. Amid the confusion the owners of the prairie schooners leaped to the seats of their wagons, lashed forward their tired horses, and disappeared in safety with the terrified women and children. It was not until the curtain fell upon this thrilling adventure that Stephen sank back into his chair and drew a long breath. "Some show, eh, son?" said Mr. Tolman, as they put on their overcoats to leave the theater after the three long acts were over. The boy looked up, his eyes wide with excitement. "I should say!" he managed to gasp. "Did you like it, sonny?" Mr. Ackerman inquired. "You bet I did!" "Think you would have preferred to cross the continent by wagon rather than by train?" Steve hesitated. "I guess a train would have been good enough for me," he replied. "Was it really as bad as that before the railroads were built?" "Quite as bad, I'm afraid," was his father's answer. "Sometimes it was even worse, for the unfortunate settlers did not always contrive to escape. It took courage to be a pioneer and travel the country in those days. Undoubtedly there was much romance in the adventure but hand in hand with it went no little peril and discomfort. We owe a great deal to the men who settled the West; and, I sometimes think, even more to the dauntless women." Stephen did not reply. Very quietly he walked down the aisle between his father and Mr. Ackerman, and when he gave his hand to the latter and said good-night he was still thoughtful. It was evident that the scenes he had witnessed had made a profound impression on him and that he was still immersed in the atmosphere of prairie schooners, lurking Indians, and desert hold-ups. Even when he reached the hotel he was too tense and broad awake to go to bed. "I wish you'd tell me, Dad, how the first railroad across the country was built," he said. "I don't see how any track was ever laid through such a wilderness. Didn't the Indians attack the workmen? I should think they would have." His father placed a hand kindly on his shoulder. "To-morrow we'll talk trans-continental railroads, son, if by that time you still wish to," said he. "But to-night we'll go to bed and think no more about them. I am tired and am sure you must be." "I'm not!" was the prompt retort. "I rather fancy you will discover you are after you have undressed," smiled his father. "At any rate we'll have to call off railroading for to-night, for if you are not sleepy, I am." "But you won't have time to tell me anything to-morrow," grumbled Steve, rising unwillingly from his chair. "You will be busy and forget all about it and--" "I have nothing to do until eleven o'clock," interrupted Mr. Tolman, "when I have a business meeting to attend. Up to that time I shall be free. And as for forgetting it--well, you might possibly remind me if the promise passes out of my mind." In spite of himself the boy grinned. "You can bank on my reminding you all right!" he said, yawning. "Very well. Then it is a bargain. You do the reminding and I will do the story-telling. Are you satisfied and ready to go to bed and to sleep now?" "I guess so, yes." "Good-night then." "Good-night, Dad. I--I've had a bully day." CHAPTER XI THE CROSSING OF THE COUNTRY In spite of the many excitements crowded into his first day in New York Stephen found that when his head actually touched the pillow sleep was not long in coming and he awoke the next morning refreshed by a heavy and dreamless slumber. He was even dressed and ready for breakfast before his father and a-tiptoe to attack whatever program the day might present. Fortunately Mr. Tolman was of a sufficiently sympathetic nature to remember how he had felt when a boy, and with generous appreciation for the lad's impatience he scrambled up and made himself ready for a breakfast that was earlier, perhaps, than he would have preferred. "Well, son," said he, as they took their places in the large dining room, "what is the prospect for to-day? Are you feeling fit for more adventures?" "I'm primed for whatever comes," smiled the boy. "That's the proper spirit! Indians, bandits and cowboys did not haunt your pillow then." "I didn't stay awake to see." "You are a model traveler! Now we must plan something pleasant for you to do to-day. I am not sure that we can keep up the pace yesterday set us, for it was a pretty thrilling one. Robberies and arrests do not come every day, to say nothing of flotillas of ships and Wild West shows. However, we will do the best we can not to let the day go stale by contrast. But first I must dictate a few letters and glance over the morning paper. This won't take me long and while I am doing it I would suggest that you go into the writing room and send a letter to your mother. I will join you there in half an hour and we will do whatever you like before I go to my meeting. How is that?" "Righto!" Accordingly, after breakfast was finished, Steve wandered off by himself in search of paper and ink, and so sumptuous did he find the writing appointments that he not only dashed off a letter to his mother recounting some of the happenings of the previous day, but on discovering a rack of post cards he mailed to Jack Curtis, Tim Barclay, Bud Taylor and some of the other boys patronizing messages informing them that New York was "great" and he was _sorry they were not there_. In fact, it seemed at the moment that all those unfortunate persons who could not visit this magic city were to be profoundly pitied. In the purchase of stamps for these egoistic missives the remainder of the time passed, and before he realized the half-hour was gone, he saw his father standing in the doorway. "I am going up to the room now to hunt up some cigars, Steve," announced the elder man. "Do you want to come along or stay here?" "I'll come with you, Dad," was the quick reply. The elevator shot them to the ninth floor in no time and soon they were in their room looking down on the turmoil in the street below. "Some city, isn't it?" commented Mr. Tolman, turning away from the busy scene to rummage through his suit case. "It's a corker!" "I thought you would like to go out to the Zoo this morning while I am busy. What do you say?" "That would be bully." "It is a simple trip which you can easily make alone. If you like, you can start along now," Mr. Tolman suggested. "But you said last night that if I would hurry to bed, to-day you would tell me about the Western railroads," objected Stephen. He saw his father's eyes twinkle. "You have a remarkable memory," replied he. "I recall now that I did say something of the sort. But surely you do not mean that you would prefer to remain here and talk railroads than to go to the Zoo." "I can go to the Zoo after you have gone out," maintained Steve, standing his ground valiantly. "You are a merciless young beggar," grinned his father. "I plainly see that like Shylock you are determined to have your pound of flesh. Well, sit down. We will talk while I smoke." As the boy settled contentedly into one of the comfortable chintz-covered chairs, Mr. Tolman blew a series of delicate rings of smoke toward the ceiling and wrinkled his brow thoughtfully. "You got a pretty good idea at the theater last night what America was before we had trans-continental railroads," began he slowly. "You know enough of geography too, I hope, to imagine to some extent what it must have meant to hew a path across such an immense country as ours; lay a roadbed with its wooden ties; and transport all this material as well as the heavy rails necessary for the project. We all think we can picture to ourselves the enormity of the undertaking; but actually we have almost no conception of the difficulties such a mammoth work represented." He paused, half closing his eyes amid the cloud of smoke. "To begin with, the promoters of the enterprise received scant encouragement to attack the problem, for few persons of that day had much faith in the undertaking. In place of help, ridicule cropped up from many sources. It was absurd, the public said, to expect such a wild-cat scheme to succeed. Why, over six hundred miles of the area to be covered did not contain a tree and in consequence there would be nothing from which to make cross-ties. And where was the workmen's food to come from if they were plunged into a wilderness beyond the reach of civilization? The thing couldn't be done. It was impossible. Of course it was a wonderful idea. But it never could be carried out. Where were the men to be found who would be willing to take their lives in their hands and set forth to work where Indians or wild beasts were liable to devour them at any moment? Moreover, to build a railroad of such length would take a lifetime and where was the money coming from? For you must remember that the men of that period had no such vast fortunes as many of them have now, and it was no easy task to finance a scheme where the outlay was so tremendous and the probability of success so shadowy. Even as late as 1856 the whole notion was considered visionary by the greater part of the populace." "But the fun of doing it, Dad!" ejaculated Stephen, with sparkling eyes. "The fun of it!" repeated his father with a shrug. "Yes, there was fun in the adventure, there is no denying that; and fortunately for the dreamers who saw the vision, men were found who felt precisely as you do. Youth always puts romance above danger, and had there not been these romance lovers it would have gone hard with the trans-continental railroads. We might never have had them. As it was, even the men who ventured to cast in their lot with the promoters had the caution to demand their pay in advance. They had no mind to be deluded into working for a precarious wage. At length enough toilers from the east and from the west were found who were willing to take a chance with their physical safety, and the enterprise was begun." Stephen straightened up in his chair. "Had the only obstacle confronting them been the reach of uncharted country ahead that would have been discouraging enough. Fancy pushing your way through eight hundred miles of territory that had never been touched by civilization! And while you are imagining that, do not forget that the slender ribbon of track left behind was your only link with home; and your only hope of getting food, materials, and sometimes water. Ah, you would have had excitement enough to satisfy you had you been one of that company of workmen! On improvised trucks they put up bunks and here they took turns in sleeping while some of their party stood guard to warn them of night raids from Indians and wild beasts. Even in the daytime outposts had to be stationed; and more than once, in spite of every precaution, savages descended on the little groups of builders, overpowered them, and slaughtered many of the number or carried away their provisions and left them to starve. Sometimes marauders tore up the tracks, thereby breaking the connection with the camps in the rear from which aid could be summoned; and in early railroad literature we find many a tale of heroic engineers who ran their locomotives back through almost certain destruction in order to procure help for their comrades. Supply trains were held up and swept clean of their stores; paymasters were robbed, and sometimes murdered, so no money reached the employees; every sort of calamity befell the men. Hundreds of the ten thousand Chinese imported to work at a microscopic wage died of sickness or exposure to the extreme heat or cold." "Gee!" gasped Stephen, "I'd no idea it was so bad as all that!" "Most persons have but a faint conception of the price paid for our railways--paid not alone in money but in human life," answered Mr. Tolman. "The route of the western railroads, you see, did not lie solely through flat, thickly wooded country. Our great land, you must remember, is made up of a variety of natural formations, and in crossing from the Atlantic coast to that of the Pacific we get them one after another. In contrast to the forests of mighty trees, with their tangled undergrowth, there were stretches of prairie where no hills broke the level ground; another region contained miles and miles of alkali desert, dry and scorching, where the sun blazed so fiercely down on the steel rails that they became too hot to touch. Here men died of sunstroke and of fever; and some died for want of water. Then directly in the railroad's path arose the towering peaks of the Sierras and Rockies whose snowy crests must be crossed, and whose cold, storms and gales must be endured. Battling with these hardships the workmen were forced to drill holes in the rocky summits and bolt their rough huts down to the earth to prevent them from being blown away." "I don't see how the thing could have been done!" Steve exclaimed, with growing wonder. "And you must not forget to add to the chapter of tribulations the rivers that barred the way; the ravines that must either be filled in or bridged; the rocks that had to be blasted out; and the mountains that must be climbed or tunneled." "I don't see how they ever turned the trick!" the boy repeated. "It is the same old tale of progress," mused his father. "Over and over again, since time began, men have given their lives that the world might move forward and you and I enjoy the benefits of civilization. Remember it and be grateful to the past and to that vast army of toilers who offered up their all that you might, without effort, profit by the things it took their blood to procure. There is scarcely a comfort you have about you that has not cost myriad men labor, weariness, and perhaps life itself. Therefore value highly your heritage and treat the fruits of all hard work with respect; and whenever you can fit your own small stone into the structure, or advance any good thing that shall smooth the path of those who are to follow you, do it as your sacred duty to those who have so unselfishly builded for you." There was a moment of silence and the rumble of the busy street rose to their ears. "I never shall build anything that will help the men of the future," observed Stephen, in a low tone. "Every human being is building all the time," replied his father. "He is building a strong body that shall mean a better race; a clean mind that shall mean a purer race; a loyalty to country that will result in finer citizenship; and a life of service to his fellows that will bring in time a broader Christianity. Will not the world be the better for all these things? It lies with us to carry forward the good and lessen the evil of the universe, or tear down the splendid ideals for which our fathers struggled and retard the upward march of the universe. If everybody put his shoulder to the wheel and helped the forward spin of our old world, how quickly it would become a better place!" As he concluded his remarks Mr. Tolman took out his watch. "Well, well!" said he. "I had no idea it was so late. I must hurry or I shall not finish my story." "As I told you the men from the east and those from the west worked toward each other from opposite ends of the country. As soon as short lengths of track were finished they were joined together. Near the great Salt Lake of Utah a tie of polished laurel wood banded with silver marked the successful crossing of Utah's territory. Five years later Nevada contributed some large silver spikes to join her length of track to the rest. California sent spikes of solid gold, symbolic both of her cooperation and her mineral wealth; Arizona one of gold, one of silver, and one of iron. Many other States offered significant tributes of similar nature. And when at last the great day came when all the short lines were connected in one whole, what a celebration there was from sea to sea! Wires had been laid so that the hammer that drove the last spike sent the news to cities all over the land. Bells rang, whistles blew, fire alarms sounded. The cost of the Union Pacific was about thirty-nine million dollars and that of the Central Pacific about one hundred and forty million dollars. The construction of the Southern Pacific presented a different set of problems from those of the Northern, but many of the difficulties encountered were the same. Bands of robbers and Indians beset the workmen and either cut the ties and spread the rails, or tore the track up altogether for long distances. Forest fires often overtook the men before they could escape, although trains sometimes contrived to get through the burning areas by drenching their roofs and were able to bring succor to those in peril. Then there were washouts and snowstorms quite as severe as any experienced in the northern country." "I'm afraid I should have given the whole thing up!" interrupted Steve. "Many another was of your mind," returned Mr. Tolman. "The frightful heat encountered when crossing the deserts was, as I have said, the greatest handicap. Frequently the work was at a standstill for months because all the metal--rails and tools--became too hot to handle. The difficulty of getting water to the men in order to keep them alive in this arid waste was in itself colossal. Tank cars were sent forward constantly on all the railroads, northern as well as southern, and the suffering experienced when such cars were for various reasons stalled was tremendous. The sand storms along the Southern Pacific route were yet another menace. So you see an eagerness for adventure had to be balanced by a corresponding measure of bravery. Those early days of railroad building were not all romance and picturesqueness." Stephen nodded as his father rose and took up his hat and coat. "I'd like to hear Mr. Ackerman tell of the early steamboating," remarked the lad. "I'll bet the story couldn't match the one you have just told." "Perhaps not," his father replied. "Nevertheless the steamships had their full share of exciting history and you must not be positive in your opinion until you have heard both tales. Now come along, son, if you are going with me, for I must be off." Obediently Stephen slipped into his ulster and tagged at his father's heels along the corridor. What a magic country he lived in! And how had it happened that it had been his luck to be born now rather than in the pioneer days when there were not only no railroads but no great hotels like this one, and no elevators? "I suppose," observed Mr. Tolman, as they went along, "we can hardly estimate what the coming of these railroads meant to the country. All the isolated sections were now blended into one vast territory which brought the dwellers of each into a common brotherhood. It was no small matter to make a unit of a great republic like ours. The seafarer and the woodsman; easterner, westerner, northerner, and southerner exchanged visits and became more intelligently sympathetic. Rural districts were opened up and made possible for habitation. The products of the seacoast and the interior were interchanged. Crops could now be transported; material for clothing distributed; and coal, steel, and iron--on which our industries were dependent--carried wherever they were needed. Commerce took a leap forward and with it national prosperity. From now on we were no longer hampered in our inventions or industries and forced to send to England for machinery. We could make our own engines, manufacture our own rails, coal our own boilers. Distance was diminished until it was no longer a barrier. Letters that it previously took days and even weeks to get came in hours, and the cost and time for freight transportation was revolutionized. In 1804, for example, it took four days to get a letter from New York to Boston; and even as late as 1817 it cost a hundred dollars to move a ton of freight from Buffalo to New York and took twenty days to do it. In every direction the railroads made for national advancement and a more solid United States. No soldiers, no statesmen of our land deserve greater honor as useful citizens than do these men who braved every danger to build across the country our trans-continental railways." CHAPTER XII NEW PROBLEMS "I have been thinking, Dad," said Steve that evening, while they sat at dinner, "of the railroad story you told me this morning. It was some yarn." His father laughed over the top of his coffee cup. "It was, wasn't it?" replied he. "And the half was not told then. I was in too much of a hurry to give you an idea of all the trials the poor railroad builders encountered. Did it occur to you, for example, that after the roads to the Pacific coast were laid their managers were confronted by another great difficulty,--the difference in time between the east and the west?" "I never thought of that," was Steve's answer. "Of course the time must have differed a lot." "Indeed it did! Every little branch road followed the time peculiar to its own section of the country, and the task of unifying this so that a basis for a common time-table could be adopted was tremendous. A convention of scientists from every section of the country was called to see what could be done about the fifty-three different times in use by the various railroads." "Fifty-three!" ejaculated Stephen, with a grin. "Why, that was almost as many as Heinz pickles." "In this case the results of the fifty-three varieties were far more menacing, I am afraid, than those of the fifty-seven," said his father, with a smile, "for travel under such a régime was positively unsafe." "I can see that it would be. What did they do?" "Well, after every sort of suggestion had been presented it was decided to divide the country up into four immense parts, separated from one another by imaginary lines running north and south." "Degrees of longitude?" "Precisely!" returned Mr. Tolman, gratified that the boy had caught the point so intelligently. "The time of each of these sections jumped fifteen degrees, or one hour, and the railroads lying in each district were obliged to conform to the standard time of their locality. Until this movement went into effect there had been, for example, six so-called standard times to reckon with in going from Boston to Washington." "I don't see why everybody didn't get smashed up!" "I don't either; and I fancy the passengers and the railroad people didn't," declared Mr. Tolman. "But with the new state of things the snarl was successfully untangled and the roads began to be operated on a more scientific basis. Then followed gradual improvements in cars which as time went on were made more comfortable and convenient. The invention of the steam engine and the development of our steel products were the two great factors that made our American railroads possible. With the trans-continental roads to carry materials and the opening up of our coal, iron and copper mines we were at last in a position to make our railroads successful. Then science began to evolve wonderful labor-saving machinery which did away with the slow, primitive methods our pioneer engineers had been obliged to employ. The steam shovel was invented, the traveling crane, the gigantic derrick, the pile driver. The early railroad builders had few if any of these devices and were forced to do by hand the work that machinery could have performed in much less time. When one thinks back it is pathetic to consider the number of lives that were sacrificed which under present-day conditions might have been saved. Yet every great movement goes forward over the dead bodies of unnamed heroes. To an extent this is unavoidable and one of the enigmas of life. If every generation were as wise at the beginning as it is at the end there would be no progress. Nevertheless, when you reflect that ten thousand Chinese and Chilean laborers died while building one of the South American railroads it does make us wonder why we should be the ones to reap the benefits of so much that others sowed, doesn't it?" mused the boy's father. "Do you mean to say that ten thousand persons were killed while that railroad was being built?" questioned Stephen, aghast. "They were not all killed," was the reply. "Many of them died of exposure to cold, and many from the effects of the climate. Epidemics swept away hundreds of lives. This particular railroad was one of the mightiest engineering feats the world had seen for in its path lay the Andes Mountains, and there was no escape from either crossing or tunneling them. The great tunnel that pierces them at a height of 15,645 feet above sea level is one of the marvels of science. In various parts of the world there are other such monuments to man's conquest of the opposing forces of nature. Honeycombing the Alps are spiral tunnels that curve round and round like corkscrews inside the mountains, rising slowly to the peaks and making it possible to reach the heights that must be traversed. Among these marvels is the Simplon Tunnel, famous the world over. The road that crosses the Semmering Pass from Trieste to Vienna is another example of what man can do if he must. By means of a series of covered galleries it makes its way through the mountains that stretch like a wall between Italy and Austria. In the early days this territory with its many ravines and almost impassable heights would have been considered too difficult to cross. The railroad over the Brenner Pass between Innsbruck and Botzen penetrates the mountains of the Tyrol by means of twenty-three tunnels." "I learned about the St. Gothard tunnel in school," Steve interrupted eagerly. "Yes, that is yet another of the celebrated ones," his father rejoined. "In fact, there are now so many of these miracles of skilful railroading that we have almost ceased to wonder at them. Railroads thread their way up Mt. Washington, Mt. Rigi, and many another dizzy altitude; to say nothing of the cable-cars and funicular roads that take our breath away when they whirl us to the top of some mountain, either in Europe or in our own land. Man has left scarce a corner of our planet inaccessible, until now, not content with scaling the highest peaks by train, he has progressed still another stage and is flying over them. Thus do the marvels of one age become the commonplace happenings of the next. Our ancestors doubtless thought, when they had accomplished the miracles of their generation, that nothing could surpass them. In the same spirit we regard our aeroplanes and submarines with triumphant pride. But probably the time will come when those who follow us will look back on what we have done and laugh at our attempts just as you laughed when I told you of the first railroad." Stephen was thoughtful for a moment. "It's a great game--living--isn't it, Dad?" "It is a great game if you make yourself one of the team and pull on the side of the world's betterment," nodded his father. "Think what such a thing as the railroad has meant to millions and millions of people. Not only has it opened up a country which might have been shut away from civilization for centuries; but it has brought men all over the world closer together and made it possible for those of one land to visit those of another and come into sympathy with them. Japan, China, and India, to say nothing of the peoples of Europe, are almost our neighbors in these days of ships and railroads." "I suppose we should not have known much about those places, should we," reflected the boy. "Certainly not so much as we do now," was his father's answer. "Of course, travelers did go to those countries now and then; but to get far into their interior in a palanquin carried by coolies, for example, was a pretty slow business." "And uncomfortable, too," Stephen decided. "I guess the natives were mighty glad to see the railroads coming." To the lad's surprise his father shook his head. "I am afraid they weren't," observed he ruefully. "You recall how even the more civilized and better educated English and French opposed the first railroads? Well, the ignorant orientals, who were a hundred times more superstitious, objected very vehemently. The Chinese in particular feared that the innovation would put to flight the spirits which they believed inhabited the earth, air, and water. Surely, they argued, if these gods were disturbed, disaster to the nation must inevitably follow. It was almost impossible to convince even the more intelligent leaders that the railroad would be a benefit instead of a menace for before the ancient beliefs argument was helpless." "Well, the railroads were built just the same, weren't they?" "Yes. Fortunately some of the more enlightened were led to see the wisdom of the enterprise, and they converted the others to their views or else overrode their protests. They were like a lot of children who did not know what was best for them and as such they had to be treated. Nevertheless, you may be quite certain that the pioneer days of railroad building in the East were not pleasant ones. Materials had to be carried for great distances both by water and by land. In 1864, when the first locomotive was taken to Ceylon, it had to be transported on a raft of bamboo and drawn from the landing place to the track by elephants." "Humph!" chuckled Steve. "It's funny to think of, isn't it?" "More funny to think of than to do, I guess," asserted his father. "Still it is the battle against obstacles that makes life interesting, and in spite of all the hardships I doubt if those first railroad men would have missed the adventure of it all. Out of their resolution, fearlessness and vision came a wonderful fulfillment, and it must have been some satisfaction to know that they had done their share in bringing it about." "I suppose that is what Mr. Ackerman meant when he spoke of the history of steamboating," said the boy slowly. "Yes. He and his family had a hand in that great game and I do not wonder he is proud of it. And speaking of Mr. Ackerman reminds me that he called up this afternoon to ask if you would like to take a motor-ride with him to-morrow morning while I am busy." "You bet I would!" was the fervent reply. "I thought as much, so I made the engagement for you. He is coming for you at ten o'clock. And he will have quite a surprise for you, too." "What is it?" the boy asked eagerly. "It is not my secret to tell," was the provoking answer. "You will know it in good time." "To-morrow?" "I think so, yes." "Can't you tell me anything about it?" "Nothing but that you were indirectly responsible for it." "_I!_" gasped Stephen. Mr. Tolman laughed. "That will give you something to wonder and to dream about," he responded, rising from the table. "Let us see how much of a Sherlock Holmes you are." Steve's mind immediately began to speculate rapidly on his father's enigmatic remark. All the way up in the elevator he pondered over the conundrum; and all the evening he turned it over in his mind. At last, tired with the day's activities, he went to bed, hoping that dreams might furnish him with a solution of the riddle. But although he slept hard no dreams came and morning found him no nearer the answer than he had been before. He must wait patiently for Mr. Ackerman to solve the puzzle. CHAPTER XIII DICK MAKES HIS SECOND APPEARANCE When Mr. Ackerman's car rolled up to the hotel later in the morning the puzzle no longer lacked a solution for in the automobile beside the steamboat magnate sat Dick Martin, the lad of the pocketbook adventure. At first glance Steve scarcely recognized the boy, such a transformation had taken place in his appearance. He wore a new suit of blue serge, a smartly cut reefer, shiny shoes, a fresh cap, and immaculate linen. Soap and water, as well as a proper style of haircut had added their part to the miracle until now, with face glowing and eyes alight with pleasure, Dick was as attractive a boy as one would care to see. "I have brought Dick along with me, you see," the New Yorker explained, when the three were in the car and speeding up Fifth Avenue. "He and I have been shopping and now he is coming home to stay with me until we hear from one of the schools to which I have written. If they can find a place for him he will start at once. Then he is going to study hard and see what sort of a man he can make of himself. I expect to be very proud of him some day." The lad flushed. "I am going to do my best," said he, in a low tone. "That is all any one can do, sonny," declared Mr. Ackerman kindly. "You'll win out. Don't you worry! I'm not." He smiled and Dick smiled back timidly. "Have you been up to Mr. Ackerman's house yet and seen the boats?" Stephen asked, to break the pause that fell between them. "His collection, you mean? Sure! I'm--staying there." "Living there, sonny," put in the financier. "Then I suppose he's told you all about them," went on Stephen, a hint of envy in his tone. "I haven't yet," laughed their host, "for there hasn't been time. Dick only left the hotel yesterday and we have had a great deal to do since. We had to go to his lodgings and say good-by to the people there who have been kind to him and tell them why he was not coming back. And then there were errands and many other things to see to. So he has not been at home much yet," concluded Mr. Ackerman, with a kindly emphasis on the final sentence. Dick beamed but it was evident that the magnitude of his good fortune had left him too overwhelmed for words. Perhaps neither of the boys minded that there was little conversation during the drive for there was plenty to see and to Dick Martin, at least, an automobile ride was such an uncommon experience that it needed no embellishments. They rode up Morningside Drive and back again, looking down on the river as they went, and exclaiming when some unusual craft passed them. Evidently Mr. Ackerman was quite content to let matters take their natural course; but he was not unmindful of his guests and when at last he saw a shadow of fatigue circle Dick's eyes and give place to the glow of excitement that had lighted them he said: "Now suppose we go back to the house for a while. We have an hour or more before Stephen has to rejoin his father and you two chaps can poke about the suite. What do you say?" Steve was all enthusiasm. He had been quietly hoping there would be a chance for him to have another peep at the wonderful steamboats. "I'd like nothing better!" was his instant reply. "I did not see half I wanted to when I was there before, and we go home to-morrow, you know. If I don't see your ships and things to-day I never shall." "Oh, don't say that!" Mr. Ackerman said quickly. "You and Dick and I are going to be great friends. We are not going to say good-by and never see one another any more. Sometime you will be coming to New York again, I hope. However, if he wants to have a second glimpse of our boats now we'll let him, won't we, Dick?" Again the boy smiled a timid smile into his benefactor's face. [Illustration: "I wish you'd tell me about this queer little old-fashioned boat." Page 181.] It did not take long to reach the house and soon the three were in the wonderful room with its panorama of ships moving past the windows and its flotilla of still more ships decorating the walls. "Now you boys go ahead and entertain yourselves as you please," Mr. Ackerman said. "I am going to sit here and read the paper; but if there is anything you want to ask me you are welcome to do so." Stephen strolled over to the mantelpiece and stood before the model of the quaint side-wheeler that had held his attention at the time of his first visit; then he stole a furtive glance at the man in the big chair. "Did you really mean, Mr. Ackerman," he faltered, "that we could ask you questions?" "Certainly." "Then I wish you'd tell me about this queer little old-fashioned boat, and how you happened to put it between this up-to-date ocean liner and this battleship." The elder man looked up. "That boat that interests you is a model of Fulton's steamboat--or at least as near a model as I could get," explained he. "I put it there to show the progress we have made in shipbuilding since that day." Steve laughed. "I see the progress all right," replied he, "but I am afraid I do not know much about Fulton and his side-wheeler." Mr. Ackerman let the paper slip into his lap. "I assumed every boy who went to school learned about Robert Fulton," answered he, half teasingly and yet with real surprise. "I suppose I ought to have learned about him," retorted Stephen, with ingratiating honesty, "and maybe I did once. But if I did I seem to have forgotten about it. You see there are such a lot of those old chaps who did things that I get them all mixed up." Apparently the sincerity of the confession pleased the capitalist for he laughed. "I know!" returned he sympathetically. "Every year more and more things roll up to remember, don't they? Had we lived long ago, before so many battles and discoveries had taken place, and so many books been written, life would have been much simpler. Now the learning of all the ages comes piling down on our heads. But at least you can congratulate yourself that you are not so badly off as the boys will be a hundred years hence; they, poor things, will have to learn all about what _we_ have been doing, and if the world progresses as rapidly in history and in science as it is doing now, I pity them. Not only will they have to go back to Fulton but to him they will probably have to add a score of other inventors." Both boys joined in the steamboat man's hearty laugh. "Well, who was Fulton, anyway, Mr. Ackerman?" Stephen persisted. "If you want me to tell you that Robert Fulton was the first American to make a successful steamboat I can give you that information in a second," was the reply. "But if you wish to hear how he did it that is a much longer story." "I like stories," piped Dick from the corner of the couch where he was sitting. "So do I," echoed Steve. "Then I see there is no help for me!" Mr. Ackerman answered, taking off his spectacles and putting them into the case. With an anticipatory smile Stephen seated himself on the great leather divan beside the other boy. "Before the steamboat came," began Mr. Ackerman, "you must remember that paddle wheels had long been used, for both the Egyptians and the Romans had built galleys with oars that moved by a windlass turned by the hands of slaves or by oxen. Later there were smaller boats whose paddle wheels were driven by horses. So you see paddle wheels were nothing new; the world was just waiting for something that would turn them around. After the Marquis of Worcester had made his steam fountain he suggested that perhaps this power might be used to propel a boat but unfortunately he died before any experiments with the idea could be made. Various scientists, however, in Spain, France, England and Scotland caught up the plan but after struggling unsuccessfully with it for a time abandoned it as impractical. In 1802 Lord Dundas, a proprietor in one of the English canals, made an encouraging start by using a tow-boat with a paddle wheel at its stern. But alas, this contrivance kicked up such a fuss in the narrow stream that it threatened to tear the banks along the edge all to pieces and therefore it was given up and for ten years afterward there was no more steamboating in England." The boys on the couch chuckled. "In the meantime in America thoughtful men were mulling over the problem of steam navigation. Watt's engine had opened to the minds of inventors endless possibilities; and the success of the early railroads made many persons feel that a new era of science, whose wonders had only begun to unfold, was at hand. In Connecticut there lived a watchmaker by the name of John Fitch, who, although he knew little of the use of steam, knew much about machinery. Through the aid of a company that furnished him with the necessary money he built a steamboat which was tried out in 1787 and made three miles an hour. Of course it was not a boat like any of ours for it was propelled by twelve oars, or paddles, operated by a very primitive steam engine. Nevertheless, it was the forerunner of later and better devices of a similar nature, and therefore Fitch is often credited with being the inventor of the steamboat. Perhaps, had he been able to go on with his schemes, he might have given the world something really significant in this direction; but as it was he simply pointed the way. His money gave out, the company would do nothing further for him, and after building a second boat that could go eight miles an hour instead of three he became discouraged and intemperate and let his genius go to ruin, dying later in poverty--a sad end to a life that might well have been a brilliant one. After Fitch came other experimenters, among them Oliver Evans of Philadelphia who seems to have been a man of no end of inventive vision." "Wasn't he the one who tried sails on a railroad train?" inquired Steve, noting with pleasure the familiar name. "He was that very person," nodded Mr. Ackerman. "He evidently had plenty of ideas; the only trouble was that they did not work very well. He had already applied steam to mills and wagons, and now he wanted to see what he could do with it aboard a boat. Either he was very impractical or else hard luck pursued his undertakings. At any rate, he had a boat built in Kentucky, an engine installed on it, and then he had the craft floated to New Orleans from which point he planned to make a trip up the Mississippi. But alas, before his boat was fully ready, there was a drop in the river and the vessel was left high and dry on the shore." "Jove!" exclaimed Dick involuntarily. "Pretty tough, wasn't it?" remarked Mr. Ackerman. "What did he do then?" demanded Stephen. "Did he resurrect the boat?" "No, it did not seem to be any use; instead he had the engine and boiler taken out and put into a saw mill where once again hard luck pursued him, for the mill was burned not long after. That was the end of Oliver Evans's steamboating." Mr. Ackerman paused thoughtfully. "Now while Fitch and those following him were working at the steamboat idea here in America, Robert Fulton, also a native of this country, was turning the notion over in his mind. Strangely enough, he had not intended to be an inventor for he was in France, studying to be a painter. During a visit to England he had already met several men who were interested in the steam engine and through them had informed himself pretty thoroughly about the uses and action of steam. In Paris he made the acquaintance of a Mr. Barlow and the two decided to raise funds and build a steamboat to run on the Rhone. This they did, but unfortunately the boat sank before any degree of success had been achieved. Then Fulton, not a whit discouraged, told the French Government that if they would furnish the money he would build a similar boat to navigate the Seine. The French, however, had no faith in the plan and promptly refused to back it." "I'll bet they wished afterward they had!" interrupted Dick. "I presume they did," agreed Mr. Ackerman. "It is very easy to see one's mistakes after a thing is all over. Anyway, Mr. Barlow came back to America, where Fulton joined him, and immediately the latter went to building a steamboat that should be practical. On his way home he had stopped in England and purchased various parts for his engine and when he got to New York he had these set up in an American boat. You must not for a moment imagine that everything about this first steamboat of Fulton's was original. On the contrary he combined what was best in the experiments of previous inventors. He adopted the English type of engine, the side paddle, everything that seemed to him workable. Barlow and a rich New Yorker named Livingston backed the enterprise. Now some time before the State of New York, half in jest and half in irony, had granted to Livingston the sole right to navigate the New York waters by means of ships driven by steam or fire engines. At the time the privilege had caused much mirth for there were nothing but sailing ships in existence, and there was no prospect of there ever being any other kind of vessel. Hence the honor was a very empty one and nobody expected a time would arrive when it would ever be of any value to its owner. But Livingston was a shrewder and more far-seeing man than were the old legislators at Albany, and to Fulton he was an indispensable ally." The boy listened breathlessly. "How these three men managed to keep their secret so well is a mystery; but apparently they did, and when Fulton suddenly appeared on the Hudson with a steamboat named the _Clermont_ for Mr. Livingston's country seat on the Palisades, the public was amazed. A model of the boat with a miniature engine had previously been tried out so the three promoters had little doubt that their project would work, and it did. As the new craft moved along without any sails to propel it the sensation it made was tremendous. People were divided as to whether to flee from it in terror or linger and marvel at it. It is a pity that the newspapers of the period did not take the advent of this remarkable invention more seriously for it would have been interesting to know more of the impression it created. As it was little is recorded about it. Probably the very silence of the press is significant of the fact that there was scant faith in the invention, and that it was considered too visionary a scheme to dignify with any notice. However that may be, the newspapers passed this wonderful event by with almost no comment. History, however, is more generous and several amusing stories have come down to us of the fright the _Clermont_ caused as she crept along the river at dusk with a shower of vermilion sparks rising from her funnel. One man who came around a bend of the stream in his boat and encountered the strange apparition for the first time told his wife afterward that he had met the devil traveling the river in a sawmill." There was a shout of laughter from the boys. "The trial trip, to which many distinguished guests were invited, took place a few days later, and after improving some of the defects that cropped up the steamboat was advertised to run regularly between New York and Albany. Now if you think this announcement was hailed with joy you are much mistaken," continued Mr. Ackerman, smiling to himself at some memory that evidently amused him. "On the contrary the owners of the sailing ships which up to this time had had the monopoly of traffic were furious with rage. So vehemently did they maintain that the river belonged to them that at last the matter went to the courts and Daniel Webster was retained as Fulton's counsel. The case attracted wide attention throughout the country, and when it was decided in Fulton's favor there was great excitement. Every sort of force was brought to bear to thwart the new steamboat company. Angry opponents tried to blow up the boat as it lay at the dock; attempts were made to burn it. At length affairs became so serious that a clause was appended to the court's decree which made it a public crime punishable by fine or imprisonment to attempt to injure the _Clermont_." Mr. Ackerman paused to light a fresh cigar. "From the moment the law took this stand the success of the undertaking became assured and it is interesting to see how quickly the very men who jeered loudest at the enterprise now came fawning and begging to have a part in it. Other steamboats were added to the line and soon rival firms began to construct steamboats of their own and try to break up Fulton's monopoly of the waters of the State. For years costly lawsuits raged, and in defiance of the right the New York legislature had granted to Livingston, the fiercest competition took place. Sometime I should like to tell you more of this phase of the story for it is a very exciting and interesting yarn. Yet in spite of all the strife and hatred that pursued him Fulton's river-boats and ferries continued to run." "The State stuck to its bargain, then," murmured Steve, "and left Livingston the rights awarded him?" "No," replied Mr. Ackerman. "For a time they clung to their agreement; but at last the courts withdrew the right as illegal, and poor Livingston, who had sunk the greater part of his fortune in the steamboat business, lived to see the fruit of his toil wrested from him. In point of fact, I believe the decision of the courts to have been a just one for no one person or group of persons should control the waterways of the country. You can see the wisdom of this yourself. Nevertheless, the decree hit Livingston pretty hard. It was the first step in the destruction of a monopoly," added Mr. Ackerman whimsically. "Since then such decrees have become common happenings in America, monopolies being considered a menace to national prosperity. Certainly in this case it was well that the Supreme Court of the United States decided that all waters of the country should be free to navigators, no matter in what kind of vessel they chose to sail." "It was tough on Fulton and his friends, though, wasn't it?" observed Dick, who was plainly unconvinced as many another had been of the justice of the arguments. "Yes," agreed Mr. Ackerman, smiling into his troubled eyes, "I grant you it was tough on them." CHAPTER XIV A STEAMBOAT TRIP BY RAIL It was with a sense of deep regret that Stephen bade good-by to Mr. Ackerman and Dick and returned to the hotel to join his father. For the steamboat financier he had established one of those ardent admirations which a boy frequently cherishes toward a man of attractive personality who is older than himself; and for Dick he had a genuine liking. There was a quality very winning in the youthful East-sider and now that the chance for betterment had come his way Steve felt sure that the boy would make good. There was a lot of pluck and grit in that wiry little frame; a lot of honesty too, Stephen reflected, with a blush. He was not at all sure but that in the matter of fearlessness and moral courage the New York lad had the lead of him. Certainly he was not one who shrank from confessing when he had been at fault which, Steve owned with shame, could not be said of himself. For several days he had not thought of his automobile escapade but now once more it came to his mind, causing a cloud to chase the joyousness from his face. Alas, was he never to be free of the nagging mortification that had followed that single act? Was it always to lurk in the background and make him ashamed to confront the world squarely? Well, it was no use regretting it now. He had made his choice and he must abide by it. Nevertheless he was not quite so spontaneously happy when he met his father at luncheon and recounted to him the happenings of the morning. "Mr. Ackerman is taking a big chance with that boy," was Mr. Tolman's comment, when a pause came in the narrative. "I only hope he will not disappoint him. There must be a great difference between the standards of the two. However, Dick has some fine characteristics to build on--honesty and manliness. I think the fact that he showed no coward blood and was ready to stand by what he had done appealed to Ackerman. It proved that although they had not had the same opportunity in life they at least had some good stuff in common. You can't do much with a boy who isn't honest." Stephen felt the blood beating in his cheeks. Fortunately his father did not notice his embarrassment and as they soon were on their way to a picture show the memory that had so importunately raised its unwelcome head was banished by the stirring story of a Californian gold mine. Therefore by the time Stephen was ready to go to bed the ghost that haunted him was once more thrust into the background and he had gained his serenity. No, he was not troubled that night by dreams of his folly nor did he awaken with any remembrance of it. Instead he and his father chatted as they packed quite as pleasantly as if no specter stood between them. "Well, son, have you enjoyed your holiday?" inquired Mr. Tolman, as they settled themselves in the great plush chairs of the parlor car and waited for the train to start. "Yes, I've had a bully time, Dad." "I'm glad of that," was the kind reply. "It was unlucky that my business took up so much more of my time than I had expected and that I had to leave you to amuse yourself instead of going about with you, as I had planned. It was too bad. However, if you have managed to get some fun out of your visit that is the main thing. In fact, I am not sure but that you rather enjoyed going about alone," concluded he mischievously. Stephen smiled but did not reply. There was no denying that he had found being his own master a pleasant experience which had furnished him with a gratifying sense of freedom and belief in his own importance. What a tale he would have to tell the fellows at home! And how shocked his mother would be to hear that he had been turned loose in a great city in this unceremonious fashion! He could hear her now saying to his father: "I don't see what you were thinking of, Henry, to let Stephen tear about all alone in a city like New York. I should have worried every instant if I had known what he was doing. Suppose anything had happened to him!" Well, mercifully, nothing had happened,--that is, nothing worse than his falling into the hands of a detective and being almost arrested for robbery, reflected the boy with a grin. Perhaps Mr. Tolman interpreted his thoughts for presently he observed with a smile: "It is time you were branching out some for yourself, anyway, son. You are old enough now to be treated like a man, not like a little boy." As he spoke he looked toward Stephen with an expression of such pride and affection that the force of it swept over the lad as it never had done before. What a bully sort his father was, he suddenly thought; and how genuinely he believed in him! Why not speak out now and clear up the wretched deception he had practiced, and start afresh with a clean conscience? With impulsive resolve he gripped the arms of the chair and pulled himself together for his confession. But just at the crucial moment there was a stir in the aisle and a porter followed by two belated passengers hurried into the train which was on the brink of departure. That they had made their connection by a very narrow margin was evident in their appearance, for both were hot and out of breath, and the stout colored porter puffed under the stress of his haste and the heavy luggage which weighed him down. "It's these two chairs, sir," he gasped, as he tossed the new leather suit case into the rack. "Is there anything else I can do for you?" "No," replied the traveler, thrusting a bill into the darkey's hand. Already the train was moving. "Keep the change," he added quickly. "Thank you, sir! Thank you!" stammered the vanishing negro. "Well, we caught it, didn't we, Dick? It didn't look at one time as if it were possible. That block of cars on the avenue was terrible. But we are off now! It was about the closest shave I ever made." Then he turned around. "Hullo!" he cried. "Who's this? Bless my soul!" Both Mr. Tolman and Steve joined in the laugh of amazement. "Well, if this isn't a great note!" went on Mr. Ackerman, still beaming with surprise. "I thought you people were not going until the afternoon train." "I managed to finish up my business yesterday and get off earlier than I planned," Mr. Tolman explained. "But I did not know _you_ had any intention of going in this direction." "I hadn't until this morning," laughed the financier. "Then a telegram arrived saying they could take Dick at the New Haven school to which I had written if he entered right away, at the beginning of the term. So I dropped everything and here we are _en route_. It was rather short notice and things were a bit hectic; but by turning the whole apartment upside down, rushing our packing, and keeping the telephone wire hot we contrived to make the train." "It is mighty nice for us," put in Mr. Tolman cordially. "So Dick is setting forth on his education, is he?" "Yes, he is starting out to make of himself a good scholar, a good sport, a good athlete, and I hope a good man," returned the New Yorker. "A pretty big order, isn't it, Dick?" laughed Mr. Tolman. "It seems so," returned the boy. "It is not a bit too big," interrupted Mr. Ackerman. "Dick knows he hasn't got to turn the trick all in a minute. He and I understand such things take time. But they _can be done_ and we expect we are going to do them." He flashed one of his rare smiles toward his protégé and the lad smiled back frankly. "I expect so, too," echoed Mr. Tolman. "You've got plenty of backers behind you, Dick, and you have a clear path ahead. That is all any boy needs." "You're going back to school, aren't you, youngster?" Mr. Ackerman suddenly inquired of Stephen. "Yes, sir. I start in next week." "Decided yet whether you will be a railroad man like your Dad, or a steamboat man like me?" went on the New Yorker facetiously. "Not yet." "Oh, for shame! It should not take you any time at all to decide a question like that," the capitalist asserted teasingly. "What's hindering you?" Stephen gave a mischievous chuckle. "I can't decide until I have heard both sides," said he. "So far I know only half the steamboat story." "I see! In other words you think that between here and New Haven I might beguile the time by going on with the yarn I began yesterday." "That thought crossed my mind, sir,--yes." "You should go into the diplomatic service, young man. Your talents are being wasted," observed Mr. Ackerman good-humoredly. "Well, I suppose I could romance for the benefit of you two boys for part of the way, at least. It will give your father, Steve, a chance to go into the other car and smoke. Where did we break off our story? Do you remember?" "Where the United States said anybody had the right to sail anywhere he wanted to, in any kind of a boat he chose," piped Dick with promptness. "Yes, yes. I recall it all now," said Mr. Ackerman. "The courts withdrew the grant giving Livingston the sole right to navigate the waters of New York State by means of steamboats. So you want to hear more about it, do you?" "Yes!" came simultaneously from both the boys. "Then all aboard! Tolman, you can read, or run off and enjoy your cigar. We are going on a steamboat cruise." "Push off! You won't bother me," was the tolerant retort, as the elder man unfolded the morning paper. Mr. Ackerman cleared his throat. "Before this decree to give everybody an equal chance in navigating the waters of the country was handed down by the courts," he began, "various companies, in defiance of Livingston's contract, began building and running steamboats on the Hudson. Two rival boats were speedily in operation and it was only after a three years' lawsuit that they were legally condemned and handed over to Fulton to be broken up. Then the ferryboat people got busy and petitioned the New York Legislature for the right to run their boats to and fro between the New York and New Jersey sides of the river, and it is interesting to remember that it was on one of these ferry routes that Cornelius Vanderbilt, the great American financier, began his career." "I never knew that!" ejaculated Dick, intent on the story. "After the ruling of the Supreme Court in 1818 that all the waters of the country were free there was a rush to construct and launch steamers on the Hudson. The route was, you see, not only the most direct one between Albany and New York but it also lay in the line of travel between the eastern States and those of the west which were just being opened to traffic by the railroads and ships of the Great Lakes. Now you must not for a moment imagine that in those days there were any such vast numbers of persons traversing the country as there are now. Our early Americans worked hard and possessed only comparatively small fortunes so they had little money to throw away on travel simply for its own sake; moreover the War of 1812 had left the country poor. Nevertheless there were a good many persons who were obliged to travel, and it followed that each of the Hudson River lines of steamers was eager to secure their patronage. Hence a bitter competition arose between the rival steamboat companies." He paused and smiled whimsically at some memory that amused him. "Every inducement was offered the public by these battling forces. The older vessels were scrapped or reduced to tug service and finer steamboats were built; and once upon the water the engines were driven at full speed that quicker trips might lure passengers to patronize the swifter boats. Captains and firemen pitted their energies against one another and without scruple raced their ships, with the result that there were many accidents. In spite of this, however, the rivalry grew rather than diminished." "It must have been great sport," remarked Stephen. "Oh, there was sport in plenty," nodded Mr. Ackerman. "Had you lived during those first days of Hudson River transportation you would have seen all the sport you wanted to see, for the steamboat feud raged with fury, the several companies trying their uttermost to get the trade away from the Fulton people and from one another. Money became no object, the only aim being to win in the game. Fares were reduced from ten dollars to one, and frequently passengers were carried for nothing simply for the sheer spite of getting them away from other lines. Vanderbilt was in the thick of the fray, having now accumulated sufficient fortune to operate no less than fifty boats. Among the finest vessels were those of the Emerald Line; and the _Swallow_ and the _Rochester_, two of the speediest rivals, were continually racing each other. The devices resorted to in order to ensnare passengers were very amusing: some boats carried bands; others served free meals; and because there were few newspapers in those days, and only limited means for advertising, runners were hired to go about the city or waylay prospective travelers at the docks and try to coax them into making their trip by some particular steamer." "That was one way of getting business!" laughed Steve. "And often a very effective way, too," rejoined Mr. Ackerman. "In June of 1847 a tremendously exciting race took place between the _Oregon_ and the _Vanderbilt_, then a new boat, for a thousand dollars a side. The steamers left the Battery at eleven o'clock in the morning and a dense crowd turned out to see them start. For thirty miles they kept abreast; then the _Oregon_ gained half a length and in passing the other boat bumped into her, damaging her wheelhouse. It was said at the time that the disaster was not wholly an accident. Certainly there were grounds for suspicion. As you may imagine, the calamity roused the rage of the competing boat. But the commander of the _Oregon_ was undaunted by what he had done. All he wished was to win the race and that he was determined to do. He got up a higher and higher pressure of steam, and used more and more coal until, when it was time to return to New York, he discovered that his supply had given out and that he had no more fuel." "And he had to give up the race?" queried Dick breathlessly. "Not he! He wasn't the giving-up kind," said Mr. Ackerman. "Finding nothing at hand to run his boilers with he ordered all the expensive fittings of the boat to be torn up and cast into the fire--woodwork, furniture, carvings; anything that would burn. In that way he kept up his furious rate of speed and came in victorious by the rather close margin of twelve hundred feet." "Bully for him!" cried Dick. But Stephen did not echo the applause. "It was not a square race," he said, "and he had no right to win. Anyway, his steamboat must have been pretty well ruined." "I fancy it was an expensive triumph," owned Mr. Ackerman. "Without doubt it cost much more than the thousand dollars he won to repair the vessel. Still, he had the glory, and perhaps it was worth it to the company." "Were there other races like that?" Dick asked. "Yes, for years the racing went on until there were so many fires, explosions and collisions, that the steamer inspection law was put through to regulate the conditions of travel. It certainly was high time that something was done to protect the public, too, for such universal recklessness prevailed that everybody was in danger. Boats were overloaded; safety valves were plugged; boilers carried several times as much steam as they had any right to do, and many lives had been sacrificed before the government stepped in and put a stop to this strife for fame and money. Since then the traffic on the Hudson has dropped to a plane of sanity and is now carried on by fine lines of boats that conform to the rules for safety and efficient service." "And what became of Mr. Vanderbilt?" interrogated Dick, who was a New Yorker to the core and had no mind to lose sight of the name with which he was familiar. "Oh, Mr. Vanderbilt was a man who had many irons in the fire," replied Mr. Ackerman, smiling at the boy's eagerness. "He did not need to be pitied for just about this time gold was discovered in California and as the interest of the country swung in that direction Vanderbilt, ever quick to seize an opening wherever it presented itself, withdrew some of his steamers from the Hudson and headed them around to the Pacific coast instead." "And your family, Mr. Ackerman, were mixed up in all this steamboat rumpus?" commented Steve suddenly. "Yes, my grandfather was one of the Hudson River racers and quite as bad as the rest of them," the man replied. "Nevertheless he was a stanch, clever old fellow, and because he did his part toward building up the commerce and prosperity of the nation I have always regarded him with the warmest respect. I do not approve of all his methods, however, any more than I approve of many of the cut-throat business methods of to-day which sometime will be looked back upon with as much shame as these have been. There are moments, I must confess, when I wonder if we, with all our supposed enlightenment, have made any very appreciable advance over the frank and open racing done by our forefathers on the Hudson," reflected he half-humorously. "Perhaps we are a trifle more humane; and yet there is certainly much to be desired in the way we still sacrifice the public to our greed for money. An evil sometimes has to come to a climax to make us conscious of our injustice. Let us hope that our generation will not be so blind that it will not heed the warnings of its conscience, and instead delay until some such catastrophe comes upon it as pursued the racing boats of the Hudson River." CHAPTER XV THE ROMANCE OF THE CLIPPER SHIP It was with genuine regret that Mr. Tolman and Stephen parted from Mr. Ackerman and Dick when the train reached New Haven. "We shall not say good-by to Dick," Mr. Tolman declared, "for he is not to be very far away and I hope sometime he will come to Coventry and spend a holiday with us. Why don't you plan to do that too, Ackerman? Run over from New York for Thanksgiving and bring the boy with you. Why not?" "That is very kind of you." "But I mean it," persisted Mr. Tolman. "It is no perfunctory invitation. Plan to do it. We should all be delighted to have you. There is nothing in the world Mrs. Tolman loves better than a houseful of guests. Doris will be home from college and I should like you to see what a fine big daughter I have. As for Steve--" "I wish you would come, Mr. Ackerman," interrupted the boy. Mr. Ackerman hesitated. "I tell you what we'll do," replied he at length. "We'll leave it to Dick. If he makes a good record at school and earns the holiday we will accept your invitation. If he doesn't we won't come. Is that a bargain, youngster?" he concluded, turning to the lad at his side. The boy flushed. "It is a rather stiff one, sir," he answered, with a laughing glance. "I think that's playing for too high stakes, Ackerman," Mr. Tolman objected. "It is a little rough to put all the burden on Dick. Suppose we divide up the responsibility and foist half of it on Stephen? Let us say you will come if both boys make good in their studies and conduct." Dick drew a breath of relief at the words, regarding the speaker with gratitude. "That is a squarer deal, isn't it?" continued Mr. Tolman. "I think so--yes," was Dick's response. "And you, Steve--do you subscribe to the contract?" "Yes, I'll sign," grinned Stephen. "Then the agreement is clinched," exclaimed his father, "and it will be the fault of you two young persons if we do not have a jolly reunion at Thanksgiving time. Good-by Ackerman! Good-by, Dick. Good luck to you! We are pinning our faith on you, remember. Don't disappoint us." "I'll try not to," the boy answered, as he stepped to the platform. "Dick is a fine, manly young chap," observed Mr. Tolman, after the train was once more under way and he and Stephen were alone. "I have a feeling that he is going to make good, too. All he needed was a chance. He has splendid stuff in him. There isn't a mean bone in his body." Stephen moved uncomfortably in his chair and a guilty blush rose to his cheek but apparently his father did not notice it. "You liked Mr. Ackerman also, didn't you, son? Indeed there is no need to ask for he is a genius with young people and no boy could help liking a man of his type. It is a pity he hasn't a dozen children, or isn't the leader of a boy's school." "He is corking at story-telling!" was Steve's comment. "He certainly is. I caught some fragments of his Hudson River tale and did not wonder that it fascinated you. What a remarkable era that was!" he mused. "There were a lot of questions I wanted to ask him," Stephen said. "Such as?" "Well, for one thing I was curious to know what happened after the steamers on the Hudson were proved a success." "I can answer that question," replied his father promptly. "After the river boats had demonstrated their practicability steamships were built for traffic along short distances of the coast. Owing to the War of 1812 and the danger to our shipping from the British, however, the launching of these new lines did not take place immediately; but in time the routes were established. The first of these was from New York to New Haven. You see, travel by steam power was still so much of a novelty that Norwich, first proposed as a destination, was felt to be too far away. It was like taking one's life in one's hands to venture such an immense distance from land on a steamboat." Stephen smiled with amusement. "But gradually," continued Mr. Tolman, "the public as well as the steamboat companies became more daring and a line from New York to Providence, with Vanderbilt's _Lexington_ as one of the ships, was put into operation. Then in 1818 a line of steamers to sail the Great Lakes was built; and afterwards steamships to travel to points along the Maine coast. The problem of navigation on the rivers of the interior of the country followed and here a new conundrum in steamboat construction confronted the builders, for the channels of many of the streams were shallow and in consequence demanded a type of boat very long and wide in proportion to its depth of hull. After such a variety of boat had been worked out and constructed, lines were established on several of the large rivers, and immediately the same old spirit of rivalry that pervaded the Hudson years before cropped up in these other localities. Bitter competition, for example, raged between the boats that plied up and down the Mississippi; and in 1870 a very celebrated race took place between the _Natchez_ and the _Robert E. Lee_. The distance to be covered was 1218 miles and the latter ship made it in three days, eighteen hours, and thirty minutes. The test, however, was not a totally fair one since the _Natchez_ ran into a fog that held her up for six hours. But the event illustrates the keen interest with which men followed the progress of American shipping; and you can see how natural it was that after the river boats, lake steamers, coastwise vessels and tugs had had their day the next logical step (and very prodigious one) was the--" "The ocean liner!" ejaculated Stephen. "Precisely!" nodded his father. "Now there are two separate romances of our ocean-going ships. The first one is of the sailing vessels and is a chronicle of adventure and bravery as enthralling as any you could wish to read. I wish I had time to tell it to you in full and do it justice, but I fear I can only sketch in a few of the facts and leave you to read the rest by yourself some time. You probably know already that whalers went out from Gloucester, New Bedford, and various of our eastern ports and often were gone on two or three-year cruises; and when you recall that in those early days there not only was no wireless but not even the charts, lighthouses, and signals of a thoroughly surveyed coast you will appreciate that setting forth on such a voyage for whale-oil (then used almost exclusively for lighting purposes) took courage. Of course the captains of the ships had compasses for the compass came into use just before the beginning of the Fifteenth Century and was one of the things that stimulated the Portuguese and Spaniards to start out on voyages of discovery. The Spaniards built ships that were then considered the largest and finest afloat, and probably Columbus caught the enthusiasm of the period and with the newly invented compass to guide him was stirred to brave the ocean and discover other territory to add to the riches of the land he loved. It was a golden age of romance and adventure and the journeys of Columbus grew out of it quite naturally. But in America shipping had its foundation in no such picturesque beginning. The first vessel made in this country was constructed as a mere matter of necessity, being built at the mouth of the Kennebec River to carry back to England a group of disheartened, homesick settlers." He paused thoughtfully a moment. "Even the ships of later date had their birth in the same motive--that of necessity. The early colonists were forced to procure supplies from England and they had no choice but to build ships for that purpose. At first these sailing packets were very small, and as one thinks of them to-day it is to marvel that they ever made so many trips without foundering. As for our coastwise ships, up to 1812 they were nothing more than schooner-rigged hulls." "I wonder where the word _schooner_ came from," commented Steve. "The legend goes that the term _scoon_ was a colloquialism used when skipping stones. When a pebble glanced along the top of the water it was said to _scoon_," answered his father, with a smile. "After the War of 1812 was over and our American vessels were safe from possible attack, and after the country itself had recovered somewhat from the stress of this financial burden so that men had more money to invest in commerce, we began to branch out and build finer vessels; and when it came to rigging them there seemed to be no name to apply to the arrangement of the sails. The story goes that one day as one of these new ships sailed out of Gloucester harbor a fisherman watching her exclaimed with admiration, 'See her _scoon_!' The phrase not only caught the public fancy but that of the shipbuilders as well, and the word _schooner_ was quickly adopted." "I never knew that before!" announced Steve, when the narrative was concluded. "Slowly the models of ships improved," went on his father, without heeding the interruption. "Vessels became larger, faster, more graceful. Even the whalers and fishing smacks took on more delicate lines. Merchants from Salem, Gloucester, New Bedford invested their hard-earned savings in whalers and trading ships, and many of them made their fortunes by so doing. The sailing packets that went to Liverpool began to make excellent time records. Although the English were now using steamers for trans-Atlantic travel they had not perfected them to a sufficient extent to make their trips faster than those of sailing ships." "About how long did it take them to cross?" inquired Stephen. "The average time to Liverpool was from nineteen to twenty-one days," was the answer. "And for the return voyage from thirty to thirty-five." "Whew, Dad! Why, one could walk it in that time!" exclaimed the lad. "It was a long time," his father agreed. "But it is not fair to measure it by present-day standards. Think how novel a thing it was to cross the ocean at all!" "I suppose so," came reflectively from Stephen. "It was not long," continued his father, "before the English improved their engines so that their steamers made better time, and then our American sailing packets were left far behind. This, as you can imagine, did not please our proud and ambitious colonists who were anxious to increase their commerce and build up their young and growing country. Something must be done! As yet they had not mastered the enigma of steam but they could make their sailing ships swifter and finer and this they set to work to do. Out of this impetus for prosperity came the remarkable clipper-ship era. "We shall probably never see such beautiful ships again," continued Mr. Tolman, a trifle sadly. "Youth and romance go hand in hand, and our country was very young, and proud and eager in those days. Our commerce was only beginning and the far corners of the world were strange, unexplored and alluring. It is like an Arabian Night's Tale to read of those wonderful ships built to carry merchandise to China, India and other foreign ports. Speed was their aim--speed, speed, speed! They must hold their own against the English steamers if they would keep their place on the seas. For in those days the methods of packing produce were very primitive, and it was imperative that such perishable things as tea, dried fruits, spices and coffee should be rushed to the markets before the dampness spoiled them. If they mildewed they would be a dead loss to the merchants handling them. Moreover as cable and telegraph were unknown there was no way to keep in touch with the demands of the public, or be sure of prices. Therefore every merchant hurried his goods home in the hope of being the first in the field and reaping the largest profits." "More racing!" exclaimed Stephen. "It was racing, indeed!" returned his father. "Ships raced one another back from China, each trying desperately to discharge her cargo before her rival did. Like great sea-birds these beautiful boats skimmed the waves, stretching every inch of canvas to be the winner at the goal. As a result the slow merchant packets with their stale cargoes could find no patrons, the clippers commanding not only all the trade but the highest prices for produce as well. Silks, chinaware, ivory, bamboo--all the wealth of the Orient began to arrive in America where it was hungrily bought up, many a man making his fortune in the East India trade. Of this fascinating epoch Hawthorne gives us a vivid picture." "It must have been great to travel on one of those ships!" said Stephen. "It was not all pleasure, by any means, son," Mr. Tolman replied. "Often the vessels encountered hurricanes and typhoons in the treacherous Eastern waters. Sometimes ships were blown out of their course and wrecked, or cast ashore on islands where their crews became the prey of cannibals." "Jove!" "It had its outs--this cruising to distant ports," announced his father. "Moreover, the charts in use were still imperfect and lighthouse protection was either very scanty or was lacking entirely." "What became of the clipper ships?" "Well, we Americans never do anything by halves, you know. When we go in we go in all over," laughed his father. "That is what we did with our clipper ships. We were so pleased with them that we built more and more, sending them everywhere we could think of. Many went around to California to carry merchandise to the gold searchers. At last there were so many of these swift vessels that they cut into one another and freight rates dropped. Besides, steamboats were coming into general use and were now running on all the more important ocean routes. The day of the sailing ship was over and the marvelous vessels were compelled to yield their place to the heralds of progress and become things of the past. Nevertheless, their part in our American commerce will never be forgotten and we have them to thank not only for the fame they brought our country but also for much of its wealth." With a quick gesture of surprise he rose hurriedly. "See!" he exclaimed. "We are almost home. We have talked 'ships and sealing-wax' for hours." "It hasn't seemed for hours," retorted Stephen, springing to collect his luggage. "Nor to me, either." "Some time I'd like to hear about the ocean liners," ventured the boy. "You must get Mr. Ackerman to tell you that story when he comes to visit us Thanksgiving," was the reply, "if he _does_ come. That part of it seems to be up to you and Dick." "I mean to do my part to get him here," Steve announced. "I hope Dick will plug, too." "I rather think you can trust him for that," was the quiet answer. CHAPTER XVI AGAIN THE MAGIC DOOR OPENS A change of trains and a brief hour's journey brought the travelers safely to Coventry where Havens met them with the automobile. "This will be our last ride this fall," observed Mr. Tolman, as he loitered on the platform while the luggage was being lifted into the car. "We shall have to put the motor up in a day or two. It will not need much of an overhauling in the way of repairs this season, I guess, for it is comparatively new and should be in pretty good condition. There may be a few slight things necessary but nothing much. Isn't that so, Havens?" "It is badly scratched, sir." "Scratched!" "Yes, sir--both inside and out. I wonder you haven't noticed it. Still you wouldn't unless you got it in just the right light. I did not myself at first. There are terrible scratches everywhere. You would think ten men had climbed all over it. Look!" "Oh, it can't be so bad as all that," laughed Mr. Tolman good-humoredly, evidently not taking the chauffeur's comment seriously. "The car was new in the spring and we have not given it very hard wear. What little luggage we have carried has been carefully put in; I have seen to that myself. Only a short time ago I thought how splendidly fresh the varnish looked. In fact, I examined it just before you were ill. It can't have become very much defaced since then for we have not had the car out of the garage except for one short excursion." Havens' brow darkened into a puzzled frown. "I don't understand it at all, sir," he replied. "I could swear the scratches were not there when I went away. If you didn't tell me yourself the car hadn't been used much I'd stake my oath it had had a great deal of knocking about while I was gone. Look here, Mr. Tolman! Look at that, and that, and that--great digs in the paint as if people with boots on had climbed over the sides." Mr. Tolman looked and so, with a sinking heart, did Stephen. "Mercy on us! I never noticed all this before!" cried Mr. Tolman, in consternation. "What in the world--" he stopped as if he could find no words to voice his amazement. "Look at this!" He placed a finger on a broad, clearly defined line that extended from the top of the tonneau to the bottom. "You would think somebody had dug his heels in here and then slid down until he reached the ground! And this! What on earth has happened to the thing, Havens? It looks as if it had been used for a gymnasium." Hot and cold by turns, Steve listened. The marks to which his father pointed told a truthful story. Somebody had braced his heels against the side and then slid to the ground; it was Bud Taylor. And that other jagged line indicated where Tim Barclay had scrambled over the edge and made his hurried exit. The history of the whole miserable adventure was etched in the varnish as vividly as if it had been traced there in words. Stephen gasped with horror when he saw how plainly the entire story stood out in the sunlight of the November day. Why, the most stupid person alive could read it! Every moment he expected that his father or Havens would wheel on him and ask accusingly: "When was it you carried all those boys to Torrington?" He could hear his heart thumping inside him and feel the beat of the blood that scorched his cheek. He had not pictured a dilemma like this. The affair had gone off so smoothly that he had flattered himself every possibility of discovery was past, and in this comforting knowledge he had basked with serenity. And now, behold, here he was at the brink of peril, and just when he had had such a glorious holiday, too! "How do you solve the riddle, Havens?" he heard his father asking. "I ain't solvin' it, sir," was the drawling answer. "Maybe Steve could give you a hint, though," he added slyly. The lad stiffened. He and Havens had never been friends. They had been through too many battles for that. The chauffeur did not like boys and took no trouble to conceal the fact, and as a result he had been the prey of many a mischievous prank. It was through his vigilance that Stephen had more than once been brought to justice and in the punishment that followed Havens had exulted without restraint. As a retaliation the boy tormented him whenever opportunity presented, the two carrying on a half-bitter, half-humorous feud which was a source of mutual gratification. Had not this been the case the confession that trembled on Stephen's tongue would doubtless have been uttered then and there. But to speak before Havens and afford him the chance to crow and rejoice,--that was not to be thought of. Therefore, drawing in his chin and holding his head a trifle higher than was his wont, he replied with hauteur: "I've no solution at all to offer. How could I have?" For the fraction of a second Mr. Tolman looked sharply at his son as if some new thought had suddenly struck him; then the piercing scrutiny faded from his eyes and he turned away. "Well, I guess we shall have to drop the matter for the present, anyway, and be getting home," said he. "It will do no good for us to stand here in the cold and argue. We shall be no nearer an answer. Come, jump in, Steve!" With a strange sense of reluctance the boy obeyed. He felt the door to confession closing with finality behind him; and now that he saw all chance for dallying on its threshold cut off, he began to regret that it should so completely close. Once again the opportunity to clear his conscience had come about in an easy, natural manner; confession had been gently and tactfully invited and he had turned his back. Never again, probably, would he have such a chance as this. Without any ignominious preamble he could have spoken the few words necessary and been a free man! But alas, he had hesitated too long. His father followed him into the car, banged the door, and they shot homeward. Perhaps, temporized the lad as they rode along, he would say something when they reached the house. Why wasn't it better anyway to wait until he and his father were quiet and alone? Who could blame him for not wanting to confess his misdemeanors before an audience? His father would understand and forgive his reticence, he was sure. Having lulled his conscience to rest with the assurance of this future reparation he sank back against the cushions and drew the robe closer about him. There was no use in letting the ride be spoiled by worry. He did not need to speak until he got back, and he needn't speak at all if he did not wish to. If no favorable opening occurred, why, he could still remain silent and wait a better chance. He had taken no vow, made no promise; nothing actually bound him to act unless he chose. It was surprising how his spirits rose with this realization. He even ventured to talk a little and make a joke or two. These overtures received only scant response from his father, however, for Mr. Tolman's brow had settled into a frown and it needed no second glance to assure Stephen that the happenings of the past half-hour had put the elder man very much out of humor. How unfortunate, mused the boy, that this mood should have come upon his father. It would take more than an ordinary measure of courage to approach him now. Why, it would be braving the lions, actually tempting fate to go to him with a confession when he looked like this. Would it not be much wiser to wait? With a sharp swerve they turned in at the gate and rolled up the long driveway; then the front door burst open and from it issued not only Mrs. Tolman and Doris but with them the girl with the wonderful hair, Jane Harden, whom he had seen at Northampton. A hubbub of greeting ensued and in the interchange of gay conversation all thought of confession was swept from Stephen's mind. Nor in the days that followed, with their round of skating, hockey, snow-shoeing, and holiday festivities, did the inclination to revert to the follies of the past arise. The big red touring-car was sent away without further allusion to its battered condition and with its departure the last link with the misfortunes that tormented him seemed destroyed. Once, it is true, when he overheard his father telling his mother that the bill for repainting and varnishing the car was going to be very large, his conscience smote him. But what, he argued, could he do? Even were he to come forward now and shoulder the blame it would not reduce the expense of which his father complained. He had no money. Therefore he decided it was better to close his ears and try and forget the entire affair. His father had evidently accepted the calamity with resignation and made up his mind to bear the consequences without further demur. Why not let the matter rest there? At this late date it would be absurd to speak, especially when it could not alter the situation. In the meantime letters came from Mr. Ackerman and from Dick. The latter was very happy at the New Haven school and was making quite a record for himself, and it was easy to detect between the lines of the steamboat magnate's epistle that he was much gratified by the progress of his protégé. Thanksgiving would soon be here and if the Tolmans still extended their invitation for the holidays the two New Yorkers would be glad to accept it. "I'll write Ackerman to-day," announced Mr. Tolman at breakfast. "The invitation has hung on Stephen and Dick, and I am glad to say they each have made good. How fine that that little East Side chap should have turned out so well! I don't wonder Ackerman is pleased. Everybody does not get appreciation in return for kindness. I know many a parent whose children repay what is done for them only with sneaking, unworthy conduct and utter ingratitude. Dick may not have been born into prosperity but he is a thoroughbred at heart and it shows in his actions. He is every inch a gentleman." At the words Stephen's blood tingled. What would his father think of him if he knew what a mean-spirited coward he was? Well, it was impossible to tell him now. It would upset the whole Thanksgiving party. CHAPTER XVII MORE STEAMBOATING The night before Thanksgiving Mr. Ackerman and Dick arrived at Coventry and it was difficult to believe the change wrought in the New York boy. Not only was his face round, rosy and radiant with happiness but along with a new manliness had stolen a gentler bearing and a courtesy that had not been there when he had set forth to school. "Why, you must have put on ten pounds, Dick!" cried Mr. Tolman, shaking hands with his young guest after greeting the steamboat magnate. "It is eleven pounds, sir," laughed Dick. "We have bully eats at school and all you want of them." The final phrase had a reminiscent ring as if it harked back to a time when three ample meals were a mirage of the imagination. "Well, I am glad to hear you have done justice to them and encouraged the cook," was Mr. Tolman's jocular reply. "Now while you stay here you must cheer on our cook in the same fashion. If you don't we shall think you like New Haven better." "I guess there is no danger of that," put in Mr. Ackerman. "Dick seems hollow down to his ankles. There is no filling him up; is there, boy?" "I couldn't eat that third ice-cream you offered me yesterday," was the humorous retort. "I hope you've saved some room for to-morrow's dinner," Mrs. Tolman interrupted, "for there will be mince pie and plum pudding and I don't know what not. And then there is the turkey--we ordered an extra large one on purpose." Dick and Steve exchanged a sheepish grin. "Well, it is jolly to see you good people," Mr. Tolman declared, as he ushered the visitors into the living room, where a bright fire burned on the hearth. "Our boys have done well, haven't they, Ackerman? I don't know which is to win the scholarship race--the steamboats or the railroads." "We could compare marks," Stephen suggested. "That would hardly be fair," Mr. Ackerman objected quickly, "for the steamboats did not start even with the railroads in this contest. Dick has had to put in a lot of hours with a tutor to make up for the work he missed at the beginning of the year. He has been compelled to bone down like a beaver to go ahead with his class; but he has succeeded, haven't you, sonny?" "I hope I have," was the modest retort. "Furthermore," went on Mr. Ackerman, "there are other things beside scholarship to be considered in this bargain. We want fine, manly boys as well as wise ones. Conduct counts for a great deal, you know." Stephen felt himself coloring. "There have been no black marks on Dick's record thus far. How about yours, Steve?" asked the New York man. "I--er--no. I haven't had any black marks, either," responded Stephen, with a gulp of shame. "That is splendid, isn't it!" commented Mr. Ackerman. "I wasn't looking for them. You have too fine a father to be anything but a square boy." Once more Stephen knew himself to be blushing. If they would only talk about something else! "Are you going to finish your steamboat story for us while you are here?" inquired he with sudden inspiration. "Why, I had not thought of doing any steamboating down here," laughed the capitalist. "Rather I came to help the Pilgrims celebrate their first harvest." "But even they had to come to America by boat," suggested Doris mischievously. "I admit that," owned the New Yorker. "And what is more, they probably would have come in a steamboat if one had been running at the time." "What was the first American steamship to cross the Atlantic, Ackerman?" questioned Mr. Tolman when they were all seated before the library fire. "I suppose the _Savannah_ had that distinction," was the reply. "She was built in New York in 1818 to be used as a sailing packet; but she had side wheels and an auxiliary engine, and although she did not make the entire trans-Atlantic distance by steam she did cover a part of it under steam power. Her paddle wheels, it is interesting to note, were so constructed that they could be unshipped and taken aboard when they were not in use, or when the weather was rough. I believe it took her twenty-seven days to make the trip from Savannah to Liverpool and eighty hours of that time she was using her engine. Although she made several trips in safety it was quite a while before the American public was sufficiently convinced of the value of steam to build other steamships. A few small ones appeared in our harbors, it is true, but they came from Norway or England; they made much better records, too, than anything previously known, the _Sirius_ crossing in 1838 in nineteen days, and the _Great Western_ in fifteen. In the meantime shipbuilders on both sides of the Atlantic were studying the steamboat problem and busy brains in Nova Scotia and on the Clyde were working out an answer to the puzzle. One of the most alert of these brains belonged to Samuel Cunard, the founder of the steamship line that has since become world famous. In May, 1840, through his instrumentality, the _Unicorn_ set out from England for Boston arriving in the harbor June third after a voyage of sixteen days. When we reflect that she was a wooden side-wheeler, not much larger than one of our tugboats, we marvel that she ever put in her appearance. Tidings of her proposed trip had already preceded her, and when after much anxious watching she was sighted there was the greatest enthusiasm along the water front, the over-zealous populace who wished to give her a royal welcome setting off a six-pounder in her honor that shattered to atoms most of her stained glass as she tied up at the dock." His audience laughed. "You see," continued the capitalist, "the ship came in answer to a circular sent out by our government to various shipbuilders asking bids from swift and reliable boats to carry our mails to England. Cunard immediately saw the commercial advantages of such an opportunity, and not having money enough to back the venture himself the Halifax man went to Scotland where he met Robert Napier, a person who like himself had had wide experience in shipping affairs. Both men were enthusiastic over the project; before long the money necessary for the undertaking was raised, and the British and North American Royal Mail Steam Packet Company, with a line of four ships, was awarded the United States Government contract. These ships were very significantly named: the _Britannia_ in honor of England, the _Arcadia_ as a compliment to Mr. Cunard's Nova Scotia home, the _Caledonia_ in memory of Napier's Scotch ancestry, and the _Columbia_ out of regard to America. And in passing it is rather interesting to recall that in homage to these pioneer ships it has become a tradition of the Cunard Line to use names that terminate in the letter _a_ for all the ships that have followed them. For, you must remember, it was this modest group of steam packets that were the ancestors of such magnificent boats as the _Mauretania_ and _Lusitania_." "There was some difference!" interrupted Stephen. "Well, rather! Had you, however, told Samuel Cunard then that such mammoth floating hotels were possible he would probably not have believed you. He had task enough on his hands to carry the mails; transport the few venturesome souls that dared to cross the sea; and compete with the many rival steamship lines that sprang up on both sides of the ocean as soon as some one had demonstrated that trans-Atlantic travel was practical. For after Cunard had blazed the path there were plenty of less daring persons ready to steal from him the fruits of his vision and courage. From 1847 to 1857 the Ocean Steamship Company carried mails between New York and Bremen, and there was a very popular line that ran from New York to Havre, up to the period of the Civil War. Among the individual ships none, perhaps, was more celebrated than the _Great Eastern_, a vessel of tremendous length, and one that more nearly approached our present-day liners as to size. Then there was the Collins Line that openly competed with the Cunard Line; and to further increase trans-Atlantic travel, in 1855 Cornelius Vanderbilt, ever at the fore in novel projects, began operating lines of steamships not only to England and France but to Bremen." Mr. Ackerman paused a moment. "By 1871 there was an American line between Philadelphia and Liverpool. In the meantime, ever since 1861, there had been a slow but steady advance in ocean shipbuilding. Although iron ships had gradually replaced wooden ones the side-wheeler was still in vogue, no better method of locomotion having been discovered. When the change from this primitive device to the screw propeller came it was a veritable leap in naval architecture. Now revolutions in any direction seldom receive a welcome and just as the conservatives had at first hooted down the idea of iron ships, asserting they would never float, so they now decried the use of the screw propeller. Indeed there was no denying that this innovation presented to shipbuilders a multitude of new and balking problems. While the clipper ships had greatly improved the designs of vessels the stern was still their weakest point and now, in addition to this already existing difficulty, came the new conundrums presented by the pitch, or full turn of the thread, in the screw propeller; also the churning of the current produced by the rapidly whirling wheel, which was found to retard the speed of the ship very materially. Valiantly engineers wrestled with one after another of these enigmas until they conquered them and put shipbuilding on the upward path where it has been ever since. In time steel ships replaced the cruder vessels of iron; finer types of engines were worked out; the wireless and the many electrical devices which herald approaching foes and announce the presence of icebergs have been invented; until now the ocean liner is practically safe from all perils except fogs, icebergs and submarines." He stopped a moment with eyes fixed on the glowing logs that crackled on the hearth. "Meanwhile," he went on, "comfort aboard ship has progressed to luxury. Better systems of ventilation, more roomy sleeping quarters, more windows and improved lighting facilities have been installed. The general arrangement of the ship has also been vastly improved since the days when the high bulwark and long deckhouse were in use. Now iron railings allow the sea to wash back and forth in time of storm, and in consequence there is less danger of vessels being swamped by the waves. Then there are watertight doors and bulkheads, double bottoms to the hulls, and along with these more practical advances have come others of a more healthful and artistic trend. The furniture is better; the decoration of the cabins and saloons prettier and more harmonious; there has been more hygienic sanitation. When the _Oceanic_ of the White Star Line was built in 1870 she had a second deck, and this novel feature was adopted broadcast and eventually ushered in the many-deck liners now in use. The _Servia_, built in 1881, was the first steel ship and the advantage of its greater elasticity was instantly seen. Builders were wise enough to grasp the fact that with the increasing length of vessels steel ships would be able to stand a greater strain. Little by little the gain went on in every direction. Nevertheless, in spite of the intelligence of the shipbuilders, it was long before trans-Atlantic navigators had the courage to trust themselves entirely to their engines and discard masts; although they shifted to steel ones instead of those of iron or wood, they still persisted in carrying them." He smiled as he spoke. "When the twin-screw propeller made its appearance it brought with it greater speed and there was a revival of the old racing spirit. Between the various shipping lines of all nations the contest for size and swiftness has raged ever since. Before the Great War, Germany had a very extensive collection of large and rapid liners, many of them built on the Clyde, that fought to surpass the Cunard ships. The White Star Line also took a hand in the game and built others. In the contest, alas, America has been far behind until gradually she has let other countries slip in and usurp the major proportion of ocean commerce. It is a pitiful thing that we should not have applied our skill and wealth of material to building fine American steamship lines of our own instead of letting so many of our tourists turn their patronage to ships of foreign nations. Perhaps if the public were not so eager for novelty, and so constantly in search for the newest, the largest and the fastest boats, we should be content to make our crossings in the older and less gaudy ships, which after all are quite as seaworthy. But we Americans must always have the superlative, and therefore many a steamer has had to be scrapped simply because it had no palm gardens, no swimming pools, no shore luxuries. We have not, however, wholly neglected naval construction for we have many fine steamships, a praiseworthy lot of battleships and cruisers and some very fine submarines. I hope and believe that the time will come when our merchant marine will once again stand at the front as it did in the days of the clipper ships. Our commerce reaches out to every corner of the earth and why should we rely on other countries to transport our goods?" "I suppose there are no pirates now, are there, Mr. Ackerman?" asked Dick, raising his eyes expectantly to the capitalist's face. "I am afraid there are very few, Dick boy," returned the elder man kindly. "I suppose that is somewhat of a disappointment to you. You would have preferred to sail the seas in the days when every small liner carried her guns as a defence against raiders and was often forced to use them, too. But when international law began to regulate traffic on the high seas and the ocean thoroughfare ceased to be such a deserted one pirates went out of fashion, and every nation was granted equal rights to sail the seas unmolested. It was because this freedom was menaced by German submarines in the late war and our privilege to travel by water threatened that our nation refused to tolerate such conditions. A code of humane laws that had been established for the universal good was being broken and we could not permit it. For you must remember that now there are almost as many laws on the ocean as on the land. There are rules for all kinds of vessels, of which there are a far greater variety than perhaps you realize. Not only have we steamships, cruisers, and battleships but we have schooners, barques, brigs, tugboats, dredgers, oil-tankers, turret ships for freight, cargo boats, steam tramps, coalers, produce ships, ice-breakers, train ferries, steam trawlers, fire boats, river boats, harbor excursion boats, coasters, whalebacks, steam yachts, launches and lake steamers. Each of these is carefully classified and has its particular traffic rules, and in addition to these is obliged to obey certain other general marine laws to which all of them are subject, in order that travel by water may be made safe." "Don't all ships have to be inspected, too?" asked Stephen. "Yes; and not only are they inspected but to protect the lives of their passengers and crew, as well as preserve their cargo, they must adhere to specified conditions. The number of passengers and crew is regulated by law, as is the amount of the cargo. Ocean liners, for example, must have aboard a certain number of lifeboats, rafts, belts, life preservers, fire extinguishers, lines of hose; and the size of all these is carefully designated. There must be frequent drills in manning the boats; the fire hose must be tested to see that it works and is in proper condition; and in thick weather the foghorns must be sounded at regular intervals. There is no such thing now as going to sea in haphazard fashion and trusting to luck. Everything that can be done for the safety of those who travel the ocean must be done." He paused a moment, then added: "And in the meanwhile, that every protection possible shall be offered to ships, we have been as busy on the land as on the water and have established a code of laws to govern our coasts, harbors and rivers. Government surveys have charted the shores of all countries so that now there are complete maps that give not only the coast line but also the outlying islands, rocks and shoals that might be a menace to ships. It is no longer possible for a State bordering on the sea to put up a low building at the water's edge and set a few candles in the windows as was done back in the year eighteen hundred." Both the boys laughed. "We can laugh now," assented Mr. Ackerman with a smile, "but in those days I fancy it was no laughing matter. Even with all our up-to-date devices there are wrecks; and think of the ships that must have gone down before charts were available, lighthouses and bell buoys in vogue, wireless signals invented and the coast patrol in operation. I shudder to picture it. Sailing the seas was a perilous undertaking then, I assure you. Even the first devices for safety were primitive. The Argand lamp of 1812 was not at all powerful and the lenses used were far from perfect. Foghorns were operated by hand or by horse power and were not strong enough to be heard at any great distance. Bell buoys were unknown although there were such things as bell-boats which were anchored in dangerous spots and rung by the wash of the waves. There were lightships, too, but more often than not their feeble light was obscured or unnoticed and they were run down by the ships they sought to protect. Altogether there was room for improvement at every point and slowly but surely it came. After the Daboll trumpet, whistle and siren had been tried finer horns operated by steam or power engines supplanted them until now all along our coasts and inland streams signals of specified strength have been installed, a commission deciding just what size signals shall be used and where they shall be placed. There are lighthouses of prescribed candle power; automatic flashlights and whistling buoys; coastguard stations with carefully drilled crews; all regulated by law and matters of compulsion. If men and ships are lost now it is because it is beyond human power to help it." "There are facts about the water that are impossible to modify," interrupted Mr. Tolman, "and I suppose we shall never be able wholly to eliminate the dangers growing out of them. There are for example silence zones where, because of the nature of air currents or atmospheric conditions, no sounds can be heard. Often a foghorn comparatively near at hand will belch forth its warning and its voice be swallowed up in this strange stillness. Many a calamity has occurred that could only be accounted for in this way. Man is ingenious, it is true, but he is not omniscient and in the face of some of the caprices of nature he is powerless." Mr. Ackerman rose and stood with his back to the fire. "And now," went on Mr. Tolman, addressing Stephen and Dick, "I should say you two had had quite a lecture on steamboating and should move that you both go to bed." Quickly Mr. Ackerman interrupted him. "I should amend the motion by suggesting that we all go to bed," laughed he. "I am quite as tired as the boys are." The amendment was passed, the motion carried, and soon the entire Tolman family was wrapped in sleep. CHAPTER XVIII A THANKSGIVING TRAGEDY Perhaps had Stephen known what was in store for him on the morrow he might not have slept so soundly. As it was, he and Dick had to be called three times before they opened their eyes on the Thanksgiving sunshine. A heavy frost had fallen during the night, touching the trees with splendor and transforming the brown earth to a jewelled sweep of gems that flashed like brilliants in the golden light. The boys scrambled into their clothes and, ruddy from a cold shower, descended to the dining room where amid the fragrance of steaming coffee the family were just sitting down to breakfast. "Well, what is up for to-day, boys?" inquired Mrs. Tolman, after the more formal greetings were over. "What are you planning to do with Dick, Stephen?" "We're going skating over to the Hollow if the ice is any good," was the prompt response. "It was fine yesterday and unless somebody has smashed it all up it ought to be good to-day." "That plan sounds rather nice, doesn't it, Jane?" Doris suggested to her roommate. "Why don't we go, too?" "I'd like nothing better," was the answer. "The youngsters have sketched a very alluring program," Mr. Ackerman said. "If I had any skates I should be tempted to join them. I have not been on the ice in years but in my day I used to be quite a hockey player." "Oh, do come, Mr. Ackerman!" cried Steve eagerly. "If you used to skate it will all come back to you. It is like swimming, you know; once you have learned you never forget how." "But I've nothing to skate with," laughed the New Yorker. "Oh, we can fix you up with skates all right, if you really want to go," Mr. Tolman said. "I have a couple of pairs and am sure you could manage to use one of them." "So you are a skater, are you, Tolman?" the capitalist observed, with surprise. "Oh, I am nothing great," Mr. Tolman protested, "but I have always enjoyed sports and muddled along at them. Coventry is quite a distance from Broadway, you see, and therefore we must get our recreation in other ways." "It is a darn sight better than anything New York has to offer," commented the other man soberly. "Good wholesome out-of-door exercise is not to be mentioned in the same breath with a hot theater where a picture show is a makeshift for something better. Give me fresh air and exercise every time!" "Well, since that is the way you feel about it we can comply with your request," Mr. Tolman rejoined, with a smile. "If you do not mind hobbling back to New York lame as a cart-horse you can certainly have your wish, for we have the ice, the skates, plenty of coats and sweaters--everything necessary. Suppose we all start for the Hollow at ten o'clock. It is a mile walk but as we are having a late dinner we shall still have a long morning." "That will suit me all right," returned Mr. Ackerman. "By the way, Henry," interrupted Mrs. Tolman, addressing her husband, "Havens is waiting to see you. He has some message for you." "Where is he?" "In the hall." "Ask Mary to tell him to go into my den. I'll be there in a minute." What a merry party it was that chatted and laughed there in the warmth of the sunny dining room! For the time being the elders dropped their cares and became as young in spirit as the boys and girls. Jokes, stories and good-humored banter passed back and forth until with one accord everybody rose from the table and sauntered into the library where a great blaze of logs glowed and crackled. "If you will excuse me I will see what Havens wants," remarked Mr. Tolman, as he lighted his cigar. "Probably the garage people have unearthed some more repairs that must be made on that car. They seem to have a faculty for that sort of thing. Every day they discover something new the matter with it. I shall have a nice little bill by the time they finish." Shrugging his shoulders, he passed into the hall. It was more than half an hour before he returned and when he did a close observer would have noticed that his face had lost its brightness and that the gaiety with which he took up the conversation with his guests was forced and unnatural. However, he tried resolutely to banish his irritation, whatever its cause. He went up to the attic with Mr. Ackerman, where the two searched out skates, woolen gloves and sweaters; he jested with Doris and Jane Harden; he challenged Dick to a race across the frozen ground. But beneath his lightness lingered a grave depression which betokened to those who knew him best that something was wrong. Yet he was evidently determined the cloud should not obtrude itself and spoil the happiness of the day. Probably some business annoyance that could not be remedied had arisen; or possibly Havens had given notice. Such contingencies were of course to be deplored but as they could not be helped, why let them ruin the entire holiday? Therefore nobody heeded Mr. Tolman's mood which was so well controlled that his guests were unconscious of it, and the group of skaters swung along over the frosty fields with undiminished merriment. The Hollow for which they were bound lay in a deserted stone quarry where a little arm of the river had penetrated the barrier of rocks and, gradually flooding the place, made at one end a deep pool; from this point the water spread itself over the meadows in a large, shallow pond. Had the spot been nearer the town it would doubtless have been overrun with skaters; but as it was isolated, and there was a larger lake near the center of the village, few persons took the trouble to seek out this remote stretch of ice. This morning it lay desolate like a gleaming mirror, not a human being marring its solitude. "We shall have the place all to ourselves!" exclaimed Mr. Ackerman. "There will be no spectators to watch me renew my youth, thank goodness!" Quickly the skates were strapped on and the young people shot out into the sunshine and began to circle about. More cautiously Mr. Tolman and his guest followed. "I wouldn't go into the quarry," shouted Mr. Tolman, "for I doubt if it has been cold enough yet to freeze the ice very solidly there. There are liable to be air holes where the river makes in." "Oh, we fellows have skated in the quarry millions of times, Dad," Stephen protested. "It is perfectly safe." "There is no way of telling whether it is or not," was the response, "so suppose for to-day we keep away from it." "But--" "Oh, don't argue, Stevie," called Doris. "If Dad doesn't want us to go there that's enough, isn't it?" "But half the fun is making that turn around the rocks," grumbled Stephen, in a lower tone. "I don't see why Dad is such a fraid-cat. I know this pond better than he does and--" "If your father says not to skate there that ought to go with you," cut in Dick. "He doesn't want you to--see? Whether it is safe or not has nothing to do with it." "But it's so silly!" went on Stephen. "Why--" "Oh, cut it out! Can it!" ejaculated the East Side lad. "Your dad says _No_ and he's the boss." The ungracious retort Steve offered was lost amid the babel of laughter that followed, and the skaters darted away up the pond. Indeed, one could not long have cherished ill humor amid such radiant surroundings. There was too much sunshine, too much sparkle in the clear air; too much jollity and happiness. Almost before he realized it Stephen's irritation had vanished and he was speeding across the glassy surface of the ice as gay as the gayest of the company. He never could explain afterward just how it happened that he found himself around the bend of the quarry and sweeping with the wind toward its farther end. He had not actually formulated the intention of slipping away from the others and invading this forbidden spot. Nevertheless, there he was alone in the tiny cove with no one in sight. What followed was all over in a moment,--the breaking ice and the plunge into the frigid water. The next he knew he was fighting with all his strength to prevent himself from being drawn beneath the jagged, crumbling edge of the hole. To clamber out was impossible, for every time he tried the thin ice would break afresh under his hands and submerge him again in the bitter cold of the moving stream. Over and over he tried to pull himself to safety but without success. Then suddenly he felt himself becoming numb and helpless. His teeth chattered and he could no longer retain his hold on the frail support that was keeping his head above water. He was slipping back into the river. _He was not going to be able to get out!_ With a piercing scream he made one last desperate lunge forward, and again the ice that held him broke and the water dashed over his ears and mouth. When he next opened his eyes it was to find himself in his own bed with a confusion of faces bending over him. "There!" he heard some one say in a very small, far-away voice. "He is coming to himself now, thank God! It was chiefly cold and fright. He is safe now, Tolman. Don't you worry! You'd better go and get off some of your wet clothing, or you will catch your death." Mr. Ackerman was speaking. "Yes, Henry, do go!" pleaded his wife. [Illustration: He was fighting to prevent himself from being drawn beneath the jagged, crumbling edge of the hole. Page 244.] As Stephen looked about him in the vague, groping uncertainty of returning consciousness his glance fell upon his father who stood beside his pillow, shivering nervously. He put out his hand and touched the dripping coat sleeve. "What--" began he weakly. Then with a rush it all came back to him and everything was clear. He had been drowning and his father had plunged into the water to save him! A sob rose in his throat and he caught the elder man's hand between both of his. "Oh, Dad," he exclaimed, "I've been so rotten to you--so mean--so cowardly. I'm ashamed to--" "Don't talk about it now, son. I know." "You know what I did?" "Yes." "But--" the boy paused bewildered. "Don't talk any more about it now, Stevie," pleaded his mother. "But I've got to know," said the lad. "Can't you see that--" "Let me talk with him alone a moment," suggested Mr. Tolman in an undertone. "He is all upset and he won't calm down until he has this thing off his mind. Leave me here with him a little while. I'll promise that he does not tire himself." The doctor, Mr. Ackerman and Mrs. Tolman moved across the room toward the window. "You asked how I knew, son," began his father with extreme gentleness. "I didn't really know. I just put two and two together. There was the scratched machine and the gasoline gone--both of which facts puzzled me not a little. But the proof that clinched it all and made me certain of what had happened came to me this morning when Havens brought me an old red sweater and some school papers of Bud Taylor's that the men who were overhauling the car found under the seat. In an instant the whole thing was solved." "You knew before we went skating then?" "Yes." "And--and--you jumped into the water after me just the same." Mr. Tolman's voice trembled: "You are my son and I love you no matter what you may do." "Oh, Dad, I'm so sorry!" sobbed the boy. "I wanted to tell you--I meant to. It was just that I was too much of a coward. I was so ashamed of what I had done that I hadn't the nerve. After it was over it all seemed so wrong. I knew you would be angry--" "Rather say _sorry_, son." "Well, sorry. And now that you have been so white to me I'm more ashamed still." "There, there, my boy, we will say no more about it," his father declared. "You and your conscience have probably had a pretty bitter battle and I judge you have not been altogether happy since your adventure. People who do wrong never are. It is no fun to carry your fault to bed with you and find it waiting when you wake up in the morning." "You bet it isn't!" replied the lad, with fervor. "But can't I do something now to make good, Dad?" Mr. Tolman checked an impulsive protest and after a moment responded gravely: "We will see. Perhaps you would like to earn something toward doing over the car." "Yes! Yes! I would!" "Well, all that can be arranged later. We--" "Henry," broke in Mrs. Tolman, "you must go this instant and get into some dry clothes. You are chilled through. The doctor says Stephen is going to be none the worse for his ducking and that he can come down stairs to dinner after he has rested a little longer. So our Thanksgiving party is not to be spoiled, after all. In fact, I believe we shall have more to give thanks for than we expected," concluded she, making an unsteady attempt to speak lightly. "I think so, too," echoed her husband. "And so do I!" added Stephen softly, as he exchanged an affectionate smile with his father. CHAPTER XIX THE END OF THE HOUSE PARTY As they were persons of strong constitution and in good athletic training neither Mr. Tolman nor Steve were any the worse for the narrow escape of the morning, and although a trifle spent with excitement both were able to take their places at the dinner table so that no cloud rested on the festivity of the day. Certainly such a dinner never was,--or if there ever had been one like it in history at least Dick Martin had never had the luck to sit down to it. The soup steaming and hot, the celery white and crisp, the sweet potatoes browned in the oven and gleaming beneath their glaze of sugar, the cranberry sauce vivid as a bowl of rubies; to say nothing of squash, and parsnips and onions! And as for the turkey,--why, it was the size of an ostrich! With what resignation it lay upon its back, with what an abject spirit of surrender,--as if it realized that resistance was futile and that it must docilely offer itself up to make perfect the feast. And the pudding, the golden-tinted pies with their delicate crust, the nuts; the pyramid of fruit, riotous in color; the candies of every imaginable hue and flavor! Was it a wonder that Dick, who had never before beheld a real New England home Thanksgiving, regarded the novelty with eyes as large as saucers and ate until there was not room for another mouthful? "Gee!" he gasped in a whisper to Stephen, as he sank weakly back into his chair when the coffee made its appearance. "This sure is some dinner." The others who chanced to overhear the observation laughed. "Had enough, sonny?" inquired Mr. Tolman. "_Enough!_" There was more laughter. "I suppose were it not for the trains and the ships we should not be having such a meal as this to-day," remarked Mrs. Tolman. "You are right," was Mr. Ackerman's reply. "Let me see! Fruit from Florida, California and probably from Italy; flour from the Middle West; coffee from South America; sugar probably from Cuba; turkey from Rhode Island, no doubt; and vegetables from scattered New England farms. Add to this cigarettes from Egypt and Turkey and you have covered quite a portion of the globe." "It is a pity we do not consider our indebtedness to our neighbors all over the world oftener," commented Mr. Tolman. "We take so much for granted these days. To appreciate our blessings to the full we should have lived in early Colonial times when the arrival of a ship from across the ocean was such an important event that the wares she brought were advertised broadcast. Whenever such a vessel came into port a list of her cargo was issued and purchasers scrambled eagerly to secure the luxuries she carried. Pipes of wine, bolts of cloth, china, silks, tea--all were catalogued. It was no ordinary happening when such a boat docked, I assure you." "I suppose it was a great event," reflected Mrs. Tolman, "although I never half realized it." "And not only was the advent of merchandise a red-letter day but so was the advent of travelers from the other side of the water. Picture if you can the excitement that ensued when Jenny Lind, the famous singer, visited this country! And the fact that we were now to hear this celebrated woman was not the only reason for our interest. She had actually come in a ship from across the sea! Others would come also. America was no longer cut off from the culture of the old world, an isolated country bereft of the advantages of European civilization. We were near enough for distinguished persons to make trips here! Charles Dickens and the Prince of Wales came--and how cosmopolitan we felt to be entertaining guests from the mother-country! Certainly the Atlantic could not be very wide if it could be crossed so easily and if we could have the same speakers, the same readers, the same singers as did the English! Our fathers and grandfathers must have thrilled with satisfaction at the thought. The ocean was conquered and was no longer an estranging barrier." "What would they have said to crossing the water by aeroplane or bobbing up in a foreign port in a submarine?" put in Doris. "And some day I suppose the marvels of our age that cause our mouths to open wide and our eyes to bulge with amazement will become as humdrum as the ocean liner and the Pullman have," Mrs. Tolman remarked. "Yes," returned her husband. "Think of the fight every one of these innovations has had to put up before it battled its way to success. The first locomotives, you remember, were not only rated as unsafe for travel but also actually destructive to property. The major part of the public had no faith in them and predicted they would never be used for general travel. As for crossing the ocean--why, one was welcome to take his life in his hands if he chose, of course; but to cross in an iron ship--it was tempting Providence! Did not iron always sink? And how people ridiculed Darius Green and his flying machine! Most of the prophets were thought to be crazy. History is filled with stories of men who wrecked their worldly fortunes to perpetuate an idea, and but too frequently an idea they never lived to see perfected." During the pause that followed Mr. Ackerman leaned across the table and as he sipped his coffee asked mischievously: "Well, Steve, having now heard both stories, have you come to a conclusion which one you are going to vote for?" "No, sir," was the dubious response. "I'm farther away from a decision than ever. Just as I get it settled in my mind that the railroads have done the biggest things and conquered the most difficulties along come the steamships and I am certain they are six times as wonderful." "And you, Dick--what do you say?" questioned the financier, smiling. "Surely you are going to stand up for the steamboat." But to his chagrin Dick shook his head. "I feel as Steve does," replied he. "No sooner do I get settled one way than something turns me round the other." "So far as I can see we shall have to leave the matter a draw, shan't we, Tolman?" observed the New Yorker. "It would be a jolly subject for a debate, wouldn't it?" put in Stephen. "Sometimes we have discussions like that at school and the next time we do I believe I'll suggest this topic. It would be mighty interesting." "It certainly would," his father echoed. "But it also would be a very sorry event if you could not demonstrate that the railroads had the supremacy for were their prestige to be threatened I might have to move out of town." "In case Connecticut did not want you, you might come to New York where you would be sure of being appreciated," put in Mr. Ackerman. "And that is not all talk, either, for I want you and the whole family to give me a promise to-day that you will come over and join Dick and me at Christmas. I've never had a boy of my own to celebrate the holiday with before, you must remember; but this time I have a real family and I am going to have a real Christmas," he continued, smiling affectionately at the lad beside him. "So I want every one of you to come and help me to make the day a genuine landmark. And if I'm a little new at playing Santa Claus some of you who have been schooled in the rôle for many years can show me how. We can't promise to stage for you such an excitement as Stephen got up for us this morning, and we never can give you a dinner equal to this; but we can give you a royal welcome. You can come by boat or come by train," added he slyly. "No guest who patronizes the railroads will be shut out, even if he is misguided. The chief thing is for you to come, one and all, and we will renew our friendship and once again bless Stephen, Dick, and my lost pocketbook, for bringing us together." FINIS ----------------------------------------------------------------------- The first volume in "The Invention Series" PAUL AND THE PRINTING PRESS By SARA WARE BASSETT With illustrations by A. O. Scott 12mo. Cloth. 218 pages. Paul Cameron, president of the class of 1920 in the Burmingham High School, conceives the idea of establishing a school paper, to the honor and glory of his class. So _The March Hare_ comes into existence, and Paul and his schoolfellows bend all their energies to making it a success. They have their difficulties and Paul in particular bears the brunt of their troubles, but _The March Hare_ lives up to its reputation for life and liveliness and becomes not only a class success, but a town institution. This is the first volume in "The Invention Series." "It is the sort of story that boys of fourteen years and upward will enjoy and ought to enjoy, a combination that is rarely achieved."--Boston Post. "A welcome volume which will appeal to boys who want a good story that will give some information as well."--New York Evening Post. "'Paul and the Printing Press' not only has a keen story interest, but has the advantage of carrying much valuable information for all young folks for whom the mysterious and all-powerful printing press has an attraction."--Boston Herald. LITTLE, BROWN & CO., PUBLISHERS 34 Beacon Street, Boston ----------------------------------------------------------------------- 
55428	----	[Illustration: Pl. XIII. AMERICAN HIGH-PRESSURE ENGINE] THE STEAM ENGINE FAMILIARLY EXPLAINED AND ILLUSTRATED; WITH AN HISTORICAL SKETCH OF ITS INVENTION AND PROGRESSIVE IMPROVEMENT; ITS APPLICATIONS TO NAVIGATION AND RAILWAYS; WITH PLAIN MAXIMS FOR RAILWAY SPECULATORS. BY THE REV. DIONYSIUS LARDNER, LL. D., F. R. S., FELLOW OF THE ROYAL SOCIETY OF EDINBURGH; OF THE ROYAL IRISH ACADEMY; OF THE ROYAL ASTRONOMICAL SOCIETY; OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY; OF THE STATISTICAL SOCIETY OF PARIS; OF THE LINNÆAN AND ZOOLOGICAL SOCIETIES; OF THE SOCIETY FOR PROMOTING USEFUL ARTS IN SCOTLAND, ETC. WITH ADDITIONS AND NOTES, BY JAMES RENWICK, LL. D., PROFESSOR OF NATURAL EXPERIMENTAL PHILOSOPHY AND CHEMISTRY IN COLUMBIA COLLEGE, NEW YORK. ILLUSTRATED BY ENGRAVINGS AND WOODCUTS. SECOND AMERICAN, FROM THE FIFTH LONDON, EDITION, CONSIDERABLY ENLARGED. PHILADELPHIA: E. L. CAREY & A. HART. 1836 Entered, according to the Act of Congress, in the year 1836, by E. L. CAREY & A. HART, in the Clerk's office of the District Court for the Eastern District of Pennsylvania. PREFACE OF THE AMERICAN EDITOR. Several of the additions, which were made by the Editor to the first American edition, have been superseded by the great extension, which the original has from time to time received from its author. This is more particularly the case, with the sections which had reference to the character of steam at temperatures other than that of boiling water, to the use of steam in navigation, and to its application to locomotion. These sections have of course been omitted. A few new sections, and several notes have been added, illustrative of such points as may be most interesting to the American reader. COLUMBIA COLLEGE, _New York, March, 1836_. PREFACE TO THE FIFTH EDITION. This volume should more properly be called a new work than a new edition of the former one. In fact the book has been almost rewritten. The change which has taken place, even in the short period which has elapsed since the publication of the first edition, in the relation of the steam engine to the useful arts, has been so considerable as to render this inevitable. The great extension of railroads, and the increasing number of projects which have been brought forward for new lines connecting various points of the kingdom, as well as the extension of steam navigation, not only through the seas and channels surrounding and intersecting these islands, and throughout other parts of Europe, but through the larger waters which are interposed between our dominions in the East and the countries of Egypt and Syria, have conferred so much interest on the application of steam to transport, that I have thought it adviseable to extend the limits of the present edition considerably beyond those of the last. The chapter on railroads has been enlarged and improved. Three chapters have been added. The twelfth chapter contains a view of steam navigation; the thirteenth contains several important points connected with the economy of steam power, which, when this work was first published, would not have offered sufficient interest to justify their admission into a popular treatise; and the fourteenth chapter contains a series of compendious maxims, for the instruction and guidance of persons desirous of making investments or speculating in railway property. _London, December, 1835._ PREFACE TO THE FIRST EDITION. There are two classes of persons whose attention may be attracted by a treatise on such a subject as the Steam Engine. One consists of those who, by trade or profession, are interested in mechanical science, and who therefore seek information on the subject of which it treats, as a matter of necessity, and a wish to acquire it in a manner and to an extent which may be practically available in their avocations. The other and more numerous class is that part of the public in general, who, impelled by choice rather than necessity, think the interest of the subject itself, and the pleasure derivable from the instances of ingenuity which it unfolds, motives sufficiently strong to induce them to undertake the study of it. Without leaving the former class altogether out of view, it is for the use of the latter principally that the following lectures are designed. To this class of readers the Steam Engine is a subject which, if properly treated of, must present strong and peculiar attractions. Whether we consider the history of its invention as to time and place, the effects which it has produced, or the means by which it has caused these effects, we find everything to gratify our national pride, stimulate our curiosity, excite our wonder, and command our admiration. The invention and progressive improvement of this extraordinary machine, is the work of our own time and our own country; it has been produced and brought to perfection almost within the last century, and is the exclusive offspring of British genius fostered and supported by British capital. To enumerate the effects of this invention, would be to count every comfort and luxury of life. It has increased the sum of human happiness, not only by calling new pleasures into existence, but by so cheapening former enjoyments as to render them attainable by those who before never could have hoped to share them. Nor are its effects confined to England alone: they extend over the whole civilized world; and the savage tribes of America, Asia, and Africa, must ere long feel the benefits, remote or immediate, of this all-powerful agent. If the effect which this machine has had on commerce and the wealth of nations raise our astonishment, the means by which this effect has been produced will not less excite our admiration. The history of the Steam Engine presents a series of contrivances, which, for exquisite and refined ingenuity, stand without a parallel in the annals of human invention. These admirable contrivances, unlike other results of scientific investigation, have also this peculiarity, that to understand and appreciate their excellence requires little previous or subsidiary knowledge. A simple and clear explanation, divested as far as possible of technicalities, and assisted by well selected diagrams, is all that is necessary to render the principles of the construction and operation of the Steam Engine intelligible to a person of plain understanding and moderate information. The purpose for which this volume is designed, as already explained, has rendered necessary the omission of many particulars which, however interesting and instructive to the practical mechanic or professional engineer, would have little attraction for the general reader. Our readers require to be informed of the general principles of the construction and operation of Steam Engines, rather than of their practical details. For the same reasons we have confined ourselves to the more striking and important circumstances in the history of the invention and progressive improvement of this machine, excluding many petty disputes which arose from time to time respecting the rights of invention, the interest of which is buried in the graves of their respective claimants. In the descriptive parts of the work we have been governed by the same considerations. The application of the force of steam to mechanical purposes has been proposed on various occasions, in various countries, and under a great variety of forms. The list of British patents alone would furnish an author of common industry and application with matter to swell his book to many times the bulk of this volume. By far the greater number of these projects have, however, proved abortive. Descriptions of such unsuccessful, though frequently ingenious machines, we have thought it adviseable to exclude from our pages, as not possessing sufficient interest for the readers to whose use this volume is dedicated. We have therefore strictly confined our descriptions either to those Steam Engines which have come into general use, or to those which form an important link in the chain of invention. _December 26, 1827._ CONTENTS. CHAPTER I. PRELIMINARY MATTER. Motion the Agent in Manufactures. -- Animal Power. -- Power depending on physical Phenomena. -- Purpose of a Machine. -- Prime Mover. -- Mechanical qualities of the Atmosphere. -- Its Weight. -- The Barometer. -- Fluid Pressure. -- Pressure of rarefied Air. -- Elasticity of Air. -- Bellows. -- Effects of Heat. -- Thermometer. -- Method of making one. -- Freezing and Boiling Points. -- Degrees. -- Dilatation of bodies. -- Liquefaction and Solidification. -- Vaporisation and Condensation. -- Latent Heat of Steam. -- Expansion of Water in Evaporating. -- Effects of Repulsion and Cohesion. -- Effect of Pressure upon Boiling Point. -- Formation of a Vacuum by Condensation. Page 17 CHAPTER II. FIRST STEPS IN THE INVENTION. Futility of early Claims. -- Watt the real Inventor. -- Hero of Alexandria. -- Blasco Garay. -- Solomon De Caus. -- Giovanni Branca. -- Marquis of Worcester. -- Sir Samuel Morland. -- Denis Papin. -- Thomas Savery. 38 CHAPTER III. ENGINES OF SAVERY AND NEWCOMEN. Savery's Engine. -- Boilers and their Appendages. -- Working Apparatus. -- Mode of Operation. -- Defects of the Engine. -- Newcomen and Cawley. -- Atmospheric Engine. -- Accidental discovery of Condensation by Jet. -- Potter's discovery of the Method of working the Valves. 51 CHAPTER IV. ENGINE OF JAMES WATT. Advantages of the Atmospheric Engine over that of Captain Savery. -- It contained no new Principle. -- Papin's Engine. -- James Watt. -- Particulars of his Life. -- His first conceptions of the Means of economising Heat. -- Principle of his projected Improvements. 69 CHAPTER V. WATT'S SINGLE-ACTING STEAM ENGINE. Expansive Principle applied. -- Failure of Roebuck, and partnership with Bolton. -- Patent extended to 1800. -- Counter. -- Difficulties in getting the Engines into Use. 80 CHAPTER VI. DOUBLE-ACTING STEAM ENGINE. The Single-acting Engine unfit to impel Machinery. -- Various Contrivances to adapt it to this Purpose. -- Double-Cylinder. -- Double-acting Cylinder. -- Various modes of connecting the Piston with the Beam. -- Rack and Sector. -- Double Chain. -- Parallel Motion. -- Crank. -- Sun and Planet Motion. -- Fly Wheel. -- Governor. 91 CHAPTER VII. DOUBLE-ACTING STEAM ENGINE, _continued_. On the Valves of the Double-acting Steam Engine. -- Original Valves. -- Spindle Valves. -- Sliding Valve. -- D Valve. -- Four-Way Cock. 108 CHAPTER VIII. BOILER AND ITS APPENDAGES. Level Gauges. -- Feeding apparatus. -- Steam Gauge. -- Barometer Gauge. -- Safety Valves. -- Self-regulating Damper. -- Edelcrantz's Valve. -- Furnace. -- Smoke-consuming Furnace. -- Brunton's Self-regulating Furnace. -- Oldham's Modification. 117 CHAPTER IX. DOUBLE-CYLINDER ENGINES. Hornblower's Engine. -- Woolf's Engine. -- Cartwright's Engine. 134 CHAPTER X. LOCOMOTIVE ENGINES ON RAILWAYS. High-pressure Engines. -- Leupold's Engine. -- Trevithick and Vivian. -- Effects of Improvement in Locomotion. -- Historical Account of the Locomotive Engine. -- Blenkinsop's Patent. -- Chapman's Improvement. -- Walking Engine. -- Stephenson's First Engines. -- His Improvements. -- Liverpool and Manchester Railway Company. -- Their Preliminary Proceedings. -- The Great Competition of 1829. -- The Rocket. -- The Sanspareil. -- The Novelty. -- Qualities of the Rocket. -- Successive Improvements. -- Experiments. -- Defects of the Present Engines. -- Inclined Planes. -- Methods of surmounting them. -- Circumstances of the Manchester Railway Company. -- Probable Improvements in Locomotives. -- Their capabilities with respect to speed. -- Probable Effects of the Projected Railroads. -- Steam Power compared with Horse Power. -- Railroads compared with Canals. 145 CHAPTER XI. LOCOMOTIVE ENGINES ON TURNPIKE ROADS. Railway and Turnpike Roads compared. -- Mr. Gurney's inventions. -- His Locomotive Steam Engine. -- Its performances. -- Prejudices and errors. -- Committee of the House of Commons. -- Convenience and safety of Steam Carriages. -- Hancock's Steam Carriage. -- Mr. N. Ogle. -- Trevithick's invention. -- Proceedings against Steam Carriages. -- Turnpike Bills. -- Steam Carriage between Gloucester and Cheltenham. -- Its discontinuance. -- Report of the Committee of the Commons. -- Present State and Prospects of Steam Carriages. 213 CHAPTER XII. STEAM NAVIGATION. Propulsion by paddle-wheels. -- Manner of driving them. -- Marine Engine. -- Its form and arrangement. -- Proportion of its cylinder. -- Injury to boilers by deposites and incrustation. -- Not effectually removed by blowing out. -- Mr. Samuel Hall's condenser. -- Its advantages. -- Originally suggested by Watt. -- Hall's _steam saver_. -- Howard's vapour engine. -- Morgan's paddle-wheels. -- Limits of steam navigation. -- Proportion of tonnage to power. -- Average speed. -- Consumption of fuel. -- Iron Steamers. -- American steam raft. -- Steam navigation to India. -- By Egypt and the Red Sea to Bombay. -- By same route to Calcutta. -- By Syria and the Euphrates to Bombay. -- Steam communication with the United States from the west coast of Ireland to St. Johns, Halifax, and New York. 241 CHAPTER XIII. GENERAL ECONOMY OF STEAM POWER. Mechanical efficacy of steam -- proportional to the quantity of water evaporated, and to the fuel consumed. -- Independent of the pressure. -- Its mechanical efficacy by condensation alone. -- By condensation and expansion combined -- by direct pressure and expansion -- by direct pressure and condensation -- by direct pressure, condensation, and expansion. -- The power of engines. -- The duty of engines. -- Meaning of horse power. -- To compute the power of an engine. -- Of the power of boilers. -- The structure of the grate-bars. -- Quantity of water and steam room. -- Fire surface and flue surface. -- Dimensions of steam pipes. -- Velocity of piston. -- Economy of fuel. -- Cornish duty reports. 277 CHAPTER XIV. Plain Rules for Railway Speculators. 307 THE STEAM ENGINE EXPLAINED AND ILLUSTRATED. CHAPTER I. PRELIMINARY MATTER. Motion the Agent in Manufactures. -- Animal Power. -- Power depending on Physical Phenomena. -- Purpose of a Machine. -- Prime Mover. -- Mechanical qualities of the Atmosphere. -- Its Weight. -- The Barometer. -- Fluid Pressure. -- Pressure of Rarefied Air. -- Elasticity of Air. -- Bellows. -- Effects of Heat. -- Thermometer. -- Method of making one. -- Freezing and Boiling Points. -- Degrees. -- Dilatation of Bodies. -- Liquefaction and Solidification. -- Vaporisation and Condensation. -- Latent heat of Steam. -- Expansion of Water in Evaporating. -- Effects of Repulsion and Cohesion. -- Effect of Pressure upon Boiling-Point. -- Formation of a Vacuum by Condensation. (1.) Of the various productions designed by nature to supply the wants of man, there are few which are suited to his necessities in the state in which the earth spontaneously offers them: if we except atmospheric air, we shall scarcely find another instance: even water, in most cases, requires to be transported from its streams or reservoirs; and food itself, in almost every form, requires culture and preparation. But if, from the mere necessities of physical existence in a primitive state, we rise to the demands of civil and social life,--to say nothing of luxuries and refinements,--we shall find that everything which contributes to our convenience, or ministers to our pleasure, requires a previous and extensive expenditure of labour. In most cases, the objects of our enjoyment derive all their excellences, not from any qualities originally inherent in the natural substances out of which they are formed, but from those qualities which have been bestowed upon them by the application of human labour and human skill. In all those changes to which the raw productions of the earth are submitted in order to adapt them to our wants, one of the principal agents is _motion_. Thus, for example, in the preparation of clothing for our bodies, the various processes necessary for the culture of the cotton require the application of moving power, first to the soil, and subsequently to the plant from which the raw material is obtained: the wool must afterwards be picked and cleansed, twisted into threads, and woven into cloth. In all these processes motion is the agent: to cleanse the wool and arrange the fibres of the cotton, the wool must be beaten, teased, carded, and submitted to other processes, by which all the foreign and coarser matter may be separated, and the fibres or threads arranged evenly, side by side. The threads must then receive a rotatory motion, by which they may be twisted into the required form; and finally peculiar motions must be given to them in order to produce among them that arrangement which characterises the cloth which it is our final purpose to produce. In a rude state of society, the motions required in the infant manufactures are communicated by the immediate application of the hand. Observation and reflection, however, soon suggest more easy and effectual means of attaining these ends: the strength of animals is first resorted to for the relief of human labour. Further reflection and inquiry suggest still better expedients. When we look around us in the natural world, we perceive inanimate matter undergoing various effects in which motion plays a conspicuous part: we see the falls of cataracts, the currents of rivers, the elevation and depression of the waters of the ocean, the currents of the atmosphere; and the question instantly arises, whether, without sharing our own means of subsistence with the animals whose force we use, we may not equally, or more effectually, derive the powers required from these various phenomena of nature? A difficulty, however, immediately presents itself: we require motion of a particular kind; but wind will not blow, nor water fall as we please, nor as suits our peculiar wants, but according to the fixed laws of nature. We want an _upward_ motion; water falls _downwards_: we want a _circular_ motion; wind blows in a _straight_ line. The motions, therefore, which are in actual existence must be modified to suit our purposes: the means whereby these modifications are produced, are called _machines_. A machine, therefore, is an instrument interposed between some natural force or motion, and the object to which force or motion is desired to be transmitted. The construction of the machine is such as to modify the natural motion which is impressed upon it, so that it may transmit to the object to be moved that peculiar species of motion which it is required to have. To give a very obvious example, let us suppose that a circular or rotatory motion is required to be produced, and that the only natural source of motion at our command is a perpendicular fall of water: a wheel is provided, placed upon the axle destined to receive the rotatory motion; this wheel is furnished with cavities in its rim; the water is conducted into the cavities near the top of the wheel on one side; and being caught by these, its weight bears down that side of the wheel, the cavities on the opposite side being empty and in an inverted position. As the wheel turns, the cavities on the descending side discharge their contents as they arrive near the lowest point, and ascend empty on the other side. Thus a load of water is continually pressing down one side of the wheel, from which the other side is free, and a continued motion of rotation is produced. In every machine, therefore, there are three objects demanding attention:--first, The power which imparts motion to it, this is called the _prime mover_; secondly, The nature of the _machine_ itself; and thirdly, The object to which the motion is to be conveyed. In the steam engine the first mover arises from certain phenomena which are exhibited when heat is applied to liquids; but in the details of the machine and in its application there are several physical effects brought into play, which it is necessary perfectly to understand before the nature of the machine or its mode of operation can be rendered intelligible. We propose therefore to devote the present chapter to the explanation and illustration of these phenomena. (2.) The physical effects most intimately connected with the operations of steam engines are some of the mechanical properties of atmospheric air. The atmosphere is the thin transparent fluid in which we live and move, and which, by respiration, supports animal life. This fluid is apparently so light and attenuated, that it might be at first doubted whether it be really a body at all. It may therefore excite some surprise when we assert, not only that it is a body, but also that it is one of considerable _weight_. We shall be able to prove that it presses on every _square inch_[1] of surface with a weight of about 15lb. avoirdupois. [Footnote 1: As we shall have frequent occasion to mention this magnitude, it would be well that the reader should be familiar with it. It is a _square_, each side of which is an inch. Such as A B C D, Fig. 1.] (3.) Take a glass tube A B (fig. 2.) more than 32 inches long, open at one end A, and closed at the other end B, and let it be filled with mercury (quicksilver.) Let a glass vessel or cistern C, containing a quantity of mercury, be also provided. Applying the finger at A so as to prevent the mercury in the tube from falling out, let the tube be inverted, and the end, stopped by the finger, plunged into the mercury in _C_. When the end of the tube is below the surface of the mercury in C (fig. 3.) let the finger be removed. It will be found that the mercury in the tube will not, as might be expected, fall to the level of the mercury in the cistern C, which it would do were the end B open so as to admit the air into the upper part of the tube. On the other hand, the level D of the mercury in the tube will be about 30 inches above the level C of the mercury in the cistern. (4.) The cause of this effect is, that the weight of the atmosphere rests on the surface C of the mercury in the cistern, and tends thereby to press it up, or rather to resist its fall in the tube; and as the fall is not assisted by the weight of the atmosphere on the surface D (since B is closed), it follows, that as much mercury remains suspended in the tube above the level C as the weight of the atmosphere is able to support. If we suppose the section of the tube to be equal to the magnitude of a square inch, the weight of the column of mercury in the tube above the level C will be exactly equal to the weight of the atmosphere on each square inch of the surface C. The height of the level D above C being about 30 inches, and a column of mercury two inches in height, and having a base of a square inch, weighing about one pound avoirdupois, it follows that the weight with which the atmosphere presses on each square inch of a level surface is about 15lb. avoirdupois. An apparatus thus constructed, and furnished with a scale to indicate the height of the level D above the level C, is the _common barometer_. The difference of these levels is subject to a small variation, which indicates a corresponding change in the atmospheric pressure. But we take 30 inches as a standard or average. (5.) It is an established property of fluids that they press equally in all directions; and air, like every other fluid, participates in this quality. Hence it follows, that since the downward pressure or weight of the atmosphere is about 15lb. on the square inch, the lateral, upward, and oblique pressures are of the same amount. But, independently of the general principle, it may be satisfactory to give experimental proof of this. Let four glass tubes A, B, C, D, (fig. 4.) be constructed of sufficient length, closed at one end A, B, C, D, and open at the other. Let the open ends of three of them be bent, as represented in the tubes B, C, D. Being previously filled with mercury, let them all be gently inverted so as to have their closed ends up as here represented. It will be found that the mercury will be sustained in all,[2] and that the difference of the levels in all will be the same. Thus the mercury is sustained in A by the upward pressure of the atmosphere, in B by its horizontal or lateral pressure, in C by its downward pressure, and in D by its oblique pressure; and as the difference of the levels is the same in all, these pressures are exactly equal. [Footnote 2: This experiment with the tube A requires to be very carefully executed, and the tube should be one of small bore.] (6.) In the experiment described in (3.) the space B D (fig. 3.) at the top of the tube from which the mercury has fallen is perfectly void and empty, containing neither air nor any other fluid: it is called therefore a _vacuum_. If, however, a small quantity of air be introduced into that space, it will immediately begin to exert a pressure on D, which will cause the surface D to descend, and it will continue to descend until the column of mercury C D is so far diminished that the weight of the atmosphere is sufficient to sustain it, as well as the pressure exerted upon it by the air in the space B D. The quantity of mercury which falls from the tube in this case is necessarily an equivalent for the pressure of the air introduced, so that the pressure of this air may be exactly ascertained by allowing about one pound per square inch for every two inches of mercury which has fallen from the tube. The pressure of the air or any other fluid above the mercury in the tube, may at once be ascertained by comparing the height of the mercury in the tube with the height of the barometer; the difference of the heights will always determine the pressure on the surface of the mercury in the tube. This principle will be found of some importance in considering the action of the modern steam engines. The air which we have supposed to be introduced into the upper part of the tube, presses on the surface of the mercury with a force much greater than its weight. For example, if the space B D (fig. 3.) were filled with atmospheric air in its ordinary state, it would exert a pressure on the surface D equal to the whole pressure of the atmosphere, although its weight might not amount to a single grain. The property in virtue of which the air exerts this pressure is its _elasticity_, and this force is diminished in precisely the proportion in which the space which the air occupies is increased. Thus it is known that atmospheric air in its ordinary state exerts a pressure on the surface of any vessel in which it is confined, amounting to about 15lb. on every square inch. If the capacity of the vessel which contains it be doubled, it immediately expands and fills the double space, but in doing so it loses half its elastic force, and presses only with the force of 7-1/2lb. on every square inch. If the capacity of the vessel had been enlarged five times, the air would still have expanded so as to fill it, but would exert only a fifth part of its first pressure, or 3lb. on every square inch. This property of losing its elastic force as its volume or bulk is increased, is not peculiar to air. It is common to all elastic fluids, and we accordingly find it in steam; and it is absolutely necessary to take account of it in estimating the effects of that agent. (7.) There are numerous instances of the effects of these properties of atmospheric air which continually fall under our observation. If the nozzle and valve-hole of a pair of bellows be stopped, it will require a very considerable force to separate the boards. This effect is produced by the diminished elastic force of the air remaining between the boards upon the least increase of the space within the bellows, while the atmosphere presses, with undiminished force, on the external surfaces of the boards. If the boards be separated so as to double the space within, the elastic force of the included air will be about 7-1/2lb. on every square inch, while the pressure on the external surfaces will be 15lb. on every square inch; consequently, it will require as great a force to sustain the boards in such a position, as it would to separate them if each board were forced against the other, with a pressure of 7-1/2lb. per square inch on their external surfaces. When boys apply a piece of moistened leather to a stone, so as to exclude the air from between them, the stone, though it be of considerable weight, may be lifted by a string attached to the leather: the cause of which is the atmospheric pressure, which keeps the leather and the stone in close contact. (8.) The next class of physical effects which it is necessary to explain, are those which are produced when heat is imparted or abstracted from bodies. In general, when heat is imparted to a body, an enlargement of bulk will be the immediate consequence, and at the same time the body will become warmer to the touch. These two effects of expansion and increase of warmth going on always together, the one has been taken as a measure of the other; and upon this principle the common thermometer is constructed. That instrument consists of a tube of glass, terminated in a bulb, the magnitude of which is considerable, compared with the bore of the tube. The bulb and part of the tube are filled with mercury, or some other liquid. When the bulb is exposed to any source of heat, the mercury contained in it, being warmed or increased in temperature, is at the same time increased in bulk, or expanded or dilated, as it is called. The bulb not having sufficient capacity to contain the increased bulk of mercury, the liquid is forced up in the tube, and the quantity of expansion is determined by observing the ascent of the column in the tube. An instrument of this kind, exposed to heat or cold, will fluctuate accordingly, the mercury rising as the heat to which it is exposed is increased, and falling by exposure to cold. In order, however, to render it an accurate measure of temperature, it is necessary to connect with it a scale by which the elevation or depression of the mercury in the tube may be measured. Such a scale is constructed for thermometers in this country in the following manner:--Let us suppose the instrument immersed in a vessel of melting ice: the column of mercury in the tube will be observed to fall to a certain point, and there maintain its position unaltered: let that point be marked upon the tube. Let the instrument be now transferred to a vessel of boiling water at a time when the barometer stands at the altitude of 30 inches: the mercury in the tube will be observed to rise until it attain a certain elevation, and will there maintain its position. It will be found, that though the water continue to be exposed to the action of the fire, and continue to boil, the mercury in the tube will not continue to rise, but will maintain a fixed position: let the point to which the mercury has risen, in this case, be likewise marked upon the tube. The two points, thus determined, are called the _freezing_ and the _boiling_ points. If the distance upon the tube between these two points be divided into 180 equal parts, each of these parts is called a _degree_; and if this division be continued, by taking equal divisions below the freezing point, until 32 divisions be taken, the last division is called the _zero_, or _nought_ of the thermometer. It is the point to which the mercury would fall, if the thermometer were immersed in a certain mixture of snow and salt. When thermometers were first invented, this point was taken as the zero point, from an erroneous supposition that the temperature of such a mixture was the lowest possible temperature. The degrees upon the instrument thus divided are counted upwards from the zero, and are expressed, like the degrees of a circle, by placing a small ° over the number. Thus it will be perceived that the freezing point is 32° of our thermometer, and the boiling-point will be found by adding 180° to 32°; it is therefore 212°. The temperature of a body is that elevation to which the thermometer would rise when the mercury enclosed in it would acquire the same temperature. Thus, if we should immerse the thermometer, and should find that the mercury would rise to the division marked 100°, we should then affirm that the temperature of the water was 100°. (9.) The dilatation which attends an increase of temperature is one of the most universal effects of heat. It varies, however, in different bodies: it is least in solid bodies; greater in liquids; and greatest of all in bodies in the aeriform state. Again, different solids are differently susceptible of this expansion. Metals are the most susceptible of it; but metals of different kinds are differently expansible. As an increase of temperature causes an increase of bulk, so a diminution of temperature causes a corresponding diminution of bulk, and the same body always has the same bulk at the same temperature. A flaccid bladder, containing a small quantity of air, will, when heated, become quite distended; but it will again resume its flaccid appearance when cold. A corked bottle of fermented liquor, placed before the fire, will burst by the effort of the air contained in it to expand when heated. Let the tube A B (fig. 5.) open at both ends, have one end inserted in the neck of a vessel C D, containing a coloured liquid, with common air above it; and let the tube be fixed so as to be air-tight in the neck: upon heating the vessel, the warm air inclosed in the vessel C D above the liquid will begin to expand, and will press upon the surface of the liquid, so as to force it up in the tube A B. In bridges and other structures, formed of iron, mechanical provisions are introduced to prevent the fracture or strain which would take place by the expansion and contraction which the metal must undergo by the changes of temperature at different seasons of the year, and even at different hours of the day. Thus all nature, animate and inanimate, organized and unorganized, may be considered to be incessantly breathing heat; at one moment drawing in that principle through all its dimensions, and at another moment dismissing it. (10.) Change of bulk, however, is not the only nor the most striking effect which attends the increase or diminution of the quantity of heat in a body. In some cases, a total change of form and of mechanical qualities is effected by it. If heat be imparted in sufficient quantity to a solid body, that body, after a certain time, will be converted into a liquid. And again, if heat be imparted in sufficient quantity to this liquid, it will cease to exist in the liquid state, and pass into the form of vapour. By the abstraction of heat, a series of changes will be produced in the opposite order. If from the vapour produced in this case, a sufficient quantity of heat be taken, it will return to the liquid state; and if again from this liquid heat be further abstracted, it will at length resume its original solid state. The transmission of a body from the solid to the liquid state, by the application of heat, is called _fusion_ or _liquefaction_, and the body is said to be fused, _liquefied_, or melted. The reciprocal transmission from the liquid to the solid state, is called _congelation_, or _solidification_; and the liquid is said to be _congealed_ or _solidified_. The transmission of a body from the liquid to the vaporous or aeriform state, is called _vaporization_, and the liquid is said to be _vaporized_ or _evaporated_. The reciprocal transmission of vapour to the liquid state is called _condensation_, and the vapour is said to be _condensed_. We shall now examine more minutely the circumstances which attend these remarkable and important changes in the state of body. (11.) Let us suppose that a thermometer is imbedded in any solid body; for example, in a mass of sulphur; and that it stands at the ordinary temperature of 60 degrees: let the sulphur be placed in a vessel, and exposed to the action of fire. The thermometer will now be observed gradually to rise, and it will continue to rise until it exhibit the temperature of 218°. Here, however, notwithstanding the continued action of the fire upon the sulphur, the thermometer will become stationary; proving, that notwithstanding the supply of heat received from the fire, the sulphur has ceased to become hotter. At the moment that the thermometer attains this stationary point, it will be observed that the sulphur has commenced the process of fusion; and this process will be continued, the thermometer being stationary, until the whole mass has been liquefied. The moment the liquefaction is complete, the thermometer will be observed again to rise, and it will continue to rise until it attain the elevation of 570°. Here, however, it will once more become stationary; and notwithstanding the heat supplied to the sulphur by the fire, the liquid will cease to become hotter: when this happens, the sulphur will boil; and if it continue to be exposed to the fire a sufficient length of time, it will be found that its quantity will gradually diminish, until at length it will all disappear from the vessel which contained it. The sulphur will, in fact, be converted into vapour. From this process we infer, that all the heat supplied during the processes of liquefaction and vaporization is consumed in effecting these changes in the state of the body; and that under such circumstances, it does not increase the temperature of the body on which the change is produced. These effects are general: all solid bodies would pass into the liquid state by a sufficient application of heat; and all liquid bodies would pass into the vaporous state by the same means. In all cases the thermometer would be stationary during these changes, and consequently the temperature of the body, in those periods, would be maintained unaltered. (12.) Solids differ from one another in the temperatures at which they become liquid. These temperatures are called their _melting points_. Thus the melting point of ice is 32°; that of lead 612°; that of gold 5237°.[3] The heat which is supplied to a body during the processes of fusion or vaporization, and which does not affect the thermometer, or increase the temperature of the body fused or vaporized, is said to become _latent_. It can be proved to exist in the body fused or vaporized, and may even be taken from that body. In parting with it the body does not fall in temperature, and consequently the loss of this heat is not indicated by the thermometer any more than its reception. The term latent heat is merely intended to express this fact, of the thermometer being insensible to the presence or absence of this portion of heat, and is not intended to express any theoretical notions concerning it. [Footnote 3: Temperatures above 650° cannot be measured by the mercurial thermometer. They can be inferred only with probability by pyrometers.] (13.) In explaining the construction and operation of the steam engine, although it is necessary occasionally to refer to the effects of heat upon bodies in general, yet the body, which is by far the most important to be attended to, so far as the effects of heat upon it are concerned, is water. This body is observed to exist in the three different states, the solid, the liquid, and the vaporous, according to the varying temperature to which it is exposed. All the circumstances which have been explained in reference to metals, and the substance sulphur in particular, will, _mutatis mutandis_, be applicable to water. But in order perfectly to comprehend the properties of the steam engine, it is necessary to render a more rigorous and exact account of these phenomena, so far as they apply to the changes produced upon water by the effects of heat. Let us suppose a mass of ice immersed in the mixture of snow and salt which determines the zero point of the thermometer: this mass, if allowed to continue a sufficient length of time submerged in the mixture, will necessarily acquire its temperature, and the thermometer immersed in it will stand at zero. Let the ice be now withdrawn from the mixture, still keeping the thermometer immersed in it, and let it be exposed to the atmosphere at the ordinary temperature, say 60°. At first the thermometer will be observed gradually and continuously to rise until it attain the elevation of 32°; it will then become stationary, and the ice will begin to melt: the thermometer will continue standing at 32° until the ice shall be completely liquefied. The liquid ice and the thermometer being contained in the same vessel, it will be found, when the liquefaction is completed, that the thermometer will again begin to rise, and will continue to rise until it attain the temperature of the atmosphere, viz. 60°. Hitherto the ice or water has received a supply of heat from the surrounding air; but now an equilibrium of temperature having been established, no further supply of heat can be received; and if we would investigate the further effects of increased heat, it will be necessary to expose the liquid to fire, or some other source of heat. But previous to this, let us observe the time which the thermometer remains stationary during the liquefaction of the ice: if noted by a chronometer, it would be found to be a hundred and forty times the time during which the water in the liquid state was elevated one degree; the inference from which is, that in order to convert the solid ice into liquid water, it was necessary to receive from the surrounding atmosphere one hundred and forty times as much heat as would elevate the liquid water one degree in temperature; or, in other words, that to liquefy a given weight of ice requires as much heat as would raise the same weight of water 140° in temperature: or from 32° to 172°. The latent heat of water acquired in liquefaction is therefore 140°. (14.) Let us now suppose that, a spirit lamp being applied to the water already raised to 60°, the effects of a further supply of heat be observed: the thermometer will continue to rise until it attain the elevation of 212°, the barometer being supposed to stand at 30 inches. The thermometer having attained this elevation will cease to rise; the water will therefore cease to become hotter, and at the same time bubbles of steam will be observed to be formed at the bottom of the vessel containing the water, near the flame of the spirit lamp. These bubbles will rise through the water, and escape at the surface, exhibiting the phenomena of ebullition, and the water will undergo the process of _boiling_. During this process, the thermometer will constantly be maintained at the same elevation of 212°; but if the time be noted, it will be found that the water will be altogether evaporated, if the same source of heat be continued to be applied to it six and a half times as long as was necessary to raise it from the freezing to the boiling-point. Thus, if the application of the lamp to water at 32°, be capable of raising that water to 212° in one hour, the same lamp will require to be applied to the boiling water for six hours and a half, in order to convert the whole of it into steam. Now if the steam into which it is thus converted were carefully preserved in a receiver, maintained at the temperature of 212°, this steam would be found to have that temperature, and not a greater one; but it would be found to fill a space about 1700 times greater than the space it occupied in the liquid state, and it would possess an elastic force equal to the pressure of the atmosphere under which it was boiled; that is to say, it would press the sides of the vessel which contained it with a pressure equivalent to that of a column of mercury of 30 inches in height; or what is the same thing, at the rate of about 15lb. on every square inch of surface. (15.) As the quantity of heat expended in raising the water from 32° to 212°, is 180°; and as the quantity of heat necessary to convert the same water into steam is six and a half times this quantity, it follows that the quantity of heat requisite for converting a given weight of water into steam, will be found by multiplying 180° by 5-1/2. The product of these numbers being 990°, it follows, that, to convert a given weight of water at 212° into steam of the same temperature, under the pressure of the atmosphere, when the barometer stands at 30 inches, requires as much heat as would be necessary to raise the same water 990° higher in temperature. The heat, not being sensible to the thermometer, is latent heat; and accordingly it may be stated, that the latent heat, necessary to convert water into steam under this pressure is, in round numbers, 1000°. (16.) All the effects of heat which we have just described may be satisfactorily accounted for, by supposing that the principle of heat imparts to the constituent atoms of bodies a force, by virtue of which they acquire a tendency to repel each other. But in conjunction with this, it is necessary to notice another force, which is known to exist in nature: there is observable among the corpuscles of bodies a force, in virtue of which they have a tendency to cohere, and collect themselves together in solid concrete masses: this force is called the attraction of cohesion. These two forces--the natural cohesion of the particles, and the repulsive energy introduced by heat--are directly opposed to one another, and the state of the body will be decided by the predominance of the one or the other, or their mutual equilibrium. If the natural cohesion of the constituent particles of the body considerably predominate over the repulsive energy introduced by the heat, then the cohesion will take effect; the particles of the body will coalesce, the mass will become rigid and solid, and the particles will hold together in one invariable mass, so that they cannot drop asunder by the mere effect of their weight. In such cases, a more or less considerable force must be applied, in order to break the body, or to tear its parts asunder. Such is the quality which characterises the state, which in mechanics is called the state of solidity. If the repulsive energy introduced by the application of heat be equal, or nearly equal, to the natural cohesion with which the particles of the body are endued, then the predominance of the cohesive force may be insufficient to resist the tendency which the particles may have to drop asunder by their weight. In such a case, the constituent particles of the body cannot cohere in a solid mass, but will separate by their weight, fall asunder, and drop into the various corners, and adapt themselves to the shape of any vessel in which the body may be contained. In fact, the body will take the liquid form. In this state, however, it does not follow that the cohesive principle will be altogether inoperative: it may, and does, in some cases, exist in a perceptible degree, though insufficient to resist the separate gravitation of the particles. The tendency which particles of liquids have, in some cases, to collect in globules, plainly indicates the predominance of the cohesive principle: drops of water collected upon the window pane; drops of rain condensed in the atmosphere; the tear which trickles on the cheek; drops of mercury, which glide over any flat surface, and which it is difficult to subdivide or scatter into smaller parts; are all obvious indications of the predominance of the cohesive principle in liquids. By the due application of heat, even this small degree of cohesion may be conquered, and a preponderance of the opposite principle of repulsion may be created. But another physical influence here interposes its aid, and conspires with cohesion in resisting the transmission of the body from the liquid to the vaporous state: this force is no other than the pressure of the atmosphere, already explained. This pressure has an obvious tendency to restrain the particles of the liquid, to press them together, and to resist their separation. The repulsive principle of the heat introduced must therefore not only neutralize the cohesion, but must also impart to the atoms of the liquid a sufficient elasticity or repulsive energy to enable them to fly asunder, and assume the vaporous form in spite of this atmospheric resistance. Now it is clear, that if this atmospheric resistance be subject to any variation in its intensity, from causes whether natural or artificial, the repulsive energy necessary to be introduced by the heat, will vary proportionally: if the atmospheric pressure be diminished, then less heat will be necessary to vaporize the liquid. If, on the other hand, this pressure be increased, a greater quantity of heat will be required to impart the necessary elasticity. (17.) From this reasoning we must expect that any cause, whether natural or artificial, which diminishes the atmospheric pressure upon the surface of a liquid, will cause that liquid to boil at a lower temperature: and on the other hand, any cause which may increase the atmospheric pressure upon the liquid, will render it necessary to raise it to a higher temperature before it can boil. These inferences we accordingly find supported by experience. Under a pressure of 15lb. on the square inch, _i. e._ when the barometer is at 30 inches, water boils at the temperature of 212° of the common thermometer. But if water at a lower temperature, suppose 180°, be placed under the receiver of an air-pump, and, by the process of exhaustion the atmospheric pressure be removed, or very much diminished, the water will boil, although its temperature still remain at 180°, as may be indicated by a thermometer placed in it. On the other hand, if a thermometer be inserted air-tight in the lid of a close digester containing water with common atmospheric air above it, when the vessel is heated the air acquires an increased elasticity; and being confined by the cover, presses, with increased force, on the surface of the water. By observing the thermometer while the vessel is exposed to the action of heat, it will be seen to rise considerably above 212°, suppose to 230°, and would continue so to rise until the strength of the vessel could no longer resist the pressure within it. The temperature at which water boils is commonly said to be 212°, which is called _the boiling-point_ of the thermometer; but, strictly speaking, this is only true when the barometer stands at 30 inches. If it be lower, water will boil at a lower temperature, because the atmospheric pressure is less; and if it be higher, as at 31, water will not boil until it receives a higher temperature, the pressure being greater. According as the cohesive forces of the particles of liquids are more or less active, they boil at greater or less temperatures. In general the lighter liquids, such as _alcohol_ and _ether_, boil at lower temperatures. These fluids, in fact, would boil by merely removing the atmospheric pressure, as may be proved by placing them under the receiver of an air-pump, and withdrawing the air. From this we may conclude that these and similar substances would never exist in the liquid state at all, but for the atmospheric pressure. (18.) The elasticity of vapour raised from a boiling liquid, is equal to the pressure under which it is produced. Thus, steam raised from water at 212°, and, therefore, under a pressure of 15lb. on the square inch, is endued with an elastic force which would exert a pressure on the sides of any vessel which confines it, also equal to 15lb. on the square inch. Since an increased pressure infers an increased temperature in boiling, it follows, that where steam of a higher pressure than the atmosphere is required, it is necessary that the water should be boiled at a higher temperature. (19.) We have already stated that there is a certain point at which the temperature of a liquid will cease to rise, and that all the heat communicated to it beyond this is consumed in the formation of vapour. It has been ascertained, that when water boils at 212°, under a pressure equal to 30 inches of mercury, a cubic inch of water forms a cubic foot[4] of steam, the elastic force of which is equal to the atmospheric pressure, and the temperature of which is 212°. Since there are 1728 cubic inches in a cubic foot, it follows, that when water at this temperature passes from the liquid to the vaporous state, it is dilated into 1728 times its bulk. [Footnote 4: The terms _cubic inch_ and _cubic foot_ are easily explained. A common die, used in games of chance, has the figure which is called a cube. It is a solid having twelve straight edges equal to one another. It has six sides, each of which is square, and which are also equal to one another. If its edges be each one inch in length, it is called a _cubic inch_, if one foot, a _cubic foot_, if one yard, a _cubic yard_, &c. This figure is represented in perspective, in fig. 6.] (20.) We have seen that about 1000 degrees of heat must be communicated to any given quantity of water at 212°, in order to convert it into steam of the same temperature, and possessing a pressure amounting to about 15 pounds on the square inch, and that such steam will occupy above 1700 times the bulk of the water from which it was raised. Now we might anticipate, that by abstracting the heat thus employed in converting the liquid into vapour, a series of changes would be produced exactly the reverse of those already described; and such is found to be actually the case. Let us suppose a vessel, the capacity of which is 1728 cubic inches, to be filled with steam, of the temperature of 212°, and exerting a pressure of 15 pounds on the square inch; let 5-1/2 cubic inches of water, at the temperature of 32°, be injected into this vessel, immediately the steam will impart the heat, which it has absorbed in the process of vaporisation to the water thus injected, and will itself resume the liquid form. It will shrink into its primitive dimensions of one cubic inch, and the heat which it will dismiss will be sufficient to raise the 5-1/2 cubic inches of injected water to the temperature of 212°. The contents of the vessel will thus be 6-1/2 cubic inches of water at the temperature of 212°. One of these cubic inches is in fact the steam which previously filled the vessel reconverted into water, the other 5-1/2 are the injected water which has been raised from the temperature of 32° to 212° by the heat which has been dismissed by the steam in resuming the liquid state. It will be observed that in this transmission no temperature is lost, since the cubic inch of water into which the steam is converted has the same temperature as the steam had before the cold water was injected. These consequences are in perfect accordance with the results already obtained from observing the time necessary to convert a given quantity of water into steam by the application of heat. From the present result it follows, that in the reduction of a given quantity of steam to water it parts with as much heat as is sufficient to raise 5-1/2 cubic inches from 32° to 212°, that is, 5-1/2 times 180° or 990°. (21.) There is an effect produced in this process to which it is material that we should attend. The steam which filled the space of 1728 cubic inches shrinks when reconverted into water into the dimensions of 1 cubic inch. It therefore leaves 1727 cubic inches of the vessel it contains unoccupied. By this property steam is rendered instrumental in the formation of a vacuum. By allowing steam to circulate through a vessel, the air may be expelled from it, and its place filled by steam. If the vessel be then closed and cooled the steam will be reduced to water, and, falling in drops on the bottom and sides of the vessel, the space which it filled will become a _vacuum_. This may be easily established by experiment. Let a long glass tube be provided with a hollow ball at one end, and having the other end open.[5] Let a small quantity of spirits be poured in at the open end, and placing the glass ball over the flame of a lamp, let the spirits be boiled. After some time the steam will be observed to issue copiously from the open end of the tube which is presented upwards. When this takes place, let the tube be inverted, and its open end plunged in a basin of cold water. The heat being thus removed, the cool air will reconvert the steam in the tube into liquid, and a vacuum will be produced, into which the pressure of the atmosphere on the surface of the water in the basin will force the water through the tube, and it will rush up with considerable force, and fill the glass ball. [Footnote 5: A common glass flask with a long neck will answer the purpose.] In this experiment it is better to use spirits than water, because they boil at a lower heat, and expose the glass to less liability to break, and also the tube may more easily be handled. CHAPTER II. FIRST STEPS IN THE INVENTION. Futility of early claims. -- Watt, the real Inventor. -- Hero of Alexandria. -- Blasco Garay. -- Solomon de Caus. -- Giovanni Branca. -- Marquis of Worcester. -- Sir Samuel Morland. -- Denis Papin. -- Thomas Savery. (22.) In the history of the progress of the useful arts and manufactures, there is perhaps no example of any invention the credit of which has been so keenly contested as that of the steam engine. Claims to it have been advanced by different nations, and by different individuals of the same nation. The partisans of the competitors for this honour have argued their pretensions, and pressed their claims, with a zeal which has occasionally outstripped the bounds of discretion; and the contest has not unfrequently been tinged with prejudices, both national and personal, and marked with a degree of asperity quite unworthy of so noble a cause, and altogether beneath the dignity of science. The efficacy of the steam engine considered as a mechanical agent depends, first, on the several physical properties from which it derives its operation, and, secondly, on the various pieces of mechanism and details of mechanical arrangement by which these properties are rendered practically available. If the merit of the invention must be ascribed to the discoverer and contriver of these, then the contest will be easily decided, because it will be obvious that the prize is not due to any one individual, but must be distributed in different proportions among several. If, however, he is best entitled to the credit of the invention, who has by the powers of his mechanical genius imparted to the machine that form and those qualities from which it has received its present extensive utility, and by which it has become an agent of transcendent power, which has spread its beneficial effects throughout every part of the civilized globe, then the universal consent of mankind will, as it were by acclamation, award the prize to one individual, whose pre-eminent genius places him far above all other competitors, and from the application of whose mental energies to this machine may be dated those grand effects which have rendered it a topic of interest to every individual for whom the progress of human civilization has any attractions. Before the era marked by the discoveries of JAMES WATT, the steam engine, which has since become an object of such universal interest, was a machine of extremely limited power, greatly inferior in importance to most other mechanical contrivances used as prime movers. But from that time it is scarcely necessary here to state that it became a subject not of British interest only, but one with which the progress of the human race became intimately mixed up. Since, however, the question of the progressive developement of those physical principles on which the steam engine depends, and of their mechanical application, has of late years received some importance, as well from the interest which the public manifest towards them as from the rank of the writers who have investigated them, we have thought it expedient to state briefly, but we trust with candour and fairness, the successive steps which appear to have led to this invention. The engine as it exists at present is not, strictly speaking, the exclusive invention of any one individual: it is the result of a series of discoveries and inventions which have for the last two centuries been accumulating. When we attempt to trace back its history, and to determine its first inventor, we experience the same difficulty as is felt in tracing the head of a great river: as we ascend its course, we are embarrassed by the variety of its tributary streams, and find it impossible to decide which of those channels into which it ramifies ought to be regarded as the principal stream; and it terminates at length in a number of threads of water, each in itself so insignificant as to be unworthy of being regarded as the source of the majestic object which has excited the inquiry. From a very early period the effects of heat upon liquids, and more especially the production of steam or vapour, was regarded as a probable source of mechanical power, and numerous speculators directed their attention to it, and exerted their inventive faculties to derive from it an effective mover. It was not, however, until the commencement of the eighteenth century that any invention was produced which was practically applied, even unsuccessfully. All the attempts previous to that time were either suggestions which were limited to paper or experiments confined to models; or, if they exceeded this, they never outlived a single trial on a larger scale. Nevertheless many of these suggestions and experiments being recorded and accessible to future inquirers doubtless offered useful hints and some practical aid to those more successful investigators who subsequently contrived engines in such forms as to be practically available on a large scale for mechanical purposes. It is right and just, therefore--mere suggestions and abortive experiments though they may have been--to record them, that each inventor and discoverer may receive the just credit due to his share in this splendid mechanical invention. We shall then in the present chapter briefly enumerate, in chronological order, the successive steps so far as they have come to our knowledge. HERO OF ALEXANDRIA, 120 B. C. [Illustration: Fig. 1.] (23.) In a work entitled _Spiritalia seu Pneumatica_, one of the numerous works of this philosopher which has remained to us, is contained a description of a machine moved by vapour of water. A hollow sphere, of which A B represents a section, is supported on two pivots at A and B, which are the extremities of tubes A C D and B E F, which pass into a boiler where steam is generated. This steam flows through small apertures at the extremities A and B, and fills the hollow sphere. One or more horizontal arms K G, I H, project from this sphere, and are likewise filled with steam, but are closed at their extremities. Conceive a small hole made near the extremity G, but at one side of one of the tubes; the steam confined in the tube and globe would immediately rush from the hole with a force proportionate to its pressure within the globe. On the common principle of mechanics a re-action would be produced, and the tube would recoil in the same manner as a gun when discharged. The tubular arm K G being thus pressed in a direction opposed to that in which the steam issues, the sphere would revolve accordingly, and would continue to revolve so long as the steam would continue to flow from the aperture. The force of recoil would be increased by making a similar aperture in two or more arms, care being taken that all the apertures should be placed so as to cause the sphere to revolve in the same direction. This motion being once produced might be transmitted by ordinary mechanical contrivance to any machinery which its power might be adequate to move. This method of using steam is not adopted in any part or any form of the modern steam engine. BLASCO DE GARAY, A. D. 1543. (24.) In the year 1826 there appeared in Zach's Correspondence a communication from Thomas Gonsalez, Director of the Royal Archives of Simancas, giving an account of an experiment reported to have been made in the year 1543 by order of Charles V. in the port of Barcelona. Blasco de Garay, a sea captain, had contrived a machine by which he proposed to propel vessels without oars or sails. Garay concealed altogether the nature of the machine which he used: all that was seen during the experiment was that it consisted of a great boiler for water, and that wheels were kept in revolution at each side of the vessel. The experiment was made upon a vessel called the Trinity, of 200 tons burden, and was witnessed by several official personages, whose presence on the occasion was commanded by the king. One of the witnesses reported that it was capable of moving the vessel at the rate of two leagues in three hours, that the machine was too complicated and expensive, and was exposed to the danger of explosion. The other witnesses, however, reported more favourably. The result of the experiment was thought to be favourable: the inventor was promoted, and received a pecuniary reward, besides having all his expenses defrayed. From the circumstance of the nature of the impelling power having been concealed by the inventor it is impossible to say in what this machine consisted, or even whether steam exerted any agency whatever in it, or, if it did, whether it might not have been, as was most probably the case, a reproduction of Hero's contrivance. It is rather unfavourable to the claims advanced by the advocates of the Spaniard, that although it is admitted that he was rewarded and promoted in consequence of the experiment, yet it does not appear that it was again tried, much less brought into practical use. SOLOMON DE CAUS, 1615. [Illustration: Fig. 2.] (25.) A work entitled "Les Raisons des Forces Mouvantes, avec diverses Machines tant utiles que plaisantes," published at Frankfort in 1615, by Solomon de Caus, a native of France, contains the following theorem:-- "_Water will mount by the help of fire higher than its level_," which is explained and proved in the following terms:-- "The third method of raising water is by the aid of fire. On this principle may be constructed various machines: I shall here describe one. Let a ball of copper marked A, well soldered in every part, to which is attached a tube and stopcock marked D, by which water may be introduced; and also another tube marked B C, which will be soldered into the top of the ball, and the lower end C of which shall descend nearly to the bottom of the ball without touching it. Let the said ball be filled with water through the tube D, then shutting the stopcock D, and opening the stopcock in the vertical tube B C, let the ball be placed upon a fire, the heat acting upon the said ball will cause the water to rise in the tube B C." Such is the description of the apparatus of De Caus as given by himself; and on this has been founded a claim to the invention of the steam engine. It will be observed, that neither in the original theorem nor in the description of the machine which accompanies it, is the word _steam_ anywhere used. Now it was well known, by all conversant in physics, long before the date of the publication containing this description, that atmospheric air when heated acquires an increased elastic force. As the experiment is described, the other part of the ball A is filled with atmospheric air; the heat of the fire acting upon the air through the external surface of the ball, and likewise transmitted through the water, would of course raise the temperature of the air contained in the vessel, would thereby increase its elasticity, and would cause the water to rise in the tube B C, upon a physical principle altogether independent of the qualities of steam. The effect produced, therefore, is just what might have been expected by any one acquainted with the common properties of air, though entirely ignorant of those of steam; and, in point of fact, the pressure of the air is as much concerned in this case in raising the water as the pressure of the steam. This objection, however, is combated by another theorem contained in the same work, in which De Caus speaks of "the strength of the vapour produced by the action of the fire, which causes water to mount; which vapour will issue from the stopcock with great violence after the water has been expelled." If De Caus be admitted to have understood the elastic property of the vapour of water, and to have attributed the ascent of the water in the tube C B to the pressure of that vapour upon the surface of the water confined in the copper ball, it must be admitted that he suggested one of the ways of using the power of steam as a mechanical agent. In the modern steam engine this pressure is not now used against a liquid surface, but against the solid surface of a piston. This, however, should not take from De Caus whatever credit be due to the suggestion of the physical property in question. GIOVANNI BRANCA, 1629. (26.) In a work published at Rome in 1629, entitled "Le Machine del G. Branca," is contained a description of a machine for propelling a wheel by a blast of steam. This contrivance consists of a wheel furnished with flat vanes upon its rim, like the boards of a paddle-wheel. The steam is produced in a close vessel, and made to issue with violence from the extremity of a pipe. Being directed against the vanes, it causes the wheel to revolve, and this motion may be imparted by the usual mechanical contrivances to any machinery which it was intended to move. This contrivance has no analogy whatever to any part of the modern steam engines in any of their various forms. EDWARD SOMERSET, MARQUIS OF WORCESTER, 1663. (27.) Of all the individuals to whom the invention of the steam engine has been ascribed the most celebrated was the Marquis of Worcester, the author of a work entitled "The Scantling of One Hundred Inventions," but which is more commonly known by the title "A Century of Inventions." It is to him that by far the greater number of writers and inquirers on this subject ascribe the merit of the discovery of the invention. This contrivance is described in the following terms in the sixty-eighth invention in the work above named:-- "I have invented an admirable and forcible way to drive up water by fire; not by drawing or sucking it upwards, for that must be, as the philosopher terms it, _infra spæram activitatis_, which is but at such a distance. But this way hath no bounder if the vessels be strong enough. For I have taken a piece of whole cannon whereof the end was burst, and filled it three quarters full of water, stopping and screwing up the broken end, as also the touch-hole and making a constant fire under it; within twenty-four hours, it burst and made a great crack. So that, having a way to make my vessels so that they are strengthened by the force within them, and the one to fill after the other, I have seen the water run like a constant fountain stream forty feet high. One vessel of water rarefied by fire driveth up forty of cold water, and a man that tends the work has but to turn two cocks; that one vessel of water being consumed, another begins to force and refill with cold water, and so successively; the fire being tended and kept constant, which the self-same person may likewise abundantly perform in the interim between the necessity of turning the said cocks." These experiments must have been made before the year 1663, in which the "Century of Inventions" was published. The description of the machine here given, like other descriptions in the same work, was only intended to express the effects produced, and the physical principle on which their production depends. It is, however, sufficiently explicit to enable any one conversant with the subsequent contrivance of Savery, to perceive that Lord Worcester must have contrived a machine containing all that part of Savery's engine in which the direct force of steam is employed. As in the above description, the separate boiler or generator of steam is distinctly mentioned; that the steam from this is conducted into another vessel containing the cold water to be raised; that this water is raised by the pressure of steam acting upon its surface; that when one vessel of water has thus been discharged, the steam acts upon the water contained in another vessel, while the first is being replenished; and that a continued upward current of water is maintained by causing the steam to act alternately upon two vessels, employing the interval to fill one while the water is discharged from the other. On comparing this with the contrivance previously suggested by De Caus, it will be observed, that even if De Caus knew the physical agent by which the water was driven upwards in the apparatus contrived by him, still it was only a means of causing a vessel of boiling water to empty itself; and before a repetition of the process could be obtained, the vessel should be refilled, and again boiled. In the contrivance of Lord Worcester, on the other hand, the agency of the steam was employed in the same manner as it is in the steam engines of the present day, being generated in one vessel, and used for mechanical purposes in another. Nor must this distinction be regarded as trifling and insignificant, because on it depends the whole practicability of using steam as a mechanical agent. Had its action been confined to the vessel in which it was produced, it never could have been employed for any useful purpose. SIR SAMUEL MORLAND, 1683. (28.) It appears, by a MS. in the Harleian Collection in the British Museum, that a mode of applying steam to raise water was proposed to Louis XIV. by Sir Samuel Morland. It contains, however, nothing more than might have been collected from Lord Worcester's description, and is only curious, because of the knowledge the writer appears to have had of the expansion which water undergoes in passing into steam. The following is extracted from the MS.: "The principles of the new force of fire invented by Chevalier Morland in 1682, and presented to his Most Christian Majesty in 1683:--'Water being converted into vapour by the force of fire, these vapours shortly require a greater space (about 2000 times) than the water before occupied, and sooner than be constantly confined would split a piece of cannon. But being duly regulated according to the rules of statics, and by science reduced to measure, weight, and balance, then they bear their load peaceably (like good horses,) and thus become of great use to mankind, particularly for raising water, according to the following table, which shows the number of pounds that may be raised 1800 times per hour to a height of six inches by cylinders half filled with water, as well as the different diameters and depths of the said cylinders.'" DENIS PAPIN, 1695. (29.) Denis Papin, a native of Blois in France, and professor of mathematics at Marbourg, had been engaged about this period in the contrivance of a machine in which the atmospheric pressure should be made available as a mechanical agent by creating a partial vacuum in a cylinder under a piston. His first attempts were directed to the production of this vacuum by mechanical means, having proposed to apply a water-wheel to work an air-pump, and so maintain the degree of rarefaction required. This, however, would eventually have amounted to nothing more than a mode of transmitting the power of the water-wheel to another engine, since the vacuum produced in this way could only give back the power exerted by the water-wheel diminished by the friction of the pumps; still this would attain the end first proposed by Papin, which was merely to transmit the force of the stream of a river, or a fall of water, to a distant point, by partially exhausted pipes or tubes. He next, however, attempted to produce a partial vacuum by the explosion of gunpowder; but this was found to be insufficient, since so much air remained in the cylinder under the piston, that at least half the power due to a vacuum would have been lost. "I have, therefore," proceeds Papin, "attempted to attain this end by another method. Since water being converted into steam by heat acquires the property of elasticity like air, and may afterwards be recondensed so perfectly by cold that there will no longer remain the appearance of elasticity in it, I have thought that it would not be difficult to construct machines in which, by means of a moderate heat, and at a small expense, water would produce that perfect vacuum which has been vainly sought by means of gunpowder." Papin accordingly constructed the model of a machine, consisting of a small pump, in which was placed a solid piston, and in the bottom of the cylinder under the piston was contained a small quantity of water. The piston being in immediate contact with this water, so as to exclude the atmospheric air, on applying fire to the bottom of the cylinder steam was produced, the elastic force of which raised the piston to the top of the cylinder: the fire being then removed, and the cylinder being cooled by the surrounding air, the steam was condensed and reconverted into water, leaving a vacuum in the cylinder into which the piston was pressed by the force of the atmosphere. The fire being applied and subsequently removed, another ascent and descent were accomplished; and in the same manner the alternate motion of the piston might be continued. Papin described no other form of machine by which this property could be rendered available in practice; but he states generally that the same end may be attained by various forms of machines easy to be imagined.[6] [Footnote 6: Recueil de diverses pièces touchant quelques nouvelles machines, p. 38.] THOMAS SAVERY, 1698. (30.) The discovery of the method of producing a vacuum by the condensation of steam was reproduced before 1688, by Captain Thomas Savery, to whom a patent was granted in that year for a steam engine to be applied to the raising of water, &c. Savery proposed to combine the machine described by the Marquis of Worcester, with an apparatus for raising water by suction into a vacuum produced by the condensation of steam. Savery appears to have been ignorant of the publication of Papin, in 1695, and states that his discovery of the condensing principle arises from the following circumstance:-- Having drunk a flask of Florence at a tavern and flung the empty flask on the fire, he called for a basin of water to wash his hands. A small quantity which remained in the flask began to boil and steam issued from its mouth. It occurred to him to try what effect would be produced by inverting the flask and plunging its mouth in the cold water. Putting on a thick glove to defend his hand from the heat, he seized the flask, and the moment he plunged its mouth in the water, the liquid immediately rushed up into the flask and filled it. (21.) Savery stated that this circumstance immediately suggested to him the possibility of giving effect to the atmospheric pressure by creating a vacuum in this manner. He thought that if, instead of exhausting the barrel of a pump by the usual laborious method of a piston and sucker, it was exhausted by first filling it with steam and then condensing the same steam, the atmospheric pressure would force the water from the well into the pump-barrel and into any vessel connected with it, provided that vessel were not more than about 34 feet above the elevation of the water in the well. He perceived, also, that, having lifted the water to this height, he might use the elastic force of steam in the manner described by the Marquis of Worcester to raise the same water to a still greater elevation, and that the same steam which accomplished this mechanical effect would serve by its subsequent condensation to repeat the vacuum and draw up more water. It was on this principle that Savery constructed the first engine in which steam was ever brought into practical operation. CHAPTER III. ENGINES OF SAVERY AND NEWCOMEN. Savery's Engine. -- Boilers and their appendages. -- Working apparatus. -- Mode of Operation. -- Defects of the Engine. -- Newcomen and Cawley. -- Atmospheric Engine. -- Accidental Discovery of Condensation by Jet. -- Potter's Discovery of the Method of Working the Valves. (31.) The steam engine contrived by Savery, like every other which has since been constructed, consists of two parts essentially distinct. The first is that which is employed to generate the steam, which is called the boiler, and the second, that in which the steam is applied as a moving power. The former apparatus in Savery's engine consists of two strong boilers, sections of which are represented at D and E in fig. 7.; D the greater boiler, and E the less. The tubes T and T´ communicate with the working apparatus which we shall presently describe. A thin plate of metal R is applied closely to the top of the greater boiler D turning on a centre C, so that by moving a lever applied to the axis C on the outside of the top, the sliding plate R can be brought from the mouth of the one tube to the mouth of the other alternately. This sliding valve is called the _regulator_, since it is by it that the communications between the boiler and two steam vessels (hereafter described,) are alternately opened and closed, the lever which effects this being constantly wrought by the hand of the attendant. Two _gauge-pipes_ are represented at G, G´, the use of which is to determine the depth of water in the boiler. One G has its lower aperture a little above the proper depth, and the other G´ a little below it. Cocks are attached to the upper ends G, G´, which can be opened or closed at pleasure. The steam collected in the top of the boiler pressing on the surface of the water forces it up in the tubes G, G´, if their lower ends be immersed. Upon opening the cocks G, G´, if water be forced from them, there is too much water in the boiler, since the mouth of G is _below_ its level. If steam issue from both there is too little water in the boiler, since the mouth of G´ is _above_ its level. But if steam issue from G and water from G´ the water in the boiler is at its proper level. This ingenious contrivance for determining the level of the water in the boiler is the invention of Savery, and is used in many instances at the present day. The mouth of G should be at a level of a little less than one-third of the whole depth, and the mouth of G´ at a level a little lower than one-third; for it is requisite that about two-thirds of the boiler should be kept filled with water. The tube I forms a communication between the greater boiler D and the lesser or feeding boiler E, descending nearly to the bottom of it. This communication can be opened and closed at pleasure by the cock K. A gauge pipe is inserted similar to G, G´, but extending nearly to the bottom. From this boiler a tube F extends which is continued to a cistern C (fig. 8.) and a cock is placed at M which, when opened, allows the water from the cistern to flow into the feeding boiler E, and which is closed when that boiler is filled. The manner in which this cistern is supplied will be described hereafter. Let us now suppose that the principal boiler is filled to the level between the gauge-pipes, and that the subsidiary boiler is nearly full of water, the cock K and the gauge cocks G, G´ being all closed. The fire being lighted beneath D and the water boiled, steam is produced and is transmitted through one or other of the tubes T T´, to the working apparatus. When evaporation has reduced the water in D below the level of G´ it will be necessary to replenish the boiler D. This is effected thus. A fire being lighted beneath the feeding boiler E, steam is produced in it above the surface of the water, which having no escape presses on the surface so as to force it up in the pipe I. The cock K being then opened, the boiling water is forced into the principal boiler D, into which it is allowed to flow until water issues from the gauge cock G´. When this takes place, the cock K is closed, and the fire removed from E until the great boiler again wants replenishing. When the feeding boiler E has been exhausted, it is replenished from the cistern C (fig. 8.) through the pipe F by opening the cock M. (32.) We shall now describe the working apparatus in which the steam is used as a moving power. Let V V´ (fig. 8.) be two steam vessels communicating by the tubes T T´ (marked by the same letters in fig. 7.) with the greater boiler D. Let S be a pipe, called the _suction pipe_, descending into the well or reservoir from which the water is to be raised, and communicating with each of the steam vessels through tubes D D´ by valves A A´ which open upwards. Let F be a pipe continued from the level of the engine of whatever higher level it is intended to elevate the water. The steam vessels V V´ communicate with the _force-pipe_ F by valves B B´ which open upward, through the tubes E E´. Over the steam vessels and on the force-pipe is placed a small cistern C already mentioned, which is kept filled with cold water from the force-pipe, and from the bottom of which proceeds a pipe terminated with a cock G. This is called the _condensing pipe_, and can be brought alternately over each steam vessel. From this cistern another pipe communicates with the feeding boiler (fig. 7.) by the cock M.[7] [Footnote 7: This pipe in fig. 9. is represented as proceeding from the force-pipe above the cistern C.] The communication of the pipes T T´ with the boiler can be opened and closed, alternately, by the regulator R, (fig. 7.) already described. Now suppose the steam vessels and tubes to be all filled with common atmospheric air, and that the regulator be placed so that the communication between the tube T and the boiler be opened, the communication between the other tube T´ and the boiler being closed, steam will flow into V through T. At first, while the vessel V is cold, the steam will be condensed and will fall in drops of water on the bottom and sides of the vessel. The continued supply of steam from the boiler will at length impart such a degree of heat to the vessel V that it will cease to condense it. Mixed with the heated air contained in the vessel V, it will have an elastic force greater than the atmospheric pressure, and will therefore force open the valve B, through which a mixture of air and steam will be driven until all the air in the vessel V will have passed out, and it will contain nothing but the pure vapour of water. When this has taken place, suppose the regulator be moved so as to close the communication between the tube T and the boiler, and to stop the further supply of steam to the vessel V; and at the same time let the condensing pipe G be brought over the vessel V and the cock opened so as to let a stream of cold water flow upon it. This will cool the vessel V, and the steam with which it is filled will be condensed and fall in a few drops of water, leaving the interior of the vessel a vacuum. The valve B will be kept closed by the atmospheric pressure. But the elastic force of the air between the valve A and the surface of the water in the well or reservoir, will open A, so that a part of this air will rush in (6.) and occupy the vessel V. The air in the suction pipe S, being thus allowed an increased space, will be proportionably diminished in its elastic force (6.), and its pressure will no longer balance that of the atmosphere acting on the external surface L[8] of the water in the reservoir. This pressure will, therefore, force water up in the tube S until its weight, together with the elastic force of the air above it, balances the atmospheric pressure on L (7.). When this has taken place, the water will cease to ascend. [Footnote 8: Not in the diagram.] Let us now suppose that, by shifting the regulator, the communication is opened between T and the boiler, so that steam flows again into V. The condensing cock G being removed, the vessel will be again heated as before, the air expelled, and its place filled by the steam. The condensing pipe being again allowed to play upon the vessel V, and the further supply of steam being stopped, a vacuum will be produced in V, and the atmospheric pressure on L will force the water through the valve A into the vessel V, which it will nearly fill, a small quantity of air, however, remaining above it. Thus far the mechanical agency employed in elevating the water is the atmospheric pressure; and the power of steam is no further employed than in the production of a vacuum. But, in order to continue the elevation of the water through the force-pipe F, above the level of the steam vessel, it will be necessary to use the elastic pressure of the steam. The vessel V is now nearly filled by the water which has been forced into it by the atmosphere. Let us suppose that, the regulator being shifted again, the communication between the tube T and the boiler is opened, the condensing cock removed, and that steam flows into V. At first coming in contact with the cold surface of the water and that of the vessel, it is condensed; but the vessel is soon heated, and the water formed by the condensed steam collects in a sheet or film on the surface of the water in V, so as to form a surface as hot as boiling water.[9] The steam then being no longer condensed, presses on the surface of the water with its elastic force; and when that pressure becomes greater than the atmospheric pressure, the valve B is forced open and the water, issuing through it, passes through E into the force-pipe F; and this is continued until the steam has forced all the water from V, and occupies its place. [Footnote 9: Hot water being lighter than cold, it floats on the surface.] The further admission of steam through T is once more stopped by moving the regulator; and the condensing pipe being again allowed to play on V, so as to condense the steam which fills it, produces a vacuum. Into this vacuum, as before, the atmospheric pressure on L will force the water, and fill the vessel V. The condensing pipe being then closed and steam admitted through T, the water in V will be forced by its pressure through the valve B and tube E into F, and so the process is continued. We have not yet noticed the other steam vessel V´, which as far as we have described, would have remained filled with common atmospheric air, the pressure of which, on the valve A´, would have prevented the water raised in the suction pipe S from passing through it. However, this is not the case; for, during the entire process which has been described in V, similar effects have been produced in V´, which we have only omitted to notice, to avoid the confusion which the two processes might produce. It will be remembered, that after the steam, in the first instance, having flowed from the boiler through T, has blown the air out of V through B, the communication between T and the boiler is closed. Now the same motion of the regulator which closes this opens the communication between T´ and the boiler; for the sliding plate R (fig. 7.) is moved from the one tube to the other, and at the same time, as we have already stated, the condensing pipe is brought to play on V. While, therefore, a vacuum is being formed in V by condensation, the steam, flowing through T´, blows out the air through B´, as already described in the other vessel V; and, while the air in S is rushing up through A into V followed by the water raised in S by the atmospheric pressure on L, the vessel V´ is being filled with steam, and the air is completely expelled from it. The communication between T and the boiler is now again opened, and the communication between T´ and the boiler closed by moving the regulator R (fig. 7.) from the tube T to T´; at the same time the condensing pipe is removed from over V and brought to play upon V´. While the steam once more expels the air from V through B, a vacuum is formed by condensation in V´, into which the water in S rushes through the valve A´. In the mean time V is again filled with steam. The communication between T and the boiler is now closed, and that between T´ and the boiler is opened, and the condensing pipe removed from V´ and brought to play on V. While the steam from the boiler forces the water in V´ through B´ into the force-pipe F, a vacuum is being produced in V into which water is raised by the atmospheric pressure at L. Thus each of the vessels V V´ is alternately filled from S and the water thence forced into F. The same steam which forces the water from the vessels into F, having done its duty, is condensed, and brings up the water from S by giving effect to the atmospheric pressure. During this process, two alternate motions or adjustments must be constantly made; the communication between T and the boiler must be opened, and that between T´ and the boiler closed, which is done by one motion of the regulator. The condensing pipe at the same time must be brought from V to play on V´ which is done by the lever placed upon it. Again the communication between T´ and the boiler is to be opened, and that between T and the boiler closed; this is done by moving back the regulator. The condensing pipe is brought from V´ to V by moving back the other lever, and so on alternately. For the clearness and convenience of description, some slight and otherwise unimportant changes have been made in the position of the parts.[10] A perspective view of this engine is presented in fig. 9. The different parts already described will easily be recognised, being marked with the same letters as in figs. 6, 7. [Footnote 10: In the diagrams used for explaining the principles and operations of machines, I have found it contribute much to the clearness of the description to adopt an arrangement of parts somewhat different from that of the real machine. When once the nature and principles on which the machine acts are well understood, the reader will find no difficulty in transferring every part to its proper place, which is represented in the perspective drawings.] (33.) In order duly to appreciate the value of improvements, it is necessary first to perceive the defects which these improvements are designed to remove. Savery's steam engine, considering how little was known of the value and properties of steam, and how low the general standard of mechanical knowledge was in his day, is certainly highly creditable to his genius. Nevertheless it had very considerable defects, and was finally found to be inefficient for the most important purposes to which he proposed applying it. At the time of this invention, the mines in England had greatly increased in depth, and the process of draining them had become both expensive and difficult; so much so, that it was found in many instances that their produce did not cover the cost of working them. The drainage of these mines was the most important purpose to which Savery proposed to apply his steam engine. It has been already stated, that the pressure of the atmosphere amounts to about 15 lbs. (3.) on every square inch. Now, a column of water, whose base is one square inch, and whose height is 34 feet, weighs about 15lbs. If we suppose that a perfect vacuum were produced in the steam-vessels V V´ (fig. 8.) by condensation, the atmospheric pressure on L would fail to force up the water, if the height of the top of these vessels exceeded 34 feet. It is plain, therefore, that the engine cannot be more than 34 feet above the water which it is intended to elevate. But in fact it cannot be so much; for the vacuum produced in the steam-vessels V V´ is never perfect. Water, when not submitted to the pressure of the atmosphere, will vaporise at a very low temperature (17.); and it was found that a vapour possessing a considerable elasticity would, notwithstanding the condensation, remain in the vessels V V´ and the pipe S, and would oppose the ascent of the water. In consequence of this, it was found that the engine could never be placed with practical advantage at a greater height than 26 feet above the level of the water to be raised. (34.) When the water is elevated to the engine, and the steam-vessels filled, if steam be introduced above the water in V, it must first balance the atmospheric pressure, before it can force the water through the valve B. Here, then, is a mechanical pressure of 15lbs. per square inch expended, without any water being raised by it. If steam of twice that elastic force be used, it will elevate a column in F of 34 feet in height; and if steam of triple the force be used, it will raise a column of 68 feet high, which, added to 26 feet raised by the atmosphere, gives a total lift of 94 feet. In effecting this, steam of a pressure equal to three times that of the atmosphere acts on the inner surface of the vessels V V´. One third of this bursting of the pressure is balanced by the pressure of the atmosphere on the external surface of the vessels; but an effective pressure of 30lbs. per square inch still remains, tending to burst the vessels. It was found, that the apparatus could not be constructed to bear more than this with safety; and, therefore, in practice the lift of such an engine was limited to about 90 perpendicular feet. In order to raise the water from the bottom of the mine by these engines, therefore, it was necessary to place one at every 90 feet of the depth; so that the water raised by one through the first 90 feet should be received in a reservoir, from which it was to be elevated the next 90 feet by another, and so on. Besides this, it was found that sufficient strength could not be given to those engines, if constructed upon a large scale. They were, therefore, necessarily very limited in their dimensions, and were incapable of raising the water with sufficient speed. Hence arose a necessity for several engines at each level, which greatly enhanced the expense. (35.) These, however, were not the only defects of Savery's engines. The consumption of fuel was enormous, the proportion of heat wasted being much more than what was used in either forcing up the water, or producing a _vacuum_. This will be very easily understood by attending to the process of working the engine already described. When the steam is first introduced from the boiler into the steam-vessels V V´, preparatory to the formation of a vacuum, it is necessary that it should heat these vessels up to the temperature of the steam itself; for until then the steam will be condensed the moment it enters the vessel by the cool surface. All this heat, therefore, spent in raising the temperature of the steam vessels is wasted. Again, when the water has ascended and filled the vessels V V´, and steam is introduced to force this water through B B´ into F, it is immediately condensed by the cold surface in V V´, and does not begin to act until a quantity of hot water, formed by condensed steam, is collected on the surface of the cold water which fills the vessel V V´. Hence another source of the waste of heat arises. When the steam begins to act upon the surface of the water in V V´, and to force it down, the cold surface of the vessel is gradually exposed to the steam, and must be heated while the steam continues its action; and when the water has been forced out of the vessel, the vessel itself has been heated to the temperature of the steam which fills it, all which heat is dissipated by the subsequent process of condensation. It must thus be evident that the steam used in forcing up the water in F, and in producing a vacuum, bears a very small proportion indeed to what is consumed in heating the apparatus after condensation. [Illustration: Pl. I.] (36.) There is also another circumstance which increases the consumption of fuel. The water must be forced through b, not only against the atmospheric pressure, but also against a column of 68 feet of water. Steam is therefore required of a pressure of 45lbs. on the square inch. Consequently the water in the boiler must be boiled under this pressure. That this should take place, it is necessary that the water should be raised to a temperature considerably above 212° (17.), even so high as 267°; and thus an increased heat must be given to the boiler. Independently of the other defects, this intense heat weakened and gradually destroyed the apparatus. Besides the drainage of mines, Savery proposed to apply his steam engine to a variety of other purposes; such as supplying cities with water, forming ornamental waterworks in pleasure grounds, turning mills, &c. Savery was the first who suggested the method of expressing the power of an engine with reference to that of horses. In this comparison, however, he supposed each horse to work but 8 hours a day, while the engine works for 24 hours. This method of expressing the power of steam engines will be explained hereafter. (37.) The failure of the engines proposed by Captain Savery in the great work of drainage, from the causes which have been just mentioned and the increasing necessity for effecting this object arising from the circumstance of the large property in mines, which became every year unproductive by it, stimulated the ingenuity of mechanics to contrive some means of rendering those powers of steam exhibited in Savery's engine practically available. Among others, Thomas Newcomen, a blacksmith of Dartmouth, and John Cawley, a plumber of the same place, turned their attention to this inquiry. Newcomen appears to have resumed the old method of raising the water from the mines by ordinary pumps, but conceived the idea of working these pumps by some moving power less expensive than that of horses. The means whereby he proposed effecting this was by connecting the end of a pump rod D (fig. 10.), by a chain, with the arch-head A of a working beam A B, playing on an axis C. The other arch-head B of this beam was connected by a chain with the rod E of a solid piston P, which moved air-tight in a cylinder F. If a vacuum be created beneath the piston P, the atmospheric pressure acting upon it will press it down with a force of 15 lbs. per square inch; and the end A of the beam being thus raised, the pump-rod D will be drawn up. If a pressure equivalent to the atmosphere be then introduced below the piston, so as to neutralize the downward pressure, the piston will be in a state of indifference as to rising or falling; and if in this case the rod D be made heavier than the piston and its rod, so as to overcome the friction, &c. it will descend, and elevate the piston again to the top of the cylinder. The vacuum being again produced, another descent of the piston, and consequent elevation of the pump-rod, will take place; and so the process may be continued. [Illustration: Pl. II. SAVERY'S STEAM ENGINE.] Such was Newcomen's first conception of the _atmospheric engine_; and the contrivance had much, even at the first view, to recommend it. The power of such a machine would depend entirely on the magnitude of the piston; and being independent of a highly elastic steam, would not expose the materials to the destructive heat which was necessary for working Savery's engine. Supposing a perfect vacuum to be produced under the piston in the cylinder, an effective downward pressure would be obtained, amounting to 15 times as many pounds as there are square inches in the section of the piston.[11] Thus, if the base of the piston were 100 square inches, a pressure equal to 1500lbs. would be obtained. [Footnote 11: As the calculation of the power of an engine depends on the number of square inches in the section of the piston, it may be useful to give a rule for computing the number of square inches in a circle. The following rule will always give the dimensions with sufficient accuracy:--_Multiply the number of inches in the diameter by itself; divide the product by 14, and multiply the quotient thus obtained by 11, and the result will be the number of square inches in the circle._ Thus if there be 12 inches in the diameter, this multiplied by itself gives 144, which divided by 14 gives 10-4/14, which multiplied by 11 gives 115, neglecting fractions. There are, therefore, 115 square inches in a circle whose diameter is 12 inches.] (38.) In order to accomplish this design, two things were necessary: 1. To make a speedy and effectual vacuum below the piston in the descent; and 2. To contrive a counterpoise for the atmosphere in the ascent. The condensation of steam immediately presented itself as the most effectual means of accomplishing the former; and the elastic force of the same steam previous to condensation an obvious method of effecting the latter. Nothing now remained to carry the design into execution, but the contrivance of means for the alternate introduction and condensation of the steam; and Newcomen and Cawley were accordingly granted a patent in 1707, in which Savery was united, in consequence of the principle of condensation for which he had previously received a patent being necessary to the projected machine. We shall now describe the _atmospheric engine_, as first constructed by Newcomen:-- The boiler K is placed over a furnace I, the flue of which winds round it, so as to communicate heat to every part of the bottom of it. In the top, which is hemispherical, two gauge-pipes G G´ are placed, as in Savery's engine, and a _puppet valve_ V, which opens upward, and is loaded at one pound per square inch; so that when the steam produced in the boiler exceeds the pressure of the atmosphere by more than one pound on the square inch, the valve V is lifted, and the steam escapes through it, and continues to escape until its pressure is sufficiently diminished, when the valve V again falls into its seat. The great steam-tube is represented at S, which conducts steam from the boiler to the cylinder; and a feeding pipe T furnished with a cock, which is opened and closed at pleasure, proceeds from a cistern L to the boiler. By this pipe the boiler may be replenished from the cistern, when the gauge cock G´ indicates that the level has fallen below it. The cistern L is supplied with hot water by means which we shall presently explain. (39.) To understand the mechanism necessary to work the piston, let us consider how the supply and condensation of steam must be regulated. When the piston has been forced to the bottom of the cylinder by the atmospheric pressure acting against a vacuum, in order to balance that pressure, and enable it to be drawn up by the weight of the pump-rod, it is necessary to introduce steam from the boiler. This is accomplished by opening the cock R in the steam-pipe S. The steam being thus introduced from the boiler, its pressure balances the action of the atmosphere upon the piston, which is immediately drawn to the top of the cylinder by the weight of the pump-rod D. It then becomes necessary to condense this steam, in order to produce a vacuum. To accomplish this the further supply of steam must be cut off, which is done by closing the cock R. The supply of steam from the boiler being thus suspended, the diffusion of cold water on the external surface of the cylinder becomes necessary to condense the steam within it. This was done by enclosing the cylinder within another, leaving a space between them.[12] Into this space cold water is allowed to flow from a cock M placed over it, which is supplied by a pipe from the cistern N. This cistern is supplied with water by a pump O, which is worked by the engine itself, from the beam above it. [Footnote 12: The external cylinder is not represented in the diagram.] The cold water supplied from M, having filled the space between the two cylinders, abstracts the heat from the inner one; and condensing the steam, produces a vacuum, into which the piston is immediately forced by the atmospheric pressure. Preparatory to the next descent, the water which thus fills the space between the cylinders, and which is warmed by the heat it has abstracted from the steam, must be discharged, in order to give room for a fresh supply of cold water from M. An aperture, furnished with a cock, is accordingly provided in the bottom of the cylinder, through which the water is discharged into the cistern L; and being warm, is adapted for the supply of the boiler through T, as already mentioned. The cock R being now again opened, steam is admitted below the piston, which, as before, ascends, and the descent is again accomplished by opening the cock M, admitting cold water between the cylinders, and thereby condensing the steam below the piston. The condensed steam, thus reduced to water, will collect in the bottom of the cylinder, and resist the descent of the piston. It is, therefore, necessary to provide an exit for it, which is done by a valve opening _outwards_ into a tube which leads to the feeding cistern L, into which the condensed steam is driven. That the piston should continue to be air-tight, it was necessary to keep a constant supply of water over it; this was done by a cock similar to M, which allowed water to flow from the pipe M on the piston. (40.) Soon after the first construction of these engines, an accidental circumstance suggested to Newcomen a much better method of condensation than the effusion of cold water on the external surface of the cylinder. An engine was observed to work several strokes with unusual rapidity, and without the regular supply of the condensing water. Upon examining the piston, a hole was found in it, through which the water, which was poured on to keep it air-tight, flowed, and instantly condensed the steam under it. On this suggestion Newcomen abandoned the external cylinder, and introduced a pipe H furnished with a cock Q into the bottom of the cylinder, so that on turning the cock the pressure of the water in the pipe H, from the level of the water in the cistern N, would force the water to rise as a jet into the cylinder, and would instantly condense the steam. This method of condensing by a jet formed a very important improvement in the engine, and is the method still used. (41.) Having taken a general view of the parts of the atmospheric engine, let us now consider more particularly its operation. When the engine is not working the weight of the pump-rod D draws down the beam A, and draws the piston to the top of the cylinder, where it rests. Let us suppose all the cocks and valves closed, and the boiler filled to the proper depth. The fire being lighted beneath it, the water is boiled until the steam acquires sufficient force to lift the valve V. When this takes place, the engine may be started. For this purpose the regulating valve R is opened. The steam rushes in and is first condensed by the cold cylinder. After a short time the cylinder acquires the temperature of the steam, which then ceases to be condensed, and mixes with the air which filled the cylinder. The steam and heated air, having a greater force than the atmospheric pressure, will open a valve placed at the end X of a small tube in the bottom of the cylinder, and which opens outwards. From this (which is called the _blowing valve_[13]) the steam and air rush in a constant stream until all the air has been expelled, and the cylinder is filled with the pure vapour of water. This process is called _blowing_ the engine preparatory to starting it. [Footnote 13: Also called the _snifting_ valve, from the peculiar noise made by the air and steam escaping from it.] When it is about to be started, the engine-man closes the regulator R, and thereby suspends the supply of steam from the boiler. At the same time he opens the _condensing valve_ H,[14] and thereby throws up a jet of cold water into the cylinder. This immediately condenses the steam contained in the cylinder, and produces the vacuum. (The atmosphere cannot enter the _blowing_ valve, because it opens _outwards_, so that no air can enter to vitiate the vacuum.) The atmospheric pressure above the piston now takes effect, and forces it down in the cylinder. The descent being completed, the engine-man closes the condensing valve H, and opens the regulator R. By this means he stops the play of the jet within the cylinder, and admits the steam from the boiler. The first effect of the steam is to expel the condensing water and condensed steam which are collected in the bottom of the cylinder through the tube Y, containing a valve which opens _outwards_, (called the _eduction valve_,) which leads to the hot cistern L, into which this water is therefore discharged. [Footnote 14: Also called the _injection valve_.] When the steam admitted through R ceases to be condensed, it balances the atmospheric pressure above the piston, and thus permits it to be drawn to the top of the cylinder by the weight of the rod D. This ascent of the piston is also assisted by the circumstance of the steam being somewhat stronger than the atmosphere. When the piston has reached the top, the regulating valve r is closed, and the condensing valve H opened, and another descent produced as before, and so the process is continued. The manipulation necessary in working this engine was, therefore, the alternate opening and closing of two valves; the regulating and condensing valves. When the piston reached the top of the cylinder, the former was to be closed, and the latter opened; and, on reaching the bottom, the former was to be opened, and the latter closed. (42.) From the imperfect attention which even an assiduous attendant could give to the management of these valves, the performance of the engines was very irregular, and the waste of fuel very great, until a boy named _Humphrey Potter_ contrived means of making the engine work its own valves. This contrivance, although made with no other design than the indulgence of an idle disposition, nevertheless constituted a most important step in the progressive improvement of the steam-engine; for by its means, not only the irregularity arising from the negligence of attendants was avoided, but the speed of the engine was doubled. Potter attached strings to the levers which worked the valves, and carrying these strings to the working beam, fastened them upon it in such a manner that as the beam ascended and descended, it pulled the strings so as to open and close the proper valves with the most perfect regularity and certainty. This contrivance was afterwards much improved by an engineer named _Beighton_, who attached to the working beam a straight beam called a _plug frame_, carrying pins which, in the ascent and descent of the beam, struck the levers attached to the valves, and opened and closed them exactly at the proper moment. The engine thus improved required no other attendance except to feed the boiler occasionally by the cock T, and to attend the furnace. CHAP. IV. ENGINE OF JAMES WATT. Advantages of the Atmospheric Engine over that of Captain Savery. -- It contained no new Principle. -- Papin's Engine. -- James Watt. -- Particulars of his Life. -- His first conceptions of the means of Economising Heat. -- Principle of his projected Improvements. (43.) Considered practically, the engine described in the last chapter possessed considerable advantages over that of Savery; and even at the present day this machine is not unfrequently used in districts where fuel is very abundant and cheap, the first cost being considerably less than that of a modern engine. The low pressure of the steam necessary to work it rendered the use of the atmospheric engine perfectly safe; there being only a bursting pressure of about 1lb. per inch, while in Savery's there was a bursting pressure amounting to 30lbs. The temperature of the steam not exceeding 216°, did not weaken or destroy the materials; while Savery's engines required steam raised from water at 267°, which in a short time rendered the engine unable to sustain the pressure. The power of Savery's engines was also very limited, both as to the quantity of water raised, and the height to which it was elevated (34.). On the other hand, the atmospheric engine had no other limit than the dimensions of the piston. In estimating the power of these engines, however, we cannot allow the full atmospheric pressure as an effective force. The condensing water being mixed with the condensed steam, forms a quantity of hot water in the bottom of the cylinder, which, not being submitted to the atmospheric pressure (17.), produces a vapour which resists the descent of the piston. In practice we find that an allowance of at least 3lbs. per square inch should be made for the resistance of this vapour, and 1lb. per square inch for friction, &c.; so that the effective force will be found by subtracting these 4lbs. per square inch from the atmospheric pressure; which, if estimated at 15lbs., leaves an effective working power of about 11lbs. per square inch. This, however, is rather above what is commonly obtained. Another advantage which this engine has over those of Savery, is the facility with which it might be applied to drive machinery by means of the working beam. The merit of this engine as an invention, must be ascribed principally to its mechanism and combinations. We find in it no new principle; the agency of atmospheric pressure acting against a vacuum, or a partial vacuum, was long known. The formation of a vacuum by the condensation of steam had been suggested by Papin and Savery, and carried into practical effect by the latter. The mechanical power derivable from the direct pressure of the elastic force of steam was distinctly pointed out by Lord Worcester, and even prior to his time; the boiler, gauge-pipes, and regulator of the atmospheric engine, were evidently borrowed from Savery's engine. The idea of working a piston in a cylinder by the atmospheric pressure against a vacuum below, was suggested by Otto Guericke, an ingenious German philosopher, the inventor of the air-pump, and subsequently by Papin; and the use of a working beam could not have been unknown. Nevertheless, considerable credit must be acknowledged to be due to Newcomen for the judicious combination of those scattered principles. "The mechanism contrived by him," says Tredgold, "produces all the difference between an efficient and inefficient engine, and should be more highly valued than the fortuitous discovery of a new principle." The rapid condensation of steam by the injection of water, the method of clearing the cylinder of air and water after the stroke, are two contrivances not before in use, and which are quite essential to the effective operation of the engine: these are wholly due to Newcomen and his associates. (44.) The patent of Newcomen was granted in 1705; and in 1707, Papin published a work, entitled "A New Method of raising Water by Fire," in which a steam engine is described, which would scarcely merit notice here but for the contests which have arisen upon the claims of different nations for a share in the invention of the steam engine. The publication of this work of Papin was nine years after Savery's patent, with which he acknowledges himself acquainted, and two years after Newcomen's. The following is a description of Papin's steam engine:-- An oval boiler, A (fig. 11.), is filled to about two thirds of its entire capacity with water, through a valve B in the top, which opens upwards, and is kept down by a lever carrying a sliding weight. The pressure on the valve is regulated by moving the weight to or from B, like the common steelyard. This boiler communicates with a cylinder, C, by a syphon tube furnished with a stopcock at D. The cylinder C has a valve F in the top, closed by a lever and weight similar to B, and a tube with a stopcock G opening into the atmosphere. In this cylinder is placed a hollow copper piston H, which moves freely in it, and floats upon the water. Another tube forms a communication between the bottom of this cylinder and the bottom of a close cylindrical vessel I, called the _air-vessel_. In this tube is a valve at K, opening _upwards_; also a pipe terminated in a funnel, and furnished with a valve L, which opens _downwards_. From the lower part of the air-vessel a tube proceeds, furnished also with a stopcock M, which is continued to whatever height the water is to be raised. Water being poured into the funnel, passes through the valve L, which opens downwards; and filling the tube, ascends into the cylinder C, carrying the floating piston H on its surface, and maintains the same level in C which it has in the funnel. In this manner the cylinder C may be filled to the level of the top of the funnel. In this process the cock G should be left open, to allow the air in the cylinder to escape as the water rises. Let us now suppose that, a fire being placed beneath the boiler, steam is being produced. On opening the cock D, and closing G, the steam, flowing through the syphon tube into the top of the cylinder, presses down the floating piston, and forces the water into the lower tube. The passage at L being stopped, since L opens _downwards_, the water forces open the valve K, and passes into the air-vessel I. When the piston H has been forced to the bottom of the cylinder, the cock D is closed, and G is opened, and the steam allowed to escape into the atmosphere. The cylinder is then replenished from the funnel as before; and the cock G being closed, and D opened, the process is repeated, and more water forced into the air-vessel I. By continuing this process, water is forced into the air-vessel, and the air which originally filled that vessel is compressed into the space above the water; and its elastic force increases exactly in the same proportion as its bulk is diminished. (6.) Now, suppose that half of the vessel I has been filled by the water which is forced in, the air above the water being reduced to half its bulk has acquired twice the elastic force, and therefore presses on the surface of the water with twice the pressure of the atmosphere. Again, if two thirds of the air-vessel be filled with water, the air is compressed into one third of its bulk, and presses on the surface of the water with three times the pressure of the atmosphere, and so on. [Illustration: Pl. III.] Now if the cock M be opened, the pressure of the condensed air will force the water up in the tube N, and it will continue to rise until the column balances the pressure of the condensed air. If, when the water is suspended in the tube, and the cock M open, the vessel I is half filled, the height of the column in N will be 34 feet, because 34 feet of water has a pressure equal to the atmosphere; and this, added to the atmospheric pressure on it, gives a total pressure equal to twice that of the atmosphere, which balances the pressure of the air in I reduced to half its bulk. If two thirds of I be filled with water, a column of 68 feet will be supported in N; for such a column, united with the atmospheric pressure on it, gives a total pressure equal to three times that of the atmosphere, which balances the air in I compressed into one third of its original bulk. By omitting the principle of condensation, this machine loses 26 feet in the perpendicular lift. But, indeed, in every point of view, it is inferior to the engines of Savery and Newcomen. (45.) From the construction of the atmospheric engine by Newcomen, in 1705, for about half a century, no very important step had been made in the improvement of the steam engine. During this time the celebrated Smeaton had given much attention to the details of the atmospheric engine, and brought that machine to as high a state of perfection as its principle seemed to admit, and as it has ever since reached. In the year 1763, JAMES WATT, a name illustrious in the history of mechanical science, commenced his experiments on steam. He was born at Greenock, in the year 1736; and at the age of 16 was apprenticed to a mathematical instrument-maker, with whom he spent four years. At the age of 20 he removed to London, where he still pursued the same trade under a mathematical instrument-maker in that city. After a short time, however, finding his health declining, he returned to Scotland, and commenced business on his own account at Glasgow. In 1757 he was appointed mathematical instrument-maker to the university of Glasgow, where he resided and carried on business. This circumstance produced an acquaintance between him and the celebrated Dr. Robison, then a student in Glasgow, who directed Watt's attention to the steam engine. In his first experiments he used steam of a high-pressure; but found it attended with so much danger of bursting the boiler, and difficulty of keeping the joints tight, and other objections, that he relinquished the inquiry at that time. (46.) In the winter of 1763, Watt was employed to repair the model of an atmospheric engine, belonging to the natural philosophy class in the university--a circumstance which again turned his attention to the subject of the steam engine. He found the consumption of steam in working this model so great, that he inferred that the quantity wasted, must have had a very large proportion to that used in working the piston. His first conclusion was, that the material of the cylinder (brass) was too good a conductor of heat, and that much was thereby lost. He made some experiments, accordingly, with wooden cylinders, soaked in linseed oil, which, however, he soon laid aside. Further consideration convinced him that a prodigious waste of steam was essential to the very principle of the atmospheric engine. This will be easily understood. When the steam has filled the cylinder so as to balance the atmospheric pressure on the piston, the cylinder must have the same temperature as the steam itself. Now, on introducing the condensing jet, the steam mixed with this water forms a mass of hot water in the bottom of the cylinder. This water, not being under the atmospheric pressure, boils at very low temperatures, and produces a vapour which resists the descent of the piston. The heat of the cylinder itself assists this process; so that in order to produce a tolerably perfect vacuum, it was found necessary to introduce a quantity of condensing water, sufficient to reduce the temperature of the water in the cylinder lower than 100°, and consequently to cool the cylinder itself to that temperature. Under these circumstances, the descent of the piston was found to suffer very little resistance from any vapour within the cylinder: but then on the subsequent ascent, an immense waste of steam ensued; for the steam, on being admitted under the piston, was immediately condensed by the cold cylinder and water of condensation, and this continued until the cylinder became again heated up to 212°, to which point the whole cylinder should be heated before the ascent could be completed. Here, then, was an obvious and an extensive cause of the waste of heat. At every descent of the piston, the cylinder should be cooled below 100°; and at every ascent it should be again heated to 212°. It, therefore, became a question whether the force gained by the increased perfection of the vacuum was adequate to the waste of fuel in producing the vacuum; and it was found, on the whole, more profitable not to cool the cylinder to so low a temperature, and consequently to work with a very imperfect vacuum, and a diminished power. Watt, therefore, found the engine involved in this dilemma: either much or little condensation-water must be used. If much were used, the vacuum would be perfect; but then the cylinder would be cooled, and would entail an extensive waste of fuel in heating it. If little were used, a vapour would remain, which would resist the descent of the piston, and rob the atmosphere of a part of its power. The great problem then pressed itself on his attention, _to condense the steam without cooling the cylinder_. From the small quantity of water in the form of steam which filled the cylinder, and the large quantity of injected water to which this communicated heat, Watt was led to inquire what proportion the bulk of water in the liquid state bore to its bulk in the vaporous state; and also what proportion subsisted between the heat which it contained in these two states. He found by experiment that a cubic inch of water formed about a cubic foot of steam; and that the cubic foot of steam contained as much heat as would raise a cubic inch of water to about 1000°. (15.) This gave him some surprise, as the thermometer indicated the same temperature, 212°, for both the steam and the water from which it was raised. What then became of all the additional heat which was contained in the steam, and not indicated by the thermometer? Watt concluded that this heat must be in some way engaged in maintaining the water in its new form. Struck with the singularity of this circumstance, he communicated it to Dr. Black, who then explained to Watt his doctrine of _latent heat_, which he had been teaching for a short time before that, but of which Watt had not previously heard; and thus, says Watt, "I stumbled upon one of the material facts on which that theory is founded." (47.) Watt now gave his whole mind to the discovery of a method of "condensing the steam without cooling the cylinder." The idea occurred to him of providing a vessel separate from the cylinder, in which a constant vacuum might be sustained. If a communication could be opened between the cylinder and this vessel, the steam, by its expansive property, would rush from the cylinder to this vessel, where, being exposed to cold, it would be immediately condensed, the cylinder meanwhile being sustained at the temperature of 212°. This happy conception formed the first step of that brilliant career which has immortalized the name of Watt, and which has spread his fame to the very skirts of civilization. He states, that the moment the notion of "separate condensation" struck him, all the other details of his improved engine followed in rapid and immediate succession, so that in the course of a day his invention was so complete that he proceeded to submit it to experiment. His first notion was, as we have stated, to provide a separate vessel, called a _condenser_, having a pipe or tube communicating with the cylinder. This condenser he proposed to keep cold by being immersed in a cistern of cold water, and by providing a jet of cold water to play within it. When the communication with the cylinder is opened, the steam, rushing into the condenser, is immediately condensed by the jet and the cold surface. But here a difficulty presented itself, viz. how to dispose of the condensing water, and condensed steam, which would collect in the bottom of the condenser. But besides this, a quantity of air or permanent uncondensible gas would collect from various sources. Water in its ordinary state always holds more or less air in combination with it: the air thus combined with the water in the boiler passes through the tubes and cylinder with the steam, and would collect in the condenser. Air also would enter in combination with the condensing water, which would be set free by the heat it would receive from admixture with the steam. The air proceeding from these sources would, as Watt foresaw, accumulate in the condenser, even though the water might be withdrawn from it, and would at length resist the descent of the piston. To remedy this he proposed _to form a communication between the bottom of the condenser and a pump which he called the_ AIR PUMP, _so that the water and air which might be collected in the condenser would be drawn off_; and it was easy to see how this pump could be worked by the machine itself. This constituted the second great step in the invention. To make it air-tight in the cylinder, it had been found necessary to keep a quantity of water supplied above the piston. In the present case, any of this water which might escape through the piston, or between it and the cylinder, would boil, the cylinder being kept at 212°; and would thus, by the steam it would produce, vitiate the vacuum. To avoid this inconvenience, Watt proposed to lubricate the piston, and keep it air-tight, by employing melted wax and tallow. Another inconvenience was still to be removed. On the descent of the piston, the air which must then enter the cylinder would lower its temperature; so that upon the next ascent, some of the steam which would enter it would be condensed, and hence would arise a source of waste. To remove this difficulty, Watt proposed to close the top of the cylinder altogether by an air-tight and steam-tight cover, allowing the piston-rod to play through a hole furnished with a stuffing-box, and _to press down the piston by steam instead of the atmosphere_. This was the third step in this great invention, and one which totally changed the character of the machine. It now became really a _steam engine_ in every sense; for the pressure above the piston was the elastic force of steam, and the vacuum below it was produced by the condensation of steam; so that steam was used both directly and indirectly as a moving power; whereas, in the atmospheric engine, the indirect force of steam only was used, being adopted merely as an easy method of producing a vacuum. The last difficulty respecting the economy of heat which remained to be removed, was the circumstance of the cylinder being liable to be cooled on the external surface by the atmosphere. To obviate this, he first proposed casing the cylinder in wood, that being a substance which conducted heat slowly. He subsequently, however, adopted a different method, and inclosed one cylinder within another, leaving a space between them, which he kept constantly supplied with steam. Thus the inner cylinder was kept continually at the temperature of the steam which surrounded it. The outer cylinder was called the _jacket_.[15] [Footnote 15: It is a remarkable circumstance, that Watt used the same means for keeping the cylinder hot as Newcomen used in his earlier engines to cool it. (38.)] (48.) Watt computed that in the atmospheric engine three times as much heat was wasted in heating the cylinder, &c. as was spent in useful effect. And, as by the improvements proposed by him nearly all this waste was removed, he contemplated, and afterwards actually effected, a saving of three fourths of the fuel. The honour due to Watt for his discoveries is enhanced by the difficulties under which he laboured from contracted circumstances at the time he made them. He relates, that when he was endeavouring to determine the heat consumed in the production of steam, his means did not permit him to use an efficient and proper apparatus, which would have been attended with expense; and it was by experiments made with apothecaries' phials, that he discovered the property already mentioned, which was one of the facts on which the doctrine of latent heat was founded. A large share of the merit of Watt's discoveries has, by some writers, been attributed to Dr. Black, to whose instructions on the subject of latent heat it is said that Watt owed the knowledge of those facts which led to his improvements. Such, however, was not the case; and the mistake arose chiefly from some passages respecting Watt in the works of Dr. Robison, in one of which he states that Watt had been a _pupil_ and intimate friend of Dr. Black; and that he attended two courses of his lectures at college in Glasgow. Such, however, was not the case; for "Unfortunately for me," says Watt in a letter to Dr. Brewster, "the necessary avocations of my business prevented me from attending his or any other lectures at college. In further noticing Dr. Black's opinion, that his fortunate observation of what happens in the formation and condensation of elastic vapour 'has contributed in no inconsiderable degree to the public good, by suggesting to my friend Mr. Watt of Birmingham, then of Glasgow, his improvements on the steam-engine,' it is very painful for me to controvert any opinion or assertion of my revered friend; yet, in the present case, I find it necessary to say, that he appears to me to have fallen into an error. These improvements proceeded upon the established fact, that steam was condensed by the contact of cold bodies, and the later known one, that water boiled at heats below 100°, and consequently that a vacuum could not be obtained unless the cylinder and its contents were cooled every stroke below the heat." CHAPTER V. WATT'S SINGLE-ACTING STEAM ENGINE. Expansive Principle applied. -- Failure of Roebuck, and Partnership with Bolton. -- Patent extended to 1800. -- Counter. -- Difficulties in getting the Engines into use. (49.) The first machine in which Watt realised the conceptions which we mentioned in the last chapter, is that which was afterwards called his _Single-acting Steam Engine_. We shall now describe the working apparatus in this machine. The cylinder is represented at C (fig. 12.)--in which the piston P moves steam-tight. It is closed at the top, and the piston-rod being very accurately turned, runs in a steam-tight collar B furnished with a stuffing-box, and constantly supplied with melted tallow or wax. Through a funnel in the top of the cylinder, melted grease flows upon the piston so as to maintain it steam-tight. Two boxes A A, containing the valves for admitting and withdrawing the steam, connected by a tube of communication T, are attached to the cylinder; the action of these valves will be presently described. Below the cylinder, placed in a cistern of cold water, is a close cylindrical vessel D, called the condenser, communicating with the cylinder by a tube T´, leading to the lower valve-box A. In the side of this condenser is inserted a tube, the inner end of which is pierced with holes like the rose of a watering-pot; and a cock E in the cold cistern is placed on the outside, through which, when open, the water passing, rises in a jet on the inside. The tube S, which conducts steam from the boiler, enters the top of the upper valve-box at F. Immediately under it is placed a valve G, which is opened and closed by a lever or rod G´. This valve, when open, admits steam to the top of the piston, and also to the tube T, which communicates between the two valve-boxes, and when closed suspends the admission of steam. There are two valves in the lower box, one H in the top worked by the lever H´, and one I in the bottom worked by the lever I´. The valve H, when open, admits steam to pass from the cylinder _above_ the piston, by the tube T, to the cylinder _below_ the piston, the valve I being supposed in this case to be closed. This valve I, when open, (the valve H being closed,) admits steam to pass from below the cylinder through T´ to the condenser. This steam, entering the condenser, meets the jet, admitted to play by the valve E, and is condensed. The valve G is called the _upper steam valve_; H, _lower steam valve_; I, the _exhausting-valve_; and E, the _condensing valve_. Let us now consider how these valves must be worked in order to produce the alternate ascent and descent of the piston. It is in the first place necessary that all the air which fills the cylinder, tubes, and condenser should be expelled. To accomplish this it is only necessary to open at once the valves G, H, and I. The steam then rushing from F through the valve G will pass into the upper part of the cylinder, and through the tube T and the valve H into the lower part, and also through the valve I into the condenser. After the steam ceases to be condensed by the cold of the apparatus, it will rush out mixed with air through the valve M, which opens outward; and this will continue until all the air has been expelled, and the apparatus filled with pure steam. Then suppose all the valves again closed. The cylinder both above and below the piston is filled with steam; and the steam which filled the condenser being cooled by the cold surface, a vacuum has been produced in that vessel. The apparatus being in this state, let the upper steam valve G, the exhausting-valve I, and the condensing valve E be opened. Steam will thus be admitted through G to press on the top of the piston; and this steam will be prevented from circulating to the lower part of the cylinder by the lower steam-valve H being closed. Also the steam which filled the cylinder below the piston rushes through the open exhausting-valve I to the condenser, where it meets the jet allowed to play by the open condensing valve E. It is thus instantly condensed, and a vacuum is left in the cylinder below the piston. Into this vacuum the piston is pressed without resistance by the steam which is admitted through G. When the piston has thus been forced to the bottom of the cylinder, let the three valves G, I, and E, which were before opened, be closed, and let the lower steam-valve H be opened. The effects of this change are easily perceived. By closing the upper steam-valve G, the further admission of steam to the apparatus is stopped. By closing the exhausting-valve I, all transmission of steam from the cylinder to the condenser is stopped. Thus the steam which is _in_ the cylinder, valve-boxes, and tubes is shut up in them, and no more admitted, nor any allowed to escape. By closing the condensing valve E, the play of the jet in the condenser is suspended. Previously to opening the valve H, the steam contained in the apparatus was confined to the part of the cylinder _above_ the piston and the tube T and the valve-box A. But on opening this valve, the steam is allowed to circulate above and below the piston; and in fact through every part included between the upper steam valve G, and the exhausting-valve I. The same steam circulating on both sides, the piston is thus equally pressed upward and downward. In this case there is no force tending to retain the piston at the bottom of the cylinder except its own weight. Its ascent is produced in the same manner as the ascent of the piston in the atmospheric engine. The piston-rod is connected by chains G to the arch-head of the beam, and the weight of the pump-rod R, or any other counterpoise acting on the chains suspended from the other arch-head, draws the piston to the top of the cylinder. When the piston has arrived at the top of the cylinder, suppose the three valves G, I, and E to be again opened, and H closed. Steam passes from the steam-pipe F through the upper steam-valve G to the top of the piston, and at the same time the steam which filled the cylinder below the piston is drawn off through the open exhausting-valve I into the condenser, where it is condensed by the jet allowed to play by the open condensing valve E. The pressure of the steam above the piston then forces it without resistance into the vacuum below it, and so the process is continued. It should be remembered, that of the four valves necessary to work the piston, three are to be opened the moment the piston reaches the top of the cylinder, and the fourth is to be closed; and on the piston arriving at the bottom of the cylinder, these three are to be closed and the fourth opened. The three valves which are thus opened and closed together are the upper steam-valve, the exhausting-valve, and the condensing valve. The lower steam-valve is to be opened at the same instant that these are closed, and _vice versâ_. The manner of working these valves we shall describe hereafter. The process which has just been described, if continued for any considerable number of reciprocations of the piston, would be attended with two very obvious effects which would obstruct and finally destroy the action of the machine. First, the condensing water and condensed steam would collect in the condenser D, and fill it; and secondly, the water in the cistern in which the condenser is placed would gradually become heated, until at last it would not be cold enough to condense the steam when introduced in the jet. Besides this, it will be recollected that water boils in a vacuum at a very low temperature (17); and, therefore, the hot water collected in the bottom of the condenser would produce steam which, rising into the cylinder through the exhausting-valve, would resist the descent of the piston, and counteract the effects of the steam above it. A further disadvantage arises from the air or other permanently elastic fluid which enters in combination with the water, both in the boiler and condensing jet, and which is disengaged by its own elasticity. To remove these difficulties, a pump is placed near the condenser communicating with it by a valve M, which opens from the condenser into the pump. In this pump is placed a piston which moves air-tight, and in which there is a valve N, which opens upwards. Now suppose the piston at the bottom of the pump. As it rises, since the valve in it opens _upwards_, no air can pass _down_ through it, and consequently it leaves a vacuum _below_ it. The water and any air which may be collected in the condenser open the valve M, and pass into the lower part of the pump from which they cannot return in consequence of the valve M opening _outwards_. On the descent of the pump-piston, the fluids which occupy the lower part of the pump, force open the piston-valve N; and passing through it, get _above_ the piston, from which their return is prevented by the valve N. In the next ascent, the piston lifts these fluids to the top of the pump, whence they are discharged through a conduit into a small cistern B by a valve K which opens outwards. The water which is thus collected in B is heated by the condensed steam, and is reserved in B, which is called the hot well for feeding the boiler, which is effected by means which we shall presently explain. The pump which draws off the hot water and air from the condenser is called the _air-pump_. (50.) We have not yet explained the manner in which the valves and the air-pump piston are worked. The rod Q of the latter is connected with the working beam, and the pump is therefore wrought by the engine itself. It is not very material to which arm of the beam it is attached. If it be on the same side of the centre of the beam with the cylinder, it rises and falls with the steam-piston; but if it be on the opposite side, the pump-piston rises when the steam-piston falls, and _vice versâ_. In the single-engine there are some advantages in the latter arrangement. As the steam-piston _descends_, the steam rushes into the condenser, and the jet is playing; and this, therefore, is the most favourable time for drawing out the water and condensed steam from the condenser by the ascent of the pump-piston, since by this means the descent of the steam-piston is assisted; an effect which would not be produced if the steam-piston and pump-piston descended together. With respect to the method of opening and closing the valves, it is evident that the three valves which are simultaneously opened and closed may be so connected as to be worked by the same lever. This lever may be struck by a pin fixed upon the rod Q of the air-pump, so that when the pistons have arrived at the top of the cylinders the pin strikes the lever and opens the three valves. A catch or detent is provided for keeping them open during the descent of the piston, from which they are disengaged in a similar manner on the arrival of the piston at the bottom of the cylinder, and they close by their own weight. In exactly the same way the lower steam-valve is opened on the arrival of the piston at the bottom of the cylinder, and closed on its arrival at the top by the action of a pin placed on the piston-rod of the air-pump. (51.) Soon after the invention of these engines, Watt found that in some instances inconvenience arose from the too rapid motion of the steam-piston at the end of its stroke, owing to its being moved with an _accelerated motion_. This was owing to the uniform action of the steam-pressure upon it: for upon first putting it in motion at the top of the cylinder, the motion was comparatively slow; but from the continuance of the same pressure the velocity with which the piston descended was continually increasing, until it reached the bottom of the cylinder, where it acquired its greatest velocity. To prevent this, and to render the descent as nearly as possible uniform, it was proposed to cut off the steam before the descent was completed, so that the remainder might be effected merely by the expansion of the steam which was admitted to the cylinder. To accomplish this, he contrived, by means of a pin on the rod of the air-pump, to close the upper steam-valve when the steam-piston had completed one-third of its entire descent, and to keep it closed during the remainder of the descent, and until the piston again reached the top of the cylinder. By this arrangement the steam pressed the piston with its full force through one-third of the descent, and thus put it into motion; during the other two thirds the steam thus admitted acted merely by its expansive force, which became less in exactly the same proportion as the space given to it by the descent of the piston increased. Thus, during the last two thirds of the descent the piston is urged by a gradually decreasing force, which in practice was found just sufficient to sustain in the piston a uniform velocity. (52.) We have already mentioned the difficulty arising from the water in the cistern, in which the condenser and air-pump are placed, becoming heated, and the condensation therefore being imperfect. To prevent this, a waste-pipe is placed in this cistern, from which the water is continually discharged, and a pump L (called the _cold-water-pump_) is worked by the engine itself, which raises a supply of cold water and sends it through a pipe in a constant stream into the cold cistern. The waste-pipe, through which the water flows from the cistern, is placed near the top of it, since the heated water, being lighter than the cold, remains on the top. Thus the heated water is continually flowing off, and a constant stream of cold water supplied. The piston-rod of the cold-water-pump is attached to the beam (by which it is worked), usually on the opposite side from the cylinder. Another pump O (called the _hot-water-pump_) enters the _hot well_ B; and raising the water from it, forces it through a tube to the boiler for the purpose of feeding it. The manner in which this is effected will be more particularly described hereafter. A part of the heat which would otherwise be lost, is thus restored to the boiler to assist in the production of fresh steam. We may consider a portion of the heat to be in this manner _circulating_ continually through the machine. It proceeds from the boiler in steam, works the piston, passes into the condenser, and is reconverted into hot water; thence it is passed to the hot well, from whence it is pumped back into the boiler, and is again converted into steam, and so proceeds in constant circulation. From what has been described, it appears that there are four pistons attached to the great beam and worked by the piston of the steam-cylinder. On the same side of the centre with the cylinder is the piston-rod of the air-pump, and on the opposite side are the piston-rods of the hot-water pump and the cold-water-pump; and lastly, at the extremity of the beam opposite to that at which the steam-piston works, is the piston of the pump to be wrought by the engine. (53.) The position of these piston-rods with respect to the centre of the beam depends on the play necessary to be given to the piston. If the play of the piston be short, its rod will be attached to the beam near the centre; and if longer, more remote from the centre. The cylinder of the air-pump is commonly half the length of the steam-cylinder, and its piston-rod is attached to the beam at the point exactly in the middle between the end of the beam and the centre. The hot-water pump not being required to raise a considerable quantity of water, its piston requires but little play, and is therefore placed near the centre of the beam, the piston-rod of the cold-water pump being farther from the centre. (54.) It appears to have been about the year 1763, that Watt made these improvements in the steam engine, and constructed a model which fully realized his expectations. Either from want of influence or the fear of prejudice and opposition, he did not make known his discovery or attempt to secure it by a patent at that time. Having adopted the profession of a land surveyor, his business brought him into communication with Dr. Roebuck, at that time extensively engaged in mining speculations, who possessed some command of capital, and was of a very enterprising disposition. By Roebuck's assistance and countenance, Watt erected an engine of the new construction at a coal mine on the estate of the Duke of Hamilton, at Kinneil near Burrowstoness. This engine being a kind of experimental one, was improved from time to time as circumstances suggested, until it reached considerable perfection. While it was being erected, Watt in conjunction with Roebuck applied for and obtained a patent to secure the property in the invention. This patent was enrolled in 1769, six years after Watt invented the improved engine. Watt was now preparing to manufacture the new engines on an extensive scale, when his partner Roebuck suffered a considerable loss by the failure of a mining speculation in which he had engaged, and became involved in embarrassments, so as to be unable to make the pecuniary advances necessary to carry Watt's designs into execution. Again disappointed, and harassed by the difficulties which he had to encounter, Watt was about to relinquish the further prosecution of his plans, when Mr. Matthew Bolton, a gentleman who had established a factory at Birmingham a short time before, made proposals to purchase Dr. Roebuck's share in the patent, in which he succeeded; and in 1773, Watt entered into partnership with Bolton. His situation was now completely changed. Bolton was not only a man of extensive capital, but also of considerable personal influence, and had a disposition which led him, from taste, to undertakings which were great and difficult, and which he prosecuted with the most unremitting ardency and spirit. "Mr. Watt," says Playfair, "was studious and reserved, keeping aloof from the world; while Mr. Bolton was a man of address, delighting in society, active, and mixing with people of all ranks with great freedom, and without ceremony. Had Mr. Watt searched all Europe, he probably would not have found another person so fitted to bring his invention before the public, in a manner worthy of its merit and importance; and although of most opposite habits, it fortunately so happened that no two men ever more cordially agreed in their intercourse with each other." The delay in the progress of the manufacture of engines occasioned by the failure of Dr. Roebuck was such, that Watt found that the duration of his patent would probably expire before he would even be reimbursed the necessary expenses attending the various arrangements for the manufacture of the engines. He therefore, with the advice and influence of Bolton, Roebuck, and other friends, in 1775, applied to parliament for an extension of the terms of his patent, which was granted for 25 years from the date of his application, so that his exclusive privilege should expire in 1800. An engine was now erected at Soho (the name of Bolton's factory) as a specimen for the examination of mining speculators, and the engines were beginning to come into demand. The manner in which Watt chose to receive remuneration from those who used his engines was as remarkable for its ingenuity as for its fairness and liberality. He required that one-third of the saving of coals effected by his engines, compared with the atmospheric engines hitherto used, should be paid to him, leaving the benefit of the other two-thirds to the public. Accurate experiments were made to ascertain the saving of coals; and as the amount of this saving in each engine depended on the length of time it was worked, or rather on the number of descents of the piston, Watt invented a very ingenious method of determining this. The vibrations of the great working beam were made to communicate with a train of wheelwork, in the same way as those of a pendulum communicate with the work of a clock. Each vibration of the beam moved one tooth of a small wheel, and the motion was communicated to a hand or index, which moved on a kind of graduated plate like the dial plate of a clock. The position of this hand marked the number of vibrations of the beam. This apparatus, which was called the _counter_, was locked up and secured by two different keys, one of which was kept by the proprietor, and the other by Bolton and Watt, whose agents went round periodically to examine the engines, when the counters were opened by both parties and examined, and the number of vibrations of the beam determined, and the value of the patent third found.[16] [Footnote 16: The extent of the saving in fuel may be judged from this: that for three engines erected at Chacewater mine in Cornwall, it was agreed by the proprietors that they would compound for the patent third at 2400_l._ per annum; so that the whole saving must have exceeded 7200_l._ per annum.] Notwithstanding the manifest superiority of these engines over the old atmospheric engines; yet such were the influence of prejudice and the dislike of what is new, that Watt found great difficulties in getting them into general use. The comparative first cost also probably operated against them; for it was necessary that all the parts should be executed with great accuracy, which entailed proportionally increased expense. In many instances they felt themselves obliged to induce the proprietors of the old atmospheric engines to replace them by the new ones, by allowing them in exchange an exorbitant price for the old engines; and in some cases they were induced to erect engines at their own expense, upon an agreement that they should only be paid if the engines were found to fulfil the expectations, and brought the advantages which they promised. It appeared since, that Bolton and Watt had actually expended a sum of nearly 50,000_l._ on these engines before they began to receive any return. When we contemplate the immense advantages which the commercial interests of the country have gained by the improvements in the steam engine, we cannot but look back with disgust at the influence of that fatal prejudice which opposes the progress of improvement under the pretence of resisting innovation. It would be a problem of curious calculation to determine what would have been lost to the resources of this country, if chance had not united the genius of such a man as Watt with the spirit, enterprise, and capital, of such a man as Bolton! The result would reflect little credit on those who think novelty alone a sufficient reason for opposition. CHAPTER VI. DOUBLE-ACTING STEAM ENGINE. The Single-Acting Engine unfit to impel Machinery. -- Various contrivances to adapt it to this purpose. -- Double-Cylinder. -- Double-Acting Cylinder. -- Various mode of connecting the Piston with the Beam. -- Rack and Sector. -- Double Chain. -- Parallel Motion. -- Crank. -- Sun and Planet Motion. -- Fly Wheel. -- Governor. In the atmospheric engine of Newcomen, and in the improved steam engine of Watt, described in the last chapter, the action of the moving power is an intermitting one. While the piston descends, the moving power is in action, but its action is suspended during the ascent. Thus the opposite or working end of the beam can only be applied in cases where a lifting power is required. This action is quite suitable to the purposes of pumping, which was the chief or only object to which the steam engine had hitherto been applied. In a more extended application of the machine, this intermission of the moving power and its action taking place only in one direction would be inadmissible. To drive the machinery generally employed in manufactures a constant and uniform force is required; and to render the steam engine available for this purpose, it would be necessary that the beam should be driven by the moving power as well in its ascent as in its descent. When Watt first conceived the notion of extending the application of the engine to manufactures generally, he proposed to accomplish this double action upon the beam by placing a steam cylinder under each end of it, so that while each piston would be ascending, and not impelled by the steam, the other would be descending, being urged downwards by the steam above it acting against the vacuum below. Thus, the power acting on each during the time when its action on the other would be suspended, a constant force would be exerted upon the beam, and the uniformity of the motion would be produced by making both cylinders communicate with the same boiler, so that both pistons would be driven by steam of the same pressure. One condenser might also be used for both cylinders, so that a similar vacuum would be produced under each. This arrangement, however, was soon laid aside for one much more simple and obvious. This consisted in the production of exactly the same effect by a single cylinder in which steam was introduced alternately above and below the piston, being at the same time withdrawn by the condenser at the opposite side. Thus the piston being at the top of the cylinder, steam is introduced from the boiler above it, while the steam in the cylinder below it is drawn off by the condenser. The piston, therefore, is pressed from above into the vacuum below, and descends to the bottom of the cylinder. Having arrived there, the top of the cylinder is cut off from all communication with the boiler; and, on the other hand, a communication is opened between it and the condenser. The steam which has pressed the piston down is therefore drawn off by the condenser, while a communication is opened between the boiler and the bottom of the cylinder, so that steam is admitted below the piston: the piston, thus pressed from below into the vacuum above, ascends, and in the same way the alternate motion is continued. Such is the principle of what is called the _Double-acting Steam Engine_, in contradistinction to that described in the last chapter, in which the steam acts only above the piston while a vacuum is produced below it. It is evident that, in the arrangement now described, the condenser must be in constant action: while the piston is descending the condenser must draw off the steam below it, and while it is ascending, it must draw off the steam above it. As steam, therefore, must be constantly drawn into the condenser, the jet of cold water which condenses the steam must be kept constantly playing. This jet, therefore, will not be worked by the valve alternately opening and closing, as in the single engine, but will be worked by a cock, the opening of which will be adjusted according to the quantity of cold water necessary to condense the steam. When the steam is used at a low pressure, and, therefore, in a less compressed state, less condensing water would be necessary than when it is used at a higher pressure and in a more compressed state. In the one case, therefore, the condensing cock would be less open than in the other. Again, the quantity of condensing water must vary with the speed of the engine, because the greater the speed of the engine, the more rapidly will the steam flow from the cylinder into the condenser; and, as the same quantity of steam requires the same quantity of condensing water, the supply of the condensing water must be proportional to the speed of the engine. In the double-acting engine, then, the jet cock is regulated by a lever or index which moves upon a graduated arch, and which is regulated by the engineer according to the manner in which the engine works. This change in the action of the steam upon the piston rendered it necessary to make a corresponding change in the mechanism by which the piston-rod was connected with the beam. In the single acting engine, the piston-rod pulled the end of the beam down during the descent, and was pulled up by it in the ascent. The connection by which this action was transmitted between the beam and piston was, as we have seen, a flexible chain passing from the end of the piston and playing upon the arch-head of the beam. Now, where the mechanical action to be transmitted is a _pull_, and not a _push_, a flexible chain, or cord, or strap, is always sufficient; but if a _push_ or _thrust_ is required to be transmitted, then the flexibility of the medium of mechanical communication afforded by a chain, renders it inapplicable. In the double-acting engine, during the descent, the piston-rod still pulls the beam down, and so far a chain connecting the piston-rod with the beam would be sufficient to transmit the action of the one to the other; but in the ascent the beam no longer pulls up the piston-rod, but is pushed up by it. A chain from the piston-rod to the arch-head, as described in the single acting engine, would fail to transmit this force. If such a chain were used with the double engine, where there is no counter weight on the opposite end of the beam, the consequence would be, that in the ascent of the piston the chain would slacken, and the beam would still remain depressed. It is therefore necessary that some other mechanical connection be contrived between the piston-rod and the beam, of such a nature that in the _descent_ the piston-rod may _pull_ the beam down, and may _push_ it up in the _ascent_. Watt first proposed to effect this by attaching to the end of the piston-rod a straight rack, faced with teeth, which should work in corresponding teeth raised on the arch-head of the beam as represented in fig. 13. If his improved steam engines required no further precision of operation and construction than the atmospheric engines, this might have been sufficient; but in these engines it was indispensably necessary that the piston-rod should be guided with a smooth and even motion through the stuffing-box in the top of the cylinder, otherwise any shake or irregularity would cause it to work loose in the stuffing-box, and either to admit the air, or to let the steam escape. In fact, it was necessary to turn these piston-rods very accurately in the lathe, so that they may work with sufficient precision in the cylinder. Under these circumstances, the motion of the rack and toothed arch-head were inadmissible, since it was impossible by such means to impart to the piston-rod that smooth and equable motion which was requisite. Another contrivance which occurred to Watt was, to attach to the top of the piston-rod a bar which should extend above the beam, and to use two chains or straps, one extending from the top of the bar to the lower end of the arch-head, and the other from the bottom of the bar to the upper end of the arch-head. By such means the latter strap would pull the beam down when the piston would descend, and the former would pull the beam up when the piston would ascend. These contrivances, however, were superseded by the celebrated mechanism, since called the _Parallel Motion_, one of the most ingenious mechanical combinations connected with the history of the steam engine. It will be observed that the object was to connect by some inflexible means the end of the piston-rod with the extremity of the beam, and so to contrive the mechanism, that while the end of the beam would move alternately up and down in a circle, the end of the piston-rod connected with the beam should move exactly up and down in a straight line. If the end of the piston-rod were fastened upon the end of the beam by a pivot without any other connexion, it is evident that, being moved up and down in the arch of a circle, it would be bent to the left and the right alternately, and would consequently either be broken, or would work loose in the stuffing box. Instead of connecting the end of the rod immediately with the end of the beam by a pivot, Watt proposed to connect them by certain moveable rods so arranged that, as the end of the beam would move up and down in the circular arch, the rods would so accommodate themselves to that motion, that the end connected with the piston-rod should not be disturbed from its rectilinear course. To accomplish this, he conceived the notion of connecting three rods in the following manner:--A B and C D (fig. 14.), are two rods or levers turning on fixed pivots or centres at A and C. A third rod, B D, is connected with them by pivots placed at their extremities, B and D, and the lengths of the rods are so adjusted that when A B and C D are horizontal, B D shall be perpendicular or vertical, and that A B and C D shall be of equal lengths. Now, let a pencil be imagined to be placed at P, exactly in the middle of the rod B D: if the rod A B be caused to move up and down like the beam of the steam engine in the arch represented in the figure, it is clear, from the mode of their connexion, that the rod C D will be moved up and down in the other arch. Now Watt conceived that, under such circumstances, the pencil P would be moved up and down in a perpendicular straight line. However difficult the first conception of this mechanism may have been, it is easy to perceive why the desired effect will be produced by it. When the rod A B rises to the upper extremity of the arch, the point B departs a little to the right; at the same time, the point D is moved a little to the left. Now the extremities of the rod B D being thus at the same time, carried slightly in opposite directions, the pencil in the middle of it will ascend directly upwards; the one extremity of the rod having a tendency to draw it as much to the right as the other has to draw it to the left. In the same manner, when the rod A B moves to the lower extremity of the arch, the rod C D will be likewise moved to the lower extremity of its arch. The point B is thus transferred a little to the right, and the point D to the left; and, for the same reason as before, the point P in the middle will move neither to the right nor to the left, but straight downwards.[17] [Footnote 17: In a strict mathematical sense, the path of the point P is a curve of a high order, but in the play which is given to it in the application used in the steam engine, it describes only a part of its entire locus; and this part extending equally on each side of a point of inflection, its radius of curvature is infinite, so that, in practice, the deviation from a straight line, when proper proportions are observed in the rods, and too great a play not given to them, is insignificant.] Now Watt conceived that his object would be attained if he could contrive to make the beam perform the part of A B in fig. 14., and to connect with it other two rods, C D and D B, attaching the end of the piston to the middle of the rod D B. The practical application of this principle required some modification, but is as elegant as the notion itself is ingenious. The apparatus adopted for carrying it into effect is represented on the arm which works the piston in fig. 15. The beam, moving on its axis C, every point in its arm moves in the arc of a circle of which C is the centre. Let B be the point which divides the arm A C into equal parts, A B and B C; and let D E be a straight rod equal in length to C B, and playing on the fixed centre or pivot D. The end E of this rod is connected by a straight bar, E B, with the point B, by pivots at B and E on which the rod B E plays freely. If the beam be supposed to move alternately on its axis C, the point B will move up and down in a circular arc, of which C is the centre, and at the same time the point E will move in an equal circular arc round the point D as a centre. According to what we have just explained, the middle point F of the rod B E will move up and down in a straight line. Also, let a rod, A G, equal in length to B E, be attached to the end A of the beam by a pivot on which it moves freely, and let its extremity G be connected with E by a rod, G E, equal in length to A B, and playing on pivots at G and E. By this arrangement the joint A G being always parallel to B E, the three points C, A, and G will be in circumstances precisely similar to the points C, B, and F, except that the system C A G will be on a scale of double the magnitude of C B F: C A being twice C B, and A G twice B F, it is clear, then, that whatever course the point F may follow, the point G must follow a similar line,[18] but will move twice as fast. But, since the point F has been already shown to move up and down in a straight line, the point G must also move up and down in a straight line, but of double the length.[19] [Footnote 18: It is, in fact, the principle of the pantograph. The points C, F, and G evidently lie in the same straight line, since C B : C A :: B F : A G, and the latter lines are parallel. Taking C as the common _pole_ of the _loci_ of the points F G, the _radius vector_ of the one will always be twice the corresponding _radius vector_ of the other; and therefore these curves are similar, similarly placed, and parallel. Hence, by the last note, the point G must move in a line differing imperceptibly from a right line.] [Footnote 19: It is not necessary that the rods, forming the parallel motion, should have the proportions which we have assigned to them. There are various proportions which answer the purpose, and which will be seen by reference to practical works on the steam engine.] By this arrangement the pistons of both the steam cylinder and air-pump are worked; the rod of the latter being attached to the point F, and that of the former to the point G. This beautiful contrivance, which is incontestably one of the happiest mechanical inventions of Watt, affords an example with what facility the mind of a mere mechanician can perceive, as it were instinctively, a result to obtain which by strict reasoning would require a very complicated mathematical analysis. Watt, when asked, by persons whose admiration was justly excited by this invention, to what process of reasoning he could trace back his discovery, replied that he was aware of none; that the conception flashed upon his mind without previous investigation, and so as to excite in himself surprise at the perfection of its action; and that on looking at it for the first time, he experienced all that pleasurable sense of novelty which arises from the first contemplation of the results of the invention of others. This and the other inventions of Watt seem to have been the pure creations of his natural genius, very little assisted by the results of practice, and not at all by the light of education. It does not even appear that he was a dexterous mechanic; for he never assisted in the construction of the first models of his own inventions. His dwelling-house was two miles from the factory, to which he never went more than once in a week, and then did not stay half an hour. (_a_) However beautiful and ingenious in principle the parallel motion may be, it has recently been shown in the United States that much simpler means are sufficient to subserve the same purpose. In the engines constructed recently, under the direction of Mr. R. L. Stevens, a substitute for the parallel motion has been introduced that performs the task equally well, and is much less complex. On the head of the piston-rod a bar is fixed, at right angles to it, and to the longitudinal section of the engine. The ends of this bar work in guides formed of two parallel and vertical bars of iron, by which the upper end of the piston-rod is constrained to move in a straight line. The cross-bar that moves in the guides is connected with the end of the working beam by an inflexible bar, having a motion on two circular gudgeons, one of which is in the working beam, the other in the cross-bar. This is therefore free to accommodate itself to the changes in the respective position of the piston-rod and working beam, and yet transmits the power exerted by the steam upon the former whether it be ascending or descending, to the latter and through it to the other parts of the machine.--A. E. (_b_) The most improved form of Watt's engine was reached by successive additions to the old atmospheric engine of Newcomen and Cawley. Hence, the working-beam, derived from the pump brake of that engine, always formed a part; and the parallel motion, or some equivalent contrivance was absolutely necessary. In many American engines, and particularly in those used in steam boats, the working beam is no longer used for the purpose of transmitting motion to the machinery. This is effected by applying a bar, called the cross-head, at right angles to the upper ends of the piston-rod. The ends of the cross-head work in iron guides, adapted to a gallows-frame of wood. On each side of the cylinder, connecting rods are applied, which take hold of the cranks of the shafts of the water-wheel. Two other connecting rods give motion to a short beam, which works the air and supply pumps. The working beam is also suppressed in engines which work horizontally. The connecting rod is in them merely a jointed prolongation of the piston-rod, extending to the crank, whose axis lies in the same horizontal plane with and at right angles to the axis of the cylinder.--A. E. (55.) A perfect motion being thus obtained of conveying the alternate motion of the piston to the working beam, the use of a counterpoise to lift the piston was discontinued, and the beam was made to balance itself exactly on its centre. The next end to be obtained was to adapt the reciprocating motion of the working end of the beam to machinery. The motion most generally useful for this purpose is one of _continued rotation_. The object, therefore, was by the _alternate_ motion of the end of the beam to transmit to a shaft or axis a _continued circular_ motion. In the first instance, Watt proposed effecting this by a _crank_, connected with the working end of the beam by a metal connector or rod. Let K be the centre or axis, or shaft by which motion is given to the machinery, and to which rotation is to be imparted by the beam C H. On the axle K, suppose a lever, K I, fixed, so that when K I is turned round the centre K, the wheel must be turned with it. Let a connector or rod, H I, be attached to the points H and I, playing freely on pivots or joints. As the end H is moved upwards and downwards, the lever K I is turned round the centre K, so as to give a continued rotatory motion to the shaft which revolves on that centre. The different positions which the connector and lever K I assume in the different parts of a revolution are represented in fig. 16. (56.) This was the first method which occurred to Watt for producing a continued rotatory motion by means of the vibrating motion of the beam, and is the method now universally used. A workman, however, from Mr. Watt's factory, who was aware of the construction of a model of this, communicated the method to Mr. Washborough of Bristol, who anticipated Watt in taking out a patent; and although it was in his power to have disputed the patent, yet rather than be involved in litigation, he gave up the point, and contrived another way of producing the same effect, which he called the _sun and planet_ wheel, and which he used until the expiration of Washborough's patent, when the crank was resumed. The toothed wheel B (fig. 17.) is fixed on the end of the connector, so that it does not turn on its axis. The teeth of this wheel work in those of another wheel, A, which is the wheel to which rotation is to be imparted, and which is turned by the wheel B revolving round it, urged by the rod H I, which receives its motion from the working-beam. The wheel A is called the sun-wheel, and B the planet-wheel, from the obvious resemblance to the motion of these bodies. This contrivance, although in the main inferior to the more simple one of the crank, is not without some advantages; among others, it gives to the sun-wheel double the velocity which would be communicated by the simple crank, for in the simple crank one revolution only on the axle is produced by one revolution of the crank, but in the sun and planet-wheel two revolutions of the sun-wheel are produced by one of the planet-wheel; thus a double velocity is obtained from the same motion of the beam. This will be evident from considering that when the planet-wheel is in its highest position, its lowest tooth is engaged with the highest tooth of the sun-wheel; as the planet-wheel passes from the highest position, its teeth drive those of the sun-wheel before them, and when it comes into the lowest position, the highest tooth of the planet-wheel is engaged with the lowest of the sun-wheel: but then half of the sun-wheel has _rolled off_ the planet-wheel, and, therefore, the tooth which was engaged with it in its higher position, must now be distant from it by half the circumference of the wheel, and must therefore be again in the highest position, so that while the planet-wheel has been carried from the top to the bottom, the sun-wheel has made a complete revolution. A little reflection, however, on the nature of the motion, will render this plainer than any description can. This advantage of giving an increased velocity, may be obtained also by the simple crank, by placing toothed wheels on its axle. Independently of the greater expense attending the construction of the sun and planet-wheel, its liability to go out of order, and the rapid wear of the teeth, and other objections, rendered it decidedly inferior to the crank, which has now entirely superseded it. (58.) Whether the simple crank or the sun and planet wheel be used, there still remains a difficulty of a peculiar nature attending the continuance of the rotatory motion. There are two positions in which the engine can give no motion whatever to the crank. These are when the end of the beam, the axle of the crank, and the pivot which joins the connector with the crank, are in the same straight line. This will be easily understood. Suppose the beam, connector, and crank to assume the position represented in fig. 15. If steam urge the piston downwards, the point H and the connector H I will be drawn directly upwards. But it must be very evident that in the present situation of the connector H I, and the lever I K, the force which draws the point I in the direction I K can have no effect whatever in turning I K round the centre K, but will merely exert a pressure on the axle or pivots of the wheel. Again, suppose the crank and connector to be in the position H I K (fig. 16.), the piston being consequently at the bottom of the cylinder. If steam now press the piston _upwards_, the pivot H and the connector H I will be pressed _downwards_, and this pressure will urge the crank I K in the direction I K. It is evident that such a force cannot turn the crank round the centre K, and can be attended with no other effect than a pressure on the axle or pivots of the wheel. Hence in these two positions, the engine can have no effect whatever in turning the crank. What, then, it may be asked, extricates the machine from this mechanical dilemma in which it is placed twice in every revolution, on arriving at those positions in which the crank escapes the influence of the power? There is a tendency in bodies, when once put in motion, to continue that motion until stopped by some opposing force, and this tendency carries the crank out of those two critical situations. The velocity which is given to it, while it is under the influence of the impelling force of the beam, is retained in a sufficient degree to carry it through that situation in which it is deserted by this impelling force. Although the rotatory motion intended to be produced by the crank is, therefore, not absolutely destroyed by this circumstance, yet it is rendered extremely irregular, since, in passing through the two positions already described, where the machine loses its power over the crank, the motion will be very slow, and, in the positions of the crank most remote from these, where the power of the beam upon it is greatest, the motion will be very quick. As the crank revolves from each of those positions where the power of the machine over it is greatest, to where that power is altogether lost, it is continually diminished, so that, in fact, the crank is driven by a varying power, and therefore produces a varying motion. This will be easily understood by considering the successive positions of the crank and connector represented in fig. 16. This variable motion becomes particularly objectionable when the engine is employed to drive machinery. To remove this defect, we have recourse to the property of bodies just mentioned, viz. their tendency to retain a motion which is communicated to them. A large metal wheel called a _fly-wheel_ is placed upon the axis of the crank (fig. 15.), and is turned by it. The effect of this wheel is to equalize the motion communicated by the action of the beam on the crank, that action being just sufficient to sustain in the fly-wheel a uniform velocity, and the tendency of this wheel to retain the velocity it receives, renders its rotation sufficiently uniform for all practical purposes. This uniformity of motion, however, will only be preserved on two conditions; _first_, that the supply of steam from the boiler shall be uniform; and secondly, that the machine have always the same resistance to overcome or be _loaded_ equally. If the supply of steam from the boiler to the cylinder be increased, the motion of the piston will be rendered more rapid, and, therefore, the revolution of the fly-wheel will also be more rapid, and, on the other hand, a diminished supply of steam will retard the fly-wheel. Again, if the resistance or load upon the engine be diminished, the supply of steam remaining the same, the velocity will be increased, since a less resistance is opposed to the energy of the moving power; and, on the other hand, if the resistance or load be increased, the speed will be diminished, since a greater resistance will be opposed to the same moving power. To insure a uniform velocity, in whatever manner the load or resistance may be changed, it is necessary to proportion the supply of steam to the resistance, so that, upon the least variation in the velocity, the supply of steam will be increased or diminished, so as to keep the engine going at the same rate. (59.) One of the most striking and elegant appendages of the steam engine is the apparatus contrived by Watt for effecting this purpose. An apparatus, called a _regulator_ or _governor_, had been long known to mill-wrights for rendering uniform the action of the stones in corn-mills, and was used generally in machinery. Mr. Watt contrived a beautiful application of this apparatus for the regulation of the steam engine. In the pipe which conducts steam from the boiler to the cylinder he placed a thin circular plate, so that when placed with its face presented towards the length of the pipe, it nearly stopped it, and allowed little or no steam to pass to the cylinder, but when its edge was placed in the direction of the pipe, it offered no resistance whatever to the passage of the steam. This circular plate, called the throttle valve, was made to turn on a diameter as an axis, passing consequently through the centre of the tube, and was worked by a lever outside the tube. According to the position given to it, it would permit more or less steam to pass. If the valve be placed with its edge nearly in the direction of the tube, the supply of steam is abundant; if it be placed with its face nearly in the direction of the tube, the supply of steam is more limited, and it appears that, by the position given to this valve, the steam may be measured in any quantity to the cylinder. At first it was proposed that the engine-man should adjust this valve with his hand; when the engine was observed to increase its speed too much, he would check the supply of steam by partially closing the valve; but if, on the other hand, the motion was too slow, he would open the valve and let in a more abundant supply of steam. Watt, however, was not content with this, and desired to make the engine itself discharge this task with more steadiness and regularity than any attendant could, and for this purpose he applied the governor already alluded to. This apparatus is represented in fig. 15.; L is a perpendicular shaft or axle to which a wheel, M, with a groove is attached. A strap or rope, which is rolled upon the axle of the fly-wheel, is passed round the groove in the wheel M, in the same manner as the strap acts in a turning lathe. By means of this strap the rotation of the fly-wheel will produce a rotation of the wheel M and the shaft L, and the speed of the one will always increase or diminish in the same proportion as the speed of the other. N, N are two heavy balls of metal placed at the ends of rods, which play on an axis fixed on the revolving shaft at O, and extend beyond the axis to Q Q. Connected with these by joints at Q Q are two other rods, Q R, which are attached to a broad ring of metal, moving freely up and down the revolving shaft. This ring is attached to a lever whose centre is S, and is connected by a series of levers with the throttle-valve T. When the speed of the fly-wheel is much increased, the spindle L is whirled round with considerable rapidity, and by their natural tendency[20] the balls N N fly from the centre. The levers which play on the axis O, by this motion, diverge from each other, and thereby depress the joints Q Q, and draw down the joints R, and with them the ring of metal which slides upon the spindle. By these means the end of the lever playing on S is depressed, and the end V raised, and the motion is transmitted to the throttle-valve, which is thereby partially closed, and the supply of steam to the cylinder checked. If, on the contrary, the velocity of the fly-wheel be diminished, the balls will fall towards the axis, and the opposite effects ensuing, the supply of steam will be increased, and the velocity restored. [Footnote 20: The _centrifugal force_.] [Illustration: Pl. IV. WATT'S SINGLE ACTING STEAM ENGINE.] The peculiar beauty of this apparatus is, that in whatever position the balls settle themselves, the velocity with which the governor revolves must be the same,[21] and in this, in fact, consists its whole efficacy as a regulator. Its regulating power is limited, and it is only small changes of velocity that it will correct. It is evident that such a velocity as, on the one hand, would cause the balls to fly to the extremity of their play, or, on the other, would cause them to fall down on their rests, would not be influenced by the governor. [Footnote 21: Strictly speaking, this is only true when the divergence of the rods from the spindle is not very great, and, in practice, this divergence is never sufficient to render the above assertion untrue. This property of the conical pendulum arises from the circumstance of the centrifugal force, in this instance, varying as the radius of the circle in which the balls are moved; and when this is the case, as is well known, the _periodic time_ is constant. The time of one revolution of the balls is equal to twice the time in which either ball, as a common pendulum, would vibrate on the centre, and as all its vibrations, though the arcs be unequal, are equal in time, provided those arcs be small, so also is the periodic time of the revolving ball invariable. These observations, however, only apply when the balls settle themselves steadily into a circular motion; for while they are ascending they describe a spiral curve with double curvature, and the period will vary. This takes place during the momentary changes in the velocity of the engine.] We have thus described the principal parts of the double-acting steam engine. The valves and the methods of working them have been reserved for the next chapter, as they admit of considerable variety, and will be better treated of separately. We have also reserved the consideration of the boiler, which is far from being the least interesting part of the modern steam engine, for a future chapter. CHAPTER VII. DOUBLE-ACTING STEAM ENGINE (_continued_.) On the Valves of the Double-Acting Steam Engine. -- Original Valves. -- Spindle Valves. -- Sliding Valve. -- D Valve. -- Four-Way Cock. (60.) The various improvements described in the last chapter were secured to Watt by patent in the year 1782. The engine now acquired an enlarged sphere of action; for its dominion over manufactures was decided by the _fly-wheel_, _crank_, and _governor_. By means of these appendages, its motions were regulated with the most delicate precision; so that while it retained a power whose magnitude was almost unlimited, that power was under as exact regulation as the motion of a time-piece. There is no species of manufacture, therefore, to which this machine is not applicable, from the power which spins the finest thread, or produces the most delicate web, to that which is necessary to elevate the most enormous weights, or overcome the most unlimited resistances. Although it be true, that in later times the steam engine has received many improvements, some of which are very creditable to the invention and talents of their projectors, yet it is undeniable that all its great and leading perfections, all those qualities by which it has produced such wonderful effects on the resources of these countries, by the extension of manufactures and commerce,--those qualities by which its influence is felt and acknowledged in every part of the civilized globe, in increasing the happiness, in multiplying the enjoyments, and cheapening the pleasures of life,--that these qualities are due to the predominating powers of one man, and that man one who possessed neither the influence of wealth, rank, nor education, to give that first impetus which is so often necessary to carry into circulation the earlier productions of genius. The method of working the valves of the double-acting steam engine, is a subject which has much exercised the ingenuity of engineers, and many elegant contrivances have been suggested, some of which we shall now proceed to describe. But even in this the invention of Watt has anticipated his successors; and the contrivances suggested by him are those which are now almost universally used. In order perfectly to comprehend the action of the several systems of valves which we are about to describe, it will be necessary distinctly to remember the manner in which the steam is to be communicated to the cylinder, and withdrawn from it. When the piston is at the top of the cylinder, the steam below it is to be drawn off to the condenser, and the steam from the boiler is to be admitted above it. Again, when it has arrived at the bottom of the cylinder, the steam above is to be drawn off to the condenser, and the steam from the boiler is to be admitted below it. In the earlier engines constructed by Watt, this was accomplished by four valves, which were opened and closed in pairs. Valve boxes were placed at the top and bottom of the cylinder, each of which communicated by tubes both with the steam-pipe from the boiler and the condenser. Each valve-box accordingly contained two valves, one to admit steam from the steam-pipe to the cylinder, and the other to allow that steam to pass into the condenser. Thus each valve-box contained a steam valve and an exhausting valve. The valves at the top of the cylinder are called the _upper steam valve_ and the _upper exhausting-valve_, and those at the bottom, the _lower steam valve_ and the _lower exhausting-valve_. In fig. 15. A´ is the upper steam valve, which, when open, admits steam above the piston; B´ is the upper exhausting-valve, which, when open, draws off the steam from the piston to the condenser. C´ is the lower steam valve, which admits steam below the piston; and D´, the lower exhausting-valve, which draws off the steam from below the piston to the condenser. Now, suppose the piston to be at the top of the cylinder, the cylinder below it being filled with steam, which has just pressed it up. Let the _upper steam valve_ A´, and the _lower exhausting-valve_ D´ be opened, and the other two valves closed. The steam which fills the cylinder below the piston will immediately pass through the valve D´ into the condenser, and a vacuum will be produced below the piston. At the same time, steam is admitted from the steam-pipe through the valve A´ above the piston, and its pressure will force the piston to the bottom of the cylinder. On the arrival of the piston at the bottom of the cylinder, the upper steam valve A´, and lower exhausting-valve D´, are closed; and the lower steam valve C´, and upper exhausting-valve B´ are opened. The steam which fills the cylinder above the piston now passes off through B´ into the condenser, and leaves a vacuum above the piston. At the same time, steam from the boiler is admitted through the lower steam valve C´, below the piston, so that it will press the piston to the top of the cylinder; and so the process is continued. It appears, therefore, that the upper steam valve, and the lower exhausting-valve, must be opened together, on the arrival of the piston at the top of the cylinder. To effect this, one lever, E´, is made to communicate by jointed rods with both these valves, and this lever is moved by a pin placed on the piston-rod of the air-pump; and such a position may be given to this pin as to produce the desired effect exactly at the proper moment of time. In like manner, another lever, F´, communicates by jointed rods with the upper exhausting valve and lower steam valve, so as to open them and close them together; and this lever, in like manner, is worked by a pin on the piston-rod of the air-pump. (61.) This method of connecting the valves, and working them, has been superseded by another, for which Mr. MURRAY of Leeds obtained a patent, which was, however, set aside by Messrs. Bolton and Watt, who showed that they had previously practised it. This method is represented in figs. 18, 19. The stems of the valves are perpendicular, and move in steam-tight sockets in the top of the valve-boxes. The stem of the upper steam valve A is a tube through which the stem of the upper exhausting-valve B passes, and in which it moves steam-tight; both these stems moving steam-tight through the top of the valve-box. The lower steam valve C, and exhausting-valve D, are similarly circumstanced; the stem of the former being a tube through which the stem of the latter passes. The stems of the upper steam valve and lower exhausting-valve are then connected by a rod, E; and those of the upper exhausting-valve and lower steam valve by another rod, F. These rods, therefore, are capable of moving the valves in pairs, when elevated and depressed. The motion which works the valves is, however, not communicated by the rod of the air-pump, but is received from the axis of the fly-wheel. This axis works an apparatus called an _eccentric_; the principle which regulates the motion of this may be thus explained:-- D E (figs. 20, 21.) is a circular metallic ring, the inner surface of which is perfectly smooth. This ring is connected with a shaft, F B, which communicates motion to the valves by levers which are attached to it at B. A circular metallic plate is fitted in the ring so as to be capable of turning within it, the surfaces of the ring and plate which are in contact being smooth and lubricated with oil or grease. This circular plate revolves, but not on its centre. It turns on an axis C, at some distance from its centre A; the effect of which, evidently, is that the ring within which it is turned is moved alternately in opposite directions, and through a space equal to twice the distance (C A) of the axis of the circular plate from the common centre of it and the ring. The eccentric in its two extreme positions is represented in figs. 20, 21. The plate and ring D E are placed on the axis of the fly-wheel, or on the axis of some other wheel which is worked by the fly-wheel. So that the motion of continued rotation in the fly-wheel is thus made to produce an alternate motion in a straight line in the shaft F B. This rod is made to communicate by levers with the rods E and F (figs. 18, 19.), which work the valves in such a manner, that, when the eccentric is in the position fig. 20., one pair of valves are opened, and the other pair closed; and when it is brought to the position fig. 21., the other pair are opened and the former closed and so on. It is by means of such an apparatus as this that the valves are worked almost universally at present. The piston being supposed to be at the top of the cylinder (fig. 18.), and the rod E raised, the valves A and D are opened, and B and C closed. The steam enters from the steam-pipe at an aperture immediately above the valve A, and, passing through the open valve, enters the cylinder above the piston. At the same time, the steam which is below the piston, and which has just pressed it up, flows through the open valve D, and through a tube immediately under it to the condenser. A vacuum being thus produced below the piston, and steam pressure acting above it, it descends; and when it arrives at the bottom of the cylinder (fig. 19.) the rod F is drawn down, and the valves A and D fall into their seats, and at the same time the rod F is raised, and the valves B and C are opened. Steam is now admitted through an aperture above the valve C, and passes below the piston, while the steam above it passes through the open valve B into a tube immediately under it, which leads to the condenser. A vacuum being thus produced above the piston, and steam pressure acting below it, the piston ascends, and thus the alternate ascent and descent is continued by the motion communicated to the rods E F from the fly-wheel. [Illustration: Pl. V. WATT'S DOUBLE-ACTING STEAM ENGINE.] [Illustration: Pl. VI.] (_c_) An improvement has been made in the United States in the mode of working the puppet valve. It consists in placing them by pairs in two different vertical planes instead of one. The rods then work through four separate stuffing boxes, and the necessity of making two of them hollow cylinders is avoided.--A. E. (62.) There are various other contrivances for regulating the circulation of steam through the cylinder. In figs. 22, 23. is represented a section of a slide valve suggested by Mr. Murray of Leeds. The steam-pipe from the boiler enters the valve-box D E at S. Curved passages, A A, B B, communicate between this valve-box and the top and bottom of the cylinder; and a fourth passage leads to the tube C, which passes to the condenser. A sliding piece within the valve-box opens a communication alternately between each end of the cylinder and the tube C, which leads to the condenser. In the position of the apparatus in fig. 22. steam is passing from the steam-pipes, through the curved passage A A above the piston, and at the same time the steam below the piston is passing through the passage B B into the tube C, and thence to the condenser. A vacuum is thus formed below the piston, and steam is introduced above it. The piston, therefore, descends; and when it arrives at the bottom of the cylinder, the slide is moved into the position represented in fig. 23. Steam now passes from S through B B below the piston, and the steam above it passes through A A and C to the condenser. A vacuum is thus produced above the piston, and steam pressure is introduced below it, and the piston ascends; and in this way the motion is continued. The slide is moved by a lever, which is worked by the eccentric from the fly-wheel. (63.) Watt suggested a method of regulating the circulation of steam, which is called the D valve, from the resemblance which the horizontal section of the valve has to the letter D. This method, which is very generally used, is represented in section in figs. 24, 25. Steam from the boiler enters through S. A rod of metal connects two solid plugs, A B, which move steam-tight in the passage D. In the position of the apparatus represented in fig. 24. the steam passes from S through the passage D, and enters the cylinder above the piston; while the steam below the piston passes through the open passage by the tube C to the condenser. A vacuum is thus formed below the piston, while the pressure of steam is introduced above it, and it accordingly descends. When it has arrived at the bottom of the cylinder, the plugs A B are moved into the position in fig. 25. Steam now passing from S through D, enters the cylinder below the piston; while the steam which is above the piston, and has just pressed it down, passes through the open passage into the condenser. A vacuum is thus produced above the piston, and the steam pressure below forces it up. When it has arrived at the top of the cylinder, the position of the plugs A B is again changed to that represented in fig. 24., and a similar effect to that already described is produced, and the piston is pressed down; and so the process is continued. The plugs A B, and the rod which connects them, are moved up and down by proper levers, which receive their motion from the eccentric. This contrivance is frequently modified, by conducting the steam from above the piston to the condenser, through a tube in the plugs A B, and their connecting rod. In figs. 26, 27. a tube passes through the plugs A B and the rod which joins them. In the position fig. 26. steam entering at S passes through the tube to the cylinder above the piston, while the steam below the piston passes through C into the condenser. A vacuum being thus made below the piston, and steam pressing above it, it descends; and when it has arrived at the bottom of the cylinder, the position of the plugs A B and the tube is changed to that represented at fig. 27. The steam now entering at S passes to the cylinder below the piston, while the steam above the piston passes through C into the condenser. A vacuum is thus produced above the piston, and steam pressure introduced below it, so that it ascends. When it has arrived at the top of the cylinder, the plugs are moved into the position represented in fig. 26., and similar effects being produced, the piston again descends; and so the motion is continued. The motion of the sliding tube may be produced as in the former contrivances, by the action of the eccentric. It is also sometimes done by a bracket fastened on the piston-rod of the air-pump. This bracket, in the descent of the piston, strikes a projection on the valve-rod, and drives it down; and in the ascent meets a similar projection, and raises it. (64.) Another method, worthy of notice for its elegance and simplicity, is the _four-way cock_. A section of this contrivance is given in figs. 28, 29.: C T S B are four passages or tubes; S leads from the boiler, and introduces steam; C, opposite to it, leads to the condenser; T is a tube which communicates with the top of the cylinder; and B one which communicates with the bottom of the cylinder. These four tubes communicate with a cock, which is furnished with two curved passages, as represented in the figures; and these passages are so formed, that, according to the position given to the cock, they may be made to open a communication between any two adjacent tubes of the four just mentioned. When the cock is placed as in fig. 28. communication is opened between the steam-pipe and the top of the cylinder by one of the curved passages, and between the condenser and the bottom of the cylinder by the other curved passage. In this case the steam passes from below the piston to the condenser, leaving a vacuum under it, and steam is introduced from the boiler above the piston. The piston therefore descends; and when it has arrived at the bottom of the cylinder, the position of the cock is changed to that represented in fig. 29. This change is made by turning the cock through one fourth of an entire revolution, which may be done by a lever moved by the eccentric, or by various other means. One of the curved passages in the cock now opens a communication between the steam-pipe and the bottom of the cylinder; while the other opens a communication between the condenser and the top of the cylinder. By these means, the steam from the boiler is introduced below the piston, while the steam above the piston is drawn off to the condenser. A vacuum being thus made above the piston, and steam introduced below it, it ascends; and when it has arrived at the top of the cylinder, the cock being moved back, it resumes the position in fig. 28., and the same consequences ensue, the piston descends; and so the process is continued. In figs. 30, 31. the four-way cock with the passages to the top and bottom of the cylinder is represented on a larger scale. This beautiful contrivance is not of late invention. It was used by Papin, and is also described by Leupold in his _Theatrum Machinarum_, a work published about the year 1720, in which an engine is described acting with steam of high pressure, on a principle which we shall describe in a subsequent chapter. The four-way cock is liable to some practical objections. The quantity of steam which fills the tubes between the cock and the cylinder, is wasted every stroke. This objection, however, also applies to the sliding valve (figs. 22, 23.), and to the sliding tube or D valves (figs. 24, 25, 26, 27.). In fact, it is applicable to every contrivance in which means of shutting off the steam are not placed at both top and bottom of the cylinder. Besides this, however, the various passages and tubes cannot be conveniently made large enough to supply steam in sufficient abundance; and consequently it becomes necessary to produce steam in the boiler of a more than ordinary strength to bear the attenuation which it suffers in its passage through so many narrow tubes. [Illustration: Pl. VII.] One of the greatest objections, however, to the use of the four-way cock, particularly in large engines, is its unequal wear. The parts of it near the passages having smaller surfaces, become more affected by the friction, and in a short time the steam leaks between the cock and its case, and becomes wasted, and tends to vitiate the vacuum. These cocks are seldom used in condensing engines, except they be small engines, but are frequently adopted in high-pressure steam-engines; for in these the leakage is not of so much consequence, as will appear hereafter. CHAPTER VIII. BOILER AND ITS APPENDAGES.--FURNACE. The Boiler and its Appendages. -- Level Gauges. -- Feeding Apparatus. -- Steam Gauge. -- Barometer Gauge. -- Safety Valves. -- Self-regulating Damper. -- Edelcrantz's Valve. -- Furnace. -- Self-consuming Furnace. -- Brunton's Self-regulating Furnace. -- Oldham's Modification. (65.) The regular action of a steam engine, as well as the economy of fuel, depends in a great degree on the construction of the boiler or apparatus for generating the steam. The boiler may be conceived as a great magazine of steam for the use of the engine; and care must be taken not only that a sufficient quantity be always ready for the supply of the machine, but also that it shall be of the proper quality; that is, that its pressure shall not exceed that which is required, nor fall short of it. Precautions should, therefore, be taken that the production of steam should be exactly proportioned to the work to be done, and that the steam so produced shall be admitted to the cylinder in the same proportion. To accomplish this, various contrivances, eminently remarkable for their ingenuity, have been resorted to, and which we shall now proceed to describe. (_d_) It may be premised that boilers have been made of various figures, each having its own peculiar advantages and defects. That which possesses the greatest degree of strength, is one of the shape of a cylinder. This form was originally introduced by Oliver Evans, in the United States. It will have its entire superiority when the fire is made beneath it in a furnace of masonry. But this method is not applicable to steam boats or locomotive engines. In these instances the weight of the separate furnace is an objection; when, therefore, this form is applied in them, the fire is usually made in a chamber of cylindric shape, within the boiler, and the smoke is conveyed to the chimney by flues, which pass through the water. These flues have, in some cases, been reduced to the size of small tubes, and of this method an example will be found in a subsequent part of this work.--A. E. (66.) Different methods have been, from time to time, suggested for indicating the level of the water in the boiler. We have already mentioned the two gauge-pipes used in the earlier steam engines (31.); and which are still generally continued. There are, however, some other methods which merit our attention. A weight, F (fig. 32.), half immersed in the water in the boiler, is supported by a wire, which, passing steam-tight through a small hole in the top, is connected by a flexible string or chain passing over a wheel, W, with a counterpoise, A, which is just sufficient to balance F, when half immersed. If F be raised above the water, A being lighter, will no longer balance it, and F will descend, pulling up A, and turning the wheel W. If, on the other hand, F be plunged deeper in the water, A, will more than balance it, and will pull it up. So that the only position in which F and A will balance each other is when F is half immersed. The wheel W is so adjusted, that when two pins, placed on its rim, are in the horizontal position, as in fig. 32., the water is at its proper level. Consequently it follows, that if the water rise above this level, the weight F is lifted, and A falls, so that the pins P P´ come into the position in fig. 33. If, on the other hand, the level of the water falls, F falls and A rises, so that the pins P P´ assume the position in fig. 34. Thus, in general, the position of the pins P P´ becomes an indication of the quantity of water in the boiler. Another method is to place a glass tube (fig. 35.) with one end, T, entering the boiler above the proper level, and the other end, T´, entering it below the proper level. It must be evident that the water in the tube will always stand at the same level as the water in the boiler; since the lower part has a free communication with that water, while the surface is submitted to the pressure of the same steam as the water in the boiler. This, and the last-mentioned gauge, have the advantage of addressing the eye of the engineer at once, without any adjustment; whereas the gauge cocks must be both opened, whenever the depth is to be ascertained. These gauges, however, require the frequent attention of the engine-man; and it becomes desirable either to find some more effectual means of awakening that attention, or to render the supply of the boiler independent of any attention. In order to enforce the attention of the engine-man to replenish the boiler when partially exhausted by evaporation, a tube was sometimes inserted at the lowest level to which it was intended that the water should be permitted to fall. This tube was conducted from the boiler into the engine-house, where it terminated in a mouth-piece or whistle, so that whenever the water fell below the level at which this tube was inserted in the boiler, the steam would rush through it, and, issuing with great velocity at the mouth-piece, would summon the engineer to his duty with a call that would rouse him even from sleep. (67.) In the most effectual of these methods, the task of replenishing the boiler should still be executed by the engineer; and the utmost that the boiler itself was made to do was to give due notice of the necessity for the supply of water. The consequence was, among other inconveniences, that the level of the water was subject to constant variation. To remedy this, a method has been invented by which the engine is made to feed its own boiler. The pipe G´ (fig. 15.), which leads from the hot water pump H´, terminates in a small cistern, C (fig. 36.), in which the water is received. In the bottom of this cistern a valve, V, is placed, which opens upwards, and communicates with a feed-pipe, which descends into the boiler below the level of the water in it. The stem of the valve V is connected with a lever turning on the centre D, and loaded with a weight, F, dipped in the water in the boiler in a manner similar to that described in fig. 32., and balanced by a counterpoise, A, in exactly the same way. When the level of the water in the boiler falls, the float F falls with it, and, pulling down the arm E of the lever, raises the valve V, and lets the water descend into the boiler from the cistern C. When the boiler has thus been replenished, and the level raised to its former place, F will again be raised, and the valve V closed by the weight A. In practice, however, the valve V adjusts itself by means of the effect of the water on the weight F, so as to permit the water from the feeding cistern C to flow in a continued stream, just sufficient in quantity to supply the consumption from evaporation, and to maintain the level of the water in the boiler constantly the same. By this singularly felicitous arrangement, the boiler is made to replenish itself, or, more properly speaking, it is made to receive such a supply as that it never wants replenishing, an effect which no effort of attention on the part of an engine-man could produce. But this is not the only good effect produced by this contrivance. A part of the steam which originally left the boiler, and having discharged its duty in moving the piston, was condensed and reconverted into water, and lodged by the air-pump in the hot-well (47.), is here again restored to the source from which it came, bringing back all the unconsumed portion of its heat preparatory to being once more put in circulation through the machine. The entire quantity of hot water pumped into the cistern C is not always required for the boiler. A waste-pipe may be provided for carrying off the surplus, which may be turned to any purpose for which it may be required; or it may be discharged into a cistern to cool, preparatory to being restored to the cold cistern (fig. 12.), in case water for the supply of that cistern be not sufficiently abundant. In cities and places in which it becomes an object to prevent the waste of water, the waste-pipes proceeding from the feed-cistern C (fig. 36.) and from the cold cistern containing the condenser and air-pump, may be conducted to a cistern A B (fig. 37.). Let C be the pipe from the feeding cistern, and D that from the cold cistern; by these pipes the waste water, from both these cisterns is deposited in A B. In the bottom of A B is a valve V, opening upwards, connected with a float F. When the quantity of water collected in the cistern A B is such that the level rises considerably, the float F is raised, and lifts the valve V, and the water flows into the main pipe, which supplies water for working the engine: G is the cold water-pump for the supply of the cold cistern. This arrangement for saving the water discharged from the feeding and condensing cisterns has been adopted in the printing office of the Bank of Ireland, and a very considerable waste of water is thereby prevented. (68.) It is necessary to have a ready method of ascertaining at all times the strength of the steam which is used in working the engine. For this purpose a bent tube containing mercury is inserted into some part of the apparatus which has free communication with the steam. It is usually inserted in the _jacket_ of the cylinder (44.). Let A B C (fig. 38.) be such a tube. The pressure of the steam forces the mercury down in the leg A B, and up in the leg B C. If the mercury in both legs be at exactly the same level, the pressure of the steam must be exactly equal to that of the atmosphere; because the steam pressure on the mercury in A B balances the atmospheric pressure on the mercury in B C. If, however, the level of the mercury in B C be above the level of the mercury in B A, the pressure of the steam will exceed that of the atmosphere. The excess of its pressure above that of the atmosphere may be found by observing the difference of the levels of the mercury in the tubes B C and B A; allowing a pressure of one pound on each square inch for every two inches in the difference of the levels. If, on the contrary, the level of the mercury in B C should fall below its level in A B, the atmospheric pressure will exceed that of the steam, and the degree or quantity of the excess may be ascertained exactly in the same way. If the tube be glass, the difference of levels of the mercury would be visible: but it is most commonly made of iron; and in order to ascertain the level, a thin wooden rod with a float is inserted in the open end of B C; so that the portion of the stick within the tube indicates the distance of the level of the mercury from its mouth. A bulb or cistern of mercury might be substituted for the leg A B, as in the common barometer. This instrument is called the STEAM-GAUGE. If the steam-gauge be used as a measure of the strength of the steam which presses on the piston, it ought to be on the same side of the throttle valve (which is regulated by the governor) as the cylinder; for if it were on the same side of the throttle valve with the boiler, it would not be affected by the changes which the steam may undergo in passing through the throttle valve, when partially closed by the agency of the governor. (69.) The force with which the piston is pressed depends on two things: 1º, the actual strength of the steam which presses on it; and 2º, on the actual strength of the vapour which resists it. For although the vacuum produced by the method of separate condensation be much more perfect than what had been produced in the atmospheric engines, yet still some vapour of a small degree of elasticity is found to be raised from the hot water in the bottom of the condenser before it can be extracted by the air-pump. One of these pressures is indicated by the steam-gauge already described; but still, before we can estimate the force with which the piston descends, it is necessary to ascertain the force of the vapour which remains uncondensed, and resists the motion of the piston. Another gauge, called the barometer-gauge, is provided for this purpose. A glass tube A B (fig. 39.), more than thirty inches long, and open at both ends, is placed in an upright or vertical position, having the lower end B immersed in a cistern of mercury C. To the upper end is attached a metal tube, which communicates with the condenser, in which a constant vacuum, or rather high degree of rarefaction, is sustained. The same vacuum must, therefore, exist in the tube A B, above the level of the mercury; and the atmospheric pressure on the surface of the mercury in the cistern C will force the mercury up in the tube A B, until the column which is suspended in it is equal to the difference between the atmospheric pressure and the pressure of the uncondensed steam. The difference between the column of mercury sustained in this instrument and in the common barometer will determine the strength of the uncondensed steam, allowing a force proportional to one pound per square inch for every two inches of mercury in the difference of the two columns. In a well-constructed engine, which is in good order, there is very little difference between the altitude in the barometer-gauge and the common barometer. To compute the force with which the piston descends, thus becomes a very simple arithmetical process. First ascertain the difference of the levels of the mercury in the steam-gauge. This gives the excess of the steam pressure above the atmospheric pressure. Then find the height of the mercury in the barometer-gauge. This gives the excess of the atmospheric pressure above the uncondensed steam. Hence, if these two heights be added together, we shall obtain the excess of the impelling force of the steam from the boiler on the one side of the piston, above the resistance of the uncondensed steam on the other side. This will give the effective impelling force. Now, if one pound be allowed for every two inches of mercury in the two columns just mentioned, we shall have the number of pounds of impelling pressure on every square inch of the piston. Then if the number of square inches in the section of the piston be found, and multiplied by the number of pounds on each square inch, the whole effective force with which it moves will be obtained. In the computation of the power of the engine, however, all this force, thus computed, is not to be allowed as the effective working power. For it requires some force, and by no means an inconsiderable portion, to move the engine itself, even when unloaded; all this, therefore, which is spent in overcoming friction, &c. is to be left out of account, and only the balance set down as the effective working power. From what we have stated, it appears that in order to estimate the effective force with which the piston is urged, it is necessary to refer to both the barometer and the steam-gauge. This double computation may be obviated by making one gauge serve both purposes. If the end C of the steam-gauge (fig. 38.) instead of communicating with the atmosphere, were continued to the condenser, we should have the pressure of the steam acting upon the mercury in the tube B A, and the pressure of the uncondensed vapour which resists the piston acting on the mercury in the tube B C. Hence the difference of the levels of the mercury in the tubes will at once indicate the difference between the force of the steam and that of the uncondensed vapour, which is the effective force with which the piston is urged. (70.) To secure the boiler from accidents arising from the steam becoming too strong, a safety valve is used, similar to those described in Papin's steam engine, loaded with a weight equal to the strength which the steam is intended to have above the atmospheric pressure; for it is found expedient, even in condensing engines, to use the steam of a pressure somewhat above that of the atmosphere. Besides this valve, another of the very opposite kind is sometimes used. Upon stopping the engine, and extinguishing the fire, it is found that the steam condensed within the boiler produces a vacuum; so that the atmosphere, pressing on the external surface of the boiler, has a tendency to crush it. To prevent this, a safety valve is provided, which opens inwards, and which being forced open by the atmospheric pressure when a vacuum is produced within, the air rushes in, and a balance is obtained between the pressures within and without. (71.) We have already explained the manner in which the governor regulates the supply of steam from the boiler to the cylinder, proportioning the quantity to the work to be done, and thereby sustaining a uniform motion. Since, then, the _consumption_ of steam in the engine is subject to variation, owing to the various quantities of work it may have to perform, it is evident that the PRODUCTION of steam in the boiler should be subject to a proportional variation. For, otherwise, one of two effects would ensue: the boiler would either fail to supply the engine with steam, or steam would accumulate in the boiler, from being produced in too great abundance, and would escape at the safety valve, and thus be wasted. In order to vary the production of steam in proportion to the demands of the engine, it is necessary to increase or mitigate the furnace, as production is to be augmented or diminished. To effect this by any attention on the part of the engine-man would be impossible; but a most ingenious method has been contrived, of making the boiler regulate itself in these respects. Let T (fig. 40.) be a tube inserted in the top of the boiler, and descending nearly to the bottom. The pressure of the steam on the surface of the water in the boiler forces water up in the tube T, until the difference of the levels is equal to the difference between the pressure of the steam in the boiler and that of the atmosphere. A weight F, half immersed in the water in the tube, is suspended by a chain which passes over the wheels P P´, and is balanced by a metal plate D, in the same manner as the float in fig. 32. is balanced by the weight A. The plate D passes through the mouth of the flue E, as it issues finally from the boiler; so that when the plate D falls, it stops the flue and thereby suspends the draught of air through the furnace, mitigates the fire, and diminishes the production of steam. If, on the contrary, the plate D be drawn up, the draught is increased, the fire rendered more effective, and the production of steam in the boiler stimulated. Now suppose that the boiler is producing steam faster than the engine consumes it, either because the load on the engine has been diminished, and therefore its consumption of steam proportionally diminished, or because the fire has become too intense. The consequence is, that the steam beginning to accumulate, will press upon the surface of the water in the boiler with increased force, and the water will rise in the tube T. The weight F will therefore be lifted, and the plate D will descend, stop the draught, mitigate the fire, and check the production of steam; and it will continue so to do, until the production of steam becomes exactly equal to the demands of the engine. If, on the other hand, the production of steam be not equal to the wants of the machine, either because of the increased load, or the insufficiency of the fire, the steam in the boiler losing its elasticity, the surface of the water rises, not sustaining a pressure sufficient to keep it at its wonted level. Therefore, the surface in the tube T falls, and the weight F falls, and the plate D rises. The draught is thus increased, by opening the flue, and the fire rendered more intense; and thus the production of steam is stimulated, until it is sufficiently rapid for the purposes of the engine. This apparatus is called the _self-acting damper_. (72.) It has been proposed to connect this damper with the safety-valve invented by the Chevalier Edelcrantz. A small brass cylinder is fixed to the boiler, and is fitted with a piston which moves in it, without much friction, and nearly steam-tight. The cylinder is closed at top, having a hole through which the piston-rod plays; so that the piston is thus prevented from being blown out of the cylinder by the steam. The side of the cylinder is pierced with small holes opening into the air, and placed at short distances above each other. Let the piston be loaded with a weight proportional to the pressure of the steam intended to be produced. When the steam has acquired a sufficient elasticity, the piston will be lifted, and steam will escape through the first hole. If the production of steam be not too rapid, and that its pressure be not increasing, the piston will remain suspended in this manner: but if it increase, the piston will be raised above the second hole, and it will continue to rise until the escape of the steam through the holes is sufficient to render the weight of the piston a counterpoise for the steam. This safety valve is particularly well adapted to cases where steam of an exactly uniform pressure is required; for the pressure must necessarily be always equal to the weight on the piston. Thus, suppose the section of the piston be equal to a square inch; if it be loaded with 10 lbs., including its own weight, the steam which will sustain it in any position in the cylinder, whether near the bottom or top, must always be exactly equal in pressure to 10 lbs. per inch. In this respect it resembles the quality already explained in the governor, and renders the pressure of the steam uniform, exactly in the same manner as the governor renders the velocity of the engine uniform. (73.) The economy of fuel depends, in a great degree, on the construction of the furnace, independently of the effects of the arrangements we have already described. The grate or fire-place of an ordinary furnace is placed under the boiler; and the atmospheric air passing through the ignited fuel, supplies sufficient oxygen to support a large volume of flame, which is carried by the draught into a flue, which circulates twice or oftener round the boiler, and in immediate contact with it, and finally issues into the chimney. Through this flue the flame circulates, so as to act on every part of the boiler near which the flue passes; and it is frequently not until it passes into the chimney, and sometimes not until it leaves the chimney, that it ceases to exist in the state of flame. The dense black smoke which is observed to issue from the chimneys of furnaces is formed of a quantity of unconsumed fuel, and may be therefore considered as so much fuel wasted. Besides this, in large manufacturing towns, where a great number of furnaces are employed, it is found that the quantity of smoke which thus becomes diffused through the atmosphere, renders it pernicious to the health, and destructive to the comforts of the inhabitants. These circumstances have directed the attention of engineers to the discovery of means whereby this smoke or wasted fuel may be consumed for the use of the engine itself, or for whatever use the furnace may be applied to. The most usual method of accomplishing this is by so arranging matters that fuel in a state of high combustion, and, therefore, producing no smoke, shall be always kept on that part of the grate which is nearest to the mouth of the flue (and which we shall call the back); by this means the smoke which arises from the imperfectly ignited fuel which is nearer to the front of the grate must pass over the surface of the red fuel, before it enters the flue, and is thereby ignited, and passes in a state of flame into the flue. A passage called the _feeding-mouth_ leads to the front of the grate, and both this passage and the grate are generally inclined at a small angle to the horizon, in order to facilitate the advance of the fuel according as its combustion proceeds. When fresh fuel for feeding the boiler is first introduced, it is merely laid in the feeding-mouth. Here it is exposed to the action of a part of the heat of the burning fuel on the grate, and undergoes, in some degree, the process of coking. The door of the feeding-mouth is furnished with small apertures for the admission of a stream of air, which carries the smoke evolved by the coking of the fresh fuel over the burning fuel on the grate, by which this smoke is ignited, and becomes flame, and in this state enters the flue, and circulates round the boiler. When the furnace is to be fed, the door of the feeding-mouth is opened, and the fuel which had been laid in it, and partially coked, is forced upon the front part of the grate. At first, its combustion being imperfect, but proceeding rapidly, a dense black smoke arises from it. The current of air from the open door through the feeding-mouth carries this over the vividly burning fuel in the back part of the grate, by which the smoke being ignited, passes in a state of flame into the flue. When the furnace again requires feeding, every part of this fuel will be in a state of active combustion, and it is forced to the back part of the grate next the flue, preparatory to the introduction of more fuel from the feeding-mouth. The apertures in the door of the feeding-mouth are furnished with covers, so that the quantity of air admitted through them can be regulated by the workmen. The efficiency of these furnaces in a great degree depends on the judicious admission of the air through the feeding-mouth: for if less than the quantity necessary to support the combustion of the fuel be admitted, a part of the smoke will remain unconsumed; and if more than the proper quantity be admitted, it will defeat the effects of the fuel by cooling the boiler. If the process which we have just described be considered, it will not be difficult to perceive the total impossibility in such a furnace of exactly regulating the draught of air, so that too much shall not pass at one time, and too little at another. When the door is open to introduce fresh fuel into the feeding-mouth, and advance that which occupied it upon the grate, the workman ceases to have any control whatever over the draught of air; and even at other times when the door is closed, his discretion and attention cannot be depended on. The consequence is, that with these defects the proprietors of steam engines found, that in the place of economising the fuel, the use of these furnaces entailed on them such an increased expense that they were generally obliged to lay them aside. (74.) Mr. Brunton of Birmingham having turned his attention to the subject, has produced a furnace which seems to be free from the objections against those we have just mentioned. The advantages of his contrivance, as stated by himself, are as follow:-- "First, I put the coal upon the grate by small quantities, and at very short intervals, say every two or three seconds. 2dly, I so dispose of the coals upon the grate, that the smoke evolved must pass over that part of the grate upon which the coal is in full combustion, and is thereby consumed. 3dly, As the introduction of coal is uniform in short spaces of time, the introduction of air is also uniform, and requires no attention from the fireman. [Illustration: Pl. VIII.] "As it respects economy: 1st, The coal is put upon the fire by an apparatus driven by the engine, and so contrived that the quantity of coal is proportioned to the quantity of work which the engine is performing, and the quantity of air admitted to consume the smoke is regulated in the same manner. 2dly, The fire-door is never opened, excepting to clean the fire; the boiler of course is not exposed to that continual irregularity of temperature which is unavoidable in the common furnace, and which is found exceedingly injurious to boilers. 3dly, The only attention required is to fill the coal receiver, every two or three hours, and clean the fire when necessary. 4thly, The coal is more completely consumed than by the common furnace, as all the effect of what is termed stirring up the fire (by which no inconsiderable quantity of coal is passed into the ash-pit) is attained without moving the coal upon the grate." The fire-place is a circular grate placed on a vertical shaft in a horizontal position. It is capable of revolving, and is made to do so by the vertical shaft, which is turned by wheelwork, which is worked by the engine itself; or this shaft or spindle may be turned by a water-wheel, on which a stream of water is allowed to flow from a reservoir into which it is pumped by the power of the engine; and by regulating the quantity of water in the stream, the grate may be made to revolve with a greater or less speed. In that part of the boiler which is over the grate, there is an aperture, in which is placed a hopper, through which fuel is let down upon the grate at the rate of any quantity per minute that may be required. The apparatus which admits the coals through this hopper is worked by the engine also, and by the same means as the grate is turned so that the grate revolves with a speed proportional to the rapidity with which the fuel is admitted through the hopper, and by this ingenious arrangement the fuel falls equally thick upon the grate. The supply of water which turns the wheel which works the grate and the machinery in the hopper, is regulated by a cock connected with the self-regulating damper; so that when the steam is being produced too fast, the supply of water will be diminished, and by that means the supply of fuel to the grate will be diminished, and the grate will revolve less rapidly: and when the steam is being produced too slowly for the demands of the engine, the contrary effects take place. In this way the fuel which is introduced into the furnace is exactly proportioned to the work which the engine has to perform. The hopper may be made large enough to hold coals for a day's work, so that the furnace requires no other attendance than to deposite coals in the hopper each morning. The coals are let down from the hopper on the grate at that part which is most remote from the flue; and as they descend in very small quantities at a time, they are almost immediately ignited. But until their ignition is complete, a smoke will arise, which, passing to the flue over the vividly burning fuel, will be ignited. Air is admitted through proper apertures, and its quantity regulated by the damper in the same manner as the supply of fuel. The superiority of this beautiful invention over the common smoke-consuming furnaces is very striking. Its principle of self-adjustment as to the supply of coals and atmospheric air, and the proportioning of these to the quantity of work to be performed by the engine, not only independent of human labour, but with a greater degree of accuracy than any human skill or attention could possibly effect, produces saving of expense, both in fuel and labour. (75.) Mr. Oldham, engineer to the Bank of Ireland, has proposed another modification of the self-regulating furnace, which seems to possess several advantages, and evinces considerable ingenuity. He uses a slightly inclined grate, at the back or lower end of which is the flue, and at the front or higher end, the hopper for admitting the coals. In the bottom or narrow end of the hopper is a moveable shelf, worked by the engine. Upon drawing back this shelf, a small quantity of fuel is allowed to descend upon a fixed shelf under it; and upon the return of the moveable shelf, this fuel is protruded forward upon the grate. Every alternate bar of the grate is fixed, but the intermediate ones are connected with levers, by which they are moved alternately up and down.[22] The effect is, that the coals upon the bars are continually stirred, and gradually advanced by their own weight from the front of the grate, where they fall from the hopper, to the back, where they are deposited in the ash-pit. By the shape and construction of the bars, the air is conducted upwards between them, and rushes through the burning fuel, so as to act in the manner of a blowpipe, and the entire surface of the fire presents a sheet of flame. [Footnote 22: Mr. Brunton used moveable bars in a furnace constructed by him before he adopted the horizontal revolving grate. That plan, however, does not appear to have been as successful as the latter, as he has abandoned it. Mr. Oldham states that his furnace has been in use for several years without any appearance of derangement in the mechanism, and with a considerable saving of fuel.] We cannot fail to be struck with the beauty of all these contrivances, by which the engine is made to regulate itself, and supply its own wants. It is in fact, all but alive. It was observed by Belidor, long before the steam engine reached the perfection which it has now acquired, that it resembled an animal, and that no mere work of man ever approached so near to actual _life_. Heat is the principle of its existence. The boiler acts the part of the heart, from which its vivifying fluid rushes copiously through all the tubes, where having discharged the various functions of life, and deposited its heat in the proper places, it returns again to the source it sprung from, to be duly prepared for another circulation. The healthfulness of its action is indicated by the regularity of its pulsations; it procures its own food by its own labour; it selects those parts which are fit for its support, both as to quantity and quality; and has its natural evacuations, by which all the useless and innutritious parts are discharged. It frequently cures its own diseases, and corrects the irregularity of its own actions, exerting something like moral faculties. Without designing to carry on the analogy, Mr. Farey, in speaking of the variations incident to the work performed by different steam engines, states some further particulars in which it maybe curiously extended. "We must observe," says he, "that the variation in the performance of different steam engines, which are constructed on the same principle, working under the same advantages, is the same as would be found in the produce of the labour of so many different horses or other animals when compared with their consumption of food; for the effects of different steam engines will vary as much from small differences in the proportion of their parts, as the strength of animals from the vigour of their constitutions; and again, there will be as great differences in the performance of the same engine when in good and bad order, from all the parts being tight and well oiled, so as to move with little friction, as there is in the labour of an animal from his being in good or bad health, or excessively fatigued: but in all these cases there will be a maximum which cannot be exceeded, and an average which we ought to expect to obtain." CHAPTER IX. DOUBLE-CYLINDER ENGINES. Hornblower's Engine. -- Woolf's Engine. -- Cartwright's Engine. (76.) The expansive property of steam, of which Watt availed himself in his single engine by cutting off the supply of steam before the descent of the piston was completed, was applied in a peculiar manner by an engineer named Hornblower, about the year 1781, and at a later period by Woolf. Hornblower was the first who conceived the idea of working an engine with two cylinders of different sizes, by allowing the steam to flow freely from the boiler until it fills the smaller cylinder, and then permitting it to expand into the greater one, employing it thus to press down two pistons in the manner which we shall presently describe. The condensing apparatus of Hornblower, as well as the other appendages of the engine, do not differ materially from those of Watt; so that it will be sufficient for our present purpose to explain the manner in which the steam is made to act in moving the piston. Let C, fig. 41., be the centre of the great working beam, carrying two arch heads, on which the chains of the piston rods play. The distances of these arch heads from the centre C must be in the same proportion as the length of the cylinders, in order that the same play of the beam may correspond to the plays of both pistons. Let F be the steam-pipe from the boiler, and G a valve to admit the steam above the lesser piston, H is a tube by which a communication may be opened by the valve I between the top and bottom of the lesser cylinder B. K is a tube communicating, by the valve L, between the bottom of the lesser cylinder B and the top of the greater cylinder A. M is a tube communicating, by the valve N, between the top and bottom of the greater cylinder A; and P a tube leading to the condenser by the exhausting valve O. At the commencement of the operation, suppose all the valves opened, and steam allowed to flow through the entire engine until the air be completely expelled, and then let all the valves be closed. To start the engine, let the exhausting valve O and the steam valves G and L be opened, as in fig. 41. The steam will flow freely from the boiler, and press upon the lesser piston, and at the same time the steam below the greater piston will flow into the condenser, leaving a vacuum in the greater cylinder. The valve L being opened, the steam which is under the piston in the lesser cylinder will flow through K, and press on the greater piston, which, having a vacuum beneath it, will consequently descend. At the commencement of the motion, the lesser piston is as much resisted by the steam below it as it is urged by the steam above it; but after a part of the descent has been effected, the steam below the lesser piston passing into the greater, expands into an increased space, and therefore loses its elastic force proportionally. The steam above the lesser piston retaining its full force by having a free communication with the boiler by the valve G, the lesser piston will be urged by a force equal to the excess of the pressure of this steam above the diminished pressure of the expanded steam below it. As the pistons descend, the steam which is between it continually increasing in its bulk, and therefore decreasing in its pressure, from whence it follows, that the force which resists the lesser piston is continually decreasing, while that which presses it down remains the same, and therefore the effective force which impels it must be continually increasing. On the other hand, the force which urges the greater piston is continually decreasing, since there is a vacuum below it, and the steam which presses it is continually expanding into an increased bulk. Impelled in this way, let us suppose the pistons to have arrived at the bottoms of the cylinders, as in fig. 42., and let the valves G, L, and O be closed, and the valves I and N opened. No steam is allowed to flow from the boiler, G being closed, nor any allowed to pass into the condenser, since O is closed, and all communications between the cylinders is stopped by closing L. By opening the valve I, a free communication is made between the top and bottom of the lesser piston through the tube H, so that the steam which presses above the lesser piston will exert the same pressure below it, and the piston is in a state of indifference. In the same manner the valve N being open, a free communication is made between the top and bottom of the greater piston, and the steam circulates above and below the piston, and leaves it free to rise. A counterpoise attached to the pump-rods in this case, draws up the piston, as in Watt's single engine; and when they arrive at the top, the valves I and N are closed, and G, L, and O opened, and the next descent of the pistons is produced in the manner already described, and so the process is continued. The valves are worked by the engine itself, by means similar to some of those already described. By computation, we find the power of this engine to be nearly the same as a similar engine on Watt's expansive principle. It does not however appear, that any adequate advantage was gained by this modification of the principle, since no engines of this construction are now made. (77.) The use of two cylinders was revived by _Arthur Woolf_, in 1804, who, in this and the succeeding year, obtained patents for the application of steam raised under a high pressure to double-cylinder engines. The specification of his patent states, that he has proved by experiment that steam raised under a safety-valve loaded with any given number of pounds upon the square inch, will, if allowed to expand into as many times its bulk as there are pounds of pressure on the square inch, have a pressure equal to that of the atmosphere. Thus, if the safety-valve be loaded with four pounds on the square inch, the steam, after expanding into four times its bulk, will have the atmospheric pressure. If it be loaded with 5, 6, or 10 lbs. on the square inch, it will have the atmospheric pressure when it has expanded into 5, 6, or 10 times its bulk, and so on. It was, however, understood in this case, that the vessel into which it was allowed to expand should have the same temperature as the steam before it expands. It is very unaccountable how a person of Mr. Woolf's experience in the practical application of steam could be led into errors so gross as those involved in the averments of this patent; and it is still more unaccountable how the experiments could have been conducted which led him to conclusions not only incompatible with all the established properties of elastic fluids--properties which at that time were perfectly understood--but even involving in themselves palpable contradiction and absurdity. If it were admitted that every additional pound avoirdupois which should be placed upon the safety-valve would enable steam, by its expansion into a proportionally enlarged space, to attain a pressure equal to the atmosphere, the obvious consequence would be, that a physical relation would subsist between the atmospheric pressure and the pound avoirdupois! It is wonderful that it did not occur to Mr. Woolf, that, granting his principle to be true at any given place, it would necessarily be false at another place where the barometer would stand at a different height. Thus if the principle were true at the foot of a mountain, it would be false at the top of it; and if it were true in fair weather, it would be false in foul weather, since these circumstances would be attended by a change in the atmospheric pressure, without making any change in the pound avoirdupois.[23] [Footnote 23: It is strange that this absurdity has been repeatedly given as unquestionable fact in various encyclopædias on the article "Steam Engine," as well as in by far the greater number of treatises expressly on the subject.] The method by which Mr. Woolf proposed to apply the principle which he imagined himself to have discovered was by an arrangement of cylinders similar to those of Hornblower, but having their magnitudes proportioned to the greater extent of expansion which he proposed to use. Two cylinders, like those of Hornblower, were placed under the working beam, having their piston-rods at distances from the axis proportioned to the lengths of their respective strokes. The relative magnitudes of the cylinders A and B must be adjusted according to the extent to which the principle of expansion is intended to be used. The valves C C´ were placed at each end of the lesser cylinder in tubes communicating with the boiler, so as to admit steam on each side of the lesser piston, and cut it off at pleasure. A tube, D´, formed a communication between the upper end of the lesser and lower end of the greater cylinder, which communication is opened and closed at pleasure by the valve E´. In like manner, the tube D forms a communication between the lower end of the lesser cylinder and the upper end of the greater, which may be opened and closed by the valve E. The top and bottom of the greater cylinder communicated with the condenser by valves F´ F. Let us suppose that the air is blown from the engine in the usual way, all the valves closed, and the engine ready to start, the pistons being at the top of the cylinders. Open the valves C, E, and F. The steam which occupies the greater cylinder below the piston will now pass into the condenser through F, leaving a vacuum below the piston. The steam which is in the lesser cylinder below the piston will pass through D and open the valve E, and will press down the greater piston. The steam from the boiler will flow in at C, and press on the lesser piston. At first the whole motion will proceed from the pressure upon the greater piston, since the steam, both above and below the lesser piston, has the same pressure. But, as the pistons descend, the steam below the less passing into the greater cylinder, expands into a greater space, and consequently exerts a diminished pressure, and, therefore, the steam on the other side exerting an undiminished pressure, acquires an impelling force exactly equal to the pressure lost in the expansion of the steam between the two pistons. Thus both pistons will be pressed to the bottoms of their respective cylinders. It will be observed that in the descent the greater piston is urged by a continually decreasing force, while the lesser is urged by continually increasing force. Upon the arrival of the pistons at the bottoms of the cylinders, let the valves, C, E, F be closed, and C´, E´, F´ be opened, as in fig. 44. The steam which is above the greater piston now flows through F´ into the condenser, leaving the space above the piston a vacuum. The steam which is above the lesser piston passes through E´ and D´ below the greater, while the steam from the boiler is admitted through C´ below the lesser piston. The pressure of the steam entering through E´ below the greater piston, pressing on it against the vacuum above it, commences the ascent. In the mean time the steam above the lesser piston passing into the enlarged space of the greater cylinder, loses gradually its elastic force, so that the steam entering from the boiler at C´ becomes in part effective, and the ascent is completed under exactly the same circumstances as the descent, and in this way the process is continued. It is evident that the valves may be easily worked by the mechanism of the engine itself. In this arrangement the pistons ascend and descend together, and their rods must consequently be attached to the beam at the same side of the centre. It is sometimes desirable that they should act on different sides of the centre of the beam, and consequently that one should ascend while the other descends. It is easy to arrange the valves so as to effect this. In fig. 45., the lesser piston is at the bottom of the cylinder, and the greater at the top. On opening the valves C´, E´, F´, a vacuum is produced below the greater piston, and steam flows from the lesser cylinder, through E´, _above_ the greater piston, and presses it down. At the same time steam being admitted from the boiler through C´ below the lesser piston, forces it up against the diminishing force of the steam above it, which expands into the greater cylinder. Thus as the greater piston descends the lesser ascends. When each has traversed its cylinder, the valves C´, E´, F´ being closed, and C, E, F opened, the lesser piston will descend, and the greater ascend, and so on. (78.) The law according to which the elastic force of steam diminishes as it expands, of which Mr. Woolf appears to have been entirely ignorant, is precisely similar to the same property in air and other elastic fluids. If steam expands into twice or thrice its volume, it will lose its elastic force in precisely the same proportion as it enlarges its bulk; and therefore will have only a half or a third of its former pressure, supposing that as it expands its temperature is kept up. Although Mr. Woolf's patent contained the erroneous principle which we have noticed, yet, so far as his invention suggested the idea of employing steam at a very high-pressure, and allowing it to expand in a much greater degree than was contemplated either by Watt or Hornblower, it became the means of effecting a considerable saving in fuel; for engines used for pumping on a large scale, the steam being produced under a pressure of forty or fifty pounds or more upon the square inch, might be worked first through a small space with intense force, and the communication with the boiler being then cut off, it might be allowed, with great advantage, to expand through a very large space. Some double-cylinder engines upon this principle have been worked in Cornwall, with considerable economy. But the form in which the expansive principle, combined with high pressure, is now applied in the engines used for raising water from the mines, is that in which it was originally proposed by Watt. A single cylinder of considerable length is employed; the piston is driven through a small proportion of this length by steam, admitted from the boiler at a very intense pressure: the steam being then cut off, the piston is urged by the expansive force of the steam which has been admitted, and is by that means brought to the bottom of the cylinder. It is evident, under such circumstances, that the pressure of the steam admitted from the boiler must be much greater than the resistance opposed to the piston, and that the motion of the piston must, in the first instance, be accelerated and not uniform. If the piston moved from the commencement with a uniform motion, the pressure of the steam urging it must necessarily be exactly equal to the resistance opposed to it, and then cutting off the supply of steam from the boiler, the piston could only continue its motion by inertia, the steam immediately becoming of less pressure than the resistance; and after advancing through a very small space, the piston would recoil upon the steam, and come to a state of rest. The steam, however, at the moment it is cut off being of much greater pressure than the amount of resistance upon the piston, will continue to drive the piston forward, until by its expansion its force is so far diminished as to become equal to the resistance of the piston. From that point the impelling power of the steam will cease, and the piston will move forward by its inertia only. The point at which the steam is cut off should therefore be so regulated that it shall acquire a pressure equal to the resistance on the piston by its expansion, just at such a distance from the end of the stroke as the piston may be able to move through by its inertia. It is evident the adjustment of this will require great care and nicety of management. (79.) In 1797 a patent was granted to the _Rev. Mr. Cartwright_, a gentleman well known for other mechanical inventions, for some improvements in the steam-engine. His contrivance is at once so elegant and simple, that, although it has not been carried into practice, we cannot here pass it over without notice. The steam-pipe from the boiler is represented cut off at B (fig. 46.); T is a spindle-valve for admitting steam above the piston, and R is a spindle-valve in the piston; D is a curved pipe forming a communication between the cylinder and the condenser, which is of very peculiar construction. Cartwright proposed effecting a condensation without a jet, by exposing the steam to contact with a very large quantity of cold surface. For this purpose, he formed his condenser by placing two cylinders nearly equal in size one within the other, allowing the water of the cold cistern in which they were placed to flow through the inner cylinder, and to surround the outer one. Thus the thin space between the two cylinders formed the condenser. [Illustration: Pl. IX.] [Illustration: Pl. X.] The air-pump is placed immediately under the cylinder, and the continuation of the piston-rod works its piston, which is solid and without a valve: F is the pipe from the condenser to the air-pump, through which the condensed steam is drawn off through the valve G on the ascent of the piston, and on the descent, this is forced through a tube into a hot well, H, for the purpose of feeding the boiler through the feed-pipe I. In the top of the hot well H is a valve which opens inwards, and is kept closed by a ball floating on the surface of the liquid. The pressure of the condensed air above the surface of the liquid in H forces it through I into the boiler. When the air accumulates in too great a degree in H, the surface of the liquid is pressed so low that the ball falls and opens the valve, and allows it to escape. The air in H is that which is pumped from the condenser with the liquid, and which was disengaged from it. Let us suppose the piston at the top of the cylinder; it strikes the tail of the valve T, and raises it, while the stem of the piston-valve R strikes the top of the cylinder, and is pressed into its seat. A free communication is at the same time open between the cylinder, below the piston and the condenser, through the tube D. The pressure of the steam thus admitted above the piston, acting against the vacuum below it, will cause its descent. On arriving at the bottom of the cylinder, the tail of the piston-valve R will strike the bottom, and it will be lifted from its seat, so that a communication will be opened through it with the condenser. At the same moment a projecting spring, K, attached to the piston-rod, strikes the stem of the steam-valve T, and presses it into its seat. Thus, while the further admission of steam is cut off, the steam above the piston flows into the condenser, and the piston being relieved from all pressure, is drawn up by the momentum of the fly-wheel, which continues the motion it received from the descending force. On the arrival of the piston again at the top of the cylinder, the valve T is opened and R closed, and the piston descends as before, and so the process is continued. The mechanism by which motion is communicated from the piston to the fly-wheel is peculiarly elegant. On the axis of the fly-wheel is a small wheel with teeth, which work in the teeth of another large wheel L. This wheel is turned by a crank, which is worked by a cross-piece attached to the end of the piston-rod. Another equal-toothed wheel, M, is turned by a crank, which is worked by the other end of the cross-arm attached to the piston-rod. One of the peculiarities of this engine is, that the liquid which is used for the production of steam in the boiler circulates through the machine without either diminution or admixture with any other fluid, so that the boiler never wants more feeding than what can be supplied from the hot-well H. This circumstance forms a most important feature in the machine, as it allows of ardent spirits being used in the boiler instead of water, which, since they boil at low heats, promised a saving of half the fuel. The inventor even proposed, that the engine should be used as a still, as well as a mechanical power, in which case the whole of the fuel would be saved. In this engine, the ordinary method of rendering the piston steam-tight, by oil or melted wax or tallow poured upon it, could not be applied, since the steam above the piston must always have a free passage through the piston-valve R. The ingenious inventor therefore contrived a method of making the piston steam-tight in the cylinder, without oil or stuffing, and his method has since been adopted with success in other engines. A ring of metal is ground into the cylinder, so as to fit it perfectly, and is then cut into four equal segments. The inner surface of this ring being slightly conical, another ring is ground into it, so as to fit it perfectly, and this is also cut into four segments, and one is placed within the other, but in such a manner that the joints or divisions do not coincide. The arrangement of the two rings is represented in fig. 47. Within the inner ring are placed four springs, which press the pieces outward against the sides of the cylinder, and are represented in the diagram. Four pairs of these rings are placed one over another, so that their joints do not coincide, and the whole is screwed together by plates placed at top and bottom. A vertical section of the piston is given in fig. 48. One of the advantages of this piston is, that the longer it is worked, the more accurately it fits the cylinder, so that, as the machine wears it improves. Metallic pistons have lately come into very general use, and such contrivances differ very little from the above. CHAPTER X. LOCOMOTIVE ENGINES ON RAILWAYS. High-pressure Engines. -- Leupold's Engine. -- Trevithick and Vivian. -- Effects of Improvement in Locomotion. -- Historical Account of the Locomotive Engine. -- Blenkinsop's Patent. -- Chapman's Improvement. -- Walking Engine. -- Stephenson's First Engines. -- His Improvements. -- Liverpool and Manchester Railway Company. -- Their Preliminary Proceedings. -- The Great Competition of 1829. -- The Rocket. -- The Sanspareil. -- The Novelty. -- Qualities of the Rocket. -- Successive Improvements. -- Experiments. -- Defects of the Present Engines. -- Inclined Planes. -- Methods of surmounting them. -- Circumstances of the Manchester Railway Company. -- Probable Improvements in Locomotives. -- Their capabilities with respect to speed. -- Probable Effects of the Projected Railroads. -- Steam Power compared with Horse Power. -- Railroads compared with Canals. (80.) In the various modifications of the steam engine which we have hitherto considered, the pressure introduced on one side of the piston derives its efficacy either wholly or partially from the vacuum produced by condensation on the other side. This always requires a condensing apparatus, and a constant and abundant supply of cold water. An engine of this kind must therefore necessarily have considerable dimensions and weight, and is inapplicable to uses in which a small and light machine only is admissible. If the condensing apparatus be dispensed with, the piston will always be resisted by a force equal to the atmospheric pressure, and the only part of the steam pressure which will be available as a moving power, is that part by which it exceeds the pressure of the atmosphere. Hence, in engines which do not work by condensation, steam of a much higher pressure than that of the atmosphere is indispensably necessary, and such engines are therefore called _high-pressure engines_. We are not, however, to understand that every engine, in which steam is used of a pressure exceeding that of the atmosphere, is what is meant by a _high-pressure engine_; for in the ordinary engines in common use, constructed on Watt's principle, the safety-valve is loaded with from 3 to 5 lbs. on the square inch; and in Woolf's engines, the steam is produced under a pressure of 40 lbs. on the square inch. These would therefore be more properly called _condensing engines_ than _high-pressure engines_; a term quite inapplicable to those of Woolf. In fact, by _high-pressure engines_ is meant engines in which no vacuum is produced, and, therefore, in which the piston works against a pressure equal to that of the atmosphere. In these engines, the whole of the condensing apparatus, _viz._ the cold-water cistern, condenser, air-pump, cold-water pump, &c. are dispensed with, and nothing is retained except the boiler, cylinder, piston, and valves. Consequently, such an engine is small, light, and cheap. It is portable also, and may be moved, if necessary, along with its load, and is therefore well adapted to locomotive purposes. (81.) High-pressure engines were one of the earliest modifications of the steam engine. The contrivance, which is obscurely described in the article already quoted (27.), from the Century of Inventions, is a high-pressure engine; for the power there alluded to is the elastic force of steam working against the atmospheric pressure. _Newcomen_, in 1705, applied the working-beam, cylinder, and piston to the atmospheric engine; and _Leupold_, about 1720, combined the working-beam and cylinder with the high-pressure principle, and produced the earliest high-pressure engine worked by a cylinder and piston. The following is a description of _Leupold's_ engine:-- A (fig. 49.) is the boiler, with the furnace beneath it; C C´ are two cylinders with two solid pistons, P P´, connected with the working-beams B B´, to which are attached the pump-rods, R R´, of two forcing-pumps, F F´, which communicate with a great force-pipe S; G is a _four-way cock_ (66.) already described. In the position in which it stands in the figure, the steam is issuing from below the piston P into the atmosphere, and the piston is descending by its own weight; steam from the boiler is at the same time pressing up the piston P´, with a force equal to the difference between the pressure of the steam and that of the atmosphere. Thus the piston R of the forcing-pump is being drawn up, and the piston P´ is forcing the piston R´ down, and thereby driving water into the force-pipe S. On the arrival of the piston P at the bottom of the cylinder C, and P´ at the top of the cylinder C´, the position of the cock is changed as represented in fig. 50. The steam, which has just pressed up the piston P´, is allowed to escape into the atmosphere, while the steam, passing from the boiler below the piston P, presses it up, and thus P ascends by the steam pressure, and P´ descends by its own weight. By these means the piston R is forced down, driving before it the water in the pump cylinder into the force-pipe S, and the piston R´ is drawn up to allow the other pump-cylinder to be re-filled; and so the process is continued. A valve is placed in the bottom of the force-pipes, to prevent the water which has been driven into it from returning. This valve opens upwards; and, consequently, the weight of the water pressing upon it only keeps it more effectually closed. On each descent of the piston, the pressure transmitted to the valve acting upwards being greater than the weight of the water resting upon it, forces it open, and an increased quantity of water is introduced. (82.) From the date of the improvement of Watt until the commencement of the present century, high-pressure engines were altogether neglected in these countries. In the year 1802, Messrs. _Trevithick_ and _Vivian_ constructed the first high-pressure engine which was ever brought into extensive practical use in this kingdom. A section of this machine, made by a vertical plane, is represented in fig. 51. The boiler A B is a cylinder with flat circular ends. The fire-place is constructed in the following manner:--A tube enters the cylindrical boiler at one end; and, proceeding onwards, near the other extremity, is turned and recurved, so as to be carried back parallel to the direction in which it entered. It is thus conducted out of the boiler, at another part of the same end at which it entered. One of the ends of this tube communicates with the chimney E, which is carried upwards, as represented in the figure. The other mouth is furnished with a door; and in it is placed the grate, which is formed of horizontal bars, dividing the tube into two parts; the upper part forming the fire-place, and the lower the ash-pit. The fuel is maintained in a state of combustion, on the bars, in that part of the tube represented at C D; and the flame is carried by the draft of the chimney round the curved flue, and issues at E into the chimney. The flame is thus conducted through the water, so as to expose the latter to as much heat as possible. A section of the cylinder is represented at F, immersed in the boiler, except a few inches of the upper end, where the four-way cock G is placed for regulating the admission of the steam. A tube is represented at H, which leads from this four-way cock into the chimney; so that the waste steam, after working the piston, is carried off through this tube, and passes into the chimney. The upper end of the piston-rod is furnished with a cross-bar, which is placed in a direction at right angles to the length of the boiler, and also to the piston-rod. This bar is guided in its motion by sliding on two iron perpendicular rods fixed to the sides of the boiler, and parallel to each other. To the ends of this cross-bar are joined two connecting rods, the lower ends of which work two cranks fixed on an axis extending across and beneath the boiler, and immediately under the centre of the cylinder. This axis is sustained in bearings formed in the legs which support the boiler, and upon its extremity is fixed the fly-wheel as represented at B. A large-toothed wheel is placed on this axis; which, being turned with the cranked axle, communicates motion to other wheels; and, through them, to any machinery which the engine may be applied to move. As the four-way cock is represented in the figure, the steam passes from the boiler through the curved passage G above the piston, while the steam below the piston is carried off through a tube which does not appear in the figure, by which it is conducted to the tube H, and thence to the chimney. The steam, therefore, which passes above the piston presses it downwards; while the pressure upwards does not exceed that of the atmosphere. The piston will therefore descend with a force depending on the excess of the pressure of the steam produced in the boiler above the atmospheric pressure. When the piston has arrived at the bottom of the cylinder, the cock is made to assume the position represented in the figure 52. This effect is produced by the motion of the piston-rod. The steam now passes from above the piston, through the tube H, into the chimney, while the steam from the boiler is conducted through another tube below the piston. The pressure above the piston, in this case, does not exceed that of the atmosphere; while the pressure below it will be that of the steam in the boiler. The piston will therefore ascend with the difference of these pressures. On the arrival of the piston at the top of the cylinder, the four-way cock is again turned to the position represented in fig. 51., and the piston again descends; and in the same manner the process is continued. A safety-valve is placed on the boiler at V, loaded with a weight W, proportionate to the strength of the steam with which it is proposed to work. [Illustration: Pl. XI.] In the engines now described, this valve was frequently loaded at the rate of from 60 to 80 lbs. on the square inch. As the boilers of high-pressure engines were considered more liable to accidents from bursting than those in which steam of a lower pressure was used, greater precautions were taken against such effects. A second safety-valve was provided, which was not left in the power of the engine-man. By this means he had a power to diminish the pressure of the steam, but could not increase it beyond the limit determined by the valve which was removed from his interference. The greatest cause of danger, however, arose from the water in the boiler being consumed by evaporation faster than it was supplied; and therefore falling below the level of the tube containing the furnace. To guard against accidents arising from this circumstance, a hole was bored in the boiler, at a certain depth, below which the water should not be allowed to fall; and in this hole a plug of metal was soldered with lead, or with some other metal, which would fuse at that temperature which would expose the boiler to danger. Thus, in the event of the water being exhausted, so that its level would fall below the plug, the heat of the furnace would immediately melt the solder, and the plug would fall out, affording a vent for the steam, without allowing the boiler to burst. The mercurial steam-gauge, already described, was also used as an additional security. When the force of the steam exceeded the length of the column of mercury which the tube would contain, the mercury would be blown out, and the tube would give vent to the steam. The water by which the boiler was replenished was forced into it by a pump worked by the engine. In order to economise the heat, this water was contained in a tube T, which surrounded the pipe H. As the waste steam, after working the piston, passed off through H, it imparted a portion of its heat to the water contained in the tube T, which was thus warmed to a certain temperature before it was forced into the boiler by the pump. Thus a part of the heat, which was originally carried from the boiler in the form of steam, was returned again to the boiler with the water with which it was fed. It is evident that engines constructed in this manner may be applied to all the purposes to which the condensing engines are applicable. (_e_) To the plates of the English edition has been added one, (plate A) representing a high-pressure engine as constructed by the West Point Foundry in the state of New York. The principal parts will be readily distinguished from their resemblance to the analogous parts of a condensing engine. The condenser and air-pump of that engine, it will be observed, are suppressed. At _v x_ and _y z_ are forcing-pumps by which a supply of water is injected into the boiler at each motion of the engine. For the four-way cock, used in the English high-pressure engines, a slide valve at _r s_, is substituted, and is found to work to much greater advantage. It is set in motion by an eccentric, in a manner that will be more obvious from an inspection of the plate than from any description.--A. E. (_f_) A very safe and convenient boiler for a high-pressure engine has been invented in the United States by Mr. Babcock. The boiler consists of small tubes, into which water is flashed by a small forcing-pump at every stroke of the engine. The tubes are kept so hot in a furnace, as to generate steam of the required temperature, but not hot enough to cause any risk of the decomposition of the water. The strength of the apparatus is such, and the quantity of water exposed to heat at one time so small, as to leave hardly any risk of danger.--A. E. (83.) Two years after the date of the patent of this engine, its inventor constructed a machine of the same kind for the purpose of moving carriages on railroads; and applied it successfully, in the year 1804, on the railroad at Merthyr Tydvil, in South Wales. It was in principle the same as that already described. The cylinder however was in a horizontal position, the piston-rod working in the direction of the line of road: the extremity of the piston-rod, by means of a connecting rod, worked cranks placed on the axletree, on which were fixed two cogged wheels: these worked in others, by which their motion was communicated finally to cogged wheels fixed on the axle of the hind wheels of the carriage, by which this axle was kept in a state of revolution. The hind wheels being fixed on the axletree, and turning with it, were caused likewise to revolve; and so long as the weight of the carriage did not exceed that which the friction of the road was capable of propelling, the carriage would thus be moved forwards. On this axle was placed a fly-wheel to continue the rotatory motion at the termination of each stroke. The fore wheels are described as being capable of turning like the fore wheels of a carriage, so as to guide the vehicle. The projectors appear to have contemplated, in the first instance, the use of this carriage on turnpike roads; but that notion seems to have been abandoned, and its use was only adopted on the railroad before mentioned. On the occasion of its first trial, it drew after it as many carriages as contained 10 tons of iron a distance of nine miles; which stage it performed without any fresh supply of water, and travelled at the rate of five miles an hour. (84.) Capital and skill have of late years been directed with extraordinary energy to the improvement of inland transport; and this important instrument of national wealth and civilisation has received a proportionate impulse. Effects are now witnessed, which, had they been narrated a few years since, could only have been admitted into the pages of fiction or volumes of romance. Who could have credited the possibility of a ponderous engine of iron, loaded with several hundred passengers, in a train of carriages of corresponding magnitude, and a large quantity of water and coal, taking flight from Manchester and arriving at Liverpool, a distance of about thirty miles, in little more than an hour? And yet this is a matter of daily and almost hourly occurrence. Neither is the road, on which this wondrous performance is effected, the most favourable which could be constructed for such machines. It is subject to undulations and acclivities, which reduce the rate of speed much more than similar inequalities affect the velocity on common roads. The rapidity of transport thus attained is not less wonderful than the weights transported. Its capabilities in this respect far transcend the exigencies even of the two greatest commercial marts in Great Britain. Loads, varying from 50 to 150 tons are transported at the average rate of 15 miles an hour; but the engines in this case are loaded below their power; and in one instance we have seen a load--we should rather say a _cargo_--of wagons, conveying merchandise to the amount of 230 tons gross, transported from Liverpool to Manchester at the average rate of 12 miles an hour. The astonishment with which such performances must be viewed, might be qualified, if the art of transport by steam on railways had been matured, and had attained that full state of perfection which such an art is always capable of receiving from long experience, aided by great scientific knowledge, and the unbounded application of capital. But such is not the present case. The art of constructing locomotive engines, so far from having attained a state of maturity, has not even emerged from its infancy. So complete was the ignorance of its powers which prevailed, even among engineers, previous to the opening of the Liverpool railway, that the transport of heavy goods was regarded as the chief object of the undertaking, and its principal source of revenue. The incredible speed of transport, effected even in the very first experiments in 1830, burst upon the public, and on the scientific world, with all the effect of a new and unlooked-for phenomenon. On the unfortunate occasion which deprived this country of Mr. Huskisson, the wounded body of that statesman was transported a distance of about fifteen miles in twenty-five minutes, being at the rate of thirty-six miles an hour. The revenue of the road arising from passengers since its opening, has, contrary to all that was foreseen, been nearly double that which has been derived from merchandise. So great was the want of experience in the construction of engines, that the company was at first ignorant whether they should adopt large steam-engines fixed at different stations on the line, to pull the carriages from station to station, or travelling engines to drag the loads the entire distance. Having decided on the latter, they have, even to the present moment, laboured under the disadvantage of the want of that knowledge which experience alone can give. The engines have been constantly varied in their weight and proportions, in their magnitude and form, as the experience of each successive month has indicated. As defects became manifest they were remedied; improvements suggested were adopted; and each quarter produced engines of such increased power and efficiency, that their predecessors were abandoned, not because they were worn out, but because they had been outstripped in the rapid march of improvement. Add to this, that only one species of travelling engine has been effectively tried; the capabilities of others remain still to be developed; and even that form of engine which has received the advantage of a course of experiments on so grand a scale to carry it towards perfection, is far short of this point, and still has defects, many of which, it is obvious, time and experience will remove. If then travelling steam engines, with all the imperfections of an incipient invention--with the want of experience, the great parent of practical improvements--with the want of the common advantage of the full application of the skill and capital of the country--subjected to but one great experiment, and that experiment limited to one form of engine; if, under such disadvantages, the effects to which we have referred have been produced, what may we not expect from this extraordinary power, when the enterprise of the country shall be unfettered, when greater fields of experience are opened, when time, ingenuity, and capital have removed the existing imperfections, and have brought to light new and more powerful principles? This is not mere speculation on possibilities, but refers to what is in a state of actual progression. Railways are in progress between the points of greatest intercourse in the United Kingdom, and travelling steam engines are in preparation for the common turnpike roads; the practicability and utility of that application of the steam engine having not only been established by experiment to the satisfaction of their projectors, but proved before the legislature in a committee of inquiry on the subject. The important commercial and political effects attending such increased facility and speed in the transport of persons and goods, are too obvious to require any very extended notice here. A part of the price (and in many cases a considerable part) of every article of necessity or luxury, consists of the cost of transporting it from the producer to the consumer; and consequently every abatement or saving in this cost must produce a corresponding reduction in the price of every article transported; that is to say, of everything which is necessary for the subsistence of the poor, or for the enjoyment of the rich, of every comfort, and of every luxury of life. The benefit of this will extend, not to the consumer only, but to the producer: by lowering the expense of transport of the produce, whether of the soil or of the loom, a less quantity of that produce will be spent in bringing the remainder to market, and consequently a greater surplus will reward the labour of the producer. The benefit of this will be felt even more by the agriculturist than by the manufacturer; because the proportional cost of transport of the produce of the soil is greater than that of manufactures. If 200 quarters of corn be necessary to raise 400, and 100 more be required to bring the 400 to market, then the net surplus will be 100. But if by the use of steam carriages the same quantity can be brought to market with an expenditure of 50 quarters, then the net surplus will be increased from 100 to 150 quarters; and either the profit of the farmer, or the rent of the landlord, must be increased by the same amount. But the agriculturist would not merely be benefited by an increased return from the soil already under cultivation. Any reduction in the cost of transporting the produce to market would call into cultivation tracts of inferior fertility, the returns from which would not at present repay the cost of cultivation and transport. Thus land would become productive which is now waste, and an effect would be produced equivalent to adding so much fertile soil to the present extent of the country. It is well known, that land of a given degree of fertility will yield increased produce by the increased application of capital and labour. By a reduction in the cost of transport, a saving will be made which may enable the agriculturist to apply to tracts already under cultivation the capital thus saved, and thereby increase their actual production. Not only, therefore, would such an effect be attended with an increased extent of cultivated land, but also with an increased degree of cultivation in that which is already productive. It has been said, that in Great Britain there are above a million of horses engaged in various ways in the transport of passengers and goods, and that to support each horse requires as much land as would, upon an average, support eight men. If this quantity of animal power were displaced by steam engines, and the means of transport drawn from the bowels of the earth, instead of being raised upon its surface, then, supposing the above calculation correct, as much land would become available for the support of human beings as would suffice for an additional population of eight millions; or, what amounts to the same, would increase the means of support of the present population by about one-third of the present available means. The land which now supports horses for transport would then support men, or produce corn for food. The objection that a quantity of land exists in the country capable of supporting horses alone, and that such land would be thrown out of cultivation, scarcely deserves notice here. The existence of any considerable quantity of such land is extremely doubtful. What is the soil which will feed a horse and not feed oxen or sheep, or produce food for man? But even if it be admitted that there exists in the country a small portion of such land, that portion cannot exceed, nor indeed equal, what would be sufficient for the number of horses which must after all continue to be employed for the purposes of pleasure, and in a variety of cases where steam must necessarily be inapplicable. It is to be remembered, also, that the displacing of horses in one extensive occupation, by diminishing their price must necessarily increase the demand for them in others. The reduction in the cost of transport of manufactured articles, by lowering their price in the market, will stimulate their consumption. This observation applies of course not only to home but to foreign markets. In the latter we already in many branches of manufacture command a monopoly. The reduced price which we shall attain by cheapness and facility of transport will still further extend and increase our advantages. The necessary consequence will be, an increased demand for manufacturing population; and this increased population again reacting on the agricultural interests, will form an increased market for that species of produce. So interwoven and complicated are the fibres which form the texture of the highly civilized and artificial community in which we live, that an effect produced on any one point is instantly transmitted to the most remote and apparently unconnected parts of the system. The two advantages of increased cheapness and speed, besides extending the amount of existing traffic, call into existence new objects of commercial intercourse. For the same reason that the reduced cost of transport, as we have shown, calls new soils into cultivation, it also calls into existence new markets for manufactured and agricultural produce. The great speed of transit which has been proved to be practicable, must open a commerce between distant points in various articles, the nature of which does not permit them to be preserved so as to be fit for use beyond a certain time. Such are, for example, many species of vegetable and animal food, which at present are confined to markets at a very limited distance from the grower or feeder. The truth of this observation is manifested by the effects which have followed the intercourse by steam on the Irish Channel. The western towns of England have become markets for a prodigious quantity of Irish produce, which it had been previously impossible to export. If animal food be transported alive from the grower to the consumer, the distance of the market is limited by the power of the animal to travel, and the cost of its support on the road. It is only particular species of cattle which bear to be carried to market on common roads and by horse carriages. But the peculiar nature of a railway, the magnitude and weight of the loads which may be transported on it, and the prodigious speed which may be attained, render the transport of cattle, of every species, to almost any distance, both easy and cheap. In process of time, when the railway system becomes extended, the metropolis and populous towns will therefore become markets, not as at present to districts within limited distances of them, but to the whole country. The moral and political consequences of so great a change in the powers of transition of persons and intelligence from place to place are not easily calculated. The concentration of mind and exertion which a great metropolis always exhibits, will be extended in a considerable degree to the whole realm. The same effect will be produced as if all distances were lessened in the proportion in which the speed and cheapness of transit are increased. Towns, at present removed some stages from the metropolis, will become its suburbs; others, now a day's journey, will be removed to its immediate vicinity; business will be carried on with as much ease between them and the metropolis, as it is now between distant points of the metropolis itself. Let those who discard speculations like these as wild and improbable, recur to the state of public opinion, at no very remote period, on the subject of steam navigation. Within the memory of persons who have not yet passed the meridian of life, the possibility of traversing by the steam engine the channels and seas that surround and intersect these islands, was regarded as the dream of enthusiasts. Nautical men and men of science rejected such speculations with equal incredulity, and with little less than scorn for the understanding of those who could for a moment entertain them. Yet we have witnessed steam engines traversing not these channels and seas alone, but sweeping the face of the waters round every coast in Europe. The seas which interpose between our Asiatic dominions and Egypt, and those which separate our own shores from our West Indian possessions, have offered an equally ineffectual barrier to its powers. Nor have the terrors of the Pacific prevented the "Enterprise" from doubling the Cape, and reaching the shores of India. If steam be not used as the only means of connecting the most distant points of our planet, it is not because it is inadequate to the accomplishment of that end, but because the supply of the material from which at the present moment it derives its powers, is restricted by local and accidental circumstances.[24] [Footnote 24: Some of the preceding observations on inland transport, as well as other parts of the present chapter, appeared in articles written by me in the Edinburgh Review for October, 1832, and October, 1834.] We propose in the present chapter to lay before our readers some account of the means whereby the effects above referred to have been produced; of the manner and degree in which the public have availed themselves of these means; and of the improvements of which they seem to us to be susceptible. (85.) It is a singular fact, that in the history of this invention considerable time and great ingenuity were vainly expended in attempting to overcome a difficulty, which in the end turned out to be purely imaginary. To comprehend distinctly the manner in which a wheel carriage is propelled by steam, suppose that a pin or handle is attached to the spoke of the wheel at some distance from its centre, and that a force is applied to this pin in such a manner as to make the wheel revolve. If the face of the wheel and the surface of the road were absolutely smooth and free from friction, so that the face of the wheel would slide without resistance upon the road, then the effect of the force thus applied would be merely to cause the wheel to turn round, the carriage being stationary, the surface of the wheel would slip or slide upon the road as the wheel is made to revolve. But if, on the other hand, the pressure of the face of the wheel upon the road is such as to produce between them such a degree of adhesion as will render it impossible for the wheel to slide or slip upon the road by the force which is applied to it, the consequence will be, that the wheel can only turn round in obedience to the force which moves it by causing the carriage to advance, so that the wheel will roll upon the road, and the carriage will be moved forward, through a distance equal to the circumference of the wheel, each time it performs a complete revolution. It is obvious that both of these effects may be partially produced; the adhesion of the wheel to the road may be insufficient to prevent slipping altogether, and yet it may be sufficient to prevent the wheel from slipping as fast as it revolves. Under such circumstances the carriage would advance and the wheel would slip. The progressive motion of the carriage during one complete revolution of the wheel would be equal to the difference between the complete circumference of the wheel and the portion through which in one revolution it has slipped. When the construction of travelling steam engines first engaged the attention of engineers, and for a considerable period afterwards, a notion was impressed upon their minds that the adhesion between the face of the wheel and the surface of the road must necessarily be of very small amount, and that in every practical case the wheels thus driven would either slip altogether, and produce no advance of the carriage, or that a considerable portion of the impelling power would be lost by the partial slipping or sliding of the wheels. It is singular that it should never have occurred to the many ingenious persons who for several years were engaged in such experiments and speculations, to ascertain by experiment the actual amount of adhesion in any particular case between the wheels and the road. Had they done so, we should probably now have found locomotive engines in a more advanced state than that to which they have attained. To remedy this imaginary difficulty, Messrs. _Trevithick_ and _Vivian_ proposed to make the external rims of the wheels rough and uneven, by surrounding them with projecting heads of nails or bolts, or by cutting transverse grooves on them. They proposed, in cases where considerable elevations were to be ascended, to cause claws or nails to project from the surface during the ascent, so as to take hold of the road. In seven years after the construction of the first locomotive engine by these engineers, another locomotive engine was constructed by Mr. _Blinkensop_, of Middleton Colliery, near Leeds. He obtained a patent, in 1811, for the application of a rack-rail. The railroad thus, instead of being composed of smooth bars of iron, presented a line of projecting teeth, like those of a cog-wheel, which stretched along the entire distance to be travelled. The wheels on which the engine rolled were furnished with corresponding teeth, which worked in the teeth of the railroad; and, in this way, produced a progressive motion in the carriage. The next contrivance for overcoming this fictitious difficulty, was that of Messrs. _Chapman_, who, in the year 1812, obtained a patent for working a locomotive engine by a chain extending along the middle of the line of railroad, from the one end to the other. This chain was passed once round a grooved wheel under the centre of the carriage; so that, when this grooved wheel was turned by the engine, the chain being incapable of slipping upon it, the carriage was consequently advanced on the road. In order to prevent the strain from acting on the whole length of the chain, its links were made to fall upon upright forks placed at certain intervals, which between those intervals sustained the tension of the chain produced by the engine. Friction-rollers were used to press the chain into the groove of the wheel, so as to prevent it from slipping. This contrivance was soon abandoned, for the very obvious reason that a prodigious loss of force was incurred by the friction of the chain. The following year, 1813, produced a contrivance, of singular ingenuity, for overcoming the supposed difficulty arising from the want of adhesion between the wheels and the road. This was no other than a pair of mechanical legs and feet, which were made to walk and propel in a manner somewhat resembling the feet of an animal. [Illustration: _Fig. 53._] A sketch of these propellers is given in fig. 53. A is the carriage moving on the railroad, L and L´ are the legs, F and F´ the feet. The foot F has a joint at O, which corresponds to the ankle; another joint is placed at K, which corresponds to the knee; and a third is placed at L, which corresponds to the hip. Similar joints are placed at the corresponding letters in the other leg. The knee-joint K is attached to the end of the piston of the cylinder. When the piston, which is horizontal, is pressed outwards, the leg L presses the foot F against the ground, and the resistance forces the carriage A onwards. As the carriage proceeds, the angle K at the knee becomes larger, so that the leg and thigh take a straighter position; and this continues until the piston has reached the end of its stroke. At the hip L there is a short lever, L M, the extremity of which is connected by a cord or chain with a point, S, placed near the shin of the leg. When the piston is pressed into the cylinder, the knee, K, is drawn towards the engine, and the cord, M S, is made to lift the foot, F, from the ground; to which it does not return until the piston has arrived at the extremity of the cylinder. On the piston being again driven out of the cylinder, the foot, F, being placed on the road, is pressed backwards by the force of the piston-rod at K; but the friction of the ground preventing its backward motion, the re-action causes the engine to advance: and in the same manner this process is continued. Attached to the thigh, at N, above the knee, by a joint, is a horizontal rod, N R, which works a rack, R. This rack has beneath it a cog-wheel. This cog-wheel acts in another rack below it. By these means, when the knee K is driven _from_ the engine, the rack R is moved _backwards_; but the cog-wheel, acting on the other rack beneath it, will move the latter _in the contrary direction_. The rack R being then moved _in the same direction with the knee_, K, it follows that the other rack will always be moved _in a contrary direction_. The lower rack is connected by another horizontal rod with the thigh of the leg, L´ F´, immediately above the knee, at N´. When the piston is forced _inwards_, the knee, K´, will thus be forced _backwards_; and when the piston is forced _outwards_, the knee, K´, will be drawn _forwards_. It therefore follows that the two knees, K and K´, are pressed alternately backwards and forwards. The foot, F´, when the knee, K´, is drawn forward, is lifted by the means already described for the foot, F. It will be apparent, from this description, that the piece of mechanism here exhibited is a contrivance derived from the motion of the legs of an animal, and resembling in all respects the fore legs of a horse. It is however to be regarded rather as a specimen of great ingenuity than as a contrivance of practical utility. (86.) It was about this period that the important fact was first ascertained that the adhesion or friction of the wheels with the rails on which they moved was amply sufficient to propel the engine, even when dragging after it a load of great weight; and that in such case, the progressive motion would be effected without any slipping of the wheels. The consequence of this fact rendered totally useless all the contrivances for giving wheels a purchase on the road, such as racks, chains, feet, &c. The experiment by which this was determined appears to have been first tried on the Wylam railroad; where it was proved, that, when the road was level, and the rails clean, the adhesion of the wheels was sufficient, in all kind of weather, to propel considerable loads. By manual labour it was first ascertained how much weight the wheels of a common carriage would overcome without slipping round on the rail; and having found the proportion which that bore to the weight, they then ascertained that the weight of the engine would produce sufficient adhesion to drag after it, on the railroad, the requisite number of wagons.[25] [Footnote 25: Wood on Railroads, 2d edit.] In 1814, an engine was constructed at Killingworth, by Mr. _Stephenson_, having two cylinders with a cylindrical boiler, and working two pair of wheels, by cranks placed at right angles; so that when the one was in full operation, the other was at its dead points. By these means the propelling power was always in action. The cranks were maintained in this position by an endless chain, which passed round two cogged wheels placed under the engine, and which were fixed on the same axles on which the wheels were placed. The wheels in this case were fixed on the axles, and turned with them. [Illustration: _Fig. 54._] This engine is represented in fig. 54., the sides being open, to render the interior mechanism visible. A B is the cylindrical boiler; C C are the working cylinders; D E are the cogged wheels fixed on the axle of the wheels of the engine, and surrounded by the endless chain. These wheels being equal in magnitude, perform their revolutions in the same time; so that, when the crank, F, descends to the lowest point, the crank, G, rises from the lowest point to the horizontal position, D; and, again, when the crank, F, rises from the lowest point to the horizontal position, E, the other crank rises to the highest point; and so on. A very beautiful contrivance was adopted in this engine, by which it was suspended on springs of steam. Small cylinders, represented at H, are screwed by flanges to one side of the boiler, and project within it a few inches; they have free communication at the top with the water or steam of the boiler. Solid pistons are represented at I, which move steam-tight in these cylinders; the cylinders are open at the bottom, and the piston-rods are screwed on the carriage of the engine, over the axle of each pair of wheels, the pistons being presented upwards. As the engine is represented in the figure, it is supported on four pistons, two at each side. The pistons are pressed upon by the water or steam which occupies the upper chamber of the cylinder; and the latter being elastic in a high degree, the engine has all the advantage of spring suspension. The defect of this method of supporting the engine is, that when the steam loses that amount of elasticity necessary for the support of the machine, the pistons are forced into the cylinders, and the bottoms of the cylinders bear upon them. All spring suspension is then lost. This mode of suspension has consequently since been laid aside. In an engine subsequently constructed by Mr. _Stephenson_, for the Killingworth railroad, the mode adopted of connecting the wheels by an endless chain and cog-wheels was abandoned; and the same effect was produced by connecting the two cranks by a straight rod. All such contrivances, however, have this great defect, that, if the fore and hind wheels be not constructed with dimensions accurately equal, there must necessarily be a slipping or dragging on the road. The nature of the machinery requires that each wheel should perform its revolution exactly in the same time; and consequently, in doing so, must pass over exactly equal lengths of the road. If, therefore, the circumference of the wheels be not accurately equal, that wheel which has the lesser circumference must be dragged along so much of the road as that by which it falls short of the circumference of the greater wheel; or, on the other hand, the greater must be dragged in the opposite direction, to compensate for the same difference. As no mechanism can accomplish a perfect equality in four, much less in six, wheels, it may be assumed that a great portion of that dragging effect is a necessary consequence of the principle of this machine; and even were the wheels, in the first instance, accurately constructed, it is not possible that their wear could be so exactly uniform as to continue equal. (87.) The next stimulus which the progress of this invention received, proceeded from the great national work undertaken at Liverpool, by which that town and the extensive commercial mart of Manchester were connected by a double line of railway. When this project was undertaken, it was not decided what moving power it might be most expedient to adopt as a means of transport on the proposed road: the choice lay between horse-power, fixed steam engines, and locomotive engines; but the first, for many obvious reasons, was at once rejected in favour of one or other of the last two. The steam engine may be applied, by two distinct methods, to move wagons either on a turnpike road or on a railway. By the one method the steam engine is fixed, and draws the carriage or train of carriages towards it by a chain extending the whole length of road on which the engine works. By this method the line of road over which the transport is conducted is divided into a number of short intervals, at the extremity of each of which an engine is placed. The wagons or carriages, when drawn by any engine to its own station, or detached, and connected with the extremity of the chain worked by the next stationary engine; and thus the journey is performed, from station to station, by separate engines. By the other method the same engine draws the load the whole journey, travelling with it. The Directors of the Liverpool and Manchester railroad, when that work was advanced towards its completion, employed, in the spring of the year 1829, Messrs. _Stephenson_ and _Lock_ and Messrs. _Walker_ and _Rastrick_, experienced engineers, to visit the different railways where practical information respecting the comparative effects of stationary and locomotive engines was likely to be obtained; and from these gentlemen they received reports on the relative merits, according to their judgment, of the two methods. The particulars of their calculations are given at large in the valuable work of Mr. _Nicholas Wood_ on railways; to which we refer the reader, not only on this, but on many other subjects connected with the locomotive steam engine into which it would be foreign to our subject to enter. The result of the comparison of the two systems was, that the capital necessary to be advanced to establish a line of stationary engines was considerably greater than that which was necessary to establish an equivalent power in locomotive engines; that the annual expense by the stationary engines was likewise greater; and that, consequently, the expense of transport by the latter was greater, in a like proportion. The subjoined table exhibits the results numerically:-- +------------------------+------------+-------------+------------------+ | | | Annual | Expense of | | | Capital. | Expense. | taking a Ton of | | | | | Goods One Mile. | +------------------------+------------+-------------+------------------+ | | £ s. d.| £ s. d.| | | Locomotive Engines | 58,000 0 0 | 25,517 8 2 | 0·164 of a penny.| | Stationary Engines |121,496 7 0 | 42,031 16 5 | 0·269 | | +------------+-------------+------------------+ | Locomotive System--less| 63,496 7 0 | 16,514 8 3 | 0·105 | +------------------------+------------+-------------+------------------+ On the score of economy, therefore, the system of locomotive engines was entitled to a preference; but there were other considerations which conspired with this to decide the choice of the Directors in its favour. An accident occurring in any part of a road worked by stationary engines must necessarily produce a total suspension of work along the entire line. The most vigilant and active attention on the part of every workman, however employed, in every part of the line, would therefore be necessary; but, independently of this, accidents arising from the fracture or derangement of any of the chains, or from the suspension of the working of any of the fixed engines, would be equally injurious, and would effectually stop the intercourse along the line. On the other hand, in locomotive engines an accident could only affect the particular train of carriages drawn by the engine to which the accident might occur; and even then the difficulty could be remedied by having a supply of spare engines at convenient stations along the line. It is true that the _probability_ of accident is, perhaps, less in the stationary than in the locomotive system; but the _injurious consequences_, when accident _does_ happen, are prodigiously greater in the former. "The one system," says Mr. _Walker_, "is like a chain extending from Liverpool to Manchester, the failure of a single link of which would destroy the whole; while the other is like a number of short and unconnected chains," the destruction of any one of which does not interfere with the effect of the others, and the loss of which may be supplied with facility. The decision of the Directors was, therefore, in favour of locomotive engines; and their next measure was to devise some means by which the inventive genius of the country might be stimulated to supply them with the best possible form of engines for this purpose. With this view, it was proposed and carried into effect to offer a prize for the best locomotive engine which might be produced under certain proposed conditions, and to appoint a time for a public trial of the claims of the candidates. A premium of 500_l._ was accordingly offered for the best locomotive engine to run on the Liverpool and Manchester Railway; under the condition that it should produce no smoke; that the pressure of the steam should be limited to 50 lbs. on the inch; and that it should draw at least three times its own weight, at the rate of not less than ten miles an hour; that the engine should be supported on springs, and should not exceed fifteen feet in height. Precautions were also proposed against the consequences of the boiler bursting; and other matters, not necessary to mention more particularly here. This proposal was announced in the spring of 1829, and the time of trial was appointed in the following October. The engines which underwent the trial were, the Rocket, constructed by Mr. _Stephenson_; the Sanspariel, by _Hackworth_; and the Novelty, by Messrs. _Braithwait_ and _Ericson_. Of these, the Rocket obtained the premium. A line of railway was selected for the trial, on a level piece of road about two miles in length, near a place called Rainhill, between Liverpool and Manchester; the distance between the two stations was a mile and a half, and the engine had to travel this distance backwards and forwards ten times, which made altogether a journey of 30 miles. The Rocket performed this journey twice: the first time in 2 hours 14 minutes and 8 seconds; and the second time, in 2 hours 6 minutes and 49 seconds. Its speed at different parts of the journey varied: its greatest rate of motion was rather above 29 miles an hour; and its least, about 11-1/2 miles an hour. The average rate of the one journey was 13-4/10 miles an hour; and of the other, 14-2/20 miles. This was the only engine which performed the complete journey proposed, the others having been stopped from accidents which occurred to them in the experiment. The Sanspariel performed the distance between the stations eight times, travelling 22-1/2 miles in 1 hour 37 minutes and 16 seconds. The greatest velocity to which this engine attained was something less than 23 miles per hour. The Novelty had only passed twice between the stations when the joints of the boiler gave way, and put an end to the experiment. (88.) The great object to be attained in the construction of these engines was, to combine with sufficient lightness the greatest possible heating power. The fire necessarily acts on the water in two ways: first, by its radiant heat; and, second, by the current of heated air which is carried by the draft through the fire, and finally passes into the chimney. To accomplish this object, therefore, it is necessary to expose to both these sources of heat the greatest possible quantity of surface in contact with the water. These ends were attained by the following admirable arrangement in the Rocket:-- [Illustration: _Fig. 55._] [Illustration: _Fig. 56._] This engine is represented in fig. 55. It is supported on four wheels; the principal part of the weight being thrown on one pair, which are worked by the engine. The boiler consists of a cylinder 6 feet in length, with flat ends; the chimney issues from one end, and to the other end is attached a square box, B, the bottom of which is furnished with the grate on which the fuel is placed. This box is composed of two casings of iron, one contained within the other, having between them a space about 3 inches in breadth; the magnitude of the box being 3 feet in length, 2 feet in width, and 3 feet in depth. The casing which surrounds the box communicates with the lower part of the boiler by a pipe marked C; and the same casing at the top of the box communicates with the upper part of the boiler by another pipe marked D. When water is admitted into the boiler, therefore, it flows freely through the pipe C, into the casing which surrounds the furnace or fire-box, and fills this casing to the same level as that which it has in the boiler. When the engine is at work, the boiler is kept about half filled with water; and, consequently, the casing surrounding the furnace is completely filled. The steam which is generated in the water contained in the casing finds its exit through the pipe D, and escapes into the upper part of the boiler. A section of the engine, taken at right angles to its length is represented at fig. 56. Through the lower part of the boiler pass a number of copper tubes of small size, which communicate at one end with the fire-box, and at the other with the chimney, and form a passage for the heated air from the furnace to the chimney. The ignited fuel spread on the grate at the bottom of the fire-box disperses its heat by radiation, and acts in this manner on the whole surface of the casing surrounding the fire-box; and thus raises the temperature of the thin shell of water contained in that casing. The chief part of the water in the casing, being lower in its position than the water in the boiler, acquires a tendency to ascend when heated, and passes into the boiler; so that a constant circulation of the heated water is maintained, and the water in the boiler must necessarily be kept at nearly the same temperature as the water in the casing. The air which passes through the burning fuel, and which fills the fire-box, is carried by the draft through the tubes which extend through the lower part of the boiler; and as these tubes are surrounded on every side with the water contained in the boiler, this air transmits its heat through these tubes to the water. It finally issues into the chimney, and rises by the draft. The power of this furnace must necessarily depend on the power of draft in the chimney; and to increase this, and at the same time to dispose of the waste steam after it has worked the piston, this steam is carried off by a pipe L, which passes from the cylinder to the chimney, and escapes there in a jet which is turned upwards. By the velocity with which it issues from this jet, and by its great comparative levity, it produces a strong current upwards in the chimney, and thus gives force to the draft of the furnace. In fig. 56. the grate-bars are represented at the bottom of the fire-box at F. There are two cylinders, one of which works each wheel; one only appearing in the drawing, fig. 55., the other being concealed by the engine. The spokes which these cylinders work are placed at right angles on the wheels; the wheels being fixed on a common axle, with which they turn. In this engine, the surface of water surrounding the fire-box, exposed to the action of radiant heat, amounted to 20 square feet, which received heat from the surface of 6 square feet of burning fuel on the bars. The surface exposed to the action of the heated air amounted to 118 square feet. The engine drew after it another carriage, containing fuel and water; the fuel used was coke, for the purpose of avoiding the production of smoke. (89.) The Sanspareil of Mr. _Hackworth_ is represented in fig. 57.; the horizontal section being exhibited in fig. 58. [Illustration: _Fig. 57._] [Illustration: _Fig. 58._] The draft of the furnace is produced in the same manner as in the Rocket, by ejecting the waste steam coming from the cylinder into the chimney; the boiler, however, differs considerably from that of the Rocket. A recurved tube passes through the boiler, somewhat similar to that already described in the early engine of Messrs. _Trevithick_ and _Vivian_. In the horizontal section (fig. 58.), D expresses the opening of the furnace at the end of the boiler, beside the chimney. The grate-bars appear at A, supporting the burning fuel; and a curved tube passing through the boiler, and terminating in the chimney, is expressed at B, the direction of the draft being indicated by the arrow; C is a section of the chimney. The cylinders are placed, as in the Rocket, on each side of the boiler; each working a separate wheel, but acting on spokes placed at right angles to each other. The tube in which the grate and flue are placed diminishes in diameter as it approaches the chimney. At the mouth where the grate was placed, its diameter was 2 feet; and it was gradually reduced, so that, at the chimney, its diameter was only 15 inches. The grate-bars extended 5 feet into the tube. The surface of water exposed to the radiant heat of the fire was 16 square feet; and that exposed to the action of the heated air and flame was about 75 square feet. The magnitude of the grate or sheet of burning fuel which radiated heat, was 10 square feet. (90.) The Novelty, of Messrs. _Braithwait_ and _Ericson_, is represented in fig. 59.; and a section of the generator and boiler is exhibited in fig. 60.: the corresponding parts in the two figures are marked by the same letters. [Illustration: _Fig. 59._] A is the generator or receiver, containing the steam which works the engine; this communicates with a lower generator, B, which extends in a horizontal direction the entire length of the carriage. Within the generator, A, is contained the furnace, F, which communicates in a tube, C; carried up through the generator, and terminated at the top by sliding shutters, which exclude the air, and which are only opened to supply fuel to the grate, F. Below the grate the furnace is not open, as usual, to the atmosphere, but communicates by a tube, E, with a bellows, D; which is worked by the engine, and which forces a constant stream of air, by the tube E, through the fuel on F, so as to keep that fuel in vivid combustion. The heated air, contained in the furnace, F, is driven on, by the same force, through a small curved tube marked _e_, which circulates like a worm (as represented in fig. 60.) through the horizontal generator or receiver; and, tapering gradually, until reduced to very small dimensions, it finally issues into the chimney, G. The air, in passing along this tube, imparts its heat to the water by which the tube is surrounded, and is brought to a considerably reduced temperature when discharged into the chimney. The cylinder, which is represented at K, works one pair of wheels, by means of a bell-crank; the other pair, when necessary, being connected with them. [Illustration: _Fig. 60._] In this engine, the magnitude of the surface of burning fuel on the grate-bars is less than 2 square feet; the surface exposed to radiant heat is 9-1/2 square feet; and the surface of water exposed to heated air is about 33 square feet. The superiority of the Rocket may be attributed chiefly to the greater quantity of surface of the water which is exposed to the action of the fire. With a less extent of grate-bars than the Sanspareil, in the proportion of 3 to 5, it exposes a greater surface of water to radiant heat, in the proportion of 4 to 3; and a greater surface of water to heated air, in the proportion of more than 3 to 2. It was found that the Rocket, compared with the Sanspareil, consumed fuel, in the evaporation of a given quantity of water, in the proportion of 11 to 28. The suggestion of using the tubes to conduct through the water the heated air to the chimney is due to Mr. _Booth_, treasurer of the Liverpool and Manchester Railway Company; and, certainly, nothing has been more conducive to the efficiency of the engines since used than this improvement. It is much to be regretted that the ingenious gentleman who suggested this has reaped none of the advantages to which a patentee would be legally entitled.[26] [Footnote 26: Mr. _Booth_ received a part of the premium of 500_l._, but has not participated in any degree in the profits of the manufacture of the engines.] (91.) The great object to be effected in the boilers of these engines is, to keep a small quantity of water at an excessive temperature, by means of a small quantity of fuel kept in the most active state of combustion. To accomplish this, it is necessary, first, so to shape the boiler, furnace, and flues, that the water shall be in contact with as extensive a surface as possible, every part of which is acted on either immediately, by the heat radiating from the fire, or mediately, by the air which has passed through the fire, and which finally rushes into the chimney: and, secondly, that such a forcible draught should be maintained in the furnace, that a quantity of heat shall be extricated from the fuel, by combustion, sufficient to maintain the water at the necessary temperature, and to produce the steam with sufficient rapidity. To accomplish these objects, therefore, the chamber containing the grate should be completely surrounded by water, and should be below the level of the water in the boiler. The magnitude of the surface exposed to radiation should be as great as is consistent with the whole magnitude of the machine. The comparative advantage which the Rocket possessed in these respects over the other engines will be evident on inspection. In the next place, it is necessary that the heat, which is absorbed by the air passing through the fuel, and keeping it in a state of combustion, should be transferred to the water before the air escapes into the chimney. Air being a bad conductor of heat, to accomplish this it is necessary that the air in the flues should be exposed to as great an extent of surface in contact with the water as possible. No contrivance can be less adapted for the attainment of this end than one or two large tubes traversing the boiler, as in the earliest locomotive engines: the body of air which passes through the centre of these tubes had no contact with their surface, and, consequently, passed into the chimney at nearly the same temperature as that which it had when it quitted the fire. The only portion of air which imparted its heat to the water was that portion which passed next to the surface of the tube. Several methods suggest themselves to increase the surface of water in contact with a given quantity of air passing through it. This would be accomplished by causing the air to pass between plates placed near each other, so as to divide the current into thin strata, having between them strata of water, or it might be made to pass between tubes differing slightly in diameter, the water passing through an inner tube, and being also in contact with the external surface of the outer tube. Such a method would be similar in principle to the steam-jacket used in _Watt's_ steam engines, or to the condenser of _Cartwright's_ engine already described. But, considering the facility of constructing small tubes, and of placing them in the boiler, that method, perhaps, is, on the whole, the best in practice; although the shape of a tube, geometrically considered, is most unfavourable for the exposure of a fluid contained in it to its surface. The air which passes from the fire-chamber, being subdivided as it passes through the boiler by a great number of very small tubes, may be made to impart all its excess of heat to the water before it issues into the chimney. This is all which the most refined contrivance can effect. The Rocket engine was traversed by 25 tubes, each 3 inches in diameter; and the principle has since been carried to a much greater extent. The abstraction of a great quantity of heat from the air before it reaches the chimney is attended with one consequence, which, at first view, would present a difficulty apparently insurmountable; the chimney would, in fact, lose its power of draught. This difficulty, however, was removed by using the waste steam, which had passed from the cylinder after working the engine, for the purpose of producing a draught. This steam was urged through a jet presented upwards in the chimney, and driven out with such force in that direction as to create a sufficient draught to work the furnace. It will be observed that the principle of draught in the Novelty is totally distinct from this: in that engine the draught is produced by a bellows worked by the engine. The question, as far as relates to these two methods, is, whether more power is lost in supplying the steam through the jet, as in the Rocket, or in working the bellows, as in the Novelty. The force requisite to impel the steam through the jet must be exerted by the returning stroke of the piston, and, consequently, must rob the working effect to an equivalent amount. On the other hand, the power requisite to work the bellows in the Novelty must be subducted from the available power of the engine. The former method is found to be the more effectual and economical. The importance of these details will be understood, when it is considered that the only limit to the attainment of speed by locomotive engines is the power to produce in a given time a certain quantity of steam. Each stroke of the piston causes one revolution of the wheels, and consumes two cylinders full of steam: consequently, a cylinder of steam corresponds to a certain number of feet of road travelled over: hence it is that the production of a rapid and abundant supply of heat, and the imparting of that heat quickly and effectually to the water, is the key to the solution of the problem to construct an engine capable of rapid motion. The method of subdividing the flue into tubes was carried much further by Mr. _Stephenson_ after the construction of the Rocket; and, indeed, the principle was so very obvious, that it is only surprising that, in the first instance, tubes of smaller diameter than 3 inches were not used. In engines since constructed, the number of tubes vary from 90 to 120, the diameter being reduced to 2 inches or less, and in some instances tubes have been introduced, even to the number of 150, of 1-1/2 inch diameter. In the Meteor, 20 square feet are exposed to radiation, and 139 to the contact of heated air; in the Arrow, 20 square feet to radiation, and 145 to the contact of heated air. The superior economy of fuel gained by this means will be apparent by inspecting the following table, which exhibits the consumption of fuel which was requisite to convey a ton weight a mile in each of four engines, expressing also the rate of the motion:-- +------------------+---------------+-----------------+ | |Average rate of|Consumption of | | Engines. | speed in miles|Coke in pounds | | | per hour. |per ton per mile.| +------------------+---------------+-----------------+ |No. 1. Rocket | 14 | 2·41 | | 2. Sanspareil | 15 | 2·47 | | 3. Phoenix | 12 | 1·42 | | 4. Arrow | 12 | 1·25 | +------------------+---------------+-----------------+ (92.) Since the period at which the railway was opened for the actual purposes of transport, the locomotive engines have been in a state of progressive improvement. Scarcely a month has passed without suggesting some change in the details, by which fuel might be economised, the production of steam rendered more rapid, the wear of the engine rendered slower, the proportionate strength of the different parts improved, or some other desirable end obtained. The consequence of this has been, that the particular engines to which we have alluded, and others of the same class, without having, as it were, lived their natural life, or without having been worn out by work, have been laid aside to give place to others of improved powers. By the exposure of the cylinders to the atmosphere in the Rocket, and engines of a similar form, a great waste of heat was incurred, and it was accordingly determined to remove them from the exterior of the boiler, and to place them within a casing immediately under the chimney: this chamber was necessarily kept warm by its proximity to the end of the boiler, but more by the current of heated air which constantly rushed into it from the tubes. This change, also, rendered necessary another, which improved the working of the engine. In the earlier engines the motion of the piston was communicated to the wheel by a connecting rod attached to one of the spokes on the exterior of the wheel, as represented in fig. 55. By the change to which we have just alluded, the cylinders being placed between the wheels under the chimney, this mode of working became inapplicable, and it was considered better to connect the piston-rods with two cranks placed at right angles on the axles of the great wheels. By this means, it was found that the working of the machine was more even, and productive of less strain than in the former arrangement. On the other hand, a serious disadvantage was incurred by the adoption of a cranked axle. The weakness necessarily arising from such a form of axle could only be counterbalanced by great thickness and weight of metal; and even this precaution does not prevent the occasional fracture of such axles at the angles of the cranks. The advantages, however, of this plan, on the whole, are considered to predominate. In the most improved engines in present use two safety-valves are provided, of which only one is in the power of the engine-man. The tubes being smaller and more numerous than in the earlier engines, the heat is more completely extracted from the air before it enters the chimney. A powerful draft is rendered still more necessary by the smallness of the tubes: this is effected by forcing the steam which has worked the pistons through a contracted orifice, presented upwards in the chimney, by the regulation of which any degree of draft may be obtained. One of the most improved engines at present in use is represented in fig. 61. A represents the cylindrical boiler, the lower half of which is traversed by tubes, as described in the Rocket. They are usually from 80 to 100 in number, and about 1-1/2 inch in diameter; the boiler is about 7 feet in length; the fire-chamber is attached to one end of it, at F, as in the Rocket, and similar in construction; the cylinders are inserted in a chamber at the other end, immediately under the chimney. The piston-rods are supported in the horizontal position by guides; and connecting rods extend from them, under the engine, to the two cranks placed on the axle of the large wheels. The effects of any inequality in the road are counteracted by springs, on which the engine rests; the springs being below the axle of the great wheels, and above that of the less. The steam is supplied to the cylinders, and withdrawn, by means of the common sliding valves, which are worked by an eccentric wheel placed on the axle of the large wheels of the carriage. The motion is communicated from this eccentric wheel to the valve by sliding rods. The stand is placed for the attendant at the end of the engine, next the fire-place, F; and two levers, L, project from the end, which communicate with the valves by means of rods, by which the engine is governed, so as to stop or reverse the motion. [Illustration: _Fig. 61._] The wheels of these engines have been commonly constructed of wood, with strong iron tires, furnished with flanges adapted to the rails. But Mr. _Stephenson_ has recently substituted, in some instances, wheels of iron with hollow spokes. The engine draws after it a tender carriage containing the fuel and water; and, when carrying a light load, is capable of performing the whole journey from Liverpool to Manchester without a fresh supply of water. When a heavy load of merchandise is drawn, it is usual to take in water at the middle of the trip. (93.) In reviewing all that has been stated, it will be perceived that the efficiency of the locomotive engines used on this railway is mainly owing to three circumstances: 1st, The unlimited power of draft in the furnace, by projecting the waste steam into the chimney; 2d, The unlimited abstraction of heat from the air passing from the furnace, by Mr. _Booth's_ ingenious arrangement of tubes traversing the boiler; and, 3d, Keeping the cylinders warm, by immersing them in the chamber under the chimney.[27] There are many minor details which might be noticed with approbation, but these constitute the main features of the improvements, and should never, for a moment, be lost sight of by projectors of locomotive engines. [Footnote 27: Mr. Robert Stephenson, whose experience and skill in the construction of locomotives attaches great importance to this condition. It has lately, however, been abandoned by some other engine-makers, for the purpose of getting rid of the cranked axle which must accompany it.] The successive introduction of improvements in the engines, some of which we have mentioned, has been accompanied by corresponding accessions to their practical power, and to the economy of fuel; and they have now arrived at a point which is as far beyond the former expectations of the most sanguine locomotive projectors, as it assuredly is short of the perfection of which these wonderful machines are still susceptible. In the spring of the year 1832, I made several experiments on the Manchester railway, with a view to determine, in the actual state of the locomotive engines at that time, their powers with respect to the amount of load and the economy of fuel. Since that time I am not aware that, in these respects, the engine has received any material improvement. The following are the particulars of three experiments thus made:-- I. On Saturday, the 5th of May, the engine called the "Victory" took 20 wagons of merchandise, weighing gross 92 tons 19 cwt. 1 qr., together with the tender containing fuel and water, of the weight of which I have no account, from Liverpool to Manchester (30 miles,) in 1 h. 34 min. 45 sec. The train stopped to take in water half-way, for 10 minutes, not included in the above mentioned time. On the inclined plane rising 1 in 96, and extending 1-1/2 mile, the engine was assisted by another engine called the "Samson," and the ascent was performed in 9 minutes. At starting, the fire-place was well filled with coke, and the coke supplied to the tender accurately weighed. On arriving at Manchester the fire-place was again filled, and the coke remaining in the tender weighed. The consumption was found to amount to 929 pounds net weight, being at the rate of one third of a pound per ton per mile. Speed on the level was 18 miles an hour; on a fall of 4 feet in a mile, 21-1/2 miles an hour; fall of 6 feet in a mile, 25-1/2 miles an hour; on the rise over Chatmoss, 8 feet in a mile 17-5/8 miles an hour; on level ground sheltered from the wind, 20 miles an hour. The wind was moderate, but direct ahead. The working wheels slipped three times on Chatmoss, and the train was retarded from 2 to 3 minutes. The engine, on this occasion, was not examined before or after the journey, but was presumed to be in good working order. II. On Tuesday, the 8th of May, the same engine performed the same journey, with 20 wagons, weighing gross 90 tons 7 cwt. 2 qrs., exclusive of the unascertained weight of the tender. The time of the journey was 1 h. 41 min. The consumption of coke 1040 lbs. net weight, estimated as before. Rate of speed:-- Level 17-5/8 miles per hour. Fall of 4 feet in a mile 22 ---- 6 22-1/2 Rise of 8 15 On this occasion there was a high wind ahead on the quarter, and the connecting rod worked hot, owing to having been keyed too tight. On arriving at Manchester, I caused the cylinders to be opened, and found that the pistons were so loose, that the steam blew through the cylinders with great violence. By this cause, therefore, the machine was robbed of a part of its power during the journey; and this circumstance may explain the slight decrease in speed, and increase in the consumption of fuel, with a lighter load in this journey compared with that performed on the 5th of May. The Victory weighs 8 tons 2 cwt., of which 5 tons 4 cwt. rest on the drawing wheels. The cylinders are 11 inches diameter, and 16 inches stroke; and the diameter of the drawing wheels is 5 feet. III. On the 29th of May, the engine called the "Samson," (weighing 10 tons 2 cwt., with 14-inch cylinders, and 16-inch stroke; wheels 4 feet 6 inches diameter, both pairs being worked by the engine; steam 50 lbs. pressure, 130 tubes) was attached to 50 wagons, laden with merchandise; net weight about 150 tons; gross weight, including wagons, tender, &c., 223 tons 6 cwt. The engine with this load travelled from Liverpool to Manchester (30 miles) in 2 h. and 40 min., exclusive of delays upon the road for watering, &c., being at the rate of nearly 12 miles an hour. The speed varied according to the inclinations of the road. Upon a level, it was 12 miles an hour; upon a descent of 6 feet in a mile, it was 16 miles an hour: upon a rise of 8 feet in a mile, it was about 9 miles an hour. The weather was calm, the rails very wet; but the wheels did not slip, even in the slowest speed, except at starting, the rails being at that place soiled and greasy with the slime and dirt to which they are always exposed at the stations. The coke consumed in this journey, exclusive of what was raised in getting up the steam, was 1762 lbs., being at the rate of a quarter of a pound per ton per mile. (94.) From the above experiments it appears that a locomotive engine, in good working order, with its full complement of load, is capable of transporting weights at an expense in fuel amounting to about 4 ounces of coke per ton per mile. The attendance required on the journey is that of an engine-man and a fire-boy; the former being paid 1_s._ 6_d._ for each trip of 30 miles, and the latter 1_s._ In practice, however, we are to consider, that it rarely happens that the full complement of load can be sent with the engines; and when lesser loads are transported, the _proportionate expense_ must for obvious reasons, be greater. The practical expenditure of fuel on the Liverpool and Manchester line may, perhaps, be fairly estimated at half a pound of coke per ton per mile. (95.) Having explained the power and efficiency of these locomotive engines, it is now right to notice some of the defects under which they labour. The great original cost, and the heavy expense of keeping the engines used on the railway in repair, have pressed severely on the resources of the undertaking. One of the best constructed of the later engines costs originally about 800_l._ It may be hoped that, by the excitement of competition, the facilities derived from practice, and from the manufacture of a greater number of engines of the same kind, some reduction of this cost may be effected. The original cost, however, is far from being the principal source of expense: the wear and tear of these machines, and the occasional fracture of those parts on which the greatest strain has been laid, have greatly exceeded what the directors had anticipated. Although this source of expense must be in part attributed to the engines not having yet attained that state of perfection, in the proportion and adjustment of their parts, of which they are susceptible, and to which experience alone can lead, yet there are some obvious defects which demand attention. The heads of the boilers are flat, and formed of iron, similar to the material of the boilers themselves. The tubes which traverse the boiler were, until recently, copper, and so inserted into the flat head or ends as to be water-tight. When the boiler is heated, the tubes are found to expand in a greater degree than the other parts of the boiler; which frequently causes them either to be loosened at the extremities, so as to cause leakage, or to bend from want of room for expansion. The necessity of removing and refastening the tubes causes, therefore, a constant expense. It will be recollected that the fire-place is situated at one end of the boiler, immediately below the mouths of the tubes: a powerful draught of air, passing through the fire, carries with it ashes and cinders, which are driven violently through the tubes, and especially the lower ones, situated near the fuel. These tubes are, by this means, subject to rapid wear, the cinders continually acting upon their interior surface. After a short time it becomes necessary to replace single tubes, according as they are found to be worn, by new ones; and it not unfrequently happens, when this is neglected, that tubes burst. After a certain length of time the engines require new tubing, which is done at the expense of about 70_l._, allowing for the value of the old tubes. This wear of the tubes might possibly be avoided by constructing the fire-place in a lower position, so as to be more removed from their mouths; or, still more effectually, by interposing a casing of metal, which might be filled with water, between the fire-place and those tubes which are the most exposed to the cinders and ashes. The unequal expansion of the tubes and boilers appears to be an incurable defect, if the present form of the engine be retained. If the fire-place and chimney could be placed at the same end of the boiler, so that the tubes might be recurved, the unequal expansion would then produce no injurious effect; but it would be difficult to clean the tubes if they were exposed, as they are at present, to the cinders. The next source of expense arises from the wear of the boiler-head, which is exposed to the action of the fire. These require constant patching and frequent renewal. A considerable improvement has lately been introduced into the method of tubing, by substituting brass for copper tubes. We are not aware that the cause of this improvement has been discovered; but it is certain, whatever be the cause, that brass tubes are subject to considerably slower wear than copper. It has been said by some whose opinions are adverse to the advantage of railways, but more especially to the particular species of locomotive engines now under consideration, that the repairs of one of these engines cost so great a sum as 1500_l._ per annum, and that the directors now think of abandoning them, or adopting either stationary engines or horse-power. As to the first of these statements I must observe, that the expense of repairs of such machines should never be computed in reference to _time_, but rather to the work done, or the distance travelled over. I have ascertained that engines frequently travel a distance of from 25,000 to 30,000 miles before they require new tubing. During that work, however, single tubes are, of course, occasionally renewed, and other repairs are made, the expense of which may safely be stated as under the original cost of the engine. The second statement, that the company contemplate substituting stationary engines, or horses, for locomotives, is altogether at variance with the truth. Whatever improvements may be contemplated in locomotives, the directors assuredly have not the slightest intention of going back in the progress of improvement, in the manner just mentioned. The expense of locomotive power having so far exceeded what was anticipated at the commencement of the undertaking, it was thought advisable, about the beginning of the year 1834, to institute an inquiry into the causes which produced the discrepancy between the estimated and actual expenses, with a view to the discovery of some practical means by which they could be reduced. The directors of the company, for this purpose, appointed a sub-committee of their own body, assisted by Mr. _Booth_, their treasurer, to inquire and report respecting the causes of the amount of this item of their expenditure, and to ascertain whether any and what measures could be devised for the attainment of greater economy. A very able and satisfactory report was made by this committee, or, to speak more correctly by Mr. _Booth_. It appears that, previous to the establishment of the railway, Messrs. _Walker_ and _Rastrick_, engineers, were employed by the company to visit various places where steam power was applied on railways, for the purpose of forming an estimate of the probable expense of working the railway by locomotive and by fixed power. These engineers recommended the adoption of locomotive power, and their estimate was, that the transport might be effected at the rate of .278 of a penny, or very little more than a farthing per ton per mile. In the year 1833, five years after this investigation took place, it was found that the actual cost was .625 of a penny, or something more than a halfpenny per ton per mile, being considerably above double the estimated rate. Mr. _Booth_ very properly directed his inquiries to ascertain the cause of this discrepancy, by comparing the various circumstances assumed by Messrs. _Walker_ and _Rastrick_, in making their estimate, with those under which the transport was actually effected. The first point of difference which he observed was the speed of transport: the estimate was founded on an assumed _speed_ of ten miles an hour, and it was stated that a fourfold speed would require an addition of 50 per cent. to the power, without taking into account wear and tear. Now the actual speed of transport being double the speed assumed in the statement, Mr. _Booth_ holds it to be necessary to add 25 per cent. on that score. The next point of difference is in the amount of the loads: the estimate is founded upon the assumption, that every engine shall start with its full complement of load, and that with this it shall go the whole distance. "The facts, however, are," says Mr. _Booth_, "that, instead of a _full load_ of profitable carriage _from_ Manchester, about half the wagons _come back empty_, and, instead of the tonnage being conveyed the whole way, many thousand tons are conveyed only half the way; also, instead of the daily work being uniform, it is extremely fluctuating." It is further remarked, that in order to accomplish the transport of goods from the branches and from intermediate places, engines are despatched several times a day, from both ends of the line, _to clear the road_; the object of this arrangement being rather to lay the foundation of a beneficial intercourse in future, than with a view to any immediate profit. Mr. _Booth_ makes a rough estimate of the disadvantages arising from these circumstances by stating them at 33 per cent. in addition to the original estimate. The next point of difference is the fuel. In the original estimate _coal_ is assumed as the fuel, and it is taken at the price of five shillings and tenpence per ton: now the act of parliament forbids the use of coal which would produce smoke; the company have, therefore, been obliged to use _coke_, at seventeen shillings and sixpence a ton. Taking coke, then, to be equivalent to coal, ton for ton, this would add .162 to the original estimate. These several discrepancies being allowed for, and a proportional amount being added to the original estimate, the amount would be raised to .601 of a penny per ton per mile, which is within one fortieth of a penny of the actual cost. This difference is considered to be sufficiently accounted for by the wear and tear produced by the very rapid motion, more especially when it is considered that many of the engines were constructed before the engineer was aware of the great speed that would be required. "What then," says Mr. _Booth_, in the Report already alluded to, "is the result of these opposite and mutually counteracting circumstances? and what is the present position of the company in respect of their moving power? Simply, that they are still in a course of experiment, to ascertain practically the best construction, and the most durable materials, for engines required to transport greater weights, and at greater velocities, than had, till very recently, been considered possible; and which, a few years ago, it had not entered into the imagination of the most daring and sanguine inventor to conceive: and, farther, that these experiments have necessarily been made, not with the calm deliberation and quiet pace which a salutary caution recommends,--making good each step in the progress of discovery before advancing another stage,--but amidst the bustle and responsibilities of a large and increasing traffic; the directors being altogether ignorant of the time each engine would last before it would be laid up as inefficient, but compelled to have engines, whether good or bad; being aware of various defects and imperfections, which it was impossible at the time to remedy, yet obliged to keep the machines in motion, under all the disadvantages of heavy repairs, constantly going on during the night, in order that the requisite number of engines might be ready for the morning's work. Neither is this great experiment yet complete; it is still going forward. But the most prominent difficulties have been in a great measure surmounted, and your committee conceive, that they are warranted in expecting, that the expenditure in this department will, ere long, be materially reduced, more especially when they consider the relative performances of the engines at the _present time_ compared with what it was two years ago." In the half year ending 31st December, 1831, the six best engines performed as follows:-- Miles. Planet 9,986 Mercury 11,040 Jupiter 11,618 Saturn 11,786 Venus 12,850 Etna 8,764 ------ Making in all 66,044 ------ In the half year ending 31st December, 1833, the six best engines performed as follows:-- Miles. Jupiter 16,572 Saturn 18,678 Sun 15,552 Etna 17,763 Ajax 11,678 Firefly 15,608 ------ Making in all 95,851 ------ (96.) The advantages derivable from railroads are greatly abridged by the difficulty arising from those changes of level to which all roads are necessarily liable; but in the case of railroads, from causes peculiar to themselves, these changes of level occasion great inconvenience. To explain the nature of these difficulties, it will be necessary to consider the relative proportion which must subsist between the power of traction on a level and on an inclined plane. On a level railroad the force of traction necessary to propel any load, placed on wheel carriages of the construction now commonly used, may perhaps be estimated at 7-1/2 pounds,[28] for every ton gross in the load; that is to say, if a load of one ton gross were placed upon wheel carriages upon a level railroad, the traces of horses drawing it would be stretched with a force equivalent to 7-1/2 pounds. If the load amounted to two or three tons, the tension of the traces would be increased to 15 or 22-1/2 pounds, and so on. The necessity of this force of traction, arising from the want of perfect smoothness in the road, and from the friction of the wheels and axles of the carriages, must be the same whether the road be level or inclined; and consequently, in ascending an inclined plane, the same force of traction will be necessary in addition to that which arises from the tendency of the load to fall down the plane. This latter tendency is always in the proportion of the elevation of the plane to its length; that is to say, a plane which rises 1 foot in 100 will give a weight of 100 tons a tendency to fall down the plane amounting to 1 ton, and would therefore add 1 ton to the force of traction necessary for such a load on a level. [Footnote 28: The estimate commonly adopted by engineers at present is 9 pounds per ton. I have no doubt, however, that this is too high. I am now (November, 1835,) engaged in an extensive course of experiments on different railways, with a view to determine with precision this and other points connected with the full developement of their theory; and I have reason to believe, from the observations I have already made, that even 7-1/2 pounds per ton is above the average force of traction upon the level.] Now since 7-1/2 pounds is very nearly the 300th part of a ton, it follows that if an inclination upon a railroad rises at the rate of 1 foot in 300, or, what is the same, 17-1/2 feet in a mile, such an acclivity will add 7-1/2 pounds per ton to the force of traction. This acclivity therefore would require a force of traction twice as great as a level. In like manner a rise of 35 feet in a mile would require three times the force of traction of a level, 52-1/2 feet in a mile four times that force, and so on. In fact, for every 7 feet in a mile which an acclivity rises, 3 pounds per ton will be added to the force of traction. If we would then ascertain the power necessary to pull a load up any given acclivity upon a railroad, we must first take 7-1/2 pounds as the force necessary to overcome the common resistance of the road, and then add 3 pounds for every 7 feet which the acclivity rises per mile. For example, suppose an acclivity to rise at the rate of 70 feet in a mile, the force of traction necessary to draw a ton up it would be thus calculated:-- Friction 7-1/2 lbs. 70 feet = 10 times 3 lbs. 30 ------ Total force 37-1/2 It will be apparent, therefore, that if a railroad undulates by inclined planes, even of the most moderate inclinations, the propelling power to be used upon it must be of such a nature as to be capable of increasing its intensity in a great degree, according to the elevation of the planes which it has to encounter. A plane which rises 52-1/2 feet per mile presents to the eye scarcely the appearance of an ascent, and yet requires the power of traction to be increased in a fourfold proportion. It is the property of animal power, that within certain limits its energy can be put forth at will, according to the exigency of the occasion; but the intensity of mechanical power, in the instance now considered, cannot so conveniently be varied, except indeed within narrow limits. In the application of locomotive engines upon railways the difficulty arising from inclined planes has been attempted to be surmounted by several methods, which we shall now explain. 1. Upon arriving at the foot of the plane the load is divided, and the engine carries it up in several successive trips, descending the plane unloaded after each trip. The objection to this method is the delay which it occasions,--a circumstance which is incompatible with a large transport of passengers. From what has been stated, it would be necessary, when the engine is fully loaded on a level, to divide its load into four parts, to be successively carried up when the incline rises 52 feet per mile. This method has been practised in the transport of merchandise occasionally, when heavy loads were carried on the Liverpool and Manchester line, upon the Rainhill incline. 2. A subsidiary or assistant locomotive engine may be kept in constant readiness at the foot of each incline, for the purpose of aiding the different trains, as they arrive, in ascending. The objection to this mode is the cost of keeping such an engine with its boiler continually prepared, and its steam up. It would be necessary to keep its fire continually lighted, whether employed or not; otherwise, when the train would arrive at the foot of the incline, it should wait until the subsidiary engine was prepared for work. In cases where trains would start and arrive at stated times, this objection, however, would have less force. This method is at present generally adopted on the Liverpool and Manchester line. This method, however, cannot be profitably applied to planes of any considerable length. 3. A fixed steam engine may be erected on the crest of the incline, so as to communicate by ropes with the train at the foot. Such an engine would be capable of drawing up one or two trains together, with their locomotives, according as they would arrive, and no delay need be occasioned. This method requires that the fixed engine should be kept constantly prepared for work, and the steam continually up in the boiler. This expedient is scarcely compatible with a large transit of passengers, except at the terminus of a line. 4. In working on the level, the communication between the boiler and the cylinder in the locomotives may be so restrained by partially closing the throttle valve, as to cause the pressure upon the piston to be less in a considerable degree than the pressure of steam in the boiler. If under such circumstances a sufficient pressure upon the piston can be obtained to draw the load on the level, the throttle valve may be opened on approaching the inclined plane, so as to throw on the piston a pressure increased in the same proportion as the previous pressure in the boiler was greater than that upon the piston. If the fire be sufficiently active to keep up the supply of steam in this manner during the ascent, and if the rise be not greater in proportion than the power thus obtained, the locomotive will draw the load up the incline without further assistance. It is, however, to be observed, that in this case the load upon the engine must be less than the amount which the adhesion of its working wheels with the railroad is capable of drawing; for this adhesion must be adequate to the traction of the same load up the incline, otherwise whatever increase of power might be obtained by opening the throttle valve, the drawing wheels would revolve without causing the load to advance. This method has been generally practised upon the Liverpool and Manchester line in the transport of passengers; and, indeed, it is the only method yet discovered, which is consistent with the expedition necessary for that species of traffic. The objections to this method are, the necessity of maintaining a much higher pressure in the boiler than is sufficient for the purposes of the load upon more level parts of the line. In the practice of this method considerable aid may be derived also by suspending the supply of feeding water during the ascent. It will be recollected that a reservoir of cold water is placed in the tender which follows the engine, and that the water is driven from this reservoir into the boiler by a forcing-pump, which is worked by the engine itself. This pump is so constructed that it will supply as much cold water as is equal to the evaporation, so as to maintain constantly the same quantity of water in the boiler. But it is evident, on the other hand, that the supply of this water has a tendency to check the rate of evaporation, since in being raised to the temperature of the water with which it mixes, it must absorb a considerable portion of the heat supplied by the fire. With a view to accelerate the production of steam, therefore, in ascending the inclines, the engine-man may suspend the action of the forcing-pump, and thereby stop the supply of cold water to the boiler; the evaporation will go on with increased rapidity, and the exhaustion of water produced by it will be repaid by the forcing-pump on the next level, or still more effectually on the next descending incline. Indeed the feeding pump may be made to act in descending an incline if necessary, when the action of the engine itself is suspended, and when the train descends by its own gravity, in which case it will perform the part of a brake upon the descending train. This method, on railroads intended for passengers, may be successfully applied on inclines which do not exceed 18 feet in a mile; and, with a sacrifice of the expense of locomotive power, inclines so steep as 36 feet in a mile may be worked in this manner. As, however, the sacrifice is considerable, it will, perhaps, be always better to work the more steep inclines by assistant engines. 5. The mechanical connexion between the piston of the cylinder and the points of contact of the working wheels with the road may be so altered, upon arriving at the incline, as to give the piston a greater power over the working wheels. This may be done in an infinite variety of ways, but hitherto no method has been suggested sufficiently simple to be applicable in practice; and even were any means suggested which would accomplish this, unless the intensity of the impelling power were at the same time increased, it would necessarily follow that the speed of the motion would be diminished in exactly the same proportion as the power of the piston over the working wheels would be increased. Thus, on the inclined plane, which rises 55 feet per mile, upon the Liverpool line, the speed would be diminished to nearly one fourth of its amount upon the level. Whatever be the method adopted to surmount inclined planes upon a railway, inconvenience attends the descent upon them. The motion down the incline by the force of gravity is accelerated; and if the train be not retarded, a descent of any considerable length, even at a small elevation, would produce a velocity which would be attended with great danger. The shoe used to retard the descent down hills on turnpike roads cannot be used upon railroads, and the application of brakes to the faces of the wheels is likewise attended with some uncertainty. The friction produced by the rapid motion of the wheel sometimes sets fire to wood, and iron would be inadmissible. The action of the steam on the piston may be reversed, so as to oppose the motion of the wheels; but even this is attended with peculiar difficulty. From all that has been stated, it will be apparent that, with our present knowledge, considerable inclines are fatal to the profitable performance on a railway, and even small inclinations are attended with great inconvenience.[29] [Footnote 29: A contrivance might be applied in changes of level in railroads somewhat similar to locks in a canal. The train might be rolled upon a platform which might be raised by machinery; and thus at the change of level there would be as it were _steps_ from one level to another, up which the loads would be lifted by any power applied to work the machinery. The advantage in this case would be, that the trains might be adapted to work always upon a level.] (97.) To obtain from the locomotive steam engines now used on the railway the most powerful effects, it is necessary that the load placed on each engine should be very considerable. It is not possible, with our present knowledge, to construct and work three locomotive engines of this kind, each drawing a load of 30 tons, at the same expense and with the same effect as one locomotive engine drawing 90 tons. Hence arises what must appear an inconvenience and difficulty in applying these engines to one of the most profitable species of transport--the transport of passengers. It is impracticable, even between places of the most considerable intercourse to obtain loads of passengers sufficiently great at each trip to maintain such an engine working on a railway.[30] The difficulty of collecting so considerable a number of persons, at any stated hour, to perform the journey, is obvious; and therefore, the only method of removing the inconvenience is _to cause the same engine which transports passengers also to transport goods_, so that the goods may make up the requisite supplement to the load of passengers. In this way, provided the traffic in goods be sufficient, such engines may start with their full complement of load, whatever be the number of passengers. [Footnote 30: On the occasion of races held at Newton, a place about 15 miles from Liverpool, two engines were sent, with trains of carriages, to take back to Liverpool the visitors to the races. Some accident prevented one of the engines from working on the occasion, and both trains were attached to the same engine: 800 persons were on this occasion drawn by the single engine to Liverpool in the space of about an hour.] (98.) In comparing the extent of capital, and the annual expenditure of the Liverpool and Manchester line, and adopting it as a modulus in estimating the expenses of similar undertakings projected elsewhere, there are several circumstances to which it is important to attend. I have already observed on the large waste of capital in the item of locomotive engines which ought to be regarded as little more than experimental machines, leading to a rapid succession of improvements. Most of these engines are still in good working order, but have been abandoned for the reasons already assigned. Other companies will, of course, profit by the experience which has been thus purchased at a high price by the Liverpool Company. This advantage in favour of future companies will go on increasing until such companies have their works completed. A large portion of the current expense of a line of railway is independent of its length; and is little less for the line connecting Liverpool and Manchester, than it would be for a line connecting Birmingham with Liverpool or London. The establishments of resident engineers, coach and wagon yards, &c. at the extremities of the line, would be little increased by a very great increase in the length of the railway; and the same observation will apply to other heads of expenditure. It has been the practice of the canal companies between Liverpool and Manchester to warehouse the goods transported between these towns, without any additional charge beyond the price of transport. The Railway Company, in competing with the canals, were, of course, obliged to offer like advantages: this compelled them to invest a considerable amount of capital in the building of extensive warehouses, and to incur the annual expense of porterage, salaries, &c. connected with the maintenance of such storage. In a longer line of railway such expenses (if necessary at all) would not be proportionally increased. (99.) The comparison of steam-transport with the transport by horses, even when working on a railway, exhibits the advantage of this new power in a most striking point of view. To comprehend these advantages fully, it will be necessary to consider the manner in which animal power is expended as a means of transport. The portion of the strength of a horse available for the purpose of a load depends on the speed of a horse's motion. To this speed there is a certain limit, at which the whole power of the horse will be necessary to move his own body, and at which, therefore, he is incapable of carrying any load; and, on the other hand, there is a certain load which the horse is barely able to support, but incapable of moving with any useful speed. Between these two limits there is a certain rate of motion at which the useful effect of the animal is greatest. In horses of the heavier class, this rate of motion may be taken on the average as that of 2 miles an hour; and in the lighter description of horses, 2-1/2 miles an hour. Beyond this speed, the load which they are capable of transporting diminishes in a very rapid ratio as the speed increases: thus, if 121 express the load which a horse is able to transport a given distance in a day, working at the rate of four miles an hour, the same horse will not be able to transport more than the load expressed by 64, _the same distance_, at 7 miles an hour; and, at 10 miles an hour, the load which he can transport will be reduced to 25. The most advantageous speed at which a horse can work being 2 miles an hour, it is found that, at this rate, working for 10 hours daily, he can transport 12 tons, on a level railway, a distance of 20 miles; so that the whole effect of a day's work may be expressed by 240 tons carried 1 mile. But this rate of transport is inapplicable to the purposes of travelling; and therefore it becomes necessary, when horses are the moving power, to have carriages for passengers distinct from those intended for the conveyance of goods; so that the goods may be conveyed at that rate of speed at which the whole effect of the horse will be the greatest possible; while the passengers are conveyed at that speed which, whatever the cost, is indispensably necessary. The weight of an ordinary mail-coach is about two tons; and, on a tolerably level turnpike road, it travels at the rate of 10 miles an hour. At this rate, the number of horses necessary to keep it constantly at work, including the spare horses indispensably necessary to be kept at the several stages, is computed at the rate of a horse per mile. Assuming the distance between London and Birmingham at 100 miles, a mail-coach running between these two places would require 100 horses; making the journey to and from Birmingham daily. The performance, therefore, of a horse working at this rate may be estimated at 2 tons carried 2 miles per day, or 4 tons carried 1 mile in a day. The force of traction on a good turnpike road is at least 20 times its amount on a level railroad. It therefore follows, that the performance of a horse on a railroad will be 20 times the amount of its performance on a common road under similar circumstances. We may, therefore, take the performance of a horse working at 10 miles an hour, on a level railroad, at 80 tons conveyed 1 mile daily. The best locomotive engines used on the Liverpool railway are capable of transporting 150 tons on a level railroad at the same rate; and, allowing the same time for stoppage, its work per day would be 150 tons conveyed 200 miles, or 30,000 tons conveyed 1 mile; from which it follows, that the performance of one locomotive engine of this kind is equivalent to that of 7500 horses working on a good turnpike road, or to 375 horses working on a railway. The consumption of fuel requisite for this performance, with the most improved engines used at present on the Manchester and Liverpool line, would be at the rate of eight[31] ounces of coke per ton per mile, including the waste of fuel incurred by the stoppages. Thus the daily consumption of fuel, under such circumstances, would amount to 15000 lbs. of coke; and 2 lbs. of coke daily would perform the work of one horse on a good turnpike road; and 40 lbs. of coke daily would perform the work of one horse on a railway. [Footnote 31: In an experimental trip with a heavy train at 12 miles an hour, I found the consumption of coke to be only _four_ ounces per ton per hour. I believe, however, the practical consumption in ordinary work to be very nearly eight ounces.] In this comparison, the engine is taken at its most advantageous speed, while horse-power is taken at its least advantageous speed, if regard be only had to the total quantity of weight transported to a given distance. But, in the case above alluded to, speed is an indispensable element; and steam, therefore, possesses this great advantage over horse power, that _its most advantageous speed is that which is at once adapted to all the purposes of transport, whether of passengers or of goods_. (100.) The effects of steam compared with horse-power, at lower rates of motion, will exhibit the advantages of the former, though in a less striking degree. An eight-horse wagon commonly weighs 8 tons, and travels at the rate of 2-1/2 miles an hour. Strong horses working in this way can travel 8 hours daily; thus each horse performs 20 miles a day. The performance, therefore, of each horse may be taken as equivalent to 20 tons transported 1 mile; and his performance on a railway being 20 times this amount, may be taken as equivalent to 400 tons transported 1 mile a day. The performance of a horse working in this manner is, therefore, 5 times the performance of a horse working at 10 miles an hour; the latter effecting only the performance of 4 tons transported 1 mile per day on a good turnpike road, or 80 tons on a railway. We shall hence obtain the proportion of the performance of horses working in wagons to that of a locomotive steam engine. Since 2 lbs. of coke are equivalent to the daily performance of a horse in a mail-coach, and 40 lbs. on a railway, at 10 miles an hour, it follows that 10 lbs. will be equivalent to the performance of a horse on a turnpike road, and 200 lbs. on a railway, at 2-1/2 miles an hour. Since a locomotive engine can perform the daily work of 7500 mail-coach horses, it follows that it performs the work of 1500 wagon horses. These results must be understood to be subject to modifications in particular cases, and to be only average calculations. Different steam-engines, as well as different horses, varying in their performance to a considerable extent; and the roads on which horses work being in different states of perfection, and subject to different declivities, the performance must vary accordingly. In the practical comparison, also, of the results of so powerful an agent as steam applied on railways, with so slight a power as that of horses on common roads, it must be considered that the great subdivision of load, and frequent times of starting, operate in favour of the performance of horses; inasmuch as it would oftener occur that engines capable of transporting enormous weights would start with loads inferior to their power, than would happen in the application of horse-power, where small loads may start at short intervals. This, in fact, constitutes a practical difficulty in the application of steam engines on railroads; and will, perhaps, for the present, limit their application to lines connecting places of great intercourse. The most striking effect of steam power, applied on a railroad, is the extreme speed of transport which is attained by it; and it is the more remarkable, as this advantage never was foreseen before experience proved it. When the Liverpool and Manchester line was projected, the transport of heavy goods was the object chiefly contemplated; and although an intercourse in passengers was expected, it was not foreseen that this would be the greatest source of revenue to the proprietors. The calculations of future projectors will, therefore, be materially altered, and a great intercourse in passengers will be regarded as a necessary condition for the prosperity of such an undertaking. If this advantage of speed be taken into account, horse-power can scarcely admit of any comparison whatever with steam-power on a railway. In the experiments which I have already detailed, it appears that a steam engine is capable of drawing 90 tons at the rate of about 20 miles an hour, and that it could transport that weight twice between Liverpool and Manchester in about 3 hours. Two hundred and seventy horses working in wagons would be necessary to transport the same load the same distance in a day. It may be objected, that this was an experiment performed under favourable circumstances, and that assistance was obtained at the difficult point of the inclined plane. In the ordinary performance, however, of the engines drawing merchandise, where great speed is not attempted, the rate of motion is not less than 15 miles an hour. In the trains which draw passengers, the chief difficulty of maintaining a great speed arises from the stoppages on the road to take up and let down passengers. There are two classes of carriages at present used: the first class stops but once, at a point half-way between Liverpool and Manchester, for the space of a few minutes. This class performs the thirty miles in an hour and a half, and sometimes in 1 hour and 10 minutes. On the level part of the road its common rate of motion is 27 miles an hour; and I have occasionally marked its rate, and found it above 30 miles an hour. But these, which are velocities obtained in the regular working of the engines for the transport of passengers and goods, are considerably inferior to the power of the present locomotives with respect to speed. I have made some experimental trips, in which more limited loads were placed upon the engines, by which I have ascertained that very considerably increased rates of motion are quite practicable. In one experiment I placed a carriage containing 36 persons upon an engine, with which I succeeded in obtaining the velocity of about 48 miles an hour, and I believe that an engine loaded only with its own tender has moved over 15 miles in 15 minutes. It will then perhaps be asked, if the engines possess these great capabilities of speed, why they have not been brought into practical operation on the railroad, where, on the other hand, the average speed when actually in motion, does not exceed 25 miles an hour? In answer to this it may be stated, that the distance of 30 miles between Liverpool and Manchester is performed in an hour and a half, and that 10 trains of passengers pass daily between these places: the mail, also, is transmitted three times a day between them. It is obvious that any greater speed than this, in so short a distance, would be quite needless. When, however, more extended lines of road shall be completed, the circumstances will be otherwise, and the despatch of mails especially will demand attention. Full trains of passengers, commonly transported upon the Manchester railroad, weigh about 50 tons gross: with a lighter load, a lighter and more expeditious engine might be used. The expense of transport with such an engine would of course be increased; but for this the increased expedition there would be ample compensation. When, therefore, London shall have been connected with Liverpool, by a line of railroad through Birmingham, the commercial interest of these places will naturally direct attention to the greatest possible expedition of intercommunication. For the transmission of mails, doubtless, peculiar engines will be built, adapted to lighter loads and greater speed. With such engines, the mails, with a limited number of passengers, will be despatched; and, apart from any possible improvement which the engines may hereafter receive, and looking only at their present capabilities, I cannot hesitate to express my conviction that such a load may be transported at the rate of above 60 miles an hour. If we may indulge in expectations of what the probable improvements of locomotive steam engines may effect, I do not think that even double that speed is beyond the limits of mechanical probability. On the completion of the line of road from the metropolis to Liverpool we may, therefore, expect to witness the transport of mails and passengers in the short space of three hours. There will probably be about three posts a day between these and intermediate places. The great extension which the application of steam to the purpose of inland transport is about to receive from the numerous railroads which are already in progress, and from a still greater number of others which are hourly projected, impart to these subjects of inquiry considerable interest. Neither the wisdom of the philosopher, nor the skill of the statistician, nor the foresight of the statesman is sufficient to determine the important consequences by which the realization of these schemes must affect the progress of the human race. How much the spread of civilization, the diffusion of knowledge, the cultivation of taste, and the refinement of habits and manners depend upon the easy and rapid inter-mixture of the constituent elements of society, it is needless to point out. Whilst population exists in detached and independent masses, incapable of transfusion amongst each other, their dormant affinities are never called into action, and the most precious qualities of each are never imparted to the other. Like solids in physics, they are slow to form combinations; but when the quality of fluidity has been imparted to them, when their constituent atoms are loosened by fusion, and the particles of each flow freely through and among those of the other, then the affinities are awakened, new combinations are formed, a mutual interchange of qualities takes place, and compounds of value far exceeding those of the original elements are produced. Extreme facility of intercourse is the fluidity and fusion of the social masses, from whence such an activity of the affinities results, and from whence such an inestimable interchange of precious qualities must follow. We have, accordingly, observed, that the advancement in civilization and the promotion of intercourse between distant masses of people have ever gone on with contemporaneous progress, each appearing occasionally to be the cause or the consequence of the other. Hence it is that the urban population is ever in advance of the rural in its intellectual character. But, without sacrificing the peculiar advantages of either, the benefits of intercourse may be extended to both, by the extraordinary facilities which must be the consequence of the locomotive projects now in progress. By the great line of railroad which is in progress from London to Birmingham, the time and expense of passing between these places will probably be halved, and the quantity of intercourse at least quadrupled, if we consider only the direct transit between the terminal points of the line; but if the innumerable tributary streams which will flow from every adjacent point be considered, we have no analogies on which to build a calculation of the enormous increase of intercommunication which must ensue. Perishable vegetable productions necessary for the wants of towns must at present be raised in their immediate suburbs; these, however, where they can be transported with a perfectly smooth motion at the rate of twenty miles an hour, will be supplied by the agricultural labourer of more distant points. The population engaged in towns, no longer limited to their narrow streets, and piled story over story in confined habitations, will be free to reside at distances which would now place them far beyond reach of their daily occupations. The salubrity of cities and towns will thus be increased by spreading the population over a larger extent of surface, without incurring the inconvenience of distance. Thus the advantages of the country will be conferred upon the town, and the refinement and civilization of the town will spread their benefits among the rural population.[32] [Footnote 32: Some of the preceding observations appeared in an article contributed by me to the British and Foreign Review.] (101.) The quantity of canal property in these countries gives considerable interest to every inquiry which has for its object the relative advantage of this mode of transport, compared with that of railways, whether worked by horses or by steam-power; and this interest has been greatly increased by the recent extension of railway projects. This is a subject which I shall have occasion, in another work, to examine in all its details; and, therefore, in this place I shall advert to it but very briefly. When a floating body is moved on a liquid, it will suffer a resistance, which will depend partly upon the transverse section of the part immersed, and partly on the speed with which it is moved. It is evident that the quantity of the liquid which it must drive before it will depend upon that transverse section, and the velocity with which it will impel the liquid will depend upon its own speed. Now, so long as the depth of its immersion remains the same, it is demonstrable that the resistance will increase in proportion to the square of the speed; that is, with a double velocity there will be a fourfold resistance, with a triple velocity a ninefold resistance, and so on. Again, if the part immersed should be increased or diminished by any cause, the resistance, on that account alone, will be increased or diminished in the same proportion. From these circumstances it will be apparent that a vessel floating on water, if moved with a certain speed, will require four times the impelling force to carry it forward with double the speed, unless the depth of its immersion be diminished as its speed is increased. Some experiments which have been made upon canals with boats of a peculiar construction, drawn by horses, have led to the unexpected conclusion, that, after a certain speed has been attained, the resistance, instead of being increased, has been diminished. This fact is not at variance with the law of resistance already explained. The cause of the phenomenon is found in the fact, that when the velocity has attained a certain point, the boat gradually rises out of the water; so that, in fact, the immersed part is diminished. The two conditions, therefore, which determine the resistance, thus modify each other: while the resistance is, on the one hand, increased in proportion to the square of the speed, it is, on the other hand, diminished in proportion to the diminution of the transverse section of the immersed part of the vessel. It would appear that, at a certain velocity, these two effects neutralise each other; and, probably, at higher velocities the immersed part may be so much diminished as to diminish the resistance in a greater degree than it is increased by the speed, and thus actually to diminish the power of traction. It is known that boats are worked on some of the Scottish canals, and also on the canal which connects Kendal with Preston, by which passengers are transported, at the rate of about ten miles an hour, exclusive of the stoppages at the locks, &c. The power of horses, exerted in this way, is, of course, exerted more economically than they could be worked at the same speed on common roads; and, probably, it is as economical as they would be worked by railroad. It is, probably, more economical than the transport of passengers by steam upon railroads; but the speed is considerably less, nor, from the nature of the impelling power, is it possible that it can be increased. There is reason to suppose that a like effect takes place with steam vessels. Upon increasing the power of the engines in some of the Post Office steam packets, it has been found, that, while the time of performing the same voyage is diminished, the consumption of fuel is also diminished. Now, since the consumption of fuel is in the direct ratio of the moving power, and the latter in the direct ratio of the resistance, it follows that the resistance must in this case be likewise diminished. (102.) When a very slow rate of travelling is considered, the useful effects of horse-power applied on canals is somewhat greater than the effect of the same power applied on railways; but at all speeds above three miles an hour, the effect on railways is greater; and when the speed is considerable, the canal becomes wholly inapplicable, while the railway loses none of its advantages. At three miles an hour, the performance of a horse on a canal and a railway is in the proportion of four to three to the advantage of the canal; but at four miles an hour his performance on a railway has the advantage in very nearly the same proportion. At six miles an hour, a horse will perform three times more work on a railway than on a canal. At eight miles an hour, he will perform nearly five times more work. But the circumstance which, so far as respects passengers, must give railways, as compared with canals, an advantage which cannot be considered as less than fatal to the latter, is the fact, that the great speed and cheapness of transit attainable upon a railway by the aid of steam-power will always secure to such lines not only a monopoly of the travelling, but will increase the actual amount of that source of profit in an enormous proportion, as has been already made manifest between Liverpool and Manchester. Before the opening of the railway there were about twenty-five coaches daily running between Liverpool and Manchester. If we assume these coaches on the average to take ten persons at each trip, it will follow that the number of persons passing daily between these towns was about 500. Let us, then, assume that 3000 persons passed weekly. This gives in six months 78,000. In the six months which terminated on the 31st of December 1831, the number of passengers between the same towns, exclusive of any taken up on the road, was 256,321; and if some allowance be made for those taken up on the road, the number may be fairly stated at 300,000. At present there is but one coach on the road between Liverpool and Manchester; and it follows, therefore, that, besides taking the monopoly of the transit in travellers, the actual number has been already increased in a fourfold proportion. The monopoly of the transit of passengers thus secured to the line of communication by railroad will always yield so large a profit as to enable merchandise to be carried at a comparatively low rate. In light goods, which require despatch, it is obvious that the railroad will always command the preference; and the question between that mode of communication and canals is circumscribed to the transit of those classes of heavy goods in which even a small saving in the cost of transport is a greater object than despatch. (103.) The first effect which the Liverpool railroad produced on the Liverpool and Manchester canals was a fall in the price of transport; and at this time, I believe, the cost of transport per ton on the railroads and on the canals is the same. It will, therefore, be naturally asked, this being the case, why the greater speed and certainty of the railroad does not in every instance give it the preference, and altogether deprive the canals of transport? This effect, however, is prevented by several local and accidental causes, as well as by direct influence and individual interest. A large portion of the commercial and manufacturing population of Liverpool and Manchester have property invested in the canals, and are deeply interested to sustain them in opposition to the railway. Such persons will give the preference to the canals in their own business, and will induce those over whom they have influence to do so in every case where speed of transport is not absolutely indispensable. Besides these circumstances, the canal communicates immediately with the shipping at Liverpool, and it ramifies in various directions through Manchester, washing the walls of many of the warehouses and factories for which the goods transported are destined. The merchandise is thus transferred from the shipping to the boat, and brought directly to the door of its owner, or _vice versâ_. If transported by the railway, on the other hand, it must be carried to the station at one extremity; and, when transported to the station at the other, it has still to be carried to its destination in different parts of the town. These circumstances will sufficiently explain why the canals still retain, and may probably continue to retain, a share of the traffic between these great marts. CHAPTER XI. LOCOMOTIVE ENGINES ON TURNPIKE ROADS. Railways and Turnpike Roads compared. -- Mr. Gurney's inventions. -- His Locomotive Steam Engine. -- Its performances. -- Prejudices and errors. -- Committee of the House of Commons. -- Convenience and safety of Steam Carriages. -- Hancock's Steam Carriage. -- Mr. N. Ogle. -- Trevithick's invention. -- Proceedings against Steam Carriages. -- Turnpike Bills. -- Steam Carriage between Gloucester and Cheltenham. -- Its discontinuance. -- Report of the Committee of the Commons. -- Present State and Prospects of Steam Carriages. (104.) We have hitherto confined our observations to steam-power as a means of transport applied on railways, but modern speculation has not stopped here. Several attempts have been made, and some of them attended with considerable success, to work steam-carriages on turnpike roads. The practicability of this project has been hitherto generally considered to be very questionable; but if we carry back our view to the various epochs in the history of the invention of the steam engine, we shall find the same doubt, and the same difficulty, started at almost every important step in its progress. In comparing the effect of a turnpike road with that of a railway, there are two circumstances which obviously give facility and advantage to the railway. One is, that the obstructions to the rolling motion of the wheels, produced by the inequalities of the surface, are very considerably less on a railway than on a road; less in the proportion of at least 1 to 20. This proportion, however, must depend much on the nature of the road with which the railway is compared. It is obvious that a well-constructed road will offer less resistance than one ill constructed; and it is ascertained that the resistance of a Macadamised road is considerably more than that of a road well paved with stones: the decision of this question, therefore, must involve the consideration of another, viz. whether roads may not be constructed by pavement or otherwise, smoother and better adapted to carriages moved in the manner of steam-carriages than the roads now used for horse-power? But besides the greater smoothness of railroads compared with turnpike roads, they have another advantage, which we suspect to have been considerably exaggerated by those who have opposed the project for steam-carriages on turnpike roads. One of the laws of adhesion, long since developed by experiment, and known to scientific men, is, that it is greater between the surfaces of bodies of the same nature than between those of a different nature. Thus between two metals of the same kind it is greater than between two metals of different kinds. Between two metals of any kind it is greater than between metal and stone, or between metal and wood. Hence, the wheels of steam-carriages running on a railroad have a greater adhesion with the road, and therefore offer a greater resistance to slip round without the advance of the carriage, than wheels would offer on a turnpike road; for on a railroad the iron tire of the wheel rests in contact with the iron rail, while on a common road the iron tire rests in contact with the surface of stone, or whatever material the road may be composed of. Besides this, the dust and loose matter which necessarily collect on a common road, when pressed between the wheels and the solid base of the road act somewhat in the manner of rollers, and give the wheels a greater facility to slip than if the road were swept clean, and the wheels rested in immediate contact with its hard surface. The truth of this observation is illustrated on the railroads themselves, where the adhesion is found to be diminished whenever the rails are covered with any extraneous matter, such as dust or moist clay. Although the adhesion of the wheels of a carriage with a common road, however, be less than those of the wheels of a steam-carriage with a railroad, yet still the actual adhesion on turnpike roads is greater in amount than has been generally supposed, and is quite sufficient to propel carriages dragging after them loads of large amount. The relative facility with which carriages are propelled on railroads and turnpike roads equally affects any moving power, whether that of horses or steam engines; and whether loads be propelled by the one power or the other, the railroad, as compared with the turnpike road, will always possess the same proportionate advantage; and a given amount of power, whether of the one kind or the other, will always perform a quantity of work less in the same proportion on a turnpike road than on a railroad. But, on the other hand, the expense of original construction, and of maintaining the repairs of a railroad, is to be placed against the certain facility which it offers to draught. In the attempts which have been made to adapt locomotive engines to turnpike roads, the projectors have aimed at the accomplishment of two objects: first, the construction of lighter and smaller engines; and, secondly, increased power. These ends, it is plain, can only be attained, with our present knowledge, by the production of steam of very high temperature and pressure, so that the smallest volume of steam shall produce the greatest possible mechanical effect. The methods of propelling the carriage have been in general similar to that used in the railroad engines, viz. either by cranks placed on the axles, the wheels being fixed upon the same axles, or by connecting the piston-rods with the spokes of the wheels, as in the engine represented in fig. 55. In some carriages, the boiler and moving power, and the body of the carriage which bears the passengers, are placed on the same wheels. In others, the engine is placed on a separate carriage, and draws after it the carriage which transports the passengers, as is always the case on railways. The chief difference between the steam engines used on railways, and those adapted to propel carriages on turnpike roads, is in the structure of the boiler. In the latter it is essential that, while the power remains undiminished, the boiler should be lighter and smaller. The accomplishment of this has been attempted by various contrivances for so distributing the water, as to expose a considerable quantity of surface in contact with it to the action of the fire; spreading it in thin layers on flat plates; inserting it between plates of iron placed at a small distance asunder, the fire being admitted between the intermediate plates; dividing it into small tubes, round which the fire has play; introducing it between the surfaces of cylinders placed one within another, the fire being admitted between the alternate cylinders,--have all been resorted to by different projectors. (105.) First and most prominent in the history of the application of steam to the propelling of carriages on turnpike roads, stands the name of Mr. GOLDSWORTHY GURNEY, a medical gentleman and scientific chemist, of Cornwall. In 1822, Mr. _Gurney_ succeeded Dr. Thompson as lecturer on chemistry at the Surrey Institution; and, in consequence of the results of some experiments on heat, his attention was directed to the project of working steam carriages on common roads; and since 1825 he has devoted his exertions in perfecting a steam engine capable of attaining the end he had in view. Numerous other projectors, as might have been expected, have followed in his wake. Whether they, or any of them, by better fortune, greater public support, or more powerful genius, may outstrip him in the career on which he has ventured, it would not, perhaps, at present, be easy to predict. But whatever be the event, to Mr. _Gurney_ is due, and will be paid, the honour of first proving the practicability of the project; and in the history of the adaptation of the locomotive engine to common roads, his name will stand before all others in point of time, and the success of his attempts will be recorded as the origin and cause of the success of others in the same race. The incredulity, opposition, and even ridicule, with which the project of Mr. _Gurney_ was met, are very remarkable. His views were from the first opposed by engineers, without one exception. The contracted habit of mind, sometimes produced by an education chiefly, if not exclusively, directed to a merely practical object, subsequently confirmed by exclusively practical pursuits, may, perhaps, in some degree, account for this. But, I confess, it has not been without surprise that I have observed, during the last ten years, the utter incredulity which has prevailed among men of general science on this subject,--an incredulity which the most unequivocal practical proof has scarcely yet dispelled. "Among scientific men," says Mr. _Gurney_, "my opinion had not a single supporter, with the exception of the late Dr. _Wollaston_." The mistake which so long prevailed in the application of locomotives on railroads, and which, as we have shown, materially retarded the progress of that invention, was shared by Mr. _Gurney_. Without reducing the question to the test of experiment, he took for granted, in his first attempts, that the adhesion of the wheels with the road was too slight to propel the carriage. He was assured, he says, by eminent engineers, that this was a point settled by actual experiment. It is strange, however, that a person of his quickness and sagacity did not inquire after the particulars of these "actual experiments." So, however, it was; and, taking for granted the inability of the wheels to propel, he wasted much labour and skill in the contrivance of levers and propellers, which acted on the ground in a manner somewhat resembling the feet of horses, to drive the carriage forward. After various fruitless attempts of this kind, the experience acquired in the trials to which they gave rise at last forced the truth upon his notice, and he found that the adhesion of the wheels was not only sufficient to propel the carriage heavily laden on level roads, but was capable of causing it to ascend all the hills which occur on ordinary turnpike roads. In this manner it ascended all the hills between London and Barnet, London and Stanmore, Stanmore Hill, Brockley Hill, and mounted Old Highgate Hill, the last at one point rising one foot in nine. It would be foreign to my present object to detail minutely all the steps by which Mr. _Gurney_ gradually improved his contrivance. This, like other inventions, has advanced by a series of partial failures; but it has at length attained that state, in which, by practice alone, on a more extensive scale, a further degree of perfection can be obtained. (106.) The boiler of this engine is so constructed that there is no part of it, not even excepting the grate-bars, in which metal exposed to the action of the fire is out of contact with water. If it be considered how rapidly the action of an intense furnace destroys metal when water is not present to prevent the heat from accumulating, the advantage of this circumstance will be appreciated. I have seen the bars of a new grate, never before used, melted in a single trip between Liverpool and Manchester; and the inventor of another form of locomotive engine has admitted to me that his grate-bars, though of a considerable thickness, would not last more than a week. In the boiler of Mr. _Gurney_, the grate-bars themselves are tubes filled with water, and form, in fact, a part of the boiler itself. This boiler consists of three strong metal cylinders placed in a horizontal position one above the other. A section, made by a perpendicular or vertical plane, is represented in fig. 62. The ends of the three cylinders, just mentioned, are represented at D, H, and I. In the side of the lowest cylinder D are inserted a row of tubes, a ground plan of which is represented in fig. 63. These tubes, proceeding from the side of the lowest cylinder D, are inclined slightly upwards, for a reason which I shall presently explain. From the nature of the section, only one of these tubes is visible in fig. 62. at C. The other extremities of these tubes at A are connected with the same number of upright tubes, one of which is expressed at E. The upper extremities G of these upright tubes are connected with another set of tubes K, equal in number, proceeding from G, inclining slightly upwards, and terminating in the second cylinder H. [Illustration: _Fig. 62._] [Illustration: _Fig. 63._] An end view of the boiler is exhibited in fig. 64., where the three cylinders are expressed by the same letters. Between the cylinders D and H there are two tubes of communication B, and two similar tubes between the cylinders H and I. From the nature of the section these appear only as a single tube in fig. 62. From the top of the cylinder I proceeds a tube N, by which steam is conducted to the engine. [Illustration: _Fig. 64._] It will be perceived that the space F is enclosed on every side by a grating of tubes, which have free communication with the cylinders D and H, which cylinders have also a free communication with each other by the tubes B. It follows, therefore, that if water be supplied to the cylinder I, it will descend through the tubes, and first filling the cylinder D and the tubes C, will gradually rise in the tubes B and E, will next fill the tubes K and the cylinder H. The grating of water pipes C E K forms the furnace, the pipes C being the fire-bars, and the pipes E and K being the back and roof of the stove. The fire-door, for the supply of fuel, appears at M, fig. 64. The flue issuing between the tubes F is conducted over the tubes K, and the flame and hot air are carried off through a chimney. That portion of the heat of the burning fuel, which in other furnaces destroys the bars of the grate, is here expended in heating the water contained in the tubes C. The radiant heat of the fire acts upon the tubes K, forming the roof of the furnace, on the tube E at the back of it, and partially on the cylinders D and H, and the tubes B. The draft of hot air and flame passing into the flue at A, acts upon the posterior surfaces of the tubes E, and the upper sides of the tubes K, and finally passes into the chimney. As the water in the tubes C E K is heated, it becomes specifically lighter than water of a less temperature, and consequently acquires a tendency to ascend. It passes, therefore, rapidly into H. Meanwhile the colder portions descend, and the inclined positions of the tubes C and K give play to this tendency of the heated water, so that a prodigiously rapid circulation is produced, when the fire begins to act upon the tubes. When the water acquires such a temperature that steam is rapidly produced, steam bubbles are constantly formed in the tubes surrounding the fire; and if these remained stationary in the tubes, the action of the fire would not only decompose the steam, but render the tubes red hot, the water not passing through them to carry off the heat. But the inclined position of the tubes, already noticed, effectually prevents this injurious consequence. A steam bubble which is formed either in the tubes C or K, having a tendency to ascend proportional to its lightness as compared with water, necessarily rushes upwards; if in C towards A, and if in K towards H. But this motion of the steam is also aided by the rapid circulation of the water which is continually maintained in the tubes, as already explained, otherwise it might be possible, notwithstanding the levity of steam compared with water, that a bubble might remain in a narrow tube without rising. I notice this more particularly, because the burning of the tubes is a defect which has been erroneously, in my opinion, attributed to this boiler. To bring the matter to the test of experiment, I have connected two cylinders, such as D and H, by a system of glass tubes, such as represented at C E K. The rapid and constant circulation of the water was then made evident: bubbles of steam were formed in the tubes, it is true; but they passed with great rapidity into the upper cylinder, and rose to the surface, so that the glass tubes never acquired a higher temperature than that of the water which passed through them. This I conceive to be the chief excellence of Mr. _Gurney's_ boiler. It is impossible that any part of the metal of which it is formed can receive a greater temperature than that of the water which it contains; and that temperature, as is obvious, can be regulated with the most perfect certainty and precision. I have seen the tubes of this boiler, while exposed to the action of the furnace, after that action has continued for a long period of time, and I have never observed the soot which covers them to redden, as it would do if the tube attained a certain temperature. Every part of the boiler being cylindrical, it has the form which, mechanically considered, is most favourable to strength, and which, within given dimensions, contains the greatest quantity of water. It is also free from the defects arising from unequal expansion, which are found to be most injurious in tubular boilers. The tubes C and K can freely expand in the direction of their length, without being loosened at their joints, and without straining any part of the apparatus; the tubes E, being short, are subject to a very slight degree of expansion; and it is obvious that the long tubes, with which they are connected, will yield to this without suffering a strain, and without causing any part of the apparatus to be loosened. When water is converted into steam, any foreign matter which may be combined with it is disengaged, and is deposited on the bottom of the vessel in which the water is evaporated. All boilers, therefore, require occasional cleansing, to prevent the crust thus formed from accumulating; and this operation, for obvious reasons, is attended with peculiar difficulty in tubular boilers. In the case before us, the crust of deposited matter would gather and thicken in the tubes C and K, and if not removed, would at length choke them. But besides this, it would be attended with a still worse effect; for, being a bad conductor, it would intercept the heat in its transit from the fire to the water and would cause the metal of the tube to become unduly heated. Mr. _Gurney_ of course foresaw this inconvenience, and contrived an ingenious chemical method of removing it by occasionally injecting through the tubes such an acid as would combine with the deposite, and carry it away. This method was perfectly effectual; and although its practical application was found to be attended with difficulty in the hands of common workmen, Mr. _Gurney_ was persuaded to adhere to it by the late Dr. _Wollaston_, until experience proved the impossibility of getting it effectually performed, under the circumstances in which boilers are commonly used. Mr. _Gurney_ then adopted the more simple, but not less effectual, method of removing the deposite by mechanical means. Opposite the mouths of the tubes, and on the other side of the cylinders D and H, are placed a number of holes, which, when the boiler is in use, are stopped by pieces of metal screwed into them. When the tubes require to be cleaned these stoppers are removed, and an iron scraper is introduced through the holes into the tubes, which being passed backwards and forwards, removes the deposite. The boiler may be thus cleaned by a common labourer in half a day, at an expense of about 1_s._ 6_d._ The frequency of the periods at which a boiler of this kind requires cleaning must depend, in a great degree, on the nature of the water which is used; one in daily use with the water of the river Thames would not require cleaning more than once in a month. Mr. _Gurney_ states that with water of the most unfavourable description, once a fortnight would be sufficient. (107.) In the more recent boilers constructed by Mr. _Gurney_, he has maintained the draught through the furnace, by the method of projecting the waste steam into the chimneys; a method so perfectly effectual, that it is unlikely to be superseded by any other. The objection which has been urged against it in locomotive engines, working on turnpike roads, is, that the noise which it produces has a tendency to frighten horses. In the engines on the Liverpool road, the steam is allowed to pass directly from the eduction pipe of the cylinder to the chimney, and it there escapes in puffs corresponding with the alternate motion of the pistons, and produces a noise, which, although attended with no inconvenience on the railroad, would certainly be objectionable on turnpike roads. In the engine used in Mr. _Gurney's_ steam-carriage, the steam which passes from the cylinders is conducted to a receptacle, which he calls a blowing box. This box serves the same purpose as the upper chamber of a smith's bellows. It receives the steam from the cylinders in alternate puffs, but lets it escape into the chimney in a continued stream by a number of small jets. Regular draught is by this means produced, and no noise is perceived. Another exit for the steam is also provided, by which the conductor is enabled to increase or diminish, or to suspend altogether, the draught in the chimney, so as to adapt the intensity of the fire to the exigencies of the road. This is a great convenience in practice; because, on some roads, a draught is scarcely required, while on others a powerful blast is indispensable. Connected with this blowing box, is another ingenious apparatus of considerable practical importance. The pipe through which the water which feeds the boiler is conducted to it from the tank is carried through this blowing box, within which it is coiled in a spiral form, so that an extensive thread of the feeding water is exposed to the heat of the waste steam which has escaped from the cylinders, and which is enclosed in this blowing box. In passing through this pipe the feeding water is raised from the ordinary temperature of about 60° to the temperature of 212°. The fuel necessary to accomplish this is, therefore, saved, and the amount of this is calculated at 1/6th of all that is necessary to evaporate the water. Thus, 1/6th of the expense of fuel is saved. But, what is much more important in a locomotive engine, a portion of the weight of the engine is saved without any sacrifice of its power. There is still another great advantage attending this process. The feeding water in the worm just mentioned, while it takes up the heat from the surrounding steam in the blowing box, condenses 1/6th of the waste steam, which is thence conducted to the tank, from which the feeding water is pumped, saving in this manner 1/6th in weight and room of the water necessary to be carried in the carriage for feeding the boiler.[33] [Footnote 33: In boilers constructed for stationary purposes, or for steam navigation, the steam-pipe, after it has passed through the blowing box, is continued and made to form a series of returned flues over the boiler, so as to take up the waste heat after it has passed the boiler, and before it reaches the chimney. But in locomotive engines for common roads, it has been found by experience, that the power gained by the waste heat is not sufficient to propel the weight of the material necessary for taking it up.] So far as the removal of all inconvenience arising from noise, this contrivance has been proved by experience to be perfectly effectual.[34] [Footnote 34: See Report of the Commons.] In all boilers, the process of violent ebullition causes a state of agitation in the water, and a number of counter currents, by which, as the steam is disengaged from the surface of the water, it takes with it a considerable quantity of water in mechanical mixture. If this be carried through the cylinders, since it possesses none of the qualities of steam, and adds nothing to the power of the vapour with which it is combined, it causes an extensive waste of heat and water, and produces other injurious effects. In every boiler therefore, some means should be provided for the separation of the water thus suspended in the steam, before the steam is conducted to the cylinder. In ordinary plate boilers, the large space which remains above the surface of the water serves this purpose. The steam being there subject to no agitation or disturbance, the water mechanically suspended in it descends by its own gravity, and leaves pure steam in the upper part. In the small tubular boilers, this has been a matter, however, of greater difficulty. The contracted spaces in which the ebullition takes place, causes the water to be mixed with the steam in a greater quantity than could happen in common plate boilers: and the want of the same steam-room renders the separation of the water from the steam a matter of some difficulty. These inconveniences have been overcome by a succession of contrivances of great ingenuity. I have already described the rapid and regular circulation effected by the arrangement of the tubes. By this a regularity in the currents is established, which alone has a tendency to diminish the mixture of water with the steam. But in addition to this, a most effectual method of separation is provided in the vessel I, which is a strong iron cylinder of some magnitude, placed out of the immediate influence of the fire. A partial separation of the steam from the water takes place in the cylinder H; and the steam with the water mechanically suspended in it, technically called moist steam, rises into the _separator_ I. Here, being free from all agitation and currents, and being, in fact, quiescent, the particles of water fall to the bottom, while the pure steam remains at the top. This separator, therefore, serves all the purposes of the steam-room above the surface of the water in the large plate boilers. The dry steam is thus collected and ready for the supply of the engine through the tube N, while the water, which is disengaged from it, is collected at the bottom of the separator, and is conducted through the tube T to the lowest vessel D, to be again circulated through the boiler. The pistons of the engine work on the axles of the hind wheels of the carriage which bears the engine, by cranks, as in the locomotives on the Manchester railway, so that the axle is kept in a constant state of rotation while the engine is at work. The wheels placed on this axle are not permanently fixed or keyed upon it, as in the Manchester locomotives; but they are capable of turning upon it in the same manner as ordinary carriage wheels. Immediately within these wheels there are fixed upon the axles two projecting spokes or levers, which revolve with the axle, and which take the position of two opposite spokes of the wheel. These may be occasionally attached to the wheel or detached from it; so that they are capable of compelling the wheels to turn with the axle, or leaving the axle free to turn independent of the wheel, or the wheel independent of the axle, at the pleasure of the conductor. It is by these levers that the engine is made to propel either or both of the wheels. If both pairs of spokes are thrown into connexion with the wheels, the crank shaft or axle will cause both wheels to turn with it, and in that case the operation of the carriage is precisely the same as those of the locomotives already described upon the Liverpool and Manchester line; but this is rarely found to be necessary, since the adhesion of one wheel with the road is generally sufficient to propel the carriage, and consequently only one pair of these fixed levers are generally used, and the carriage propelled by only one of the two hind wheels. The fore wheels of the carriage turn upon a pivot similar to those of a four-wheeled coach. The position of these wheels is changed at pleasure by a simple pinion and circular rack, which is moved by the conductor, and in this manner the carriage is guided with precision and facility. The force of traction necessary to propel a carriage upon common roads must vary with the variable quality of the road, and consequently the propelling power, or the pressure upon the pistons of the engine, must be susceptible of a corresponding variation; but a still greater variation becomes necessary from the undulations and hills which are upon all ordinary roads. This necessary change in the intensity of the impelling power is obtained by restraining the steam in the boiler by the throttle valve, as already described in the locomotive engines on the railroad. This principle, however, is carried much further in the present case. The steam in the boiler may be at a pressure of from 100 to 200 lbs. on the square inch; while the steam on the working piston may not exceed 30 or 40 lbs. on the inch. Thus an immense increase of power is always at the command of the conductor; so that when a hill is encountered, or a rough piece of road, he is enabled to lay on power sufficient to meet the exigency of the occasion. The two difficulties which have been always apprehended in the practical working of steam carriages upon common roads are, first, the command of sufficient power for hills and rough pieces of road; and, secondly, the apprehended insufficiency of the adhesion of the wheels with the road to propel the carriage. The former of these difficulties has been met by allowing steam of a very great pressure to be constantly maintained in the boiler with perfect safety. As to the second, all experiments tend to show that there is no ground for the supposition that the adhesion of the wheels is in any case insufficient for the purposes of propulsion. Mr. _Gurney_ states, that he has succeeded in driving carriages thus propelled up considerable hills on the turnpike roads about London. He made a journey to Barnet with only one wheel attached to the axle, which was found sufficient to propel the carriage up all the hills upon that road. The same carriage, with only one propelling wheel, also went to Bath, and surmounted all the hills between Cranford Bridge and Bath, going and returning. A double stroke of the piston produces one revolution of the propelling wheels, and causes the carriage to move through a space equal to the circumference of those wheels. It will therefore be obvious, that the greater the diameter of the wheels, the better adapted the carriage is for speed; and, on the other hand, wheels of smaller diameter are better adapted for power. In fact, the propelling power of an engine on the wheels will be in the inverse proportion to their diameter. In carriages designed to carry great weights at a moderate speed, smaller wheels will be used; while in those intended for the transport of passengers at considerable velocities, wheels of at least 5 feet in diameter are most advantageous. Among the numerous popular prejudices to which this new invention has given rise, one of the most mischievous in its effects, and most glaring in its falsehood, is the notion that carriages thus propelled are more injurious to roads than carriages drawn by horses. This error has been most clearly and successfully exposed in the evidence taken before the committee of the House of Commons upon steam carriages. It is there fully demonstrated, not only that carriages thus propelled did not wear a turnpike road more rapidly than those drawn by horses, but that, on the other hand, the wear by the feet of horses is far more rapid and destructive than any which could be produced by the wheels of carriages. Steam carriages admit of having the tires of the wheels broad, so as to act upon the road more in the manner of rollers, and thereby to give consistency and firmness to the material of which the road is composed. The driving wheels, being fully proved not to slip upon the road, do not produce any effects more injurious than the ordinary rolling wheels; consequently the wear occasioned by a steam carriage upon a road is not more than that produced by a carriage drawn by horses of an equivalent weight and the same or equal tires; but the wear produced by the pounding and digging of horses' feet in draught is many times greater than that produced by the wear of any carriage. Those who still have doubts upon this subject, if there be any such persons, will be fully satisfied by referring to the evidence which accompanies the report of the committee of the House of Commons, printed in October, 1831. In that report they will not only find demonstrative evidence that the introduction of steam carriages will materially contribute to the saving in the wear of turnpike roads, but also that the practicability of working such carriages with a great saving to the public--with great increase of speed and other conveniences to the traveller--is fully established. The weight of machinery necessary for steam carriages is sometimes urged as an objection to their practical utility. Mr. _Gurney_ states, that, by successive improvements in the details of the machinery, the weight of his carriages, without losing any of the propelling power, may be reduced to 35 cwt., exclusive of the load and fuel and water: but thinks that it is possible to reduce the weight still further. A steam carriage constructed by Mr. _Gurney_, weighing 35 cwt., working for 8 hours, is found, according to his statement, to do the work of about 30 horses. He calculates that the weight of his propelling carriage, which would be capable of drawing 18 persons, would be equal to the weight of 4 horses; and the carriage in which these persons would be drawn would have the same weight as a common stage coach capable of carrying the same number of persons. Thus the weight of the whole--the propelling carriage and the carriage for passengers taken together--would be the same with the weight of a common stage coach, with 4 horses inclusive. (108.) There are two methods of applying locomotives upon common roads to the transport of passengers or goods; the one is by causing the locomotive to carry, and the other to draw the load; and different projectors have adopted the one and the other method. Each is attended with its advantages and disadvantages. If the same carriage transport the engine and the load, the weight of the whole will be less in proportion to the load carried; also a greater pressure may be produced on the wheels by which the load is propelled. It is also thought that a greater facility in turning and guiding the vehicle, greater safety in descending the hills, and a saving in the original cost, will be obtained. On the other hand, when the passengers are placed in the same carriage with the engine, they are necessarily more exposed to the noise of the machinery and to the heat of the boiler and furnace. The danger of explosion is so slight, that, perhaps, it scarcely deserves to be mentioned; but still _the apprehension_ of danger on the part of the passengers, even though groundless, should not be disregarded. This apprehension will be obviously removed or diminished by transferring the passengers into a carriage separate from the engine; but the greatest advantage of keeping the engine separate from the passengers is the facility which it affords of changing one engine for another in case of accident or derangement on the road, in the same manner as horses are changed at the different stages: or, if such an accident occur in a place where a new engine cannot be procured, the load of passengers may be carried forward by horses, until it is brought to some station where a locomotive may be obtained. There is also an advantage arising from the circumstance that when the engines are under repair, or in process of cleaning, the carriages for passengers are not necessarily idle. Thus the same number of carriages for passengers will not be required when the engine is used to draw as when it is used to carry. In case of a very powerful engine being used to carry great loads, it would be quite impracticable to place the engine and loads on four wheels, the pressure being such as no turnpike road could bear. In this case it would be indispensably necessary to place a part of the load at least upon separate carriages to be drawn by the engine. In the comparison of carriages propelled by steam with carriages drawn by horses, there is no respect in which the advantage of the former is so apparent as the safety afforded to the passenger. Steam power is under the most perfect control, and a carriage thus propelled is capable of being guided with the most admirable precision. It is also capable of being stopped almost suddenly, whatever be its speed; it is capable of being turned within a space considerably less than that which would be necessary for four-horse coaches. In turning sharp corners, there is no danger, with the most ordinary care on the part of the conductor. On the other hand, horse-power, as is well known, is under very imperfect control, especially when horses are used, adapted to that speed which at present is generally considered necessary for the purpose of travelling. "The danger of being run away with and overturned," says Mr. _Farey_, in his evidence before the House of Commons, "is greatly diminished in a steam coach. It is very difficult to control four such horses as can draw a heavy stage coach ten miles an hour, in case they are frightened or choose to run away; and, for such quick travelling, they must be kept in that state of courage that they are always inclined to run away, particularly down hill, and at sharp turns in the road. Steam power has very little corresponding danger, being perfectly controllable, and capable of having its power reversed to retard in going down hill. It must be carelessness that would occasion the overturning of a steam carriage. The chance of breaking down has been hitherto considerable, but it will not be more than in stage coaches when the work is truly proportioned and properly executed. The risk from explosion of the boiler is the only new cause of danger, and that I consider not equivalent to the danger from horses." That the risk of accident from explosion is very slight indeed, if any such risk exists, may be proved from the fact that the boilers used on the Liverpool and Manchester railroad being much larger, and, in proportion, inferior in strength to those of Mr. _Gurney_, and other steam carriage projectors, have never yet been productive of any injurious consequences by explosion, although they have frequently burst. I have stood close to a locomotive on the railroad when the boiler burst. The effect was that the water passed through the tubes into the fire and extinguished it, but no other consequence ensued. In fig. 65. is represented the appearance of a locomotive of Mr. _Gurney's_ drawing after it a carriage for passengers. [Illustration: Fig. 65.] (109.) One of the greatest difficulties which locomotives upon a turnpike road have to encounter is the ascent of very steep hills, for it is agreed upon all hands that hills of very moderate inclinations present no difficulty which may not be easily overcome, even in the present state of our knowledge. The fact of Mr. _Gurney_ having propelled his carriage up Old Highgate Hill, when the apparatus was in a a much more imperfect state than that to which it has now attained, establishes the mere question of the possibility of overcoming the difficulty; but it remains still to be decided whether the inconvenience caused by providing means of meeting the exigency of very steep hills may not be greater than the advantage of being able to surmount them can compensate for: and Mr. _Farey_, whose authority upon subjects of this kind is entitled to the highest respect, thinks that it is upon the whole more advantageous to provide, at very steep hills, post horses to assist the steam carriage up them, than to incur the inconvenience of providing the necessary power and strength of machinery for occasions which at best but rarely occur. If the question merely referred to the command of motive power, it appears to me that Mr. _Gurney's_ boiler would be amply sufficient to supply all that could be required for any hills which occur upon turnpike roads; but it is not to be forgotten, that not merely an ample supply of motive power, but also a strength and weight in the machinery proportionate to the power to be exerted, is indispensably necessary. The strength and weight necessary to ascend a very steep hill will be considerably greater than that which is necessary for a level road, or for hills of moderate inclinations; and it follows that if we ascend those steep hills by the unaided power of the locomotive, we must load the engine with all the weight of machinery requisite for such emergencies, such additional weight being altogether unnecessary, and therefore a serious impediment upon all other parts of the road, inasmuch as it must exclude an equivalent weight of goods or passengers, which might otherwise be transported, and thereby in fact diminish proportionally the efficiency of the machine. It is right, however, to observe, that this is a point upon which a difference of opinion is entertained by persons equally competent to form a judgment, and that some consider that it is practicable to construct an engine without inconvenient weight which will ascend all the hills which occur upon turnpike roads. However this may be, the difficulty is one which the improved system of roads in England renders of a comparatively trifling nature. If horses were resorted to as the means of assistance up such hills as the engine would be incapable of surmounting, such aid would not be requisite more than twice or thrice upon the mail-coach road between London and Holyhead; and the same may be said of the roads connecting the greatest points of intercourse in the kingdom. Such hills as the ascent at Pentonville upon the New Road, the ascent in St. James's Street, the ascent from Waterloo Place to the County Fire Office, the ascent at Highgate Archway, present no difficulty whatever. It is only Old Highgate Hill, and hills of a similar kind, which would ever require a supply of horses in aid of the engine. I therefore incline to agree with Mr. _Farey_, that, at least for the present, it will be more expedient to construct carriages adapted to surmount moderate hills only, and to provide post horses in aid of the extreme emergencies to which I have just alluded. (110.) In the boiler to be used in the steam carriage projected by Mr. _Walter Hancock_, the subdivision of the water is accomplished by dividing a case or box by a number of thin plates of metal like a galvanic battery, the water being allowed to flow between every alternate pair of plates, at E, fig. 66., and the intermediate spaces H forming the flue through which the flame and hot air are propelled. [Illustration: Fig. 66.] In fact, a number of thin plates of water are exposed on both sides to the most intense action of flame and heated air; so that steam of a high-pressure is produced in great abundance and with considerable rapidity. The plates forming the boiler are bolted together by strong iron ties, extending across the boiler, at right angles to the plates, as represented in the figure. The distance between the plates is two inches. There are ten flat chambers of this kind for water, and intermediately between them ten flues. Under the flues is the fire-place, or grate; containing six square feet of fuel in vivid combustion. The chambers are all filled to about two thirds of their depth with water, and the other third is left for steam. The water-chambers, throughout the whole series, communicate with each other both at top and bottom, and are held together by two large bolts. By releasing these bolts, at any time, the chambers fall asunder; and by screwing them up they may be all made tight again. The water is supplied to the boiler by a forcing-pump, and the steam issues from the centre of one of the flues at the top. These boilers are constructed to bear a pressure of 400 or 500 lbs. on the square inch; but the average pressure of the steam on the safety valve is from 60 to 100. There are 100 square feet of surface in contact with the water exposed to the fire. The stages which such an engine performs are eight miles, at the end of which a fresh supply of fuel and water are taken in. It requires about two bushels of coke for each stage. The steam carriage of Mr. _Hancock_ differs from that of Mr. _Gurney_ in this,--that in the former the passengers and engine are all placed on the same carriage. The boiler is placed behind the carriage; and there is an engine-house between the boiler and the passengers, who are placed on the fore part of the vehicle; so that all the machinery is behind them. The carriages are adapted to carry 14 passengers, and weigh, exclusive of their load, about 3-1/2 tons, the tires of the wheels being about 3-1/2 inches in breadth. Mr. _Hancock_ states, that the construction of his boiler is of such a nature, that, even in the case of bursting, no danger is to be apprehended, nor any other inconvenience than the stoppage of the carriage. He states that, while travelling about 9 miles an hour, and working with a pressure of about 100 lbs. on the square inch, loaded with 13 passengers, the carriage was suddenly stopped. At first the cause of the accident was not apparent; but, on opening one of the cocks of the boiler, it was found that it contained neither steam nor water. Further examination proved that the boiler had burst. On unscrewing the bolts, it was found there were several large holes in the plates of the water-chamber, through which the water had flowed on the fire; but neither noise nor explosion, nor any dangerous consequences ensued. This boiler has some obvious defects. It is evident that thin flat plates are the form which, mechanically considered, is least favourable to strength; nor does it appear that any material advantage is gained to compensate for this by the magnitude of the surface exposed to the action of the fire. It is a great defect that a part of the surface of each of the plates is exposed to the action of the fire while it is out of contact with the water; in fact, in the upper part of the spaces marked E, fig. 66., steam only is contained. It has been observed by engineers, and usually shown by experiment, that if steam be heated on the surface of water it will be decomposed, and its elasticity destroyed; this is not the only evil connected with the arrangement, for on this part of the metal, nevertheless, the fire acts,--with less intensity, it is true, than on that part which contains the water,--but still with sufficient intensity to destroy the metal. Mr. _Hancock_ appears to have attempted to remedy this defect by occasionally inverting the position of the flat chambers, placing that which at one time was at the bottom at the top, and _vice versâ_. This may equalise the wear produced by the action of the fire upon the metal out of contact with water, but still the wear on the whole will not be less rapid. There appears to be no provision or space for separating the steam from the water with which it is charged; in fact, there are no means in this engine of discharging the function of Mr. _Gurney's_ separator. This will be found to produce considerable waste and loss of power in practice. The bars upon which the fire rests are of solid metal; and such is the intense heat to which they are subject, that, in an engine constantly at work, it is unlikely that they will last, without being renewed, more than about a week, if so much. The draft is maintained in this engine by means of a revolving fan worked by the engine. This, perhaps, is one of the greatest defects as compared with other locomotives. The quantity of power requisite to work this bellows, and of which the engine is robbed, is very great. This defect is so fatal, that I consider it is quite impossible that the ingenious inventor can persevere in the use of it. Mr. _Hancock_ has abandoned the use of the cranks upon his working axle, and has substituted an endless chain and rag-wheels. This also appears to me defective, and a source by which considerable power is lost. On the other hand, however, the weakness of the axle which is always produced by cranks is avoided. (111.) Mr. _Nathaniel Ogle_ of Southampton obtained a patent for a locomotive carriage, and worked it for some time experimentally; but as his operations do not appear to have been continued, I suppose he was unsuccessful in fulfilling those conditions, without which the machine could not be worked with economy and profit. In his evidence before a committee of the House of Commons, he has thus described his contrivance:-- "The base of the boiler and the summit are composed of cross pieces, cylindrical within and square without; there are holes bored through these cross pieces, and inserted through the whole is an air tube. The inner hole of the lower surface, and the under hole of the upper surface, are rather larger than the other ones. Round the air tube is placed a small cylinder, the collar of which fits round the larger aperture on the inner surface of the lower frame, and the under surface of the upper frame-work. These are both drawn together by screws from the top; these cross pieces are united by connecting pieces, the whole strongly bolted together; so that we obtain, in one tenth of the space, and with one tenth of the weight, the same heating surface and power as is now obtained in other and low-pressure boilers, with incalculably greater safety. Our present experimental boiler contains 250 superficial feet of heating surface in the space of 3 feet 8 inches high, 3 feet long, and 2 feet 4 inches broad, and weighs about 8 cwt. We supply the two cylinders with steam, communicating by their pistons with a crank axle, to the ends of which either one or both wheels are affixed, as may be required. One wheel is found to be sufficient, except under very difficult circumstances, and when the elevation is about one foot in six, to impel the vehicle forward. "The cylinders of which the boiler is composed are so small as to bear a greater pressure than could be produced by the quantity of fire beneath the boiler; and if any one of these cylinders should be injured by violence, or any other way, it would become merely a safety valve to the rest. We never, with the greatest pressure, burst, rent, or injured our boiler; and it has not once required cleaning, after having been in use twelve months." (112.) Dr. _Church_ of Birmingham has obtained a succession of patents for contrivances connected with a locomotive engine for stone roads; and a company, consisting of a considerable number of individuals, possessing sufficient capital, has been formed in Birmingham for carrying into effect his designs, and working carriages on his principle. The present boiler of Dr. _Church_ is formed of copper. The water is contained between two sheets of copper, united together by copper nails, in a manner resembling the way in which the cloth forming the top of a mattress or cushion is united with the cloth which forms the bottom of it, except that the nails or pins, which bind the sheets of copper, are much closer together. The water, in fact, seems to be "quilted" or "padded," in between two sheets of thin copper. This double sheet of copper is formed into an oblong rectangular box, the interior of which is the fire-place and ash-pit, and over the end of which is the steam-chest. The great extent of surface exposed to the immediate action of the fire causes steam to be produced with great rapidity. An obvious defect which such a boiler presents is the difficulty of removing from it any deposite or incrustation, which may collect between the sheets of copper so closely and intricately connected. Dr. Church proposes to effect this, when it is required, by the use of an acid, which will combine readily with the incrustation, and by which the boiler may therefore be washed. This method of cleansing boilers was recommended by Dr. Wollaston to Mr. Gurney, who informed me, however, that he found that it was not practicable in the way in which boilers must commonly be used. I apprehend, also, that the spaces between the sheets of copper, in Dr. Church's boiler just described, will hardly permit the steam bubbles which will be formed to escape with sufficient facility into the steam-chest; and being retained in that part of the boiler which is exposed to the action of the fire, the metal will be liable to receive an undue temperature. I have, however, seen this engine working, and its performance was very satisfactory. (113.) Various other projects for steam carriages on common roads are in various degrees of advancement, among which may be mentioned those of Messrs. Maudslay and Field, Col. Macerone, and Mr. Russell of Edinburgh; but our limits compel us to omit any detailed account of them. CHAPTER XII. STEAM NAVIGATION. Propulsion by paddle-wheels. -- Manner of driving them. -- Marine Engine. -- Its form and arrangement. -- Proportion of its cylinder. -- Injury to boilers by deposites and incrustation. -- Not effectually removed by _blowing out_. -- Mr. Samuel Hall's condenser. -- Its advantages. -- Originally suggested by Watt. -- Hall's _steam saver_. -- Howard's vapour engine. -- Morgan's paddle-wheels. -- Limits of steam navigation. -- Proportion of tonnage to power. -- Average speed. -- Consumption of fuel. -- Iron steamers. -- American steam raft. -- Steam navigation to India. -- By Egypt and the Red Sea to Bombay. -- By same route to Calcutta. -- By Syria and the Euphrates to Bombay. -- Steam communication with the United States from the west coast of Ireland to St. John's, Halifax, and New York. (114.) Among the various ways in which the steam engine has ministered to the social progress of our race, none is more important and interesting than the aid it has afforded to navigation. Before it lent its giant powers to that art, locomotion over the waters of the deep was attended with a degree of danger and uncertainty, which seemed so necessary and so inevitable, that, as a common proverb, it became the type and representative of everything else which was precarious and perilous. The application, however, of steam to navigation has rescued the mariner from much of the perils of the winds and waves; and even in its actual state, apart from the improvements which it is still likely to receive, it has rendered all voyages of moderate length as safe and as regular as journeys over land. We are even now upon the brink of such improvements as will probably so extend the powers of the steam engine, as to render it available as the means of connecting the most distant points of the earth. The manner in which the steam engine is commonly applied to propel vessels must be so familiar as to require but short explanation. A pair of wheels, like common under-shot water-wheels, bearing on their rims a number of flat boards called _paddle boards_, are placed one at each side of the vessel, in such a position that when the vessel is immersed to her ordinary depth the lowest paddle boards shall be submerged. These wheels are fixed upon a shaft, which is made to revolve by cranks placed upon it, in the same manner as the fly-wheel of a common steam engine is turned. It is now the invariable custom to place in steam vessels two engines, each of which works a crank: these two cranks are placed at right angles to each other, in the same manner as the cranks already described upon the working axles of locomotive engines. When either crank is at its dead point, the other is in full activity, so that the necessity for a fly wheel is superseded. The engines may be either condensing or high-pressure engines; but in Europe the low-pressure condensing engine has been invariably used for nautical purposes. In the United States, where steam navigation had its origin, and where it was, until a recent period, much more extensively practised than in Europe, less objection was felt to the use of high-pressure engines; and their limited bulk, their small original cost, and simplicity of structure, strongly recommended them, more especially for the purposes of river navigation. (_g._) The original type of nearly all the engines used in steam navigation was that constructed at Soho by Watt and Bolton for Mr. Fulton, and first used by him upon the Hudson river. This had the beam below the piston-rod as in the English boat-engines, but the cylinder above deck, as in the American. From this primitive form, the two nations have diverged in opposite directions. The Americans, navigating rivers, and having speed for their principal object, have not hesitated to keep the cylinder above deck, and have lengthened the stroke of the piston in order to make the power cut on a more advantageous point of the wheel. Compactness has been gained by the suppression of the working beam. On the other hand, the English, having the safe navigation of stormy seas as their more important object, have shortened the cylinder in order that the piston-rod may work wholly under the deck, and the arrangement of Fulton's working beam has been retained by them. In this way there can be no doubt, that they have lost the power of obtaining equal speed from a given expenditure of power, and those conversant in the practice and theory of stowing ships may well doubt whether security is not also sacrificed.--A. E. The arrangement of the parts of the maritime engine differs in some respects, from that of the land engine. Want of room renders greater compactness necessary; and in order to diminish the height of the machine, the working beam is transferred from above the cylinder to below it. In fact, there are two beams, one at each side of the engine, which are connected by a parallel motion with the piston, the rods of the parallel motion extending from the lower part of the engine to the top of the piston-rod. The working end of the beam is connected with the crank by a connecting rod, presented upwards instead of downwards, as in the land engine. The proportion of the length and diameters of the cylinders differ from those of land engines for a like reason: to save height, short cylinders with large diameters are used. Thus, in an engine of 200 horse-power, the length of the cylinder is sometimes 60 inches, and its diameter 53 inches: the valves and the gearing which work them, the air-pump, condenser, and other parts of the machine, do not differ materially from those already described in the land engines. (_h._) The action of machinery may be rendered more equable by using two engines, each of half the power, instead of a single one. If one of these be working with its maximum force when the other is changing the direction of its motion, the result of their joint action will be a force nearly constant. Such a combination was invented by Mr. Francis Ogden, and has been used in several steam boats constructed under his directions. It would however be far more valuable in other cases, particularly where great uniformity in the velocity is indispensable. This method has now become almost universal in the engines used in the English steam boats, each of which has usually two, both applied to the same shaft, and therefore capable of being used singly or together to turn the paddle wheels. In the American steam boats, although two engines have been often applied, each usually acts upon no more than one of the wheels. We can see no other good reason for this, than that our engineers do not wish to be thought to copy Mr. Ogden.--A. E. The nature of the work which the marine engine has to perform, is such, that great regularity of action is neither necessary nor possible. The agitation of the surface of the sea will cause the immersion of the paddle-wheels to vary very much, and the resistance to the engine will undergo a corresponding change: the governor, and other parts of the apparatus already described, contrived for imparting to the engine that extreme regularity which is indispensable in its application to manufactures, are therefore here omitted; and nothing is introduced except what is necessary to maintain the engine in its full working power. It is evident that it must be a matter of considerable importance to reduce the space occupied by the machinery on board a vessel to the least possible dimensions. The marine boilers, therefore, are constructed so as to yield the necessary quantity of steam with the smallest practical dimensions. With this view a much more extensive surface in proportion to the size of the boiler is exposed to the action of the fire. In fact, the flues which carry off the heated air to the chimney are conducted through the boiler, so as to act upon the water on every side in thin oblong shells, which traverse the boiler backward and forward repeatedly, until finally they terminate in the chimney. By this arrangement the original expense of the boilers is very considerably increased; but, on the other hand, their steam-producing power is also greatly augmented; and from experiments lately made by Mr. Watt at Birmingham, it appears that they work with an economy of fuel compared with common land boilers in the proportion of about two to three. Thus they have the additional advantage of saving the tonnage as well as the expense of one third of the fuel. One of the most formidable difficulties which has been encountered in applying the steam engine to the purposes of navigation has arisen from the necessity of supplying the boiler with sea water, instead of pure fresh water. This water (also used for the purpose of condensation) being injected into the condenser and mixed with the condensed steam, is conducted as feeding water into the boiler. The salt contained in the sea water, not being evaporated, remains in the boiler. In fact, it is separated from the water in the same manner as by the process of distillation. As the evaporation in the boiler is continued, the proportion of salt contained in the water is, therefore, constantly increased, until a greater proportion is accumulated than the water is capable of holding in solution; a deposition of salt then commences, and is lodged in the cavities at the bottom of the boiler. The continuance of this process, it is evident, would at length fill the boiler with salt. But besides this, under some circumstances, a deposition of lime[35] is made, and a hard incrustation is formed on the inner surface of the boiler. In some situations, also, sand and mud are received into the boiler, being suspended in the water pumped in for feeding it. All these substances, whether deposited in a loose form in the lower parts of the boiler or collected in a crust on its inner surface, form obstructions to the passage of heat from the fire to the water. The crust thus formed is not unfrequently an inch or more in thickness, and so hard that good chisels are broken in removing it. The heat more or less intercepted by these substances collects in the metal of the boiler, and raises it to a temperature far exceeding that of the water within. It may even, if the incrustation be great, be sufficient to render the boiler red-hot. These circumstances occasion the rapid wear of the boiler, and endanger its safety by softening it. [Footnote 35: Ten thousand grains of pure sea water contain muriate of soda 220 grs., sulphate of soda 33 grs., muriate of magnesia 42 grs., and muriate of lime 8 grs.] The remedy which has generally been adopted to remove or diminish these injurious effects consists in allowing a stream of hot water continually to flow from the boiler, and supplying from the feed-pipe a corresponding portion of cold water. While the hot water which flows from the boiler in this case contains, besides its just proportion of salt, that portion which has been liberated from the water converted into vapour, the cold water which is supplied through the feed-pipe contains less than its just proportion of salt, since it is composed of the natural sea water, mixed with the condensed steam, which latter contains no salt. In this manner, the proportion of the salt in the boiler may be prevented from accumulating; but this is attended with considerable inconvenience and loss. It is evident that the discharge of the hot water, and the introduction of so considerable a quantity of cold water, entails upon the machine a great waste of fuel, and, consequently, renders it necessary that the vessel should be supplied with a much larger quantity of coals than are merely necessary for propelling it. In long voyages, where this inconvenience is most felt, this is a circumstance of obvious importance. But besides the waste of fuel, the speed of the vessel is diminished by the rate of evaporation in the boiler being checked by the constant stream of cold water flowing into it. This process of discharging the water, which is called _blowing out_, is only practised occasionally. In the Admiralty steamers, the engineers are ordered to blow out every two hours. But it is more usual to do so only once a day. This method, however, of blowing out furnishes but a partial remedy for the evils we have alluded to: a loose deposite will perhaps be removed by such means, but an incrustation, more or less according to the circumstances and quality of the water, will be formed; besides which, the temptation to work the vessel with efficiency for the moment influences the engine men to neglect blowing out; and it is found that this class of persons can rarely be relied upon to resort to this remedy with that constancy and regularity which are essential for the due preservation of the boilers. The class of steam vessels which, at present, are exposed to the greatest injury from these causes are the sea-going steamers employed by the Admiralty; and we find, by a report made by Messrs. Lloyd and Kingston to the Admiralty, in August, 1834, that it is admitted that the method of blowing out is, even when daily attended to, ineffectual. "The water in the boiler," these gentlemen observe, "is kept from exceeding a certain degree of saltness, by periodically blowing a portion of it into the sea; but whatever care is taken, in long voyages especially, salt will accumulate, and sometimes in great quantities and of great hardness, so that it is with difficulty it can be removed. Boilers are thus often injured as much in a few months as they would otherwise be in as many years. The other evil necessarily resulting from this state of things is, besides the rapid destruction of the boilers, a great waste of fuel, occasioned by the difficulty with which the heat passes through the incrustation on the inside, by the leaks which are thereby caused, and by the practice of blowing out periodically, as before mentioned, a considerable portion of the boiling water." It would be impracticable to carry on board the vessel a sufficient quantity of pure fresh water to work the engine exclusively by its means. To accomplish this, it would be necessary to have a sufficient supply of cold water to keep the condensing cistern cold, to supply the jet in the condenser, and to have a reservoir in which the warm water coming from the waste pipe of the cold cistern might be allowed to cool. Engineers have therefore directed their attention to some method by which the steam may be condensed without a jet, and after condensation be preserved for the purpose of feeding the boiler. If this could be accomplished, it would not be necessary to provide a greater quantity of pure water than would be sufficient to make up the small portion of waste which might proceed from leakage and from other causes; and it is evident that this portion might always be readily obtained by the distillation of sea water, which might be effected by a small vessel exposed to the same fire which acts upon the boiler. (115.) Mr. _Samuel Hall_ of _Basford_, near Nottingham, has taken out patents for a new form of condenser, contrived for the attainment of these ends, besides some other improvements in the engine. The condenser of Mr. _Hall_ consists of a great number of narrow tubes immersed in a cistern of cold water: the steam as it passes from the cylinder, after having worked the piston, enters these tubes, and is immediately condensed by their cold surfaces. It flows in the form of water from their remote extremities, and is drawn off by the air-pump, and conducted in the usual way to a cistern from which the boiler is fed. In the marine engines constructed under Mr. _Hall_'s patents, the tubes of the condenser being in an upright or vertical position, the steam flows from the cylinder into the upper part of the condenser, which is a low flat chamber, in the bottom of which is inserted the upper extremities of the tubes, through which the steam passes downwards, and as it passes is condensed. It flows thence into a similar chamber below, from whence it is drawn off by the air-pump. It is evident that at sea an unlimited supply of cold water may be obtained to keep the condensing cistern cold, so that a perfect condensation may always be effected by these tubes, if they be made sufficiently small. The water formed by the condensed steam will be pure distilled water; and if the boiler be originally filled with water which does not hold in solution any earthy or other matter which might be deposited or encrusted, it may be worked for any length of time without injury. The small quantity of waste from leakage is supplied in Mr. Hall's engine by a simple apparatus in which a sufficient quantity of sea water may be distilled. The following are the advantages, as stated by Mr. Hall, to be gained by his condenser:-- 1. A saving of fuel, amounting in some cases to so much as a third of the ordinary consumption. 2. The preservation of the boilers from the destruction produced in common engines by the corrosive action of sea or other impure water, and by encrustations of earthy matter. 3. The saving of the time spent in cleaning the boilers. 4. A considerable increase of power, owing to the cleanness of the boilers; the absence of injected water to be pumped out of a vacuum; the greater perfection of the vacuum; the better preservation of the piston and valves of the air-pump; and (by another contrivance of his) the more perfect lubrication of the parts of the engine. 5. The water in the boiler being constantly maintained at the same height by self-acting arrangement. 6. The size of a boiler exerting a given power, being much smaller than the common kind, owing to its more perfect action. Messrs. _Lloyd_ and _Kingston_ were employed by government to examine and report the effects of Mr. Hall's boilers, and they stated in their report, already referred to, that the result is so successful as to leave nothing to be wished for. Among the advantages which they enumerate are the increased durability of the engines; the prevention of accidents through carelessness, or otherwise, arising from the condenser and air-pump becoming choked with injection water; and the additional security against the boilers being burnt in consequence of the water being suffered to get too low. But the greatest advantages, compared with which they consider all others to be of secondary importance, are the increased durability of the boilers and the saving of fuel. About 16 engines, built either wholly upon Mr. Hall's principle or having his condenser attached to them, have now (October, 1835) been working in different parts of England, and on board different vessels for various periods, from three years to three months; and it appears from the concurrent testimony of the proprietors and managers of them, that they are attended with all the advantages which the patentee engaged for. The part of the contrivance the performance of which would have appeared most doubtful would have been the maintenance of a sufficiently good vacuum in the condenser, in the absence of the usual method of condensation by the injection of cold water; nevertheless it appears that a better vacuum is sustained in these engines than in the ordinary engines which condense by jet. The barometer-gauge varies from 29 to 29-1/2 inches, and in some cases comes up to 30 inches, according to the state of the barometer: this is a vacuum very nearly perfect, and indeed may be said to be so for all practical purposes. The _Prince Llewellyn_ and the _Air_ steam packets, belonging to the St. George Steam Packet Company, have worked such a pair of these engines for about a year. The _City of London_ steam packet, the property of the General Steam Navigation Company, has been furnished with two fifty-horse engines, and has worked them during the same period. In all cases the boilers have been found perfectly free from scale or incrustation; and the deposite is either absolutely nothing or very trifling, requiring the boiler to be swept about once in half a year, and sometimes not so often. The trial which has been made of these engines in the navy has proved satisfactory, so far as it has been carried. The Lords of the Admiralty have lately ordered a pair of seventy-horse engines to be constructed on this principle for a vessel now (October, 1835) in process of construction;[36] and another vessel in all respects similar, except having copper boilers, is likewise ordered; so that a just comparison may be made. It would, however, have been more fair if both vessels had been provided with iron boilers, since copper does not receive incrustation as readily as iron. [Footnote 36: This order has, as Mr. Hall informs me, been given without requiring any guarantee as to the performance of the engines.] It would seem that the advantages of these boilers in the vessels of the St. George Steam Packet Company were regarded by the directors as sufficiently evident, since, after more than a year's experience, they are about to place a pair of ninety-horse engines of this kind in a new and powerful steamer called the _Hercules_. Engines furnished with Mr. Hall's apparatus have not yet, so far as I am informed, been tried with reference to the power exerted by the consumption of a given quantity of fuel. The mere fact of a good vacuum being sustained in the condenser cannot by itself be regarded as a conclusive proof of the efficiency of the engine, without the water or air introduced by a condensing jet. Mr. Hall, nevertheless, uses as large an air-pump as that of an ordinary condensing engine, and recommends even a larger one. For what purpose, it may be asked, is such an appendage introduced? If there be nothing to be removed but the condensed steam, a very small pump ought to be sufficient. It is not wonderful that a good vacuum is sustained in the condenser, if the power expended on the air-pump is employed in _pumping away uncondensed steam_. Such a contrivance would be merely a deception, giving an apparent but no real advantage to the engine. Having mentioned these advantages, which are said to arise from Mr. Hall's condenser, it is right to state that it is in fact a reproduction of an early invention of Mr. Watt. There is in possession of James Watt, esquire, a drawing of a condenser laid before parliament in 1776, in which the same method of condensing without a jet is proposed. Mr. Watt, however, finding that he could not procure by that means so sudden or so perfect a vacuum as by injection, abandoned it. I believe he also found that the tubes of the condenser became furred with a deposite which impeded the process of condensation. It would seem, however, that Mr. Hall has found means to obviate these effects. It is right to add, that Mr. Hall, in his specification, distinctly disclaims all claim to the method of condensing by tubes without jet. There is another part of Mr. Hall's contrivance which merits notice. In all engines, a considerable quantity of steam is allowed to escape from the safety valve. Whenever the vessel stops, the steam, which would otherwise be taken from the boiler by the cylinders, passes out through this valve into the atmosphere. Also, whenever the cylinders work at under-power, and do not consume the steam as fast as it is produced by the boiler, the surplus steam escapes through the valve. Now, according to the principle of Mr. Hall's method, it is necessary to save the water which thus escapes in vapour, since otherwise the pure water of the boiler would be more rapidly wasted. Mr. Hall accordingly places a safety valve of peculiar construction in communication with a tube which leads to the condenser, so that whenever, either by stopping the engine or diminishing its working power, steam accumulates in the boiler, its increased pressure opens the safety valve, and it passes through this pipe to the condenser, where it is reconverted into water, and pumped off by the air-pump into the cistern from which the boiler is fed. The attainment of an object so advantageous as to extend the powers of steam navigation, and to render the performance of voyages of any length practicable, so far as the efficiency of the machinery is concerned, has naturally stimulated the inventive genius of the country. The preservation of the boiler by the prevention of deposite and incrustation is an object of paramount importance; and its attainment necessarily involves, to a certain degree, another condition on which the extension of steam voyages must depend, viz. the economy of fuel. In proportion as the economy of fuel is increased, in the same proportion will the limit to which steam navigation may be carried be extended. (116.) A patent has been obtained by Mr. Thomas Howard of London for a form of engine possessing much novelty and ingenuity, and having pretensions to the attainment of a very extraordinary economy of fuel, in addition to those advantages which have been already explained as attending Mr. Hall's engines. In these engines, as in Mr. Hall's, the steam is constantly reproduced from the same water, so that pure or distilled water may be used; but Mr. Howard dispenses with the use of a boiler altogether. The steam also with which he works is in a state essentially different from the steam used in ordinary engines. In these, the vapour is raised directly from the water in a boiling state, and it contains as much water as it is capable of holding at its temperature. Thus, at the temperature of 212°, a cubic foot of steam used in common engines will contain about a cubic inch of water; but in the contrivance of Mr. Howard, a considerable quantity of heat is imparted to the steam before it passes into the cylinder in addition to what is necessary to maintain it in the vaporous form. A quantity of mercury is placed in a shallow wrought-iron vessel over a coke fire, by which it is maintained at the temperature of from 400° to 500°. The surface exposed to the fire is three fourths of a square foot for each horse-power. The upper surface of the mercury is covered by a very thin plate of iron, which rests in contact with it, and which is so contrived as to present about four times as much surface as that exposed beneath to the fire. Adjacent to this a vessel of water is placed, kept heated nearly to the boiling-point, which communicates by a nozzle and valve with the chamber or vessel immediately above the mercury. At intervals corresponding to the motion of the piston, a small quantity of water is injected from this vessel, and thrown upon the plate of iron which rests upon the hot mercury: from this it receives the heat necessary not only to convert it into steam, but to expand that steam, and raise it to a temperature above the temperature it would receive if raised in immediate contact with water. In fact, the steam thus produced will have a temperature not corresponding to its pressure, but considerably above that point, and it will therefore be in circumstances under which it will part with more or less of its heat, and allow its temperature to be lowered without being even partially condensed, whereas steam used in the ordinary steam engines must be more or less condensed by the slightest diminution of its temperature. The quantity of liquid injected into the steam chamber must be regulated by the power at which the engine is intended to work. The fire is supplied with air by a blowing machine, which is subject to exact regulation. The steam, produced in the manner already explained, passes into a chamber which surrounds the working cylinder; and this chamber itself is enclosed by another space, through which the air from the furnace must pass before it reaches the flue. In this way it imparts its redundant heat to the steam which is about to work the cylinder, and raises it to a temperature of about 400°; the pressure, however, not exceeding 25 lbs. per square inch. The arrangement of valves for the admission of the steam to the cylinder is such as to cause the steam to act expansively. The vacuum on the opposite side of the piston is maintained by condensation in the following manner:--The condenser is a copper vessel placed in a cistern constantly supplied with cold water, and the steam flows to it from the cylinder by an eduction pipe in the usual way: a jet is admitted to it from an adjacent vessel, which, before the engine commences work, is filled with distilled water; the condensing water and condensed steam are pumped from the condenser by air-pumps of the usual construction, but smaller, inasmuch as there is no air to be withdrawn, as in common engines. The warm water thus pumped out of the condenser is driven into a copper pipe or worm, which is carried with many coils through a cistern of cold water, so that when it arrives at the end of this pipe it is reduced to the common temperature of the atmosphere. The pipe is then conducted into the vessel of distilled water already mentioned, and the water flowing from it continually replaces the water which flows into the condenser through the condensing jet. The condensing water being purged of air, a very small air-pump is sufficient; since it has only to exhaust the condenser and tubes at starting, and to remove whatever air may enter by casual leakage. The patentee states that the condensation takes place as rapidly and as perfectly as in the best steam engine, and it is evident that this method of condensation is applicable even where the mercurial generator already described may not be employed. The vessel from which the water is injected into the mercurial generator is likewise fed by the air-pump connected with the condenser. There is another pipe besides the copper worm already described, which is carried from the hot well to this vessel, and the water is of course returned through it without being cooled. This vessel is likewise sufficiently exposed to the action of the fire to maintain it at a temperature somewhat below the boiling point. An apparatus of this construction was in the spring of the present year (1835) placed in the Admiralty steamer called the COMET, in connexion with a pair of 40-horse engines. The patentee states that these engines were ill adapted to the contrivance; nevertheless, the vessel was successfully worked in the Thames for 800 miles: she also performed a voyage from Falmouth to Lisbon, but was prevented from returning by an accident which occurred to the machinery near the latter port. In this experimental voyage, the consumption of fuel is stated never to have exceeded a third of her former consumption, when worked by Bolton and Watt's engines; the former consumption of coals being about 800 lbs. per hour, and the consumption with Mr. Howard's engine being under 250 lbs. of coke per hour. After this failure (which, however, was admitted to be one of accident and not of principle) the government did not consider itself justified in bestowing further time or incurring greater expense in trying this engine. Mr. Howard, however, has himself built a new vessel, in which he is about to place a pair of forty-horse engines. This vessel is now (December, 1835) nearly ready, and will bring the question to issue by a fair experiment. The advantages of the contrivance as enumerated by the patentee are:-- _First_, The small space and weight occupied by the machinery, arising from the absence of a boiler. _Secondly_, The diminished consumption of fuel. _Thirdly_, The reduced size of the flues. _Fourthly_, The removal of the injurious effects arising from deposite and incrustation. _Fifthly_, The absence of smoke. Some of these improvements, if realized, will be attended with important advantages in steam navigation. Steamers of a given tonnage and power will have more disposable space for lading and fuel, and in short voyages may carry greater freight, or an increased number of passengers; or by taking a larger quantity of fuel,[37] may make greater runs than are now attainable; or, finally, with the same tonnage and the same lading, they may be supplied with more powerful machinery. [Footnote 37: The fuel used in this form of engine is coke, and not coal. A ton of coke occupies the same space as two tons of coal; the saving of tonnage, therefore, by the increased economy of fuel will not be in so great a proportion as the saving of fuel. A quantity of fuel of equivalent power will occupy about half the present space, but the displacement or immersion which it produces will be only one fourth of its present effect.] (117.) To obtain from the moving power its full amount of mechanical effect in propelling the vessel, it would be necessary that its force should propel, by constantly acting against the water in a horizontal direction, and with a motion contrary to the course of the vessel. No system of mechanical propellers has, however, yet been contrived capable of perfectly attaining this end. Patents have been granted for many ingenious mechanical combinations to impart to the propelling surfaces such angles as appeared to the respective contrivers most advantageous. In most of these, however, the mechanical complexity has formed a fatal objection. No part of the machinery of a steam vessel is so liable to become deranged at sea as the paddle-wheels; and, therefore, such simplicity of construction as is compatible with those repairs which are possible on such emergencies is quite essential for safe practical use. [Illustration: Fig. 67.] The ordinary paddle-wheel, as I have already stated, is a wheel revolving upon a shaft driven by the engine, and carrying upon its circumference a number of flat boards, called paddle boards, which are secured by nuts or braces in a fixed position; and that position is such that the planes of the paddle boards diverge nearly from the centre of the shaft on which the wheel turns. The consequence of this arrangement is that each paddle board can only act in that direction which is most advantageous for the propulsion of the vessel when it arrives near the lowest point of the wheel. In figure 67. let o be the shaft on which the common paddle wheel revolves; the position of the paddle boards are represented at A, B, C, &c.; X, Y represents the water line, the course of the vessel being supposed to be from X to Y; the arrows represent the direction in which the paddle-wheel revolves. The wheel is immersed to the depth of the lowest paddle board, since a less degree of immersion would render a portion of the surface of each paddle board mechanically useless. In the position A the whole force of the paddle board is efficient for propelling the vessel; but, as the paddle enters the water in the position H, its action upon the water, not being horizontal, is only partially effective for propulsion: a part of the force which drives the paddle is expended in depressing the water, and the remainder in driving it contrary to the course of the vessel, and, therefore, by its reaction producing a certain propelling effect. The tendency, however, of the paddle entering the water at H, is to form a hollow or trough, which the water, by its ordinary property, has a continual tendency to fill up. After passing the lowest point A, as the paddle approaches the position B, where it emerges from the water, its action again becomes oblique, a part only having a propelling effect, and the remainder having a tendency to raise the water, and throw up a wave and spray behind the paddle-wheel. It is evident that the more deeply the paddle-wheel becomes immersed the greater will be the proportion of the propelling power thus wasted in elevating and depressing the water; and, if the wheel were immersed to its axis, the whole force of the paddle boards, on entering and leaving the water, would be lost, no part of it having a tendency to propel. If a still deeper immersion takes place, the paddle boards above the axis would have a tendency to retard the course of the vessel. When the vessel is, therefore, in proper trim, the immersion should not exceed nor fall short of the depth of the lowest paddle; but for various reasons it is impossible in practice to maintain this fixed immersion: the agitation of the surface of the sea, causing the vessel to roll, will necessarily produce a great variation in the immersion of the paddle-wheels, one becoming frequently immersed to its axle, while the other is raised altogether out of the water. Also the draught of water of the vessel is liable to change, by the variation in her cargo: this will necessarily happen in steamers which take long voyages. At starting they are heavily laden with fuel, which as they proceed is gradually consumed, whereby the vessel is lightened; and it does not appear that it is practicable to use sea water as ballast to restore the proper degree of immersion. (118.) Among the contrivances which have been proposed for remedying these defects of the common paddle wheel by introducing paddle boards capable of shifting their position as they revolve with the circumference of the wheel, the only one which has been adopted to any considerable extent in practice is that which is commonly known as Morgan's Paddle Wheel. The original patent for this contrivance was granted to Elijah Galloway, and sold by him to Mr. William Morgan. Subsequently to the purchase some improvements in its structure and arrangements were introduced, and it is now extensively adopted by Government in the Admiralty steamers. It was first tried on board His Majesty's steamer the CONFIANCE; and after several successful experiments was ordered by the Lords of the Admiralty to be introduced on board the FLAMER, the FIREBRAND, the COLUMBIA, the SPITFIRE, the LIGHTNING, a large war steamer called the MEDEA,[38] the TARTARUS, the BLAZER, &c. It has been tried by Government in several well-conducted experiments, where two vessels of precisely the same model, supplied with similar engines of equal power, and propelled, one by Morgan's paddle-wheels, and the other by the common paddle-wheels; when it was found that the advantage of the former, whether in smooth or in rough water, was quite apparent. One of the commanders in these experiments (Lieutenant Belson) states that the improvement in the speed of the CONFIANCE, after being supplied with these wheels, was proportionately greater in a sea way than in smooth water; that their action was not impeded by the waves, since the variation of the velocity of the engine did not exceed one or two revolutions per minute: the vessel's way was never stopped, and there was no sensible increase of vibration on the paddle boxes during the gale. Another commander reported that on a comparison of the CONFIANCE and a similar and equally powerful vessel, the CARRON, the CONFIANCE performed in fifty-four hours the voyage which occupied the CARRON eighty-four hours in running. Independently of the great saving of fuel effected (namely, ten bushels per hour[39]), or the time saved in running the same distance, other advantages have been secured by the modification in question. On a comparison of the respective logs of the two vessels, it appeared that the CONFIANCE had gained by the alteration in her wheels an increase of speed amounting to 2 knots on 7 in smooth water, and 2-1/2 knots on 4 to 4-1/2 knots in rough weather; that the action of the paddles did not bring up the engine or retard their velocity in a head sea; that in rolling their action assisted in righting the vessel; and that the wear and strain, as well on the vessel as on the engines, were materially reduced. With respect to the durability of these wheels, the commander of the FLAMER reported in January, 1834, that in six weeks of the most tempestuous weather they found them to act remarkably well, without even a single float being shifted.[40] [Footnote 38: This splendid ship is 860 tons burden, with engines of 220 horse power.] [Footnote 39: See Report quoted in Mechanic's Magazine, vol. xxii. p. 275. This saving cannot amount to less than 40 per cent. upon the whole consumption of fuel; it certainly is considerably beyond what I should have conceived to be possible; but I have no reason to doubt the accuracy of the Report. I estimate the former consumption at 10 pounds per horse power per hour, which on 220 horse-power would be 2200 pounds, of which 840 pounds = 10 bushels, would be about 4-10ths.] [Footnote 40: See a more detailed account of these reports in the Mechanic's Magazine, vol. xxii. p. 274., from which I have taken the drawing of this paddle-wheel; and also see Report of the Committee of the House of Commons on Steam Navigation to India, Evidence of William Morgan, p. 95.] This paddle-wheel is represented in figure 68. The contrivance may be shortly stated to consist in causing the wheel which bears the paddles to revolve on one centre, and the radial arms which move the paddles to revolve on another centre. Let A B C D E F G H I be the polygonal circumference of the paddle-wheel, formed of straight bars, securely connected together at the extremities of the spokes or radii of the wheel which turns on the shaft which is worked by the engine; the centre of this wheel being at O. So far this wheel is similar to the common paddle-wheel; but the paddle boards are not, as in the common wheel, fixed at A B C, &c., so as to be always directed to the centre O, but are so placed that they are capable of turning on axles which are always horizontal, so that they can take any angle with respect to the water which may be given to them. From the centres, or the line joining the pivots on which these paddle boards turn, there proceed short arms K, firmly fixed to the paddle boards at an angle of about 120°. On a motion given to this arm K, it will therefore give a corresponding angular motion to the paddle board, so as to make it turn on its pivots. At the extremities of the several arms marked K is a pin or pivot, to which the extremities of the radial arms L are severally attached, so that the angle between each radial arm L and the short paddle arm K is capable of being changed by any motion imparted to L; the radial arms L are connected at the other end with a centre P, round which they are capable of revolving. Now since the points A B C, &c., which are the pivots on which the paddle boards turn, are moved in the circumference of a circle, of which the centre is O, they are always at the same distance from that point; consequently they will continually vary their distance from the other centre P. Thus, when a paddle board arrives at that point of its revolution at which the centre P lies precisely between it and the centre O, its distance from P is less than in any other position. As it departs from that point, its distance from the centre P gradually increases until it arrives at the opposite point of its revolution, where the centre O is exactly between it and the centre P; then the distance of the paddle board from the centre P is greatest. This constant change of distance between each paddle board and the centre P is accommodated by the variation of the angle between the radial arm L and the short paddle board arm K; as the paddle board approaches the centre P this gradually diminishes; and as the distance of the paddle board from P increases, the angle is likewise augmented. This change in the magnitude of the angle, which thus accommodates the varying position of the paddle board with respect to the centre P, will be observed in the figure. The paddle board D is nearest to P; and it will be observed that the angle contained between L and K is there very acute; at E the angle between L and K increases, but is still acute; at F it increases to a right angle; at G it becomes obtuse; and at K, where it is most distant from the centre P, it becomes most obtuse. It again diminishes at I, and becomes a right angle between A and B. Now this continual shifting of the direction of the short arm K is necessarily accompanied by an equivalent change of position in the paddle board to which it is attached; and the position of the second centre P is, or may be, so adjusted that this paddle board, as it enters the water and emerges from it, shall be such as shall be most advantageous for propelling the vessel, and therefore attended with less of that vibration which arises chiefly from the alternate depression and elevation of the water, owing to the oblique action of the paddle boards.[41] [Footnote 41: A paddle-wheel resembling this has lately been constructed by Messrs. Seawards. It has been charged by Mr. Morgan as being a colourable invasion of his patent, and the dispute has been brought into the courts of law.] (_i_) The relative value of the two wheels, namely, the common paddle-wheel, and that of Morgan has been investigated by Professor Barlow of the Military School, at Woolwich, and the results published in a paper of much ability in the Philosophical Transactions for 1834. By this paper it appears, that, when the paddles are not wholly immersed, the wheel of Morgan has no important advantage over the other, and only acquires one when the wheel wallows. But the most important of his inferences is that the common paddle is least efficient when in a vertical position, contrary to the usual opinion. From this we have a right to infer that the search for a form of wheel which shall always keep the paddle vertical is one whose success need not be attended with any important consequence. The superior qualities of Morgan's wheel when the paddles are deeply immersed is ascribed by Barlow to the lessening of the shock sustained by the common paddle-wheel when it strikes the water. This being the case, the triple wheel of Stevens is probably superior to that of Morgan in its efficiency, while it has the advantage of being far simpler and less liable to be put out of order.--A. E. (119.) To form an approximate estimate of the limit of the present powers of steam navigation, it will be necessary to consider the mutual relation of the capacity or tonnage of the vessel; the magnitude, weight, and power of the machinery; the available stowage for fuel; and the average speed attainable in all weathers, as well as the general purposes to which the vessel is to be appropriated, whether for the transport of goods and merchandise, or merely of despatches and passengers. That portion of the capacity of the vessel which is appropriated to the moving power consists of the space occupied by the machinery and the space occupied by the fuel; the magnitude of the latter will necessarily depend upon the length of the voyage which the vessel must make without receiving a fresh supply of coals. If the voyage be short, this space may be proportionally limited, and a greater portion of room will be left for the machinery. If, on the contrary, the voyage be longer, a greater stock of coals will be necessary, and a less space will remain for the machinery. More powerful vessels, therefore, in proportion to their tonnage, may be used for short than for long voyages. [Illustration: Pl. XII.] Taking an average of fifty-one voyages made by the Admiralty steamers, from Falmouth to Corfu and back during four years ending June, 1834, it was found that the average rate of steaming, exclusive of stoppages, was 7-1/4 miles per hour, taken in a direct line between the places, and without allowing for the necessary deviations in the course of the vessel. The vessels which performed this voyage varied from 350 to 700 tons burthen by measurement, and were provided with engines varying from 100 horse to 200 horse-power, with stowage for coals varying from 80 to 240 tons. The proportion of the power to the tonnage varied from 1 horse to 3 tons to 1 horse to 4 tons; thus, the MESSENGER had a power of 200 horses, and measured 730 tons; the FLAMER had a power of 120 horses, and measured 500 tons; the COLUMBIA had 120 horses, and measured 360 tons. In general, it may be assumed that for the shortest class of trips, such as those of the Margate steamers, and the packets between Liverpool or Holyhead and Dublin, the proportion of the power to the tonnage should be that of 1 horse-power to every 2 tons by measure; while for the longest voyages the proportion would be reduced to 1 horse to 4 tons, voyages of intermediate lengths having every variety of intermediate proportion. Steamers thus proportioned in their power and tonnage may then, on an average of weathers, be expected to make 7-1/4 miles an hour while steaming, which is equivalent to 174 miles per day of twenty-four hours. But, in very long voyages, it rarely happens that a steamer can work constantly without interruption. Besides stress of weather, in which she must sometimes lie-to, she is liable to occasional derangements of her machinery, and more especially of her paddles. In almost every long voyage hitherto attempted, some time has been lost in occasional repairs of this nature while at sea. We shall perhaps, therefore, for long voyages, arrive at a more correct estimate of the daily run of a steamer by taking it at 160 miles.[42] [Footnote 42: The American reader will hardly be able to refrain from a smile at this estimate of Dr. Lardner of the speed of steamboats, founded upon the most improved practice of Europe at the close of the year 1835. The boats on the Hudson River have for years past averaged a speed of 15 miles per hour, and the Lexington, which was constructed for a navigation part of which is performed in the open ocean, could probably keep up a speed of the same amount, except in severe storms. With boats, constructed on the principles of those which navigate Long Island Sound and the Chesapeake, we should not fear to assume 12 miles per hour, or, upwards of 280 miles per day as their average rate of crossing the ocean.--A. E.] By a series of carefully conducted experiments on the consumption of coals, under marine boilers and common land boilers, which have been lately made at the works of Mr. Watt, near Birmingham, it has been proved that the consumption of fuel under marine boilers is less than under land boilers, in the proportion of 2 to 3 very nearly. On the other hand, I have ascertained from general observation throughout the manufacturing districts in the North of England, that the average consumption of coals under land boilers of all powers above the very smallest class is at the rate of 15 pounds of coals per horse-power per hour. From this result, the accuracy of which may be fully relied upon, combined with the result of the experiments just mentioned at Soho, we may conclude that the average consumption of marine boilers will be at the rate of 10 lbs. of coal per horse power per hour. Mr. Field, of the firm of Maudslay and Field, in his evidence before a Select Committee of the House of Commons on Steam Navigation to India, has stated from his observation, and from experiments made at different periods, that the consumption is only 8 lbs. per horse-power per hour. In the evidence of Mr. William Morgan, however, before the same committee, the actual consumption of fuel on board the Mediterranean packets is estimated at 16 cwt. per hour for engines of 200 horse power, and 8-1/4 cwt. for engines of 100 horse-power. From my own observation, which has been rather extensive both with respect to land and marine boilers, I feel assured that 10 lbs. per hour more nearly represents the practical consumption than the lower estimate of Mr. Field. We may then assume the daily consumption of coal by marine boilers, allowing them to work upon an average for 22 hours, the remainder of the time being left for casual stoppages, at 220 lbs. of coal per horse-power, or very nearly 1 ton for every ten horses' power. In short voyages, where there will be no stoppage, the daily consumption will a little exceed this; but the distance traversed will be proportionally greater. When the proportion of the power to the tonnage remains unaltered, the speed of the vessel does not materially change. We may therefore assume that 10 pounds of coal per horse power will carry a sea-going steamer adapted for long voyages 7-1/4 miles direct distance; and therefore to carry her 100 miles will require 138 pounds, or the 1/16th part of a ton nearly. Now, the Mediterranean steamers are capable of taking a quantity of fuel at the rate of 1-1/4 tons per horse power; but the proportion of their power to their tonnage is greater than that which would probably be adapted for longer runs. We shall, therefore, perhaps be warranted in assuming that it is practicable to construct a steamer capable of taking 1-1/2 tons of fuel per horse-power. At the rate of consumption just mentioned, this would be sufficient to carry her 2400 miles in average weather; but as an allowance of fuel must always be made for emergencies, we cannot suppose it possible for her to encounter this extreme run. Allowing, then, spare fuel to the extent of a quarter of a ton per horse-power, we should have as an extreme limit of a steamer's practicable voyage, without receiving a relay of coals, a run of about 2000 miles. (120.) This computation is founded upon results obtained from the use chiefly of the North of England coal. It has, however, been stated in evidence before the select committee above mentioned, that the _Llangennech_ coal of Wales is considerably more powerful. Captain Wilson, who commanded the HUGH LINDSAY steamer in India, has stated that this coal is more powerful than Newcastle, in the proportion of 9 to 6-1/2.[43] Some of the commanders of the Mediterranean packets have likewise stated that the strength of this coal is greater than that of Newcastle in the proportion of 16 to 11.[44] So far then as relates to this coal, the above estimate must be modified, by reducing the consumption nearly in the proportion of 3 to 2. [Footnote 43: Vide Report of Select Committee on Steam Navigation, p. 152.] [Footnote 44: Ibid. p. 7.] The class of vessels best fitted for undertaking long voyages, without relays of coal, would be one from about 800 to 1000 tons measurement furnished with engines from 200 to 250 horse-power.[45] Such vessels could take a supply of from 300 to 400 tons of coals, which being consumed at the rate of from 20 to 25 tons per day, would last about fifteen days. [Footnote 45: Engines in steam vessels generally work considerably above their nominal power. The power, however, to which we uniformly refer is the nominal power, or that power at which they would work with steam of the ordinary pressure.] Applying these results, however, to particular cases, it will be necessary to remember that they are average calculations, and must be subject to such modifications as the circumstances may suggest in the particular instances: thus, if a voyage is contemplated under circumstances in which an adverse wind generally prevails, less than the average speed must be allowed, or, what is the same, a greater consumption of fuel for a given distance. Against a strong head wind, in which a sailing vessel would double-reef her top-sails, even a powerful steamer cannot make more than from 2 to 3 miles an hour, especially if she has a head sea to encounter. (121.) In considering the general economy of fuel, it may be right to state, that the results of experience obtained in the steam navigation of our channels, and particularly in the case of the Post Office packets on the Liverpool station, have clearly established the fact, that by increasing the ratio of the power to the tonnage, an actual saving of fuel in a given distance is effected, while at the same time the speed of the vessel is increased. In the case of the Post Office steamers called the DOLPHIN and the THETIS (Liverpool station,) the power has been successively increased, and the speed proportionably augmented; but the consumption of fuel per voyage between Liverpool and Dublin has been diminished. This, at first view, appears inconsistent with the known theory of the resistance of solids moving through fluids; since this resistance increases in the same proportion as the square of the speed. But this physical principle is founded on the supposition that the immersed part of the floating body remains the same. Now I have myself proved by experiments on canals, that when the speed of the boat is increased beyond a certain limit, its draught of water is rapidly diminished; and in the case of a large steam raft constructed upon the river Hudson, it was found that when the speed was raised to 20 miles an hour, the draught of water was diminished by 7 inches. I have therefore no doubt that the increased speed of steamers is attended with a like effect; that, in fact, they rise out of the water; so that, although the resistance is increased by reason of their increased speed, it is diminished in a still greater proportion by reason of their diminished immersion. Meanwhile, whatever be the cause, it is quite certain that the resistance in moving through the water must be diminished, because the moving power is always in proportion to the quantity of coals consumed, and at the same time in the proportion to the resistance overcome. Since, then, the quantity of coals consumed in a given distance is diminished while the speed is increased, the resistance encountered throughout the same distance must be proportionally diminished. (122.) Increased facility in the extension and application of steam navigation is expected to arise from the substitution of iron for wood, in the construction of vessels. Hitherto iron steamers have been chiefly confined to river navigation; but there appears no sufficient reason why their use should be thus limited. For sea voyages they offer many advantages; they are not half the weight of vessels of equal tonnage constructed of wood; and, consequently, with the same tonnage they will have less draught of water, and therefore less resistance to the propelling power; or, with the same draught of water and the same resistance, they will carry a proportionally heavier cargo. The nature of their material renders them more stiff and unyielding than timber; and they do not suffer that effect which is called _hogging_, which arises from a slight alteration which takes place in the figure of a timber vessel in rolling, accompanied by an alternate opening and closing of the seams. Iron vessels have the further advantage of being more proof against fracture upon rocks. If a timber vessel strike, a plank is broken, and a chasm opened in her many times greater than the point of rock which produces the concussion. If an iron vessel strike she will either merely receive a dinge, or be pierced by a hole equal in size to the point of rock which she encounters. Some examples of the strength of iron vessels was given by Mr. Macgregor Laird, in his evidence before the Committee of the Commons on Steam Navigation, among which the following may be mentioned:--An iron vessel, called the ALBURKAH, in one of their experimental trials got aground, and lay upon her anchor: in a wooden vessel the anchor would probably have pierced her bottom; in this case, however, the bottom was only dinged. An iron vessel, built for the Irish Inland Navigation Company, was being towed across Lough Derg in a gale of wind, when the towing rope broke, and she was driven upon rocks, on which she bumped for a considerable time without any injury. A wooden vessel would in this case have gone to pieces. A further advantage of iron vessels (which in warm climates is deserving of consideration) is their greater coolness and perfect freedom from vermin. (123.) The greatest speed which has yet been attained upon water by the application of steam has been accomplished in the case of a river steamer of peculiar form, which has been constructed upon the river Hudson. This boat, or rather raft, consisted of two hollow vessels formed of thin sheet iron, somewhat in the shape of spindles or cigars (from whence it was called the _cigar boat_.) In the thickest part these floats were eight feet in diameter, tapering towards the ends, and about 300 feet long: these floats or buoys, being placed parallel to each other, having a distance of more than 16 feet between them, supported a deck or raft 300 feet long, and 32 feet wide. A paddle-wheel 30 feet in diameter and 16 feet broad revolved between the spindles, impelled by a steam engine placed upon the deck. This vessel drew about 30 inches of water, and attained a speed of from 20 to 25 miles an hour: she ran upon a bank in the river Hudson, and was lost. The projector is now employed in constructing another vessel of still larger dimensions. It is evident that such a structure is altogether unfitted for sea navigation. In the case of a wide navigable river, however, such as the Hudson, it will no doubt be attended with the advantage of greater expedition. (124.) Several projects for the extension of steam navigation to voyages of considerable length have lately been entertained both by the public and by the legislature, and have imparted to every attempt to improve steam navigation increased interest. A committee of the House of Commons collected evidence and made a report in the last session in favour of an experiment to establish a line of steam communication between Great Britain and India. Two routes have been suggested by the committee, each being a continuation of the line of Admiralty steam packets already established to Malta and the Ionian Isles. One of the routes proposed is through Egypt, the Red Sea, and across the Indian Ocean to Bombay, or some of the other Presidencies; the other across the north part of Syria to the banks of the Euphrates, by that river to the Persian Gulf, and from thence to Bombay. Each of these routes will be attended with peculiar difficulties, and in both a long sea voyage will be encountered. In the route by the Red Sea, it is proposed to establish steamers between Malta and Alexandria (860 miles). A steamer of 400 tons burthen and 100 horse-power would perform this voyage, upon an average of all weathers incident to the situation, in from 5 to 6 days, consuming 10 tons of coal per day. But it is probable that it might be found more advantageous to establish a higher ratio between the power and the tonnage. From Alexandria, the transit might be effected by land across the Isthmus to Suez--a journey of from 4 to 5 days--by caravan and camels; or the transit might be made either by land or water from Alexandria to Cairo, a distance of 173 miles; and from Cairo to Suez, 93 miles, across the desert, in about 5 days. At Suez would be a station for steamers, and the Red Sea would be traversed in 3 runs or more. If necessary, stations for coals might be established at Cosseir, Judda, Mocha, and finally at Socatra--an island immediately beyond the mouth of the Red Sea, in the Indian Ocean: the run from Suez to Cosseir would be 300 miles--somewhat more than twice the distance from Liverpool to Dublin. From Cosseir to Judda, 450 miles; from Judda to Mocha, 517 miles; and from Mocha to Socatra, 632 miles. It is evident that all this would, without difficulty, in the most unfavourable weather, fall within the present powers of steam navigation. If the terminus of the passage be Bombay, the run from Socatra to Bombay will be 1200 miles, which would be, upon an average of weather, about 8 days' steaming. The whole passage from Alexandria to Bombay, allowing 3 days for delay between Suez and Bombay, would be 26 days: the time from Bombay to Malta would therefore be about 33 days; and adding 14 days to this for the transit from Malta to England, we should have a total of 47 days from London to Bombay, or about 7 weeks. If the terminus proposed were Calcutta, the course from Socatra would be 1250 miles south-east to the Maldives, where a station for coals would be established. This distance would be equal to that from Socatra to Bombay. From the Maldives, a run of 400 miles would reach the southern point of Ceylon, called the Point de Galle, which is the best harbour (Bombay excepted) in British India: from the Point de Galle, a run of 600 miles will reach Madras; and from Madras to Calcutta would be a run of about 600 miles. The voyage from London to Calcutta would be performed in about 60 days. At a certain season of the year there exists a powerful physical opponent to the transit from India to Suez: from the middle of June until the end of September, the south-west monsoon blows with unabated force across the Indian Ocean, and more particularly between Socatra and Bombay. This wind is so violent as to leave it barely possible for the most powerful steam packet to make head against it, and the voyage could not be accomplished without serious wear and tear upon the vessels during these months--if indeed it would be practicable at all for any continuance in that season. The attention of parliament has therefore been directed to another line of communication, not liable to this difficulty: it is proposed to establish a line of steamers from Bombay through the Persian Gulf to the Euphrates. The run from Bombay to a place called Muscat, on the southern shore of the Gulf, would be 840 miles in a north-west direction, and therefore not opposed to the south-west monsoon. From Muscat to Bassidore, a point upon the northern coast of the strait at the mouth of the Persian Gulf, would be a run of 255 miles; from Bassidore to Bushire, another point on the eastern coast of the Persian Gulf, would be a run of 300 miles; and from Bushire to the mouth of the Euphrates, would be 120 miles. It is evident that the longest of these runs would offer no more difficulty than the passage from Malta to Alexandria. From Bussora near the mouth of the Euphrates, to Bir, a town upon its left bank near Aleppo, would be 1143 miles, throughout which there are no physical obstacles to the river navigation which may not be overcome. Some difficulties arise from the wild and savage character of the tribes who occupy its banks. It is, however, thought that by proper measures, and securing the co-operation of the Pacha of Egypt, any serious obstruction from this cause may be removed. From Bir, by Aleppo, to Scanderoon, a port upon the Mediterranean, opposite Cyprus, is a land journey, said to be attended with some difficulty but not of great length; and from Scandaroon to Malta is about the same distance as between the latter place and Alexandria. It is calculated that the time from London to Bombay by the Euphrates--supposing the passage to be successfully established--would be a few days shorter than by Egypt and the Red Sea. Whichever of these courses may be adopted, it is clear that the difficulties, so far as the powers of the steam engine are concerned, lie in the one case between Socatra and Bombay, or between Socatra and the Maldives, and in the other case between Bombay and Muscat. Even the run from Malta to Alexandria or Scandaroon is liable to objection, from the liability of the boiler to deposite and incrustation, unless some effectual method be taken to remove this source of injury. If, however, the contrivance of Mr. Hall, or of Mr. Howard, or any other expedient for a like object, be successful, the difficulty will then be limited to the necessary supply of coals for so long a voyage. This, however, has already been encountered and overcome on four several voyages by the HUGH LINDSAY steamer from Bombay to Suez: that vessel encountered a still longer run on these several trips, by going, not to Socatra but to Aden, a point on the coast of Arabia near the Straits of Babel Mandeb, being a run of 1641 miles, which she performed in 10 days and 19 hours. The entire distance from Bombay to Suez was in one case performed in 16 days and 16 hours; and under the most unfavourable circumstances, in 23 days. The average was 21 days for each trip. (125.) Another projected line of steam communication, which offers circumstances of equal interest to the people of these countries and the United States, is that which is proposed to be established between London and New York. On the completion of the London and Liverpool railroad, Dublin will be connected with London, by a continuous line of steam transport. It is proposed to continue this line by a railroad from Dublin to some point on the western coast of Ireland; among others, the harbour of VALENTIA has been mentioned. The nearest point of the western continent is St. John's, Newfoundland, the distance of which from Valentia is 1900 miles; the distance from St. John's to New York is about 1200 miles, Halifax (Nova Scotia) being a convenient intermediate station. The distance from Valentia to St. John's comes very near the point which we have already assigned as the probable present limit of steam navigation. The Atlantic Ocean also offers a formidable opponent in the westerly winds which almost constantly prevail in it. These winds are, in fact, the reaction of the trades, which blow near the equator in a contrary direction, and are produced by those portions of the equatorial atmosphere which, rushing down the northern latitudes, carry with them the velocity from west to east proper to the equator. Besides this difficulty, St. John's and Halifax are both inaccessible, by reason of the climate, during certain months of the year. Should these causes prevent this project from being realized, another course may be adopted. We may proceed from the southern point of Ireland or England to the Azores, a distance of about 1800 miles: from the Azores to New York would be a distance of about 2000 miles, or from the Azores to St. John's would be 1600 miles.[46] [Footnote 46: A treatise on the Steam Engine is not the place to enter into discussion on the causes of the several constant, periodic, and prevailing winds, otherwise we should feel it our duty to correct the opinion adopted by Dr. Lardner from the older authorities, in relation to the course of the westerly winds. These winds are, in the South Atlantic, and in both South and North Pacific, constant winds. In the North Atlantic between the latitudes, of 35° and 45°, and, therefore, in the track of the vessels which navigate between the United States and Great Britain, they are the most frequent prevailing winds, except in the months of April and October. They are certainly not the reaction of the trade winds, which is in a well known zone, to the south of the region in which these westerly winds prevail, under the name of the Horse latitudes of our navigations, and the Grassy sea of the Spaniards. Those who wish to study the true theory of these winds will find it in Daniell's learned and ingenious work, "On Atmospheric Phenomena," or in the analysis of that work in the American Quarterly Review.] (_k_) While the inhabitants of Great Britain are discussing the project of the communication with New York, by means of the stations described by Dr. Lardner, those of the United States appear to be seriously occupied in carrying into effect a direct communication from New York to Liverpool. At the speed which has been given to the American steam boats, this presents no greater difficulties than the voyage from the Azores to New York, would, to one having the speed of no more than 7-1/4 miles per hour. As this attempt is beyond the limit of individual enterprise, there is, at the present moment, an application before the Legislature of the State of New York for a charter to carry this project into effect. It will be difficult to estimate the results of this enterprise, which will bring the old and new world within 12 or 15 days voyage of each other.--A. E.[47] [Footnote 47: Dr. Lardner appears purposely to have omitted any detail of the history of Steam Navigation. It would be an invidious task on the part of a mere editor to attempt to supply what he has thought proper to avoid. We therefore merely refer to this subject for the purpose of expressing the hope, that this silence is an earnest that the writers of Europe are about to abandon the claims they have set up for their countrymen to the merit of introducing the successful practice of Steam navigation, and that the respective services of Fitch, Evans, Fulton, and the elder Stevens will soon be universally acknowledged.--A. E.] CHAPTER XII. GENERAL ECONOMY OF STEAM POWER. Mechanical efficacy of steam -- proportional to the quantity of water evaporated, and to the fuel consumed -- Independent of the pressure. -- Its mechanical efficacy by condensation alone. -- By condensation and expansion combined -- by direct pressure and expansion -- by direct pressure and condensation -- by direct pressure, condensation, and expansion. -- The power of engines. -- The duty of engines. -- Meaning of horse power. -- To compute the power of an engine. -- Of the power of boilers. -- The structure of the grate-bars. -- Quantity of water and steam room. -- Fire surface and flue surface. -- Dimensions of steam pipes. -- Velocity of piston. -- Economy of fuel. -- Cornish duty reports. (130.) Having explained in the preceding chapters the most important circumstances connected with the principal varieties of steam engines, it remains now to explain some matters of detail connected with the power, efficiency, and economy of these machines, which, though perhaps less striking and attractive than the subjects which have hitherto engaged us, are still not undeserving of attention. It has been shown in the first chapter, that water exposed to the ordinary atmospheric pressure (the amount of which may be expressed by a column of 30 inches of mercury) will pass from the liquid into the vaporous state when it arrives at the temperature of 212°; and the vapour thus produced from it will have an elastic force equal to that of the atmosphere. If the water, however, to which heat is applied, be submitted to a greater or less pressure than that of the atmosphere, it will boil at a greater or less temperature, and will always produce steam of an elastic force equal to the pressure under which it boils. Now it is a fact as remarkable as it is important, that to convert a given weight of water into vapour will require the same quantity of heat, under whatever pressure, and at whatever temperature the water may boil. Let us suppose a tube, the base of which is equal to a square foot, in which a piston fits air-tight and steam-tight. Immediately under the piston, let a cubic inch of water be placed, which will be spread in a thin layer over the bottom of the tube. Let the piston be counterbalanced by a weight (acting over a pulley) which will be equivalent to the weight of the piston, so that it shall be free to ascend by the application of any pressure below it. Now let the flame of a lamp be applied at the bottom of the tube: the water under the piston being affected by no pressure from above, except that of the atmosphere acting upon the piston, will boil at the temperature of 212°, and by the continued application of the lamp it will at length be converted into steam. The steam into which the cubic inch of water is converted will expand into the magnitude of a cubic foot, exerting an elastic force equal to the atmospheric pressure; consequently the piston will be raised one foot above its first position in the tube, and the cubic foot beneath it will be completely filled with steam. Let us suppose, that to produce this effect required the lamp to be applied to the tube for the space of fifteen minutes. The water being again supposed at its original temperature, and the piston in its first position, let a weight be placed upon the piston equal to the pressure of the atmosphere, so that the water beneath the piston will be pressed down by double the atmospheric pressure. If the lamp be once more applied, the water will, as before, be converted into vapour; but the piston will now be raised to the height of only six inches[48] from the bottom, the steam expanding into only half its former bulk. The temperature at which the water would commence to be converted into vapour, instead of being 212°, would be 250°; but the time elapsed between the moment of the first application of the lamp, and the complete conversion of the water into steam, will still be fifteen minutes. [Footnote 48: Strictly speaking, the height to which the piston would be raised would not diminish in so great a proportion as the pressure is increased, because the increase of pressure being necessarily accompanied by an increase of temperature, a corresponding expansion would be produced. Therefore there will be a slight increase in the total mechanical effect of the steam. The difference, however, is not very important in practice, and it is usual to consider the density of steam as proportional to the pressure.] Again, if the piston be loaded with a weight equal to double the atmospheric pressure, the water will be pressed down by the force of three atmospheres. If the lamp be applied as before, the water would be converted into steam in the same time; but the piston will now be raised only four inches above its first position, and the steam will consequently be three times as dense as when the piston was pressed down only by the atmosphere. From these and similar experiments we infer:-- _First_, That the elastic pressure of steam is equal to the mechanical pressure under which the water producing the steam has been boiled. _Secondly_, That the bulk which steam fills is diminished in the same proportion as the pressure of the steam is increased; or, in other words, that the density of steam is always in the same proportion as its pressure. _Thirdly_, That the same quantity of heat is sufficient to convert the same weight of water into steam, whatever be the pressure under which the water is boiled, or whatever be the density and pressure of the steam produced. _Fourthly_, That the same quantity of water being converted into steam, produces the same mechanical effect, whatever be the pressure or the density of the steam. Thus, in the first case, the weight of one atmosphere was raised a foot high; in the second case, the weight of two atmospheres was raised through half a foot; and, in the third case, the weight of three atmospheres was raised through the third of a foot; the weight raised being in every case increased in the same proportion as the height through which it is elevated is diminished. Every increase of the weight is, therefore, compensated by a proportionate diminution of the height through which it is raised, and the mechanical effect is consequently the same. _Fifthly_, That the same quantity of heat or fuel is necessary and sufficient to produce the same mechanical effect, whatever be the pressure of the steam which it produces. If steam be used to raise a piston against the atmospheric pressure only, although a definite physical force will be exerted by it, and a mechanical effect produced, yet under such circumstances it will exert no directly useful efficiency; but after the piston has been raised, and the tube beneath it filled with steam balancing the atmosphere above it, a useful effect to the same amount may be obtained by cooling the tube, and thereby reconverting the steam into water. The piston will thus be urged downwards by the unresisted force of the atmosphere, and any chain or rod attached to it will be drawn downwards with a corresponding force. If the area of the piston be, as already supposed, equal to the magnitude of one square foot, the atmospheric pressure upon it, being 15 pounds for each square inch, will amount to 144 times 15 pounds, or 2160 pounds. By drawing down a chain or rope acting over a pulley, the piston would in its descent (omitting the consideration of friction, &c.) raise a weight of 2160 pounds a foot high. Since 2160 pounds are nearly equal to one ton, it may, for the sake of round numbers be stated thus:-- "_A cubic inch of water, being converted into steam, will, by the condensation of that steam, raise a ton weight a foot high._" Such is the way in which the force of steam is rendered practically available in the atmospheric engine. (131.) The method by which steam is used in the single-acting steam engine of Watt is, in all respects, similar, except that the piston, instead of being urged downwards by the force of the atmosphere, is pressed by steam of a force equal to the atmospheric pressure. It is evident, however, that this does not alter the mechanical result. We have stated that a considerable increase of power, from a given quantity of steam, was produced by cutting off the steam after the piston had made a part of its descent, and allowing the remainder of the descent to be produced by the expansive force of the steam already admitted. We shall now more fully explain the principle on which this increase of power depends. Let A B (_fig. 69._,) as before, represent a tube, the bottom of which is equal to a square foot, and let P be a piston in it, resting upon a cubic inch of water spread over the bottom; and let w be an empty vessel, the weight of which exactly counterpoises the piston. By the application of the lamp, the water will be converted into steam of the atmospheric pressure, and the piston will be raised from P to P´, through the height of one foot, the space in the tube beneath it being filled with steam, and the vessel w will have descended through one foot. Let half a ton of water be now poured into the vessel W; its weight will draw the piston P´ upwards, so that the steam below it will expand into a larger space. When the piston P´ was only balanced by the empty vessel W, it was pressed downwards by the whole weight of the atmosphere above, which amounts to about one ton: now, however, half of this pressure is balanced by the half ton of water poured into the vessel W; consequently the effective downward pressure on the piston P´ will be only half a ton, or half its former amount. The piston will therefore rise, until the pressure of the steam below it is diminished to the same extent. By what has been already explained, this will take place when the steam is allowed to expand into double its former bulk; consequently, when the piston has risen to P´´, one foot higher, or two feet from the bottom of the tube, the steam will then exactly balance the downward pressure on the piston, and the latter will remain stationary; the vessel W, with the half ton of water it contains, will have descended one foot lower, or two feet below its first position. Let the steam now be cooled and reconverted into water, and at the same time let another half ton of water be supplied to the vessel W; the pressure below the piston being entirely removed, the atmospheric pressure will act above it with undiminished force; and this force, amounting to one ton, will draw up the vessel W, with its contents. When the piston descends, as it will do, to the bottom of the tube, the ton of water contained in the vessel W will be raised through two perpendicular feet.[49] [Footnote 49: Strictly speaking, the quantity of water supposed in these cases to be placed in the vessel W would just _balance_ the atmospheric pressure. A slight preponderance must therefore be given to the piston, to produce the motion.] Now, in this process it will be observed that the quantity of steam consumed is not more than in the former case, viz. the vapour produced by boiling one cubic inch of water. Let us consider, however, the mechanical effect which has resulted from it; half a ton of water has been allowed to descend through one foot, while a ton has been raised through two feet: deducting the force lost by the descent of half a ton through one foot from the force obtained by the ascent of one ton through the two feet, we obtain for the whole mechanical effect one ton and a half raised through one foot; for it is evident that half a ton has been raised from the lowest point to which the vessel W descended one foot above that point, and one ton has been raised through the other foot, which is equivalent to one ton and a half through one foot. Comparing this with the effect produced in the first case, where the steam was condensed without causing its expansion, it will be evident that there is an increase of 50 per cent. upon the whole mechanical effect produced. But this is not the limit of the increase of power by expansion. Instead of condensing the steam when the piston had arrived at P´´, let a further quantity of water amounting to one sixth of a ton be poured into the vessel W, in addition to the half ton which it previously contained; the effective pressure on the piston P´´, being only half a ton, will be overbalanced by the preponderating weight in the vessel w, and the piston will consequently ascend. It will become stationary when the steam by expansion loses a quantity of force equal to the additional weight which the vessel W has received: now, that vessel, having successively received a half and a sixth of a ton will contain two thirds of a ton; consequently the effective downward pressure on the piston will be only a third of a ton, and the steam to balance this must expand into three times the space it occupied when equal, to the atmospheric pressure. It must therefore ascend to P´´´, three feet above the bottom of the tube. If the steam in the tube be now condensed, and at the same time one third of a ton of water be supplied to the vessel W, so as to make its total contents amount to one ton, the piston will descend, being urged downwards by the unresisted atmospheric pressure, and the ton of water contained in the vessel W will be raised through three perpendicular feet. In this case, as in the former, the total quantity of steam consumed is that of one cubic inch of water; but the mechanical effect it produces is still further increased. To calculate its amount, we must consider that half a ton of water has fallen through two feet, which is equivalent to a ton falling through one foot, besides which the sixth part of a ton has fallen through one foot. The total loss, therefore, by the fall of water has been one ton and one sixth through one foot, while the force gained by the ascent of water has been one ton raised through three feet, which is equivalent to three tons through one foot. If, then, from three tons we deduct one and one sixth, the remainder will be one ton and five sixths raised through one foot; this effect being above 80 per cent. more than that which is produced in the first case, where the steam was not allowed to expand. To carry the inquiry one step further: Let us suppose that, upon the arrival of the piston at P´´´, a further addition of water to the amount of one twelfth of a ton be added to it: this, with the water it already contained, would make the total contents three fourths of a ton; consequently, the effective pressure upon the piston would now be reduced to one fourth of the atmospheric pressure. The atmospheric steam would balance this when expanded into four times its original volume: consequently, the piston would come to a state of rest at P´´´´, four feet above the bottom of the tube, and the vessel W would consequently have descended through four perpendicular feet. If the steam in the tube be now condensed as in the former cases, and at the same time a quarter of a ton of water be added to the vessel W, the piston will descend to the bottom of the tube, and the ton of water in the vessel W will be raised through four perpendicular feet. To estimate the mechanical effect thus produced, we have, as before, to deduct the total force lost by the fall of water from the force gained by its elevation: the water has fallen in three distinct portions: first, half a ton has fallen through three perpendicular feet, which is equivalent to one ton and a half through one foot; secondly, one sixth of a ton has fallen through two perpendicular feet, which is equivalent to one third of a ton through one foot; and thirdly, one twelfth of a ton has fallen through one foot: these added together will be equivalent to one ton and eleven twelfths through one foot. One ton has been raised through four feet, which is equivalent to four tons through one foot: deducting from this the force lost by the descent, the surplus gained will be two tons and one twelfth through one foot, being about 108 per cent. more than the force resulting from the condensation of steam without expansion. To the increase of mechanical effect to be produced in this way, there is no theoretical limit. According to the manner in which we have here explained it, to produce the greatest possible effect by a given extent of expansion, it would be necessary to supply the water or other counterpoise to the vessel W, not in separate masses, as we have here supposed, but continuously, so as to produce a regular motion of the piston upwards. Such is the principle on which the advantages of the expansive engine of Watt and Hornblower depend, explained so far as it can be without the aid of the language and reasoning of analysis.[50] [Footnote 50: A strict investigation of this important property, as well as of the other consequences of the quality of expansion, would require more abstruse mathematical processes than would be consistent with the nature of this work.] (132.) We have here, however, only considered the mechanical effect produced by the condensation of steam. Let us now examine its direct action. Let the piston P be supposed to be connected by a rod with a load or resistance which it is intended to raise, and let the load placed upon it be supposed to amount to one ton, the total pressure on the piston will then be two tons; one due to the atmospheric pressure, and the other to the amount of the load. Upon applying heat to the water, steam will be produced; and when the water has been completely evaporated, the piston will rise to the height of six inches from the bottom of the tube. The total mechanical effect thus produced will be one ton weight raised through six perpendicular inches, which is equivalent to half a ton raised through one foot. Again, let the load upon the piston be two tons; this will produce a total pressure upon the water below it amounting to three tons, including the atmospheric pressure. The water, when converted into vapour under this pressure, will raise the piston and its load through four perpendicular inches: the useful mechanical effect will then be two tons raised through the third of a foot, which is equivalent to two thirds of a ton raised one foot. In the same manner, if the piston were loaded with three tons, the mechanical effect would be equivalent to three fourths of a ton raised through one foot, and so on. It appears therefore from this reasoning, that when the direct force of steam of greater pressure than the atmosphere is used without condensation, the total mechanical effect is always less than that produced by the condensation of atmospheric steam without expansion; but that the greater the pressure under which the steam is produced, the less will be the difference between these effects. In general, the proportion of the mechanical effect of high-pressure steam to the effect produced by the condensation of atmospheric steam, will be as the number of atmospheres expressing the pressure of the steam to the same number increased by one. Thus, if steam be produced under the pressure of six atmospheres, the proportion of its effect to that of the condensation of atmospheric steam will be as six to seven. (133.) Another method of applying the power of steam mechanically is, to combine its direct action with condensation but without expansion. The piston being, as before, loaded with one ton, the evaporation of the water will raise it through six perpendicular inches, and the result so far will be equivalent to a ton raised half a foot; but if the piston-rod be supposed also to act by a chain or cord over a wheel, so as to pull a weight up, the steam which has just raised the ton weight through six inches, may be condensed, and the piston will descend with a force of one ton into the vacuum thus produced, and another ton may be thus raised through half a foot. The total mechanical power thus yielded by the steam, adding to its direct action its effect by condensation, will then be one ton raised through one foot, being an effect exactly equal to that obtained by the condensation of atmospheric steam. If the piston be loaded with two tons, its direct action will, as we have shown, raise these two tons through four inches, which is equivalent to two thirds of a ton raised a foot. By condensing this steam a ton weight may be raised in the same manner, by the descent of the piston through a third of a foot, which is equivalent to the third of a ton raised through one foot. By pursuing like reasoning, it will appear that, if the direct force of high-pressure steam be combined with the indirect force produced by its condensation, the total mechanical effect will be precisely equal to the mechanical effect by the mere condensation of atmospheric steam. (134.) In applying the principle of expansion to the direct action of high-pressure steam, advantages are gained analogous to those already explained with reference to the method of condensation. Let the piston be supposed to be loaded with three tons: the evaporation of the water beneath it will raise this weight, including the atmospheric pressure, through three perpendicular inches. Let one ton be now removed, and the remaining two tons will be raised, by the expansion of the steam, through another perpendicular inch. Let the second ton be now removed, and the piston loaded with the remaining ton will rise, by the expansion of the steam, to the height of six inches from the bottom. These consequences follow immediately from the principle that steam will expand in proportion as the pressure upon it is diminished, observing that in this case the atmospheric pressure, amounting to one ton, must always be added to the load. In this process three separate effects are produced: one ton is raised through three inches, which is equivalent to a quarter of a ton raised through one foot; another ton is raised through four inches, which is equivalent to a third of a ton through a foot, and the third ton is raised through six inches, which is equivalent to half a ton raised through a foot. The total of these effects amounts to one and one-twelfth of a ton raised through one foot, while the same load, raised by the high-pressure steam without expansion, would be equivalent to only half a ton raised through one foot. Again, let the load placed upon the piston be five tons: the evaporation of the water will raise this through the sixth part of a foot; if one ton be now removed, the other four tons will be raised to a height above the bottom of the tube equal to a fifth part of a foot; another ton being removed, the remaining three will be raised to a height from the bottom equal to a fourth of a foot; and so on, the last ton being raised through half a foot. To estimate the total mechanical effect thus produced, we are to consider that the several tons raised from their first position are raised through the sixth, fifth, fourth, third, and half of a perpendicular foot, giving a total effect equal to the sixth, fifth, fourth, third, and half of a ton severally raised through one foot; these, therefore, added together, will give a total of nineteen twentieths of a ton raised through one foot. In general, the expansive force applied to the direct action of high-pressure steam, therefore, will increase its effect according to the same law, and subject to the same principles as were shown with respect to the method of condensation accompanied with expansion. The expansive action of high-pressure steam may be accompanied with condensation, so as considerably to increase the mechanical effect produced; for, after the weights with which the piston is loaded have been successively raised to the extent permitted by the elastic force of the steam, and are removed from the piston, the steam will expand until it balances the atmospheric pressure. It may afterwards be made further to expand, by adding weights to the counterpoise W in the manner already explained; and, the steam being subsequently condensed, all the effects will be produced upon the descent of the piston which we have before noticed. It is evident that by this means the mechanical effect admits of very considerable increase. (135.) We have hitherto considered the piston to be resisted by the atmospheric pressure above it; but, as is shown in the preceding chapters, in the modern steam engines, the atmosphere is expelled from the interior of the machine by allowing the steam to pass freely through all its cavities in the first instance, and to escape at some convenient aperture, which, opening outwards, will effectually prevent the subsequent re-admission of air. The piston-rod and other parts which pass from the external atmosphere to the interior of the machine, are likewise so constructed and so supplied with oil or other lubricating matter that neither the escape of steam nor the entrance of air is permitted. We are therefore now to consider the effect of the action of steam against the piston P, when subjected to a resistance which may be less in amount, to any extent, than the atmospheric pressure. In such machines the steam always acts both directly by its power, and indirectly by its condensation. In calculating its effects, excluding friction, &c., we have therefore only to estimate its total force upon the piston, and to deduct the force of the uncondensed vapour which will resist the motion of the piston. Supposing, then, the total force exerted upon the piston, after deducting the resistance from the uncondensed vapour, to be one ton, and the length of the cylinder to be one foot, each motion of the piston from end to end of the cylinder will produce a mechanical force equivalent to a ton weight raised one foot high. If in this case the magnitude of the piston be equivalent to one square foot, the pressure of the steam will be equal to that of the atmosphere, and the quantity of water in the form of steam which the cylinder will contain will be a cubic inch, while the quantity of steam in it will be a cubic foot. In proportion as the area of the piston is enlarged the pressure of the steam will be diminished, if the moving force is required to remain the same; but with every diminution of pressure the density of the steam will be diminished in the same proportion, and the cylinder will still contain the same quantity of water in the form of vapour. In this way steam may be used, as a mechanical agent, with a pressure to almost any extent less than that of the atmosphere, and at temperatures considerably lower than 212°. To obtain the same mechanical force, it is only necessary to enlarge the piston in the same proportion as the pressure of the steam is diminished. By a due attention to this circumstance, the expansive power of steam, both in its direct action and by condensation, may be used with very much increased advantage; and such is the principle on which the benefits derived from Woolf's contrivances depend. If steam of a high-pressure, say of three or four atmospheres, be admitted to the piston, and allowed to impel it through a very small portion of the descent, it may then be cut off and its expansion may be allowed to act upon the piston until the pressure of the steam is diminished considerably below the atmospheric pressure; the steam may then be condensed and a vacuum produced, and the process repeated. In the double-acting engines, commonly used in manufactures and in navigation, and still more in the high-pressure engines used for locomotion, the advantageous application of the principle of expansion appears to have been hitherto attended with difficulties; for, notwithstanding the benefits which unquestionably attend it in the economy of fuel, it has not been generally resorted to. To derive from this principle full advantage, it would be necessary that the varying power of the expanding steam should encounter a corresponding, or a nearly corresponding, variation in the resistance: this requisite may be attained, in engines applied to the purpose of raising water, by many obvious expedients; but when they have, as in manufactures, to encounter a nearly uniform resistance, or, in navigation and locomotion, a very irregular resistance, the due application of expansion is difficult, if indeed it be practicable. We have seen that the mechanical effect produced by steam when the principle of expansion is not used, is always proportional to the quantity of water contained in the steam, and is likewise in the same proportion so long as a given degree of expansion is used. It is apparent, therefore, that the mechanical power which is or ought to be exerted by an engine is in the direct proportion of the quantity of water evaporated. It has also been shown that the quantity of water evaporated, whatever be the pressure of the steam, will be in the direct proportion of the quantity of heat received from the fuel, and therefore in the direct proportion of the quantity of fuel itself, so long as the same proportion of its heat is imparted to the water. (136.) The POWER of an engine is a term which has been used to express the rate at which it is able to raise a given load, or overcome a given resistance. The DUTY of an engine is another term, which has been adopted to express the load which may be raised a given perpendicular height, by the combustion of a given quantity of fuel. When steam engines were first introduced, they were commonly applied to work pumps or mills which had been previously wrought by horses. It was, therefore, convenient, and indeed necessary, in the first instance, to be able to express the performance of these machines by reference to the effects of animal power, to which manufacturers, miners, and others, had been long accustomed. When an engine, therefore, was capable of performing the same work in a given time, as any given number of horses of average strength usually performed, it was said to be an engine of so many _horses' power_. This term was long used with much vagueness and uncertainty: at length, as the use of steam engines became more extended, it was apparent that confusion and inconvenience would ensue, if some fixed and definite meaning were not assigned to it, so that the engineers and others should clearly understand each other in expressing the powers of these machines. The term _horse-power_ had so long been in use, that it was obviously convenient to retain it. It was only necessary to agree upon some standard by which it might be defined. The performance of a horse of average strength, working for eight hours a day, was, therefore, selected as a standard or unit of steam-engine power. Smeaton estimated the amount of mechanical effect which the animal could produce at 22,916 pounds, raised one foot per minute; Desaguiliers makes it 27,500 pounds, raised through the same height. Messrs. Bolton and Watt caused experiments to be made with the strong horses used in the breweries in London; and from the result of these they assigned 33,000 pounds raised one foot per minute, as the value of a horse's power: this is, accordingly, the estimate now generally adopted; and, when an engine is said to be of so many horses' power, it is meant that, when in good working order and properly managed, it is capable of overcoming a resistance equivalent to so many times 33,000 pounds raised one foot per minute. Thus, an engine of ten-horse-power would be capable of raising 330,000 pounds one foot per minute. As the same quantity of water converted into steam will always produce the same mechanical effect, whatever be the density of the steam produced from it, and at whatever rate the evaporation may proceed, it is evident that the _power_ of a steam engine will depend on two circumstances: first, the rate at which the boiler with its appendages is capable of evaporating water; and, secondly, the rate at which the engine is capable of consuming the steam by its work. We shall consider these two circumstances separately. The rate at which the boiler produces steam will depend upon the rate at which heat can be transmitted from the fire to the water which it contains. Now this heat is transmitted in two ways: either by the direct action of the fire radiating heat against the surface of the boiler; or by the flame, and heated air which escapes from the fire, passing through the flues, as already explained. The surface of the boiler exposed to the direct radiation of the fire is technically called _fire surface_; and that which takes heat from the flame and air, on its way to the chimney, is called _flue surface_. Of these the most efficient in the generation of steam is the former. In stationary boilers, used for condensing engines, where magnitude and weight are matters of little importance, it has been found that the greatest effect has been produced in general by allowing four and a half square feet of fire surface, and four and a half square feet of flue surface, for every horse-power. By means of this quantity of fire and flue surface, a cubic foot of water per hour may be evaporated. It has been already shown that the total power exerted by a cubic inch of water, converted into steam, will be equivalent to 2160 pounds raised one foot. A cubic foot of water consists of 1728 cubic inches, and the power produced by its evaporation will therefore be found by multiplying 2160 by 1728; the product, 3,732,480, expresses the number of pounds' weight which the evaporation of a cubic foot of water would raise one foot high, supposing that its entire mechanical force were rendered available: but to suppose this in practice, would be to suppose the machine, through the medium of which it is worked, moved without any power being expended upon its own parts. It would be, in fact, supposing all its moving parts to be free from friction and other causes of resistance. To form a practical estimate, then, of the real quantity of available mechanical power obtained from the evaporation of a given quantity of water, it will be necessary to inquire what quantity of this power is intercepted by the engine through which it is transmitted. In different forms of steam engine--indeed, we may say in every individual steam engine--the amount thus lost is different; nevertheless, an approximate estimate may be obtained, sufficiently exact to form the basis of a general conclusion. Let us consider, then, severally, the means by which mechanical power is intercepted by the engine. _First_, The steam must flow from the boiler into the cylinder to work the piston; it passes necessarily through pipes more or less contracted, and is, therefore, subject to friction as well as cooling in its passage. _Second_, Force is lost by the radiation of heat from the cylinder and its appendages. _Third_, The friction of the piston in the cylinder must be overcome. _Fourth_, Loss of steam takes place by leakage. _Fifth_, Force is expended in expelling the steam after having worked the piston. _Sixth_, Force is required to open and close the several valves, to pump up the water for condensation, and to overcome the friction of the various axes. _Seventh_, Force is expended upon working the air-pump. In engines which do not condense the steam, and which, therefore, work with steam of high-pressure, some of these sources of waste are absent, but others are of increased amount. If we suppose the total effective force of the water evaporated per hour in the boiler to be expressed by 1000, it is calculated that the waste in a high-pressure engine will be expressed by the number 392; or, in other words, taking the whole undiminished force obtained by evaporation as expressed by 10, very nearly 4 of these parts will be consumed in moving the engine, and the other 6 only will be available. In a single-acting engine which condenses the steam, taking, as before, 1000 to express the total mechanical power of the water evaporated in the boiler, 402 will express the part of this consumed in moving the engine, and 598, therefore, will express the portion of the power practically available; or, taking round numbers, we shall have the same result as in the non-condensing engine, viz. the whole force of the water evaporated being expressed by 10, 4 will express the waste, and 6 the available part. In a double-acting engine the available part of the power bears a somewhat greater proportion to the whole. Taking, as before, 1000 to express the whole force of the water evaporated, 368 will express the proportion of that force expended on the engine, and 632 the proportion which is available for work. In general, then, taking round numbers, we may consider that the mechanical force of four tenths of the water evaporated in the boiler is intercepted by the engine, and the other six tenths are available as a moving force. In this calculation, however, the resistance produced in the condensing engine by the uncondensed steam is not taken into account: the amount of this force will depend upon the temperature at which the water is maintained in the condenser. If this water be kept at the temperature of 120°, the vapour arising from it will have a pressure expressed by three inches seven tenths of mercury; if we suppose the pressure of steam in the boiler to be measured by 37 inches of mercury, then the resistance from the uncondensed steam will amount to one tenth of the whole power of the boiler; this, added to the four tenths already accounted for, would show a waste amounting to half the whole power of the boiler, and consequently only half the water evaporated would be available as a moving power. If the temperature of the condenser be kept down to 100°, then the pressure of uncondensed steam will be expressed by two inches of mercury, and the loss of power consequent upon it would amount to a proportionally less fraction of the whole power. The following example will illustrate the method of estimating the effective power of an engine. In a double-acting engine, in good working condition, the total power of steam in the boiler being expressed by 1000, the proportion intercepted by the engine, exclusive of the resistance of the uncondensed steam, will be 368, and the effective part 632. Now, suppose the pressure of steam in the boiler to be measured by a column of 35 inches of mercury; the thousandth part of this will be seven two hundredths of an inch of mercury, and 632 of these parts will express the effective portion of the power. By multiplying seven two hundredths by 632, we obtain 22 nearly. Now, suppose the temperature in the condenser is 1200, the pressure of steam corresponding to that temperature will be measured by 3-7/10 inches of mercury. Subtracting this from 22, there will remain 18-3/10 inches of mercury, as the effective moving force upon the piston; this will be equivalent to about 7 lbs. on each circular inch. If the diameter of the piston then be 24 inches, its surface will consist of a number of circular inches expressed by the square of 24, or 24 × 24 = 576; and, as upon each of these circular inches there is an effective pressure of 7 lbs., we shall find the total pressure in pounds by multiplying 576 by 7, which gives 4032 lbs. We shall find the space through which this force works per minute, by knowing the length of the cylinder and the number of strokes per minute. Suppose the length of the cylinder to be 5 feet, and the number of strokes per minute 21-1/2. In each stroke[51] the piston will, therefore, move through 10 feet, and in one minute it will move through 215 feet. The moving force, therefore, is 4032 lbs. moved through 215 feet per minute, which is equivalent to 215 times 4032 lbs., or 866,880 lbs., raised one foot per minute. [Footnote 51: By a stroke of the piston is meant its motion from one end of the cylinder and back again.] For every 33,000 lbs. contained in this, the engine has a horse-power. To find the horse-power, then, of the engine, we have only to divide 866,880 by 33,000; the quotient is 26 nearly, and, therefore, the engine is one of 26 horse power. Let it be required to determine the quantity of water which a boiler must evaporate per hour, for each horse-power of the engine which it works. It has been already explained that one horse-power expresses 33,000 lbs. raised one foot high per minute, or, 1,980,000 lbs. raised one foot high per hour. The quantity of water necessary to produce this mechanical effect by evaporation, will be found by considering that a cubic inch of water, being evaporated, will produce a mechanical force equivalent to 2160 lbs. raised a foot high. If we divide 1,980,000, therefore, by 2160, we shall find the number of cubic inches of water which must be evaporated per hour, in order to produce the mechanical effect expressed by one horse-power; the result of this division will be 916,6, which is therefore the number of cubic inches of water per hour, whose evaporation is equivalent to one horse-power. But it has been shown that, for every 6 cubic inches of water evaporated in the boiler which are available as a moving power, there will be 4 cubic inches intercepted by the engine. To find, then, the quantity of waste corresponding to 916 cubic inches of water, it will be necessary to divide that number by 6, and to multiply the result by 4: this process will give 610 as the number of cubic inches of water wasted. The total quantity of water, therefore, which must be evaporated per hour, to produce the effect of one horse-power, will be found by adding 610 to 916, which gives 1526. This result, however, being calculated upon a supposition of a degree of efficiency in the engines which is, perhaps, somewhat above their average state, it has been customary with engineers to allow a cubic foot of water per hour for each horse-power, a cubic foot being 1728 cubic inches, or above 11 per cent. more than the above estimate. (137.) It has been stated, that to evaporate a cubic foot of water per hour requires 9 square feet of surface exposed to the action of the fire and heated air. This, therefore, is the quantity of surface necessary for each horse-power, and we shall find the total quantity of fire and flue surface necessary for a boiler of a given power, by multiplying the number of horses in the power by 9; the product will express, in square feet, the quantity of boiler surface which must be exposed to the fire, one half of this being fire surface and the other half flue surface. Since the supply of heat to the boiler must be proportionate to the quantity of fuel maintained in combustion, and the quantity of that fuel must depend on the extent of grate surface, it is clear that a determinate proportion must exist between the power of the boiler, and the extent of grating in the fire place. The quantity of oxygen which combines with the fuel varies with the quality of that fuel; for different kinds of coal it varies from two to three pounds for each pound of coal. We shall take it an average of 2-1/2 pounds. Now 2-1/2 pounds of oxygen will measure 30 cubic feet; also 5 cubic feet of atmospheric air contain 1 cubic foot of oxygen; and consequently 150 cubic feet of atmospheric air will be necessary for the combustion of 1 pound of average coals. At least one third of the air, which passes through a fire, escapes uncombined into the chimney. We must, therefore, allow 220 cubic feet of atmospheric air to pass through the grate-bars for every pound of fuel which is consumed. Now since land boilers will consume 15 pounds, and marine boilers 10 pounds, per hour per horse-power, it follows that the spaces between the grate-bars, and the extent of grate surface, must be sufficient to allow 3000 cubic feet of air per hour in land boilers, and 2000 cubic feet in marine boilers, to pass through them for each horse-power, or, what is the same, for each foot of water converted into steam per hour. The quantity of grate surface necessary for this does not seem to be ascertained with precision; but, perhaps, we may take as an approximate estimate for land boilers one square foot of grate surface per horse-power, and for marine boilers two thirds of a square foot, the spaces between the grate-bars being equal to their breadth. It is evident that the capacity of a boiler for water and steam must have a determinate relation to the power of the engine it is intended to supply. For each horse-power of the engine, it has been shown that a cubic foot of water must pass from the boiler in the form of steam per hour. Now, it is evident that the steam could not be supplied of a uniform force, if the quantity of steam contained at any moment in the boiler were not considerably greater than the contents of the cylinder. For example, if the volume of steam in the boiler were precisely equal to the capacity of the cylinder, then one measure of the cylinder would for the moment cause the steam to expand into double its bulk and to lose half its force, supposing it to pass freely from the boiler to the cylinder. In the same manner, if the volume of steam contained in the boiler were twice the contents of the cylinder, the steam would for a moment lose a third of its force, and so on. It is clear, therefore, that the space allotted to steam in the boiler must be so many times greater than the magnitude of the cylinder, that the abstraction of a cylinder full of steam from it shall cause a very trifling diminution of its force. In the same manner, we may perceive the necessity of maintaining a large proportion between the total quantity of water in the boiler, and the quantity supplied in the form of steam to the cylinder. If, for example (taking as before an extreme case,) the quantity of water in the boiler were only equal to the quantity supplied in the form of steam to the cylinder in a minute, it would be necessary that the contents of the boiler should be replaced by cold water once in each minute: and, under such circumstances, it is evident that the action of the heat upon the water would be quite unmanageable. But, independent of this, the quantity of water must be sufficient to fill the boiler above the point at which the flue surface terminates, otherwise the heat of the fuel would act upon the part of the boiler containing steam and not water; and, steam receiving heat sluggishly, the metal of the boiler would be gradually destroyed by undue temperature. The total quantity of space for water and steam in boilers is subject to considerable variation in proportion to their power. Small boilers require a greater proportion of steam and water-room, or a greater capacity of boiler, in proportion, than large ones; and the same applies to their fire surface and flue surface. The general experience of engineers has led to the conclusion, that a low-pressure boiler of the common kind requires ten cubic feet of water-room, and ten cubic feet of steam-room in the boiler, for every cubic foot which the engine consumes per hour, or, what is the same, for each horse-power of the engine. Thus, an engine of ten-horse-power, according to this rule, would require a boiler having the capacity of 200 cubic feet which should be constantly kept half filled with water. There are, however, different estimates of this. Some engineers hold that a boiler should have twenty-five cubic feet of capacity for each horse-power of the engine, while others reduce the steam so low as eight cubic feet. In a table of the capacities of boilers of different powers, and the feed of water necessary to be maintained in them, Mr. Tredgold assigns to a boiler of five-horse-power fourteen cubic feet of water per horse-power; for one of ten-horse power, twelve and a half cubic feet; and, for one of forty-horse, eleven cubic feet. For engines of greater power it is generally found advantageous to have two or more boilers of small power, instead of one of large power. This method is almost invariably adopted on board steam boats, and has the advantage of securing the continuance of the working of the engine, in case of one of the boilers being deranged. It is also found convenient to keep an excess of power in the boilers, above the wants of the engine. Thus, an engine of sixty-horse-power may be advantageously supplied with two forty-horse boilers, and an engine of eighty-horse-power with two fifty-horse boilers, and so on. (138.) The pressure of steam in the cylinder of an engine is always less than the pressure of steam in the boiler, owing to the obstructions which it encounters in its passage through the steam pipes and valves. The difference between these pressures will depend upon the form and magnitude of the passages: the straighter and wider they are, the less the difference will be; if they are contracted and subject to bends, especially to angular inflexions, the steam will be considerably diminished in its pressure before it reaches the cylinder. The throttle valve placed in the steam pipe may also be so managed as to diminish the pressure of steam in the cylinder to any extent: this effect, which is well understood by practical engineers, is called _wire-drawing_ the steam. By such means it is evidently possible for the steam in the boiler to have any degree of high-pressure while the engine is worked at any degree of low pressure. Since, however, the pressure of the steam in the cylinder is a material element in the performance of the engine, the magnitude, position, and shape of the steam pipe and of the valves are a matter of considerable practical importance. But theory furnishes us with little more than very general principles to guide us. One practical rule which has been adopted is, to make the diameter of the steam pipe about one fifth of that of the cylinder: by this means the area of the transverse action of the pipe will be one twenty-fifth part of the superficial magnitude of the piston; and, since the same quantity of steam per minute must flow through this pipe as through the cylinder, it follows that the velocity of the steam, in passing through the steam pipe, will be twenty-five times the velocity of the piston. (139.) Another rule which has been adopted is, to allow a square inch of magnitude, in the section of the steam pipe, for each horse-power of the engine. The result of this and all similar rules is, that the steam should always pass through the steam pipe with the same velocity, whatever be the power of the engine. In engines of the same power, the piston will have very different velocities in the cylinder, according to the effective pressure of the steam, and the proportions and capacity of the cylinder. It is clear from what has been already explained, that, when the power is the same, the same actual quantity of water, in the form of steam, must pass through the cylinder per minute: but, if the steam be used with a considerable pressure, being in a condensed state, the same weight of it will occupy a less space; and consequently the cylinders of high-pressure engines are smaller than those of the same power in low-pressure engines: the magnitude of the cylinder and the piston therefore, as well as the velocity of the latter, will depend first upon the pressure of the steam. But with steam of a given pressure, the velocity of the piston will be different: with a given capacity of cylinder, and a given pressure of steam, the power of the engine will determine the number of strokes per minute. But the actual velocity of the piston will depend, in that case, on the proportion which the diameter of the cylinder bears to its length; the greater the diameter of the piston is with respect to its length, the less will be its velocity. In case of stationary engines used on land, that proportion of the diameter of the cylinder to its length is selected, which is thought to contribute to the most efficient performance of the machine. According to some engineers, the length of the cylinder should be twice its diameter;[52] others make the length equal to two diameters and a half; but there are circumstances in which considerations of practical convenience render it necessary to depart from these proportions. In marine engines, where great length of cylinder would be inadmissible, and where, on the other hand, considerable power is required, cylinders of short stroke and great diameter are used. In these engines the length of the stroke is often not greater than the diameter of the piston, and sometimes even less. [Footnote 52: This is the proportion under which the cylinder with a given capacity will present the least possible surface to the cooling effect of the atmosphere.] The actual velocity which has been found to have the best practical effect, for the piston in low-pressure engines, is about 200 feet per minute. This, however, is subject to some variation. (140.) A given weight or measure of fuel burnt under the boiler of an engine is capable of producing a mechanical effect through the means of that engine, which, when expressed in an equivalent number of pounds' weight lifted a foot high, is called the _duty_ of the engine. If all the heat developed in the combustion of the fuel could be imparted to the water in the boiler, and could be rendered instrumental in producing its evaporation; and if, besides, the steam thus produced could be all rendered mechanically available at the working point; then the duty of the engine would be the entire undiminished effect of the heat of combustion; but it is evident that this can never practically be the case. In the first place, the heat developed by the combustion can never be wholly imparted to the water in the boiler: some part of it will necessarily escape without reaching the boiler at all; another portion will be consumed in heating the metal of the boiler, and in supplying the loss by radiation from its surface; another portion will be abstracted by the various sources of the waste and leakage of steam; another portion will be abstracted by the reaction of the condensed steam; and another portion of the power will be consumed in overcoming the friction and resistance of the engine itself. It is apparent that all these sources of waste will vary according to the circumstances and conditions of the machine, and according to the form and construction of the furnace, flues, boilers, &c. The duty, therefore, of different engines will be different; and when such machines are compared, with a view to ascertain their economy of fuel, it has been found necessary carefully to register and to compare the fuel consumed with the weight or resistance overcome. In engines applied to manufactures generally or navigation, it is not easy to measure the amount of resistance which the engine encounters, but when the engine is applied to the pumping of water, its performance is more easily determined. In the year 1811, several of the proprietors of the mines in Cornwall, suspecting that some of their engines might not be doing a duty adequate to their consumption of fuel, came to a determination to establish a uniform method of testing the performance of their engines. For this purpose a counter was attached to each engine, to register the number of strokes of the piston. All the engines were put under the superintendence of Messrs. Thomas and John Lean, engineers; and the different proprietors of the mines, as well as their directing engineers, respectively pledged themselves to give every facility and assistance in their power for the attainment of so desirable an end. Messrs. Lean were directed to publish a monthly report of the performance of each engine, specifying the name of the mine, the size of the cylinder, the load upon the engine, the length of the stroke, the number of pump lifts, the depth of the lift, the diameter of the pumps, the time worked, the consumption of coals, the load on the pump, and, finally, the duty of the engine, or the number of pounds lifted one foot high by a bushel of coals. The publication of these monthly reports commenced in August, 1811, and have been regularly continued to the present time. The favourable effect which these reports have produced upon the vigilance of the several engineers, and the emulation they have excited, both among engine-makers and those to whom the working of the machines are intrusted, are rendered conspicuous in the improvement which has gradually taken place in the performance of the engines, up to the present time. In a report published in December, 1826, the highest duty was that of an engine at Wheal Hope mine in Cornwall. By the consumption of one bushel of coals, this engine raised 46,838,246 pounds a foot high, or, in round numbers, forty-seven millions of pounds. In a report published in the course of the present year (1835) it was announced that a steam engine, erected at a copper mine near St. Anstell, in Cornwall, had raised by its average work 95 millions of pounds 1 foot high, with a bushel of coals. This enormous mechanical effect having given rise to some doubts as to the correctness of the experiments on which the report was founded, it was agreed that another trial should be made in the presence of a number of competent and disinterested witnesses. This trial accordingly took place a short time since, and was witnessed by a number of the most experienced mining engineers and agents: the result was, that for every bushel of coal consumed under the boiler the engine raised 125-1/2 millions of pounds weight one foot high. (141.) It may not be uninteresting to illustrate the amount of mechanical virtue, which is thus proved to reside in coals, in a more familiar manner. Since a bushel of coal weighs 84 lbs. and can lift 56,027 tons a foot high, it follows that a pound of coal would raise 667 tons the same height; and that an ounce of coal would raise 42 tons one foot high, or it would raise 18 lbs. a mile high. Since a force of 18 lbs. is capable of drawing 2 tons upon a railway, it follows that an ounce of coal possesses mechanical virtue sufficient to draw 2 tons a mile, or 1 ton 2 miles, upon a level railway.[53] [Footnote 53: The actual consumption of coal upon railways is in practice about eight ounces per ton per mile. It is, therefore, worked with sixteen times less effect than in the engine above mentioned.] The circumference of the earth measures 25,000 miles. If it were begirt by an iron railway, a load of one ton would be drawn round it in six weeks by the amount of mechanical power which resides in the third part of a ton of coals. The great pyramid of Egypt stands upon a base measuring 700 feet each way, and is 500 feet high; its weight being 12,760,000,000 lbs. To construct it, cost the labour of 100,000 men for 20 years. Its materials would be raised from the ground to their present position by the combustion of 479 tons of coals. The weight of metal in the Menai bridge is 4,000,000 lbs., and its height above the level of the water is 120 feet: its mass might be lifted from the level of the water to its present position by the combustion of 4 bushels of coals.[54] [Footnote 54: Some of these examples were given by Sir John Herschel, in his Preliminary Discourse on Natural Philosophy; but since that work was written an increased power has been obtained from coals, in the proportion of 7 to 12-1/2.] The enormous consumption of coals in the arts and manufactures, and in steam navigation, has of late years excited the fears of some persons as to the possibility of the exhaustion of our mines. These apprehensions, however, may be allayed by the assurance received from the highest mining and geological authorities, that, estimating the present demand from our coal mines at 16 millions of tons annually, the coal fields of Northumberland and Durham alone are sufficient to supply it for 1700 years, and after the expiration of that time the great coal basin of South Wales will be sufficient to supply the same demand for 2000 years longer. But, in speculations like these, the probable, if not certain, progress of improvement and discovery ought not to be overlooked; and we may safely pronounce that, long before a minute fraction of such a period of time shall have rolled over, other and more powerful mechanical agents will altogether supersede the use of coal. Philosophy already directs her finger at sources of inexhaustible power in the phenomena of electricity and magnetism. The alternate decomposition and recomposition of water, by magnetism and electricity, has too close an analogy to the alternate processes of vaporisation and condensation, not to occur at once to every mind: the development of the gases from solid matter by the operation of the chemical affinities, and their subsequent condensation into the liquid form, has already been essayed as a source of power. In a word, the general state of physical science, at the present moment, the vigour, activity, and sagacity with which researches in it are prosecuted in every civilized country, the increasing consideration in which scientific men are held, and the personal honours and rewards which begin to be conferred upon them, all justify the expectation that we are on the eve of mechanical discoveries still greater than any which have yet appeared; and that the steam engine itself, with the gigantic powers conferred upon it by the immortal Watt, will dwindle into insignificance in comparison with the hidden powers of nature still to be revealed; and that the day will come when that machine, which is now extending the blessings of civilisation to the most remote skirts of the globe, will cease to have existence except in the page of history. CHAPTER XIX. PLAIN RULES FOR RAILWAY SPECULATORS. (142.) For some time after the completion of the Liverpool and Manchester railway, doubts were entertained of its ultimate success as a commercial speculation; and, even still, after several years' continuance, some persons are found, sceptical by temperament, who have not acquired full confidence in the permanency of its advantages. The possibility of sustaining a system of regular transport upon it, with the unheard of speed effected at the commencement of the undertaking, was, for a long period, questioned by a considerable portion even of the scientific world; and, after that possibility was established, by the regular performance of some years, the practicability of permanently profitable work, at that rate of speed, was still doubted by many, and altogether denied by some. The numerous difficulties to be encountered, and the enormous expense of locomotive power, have been fully admitted by the directors in their semi-annual reports. Persons interested in canals and other rival establishments, and others constitutionally doubtful of everything, attributed the dividends to the indirect proceedings of the managers, and asserted that when they appeared to be sharing their profit's, they, in reality, were sharing their capital. This delusion, however, could not long continue, and the payment of a steady semi-annual dividend of 4-1/2 per cent. since the opening of the railway, together with the commencement of a reserved fund of a considerable amount, with a premium of above 100 per cent. on the original shares, has brought conviction to understandings impenetrable to general reasoning; and the tide of opinion, which, for a time, had turned against railways, has now, by the usual reaction, set in so violently in their favour, that it becomes the duty of those who professionally devote themselves to such inquiries, to restrain and keep within moderate bounds the public ardour, rather than to stimulate it. The projects for the construction of great lines of internal communication which have been announced would require, if realized, a very large amount of capital. Considering that the estimated capital is invariably less than the amount actually required, we shall not, perhaps, overrate the extent of the projected investments if we estimate them at fifty millions. The magnitude of this amount has created alarm in the minds of some persons, lest a change of investment so extensive should produce a serious commercial shock. It should, however, be considered that, even if all the projected undertakings should be ultimately carried into execution, a long period must elapse, perhaps not less than fifteen or twenty years, before they can be all completed: the capital will be required, not suddenly, but by small instalments, at distant intervals of time. Even if it were true, therefore, that, to sustain their enterprises, an equivalent amount of capital must be withdrawn from other investments, the transfer would lake place by such slow degrees as to create no serious inconvenience. But, in fact, it is not probable that any transfer of capital whatever will be necessary. Trade and manufacturers are at the present moment in a highly flourishing condition; and the annual accumulation of capital in the country is so great, that the difficulty will probably be, not to find capital to meet investments, but to find suitable investments for the increasing capital. In Manchester alone, it is said that the annual increment on capital is no less than three millions. In fifteen years, therefore, this mart alone would be sufficient to supply all the funds necessary for the completion of all the proposed railroads, without withdrawing capital from any other investment. The facilities which these Joint Stock Companies offer for the investment of capital, even of the smallest amount, the temptations which the prospect of large profits hold out, and the low interest obtained on national stock of every description, have attracted a vast body of capitalists, small and great, who have subscribed to these undertakings with the real intention of investment. But, on the other hand, there is a very extensive body of speculators who engage in them upon a large scale, without the most distant intention, and, indeed, without the ability, of paying up the amount of their shares. The loss which the latter class of persons may sustain would, probably, excite little commiseration, were it not for the consequences which must result to the former, should a revolution take place, and the market be inundated with the shares of these gambling speculators, who buy only to sell again. Effects would be produced which must be ruinous to a large proportion of the _bonâ fide_ subscribers. It may, therefore, be attended with some advantage to persons who really intend to make permanent investments of this nature, to state, in succinct and intelligible terms, the principal circumstances on which the efficiency and economy of railroads depend, so as to enable them, in some measure, to form a probable conjecture of the prospective advantages which the various projects hold out. In doing this, we shall endeavour, as much as possible, to confine our statements to simple facts and results, which can neither be denied nor disputed, leaving, for the most part, the inferences to which they lead to be deduced from them by others. It may be premised, that persons proposing to engage in any railroad speculation should obtain _first_ a table of _gradients_; that is, an account of all the acclivities upon the line from terminus to terminus, stating how many feet in a mile each incline rises or falls, and its length. _Secondly_, it would also be advantageous to have a statement of the lengths of the radii of the different _curves_ as well as the lengths of the curves themselves. _Thirdly_, an account of the actual intercourse which has taken place, for a given time, upon the turnpike road connecting the proposed termini, stating the number of coaches licensed, and the average number of passengers they carry; also as near an account of the transport of merchandise as may be obtained. The latter, however, is of less moment. An approximate estimate may be made of the intercourse in passengers, by allowing for each coach, upon each trip, half its licensed complement of load. _Fourthly_, the water communication by canal or otherwise between the places; and the amount of tonnage transported by it. With the information thus obtained, the following succinct maxims will be found useful:-- I. No railroad can be profitably worked without a large intercourse of passengers. Goods, merchandise, agricultural produce, &c., ought to be regarded as of secondary importance. II. A probable estimate of the number of passengers to be expected upon a projected line of railroad may be made by increasing the average number of passengers for the last three years, by the common road, in a twofold proportion. The average number of passengers daily between Liverpool and Manchester, before the formation of the railway, was about 450; the present average number is above 1300. A short railroad of about five miles is constructed between Dublin and Kingstown: on which the average number of passengers daily between those places has increased in nearly the same proportion. III. Passengers can be profitably transported by canal, at a speed not exceeding nine miles an hour, exclusive of delays at locks, at the rate of one penny per head per mile. The average fares charged upon the Manchester railway are at the rate of 1-84/100_d._ per head per mile, the average speed being twenty miles an hour. To transport passengers at the rate of ten miles an hour on a railway, would cost very little less than the greater speed of twenty miles an hour, so that a railroad could not enter into competition on equal terms with a canal by equalising the speed. The canal between Kendal and Preston measures 57 miles: passengers are transported upon it between these places at the average speed of a mile in 6-1/2 minutes, or 9-1/4 miles an hour nearly, exclusive of delays at locks. The fare charged is at the average rate of a penny a mile. There are eight locks, rising 9 feet each, and a tunnel 400 yards long, through which the boat is tracked by hand; the tunnel requires 5 minutes, and the locks from 25 to 28 minutes, in descending, and 45 to 48 minutes in ascending. Similar boats are worked on the Forth and Clyde, and the Union canals in Scotland, and on the Paisley and Johnstone canal at nearly the same fares. IV. At the fare of 1-84/100_d._ per head per mile, the profit on the Manchester railroad is 100 per cent. on the disbursements for passengers. V. Goods can be profitably transported by canal at a lower tonnage than by railroads; the speed on the canal (for goods) being, however, but one-fifth of the speed on the railroad. VI. Goods are transported on the Liverpool and Manchester railroad at three-pence three farthings per ton per mile, with a profit of about 40 per cent. upon the disbursement, having the competition of a canal between its termini. VII. A long railroad can be worked with greater relative economy than a short one. VIII. Steam engines work with the greatest efficiency and economy, when the resistance they have to overcome is perfectly uniform and invariable. IX. The variation of resistance on railroads depends, first, on acclivities, secondly, on curves. By curves are meant the changes of direction of the road to the right or to the left. The direction of a railroad cannot be changed suddenly by an angle, but must be effected gradually by a curve. Supposing the curve to be (as it generally is) the arc of a circle, the radius of the curve is the distance of the centre of the circle from the curve. This radius is an important element in the estimate of the road. X. The more nearly a railroad approaches to an absolute level, and perfect straightness, the more profitably will it be worked. XI. The total amount of mechanical power necessary to transfer a given load from one extremity of a railroad to another is a matter of easy and exact calculation, when the gradients and curves are known; and the merits of different lines may be compared together in this respect: but it is not the only test of their efficiency which must be applied. XII. A railroad having gradients exceeding seventeen feet in a mile will require more mechanical power to work it than it would were it level; and the more of these excessive gradients there are upon it, and the more steep they are, the greater will be this disadvantage. XIII. Although a railroad having no gradients exceeding seventeen feet in a mile does not require more mechanical power than a level, yet the mechanical power which it requires will not be so advantageously expended, and, therefore, it will not be so economical. XIV. A railroad which has gradients above thirty feet in a mile will require such gradients to be worked by assistant locomotive engines, which will be attended with a waste of power, and an increase of expenditure, more or less, according to the number and length of such gradients. XV. A very long inclined plane cannot be worked by an assistant locomotive without a wasteful expense. Gradients exceeding seventeen feet per mile must, therefore, be short. XVI. Gradients exceeding fifty feet in a mile cannot be profitably worked except by stationary engines and ropes, an expedient attended with so many objections as to be scarcely compatible with a large intercourse of passengers. XVII. Steep gradients, provided they descend from the extremities of a line, are admissible provided they be short. It is evident that in this case the inclined planes will help at starting to put the trains in motion, at the time when, in general, there would be the greatest strain upon the moving power; and, in approaching the terminus, the momentum would be sufficient to carry the train to the top of the plane, if its length were not great, since it must, at all events, come to a stop at the extremity. XVIII. The effect of gradients in increasing the resistance during the ascent may be estimated by considering that a gradient of seventeen feet in a mile doubles the resistance of the level, thirty-four feet in a mile triples it, and eight and a half feet in a mile adds one half its amount, and so on. XIX. With the speed now attainable on railways, curves should be avoided with radii shorter than a mile. Expedients may diminish the resistance, but, through the negligence of engine drivers, they must always be attended with danger. Curves are not objectionable near the extremities of a line. XX. The worst position for a curve is the foot of an inclined plane, because of the velocity which the trains acquire in the descent, and the occasional impracticability of checking them. XXI. In proportion as the speed of locomotives is increased by the improvements they are likely to receive, the objections and dangers incident to curves will be increased. XXII. The difficulty which attends the use of long tunnels arises from the destruction of the vital air which is produced by the combustion in the furnaces of the engines. Tunnels on a level should, therefore, be from twenty-five to thirty feet high, and should be ventilated by shafts or other contrivances. XXIII. The transition from light to darkness, the sensation of humidity, and the change in summer from a warm atmosphere to a cold one, will always form an objection to long tunnels on lines of railroad intended for a large intercourse of passengers. XXIV. All the objections to a tunnel are aggravated when it happens to be upon an acclivity. The destruction of vital air in ascending it will be increased in exactly the same proportion as the moving power is increased. Thus, if it ascend 17 feet in a mile, the destruction of vital air will be twice as great as on a level; if it ascend 34 feet in a mile, it will be three times as great; 51 feet in a mile, four times as great, and so on. XXV. If by an overruling necessity a tunnel is constructed on an acclivity, its magnitude and means of ventilation should be greater than on a level, in the same proportion as the resistance produced by the acclivity is greater than the resistance upon a level. XXVI. Tunnels should be ventilated by shafts at intervals of not more than 200 yards. XXVII. While a train is passing through a tunnel, no beneficial ventilation can be obtained from shafts. The engine will leave behind it the impure air which it produces, and the passengers will be enveloped in it before it has time to ascend the shafts. Sufficient magnitude, however, may be given to the tunnel to prevent any injurious consequences from this cause. A disagreeable and inconvenient odour will be experienced. XXVIII. Tunnels on a level, the length of which do not exceed a third of a mile, will probably not be objectionable. Tunnels of equal length upon acclivities would be more objectionable. I may observe generally that we have as yet little or no experience of the effect of tunnels on lines of railroad worked by locomotive engines, where there is a large intercourse of passengers. On the Leicester and Swannington railroad, there is a tunnel of about a mile long, on a part of the road which is nearly level; it is ventilated by eight shafts, and I have frequently passed through it with a locomotive engine. Even when shut up in a close carriage the annoyance is very great, and such as would never be tolerated on a line of road having a large intercourse in passengers. This railroad is chiefly used to take coals from some collieries near Swannington, and there is no intercourse in passengers upon it, except of the labouring classes from the adjacent villages: the engines burn coal, and not coke; and they consequently produce smoke, which is more disagreeable than the gases which result from the combustion of coke. This tunnel also is of small calibre. On the Leeds and Selby railroad there is a tunnel, on a part which is nearly level, the length of which is 700 yards, width 22 feet, height 17. It is ventilated by three shafts of about 10 feet diameter and 60 feet high. There is an intercourse of passengers amounting to four hundred per day, upon this road, and, generally speaking, they do not object to go through the tunnel with a locomotive engine. The fuel is coke. (_l_) In order to show the present state of railroad transportation in the United States, and enable our readers to compare it with the opinions and facts adduced by Dr. Lardner, we take the latest accounts from the Charleston and Hamburgh Railroad. The engines drag a train of cars which carry a load of 130 tons, and perform the distance (240 miles) in three days, travelling only by day-light. With these loads they mount planes having inclinations of 37 feet per mile. The same engines are capable of carrying passengers at the rate of 40 miles per hour, and often perform 30, but their average speed is limited by regulation to 20 miles per hour. This railroad is remarkable for being the largest which has yet been constructed, and is besides an object of just pride, in as much as it was commenced at a time, when according to Dr. Lardner, the subject was but imperfectly understood even in Europe, and all its arrangements are due to native talent and skill, unassisted by previous discoveries in Europe.--A. E. INDEX. A. Atmospheric air, elastic force of, 23 Atmospheric pressure rendered available as a mechanic agent by Denis Papin, 48 Atmospheric engine, first conception of by Newcomen, 61. Description of, 63. Advantage of over that of Savery, 69 B. Barometer, the, 21 Barometer gauge, the, 123 Belidor, 133 Birmingham and London railroad, probable advantages to be derived from, 206 Black, Dr., his doctrine of latent heat, 76 Blasco de Garay, his contrivance to propel vessels, 42 Blinkensop, Mr., constructs a locomotive engine, 161 Boiler, methods for showing the level of water in the, 118. Its power and proportions, 297 Bolton, Matthew, his connexion with Watt, 88 ---- and Watt, Messrs., immense expenditure of, in bringing their engines into use, 91 Booth, Mr., his method of using tubes to conduct heated air through locomotive boilers, 176. His report to the directors of the Liverpool and Manchester railway on the apparent discrepancies of Messrs. Walker and Rastrick's estimate of locomotive power, 189 Braithwaite and Ericsson, Messrs., their "Novelty" described, 175 Branca, Giovanni, his machine for propelling a wheel by a blast of steam, 45 Brewster, Dr., 79 Brunton, Mr., his improved furnace described, 130 C. Canals, transport on, 208. Experiments with boats on, 209, Comparison of with railroads, 210 Cartwright, Rev. Mr., description of his improvements in the steam engine, 142 Cawley, John, 61 "Century of Inventions" by the Marquis of Worcester, 46 Chapman, Messrs., obtain a patent for working a locomotive by means of a chain, 162 Church, Dr., his steam carriage, 239 Cohesion, attraction of, 32 Condensation of solids, 28 Condensation by jet, accidental discovery of, 65 Cornwall, reports of duty of steam engines in, 303 Cotton, processes in the culture of, 18 Cylinder, its proportions, 300 D. D valve, description of the, 113 Damper, the, 126 Duty of a steam engine, 291 Duty, reports of, in Cornwall, 303 E. Eccentric; description of the, 111 Edelcrantz, the Chevalier, 127 F. Farey, Mr., his statement respecting the variations in the work of different steam engines, 133 Fluids, property of, 21 Fly-wheel, introduction of the, 104 Four-way cock, description of the, 115 Fuel, table of the consumption of, in different locomotives, 180 G. Governor, description of the, 105 Guericke, Otto, inventor of the air-pump, 70 Gurney, Mr., his steam carriage, 216 H. Hackworth, Mr., description of his engine, the "Sanspareil," 173 Hall, Mr. Samuel, his patent steam engine, 248. Its advantages for navigation, 249. Its successful application, 250 Hamilton, Duke of, 88 Hancock, Mr. Walter, his steam carriage, 235 Heat, phenomena of, 29 Hero of Alexandria, description of his machine, 41 Hopper, the, or apparatus for supplying the fire-place with coals, 131 Hornblower, Mr., his double-cylinder engine, 134 Horse power and steam power, comparison between, 202 Horse power of an engine, 291. Method of calculating it, 293 Howard, Mr. Thomas, his patent steam engine, 253. Its advantages in navigation, 256 Huskisson, Mr., 154 I. Inclined planes, their injurious effects on railroads, 194. Methods proposed to remedy these, 194 India, steam communication with, 271 K. Kendal and Preston canal, speed of boats on, 209 L. Leeds and Selby railroad, 317 Leicester and Swannington railroad, 317 Leupold, his "Theatrum Machinarum," 116. His engine described, 147 Liquids converted into vapour by the application of heat, 27. Difference of temperatures of, 35 Liverpool and Manchester railroad, effects of the introduction of steam transport on, 152. Want of experience in the construction of the engines, 154. Proceedings of the directors, 167. Premium offered by them for the best engine, 169. Experiments made on, 183. Passengers the chief source of profit to the proprietors, 204 Liverpool and London, supposed advantages from the connexion of these places by railroad, 206 Llangennech coal, its economy, 267 Locomotive engines, description of the "Rocket," 171. The "Sanspareil," 173. The "Novelty," 175. Mr. Booth's method of using tubes to conduct heated air through boilers, 177. Mr. Stephenson's method of subdividing the flue, 179. Amount of fuel consumed in, 180. Progressive improvement of, 180. Description of an improved form of engine, 181. Circumstances on which their efficiency depends, 183. Experiments with, on Liverpool and Manchester railroad, 184. Defects of, 186. Improvement in the method of tubing, 188. Proposed methods for working them on levels and inclined planes, 194. Extraordinary speed and power of, 204. Their introduction on turnpike roads, 213 Locomotive power, expense of, 188 Locomotive boilers, improved form of, 177 M. Machines, definition of, 19 Manufactures, motions required in, 19 Morgan, Mr., his patent paddle-wheel, 259 Morland, Sir Samuel, his application of steam to raise water, 47 Motion, a primary agent in the cultivation of cotton, 18. Variety of, 19 Murray, Mr., description of his suggested slide valve, 113 N. Newcomen, Thomas, and John Cawley, turn their attention to the practicability of applying steam engines to the drainage of mines, 61 Newcomen, Thomas, his construction of the atmospheric engine, 63 "Novelty," description of the, 175 O. Ogle, Mr., his steam carriage, 239 Oldham, Mr., his modification of the self-regulating furnace, 132 P. Paddle-wheel, the common one, 257. Mr. Morgan's patent one, 259 Papin, Denis, his contrivance, by which atmospheric pressure is rendered available as a mechanical agent, 48. Description of his steam engine, 71 Parallel motion, description of the, 95 Piston, its velocity, 302 Post-office steam packets, their speed, 268 Potter, Humphrey, his contrivance for working the valves, 67 Power of a steam engine, how estimated, 291 R. Railroads, first introduction of locomotives on, 151. Important effects to be expected from their adoption, 155. Imaginary difficulty respecting the progression of carriages on, 160. Various methods resorted to, to remedy this supposed difficulty, 161. One of these methods described, 162. Comparative estimate of the expenses of locomotive and stationary engines, 168. Difficulties arising from changes of level, 192. Their great extension, 206. Comparison of, with turnpike roads, 213. Inclined planes on, 194 Railway speculators, plain rules for, 307 Roads, their resistance to draft, 213. Compared with railroads, 213 Robinson, Dr., 73 Roebuck, Dr., assistance rendered by him to Watt, 87. His embarrassments, 88 "Rocket," description of the, 171 S. Savery, Thomas, obtains a patent for an engine to raise water, 49. His discovery of the principle of condensation, 49. Constructs the first engine brought into operation, 50. Description of, 51. Inefficiency of, 57. Great consumption of fuel necessary in his engines, 60. Different purposes to which he proposed to apply the steam engine, 61. Limited power of his engine, 69 "Sanspareil", description of the, 173 Smeaton turns his attention to the details of the atmospheric engines, 73 Solids converted into liquids by the application of heat, 27 Solomon De Caus, description of the apparatus of, 43 Somerset, Edward, Marquis of Worcester, invention of the steam engine ascribed to him, 45. Description of his contrivance, 45. Similar to Savery's, 46. His "Century of Inventions," 46 Steam carriages, Mr. Gurney's, 216. Mr. Hancock's, 235. Mr. Ogle's, 238. Dr. Church's, 239 Steam, its properties described, 30. Its mechanical power in proportion to the water evaporated, 277. Its volume, 279. Its quantity of heat, 279. Its power in respect of fuel, 280. Its expansive action, how advantageous, 280. Combination of expansion with condensation, 285. High-pressure, its expansive action, 288. Examples illustrative of its mechanical force, 305 Steam engine, first mover in, 19. Physical effects connected with, 20. Claims to the invention of, 38. Efficacy of, as a mechanical agent, 39. First brought into operation by Savery, 50. Its inefficiency, 58. First proposed to be applied to the drainage of mines, 61. Accidental discovery of condensation by jet, 65. Further improvements by Humphrey Potter and Beighton, 67, 68. Description of Papin's engine, 71. First experiments of Watt and subsequent improvements, 73. Dr. Black's theory of latent heat, 76. Watt's method of condensation, 76. Further improvements of Watt, 77. Description of Watt's single-acting engine, 80. The cold water pump, 86. The hot water pump, 86. Erection of a specimen engine at Soho, and gradual demand for them, 89. The single-acting engine inapplicable to manufactures, 91. The double-acting engine, 92. Invention of the parallel motion, 95. Introduction of the rotatory motion, 100. The fly-wheel, 104. The governor, 105. The throttle valve, 105. The eccentric, 111. The D valve, 113. The four-way cock, 115. Methods for ascertaining the level of water in the boiler, 118. The engine made to feed its own boiler, 120. Waste of water prevented, 121. The steam gauge, 122. Barometer gauge, 123. The damper, 125. Methods proposed for preventing the waste of fuel, 128. Mr. Brunton's furnace described, 130. Mr. Oldham's modification of the self-regulating furnace, 132. Improvements by Hornblower and Woolf, 134. Description of the improvements of Mr. Cartwright, 142. High-pressure engines, 145. Leupold's engine described, 147. Construction of the first high-pressure engine by Messrs. Trevithick and Vivian, 148. First application of the steam engine to propel carriages on railroads, 151. How applied to navigation, 242. Marine engine; its form and arrangement, 243. Mr. Howard's patent engine described, 253. Mr. Hall's engine described, 248 Steam gauge, the, 122 Steam navigation, incredulity which existed respecting, 159. The limit of its present powers, 264 Steam vessels, their average speed, 265. Their average consumption of fuel, 265. Proportion of their power to their tonnage, 266. Speed of post-office packets, 268. Iron steam vessels, 269. American vessel called the "Cigar Boat," its great speed, 270 Stephenson's, Mr., description of an engine constructed by him, 164. Premium awarded to this engine by the Liverpool and Manchester Railway Directors, 170. His method of dividing the flues, 179 Stephenson and Lock, Messrs., appointed by the Directors of the Liverpool and Manchester Railroad to make reports on the merits of various railroads, 167 Sun and planet wheels, 101 T. Thermometer, description of, 24 Throttle valve, use of, 104 Traction, force of, on a railroad, 192 Tredgold,70 Trevithick and Vivian, Messrs., construct the first high-pressure engine used in this country, 148 U. United States, steam communication with, 274 V. Vacuum, production of, by experiment, 37 Vapour, elastic, force of, 35 Valves, Watt's method of working the, 109 W. Walker and Rastrick, Messrs., apparent discrepancy of their estimated expense of locomotive power, 189 Washborough takes out a patent for Watt's invention of the rotatory motion, 100 Water, sea, injurious to marine boilers, 245. How remedied by blowing out, 246 Watt, James, important discoveries of, 39. His acquaintance with Dr. Robinson and first experiments on the steam engine, 73. His subsequent improvements, 75. His method of condensation, 76. His first introduction of the air-pump into the steam engine, 77. Further improvements, 78. His difficulties, 78. Description of his single-acting engine, 80. His introduction to Dr. Roebuck, 88. Erects his first engine on the estate of the Duke of Hamilton, 88. After further improvements, obtains a patent for this engine, in conjunction with Roebuck, 88. His difficulties owing to Dr. Roebuck's failure, and subsequent connexion with Bolton, 88. Obtains an extension of his patent, 89. Ingenious invention of, to determine the rate of remuneration he should receive, 89. His invention of the parallel motion, 95. His method for producing a rotatory motion anticipated by Washborough, who takes out a patent for it, 101. His contrivance of the governor, 104. His method of working the valves, 109. His suggestion of the D valve, 113 Wood, Mr. Nicholas, 168 Woolf, Mr., his improvements in the steam engine, 134. Obtains a patent for the double-cylinder engine, 137 * * * * * JUST PUBLISHED, IN ONE VOLUME, 8VO. MATHEMATICS FOR PRACTICAL MEN; BEING A COMMON-PLACE BOOK OF PRINCIPLES, THEOREMS, RULES AND TABLES, IN VARIOUS DEPARTMENTS OF PURE AND MIXED MATHEMATICS, With their applications; especially to the pursuits of Surveyors, Architects, Mechanics, and Civil Engineers. With numerous engravings. BY OLINTHUS GREGORY, LL. D., F. R. A. S. "Only let men awake, and fix their eyes, one while on the nature of things, another while on the application of them to the use and service of mankind."--_Lord Bacon._ SECOND EDITION, CORRECTED AND IMPROVED. _Extract of a Letter from_ WALTER R. JOHNSON, _Professor of Mechanics and Natural Philosophy in the Franklin Institute_. "This treatise is intended and admirably calculated to supply the deficiency in the means of mathematical instruction to those who have neither time nor inclination to peruse numerous abstract treatises in the same departments. It has, besides the claims of a good elementary manual, the merit of embracing several of the most interesting and important departments of Mechanics, applying to these the rules and principles embraced in the earlier sections of the work. "Questions in Statics, Dynamics, Hydrostatics, Hydrodynamics, &c., are treated with a clearness and precision which must increase the powers of the student over his own intellectual resources by the methodical habits which a perusal of such works cannot fail to impart. "With respect to Engineering, and the various incidents of that important profession, much valuable matter is contained, in this volume; and the results of many laborious series of experiments are presented with conciseness and accuracy." _Letter from_ ALBERT B. DOD, _Professor of Mathematics in the College of New Jersey_. "MESSRS. CAREY & HART, "Gentlemen,--I am glad to learn that you have published an American edition of Dr. Gregory's 'Mathematics for Practical Men.' I have for some time been acquainted with this work, and I esteem it highly. It contains the best digest, within my knowledge, of such scientific facts and principles, involved in the subjects of which it treats, as are susceptible of direct practical application. While it avoids such details of investigation and processes of mathematical reasoning as would render it unintelligible to the general reader, it equally avoids the sacrifice of precision in its statement of scientific results, which is too often made in popular treatises upon the Mathematics and Natural Philosophy. The author has succeeded to a remarkable degree in collecting such truths as will be found generally useful, and in presenting them, in an available form, to the practical mechanic. To such, the work cannot be too strongly recommended; and to the student, too, it will often be found highly useful as a book of reference. "With much respect, "Your obedient servant, "ALBERT B. DOD, "Professor of Mathematics in the College of New Jersey. "_Princeton, Nov. 11, 1834._" _Extract of a Letter from_ EDWARD H. COURTENAY, _Professor of Mathematics in the University of Pennsylvania_. "The design of the author--that of furnishing a valuable collection of rules and theorems for the use of such as are unable, from the want of time and previous preparation, to investigate mathematical principles--appears to have been very successfully attained in the present volume. The information which it affords in various branches of the pure and mixed Mathematics embraces a great variety of subjects, is arranged conveniently, and is in general conveyed in accurate and concise terms. To THE ENGINEER, THE ARCHITECT, THE MECHANIC--indeed to all for whom _results_ are chiefly necessary--the work will doubtless form a very valuable acquisition." _Letter from_ CHARLES DAVIES, _Professor of Mathematics in the Military Academy, West Point_. "MILITARY ACADEMY, West Point, May 14th, 1835. "_To Messrs. E. L. Carey & A. Hart_,-- "The 'Mathematics for Practical Men,' by Dr. Gregory, which you have recently published, is a work that cannot fail to be extensively useful. "It embraces, within a comparatively small compass, all the rules and formulas for mathematical computation, and all the practical results of mechanical philosophy. It is, indeed, a collection of the useful results of science and the interesting facts which have been developed by experience. It may safely be said, that no work, of the same extent, contains so much information, with the rules for applying it to practical purposes. "I have the honour to be, "With great respect, "Your obedient servant, "CHARLES DAVIES, "_Professor of Mathematics_." _Extract from a Letter from_ J. A. MILLER, _Professor of Mathematics in Mount St. Mary's College, Emmettsburg, Md._ "Since the London edition of Gregory's Mathematics for Practical Men appeared in this country, it has been much used in this institution. The accuracy of its definitions, its beautiful systematic arrangement, the many simplified and facilitated methods which it proposes, and its highly practical character, must recommend it strongly to public patronage, as one of the very best works which have lately issued from the press. I have examined your edition of this valuable work sufficiently to say with confidence that it is very accurately printed." * * * * * [Transcriber's note: Only obvious printer's errors have been corrected (e.g.: 3 s instead of 2, etc.). The author's spelling has been maintained and inconsistencies have not been standardised. The advertisement page has been move from the front to the end of the book. Other corrections made: --Page x: "the wealth of rations" has been replaced by "the wealth of nations". --Page 17: "Pressure of Rarified Air." has been replaced by "Pressure of Rarefied Air." --Page 98: "This beautiful contrivance, which is incontestibly" has been replaced by "This beautiful contrivance, which is incontestably". --Page 100: "the working beam no longer used" has been replaced by "the working beam is no longer used". --Page 223: "is attended with peliar difficulty" has been replaced by "is attended with peculiar difficulty". --Page 271: "The projecter is now employed in" has been replaced by "The projector is now employed in".] 
10998	----	generously provided by the Digital & Multimedia Center, Michigan State University Libraries. A CATECHISM OF THE STEAM ENGINE IN ITS VARIOUS APPLICATIONS TO MINES, MILLS, STEAM NAVIGATION, RAILWAYS, AND AGRICULTURE. WITH PRACTICAL INSTRUCTIONS FOR THE MANUFACTURE AND MANAGEMENT OF ENGINES OF EVERY CLASS. BY JOHN BOURNE, C.E. _NEW AND REVISED EDITION._ [Transcriber's Note: Inconsistencies in chapter headings and numbering of paragraphs and illustrations have been retained in this edition.] PREFACE TO THE FOURTH EDITION. For some years past a new edition of this work has been called for, but I was unwilling to allow a new edition to go forth with all the original faults of the work upon its head, and I have been too much engaged in the practical construction of steam ships and steam engines to find time for the thorough revision which I knew the work required. At length, however, I have sufficiently disengaged myself from these onerous pursuits to accomplish this necessary revision; and I now offer the work to the public, with the confidence that it will be found better deserving of the favorable acceptation and high praise it has already received. There are very few errors, either of fact or of inference, in the early editions, which I have had to correct; but there are many omissions which I have had to supply, and faults of arrangement and classification which I have had to rectify. I have also had to bring the information, which the work professes to afford, up to the present time, so as to comprehend the latest improvements. For the sake of greater distinctness the work is now divided into chapters. Some of these chapters are altogether new, and the rest have received such extensive additions and improvements as to make the book almost a new one. One purpose of my emendations has been to render my remarks intelligible to a tyro, as well as instructive to an advanced student. With this view, I have devoted the first chapter to a popular description of the Steam Engine--which all may understand who can understand anything--and in the subsequent gradations of progress I have been careful to set no object before the reader for the first time, of which the nature and functions are not simultaneously explained. The design I have proposed to myself, in the composition of this work, is to take a young lad who knows nothing of steam engines, and to lead him by easy advances up to the highest point of information I have myself attained; and it has been a pleasing duty to me to smooth for others the path which I myself found so rugged, and to impart, for the general good of mankind, the secrets which others have guarded with so much jealousy. I believe I am the first author who has communicated that practical information respecting the steam engine, which persons proposing to follow the business of an engineer desire to possess. My business has, therefore, been the rough business of a pioneer; and while hewing a road through the trackless forest, along which all might hereafter travel with ease, I had no time to attend to those minute graces of composition and petty perfection of arrangement and collocation, which are the attribute of the academic grove, or the literary parterre. I am, nevertheless, not insensible to the advantages of method and clear arrangement in any work professing to instruct mankind in the principles and practice of any art; and many of the changes introduced into the present edition of this work are designed to render it less exceptionable in this respect. The woodcuts now introduced into the work for the first time will, I believe, much increase its interest and utility; and upon the whole I am content to dismiss it into circulation, in the belief that those who peruse it attentively will obtain a more rapid and more practical acquaintance with the steam engine in its various applications, than they would be likely otherwise to acquire. I have only to add that I have prepared a sequel to the present work, in the shape of a Hand-Book of the Steam Engine, containing the whole of the rules given in the present work, illustrated by examples worked out at length, and also containing such useful tables and other data, as the engineer requires to refer to constantly in the course of his practice. This work may be bound up with the "Catechism," if desired, to which it is in fact a Key. I shall thankfully receive from engineers, either abroad or at home, accounts of any engines or other machinery, with which they may become familiar in their several localities; and I shall be happy, in my turn, to answer any inquiries on engineering subjects which fall within the compass of my information. If young engineers meet with any difficulty in their studies, I shall be happy to resolve it if I can; and they may communicate with me upon any such point without hesitation, in whatever quarter of the world they may happen to be. JOHN BOURNE. 9 BILLITER STREET, LONDON, _March 1st, 1856_. PREFACE TO THE FIFTH EDITION. The last edition of the present work, consisting of 3,500 copies, having been all sold off in about ten months, I now issue another edition, the demand for the work being still unabated. It affords, certainly, some presumption that a work in some measure supplies an ascertained want, when, though addressing only a limited circle--discoursing only of technical questions, and without any accident to stimulate it into notoriety,--it attains so large a circulation as the present work has reached. Besides being reprinted in America, it has been translated into German, French, Dutch, and I believe, into some other languages, so that there is, perhaps, not too much vanity in the inference that it has been found serviceable to those perusing it. I can with truth say, that the hope of rendering some service to mankind, in my day and generation, has been my chief inducement in writing it, and if this end is fulfilled, I have nothing further to desire. I regret that circumstances have prevented me from yet issuing the "Hand-Book" which I have had for some time in preparation, and to which, in my Preface of the last year, I referred. I hope to have sufficient leisure shortly, to give that and some other of my literary designs the necessary attention. Whatever may have been the other impediments to a more prolific authorship, certainly one of them has not been the coldness of the approbation with which my efforts have been received, since my past performances seem to me to have met with an appreciation far exceeding their deserts. JOHN BOURNE. _February 2d, 1857_. PUBLISHERS' NOTICE. In offering to the American public a reprint of a work on the Steam Engine so deservedly successful, and so long considered standard, the publishers have not thought it necessary that it should be an exact copy of the English edition; there were some details in which they thought it could be improved, and better adapted to the use of American engineers. On this account, the size of the page has been increased to a full 12mo, to admit of larger illustrations, which in the English edition are often on too small a scale; and some of the illustrations themselves have been supplied by others equally applicable, more recent, and to us more familiar examples. The first part of Chapter XI, devoted in the English edition to English portable and fixed agricultural engines, in this edition gives place entirely to illustrations from American practice, of steam engines as applied to different purposes, and of appliances and machines necessary to them. But with the exception of some of the illustrations and the description of them, and the correction of a few typographical errors, this edition is a faithful transcript of the latest English edition. CONTENTS. Classification of Engines. Nature and uses of a Vacuum. Velocity of falling Bodies and Momentum of moving Bodies. Central Forces. Centres of Gravity, Gyration, and Oscillation. The Pendulum and Governor. The Mechanical Powers. Friction. Strength of materials and Strains subsisting in Machines. CHAP. I.--GENERAL DESCRIPTION OF THE STEAM ENGINE. The Boiler. The Engine. The Marine Engine. Screw Engines. The Locomotive Engine. CHAP. II.--HEAT, COMBUSTION, AND STEAM. Heat. Combustion. Steam. CHAP. III.--EXPANSION OF STEAM AND ACTION OF THE VALVES. CHAP. IV.--MODES OF ESTIMATING THE POWER AND PERFORMANCE OF ENGINES AND BOILERS. Horses Power. Duty of Engines and Boilers. The Indicator. Dynamometer, Gauges, and Cataract. CHAP. V.--PROPORTIONS OF BOILERS. Heating and Fire Grate Surface. Calorimeter and Vent. Evaporative Power of Boilers. Modern Marine and Locomotive Boilers. The Blast in Locomotives. Boiler Chimneys. Steam Room and Priming. Strength of Boilers. Boiler Explosions. CHAP. VI.--PROPORTIONS OF ENGINES. Steam Passages. Air Pump, Condenser, and Hot and Cold Water Pumps. Fly Wheel. Strengths of Land Engines. Strengths of Marine and Locomotive Engines. CHAP. VII.--CONSTRUCTIVE DETAILS OF BOILERS. Land and Marine Boilers. Incrustation and Corrosion of Boilers. Locomotive Boilers. CHAP. VIII.--CONSTRUCTIVE DETAILS OF ENGINES. Pumping Engines. Various forms of Marine Engines. Cylinders, Pistons, and Valves. Air Pump and Condenser. Pumps, Cocks, and Pipes. Details of the Screw and Screw Shaft. Details of the Paddles and Paddle Shaft. The Locomotive Engine. CHAP. IX.--STEAM NAVIGATION. Resistance of Vessels in Water. Experiments on the Resistance of Vessels. Influence of the size of Vessels upon their Speed. Structure and Operation of Paddle Wheels. Configuration and Action of the Screw. Comparative Advantages of Paddle and Screw Vessels. Comparative Advantages of different kinds of Screws. Proportions of Screws. Screw Vessels with full and auxiliary Power. Screw and Paddles combined. CHAP. X.--EXAMPLES OF ENGINES OF RECENT CONSTRUCTION. Oscillating Paddle Engines. Direct acting Screw Engine. Locomotive Engine. CHAP. XI.--ON VARIOUS FORMS AND APPLICATIONS OF THE STEAM ENGINE. Governor. Donkey Pumps. Portable Steam Engines. Stationary Engines. Steam Fire Engines. Steam Excavator. CHAP. XII.--MANUFACTURE AND MANAGEMENT OF STEAM ENGINES. Construction of Engines. Erection of Engines. Management of Marine Boilers. Management of Marine Engines. Management of Locomotives. MECHANICAL PRINCIPLES OF THE STEAM ENGINE. CLASSIFICATION OF ENGINES. 1. _Q._--What is meant by a vacuum? _A._--A vacuum means an empty space; a space in which there is neither water nor air, nor anything else that we know of. 2. _Q._--Wherein does a high pressure differ from a low pressure engine? _A._--In a high pressure engine the steam, after having pushed the piston to the end of the stroke, escapes into the atmosphere, and the impelling force is therefore that due to the difference between the pressure of the steam and the pressure of the atmosphere. In the condensing engine the steam, after having pressed the piston to the end of the stroke, passes into the condenser, in which a vacuum is maintained, and the impelling force is that due to the difference between the pressure of the steam above the piston, and the pressure of the vacuum beneath it, which is nothing; or, in other words, you have then the whole pressure of the steam urging the piston, consisting of the pressure shown by the safety-valve on the boiler, and the pressure of the atmosphere besides. 3. _Q._--In what way would you class the various kinds of condensing engines? _A._--Into single acting, rotative, and rotatory engines. Single acting engines are engines without a crank, such as are used for pumping water. Rotative engines are engines provided with a crank, by means of which a rotative motion is produced; and in this important class stand marine and mill engines, and all engines, indeed, in which the rectilinear motion of the piston is changed into a circular motion. In rotatory engines the steam acts at once in the production of circular motion, either upon a revolving piston or otherwise, but without the use of any intermediate mechanism, such as the crank, for deriving a circular from a rectilinear motion. Rotatory engines have not hitherto been very successful, so that only the single acting or pumping engine, and the double acting or rotative engine can be said to be in actual use. For some purposes, such, for example, as forcing air into furnaces for smelting iron, double acting engines are employed, which are nevertheless unfurnished with a crank; but engines of this kind are not sufficiently numerous to justify their classification as a distinct species, and, in general, those engines may be considered to be single acting, by which no rotatory motion is imparted. 4. _Q._--Is not the circular motion derived from a cylinder engine very irregular, in consequence of the unequal leverage of the crank at the different parts of its revolution? _A._--No; rotative engines are generally provided with a fly-wheel to correct such irregularities by its momentum; but where two engines with their respective cranks set at right angles are employed, the irregularity of one engine corrects that of the other with sufficient exactitude for many purposes. In the case of marine and locomotive engines, a fly-wheel is not employed; but for cotton spinning, and other purposes requiring great regularity of motion, its use with common engines is indispensable, though it is not impossible to supersede the necessity by new contrivances. 5. _Q._--You implied that there is some other difference between single acting and double acting engines, than that which lies in the use or exclusion of the crank? _A._--Yes; single acting engines act only in one way by the force of the steam, and are returned by a counter-weight; whereas double acting engines are urged by the steam in both directions. Engines, as I have already said, are sometimes made double acting, though unprovided with a crank; and there would be no difficulty in so arranging the valves of all ordinary pumping engines, as to admit of this action; for the pumps might be contrived to raise water both by the upward and downward stroke, as indeed in some mines is already done. But engines without a crank are almost always made single acting, perhaps from the effect of custom, as much as from any other reason, and are usually spoken of as such, though it is necessary to know that there are some deviations from the usual practice. NATURE AND USES OF A VACUUM. 6. _Q._--The pressure of a vacuum you have stated is nothing; but how can the pressure of a vacuum be said to be nothing, when a vacuum occasions a pressure of 15 lbs. on the square inch? _A._--Because it is not the vacuum which exerts this pressure, but the atmosphere, which, like a head of water, presses on everything immerged beneath it. A head of water, however, would not press down a piston, if the water were admitted on both of its sides; for an equilibrium would then be established, just as in the case of a balance which retains its equilibrium when an equal weight is added to each scale; but take the weight out of one scale, or empty the water from one side of the piston, and motion or pressure is produced; and in like manner pressure is produced on a piston by admitting steam or air upon the one side, and withdrawing the steam or air from the other side. It is not, therefore, to a vacuum, but rather to the existence of an unbalanced plenum, that the pressure made manifest by exhaustion is due, and it is obvious therefore that a vacuum of itself would not work an engine. 7. _Q._--How is the vacuum maintained in a condensing engine? _A._--The steam, after having performed its office in the cylinder, is permitted to pass into a vessel called the condenser, where a shower of cold water is discharged upon it. The steam is condensed by the cold water, and falls in the form of hot water to the bottom of the condenser. The water, which would else be accumulated in the condenser, is continually being pumped out by a pump worked by the engine. This pump is called the air pump, because it also discharges any air which may have entered with the water. 8. _Q._--If a vacuum be an empty space, and there be water in the condenser, how can there be a vacuum there? _A._--There is a vacuum above the water, the water being only like so much iron or lead lying at the bottom. 9. _Q._--Is the vacuum in the condenser a perfect vacuum? _A._--Not quite perfect; for the cold water entering for the purpose of condensation is heated by the steam, and emits a vapor of a tension represented by about three inches of mercury; that is, when the common barometer stands at 30 inches, a barometer with the space above the mercury communicating with the condenser, will stand at about 27 inches. 10. _Q._--Is this imperfection of the vacuum wholly attributable to the vapor in the condenser? _A._--No; it is partly attributable to the presence of a small quantity of air which enters with the water, and which would accumulate until it destroyed the vacuum altogether but for the action of the air pump, which expels it with the water, as already explained. All common water contains a certain quantity of air in solution, and this air recovers its elasticity when the pressure of the atmosphere is taken off, just as the gas in soda water flies up so soon as the cork of the bottle is withdrawn. 11. _Q._--Is a barometer sometimes applied to the condensers of steam engines? _A._--Yes; and it is called the vacuum gauge, because it shows the degree of perfection the vacuum has attained. Another gauge, called the steam gauge, is applied to the boiler, which indicates the pressure of the steam by the height to which the steam forces mercury up a tube. Gauges are also applied to the boiler to indicate the height of the water within it so that it may not be burned out by the water becoming accidentally too low. In some cases a succession of cocks placed a short distance above one another are employed for this purpose, and in other cases a glass tube is placed perpendicularly in the front of the boiler and communicating at each end with its interior. The water rises in this tube to the same height as in the boiler itself, and thus shows the actual water level. In most of the modern boilers both of these contrivances are adopted. 12. _Q._--Can a condensing engine be worked with a pressure less than that of the atmosphere? _A._--Yes, if once it be started; but it will be a difficult thing to start an engine, if the pressure of the steam be not greater than that of the atmosphere. Before an engine can be started, it has to be blown through with steam to displace the air within it, and this cannot be effectually done if the pressure of the steam be very low. After the engine is started, however, the pressure in the boiler may be lowered, if the engine be lightly loaded, until there is a partial vacuum in the boiler. Such a practice, however, is not to be commended, as the gauge cocks become useless when there is a partial vacuum in the boiler; inasmuch as, when they are opened, the water will not rush out, but air will rush in. It is impossible, also, under such circumstances, to blow out any of the sediment collected within the boiler, which, in the case of the boilers of steam vessels, requires to be done every two hours or oftener. This is accomplished by opening a large cock which permits some of the supersalted water to be forced overboard by the pressure of the steam. In some cases, in which the boiler applied to an engine is of inadequate size, the pressure within the boiler will fall spontaneously to a point considerably beneath the pressure of the atmosphere; but it is preferable, in such cases, partially to close the throttle valve in the steam pipe, whereby the issue of steam to the engine is diminished; and the pressure in the boiler is thus maintained, while the cylinder receives its former supply. 13. _Q._--If a hole be opened into a condenser of a steam engine, will air rush into it? _A._--If the hole communicates with the atmosphere, the air will be drawn in. 14. _Q._--With what Velocity does air rush into a vacuum? _A._--With the velocity which a body would acquire by falling from the height of a homogeneous atmosphere, which is an atmosphere of the same density throughout as at the earth's surface; and although such an atmosphere does not exist in nature, its existence is supposed, in order to facilitate the computation. It is well known that the velocity with which water issues from a cistern is the same that would be acquired by a body falling from the level of the head to the level of the issuing point; which indeed is an obvious law, since every particle of water descends and issues by virtue of its gravity, and is in its descent subject to the ordinary laws of falling bodies. Air rushing into a vacuum is only another example of the same general principle: the velocity of each particle will be that due to the height of the column of air which would produce the pressure sustained; and the weight of air being known, as well as the pressure it exerts on the earth's surface, it becomes easy to tell what height a column of air, an inch square, and of the atmospheric density, would require to be, to weigh 15 lbs. The height would be 27,818 feet, and the velocity which the fall of a body from such a height produces would be 1,338 feet per second. VELOCITY OF FALLING BODIES AND MOMENTUM OF MOVING BODIES. 15. _Q._--How do you determine the velocity of falling bodies of different kinds? _A._--All bodies fall with the same velocity, when there is no resistance from the atmosphere, as is shown by the experiment of letting fall, from the top of a tall exhausted receiver, a feather and a guinea, which reach the bottom at the same time. The velocity of falling bodies is one that is accelerated uniformly, according to a known law. When the height from which a body falls is given, the velocity acquired at the end of the descent can be easily computed. It has been found by experiment that the square root of the height in feet multiplied by 8.021 will give the velocity. 16. _Q._--But the velocity in what terms? _A._--In feet per second. The distance through which a body falls by gravity in one second is 16-1/12 feet; in two seconds, 64-4/12 feet; in three seconds, 144-9/12 feet; in four seconds, 257-4/12 feet, and so on. If the number of feet fallen through in one second be taken as unity, then the relation of the times to the spaces will be as follows:-- Number of seconds | 1| 2| 3| 4| 5| 6| Units of space passed through | 1| 4| 9|16|25|36| &c. so that it appears that the spaces passed through by a falling body are as the squares of the times of falling. 17. _Q._--Is not the urging force which causes bodies to fall the force of gravity? _A._--Yes; the force of gravity or the attraction of the earth. 18. _Q._--And is not that a uniform force, or a force acting with a uniform pressure? _A._--It is. 19. _Q._--Therefore during the first second of falling as much impelling power will be given by the force of gravity as during every succeeding second? _A._--Undoubtedly. 20. _Q._--How comes it, then, that while the body falls 64-4/12 feet in two seconds, it falls only 16-1/12 feet in one second; or why, since it falls only 16-1/12 feet in one second, should it fall more than twice 16-1/12 feet in two? _A._--Because 16-1/12 feet is the average and not the maximum velocity during the first second. The velocity acquired _at the end_ of the 1st second is not 16-1/12, but 32-1/6 feet per second, and at the end of the 2d second a velocity of 32-1/6 feet has to be added; so that the total velocity at the end of the 2d second becomes 64-2/6 feet; at the end of the 3d, the velocity becomes 96-3/6 feet, at the end of the 4th, 128-4/6 feet, and so on. These numbers proceed in the progression 1, 2, 3, 4, &c., so that it appears that the velocities acquired by a falling body at different points, are simply as the times of falling. But if the velocities be as the times, and the total space passed through be as the squares of the times, then the total space passed through must be as the squares of the velocity; and as the _vis viva_ or mechanical power inherent in a falling body, of any given weight, is measurable by the height through which it descends, it follows that the _vis viva_ is proportionate to the square of the velocity. Of two balls therefore, of equal weight, but one moving twice as fast as the other, the faster ball has four times the energy or mechanical force accumulated in it that the slower ball has. If the speed of a fly-wheel be doubled, it has four times the _vis viva_ it possessed before--_vis viva_ being measurable by a reference to the height through which a body must have fallen, to acquire the velocity given. 21. _Q._--By what considerations is the _vis viva_ or mechanical energy proper for the fly-wheel of an engine determined? _A._--By a reference to the power produced every half-stroke of the engine, joined to the consideration of what relation the energy of the fly-wheel rim must have thereto, to keep the irregularities of motion within the limits which are admissible. It is found in practice, that when the power resident in the fly-wheel rim, when the engine moves at its average speed, is from two and a half to four times greater than the power generated by the engine in one half-stroke--the variation, depending on the energy inherent in the machinery the engine has to drive and the equability of motion required--the engine will work with sufficient regularity for most ordinary purposes, but where great equability of motion is required, it will be advisable to make the power resident in the fly-wheel equal to six times the power generated by the engine in one half-stroke. 22. _Q._---Can you give a practical rule for determining the proper quantity of cast iron for the rim of a fly-wheel in ordinary land engines? _A._--One rule frequently adopted is as follows:--Multiply the mean diameter of the rim by the number of its revolutions per minute, and square the product for a divisor; divide the number of actual horse power of the engine by the number of strokes the piston makes per minute, multiply the quotient by the constant number 2,760,000, and divide the product by the divisor found as above; the quotient is the requisite quantity of cast iron in cubic feet to form the fly-wheel rim. 23. _Q._--What is Boulton and Watt's rule for finding the dimensions of the fly-wheel? _A._--Boulton and Watt's rule for finding the dimensions of the fly-wheel is as follows:--Multiply 44,000 times the length of the stroke in feet by the square of the diameter of the cylinder in inches, and divide the product by the square of the number of revolutions per minute multiplied by the cube of the diameter of the fly-wheel in feet. The resulting number will be the sectional area of the rim of the fly-wheel in square inches. CENTRAL FORCES. 24. _Q._--What do you understand by centrifugal and centripetal forces? _A._--By centrifugal force, I understand the force with which a revolving body tends to fly from the centre; and by centripetal force, I understand any force which draws it to the centre, or counteracts the centrifugal tendency. In the conical pendulum, or steam engine governor, which consists of two metal balls suspended on rods hung from the end of a vertical revolving shaft, the centrifugal force is manifested by the divergence of the balls, when the shaft is put into revolution; and the centripetal force, which in this instance is gravity, predominates so soon as the velocity is arrested; for the arms then collapse and hang by the side of the shaft. 25. _Q._--What measures are there of the centrifugal force of bodies revolving in a circle? _A._--The centrifugal force of bodies revolving in a circle increases as the diameter of the circle, if the number of revolutions remain the same. If there be two fly-wheels of the same weight, and making the same number of revolutions per minute, but the diameter of one be double that of the other, the larger will have double the amount of centrifugal force. The centrifugal force of the _same wheel_, however, increases as the square of the velocity; so that if the velocity of a fly-wheel be doubled, it will have four times the amount of centrifugal force. 26. _Q._--Can you give a rule for determining the centrifugal force of a body of a given weight moving with a given velocity in a circle of a given diameter? _A._--Yes. If the velocity in feet per second be divided by 4.01, the square of the quotient will be four times the height in feet from which a body must have fallen to have acquired that velocity. Divide this quadruple height by the diameter of the circle, and the quotient is the centrifugal force in terms of the weight of the body, so that, multiplying the quotient by the actual weight of the body, we have the centrifugal force in pounds or tons. Another rule is to multiply the square of the number of revolutions per minute by the diameter of the circle in feet, and to divide the product by 5,870. The quotient is the centrifugal force in terms of the weight of the body. 27. _Q._--How do you find the velocity of the body when its centrifugal force and the diameter of the circle in which it moves are given? _A._--Multiply the centrifugal force in terms of the weight of the body by the diameter of the circle in feet, and multiply the square root of the product by 4.01; the result will be the velocity of the body in feet per second. 28. _Q._--Will you illustrate this by finding the velocity at which the cast iron rim of a fly-wheel 10 feet in diameter would burst asunder by its centrifugal force? _A._--If we take the tensile strength of cast iron at 15,000 lbs. per square inch, a fly-wheel rim of one square inch of sectional area would sustain 30,000 lbs. If we suppose one half of the rim to be so fixed to the shaft as to be incapable of detachment, then the centrifugal force of the other half of the rim at the moment of rupture must be equal to 30,000 lbs. Now 30,000 lbs. divided by 49.48 (the weight of the half rim) is equal to 606.3, which is the centrifugal force in terms of the weight. Then by the rule given in the last answer 606.3 x 10 = 6063, the square root of which is 78 nearly, and 78 x 4.01 = 312.78, the velocity of the rim in feet per second at the moment of rupture. 29. _Q._--What is the greatest velocity at which it is safe to drive a cast iron fly-wheel? _A._--If we take 2,000 lbs. as the utmost strain per square inch to which cast iron can be permanently subjected with safety; then, by a similar process to that just explained, we have 4,000 lbs./49.48 = 80.8 which multiplied by 10 = 808, the square root of which is 28.4, and 28.4 x 4.01 = 113.884, the velocity of the rim in feet per second, which may be considered as the highest consistent with safety. Indeed, this limit should not be approached in practice on account of the risks of fracture from weakness or imperfections in the metal. 30. _Q._--What is the velocity at which the wheels of railway trains may run if we take 4,000 lbs. per square inch as the greatest strain to which malleable iron should be subjected? _A._--The weight of a malleable iron rim of one square inch sectional area and 7 feet diameter is 21.991 feet x 3.4 lbs. = 74.76, one half of which is 37.4 lbs. Then by the same process as before, 8,000/37.4 = 213.9, the centrifugal force in terms of the weight: 213.9 x 7, the diameter of the wheel = 1497.3, the square root of which, 38.3 x 4.01 = 155.187 feet per second, the highest velocity of the rims of railway carriage wheels that is consistent with safety. 155.187 feet per second is equivalent to 105.8 miles an hour. As 4,000 lbs. per square inch of sectional area is the utmost strain to which iron should be exposed in machinery, railway wheels can scarcely be considered safe at speed even considerably under 100 miles an hour, unless so constructed that the centrifugal force of the rim will be counteracted, to a material extent, by the centripetal action of the arms. Hooped wheels are very unsafe, unless the hoops are, by some process or other, firmly attached to the arms. It is of no use to increase the dimensions of the rim of a wheel with the view of giving increased strength to counteract the centrifugal force, as every increase in the weight of the rim will increase the centrifugal force in the same proportion. CENTRES OF GRAVITY, GYRATION, AND OSCILLATION. 31. _Q._--What do you understand by the centre of gravity of a body? _A._--That point within it, in which the whole of the weight may be supposed to be concentrated, and which continually endeavors to gain the lowest possible position. A body hung in the centre of gravity will remain at rest in any position. 32. _Q._--What is meant by the centre of gyration? _A._--The centre of gyration is that point in a revolving body in which the whole momentum may be conceived to be concentrated, or in which the whole effect of the momentum resides. If the ball of a governor were to be moved in a straight line, the momentum might be said to be concentrated at the centre of gravity of the ball; but inasmuch as, by its revolution round an axis, the part of the ball furthest removed from the axis moves more quickly than the part nearest to it, the momentum cannot be supposed to be concentrated at the centre of gravity, but at a point further removed from the central shaft, and that point is what is called the centre of gyration. 33. _Q._--What is the centre of oscillation? _A._--The centre of oscillation is a point in a pendulum or any swinging body, such, that if all the matter of the body were to be collected into that point, the velocity of its vibration would remain unaffected. It is in fact the mean distance from the centre of suspension of every atom, in a ratio which happens not to be an arithmetical one. The centre of oscillation is always in a line passing through the centre of suspension and the centre of gravity. THE PENDULUM AND GOVERNOR. 34. _Q._--By what circumstance is the velocity of vibration of a pendulous body determined? _A._--By the length of the suspending rod only, or, more correctly, by the distance between the centre of suspension and the centre of oscillation. The length of the arc described does not signify, as the times of vibration will be the same, whether the arc be the fourth or the four hundredth of a circle, or at least they will be nearly so, and would be so exactly, if the curve described were a portion of a cycloid. In the pendulum of clocks, therefore, a small arc is preferred, as there is, in that case, no sensible deviation from the cycloidal curve, but in other respects the size of the arc does not signify. 35. _Q._--If then the length of a pendulum be given, can the number of vibrations in a given time be determined? _A._--Yes; the time of vibration bears the same relation to the time in which a body would fall through a space equal to half the length of the pendulum, that the circumference of a circle bears to its diameter. The number of vibrations made in a given time by pendulums of different lengths, is inversely as the square roots of their lengths. 36. _Q._--Then when the length of the second's pendulum is known the proper length of a pendulum to make any given number of vibrations in the minute can readily be computed? _A._--Yes; the length of the second's pendulum being known, the length of another pendulum, required to perform any given number of vibrations in the minute, may be obtained by the following rule: multiply the square root of the given length by 60, and divide the product by the given number of vibrations per minute; the square of the quotient is the length of pendulum required. Thus if the length of a pendulum were required that would make 70 vibrations per minute in the latitude of London, then SQRT(39.1393) x 60/70 = (5.363)^2 = 28.75 in. which is the length required. 37. _Q._--Can you explain how it comes that the length of a pendulum determines the number of vibrations it makes in a given time? _A._--Because the length of the pendulum determines the steepness of the circle in which the body moves, and it is obvious, that a body will descend more rapidly over a steep inclined plane, or a steep arc of a circle, than over one in which there is but a slight inclination. The impelling force is gravity, which urges the body with a force proportionate to the distance descended, and if the velocity due to the descent of a body through a given height be spread over a great horizontal distance, the speed of the body must be slow in proportion to the greatness of that distance. It is clear, therefore, that as the length of the pendulum determines the steepness of the arc, it must also determine the velocity of vibration. 38. _Q._--If the motions of a pendulum be dependent on the speed with which a body falls, then a certain ratio must subsist between the distance through which a body falls in a second, and the length of the second's pendulum? _A._--And so there is; the length of the second's pendulum at the level of the sea in London, is 39.1393 inches, and it is from the length of the second's pendulum that the space through which a body falls in a second has been determined. As the time in which a pendulum vibrates is to the time in which a heavy body falls through half the length of the pendulum, as the circumference of a circle is to its diameter, and as the height through which a body falls is as the square of the time of falling, it is clear that the height through which a body will fall, during the vibration of a pendulum, is to half the length of the pendulum as the square of the circumference of a circle is to the square of its diameter; namely, as 9.8696 is to 1, or it is to the whole length of the pendulum as the half of this, namely, 4.9348 is to 1; and 4.9348 times 39.1393 in. is 16-1/12 ft. very nearly, which is the space through which a body falls by gravity in a second. 39. _Q._--Are the motions of the conical pendulum or governor reducible to the same laws which apply to the common pendulum? _A._--Yes; the motion of the conical pendulum may be supposed to be compounded of the motions of two common pendulums, vibrating at right angles to one another, and one revolution of a conical pendulum will be performed in the same time as two vibrations of a common pendulum, of which the length is equal to the vertical height of the point of suspension above the plane of revolution of the balls. 40. _Q._--Is not the conical pendulum or governor of a steam engine driven by the engine? _A._--Yes. 41. _Q._--Then will it not be driven round as any other mechanism would be at a speed proportional to that of the engine? _A._--It will. 42. _Q._--Then how can the length of the arms affect the time of revolution? [Illustration: Fig. 1.] _A._--By flying out until they assume a vertical height answering to the velocity with which they rotate round the central axis. As the speed is increased the balls expand, and the height of the cone described by the arms is diminished, until its vertical height is such that a pendulum of that length would perform two vibrations for every revolution of the governor. By the outward motion of the arms, they partially shut off the steam from the engine. If, therefore, a certain expansion of the balls be desired, and a certain length be fixed upon for the arms, so that the vertical height of the cone is fixed, then the speed of the governor must be such, that it will make half the number of revolutions in a given time that a pendulum equal in length to the height of the cone would make of vibrations. The rule is, multiply the square root of the height of the cone in inches by 0.31986, and the product will be the right time of revolution in seconds. If the number of revolutions and the length of the arms be fixed, and it is wanted to know what is the diameter of the circle described by the balls, you must divide the constant number 187.58 by the number of revolutions per minute, and the square of the quotient will be the vertical height in inches of the centre of suspension above the plane of the balls' revolution. Deduct the square of the vertical height in inches from the square of the length of the arm in inches, and twice the square root of the remainder is the diameter of the circle in which the centres of the balls revolve. 43. _Q._ Cannot the operation of a governor be deduced merely from the consideration of centrifugal and centripetal forces? _A._--It can; and by a very simple process. The horizontal distance of the arm from the spindle divided by the vertical height, will give the amount of centripetal force, and the velocity of revolution requisite to produce an equivalent centrifugal force may be found by multiplying the centripetal force of the ball in terms of its own weight by 70,440, and dividing the product by the diameter of the circle made by the centre of the ball in inches; the square root of the quotient is the number of revolutions per minute. By this rule you fix the length of the arms, and the diameter of the base of the cone, or, what is the same thing, the angle at which it is desired the arms shall revolve, and you then make the speed or number of revolutions such, that the centrifugal force will keep the balls in the desired position. 44. _Q._--Does not the weight of the balls affect the question? _A._--Not in the least; each ball may be supposed to be made up of a number of small balls or particles, and each particle of matter will act for itself. Heavy balls attached to a governor are only requisite to overcome the friction of the throttle valve which shuts off the steam, and of the connections leading thereto. Though the weight of a ball increases its centripetal force, it increases its centrifugal force in the same proportion. THE MECHANICAL POWERS. 45. _Q._--What do you understand by the mechanical powers? _A._--The mechanical powers are certain contrivances, such as the wedge, the screw, the inclined plane, and other elementary machines, which convert a small force acting through a great space into a great force acting through a small space. In the school treatises on mechanics, a certain number of these devices are set forth as the mechanical powers, and each separate device is treated as if it involved a separate principle; but not a tithe of the contrivances which accomplish the stipulated end are represented in these learned works, and there is no very obvious necessity for considering the principle of each contrivance separately when the principles of all are one and the same. Every pressure acting with a certain velocity, or through a certain space, is convertible into a greater pressure acting with a less velocity, or through a smaller space; but the quantity of mechanical force remains unchanged by its transformation, and all that the implements called mechanical powers accomplish is to effect this transformation. 46. _Q._--Is there no power gained by the lever? _A._--Not any: the power is merely put into another shape, just as the contents of a hogshead of porter are the same, whether they be let off by an inch tap or by a hole a foot in diameter. There is a greater gush in the one case than the other, but it will last a shorter time; when a lever is used there is a greater force exerted, but it acts through a shorter distance. It requires just the same expenditure of mechanical power to lift 1 lb. through 100 ft., as to lift 100 lbs. through 1 foot. A cylinder of a given cubical capacity will exert the same power by each stroke, whether the cylinder be made tall and narrow, or short and wide; but in the one case it will raise a small weight through a great height, and in the other case, a great weight through a small height. 47. _Q._--Is there no loss of power by the use of the crank? _A._--Not any. Many persons have supposed that there was a loss of power by the use of the crank, because at the top and bottom centres it is capable of exerting little or no power; but at those times there is little or no steam consumed, so that no waste of power is occasioned by the peculiarity. Those who imagine that there is a loss of power caused by the crank perplex themselves by confounding the vertical with the circumferential velocity. If the circle of the crank be divided by any number of equidistant horizontal lines, it will be obvious that there must be the same steam consumed, and the same power expended, when the crank pin passes from the level of one line to the level of the other, in whatever part of the circle it may be, those lines being indicative of equal ascents or descents of the piston. But it will be seen that the circumferential velocity is greater with the same expenditure of steam when the crank pin approaches the top and bottom centres; and this increased velocity exactly compensates for the diminished leverage, so that there is the same power given out by the crank in each of the divisions. 48. _Q._--Have no plans been projected for gaining power by means of a lever? _A._--Yes, many plans,--some of them displaying much ingenuity, but all displaying a complete ignorance of the first principles of mechanics, which teach that power cannot be gained by any multiplication of levers and wheels. I have occasionally heard persons say: "You gain a great deal of power by the use of a capstan; why not apply the same resource in the case of a steam vessel, and increase the power of your engine by placing a capstan motion between the engine and paddle wheels?" Others I have heard say: "By the hydraulic press you can obtain unlimited power; why not then interpose a hydraulic press between the engines and the paddles?" To these questions the reply is sufficiently obvious. Whatever you gain in force you lose in velocity; and it would benefit you little to make the paddles revolve with ten times the force, if you at the same time caused them to make only a tenth of the number of revolutions. You cannot, by any combination of mechanism, get increased force and increased speed at the same time, or increased force without diminished speed; and it is from the ignorance of this inexorable condition, that such myriads of schemes for the realization of perpetual motion, by combinations of levers, weights, wheels, quicksilver, cranks, and other mere pieces of inert matter, have been propounded. 49. _Q._--Then a force once called into existence cannot be destroyed? _A._--No; force is eternal, if by force you mean power, or in other words pressure acting though space. But if by force you mean mere pressure, then it furnishes no measure of power. Power is not measurable by force but by force and velocity combined. 50. _Q._--Is not power lost when two moving bodies strike one other and come to a state of rest? _A._--No, not even then. The bodies if elastic will rebound from one another with their original velocity; if not elastic they will sustain an alteration of form, and heat or electricity will be generated of equivalent value to the power which has disappeared. 51. _Q._--Then if mechanical power cannot be lost, and is being daily called into existence, must not there be a daily increase in the power existing in the world? _A._--That appears probable unless it flows back in the shape of heat or electricity to the celestial spaces. The source of mechanical power is the sun which exhales vapors that descend in rain, to turn mills, or which causes winds to blow by the unequal rarefaction of the atmosphere. It is from the sun too that the power comes which is liberated in a steam engine. The solar rays enable plants to decompose carbonic acid gas, the product of combustion, and the vegetation thus rendered possible is the source of coal and other combustible bodies. The combustion of coal under a steam boiler therefore merely liberates the power which the sun gave out thousands of years before. FRICTION. 52. _Q._--What is friction? _A._--Friction is the resistance experienced when one body is rubbed upon another body, and is supposed to be the result of the natural attraction which bodies have for one another, and of the interlocking of the impalpable asperities upon the surfaces of all bodies, however smooth. There is, no doubt, some electrical action involved in its production, not yet recognized, nor understood; and it is perhaps traceable to the disturbance of the electrical equilibrium of the particles of the body owing to the condensation or change of figure which all bodies must experience when subjected to a strain. When motion in opposite directions is given to smooth surfaces, the minute asperities of one surface must mount upon those of the other, and both will be abraded and worn away, in which act power must be expended. The friction of smooth rubbing substances is less when the composition of those substances is different, than when it is the same, the particles being supposed to interlock less when the opposite prominences or asperities are not coincident. 53. _Q._--Does friction increase with the extent of rubbing surface? _A._--No; the friction, so long as there is no violent heating or abrasion, is simply in the proportion of the pressure keeping the surfaces together, or nearly so. It is, therefore, an obvious advantage to have the bearing surfaces of steam engines as large as possible, as there is no increase of friction by extending the surface, while there is a great increase in the durability. When the bearings of an engine are made too small, they very soon wear out. 54. _Q._--Does friction increase in the same ratio as velocity? _A._--No; friction does not increase with the velocity at all, if the friction over a given amount of surface be considered; but it increases as the velocity, if the comparison be made with the time during which the friction acts. Thus the friction of each stroke of a piston is the same, whether it makes 20 strokes in the minute, or 40: in the latter case, however, there are twice the number of strokes made, so that, though the friction per stroke is the same, the friction per minute is doubled. The friction, therefore, of any machine per hour varies as the velocity, though the friction per revolution remains, at all ordinary velocities, the same. Of excessive velocities we have not sufficient experience to enable us to state with confidence whether the same law continues to operate among them. 55. _Q._--Can you give any approximate statement of the force expended in overcoming friction? _A._--It varies with the nature of the rubbing bodies. The friction of iron sliding upon iron, has generally been taken at about one tenth of the pressure, when the surfaces are oiled and then wiped again, so that no film of oil is interposed. The friction of iron rubbing upon brass has generally been taken at about one eleventh of the pressure under the same circumstances; but in machines in actual operation, where a film of some lubricating material is interposed between the rubbing surfaces, it is not more than one third of this amount or 1/33d of the weight. While this, however, is the average result, the friction is a good deal less in some cases. Mr. Southern, in some experiments upon the friction of the axle of a grindstone--an account of which may be found in the 65th volume of the Philosophical Transactions--found the friction to amount to less than 1/40th of the weight; and Mr. Wood, in some experiments upon the friction of locomotive axles, found that by ample lubrication the friction may be made as little as 1/60th of the weight. In some experiments upon the friction of shafts by Mr. G. Rennie, he found that with a pressure of from 1 to 5 cwt. the friction did not exceed 1/39th of the pressure when tallow was the unguent employed; with soft soap it became 1/34th. The fact appears to be that the amount of the resistance denominated friction depends, in a great measure, upon the nature of the unguent employed, and in certain cases the viscidity of the unguent may occasion a greater retardation than the resistance caused by the attrition. In watchwork therefore, and other fine mechanism, it is necessary both to keep the bearing surfaces small, and to employ a thin and limpid oil for the purpose of lubrication, for the resistance caused by the viscidity of the unguent increases with the amount of surface, and the amount of surface is relatively greater in the smaller class of works. 56. _Q._--Is a very thin unguent preferable also for the larger class of bearings? _A._--The nature of the unguent, proper for different bearings, appears to depend in a great measure upon the amount of the pressure to which the bearings are subjected,--the hardest unguents being best where the pressure is greatest. The function of lubricating substances is to prevent the rubbing surfaces from coming into contact, whereby abrasion would be produced, and unguents are effectual in this respect in the proportion of their viscidity; but if the viscidity of the unguent be greater than what suffices to keep the surfaces asunder, an additional resistance will be occasioned; and the nature of the unguent selected should always have reference, therefore, to the size of the rubbing surfaces, or to the pressure per square inch upon them. With oil the friction appears to be a minimum when the pressure on the surface of a bearing is about 90 lbs. per square inch. The friction from too small a surface increases twice as rapidly as the friction from too large a surface, added to which, the bearing, when the surface is too small, wears rapidly away. 57. _Q._--Has not M. Morin, in France, made some very complete experiments to determine the friction of surfaces of different kinds sliding upon one another? _A._--He has; but the result does not differ materially from what is stated above, though, upon the whole, M. Morin, found the resistance due to friction to be somewhat greater than it has been found to be by various other engineers. When the surfaces were merely wiped with a greasy cloth, but had no film of lubricating material interposed, the friction of brass upon cast iron he found to be .107, or about 1/10th of the load, which was also the friction of cast iron upon oak. But when a film of lubricating material was interposed, he found that the friction was the same whether the surfaces were wood on metal, wood on wood, metal on wood, or metal on metal; and the amount of the friction in such case depended chiefly on the nature of the unguent. With a mixture of hog's lard and olive oil interposed between the surfaces, the friction was usually from 1/12th to 1/14th of the load, but in some cases it was only 1/20th of the load. 58. _Q._--May water be made to serve for purposes of lubrication? _A._--Yes, water will answer very well if the surface be very large relatively with the pressure; and in screw vessels where the propeller shaft passes through a long pipe at the stern, the stuffing box is purposely made a little leaky. The small leakage of water into the vessel which is thus occasioned, keeps the screw shaft in this situation always wet, and this is all the lubrication which this bearing requires or obtains. 59. _Q._--What is the utmost pressure which may be employed without heating when oil is the lubricating material? _A._--That will depend upon the velocity. When the pressure exceeds 800 lbs. per square inch, however, upon the section of the bearing in a direction parallel with the axis, then the oil will be forced out and the bearing will necessarily heat. 60. _Q._--But, with, a given velocity, can you tell the limit of pressure which will be safe in practice; or with a given pressure, can you tell the limit of velocity? _A._--Yes; that may be done by the following empirical rule, which has been derived from observations made upon bearings of different sizes and moving with different velocities. Divide the number 70,000 by the velocity of the surface of the bearing in feet per minute. The quotient will be the number of pounds per square inch of section in the line of the axis that may be put upon the bearing. Or, if we divide 70,000 by the number of pounds per square inch of section, then the quotient will be the velocity in feet per minute at which the circumference of the bearing may work. 61. _Q._--The number of square inches upon which the pressure is reckoned, is not the circumference of the bearing multiplied by its length, but the diameter of the bearing multiplied by its length? _A._--Precisely so, it will be the diameter multiplied by the length of the bearing. 62. _Q._--What is the amount of friction in the case of surfaces sliding upon one another in sandy or muddy water--such surfaces, for example, as are to be found in the sluices of valves for water? _A._--Various experiments have been made by Mr. Summers of Southampton to ascertain the friction of brass surfaces sliding upon each other in salt water, with the view of finding the power required for moving sluice doors for lock gates and for other similar purposes. The surfaces were planed as true and smooth as the planing machine would make them, but were _not_ filed or scraped, and the result was as follows: Area of Slide Weight or Pressure on Power required to move the rubbing rubbing Surface. Slide _slowly_ in muddy Surface. Salt Water, kept stirred up. Sq. in. Lb. Lb. 8 56 21.5 " 112 44. " 168 65.5 " 224 88.5 " 336 140.5 " 448 170.75 [Illustration: Fig. 2. Sketch of Slide. The facing on which the slide moved was similar, but three or four times as long.] These results were the average of eight fair trials; in each case, the sliding surfaces were totally immersed in muddy salt water, and although the apparatus used for drawing the slide along was not very delicately fitted up, the power required may be considered as a sufficient approximation for practical purposes. It appears from these experiments, that rough surfaces follow the same law as regards friction that is followed by smooth, for in each case the friction increases directly as the pressure. STRENGTH OF MATERIALS AND STRAINS SUBSISTING IN MACHINES. 63. _Q._--In what way are the strengths of the different parts of a steam engine determined? _A._--By reference to the amount of the strain or pressure to which they are subjected, and to the cohesive strength of the iron or other material of which they are composed. The strains subsisting in engines are usually characterized as tensile, crushing, twisting, breaking, and shearing strains; but they may be all resolved into strains of extension and strains of compression; and by the power of the materials to resist these two strains, will their practical strength be measurable. 64. _Q._--What are the ultimate strengths of the malleable and cast iron, brass, and other materials employed in the construction of engines? _A._--The tensile and crushing strengths of any given material are by no means the same. The tensile strength, or strength when extended, of good bar iron is about 60,000 lbs., or nearly 27 tons per square inch of section; and the tensile strength of cast iron is about 15,000 lbs., or say 6 3/4 to 7 tons per square inch of section. These are the weights which are required to break them. The crushing strain of cast iron, however, is about 100,000 lbs., or 44 1/2 tons; whereas the crushing strength of malleable iron is not more than 27,000 lbs., or 12 tons, per square inch of section, and indeed it is generally less than this. The ultimate tensile strength, therefore, of malleable iron is four times greater than that of cast iron, but the crushing strength of cast iron is between three and four times greater than that of wrought iron. It may be stated, in round numbers, that the tensile strength of malleable iron is twice greater than its crushing strength; or, in other words, that it will take twice the strain to break a bar of malleable iron by drawing it asunder endways, than will cripple it by forcing it together endways like a pillar; whereas a bar of cast iron will be drawn asunder with one sixth of the force that will be required to break or cripple it when forced together endways like a pillar. 65. _Q._--What is the cohesive strength of steel? _A._--The ultimate tensile strength of good cast or blistered steel is about twice as great as that of wrought iron, being about 130,000 lbs. per square inch of section. The tensile strength of gun metal, such as is used in engines, is about 36,000 lbs. per square inch of section; of wrought copper about 33,000 lbs.; and of cast copper about 19,000 lbs. per square Inch of section. 66. _Q._--Is the crushing strength of steel greater or less than its tensile strength? _A._--It is about twice greater. A good steel punch will punch through a plate of wrought iron of a thickness equal to the diameter of the punch. A punch therefore of an inch diameter will pierce a plate an inch thick. Now it is well known, that the strain required to punch a piece of metal out of a plate, is just the same as that required to tear asunder a bar of iron of the same area of cross section as the area of the surface cut. The area of the surface cut in this case will be the circumference of the punch, 3.1416 inches, multiplied by the thickness of the plate, 1 inch, which makes the area of the cut surface 3.1416 square inches. The area of the point of the punch subjected to the pressure is .7854 square inches, so that the area cut to the area crushed is as four to one. In other words, it will require four times the strain to crush steel that is required to tear asunder malleable iron, or it will take about twice the strain to crush steel that it will require to break it by extension. 67. _Q._--What strain may be applied to malleable iron in practice? _A._--A bar of wrought iron to which a tensile or compressing strain is applied, is elongated or contracted like a very stiff spiral spring, nearly in the proportion of the amount of strain applied up to the limit at which the strength begins to give way, and within this limit it will recover its original dimensions when the strain is removed. If, however, the strain be carried beyond this limit, the bar will not recover its original dimensions, but will be permanently pulled out or pushed in, just as would happen to a spring to which an undue strain had been applied. This limit is what is called the limit of elasticity; and whenever it is exceeded, the bar, though it may not break immediately, will undergo a progressive deterioration, and will break in the course of time. The limit of elasticity of malleable iron when extended, or, in other words, the tensile strain to which a bar of malleable iron an inch square may be subjected without permanently deranging its structure, is usually taken at 17,800 lbs., or from that to 10 tons, depending on the quality of the iron. It has also been found that malleable iron is extended about one ten-thousandth part of its length for every ton of direct strain applied to it. 68. _Q._--What is the limit of elasticity of cast iron? _A._--It is commonly taken at 15,300 lbs. per square inch of section; but this is certainly much too high, as it exceeds the tensile strength of irons of medium quality. A bar of cast iron if compressed by weights will be contracted in length twice as much as a bar of malleable iron under similar circumstances; but malleable iron, when subjected to a greater strain than 12 tons per square inch of section, gradually crumples up by the mere continuance of the weight. A cast-iron bar one inch square and ten feet long, is shortened about one tenth of an inch by a compressing force of 10,000 lbs., whereas a malleable iron bar of the same dimensions would require to shorten it equally a compressing force of 20,000 lbs. As the load, however, approaches 12 tons, the compressions become nearly equal, and above that point the rate of the compression of the malleable iron rapidly increases. A bar of cast iron, when at its breaking point by the application of a tensile strain, is stretched about one six-hundredth part of its length; and an equal strain employed to compress it, would shorten it about one eight-hundredth part of its length. 69. _Q._--But to what strain may the iron used in the construction of engines be safely subjected? _A._--The most of the working parts of modern engines are made of malleable iron, and the utmost strain to which wrought iron should be subjected in machinery is 4000 lbs. per square inch of section. Cast iron should not be subjected to more than half of this. In locomotive boilers the strain of 4000 lbs. per square inch of section is sometimes exceeded by nearly one half; but such an excess of strain approaches the limits of danger. 70. _Q._--Will you explain in what way the various strains subsisting in a steam engine may be resolved into tensile and crushing strains; also in what way the magnitude of those strains may be determined? _A._--To take the case of a beam subjected to a transverse strain, such as the great beam of an engine, it is clear, if we suppose the beam broken through the middle, that the amount of strain at the upper and lower edges of the beam, where the whole strain may be supposed to be collected, will, with any given pressure on the piston, depend upon the proportion of the length to the depth of the beam. One edge of the beam breaks by extension, and the other edge by compression; and the upper and lower edges may be regarded as pillars, one of which is extended by the strain, and the other is compressed. If, to make an extreme supposition, the depth of the beam is taken as equal to its length, then the pillars answering to the edges of the beam will be compressed, and extended by what is virtually a bellcrank lever with equal arms; the horizontal distance from the main centre to the end of the beam being one of the arms, and the vertical height from the main centre to the top edge of the beam being the other arm. The distance, therefore, passed through by the fractured edge of the beam during a stroke of the engine, will be equal to the length of the stroke; and the strain it will have to sustain will consequently be equal to the pressure on the piston. If its motion were only half that of the piston, as would be the case if its depth were made one half less, the strain the beam would have to bear would be twice as great; and it may be set down as an axiom, that the strain upon any part of a steam engine or other machine is inversely equal to the strain produced by the prime mover, multiplied by the comparative velocity with which the part in question moves. If any part of an engine moves with a less velocity than the piston, it will have a greater strain on it, if resisted, than is thrown upon the piston. If it moves with a greater velocity than the piston, it will have a less strain upon it, and the difference of strain will in every case be in the inverse proportion of the difference of the velocity. 71. _Q._--Then, in computing the amount of metal necessary to give due strength to a beam, the first point is to determine the velocity with which the edge of the beam moves at that point were the strain is greatest? _A._--The web of a cast-iron beam or girder serves merely to connect the upper and lower edges or flanges rigidly together, so as to enable the extending and compressing strains to be counteracted in an effectual manner by the metal of those flanges. It is only necessary, therefore, to make the flanges of sufficient strength to resist effectually the crushing and tensile strains to which they are exposed, and to make the web of the beam of sufficient strength to prevent a distortion of its shape from taking place. 72. _Q._--Is the strain greater from being movable or intermittent than if it was stationary? _A._--Yes it is nearly twice as great from being movable. Engineers are in the habit of making girders intended to sustain a stationary load, about three times stronger than the breaking weight; but if the load be a movable one, as is the case in the girders of railway bridges, they make the strength equal to six times the breaking weight. 73. _Q._--Then the strain is increased by the suddenness with which it is applied? _A._--If a weight be placed on a long and slender beam propped up in the middle, and the prop be suddenly withdrawn, so as to allow deflection to take place, it is clear that the deflection must be greater than if the load had been gradually applied. The momentum of the weight and also of the beam itself falling through the space through which it has been deflected, has necessarily to be counteracted by the elasticity of the beam; and the beam will, therefore, be momentarily bent to a greater extent than what is due to the load, and after a few vibrations up and down it will finally settle at that point of deflection which the load properly occasions. It is obvious that a beam must be strong enough, not merely to sustain the pressure due to the load, but also that accession of pressure due to the counteracted momentum of the weight and of the beam itself. Although in steam engines the beam is not loaded by a weight, but by the pressure of the steam, yet the momentum of the beam itself must in every case be counteracted, and the momentum will be considerable in every case in which a large and rapid deflection takes place. A rapid deflection increases the amount of the deflection as well as the amount of the strain, as is seen in the cylinder cover of a Cornish pumping engine, into which the steam is suddenly admitted, and in which the momentum of the particles of the metal put into motion increases the deflection to an extent such as the mere pressure of the steam could not produce. 74. _Q._--What will be the amount of increased strain consequent upon deflection? _A._--The momentum of any moving body being proportional to the square of its velocity, it follows that the strain will be proportional to the square of the amount of deflection produced in a specified time. 75. _Q._--But will not the inertia of a beam resist deflection, as well as the momentum increase deflection? _A._--No doubt that will be so; but whether in practical cases increase of mass without reference to strength or load will, upon the whole, increase or diminish deflection, will depend very much upon the magnitude of the mass relatively with the magnitude of the deflecting pressure, and the rapidity with which that pressure is applied and removed. Thus if a force or weight be very suddenly applied to the middle of a ponderous beam, and be as suddenly withdrawn, the inertia of the beam will, as in the case of the collision of bodies, tend to resist the force, and thus obviate deflection to a considerable extent; but if the pressure be so long continued as to produce the amount of deflection due to the pressure, the effect of the inertia in that case will be to increase the deflection. 76. _Q._--Will the pressure given to the beam of an engine in different directions facilitate its fracture? _A._--Iron beams bent alternately in opposite directions, or alternately deflected and released, will be broken in the course of time with a much less strain than is necessary to produce immediate fracture. It has been found, experimentally, that a cast-iron bar, deflected by a revolving cam to only half the extent due to its breaking weight, will in no case withstand 900 successive deflections; but, if bent by the cam to only one third of its ultimate deflection, it will withstand 100,000 deflections without visible injury. Looking, however, to the jolts and vibrations to which engines are subject, and the sudden strains sometimes thrown upon them, either from water getting into the cylinder or otherwise, it does not appear that a strength answering to six times the breaking weight will give sufficient margin for safety in the case of cast-iron beams. 77. _Q._--Does the same law hold in the case of the deflection of malleable iron bars? _A._--In the case of malleable iron bars it has been found that no very perceptible damage was caused by 10,000 deflections, each deflection being such as was due to half the load that produced a large permanent deflection. 78. _Q._--The power of a rod or pillar to resist compression becomes very little when the diameter is small and the length great? _A._--The power of a rod or pillar to resist compression, varies nearly as the fourth power of the diameter divided by the square of the length. In the case of hollow cylindrical columns of cast iron, it has been found, experimentally, that the 3.55th power of the internal diameter, subtracted from the 3.55th power of the external diameter, and divided by the 1.7th power of the length, will represent the strength very nearly. In the case of hollow cylindrical columns of malleable iron, experiment shows that the 3.59th power of the internal diameter, subtracted from the 3.59th power of the external diameter, and divided by the square of the length, gives a proper expression for the strength; but this rule only holds where the strain does not exceed 8 or 9 tons on the square inch of section. Beyond 12 or 13 tons per square inch of section, the metal cannot be depended upon to withstand the strain, though hollow pillars will sometimes bear 15 or 16 tons per square inch of section. 79. _Q._--Does not the thickness of the metal of the pillars or tubes affect the question? _A._--It manifestly does; for a tube of very thin metal, such as gold leaf or tin foil, would not stand on end at all, being crushed down by its own weight. It is found, experimentally, that in malleable iron tubes of the respective thicknesses of .525, .272, and .124 inches, the resistances per square inch of section are 19.17, 14.47, and 7.47 tons respectively. The power of plates to resist compression varies nearly as the cube, or more nearly as the 2.878th power of their thickness; but this law only holds so long as the pressure applied does not exceed from 9 to 12 tons per square inch of section. When the pressure is greater than this the metal is crushed, and a new law supervenes, according to which it is necessary to employ plates of twice or three times the thickness, to obtain twice the resisting power. 80. _Q._--In a riveted tube, will the riveting be much, damaged by heavy strains? _A._--It will be most affected by percussion. Long-continued impact on the side of a tube, producing a deflection of only one fifth of that which would be required to injure it by pressure, is found to be destructive of the riveting; but in large riveted structures, such as a ship or a railway bridge, the inertia of the mass will, by resisting the effect of impact, prevent any injurious action from this cause from taking place. 81. _Q._--Will the power of iron to resist shocks be in all cases proportional to its power to resist strains? _A._--By no means. Some cast iron is very hard and brittle; and although it will in this state resist compression very strongly, it, will be easily broken by a blow. Iron which has been remelted many times generally falls into this category, as it will also do if run into very small castings. It has been found, by experiment, that iron of which the crushing weight per square inch is about 42 tons, will, if remelted twelve times, bear a crushing weight of 70 tons, and if remelted eighteen times it will bear a crushing weight of 83 tons; but taking its power to resist impact in its first state at 706, this power will be raised at the twelfth remelting to 1153, and will be sunk at the eighteenth remelting to 149. 82. _Q._--From all this it appears that a combination of cast iron and malleable iron is the best for the beams of engines? _A._--Yes, and for all beams. Engine beams should be made deeper at the middle than they are now made; the web should be lightened by holes pierced in it, and round the edge of the beam there should be a malleable iron hoop or strap securely attached to the flanges by riveting or otherwise. The flanges at the edges of engine beams are invariably made too small. It is in them that the strength of the beam chiefly resides. CHAPTER I. GENERAL DESCRIPTION OF THE STEAM ENGINE. * * * * * THE BOILER. 83. _Q._--What are the chief varieties of the steam engine in actual practical use? _A._--There is first the single-acting engine, which is used for pumping water; the rotative land engine, which is employed to drive mills and manufactories; the rotative marine engine, which is used to propel steam vessels; and the locomotive engine, which is employed on railways. The last is always a high-pressure engine; the others are, for the most part, condensing engines. 84. _Q._--Will you explain the construction and action of the single-acting engine, used for draining mines? _A._--Permit me then to begin with the boiler, which is common and necessary to all engines; and I will take the example of a wagon boiler, such as was employed by Boulton and Watt universally in their early engines, and which is still in extensive use. This boiler is a long rectangular vessel, with a rounded top, like that of a carrier's wagon, from its resemblance to which it derives its name. A fire is set beneath it, and flues constructed of brickwork encircle it, so as to keep the flame and smoke in contact with the boiler for a sufficient time to absorb the heat. [Illustration: Fig. 3] 85. _Q._--This species of boiler has not an internal furnace, but is set in brickwork, in which the furnace is formed? _A._--Precisely so. The general arrangement and configuration will be at once understood by a reference to the annexed figure (fig. 3), which is a transverse section of a wagon boiler. The line b represents the top of the grate or fire bars, which slope downward from the front at an angle of about 25°, giving the fuel a tendency to move toward the back of the grate. The supply of air ascends from the ash pit through the grate bars, and the flame passes over a low wall or bridge, and traverses the bottom of the boiler. The smoke rises up at the back of the boiler, and proceeds through the flue F along one side to the front, and returns along the other side of the boiler, and then ascends the chimney. The performance of this course by the smoke is what is termed a wheel draught, as the smoke wheels once round the boiler, and then ascends the chimney. 86. _Q._--Is the performance of this course by the smoke universal in wagon boilers? _A._--No; such boilers sometimes have what is termed a split draught. The smoke and flame, when they reach the end of the boiler, pass in this case through an iron flue or tube, reaching from end to end of the boiler; and on arriving at the front of the boiler, the smoke splits or separates--one half passing through a flue on the one side of the boiler, and the other half passing through a flue on the other side of the boiler--both of these flues having their debouch in the chimney. 87. _Q._--What are the appliances usually connected with a wagon boiler? _A._--On the top of the boiler, near the front, is a short cylinder, with a lid secured by bolts. This is the manhole door, the purpose of which is to enable a man to get into the inside of the boiler when necessary for inspection and repair. On the top of this door is a small valve opening downward, called the atmospheric valve. The intention of this valve is to prevent a vacuum from being formed accidentally in the boiler, which might collapse it; for if the pressure in the boiler subsides to a point materially below the pressure of the atmosphere, the valve will open and allow air to get in. A bent pipe, which rises up from the top of the boiler, immediately behind the position of the manhole, is the steam pipe for conducting the steam to the engine; and a bent pipe which ascends from the top of the boiler, at the back end, is the waste-steam pipe for conducting away the steam, which escapes through the safety valve. This valve is set in a chest, standing on the top of the boiler, at the foot of the waste-steam pipe, and it is loaded with iron or leaden weights to a point answerable to the intended pressure of the steam. 88. _Q._--How is the proper level of the water in the boiler maintained? _A._--By means of a balanced buoy or float. This float is attached to a rod, which in its turn is attached to a lever set on the top of a large upright pipe. The upper part of the pipe is widened out into a small cistern, through a short pipe in the middle of which a chain passes to the damper; but any water emptied into this small cistern cannot pass into the pipe, except through a small valve fixed to the lever to which the rod is attached. The water for replenishing the boiler is pumped into the small cistern on the top of the pipe; and it follows from these arrangements that when the buoy falls, the rod opens the small valve and allows the feed water to enter the pipe, which communicates with the water in the boiler; whereas, when the buoy rises, the feed cannot enter the pipe, and it has, therefore, to run to waste through an overflow pipe provided for the purpose. 89. _Q._--How is the strength of the fire regulated? _A._--The draught through the furnaces of land boilers is regulated by a plate of metal or a damper, as it is called, which slides like a sluice up and down in the flue, and this damper is closed more or less when the intensity of the fire has to be moderated. In wagon boilers this is generally accomplished by self-acting mechanism. In the small cistern pipe, which is called a stand pipe, the water rises up to a height proportional to the pressure of the steam, and the surface of the water in this pipe will rise or fall with the fluctuations in the pressure of the steam. In this pipe a float is placed, which communicates by means of a chain with the damper. If the pressure of the steam rises, the float will be raised and the damper closed, whereas, if the pressure in the boiler falls, the reverse of this action will take place. [Illustration: Fig. 4.] [Illustration: Fig. 5.] 90. _Q._--Are all land boilers of the same construction as that which you have just described? _A._--No; many land boilers are now made of a cylindrical form, with one or two internal flues in which the furnace is placed. A boiler of this kind is represented in Figs. 4 and 5, and which is the species of boiler principally used in Cornwall. In this boiler a large internal cylinder or flue runs from end to end. In the fore part of this cylinder the furnace is placed, and behind the furnace a large tube filled with water extends to the end of the boiler. This internal tube is connected to the bottom part of the boiler by a copper pipe standing vertically immediately behind the furnace bridge, and to the top part of the boiler by a bent copper pipe which stands in a vertical position near the end of the boiler. The smoke, after passing through the central flue, circulates round the sides and beneath the bottom of the boiler before its final escape into the chimney. The boiler is carefully covered over to prevent the dispersion of the heat. [Illustration: Fig. 6] 91. _Q._--Will you describe the construction of the boilers used in steam vessels? _A._--These are of two classes, flue boilers and tubular boilers, but the latter are now most used. In the flue boiler the furnaces are set within the boiler, and the flues proceeding from them wind backwards and forwards within the boiler until finally they meet and enter the chimney. Figs. 6, 7, and 8 are different views of the flue boilers of the steamer Forth. There are 4 boilers (as shown in plan, Fig. 6), with 3 furnaces in each, or 12 furnaces in all. Fig. 7 is an elevation of 2 boilers, the one to the right being the front view, and that to the left a transverse section. Fig. 8 is a longitudinal section through 2 boilers. The direction of the arrows in plan and longitudinal section, will explain the direction of the smoke current. [Illustration: Fig. 7.] [Illustration: Fig. 8.] 92. _Q._--Is this arrangement different from that obtaining in tubular boilers? _A._--In tubular boilers, the smoke after leaving the furnace just passes once through a number of small tubes and then enters the chimney. These tubes are sometimes of brass, and they are usually about 3 inches in diameter, and 6 or 7 feet long. [Illustration: Fig. 9.] [Illustration: Fig. 10.] [Illustration: Fig. 11.] Figs. 9, 10, and 11 represent a marine tubular boiler; fig. 9 being a vertical longitudinal section, fig. 10 half a front elevation and half a transverse section, and fig. 11 half a back elevation and half a transverse section near the end. There is a projecting part on the top of the boiler called the "steam chest," of which the purpose is to retain for the use of the cylinder a certain supply of steam in a quiescent state, in order that it may have time to clear itself of foam or spray. A steam chest is a usual part of all marine boilers. In fig. 9 A is the furnace, B the steam chest, and C the smoke box which opens into the chimney. The front of the smoke box is usually closed by doors which may be opened when necessary to sweep the soot out of the tubes. The following are some forms of American boilers: Figs. 12 and 13 are the transverse and longitudinal sections of a common form of American marine boiler. Figs. 14 and 15 are the front and sectional elevation of one of the boilers of the U.S. steamer Water Witch. [Illustration: Fig. 12.] [Illustration: Fig. 13.] [Illustration: Fig. 14.] [Illustration: Fig. 15.] Fig. 16 is a longitudinal section of a boiler of the drop flue variety. For land purposes the lowest range of tubes is generally omitted, and the smoke makes a last return beneath the bottom of the boiler. Figs. 17 and 18 are the transverse and longitudinal sections of a tubular boiler, built in 1837 by R.L. Stevens for the steamboat Independence. [Illustration: Fig. 16.] [Illustration: Fig. 17.] [Illustration: Fig. 18.] Fig. 19 is a longitudinal section of a common wood-burning locomotive. [Illustration: Fig. 19.] THE ENGINE. 93. _Q._--The steam passes from the boiler through, the steam pipe into the cylinder of the engine? _A._--And presses up and down the piston alternately, being admitted alternately above and below the piston by suitable valves provided for that purpose. 94. _Q._--This reciprocating motion is all that is required in a pumping engine? _A._--The prevailing form of the pumping engine consists of a great beam vibrating on a centre like the beam of a pair of scales, and the cylinder is in connection with one end of the beam and the pump stands at the other end. The pump end of the beam is usually loaded, so as to cause it to preponderate when the engine is at rest; and the whole effort of the steam is employed in overcoming this preponderance until a stroke is performed, when, the steam being shut off, the heavy end of the beam again falls and the operation is repeated. 95. _Q._--in the double-acting engine the piston is pushed by the steam both ways, whereas in the single-acting engine it is only pushed one way? _A._--The structure and action of a double-acting land engine of the kind introduced by Mr. Watt, will be understood by a reference to the annexed figure (fig. 20), where an engine of this kind is shown in section. A is the cylinder in which a movable piston, T, is forced alternately up and down by the alternate admission, to each side, of the steam from the boiler. The piston, by means of a rod called the piston rod, gives motion to the beam V W, which by means of a heavy bar, P, called the connecting rod, moves the crank, Q, and with it the fly wheel, X, from which the machinery to be driven derives its motion. 96. _Q._--Where does the steam enter from the boiler? [Illustration: Fig. 20.] _A._--At the steam pipe, B. The throttle valve in that pipe is an elliptical plate of metal swivelling on a spindle passing through its edge from side to side, and by turning which more or less the opening through the pipe will be more or less closed. The extent to which this valve is opened or closed is determined by the governor, D, the balls of which, as they collapse or expand, move up or down a collar on the governor spindle, which motion is communicated to the throttle valve by suitable rods and bell-cranks. The governor, it will be seen, consists substantially of two heavy balls attached to arms fixed upon an upright shaft, which is kept in revolution by means of a cord driven by a pulley on the fly wheel shaft. The velocity with which the balls of the governor revolve being proportional to that of the fly wheel, it will follow, that if by reason of too rapid a supply of steam, an undue speed be given to the fly wheel, and therefore to the balls, a divergence of the balls will take place to an extent corresponding to the excess of velocity, and this movement being communicated to the throttle valve it will be partly closed (see fig. 1), the supply of steam to the engine will be diminished, and the velocity of its motion will be reduced. If, on the other hand, the motion of the engine is slower than is requisite, owing to a deficient supply of steam through B, then the balls, not being sufficiently affected by centrifugal force, will fall towards the vertical spindle, and the throttle valve, C, will be more fully opened, whereby a more ample supply of steam will be admitted to the cylinder, and the speed of the engine will be increased to the requisite extent. 97. _Q._--The piston must be made to fit the cylinder accurately so as to prevent the passage of steam? _A._--The piston is accurately fitted to the cylinder, and made to move in it steam tight by a packing of hemp driven tightly into a groove or recess round the edge of the piston, and which is squeezed down by an iron ring held by screws. The piston divides the cylinder into two compartments, between which there is no communication by which steam or any other elastic fluid can pass. A casing set beside the cylinder contains the valves, by means of which the steam which impels the piston is admitted and withdrawn, as the piston commences its motion in each direction. The upper steam box B, is divided into three compartments by two valves. Above the upper steam valve V, is a compartment communicating with the steam pipe B. Below the lower valve E is another compartment communicating with a pipe called the eduction pipe, which leads downwards from the cylinder to the condenser, in which vessel the steam is condensed by a jet of cold water. By the valve V, a communication may be opened or closed between the boiler and the top of the cylinder, so as to permit or prevent a supply of steam from the one to pass to the other. By the valve E a communication may be open or closed between the top of the cylinder and the condenser, so that the steam in the top compartment of the cylinder may either be permitted to escape into the condenser, or may be confined to the cylinder. The continuation of the steam pipe leads to the lower steam box B', which, like the upper, is divided into three compartments by two valves V' and E', and the action of the lower valves is in all respects the same as that of the upper. 98. _Q._--Are all these valves connected together so that they act simultaneously? _A._--The four valves V, E, V', E' are connected by rods to a single handle H, which handle is moved alternately up and down by means of pins or tappets, placed on the rod which works the air pump. When the handle H is pressed down, the levers in connexion with it open the upper exhausting valve E, and the lower steam valve V', and close the upper steam valve V and the lower exhausting valve E'. On the other hand, when the handle H is pressed up it opens the upper steam valve V and the lower exhausting valve E', and at the same time closes the upper exhausting valve E, and the lower steam valve V'. 99. _Q._--Where is the condenser situated? _A._--The condenser K is immerged in a cistern of cold water. At its side there is a tube I, for the admission of water to condense the steam, and which is governed by a cock, by opening which to any required extent, a jet of cold water may be made to play in the condenser. From the bottom of the condenser a short pipe leads to the air pump J, and in this pipe there is a flap valve, called the foot valve, opening towards the air pump. The air pump is a pump set in the same cistern of cold water that holds the condenser, and it is fitted with a piston or bucket worked by the rod L, attached to the great beam, and fitted with a valve opening upwards in the manner of a common sucking pump. The upper part of the air pump communicates with a small cistern S, called the hot well, through a valve opening outwards and called the delivery valve. A pump M, called the hot water pump, lifts hot water out of the hot well to feed the boiler, and another pump N lifts cold water from a well or other source of supply, to maintain the supply of water to the cold water cistern, in which the condenser and air pump are placed. 100. Q.--Will you explain now the manner in which the engine acts? A.--The piston being supposed to be at the top of the cylinder, the handle H will be raised by the lower pin or tappet on the air pump rod, and the valves V and E' will be opened, and at the same time the other pair of valves V' and E will be closed. Steam will therefore be admitted above the piston and the steam or air which had previously filled the cylinder below the piston will be drawn off to the condenser. It will there encounter the jet of cold water, which is kept constantly playing there by keeping the cock I sufficiently open. It will thus be immediately condensed or reduced to water, and the cylinder below the piston will have a vacuum in it. The steam therefore admitted from the steam pipe through the open valve V to the top of the cylinder, not being resisted by pressure below, will press the piston to the bottom of the cylinder. As it approaches that position, the handle H will be struck down by the upper pin or tappet on the air pump rod, and the valves V and E', previously open, will be closed, while the valves V' and E, previously closed, will be opened. The steam which has just pressed down the piston, and which now fills the cylinder above the piston, will then flow off, through the open valve E, to the condenser, where it will be immediately condensed by the jet of cold water; and steam from the boiler, admitted through the open valve V', will fill the cylinder below the piston, and press the piston upwards. When the piston has reached the top of the cylinder, the lower pin on the air pump rod will have struck the handle upwards, and will thereby have closed the valves V' and E, and opened the valves V and E'. The piston will then be in the same situation as in the commencement, and will again descend, and so will continue to be driven up and down by the steam. 101. Q.--But what becomes of the cold water which is let into the condenser to condense the steam? A.--It is pumped out by the air pump in the shape of hot water, its temperature having been raised considerably by the admixture of the steam in it. When the air pump piston ascends it leaves behind it a vacuum; and the foot valve being relieved from all pressure, the weight of the water in the condenser forces it open, and the warm water flows from the condenser into the lower part of the air pump, from which its return to the condenser is prevented by the intervening valve. When the air pump piston descends, its pressure on the liquid under it will force open the valve in it, through which the hot water will ascend; and when the bucket descends to the bottom of the pump barrel, the warm water which was below it will all have passed above it, and cannot return. When the bucket next ascends, the water above it, not being able to return through the bucket valve, will be forced into the hot well through the delivery valve S. The hot water pump M, pumps a small quantity of this hot water into the boiler, to compensate for the abstraction of the water that has passed off in the form of steam. The residue of the hot water runs to waste. 102. _Q._--By what expedient is the piston rod enabled to pass through the cylinder cover without leaking steam out of the cylinder or air into it? _A._--The hole in the cylinder lid, through which the piston rod passes, is furnished with a recess called a stuffing box, into which a stuffing or packing of plaited hemp is forced, which, pressing on the one side against the interior of the stuffing box, and on the other side against the piston rod, which is smooth and polished, prevents any leakage in this situation. The packing of this stuffing box is forced down by a ring of metal tightened by screws. This ring, which accurately fits the piston rod, has a projecting flange, through which bolts pass for tightening the ring down upon the packing; and a similar expedient is employed in nearly every case in which packing is employed. 103. _Q._--In what way is the piston rod connected to the great beam? _A._--The piston rod is connected to the great beam by means of two links, one at each side of the beam shown at _f g_, (fig. 21.) These links are usually made of the same length as the crank, and their purpose is to enable the end of the great beam to move in the arc of a circle while the piston rod maintains the vertical position. The point of junction, therefore, of the links and the piston rod is of the form of a knuckle or bend at some parts of the stroke. 104. _Q._--But what compels the top of the piston rod to maintain the vertical position? _A._--Some engines have guide rods set on each side of the piston rod, and eyes on the top of the piston rod engage these guide rods, and maintain the piston rod in a vertical position in every part of the stroke. More commonly, however, the desired end is attained by means of a contrivance called the parallel motion. 105. _Q._--What is the parallel motion? _A._--The parallel motion is an arrangement of jointed rods, so connected together that the divergence from the vertical line at any point in the arc described by the beam is corrected by an equal and opposite divergence due to the arc performed by the jointed rods during the stroke; and as these opposite deviations mutually correct one another, the result is that the piston rod moves in a vertical direction. 106. _Q._--Will you explain the action more in detail? _A._--The pin, fig 21, which passes through the end of the beam at _f_ has a link _f g_ hung on each side of the beam, and a short cross bar, called a cross head, extends from the bottom of one of these links to the bottom of the other, which cross head is perforated with a hole in the middle for the reception of the piston rod. There are similar links _b d_ at the point of the main beam, where the air pump rod is attached. There are two rods _d g_ connecting the links _b d_ with the links _f g_, and these rods, as they always continue parallel to the main beam throughout the stroke, are called _parallel bars_. Attached to the end of these two rods at _d_ are two other rods _c d_, of which the ends at _c_ are attached to stationary pins, while the ends at _d_ follow the motion of the lower ends of the links _b d_. These rods are called the _radius bars_. Now it is obvious that the arc described by the point _d_, with _c_ as a centre, is opposite to the arc described by the point _g_ with _d_ as a centre. The rod _d g_ is, therefore, drawn back horizontally by the arc described at _d_ to an extent equal to the versed sine of the arc described at _g_, or, in other words, the line described by the point _g_ becomes a straight line instead of a curve. [Illustration: Fig. 21.] 107. _Q._--Does the air pump rod move vertically as well as the piston rod? _A._--It does. The air pump rod is suspended from a cross head, passing from the centre of one of the links _b d_ to the centre of the other link, on the opposite side of the beam. Now, as the distance from the central axis of the great beam to the point _b_ is equal to the length of the rod _c d_, it will follow that the upper end of the link will follow one arc, and the lower end an equal and opposite arc. A point in the centre of the link, therefore, where these opposite motions meet, will follow no arc at all, but will move up and down vertically in a straight line. 108. _Q._--The use of the crank is to obtain a circular motion from a reciprocating motion? _A._--That is the object of it, and it accomplishes its object in a very perfect manner, as it gradually arrests the velocity of the piston towards the end of the stroke, and thus obviates what would otherwise be an injurious shock upon the machine. When the crank approaches the lowest part of its throw, and at the same time the piston is approaching the top of the cylinder, the motion of the crank becomes nearly horizontal, or, in other words, the piston is only advanced through a very short distance, for any given distance measured on the circle described by the crank pin. Since, then, the velocity of rotation of the crank is nearly uniform, it will follow that the piston will move very slowly as it approaches the end of the stroke; and the piston is brought to a state of rest by this gradually retarded motion, both at the top and the bottom of the stroke. 109. _Q._--What causes the crank to revolve at a uniform velocity? _A._--The momentum of the machinery moved by the piston, but more especially of the fly wheel, which by its operation redresses the unequal pressures communicated by the crank, and compels the crank shaft to revolve at a nearly uniform velocity. Everyone knows that a heavy wheel if put into rapid rotation cannot be immediately stopped. At the beginning and end of the stroke when the crank is vertical, no force of torsion can be exerted on the crank shaft by the crank, but this force is at its maximum when the crank is horizontal. From the vertical point, where this force is nothing, to the horizontal point, where it is at its maximum, the force of torsion exerted on the crank shaft is constantly varying; and the fly wheel by its momentum redresses these irregularities, and carries the crank through that "dead point," as it is termed, where the piston cannot impart any rotative force. 110. _Q._--Are the configuration and structure of the steam engine, as it left the hand of Watt, materially different from those of modern engines? _A._--There is not much difference. In modern rotative land engines, the valves for admitting the steam to the cylinder or condenser, instead of being clack or pot-lid valves moved by tappets on the air pump rod, are usually sluice or sliding valves, moved by an eccentric wheel on the crank shaft. Sometimes the beam is discarded altogether, and malleable iron is more largely used in the construction of engines instead of the cast iron, which formerly so largely prevailed. But upon the whole the steam engine of the present day is substantially the engine of Watt; and he who perfectly understands the operation of Watt's engine, will have no difficulty in understanding the operation of any of the numerous varieties of engines since introduced. THE MARINE ENGINE. 111. _Q._--Will you describe the principal features of the kind of steam engine employed for the propulsion of vessels? _A._--Marine engines are of two kinds,--paddle engines and screw engines. In the one case the propelling instrument is paddle wheels kept in rotation at each side of the ship: in the other case, the propelling instrument is a screw, consisting of two or more twisted vanes, revolving beneath the water at the stern. Of each class of engines there are many distinct varieties. 112. _Q._--What are the principal varieties of the paddle engine? [Illustration: Fig. 22.] [Illustration: Fig. 23.] _A._--There is the side lever engine (fig. 26), and the oscillating engine (fig. 27), besides numerous other forms of engine which are less known or employed, such as the trunk (fig. 22), double cylinder (fig. 23), annular, Gorgon (fig. 24), steeple (fig. 25), and many others. The side lever engine, however, and the oscillating engine, are the only kinds of paddle engines which have been received with wide or general favor. [Illustration: Fig. 24.] 113. _Q._--Will you explain the main distinctive features of the side lever engine? _A._--In all paddle vessels, whatever be their subordinate characteristics, a great shaft of wrought iron, s, turned round by the engine, has to be carried from side to side of the vessel, on which shaft are fixed the paddle wheels. The paddle wheels may either be formed with fixed float boards for engaging the water, like the boards of a common undershot water wheel, or they may be formed with _feathering_ float boards as they are termed, which is float boards movable on a centre, and so governed by appropriate mechanism that they enter and leave the water in a nearly vertical position. The common fixed or radial floats, however, are the kind most widely employed, and they are attached to the arms of two or more rings of malleable iron which are fixed by appropriate centres on the paddle shaft. It is usual in steam vessels to employ two engines, the cranks of which are set at right angles with one another. When the paddle wheels are turned by the engines, the float boards engaging the water cause a forward thrust to be imparted to the shaft, which propels forward the vessel on the same principle that a boat is propelled by the action of oars. [Illustration: Fig. 25.] 114. _Q._--These remarks apply to all paddle vessels? _A._--They do. With respect to the side lever engine, it may be described to be such a modification of the land beam engine already described, as will enable it to be got below the deck of a vessel. With this view, instead of a single beam being placed overhead, two beams are used, one of which is set on each side of the engine as low down as possible. The cross head which engages the piston rod is made somewhat longer than the diameter of the cylinder, and two great links or rods proceed one from each end of the cross head to one of the side levers or beams. A similar cross bar at the other end of the beams serves to connect them together and to the connecting rod which, proceeding from thence upwards, engages the crank, and thereby turns round the paddle wheels. 115. _Q._--Will you further illustrate this general description by an example? [Illustration: Fig. 26.] _Q._--Fig. 26 is a side elevation of a side lever engine; x x represent the beams or keelsons to which the engines are attached, and on which the boilers rest. The engines are tied down by strong bolts passing through the bottom of the vessel, but the boiler keeps its position by its weight alone. The condenser and air pump are worked off the side levers by means of side rods and a cross head. A strong gudgeon, called the _main centre_, passes through the condenser at K, the projecting ends of which serve to support the side levers or beams. L is the piston rod, which, by means of the cross head and side rods, is connected to the side levers or beams, one of which is shown at H H. The line M represents the connecting rod, to which motion is imparted by the beams, through the medium of the cross tail extending between the beams, and which by means of the crank turns the paddle shaft S. The eccentric which works the slide valve is placed upon the paddle shaft. It consists of a disc of metal encircled by a hoop, to which a rod is attached, and the disc is perforated with a hole for the shaft, not in the centre, but near one edge. When, therefore, the shaft revolves, carrying the eccentric with it, the rod attached to the encircling hoop receives a reciprocating motion, just as it would do if attached to a crank in the shaft. 116. _Q._--Will you describe the mode of starting the engine? _A._--I may first mention that when the engine is at rest, the connection between the eccentric and the slide valve is broken, by lifting the end of the eccentric rod out of a notch which engages a pin on the valve shaft, and the valve is at such times free to be moved by hand by a bar of iron, applied to a proper part of the valve gear for that purpose. This being so, the engineer, when he wishes to start the engine, first opens a small valve called the _blow through valve_, which permits steam from the boiler to enter the engine both above and below the piston, and also to fill the condenser and air pump. This steam expels the air from the interior of the engine, and also any water which may have accumulated there; and when this has been done, the blow through valve is shut, and a vacuum very soon forms within the engine, by the condensation of the steam. If now the slide valve be moved by hand, the steam from the boiler will be admitted on one side of the piston, while there is a vacuum on the other side, and the piston will, therefore, be moved in the desired direction. When the piston reaches the end of the stroke, the valve has to be moved in the reverse direction, when the piston will return, and after being moved thus by hand, once or twice, the connection of the valve with the eccentric is to be restored by allowing the notch on the end of the eccentric rod to engage the pin on the valve lever, when the valve will be thereafter moved by the engine in the proper manner. It will, of course, be necessary, when the engine begins to move, to open the injection cock a little, to enable water to enter for the condensation of the steam. In the most recent marine engines, a somewhat different mechanism from this is used for giving motion to the valves, but that mechanism will be afterwards described. 117. _Q._--Are all marine engines condensing engines? _A._--Nearly all of them are so; but recently a number of gunboats have been constructed, with high pressure engines. In general, however, marine engines are low pressure or condensing engines. 118. _Q._--Will you now describe the chief features of the oscillating paddle marine engine? _A._--In the oscillating paddle marine engine, the arrangement of the paddle shaft and paddle wheels is the same as in the case already described, but the whole of the side levers, side rods, cross head, cross tail, and connecting rod are discarded. The cylinder is set immediately under the crank; the top of the piston rod is connected immediately to the crank pin; and, to enable the piston rod to accommodate itself to the movement of the crank, the cylinder is so constructed as to be susceptible of vibrating or oscillating upon two external axes or trunnions. These trunnions are generally placed about half way up on the sides of the cylinder; and through one of them steam is received from the boiler, while through the other the steam escapes to the condenser. The air pump is usually worked by means of a crank in the shaft, which crank moves the air pump bucket up and down as the shaft revolves. 119. _Q._--Will you give an example of a paddle oscillating engine? _A._--I will take as an example the oscillating engines constructed by Messrs. Ravenhill & Salked, for the Holyhead Packets. Fig. 27 is a longitudinal section of this vessel, showing an engine and boiler; and fig. 28 is a transverse section of one of the engines, showing also one of the wheels. There are two cylinders in this vessel, and one air pump, which lies in an inclined position, and is worked by a crank in the shaft which stretches between the cylinders, and which is called the _intermediate shaft_. A A, is one of the cylinders, B B the piston rod, and C C the crank. D is the crank in the intermediate shaft, which works the air pump E. There are double eccentrics fixed on the shaft, whereby the movement of the slide valves is regulated. The purpose of the double eccentrics is to enable an improved arrangement of valve gear to be employed, which is denominated the _link motion_, and which will be described hereafter. I I are the steam pipes leading to the steam trunnions K K, on which, and on the eduction trunnions connected with the pipe M, the cylinders oscillate. 120. _Q._--By what species of mechanism are the positions of the paddle floats of feathering wheels governed? _A._--The floats are supported by spurs projecting from the rim of the wheel, and they may be moved upon the points of the spurs, to which they are attached by pins, by means of short levers proceeding from the backs of the floats, and connected to rods which proceed towards the centre of the wheel. The centre, however, to which these rods proceed is not concentric with the wheel, and the rods, therefore, are moved in and out as the wheel revolves, and impart a corresponding motion to the floats. In some feathering wheels the proper motion is given to the rods by means of an eccentric on the ship's side. The action of paddle wheels, whether radial or feathering, will be more fully described in the chapter on Steam Navigation. SCREW ENGINES. 121. _Q._--What are the principal varieties of screw engines? [Illustration: Fig. 27.] [Illustration: Fig. 28.] _A._--The engines employed for the propulsion of screw vessels are divided into two great classes,--geared engines and direct acting engines; and each of these classes again has many varieties. In screw vessels, the shaft on which the screw is set requires to revolve at a much greater velocity than is required in the case of the paddle shaft of a paddle vessel; and in geared engines this necessary velocity of rotation is obtained by the intervention of toothed wheels,--the engines themselves moving with the usual velocity of paddle engines; whereas in direct acting engines the required velocity of rotation is obtained by accelerating the speed of the engines, and which are connected immediately to the screw shaft. 122. _Q._--Will you describe some of the principal varieties of geared engines? _A._--A good many of the geared engines for screw vessels are made in the same manner as land engines, with a beam overhead, which by means of a connecting rod extending downwards, gives motion to the crank shaft, on which are set the cog wheels which give motion to pinions on the screw shaft,--the teeth of the wheels being generally of wood and the teeth of the pinions of iron. There are usually several wheels on the crank shaft and several pinions on the screw shaft; but the teeth of each do not run in the same line, but are set a little in advance of one another, so as to divide the thickness of the tooth into as many parts as there are independent wheels or pinions. By this arrangement the wheels work more smoothly than they would otherwise do. 123. _Q._--What other forms are there of geared screw engines? _A._--In some cases the cylinders lie on their sides in the manner of the cylinders of a locomotive engine. In other cases vertical trunk engines are employed; and in other cases vertical oscillating engines. 124. _Q._--Will you give an example of a geared vertical oscillating engine? _A._--The engines of a geared oscillating engine are similar to the paddle wheel engines (figs. 27 and 28), but the engines are placed lengthways of the ship, and instead of a paddle wheel on the main shaft, there is a geared wheel which connects with a pinion on the screw shaft. The engines of the Great Britain are made off the same patterns as the paddle engines constructed by Messrs. John Penn & Son, for H.M.S. Sphinx. The diameter of each cylinder is 82-1/2 inches, the length of travel or stroke of the piston is 6 feet, and the nominal power is 500 horses. The Great Britain is of 3,500 tons burden, and her displacement at 16 feet draught of water is 2,970 tons. The diameter of the screw is 15-1/2 feet, length of screw in the line of the shaft, 3 feet 2 inches, and the pitch of the screw, 19 feet. 125. _Q._--What do you mean by the pitch of the screw? _A._--A screw propeller may be supposed to be a short piece cut off a screw of large diameter like a spiral stair, and the pitch of a spiral stair is the vertical height from any given step to the step immediately overhead. 126. _Q._--What is the usual number of arms? _A._--Generally a screw has two arms, but sometimes it has three or more. The Great Britain had three arms or twisted blades resembling the vanes of a windmill. The multiple of the gearing in the Great Britain is 3 to 1, and there are 17-1/2 square feet of heating surface in the boiler for each nominal horse power. The crank shaft being put into motion by the engine, carries round with it the great cog wheel, or aggregation of cog wheels, affixed to its extremity; and these wheels acting on suitable pinions on the screw shaft, cause the screw to make three revolutions for every revolution made by the engine. 127. _Q._--What are the principal varieties of direct acting screw engines? _A._--In some cases four engines have been employed instead of two, and the cylinders have been laid on their sides on each side of the screw shaft. This multiplication of engines, however, introduces needless complication, and is now but little used. In other cases two inverted cylinders are set above the screw shaft on appropriate framing; and connecting rods attached to the ends of the piston rods turn round cranks in the screw shaft. 128. _Q._--What is the kind of direct acting screw engine employed by Messrs. Penn. _A._--It is a horizontal trunk engine. In this engine a round pipe called a trunk penetrates the piston, to which it is fixed, being in fact cast in one piece with it; and the trunk also penetrates the top and bottom of the cylinder, through which it moves, and is made tight therein by means of stuffing boxes. The connecting rod is attached at one end to a pin fixed in the middle of the trunk, while the other end engages the crank in the usual manner. The air pump is set within the condenser, and is wrought by a rod which is fixed to the piston and derives its motion therefrom. The air pump is of that species which is called double-acting. The piston or bucket is formed without valves in it, but an inlet and outlet valve is fixed to each end of the pump, through the one of which the water is drawn into the pump barrel, and through the other of which it is expelled into the hot well. THE LOCOMOTIVE ENGINE. 129. _Q._--Will you describe the more important features of the locomotive engine? _A._--The locomotive employed to draw carriages upon railways, consists of a cylindrical boiler filled with brass tubes, through which the hot air passes on its progress from the furnace to the chimney, and attached to the boiler are two horizontal cylinders fitted with pistons, valves, connecting rods, and other necessary apparatus to enable the power exerted by the pistons to turn round the cranked axle to which the driving wheels are attached. There are, therefore, two independent engines entering into the composition of a locomotive, the cranks of which are set at right angles with one another, so that when one crank is at its dead point, the other crank is in a position to act with its maximum efficacy. The driving wheels, which are fixed on the crank shaft and turn round with it, propel the locomotive forward on the rails by the mere adhesion of friction, and this is found sufficient not merely to move the locomotive, but to draw a long train of carriages behind it. 130. _Q._--Are locomotive engines condensing or high pressure engines. _A._--They are invariably high pressure engines, and it would be impossible or at least highly inconvenient, to carry the water necessary for the purpose of condensation. The steam, therefore, after it has urged the piston to the end of the stroke, escapes into the atmosphere. In locomotive engines the waste steam is always discharged into the chimney through a vertical pipe, and by its rapid passage it greatly increases the intensity of the draught in the chimney, whereby a smaller fire grate suffices for the combustion of the fuel, and the evaporative power of the boiler is much increased. 131. _Q._--Can you give an example of a good locomotive engine of the usual form? _A._--To do this I will take the example of one of Hawthorn's locomotive engines with six wheels represented in fig. 29; not one of the most modern construction now in use, nor yet one of the most antiquated. M is the cylinder, R the connecting rod, C C the eccentrics by which the slide valve is moved; J J is the steam pipe by which the steam is conducted from the steam dome of the boiler to the cylinder. Near the smoke stack end of this pipe is a valve K or regulator moved by a handle _p_ at the front of the boiler, and of which the purpose is to regulate the admission of the steam to the cylinder; _f_ is a safety valve kept closed by springs; N is the eduction pipe, or, as it is commonly termed in locomotives, the _blast pipe_, by which the steam, escaping from the cylinder after the stroke has been performed, is projected up the chimney H. The water in the boiler of course covers the tubes and also the top of the furnace or fire box. It will be understood that there are two engines in each locomotive, though, from the figure being given in section, only one engine can be shown. The cylinders of this engine are each 14 inches diameter; the length of the stroke of the piston is 21 inches. There are two sets of driving wheels, 5 feet diameter, with outside connections. [Illustration: Fig. 29.] 132. _Q._--What is the tender of a locomotive? _A._--It is a carriage attached to the locomotive, of which the purpose is to contain coke for feeding the furnace, and water for replenishing the boiler. 133. _Q._--Can you give examples of modern locomotives? [Illustration: Fig. 30.] [Illustration: Fig. 31.] _A._--The most recent locomotives resemble in their material features the locomotive represented in fig. 29. I can, however, give examples of some of the most powerful engines of recent construction. Fig. 30 represents Gooch's express engine, adapted for the wide gauge of the Great Western Railway; and fig. 31 represents Crampton's express engine, adapted for the ordinary or narrow gauge railways. The cylinders of Gooch's engine are each 18 inches diameter, and 24 inches stroke; the driving wheels are 8 feet in diameter; the fire grate contains 21 square feet of area; and the heating surface of the fire box is 153 square feet. There are in all 305 tubes in the boiler, each of 2 inches diameter, giving a heating surface in the tubes of 1799 square feet. The total heating surface, therefore, is 1952 square feet. Mr. Gooch states that an engine of this class will evaporate from 300 to 360 cubic feet of water in the hour, and will convey a load of 236 tons at a speed of 40 miles an hour, or a load of 181 tons at a speed of 60 miles an hour. The weight of this engine empty is 31 tons; of the tender 8-1/2 tons; and the total weight of the engine when loaded is 50 tons. In one of Crampton's locomotives, the Liverpool, with one set more of carrying wheels than the fig., the cylinders are of 24 inches diameter and 18 inches stroke; the driving wheels are 8 feet in diameter; the fire grate contains 21-1/2 square feet of area; and the heating surface of the fire box is 154 square feet. There are in all 300 tubes in the boiler of 2-3/16 inches external diameter, giving a surface in the tubes of 2136 square feet, and a total heating surface of 2290 square feet. The weight of this engine is stated to be 35 tons when ready to proceed on a journey. Both engines were displayed at the Great Exhibition in 1851, as examples of the most powerful locomotive engines then made. The weight of such engines is very injurious to the railway; bending, crushing, and disturbing the rails, and trying very severely the whole of the railway works. No doubt the weight may be distributed upon a greater number of wheels, but if the weight resting on the driving wheels be much reduced, they will not have sufficient bite upon the rails to propel the train without slipping. This, however, is only one of the evils which the demand for high rates of speed has produced. The width of the railway, or, as it is termed, the _gauge_ of the rails, being in most of the railways in this kingdom limited to 4 feet 8-1/2 inches, a corresponding limitation is imposed on the diameter of the boiler; which in its turn restricts the number of the tubes which can be employed. As, however, the attainment of a high rate of speed requires much power, and consequently much heating surface in the boiler, and as the number of tubes cannot be increased without reducing their diameter, it has become necessary, in the case of powerful engines, to employ tubes of a small diameter, and of a great length, to obtain the necessary quantity of heating surface; and such tubes require a very strong draught in the chimney to make them effective. With a draught of the usual intensity the whole of the heat will be absorbed in the portion of the tube nearest the fire box, leaving that portion nearest the smoke box nothing to do but to transmit the smoke; and with long tubes of small diameter, therefore, a very strong draught is indispensable. To obtain such a draught in locomotives, it is necessary to contract the mouth of the blast pipe, whereby the waste steam will be projected into the chimney with greater force; but this contraction involves an increase of the pressure on the eduction side of the piston, and consequently causes a diminution in the power of the engine. Locomotives with small and long tubes, therefore, will require more coke to do the same work than locomotives in which larger and shorter tubes may be employed. CHAPTER II. HEAT, COMBUSTION, AND STEAM. HEAT. 134. _Q._--What is meant by latent heat? _A._--By latent heat is meant the heat existing in bodies which is not discoverable by the touch or by the thermometer, but which manifests its existence by producing a change of state. Heat is absorbed in the liquefaction of ice, and in the vaporization of water, yet the temperature does not rise during either process, and the heat absorbed is therefore said to become latent. The term is somewhat objectionable, as the effect proper to the absorption of heat has in each case been made visible; and it would be as reasonable to call hot water latent steam. Latent heat, in the present acceptation of the term, means sensible liquefaction or vaporization; but to produce these changes heat is as necessary as to produce the expansion of mercury in a thermometer tube, which is taken as the measure of temperature; and it is hard to see on what ground heat can be said to be latent when its presence is made manifest by changes which only heat can effect. It is the _temperature_ only that is latent, and latent temperature means sensible vaporization or liquefaction. 135. _Q._--But when you talk of the latent heat of steam, what do you mean to express? _A._--I mean to express the heat consumed in accomplishing the vaporization compared with that necessary for producing the temperature. The latent heat of steam is usually reckoned at about 1000 degrees, by which it is meant that there is as much heat in any given weight of steam as would raise its constituent water 1000 degrees if the expansion of the water could be prevented, or as would raise 1000 times that quantity of water one degree. The boiling point of water, being 212 degrees, is 180 degrees above the freezing point of water--the freezing point being 32 degrees; so that it requires 1180 times as much heat to raise 1 lb. of water into steam, as to raise 1180 lbs. of water one degree; or it requires about as much heat to raise a pound of boiling water into steam, as would raise 5-1/2 lbs. of water from the freezing to the boiling point; 5-1/2 multiplied by 180 being 990 or 1000 nearly. 136. _Q._--When it is stated that the latent heat of steam is 1000 degrees, it is only meant that this is a rough approximation to the truth? _A._--Precisely so. The latent heat, in point of fact, is not uniform at all temperatures, neither is the total amount of heat the same at all temperatures. M. Regnault has shown, by a very elaborate series of experiments on steam, which he has lately concluded, that the total heat in steam increases somewhat with the pressure, and that the latent heat diminishes somewhat with the pressure. This will be made obvious by the following numbers: Pressure. Temperature. Total Heat. Latent Heat. 15 lbs. 213.1° 1178.9° 965.8° 50 281.0 1199.6 918.6 100 327.8 1213.9 886.1 If, then, steam of 100 lbs. be expanded down to steam of 15 lbs., it will have 35 degrees of heat over that which is required for the maintenance of the vaporous state, or, in other words, it will be surcharged with heat. 137. _Q._--What do you understand by specific heat? _A._--By specific heat, I understand the relative quantities of heat in bodies at the same temperature, just as by specific gravity I understand the relative quantities of matter in bodies of the same bulk. Equal weights of quicksilver and water at the same temperature do not contain the same quantities of heat, any more than equal bulks of those liquids contain the same quantity of matter. The absolute quantity of heat in any body is not known; but the relative heat of bodies at the same temperature, or in other words their specific heats, have been ascertained and arranged in tables,-- the specific heat of water being taken as unity. 138. _Q._--In what way does the specific heat of a body enable the quantity of heat in it to be determined? _A._--If any body has only half the specific heat of water, then a pound of that body will, at any given temperature, have only half the heat in it that is in a pound of water at the same temperature. The specific heat of air is .2669, that of water being 1; or it is 3.75 times less than that of water. An amount of heat, therefore, which would raise a pound of water 1 degree would raise a pound of air 3.75 degrees. COMBUSTION. 139. _Q._--What is the nature of combustion? _A._--Combustion is nothing more than an energetic chemical combination, or, in other words, it is the mutual neutralization of opposing electricities. When coal is brought to a high temperature it acquires a strong affinity for oxygen, and combination with oxygen will produce more than sufficient heat to maintain the original temperature; so that part of the heat is rendered applicable to other purposes. 140. _Q._--Does air consist of oxygen? _A._--Air consists of oxygen and nitrogen mixed together in the proportion of 3.29 lbs. of nitrogen to 1 lb. of oxygen. Every pound of coal requires about 2.66 lbs. of oxygen for its saturation, and therefore for every pound of coal burned, 8.75 pounds of nitrogen must pass through the fire, supposing all the oxygen to enter into combination. In practice, however, this perfection of combination does not exist; from one-third to one-half of the oxygen will pass through the fire without entering into combination at all; so that from 16 to 18 lbs. of air are required for every pound of coal burned. 18 lbs. of air are about 240 cubic feet, which may be taken as the quantity of air required for the combustion of a pound of coal in practice. 141. _Q._--What are the constituents of coal? _A._--The chief constituent of coal is carbon or pure charcoal, which is associated in various proportions with volatile and earthy matters. English coal contains 80 to 90 per cent. of carbon, and from 8 to 18 per cent. of volatile and earthy matters, but sometimes more than this. The volatile matters are hydrogen, nitrogen, oxygen, and sulphur. 142. _Q._--What is the difference between anthracite and bituminous coal? _A._--Anthracite consists almost entirely of carbon, having 91 per cent. of carbon, with about 7 per cent. of volatile matter and 2 per cent. of ashes. Newcastle coal contains about 83 per cent. of carbon, 14 per cent. of volatile matter, and 3 per cent. of ashes. 143. _Q._--Will you recapitulate the steps by which you determine the quantity of air required for the combustion of coal? _A._--Looking to the quantity of oxygen required to unite chemically with the various constituents of the coal, we find for example that in 100 lbs. of anthracite coal, consisting of 91.44 lbs. of carbon, and 3.46 lbs. of hydrogen, we shall for the 91.44 lbs. of carbon require 243.84 lbs. of oxygen--since to saturate a pound of carbon by the formation of carbonic acid, requires 2-2/3 lbs. of oxygen. To saturate a pound of hydrogen in the formation of water, requires 8 lbs. of oxygen; hence 3.46 Fibs. of hydrogen will take 27.68 lbs. of oxygen for its saturation. If then we add 243.84 lbs. to 27.68 lbs. we have 271.52 lbs. of oxygen required for the combustion of 100 lbs. of coal. A given weight of air contains nearly 23.32 per cent of oxygen; hence to obtain 271.52 lbs. of oxygen, we must have about four times that quantity of atmospheric air, or more accurately, 1164 lbs. of air for the combustion of 100 lbs. of coal. A cubic foot of air at ordinary temperature weighs about .075 lbs.; so that 100 lbs. of coal require 15,524 cubic feet of air, or 1 lb. of coal requires about 155 cubic feet of air, supposing every atom of the oxygen to enter into combination. If, then, from one-third to one-half of the air passes unconsumed through the fire, an allowance of 240 cubic feet of air for each pound of coal will be a small enough allowance to answer the requirements of practice, and in some cases as much as 300 cubic feet will be required,--the difference depending mainly on the peculiar configuration of the furnace. 144. _Q._--Can you state the evaporative efficacy of a pound of coal? _A._--The evaporative efficacy of a pound of carbon has been found experimentally to be equivalent to that necessary to raise 14,000 lbs. of water through 1 degree, or 14 lbs. of water through 1000 degrees, supposing the whole heat generated to be absorbed by the water. Now, if the water be raised into steam from a temperature of 60°, then 1118.9° of heat will have to be imparted to it to convert it into steam of 15 lbs. pressure per square inch. 14,000 / 1118.9 = 12.512 Lbs. will be the number of pounds of water, therefore, which a pound of carbon can raise into steam of 15 lbs. pressure from a temperature of 60°. This, however, is a considerably larger result than can be expected in practice. 145. _Q._--Then what is the result that may be expected in practice? _A._--The evaporative powers of different coals appear to be nearly proportional to the quantity of carbon in them; and bituminous coal is, therefore, less efficacious than coal consisting chiefly of pure carbon. A pound of the best Welsh or anthracite coal is capable of raising from 9-1/2 to 10 lbs. of water from 212° into steam, whereas a pound of the best Newcastle is not capable of raising more than about 8-1/2 lbs. of water from 212° into steam; and inferior coals will not raise more than 6-1/2 lbs. of water into steam. In America it has been found that 1 lb. of the best coal is equal to 2-1/2 lbs. of pine wood, or, in some cases to 3 lbs.; and a pound of pine wood will not usually evaporate more than about 2 1/2 lbs. of water, though, by careful management, it may be made to evaporate 4 1/2 lbs. Turf will generate rather more steam than wood. Coke is equal or somewhat superior to the best coal in evaporative effect. 146. _Q._--How much water will a pound of coal raise into steam in ordinary boilers? _A._--From 6 to 8 lbs. of water in the generality of land boilers of medium quality, the difference depending on the kind of boiler, the kind of coal, and other circumstances. Mr. Watt reckoned his boilers as capable of evaporating 10.08 cubic feet of water with a bushel or 84 lbs. of Newcastle coal, which is equivalent to 7 1/2 lbs. of water evaporated by 1 lb. of coal, and this may be taken as the performance of common land boilers at the present time. In some of the Cornish boilers, however, a pound of coal raises 11.8 lbs. of boiling water into steam, or a cwt. of coal evaporates about 21 cubic feet of water from 212°. 147. _Q._--What method of firing ordinary furnaces is the best? _A._--The coals should be broken up into small pieces, and sprinkled thinly and evenly over the fire a little at a time. The thickness of the stratum of coal upon the grate should depend upon the intensity of the draught: in ordinary land or marine boilers it should be thin, whereas in locomotive boilers it requires to be much thicker. If the stratum of coal be thick while the draught is sluggish, the carbonic acid resulting from combustion combines with an additional atom of carbon in passing through the fire, and is converted into carbonic oxide, which may be defined to be invisible smoke, as it carries off a portion of the fuel: if, on the contrary, the stratum of coal be thin while the draught is very rapid, an injurious refrigeration is occasioned by the excess of air passing through the furnace. The fire should always be spread of uniform thickness over the bars of the grate, and should be without any holes or uncovered places, which greatly diminish the effect of the fuel by the refrigeratory action of the stream of cold air which enters thereby. A wood fire requires to be about 6 inches thicker than a coal one, and a turf fire requires to be 3 or 4 inches thicker than a wood one, so that the furnace bars must be placed lower where wood or turf is burned, to enable the surface of the fire to be at the same distance from the bottom of the boiler. 148. _Q._--Is a slow or a rapid combustion the most beneficial? _A._--A slow combustion is found by experiment to give the best results as regards economy of fuel, and theory tells us that the largest advantage will necessarily be obtained where adequate time has been afforded for a complete combination of the constituent atoms of the combustible, and the supporter of combustion. In many of the cases, however, which occur in practice, a slow combustion is not attainable; but the tendencies of slow combustion are both to save the fuel, and to burn the smoke. 149. _Q._--Is not the combustion in the furnaces of the Cornish boilers very slow? A.--Yes, very slow; and there is in consequence very little smoke evolved. The coal used in Cornwall is Welsh coal, which evolves but little smoke, and is therefore more favorable for the success of a smokeless furnace; but in the manufacturing districts, where the coal is more bituminous, it is found that smoke may be almost wholly prevented by careful firing and by the use of a large capacity of furnace. 150. _Q._--Do you consider slow combustion to be an advisable thing to practise in steam vessels? _A._--No, I do not. When the combustion is slow, the heat in the furnaces and flues is less intense, and a larger amount of heating surface consequently becomes necessary to absorb the heat. In locomotives, where the heat of the furnace is very intense, there will be the same economy of fuel with an allowance of 5 or 6 square feet of surface to evaporate a cubic foot of water as in common marine boilers with 10 or 12. 151. _Q._--What is the method of consuming smoke pursued in the manufacturing districts? _A._--In Manchester, where some stringent regulations for the prevention of smoke have for some time been in force, it is found that the readiest way of burning the smoke is to have a very large proportion of furnace room, whereby slow combustion may be carried on. In some cases, too, a favourable result is arrived at by raising a ridge of coal across the furnace lying against the bridge, and of the same height: this ridge speedily becomes a mass of incandescent coke, which promotes the combustion of the smoke passing over it. 152. _Q._--Is the method of admitting a stream of air into the flues to burn the smoke regarded favorably? _A._--No; it is found to be productive of injury to the boiler by the violent alternations of temperature it occasions, as at some times cold air impinges on the iron of the boiler, and at other times flame,--just as there happens to be smoke or no smoke emitted by the furnace. Boilers, therefore, operating upon this principle, speedily become leaky, and are much worn by oxidation, so that, if the pressure is considerable, they are liable to explode. It is very difficult to apportion the quantity of air admitted, to the varying wants of the fire; and as air may at some times be rushing in when there is no smoke to consume, a loss of heat, and an increased consumption of fuel may be the result of the arrangement; and, indeed, such is the result in practice, though a carefully performed experiment usually demonstrates a saving in fuel of 10 or 12 per cent. 153. _Q._--What other plans have been contrived for obviating the nuisance of smoke? _A._--They are too various for enumeration, but most of them either operate upon the principle of admitting air into the flues to accomplish the combustion of the uninflammable parts of the smoke, or seek to attain the same object by passing the smoke over or through the fire or other incandescent material. Some of the plans, indeed, profess to burn the inflammable gases as they are evolved from the coal, without permitting the admixture of any of the uninflammable products of combustion which enter into the composition of smoke; but this object has been very imperfectly fulfilled in any of the contrivances yet brought under the notice of the public, and in some cases these contrivances have been found to create weightier evils than they professed to relieve. 154. _Q._--You refer, I suppose, to Mr. Charles Wye Williams' Argand furnace? _A._--I chiefly refer to it, though I also comprehend all other schemes in which there is a continuous admission of air into the flues, with an intermittent generation of smoke. 155. _Q._--This is not so in Prideaux's furnace? _A._--No; in that furnace the air is admitted only during a certain interval, or for so long, in fact, as there is smoke to be consumed. 156. _Q._--Will you explain the chief peculiarities of that furnace? _A._--The whole peculiarity is in the furnace door. The front of the door consists of metal Venetians, which are opened when the top lever is lifted up, and shut when that lever descends to its lowest position. When the furnace door is opened to replenish the fire with coals, the top lever is raised up, and with it the piston of the small cylinder attached to the side of the furnace. The Venetians are thereby opened, and a stream of air enters the furnace, which, being heated in its passage among the numerous heated plates attached to the back of the furnace door, is in a favorable condition for effecting the combustion of the inflammable parts of the smoke. The piston in the small cylinder gradually subsides and closes the Venetians; and the rate of the subsidence of the piston may obviously be regulated by a cock, or, as in this case, a small screw valve, so that the Venetians shall just close when there is no more smoke to be consumed;--the air or other fluid within the cylinder being forced out by the piston in its descent. 157. _Q._--Had Mr. Watt any method of consuming smoke? _A._--He tried various methods, but eventually fixed upon the method of coking the coal on a dead plate at the furnace door, before pushing it into the fire. That method is perfectly effectual where the combustion is so slow that the requisite time for coking is allowed, and it is much preferable to any of the methods of admitting air at the bridge or elsewhere, to accomplish the combustion of the inflammable parts of the smoke. 158. _Q._--What are the details of Mr. Watt's arrangement as now employed? _A._--The fire bars and the dead plate are both set at a considerable inclination, to facilitate the advance of the fuel into the furnace. In Boulton and Watt's 30 horse power land boiler, the dead plate and the furnace bars are both about 4 feet long, and they are set at the angle of 30 degrees with the horizon. 159. _Q._--Is the use of the dead plate universally adopted in Boulton and Watt's land boilers? _A._--It is generally adopted, but in some cases Boulton and Watt have substituted the plan of a revolving grate for consuming the smoke, and the dead plate then becomes both superfluous and inapplicable. In this contrivance the fire is replenished with coals by a self-acting mechanism. 160. _Q._--Will you explain the arrangement of the revolving grate? _A._--The fire grate is made like a round table capable of turning horizontally upon a centre; a shower of coal is precipitated upon the grate through a slit in the boiler near the furnace mouth, and the smoke evolved from the coal dropped at the front part of the fire is consumed by passing over the incandescent fuel at the back part, from which all the smoke must have been expelled in the revolution of the grate before it can have reached that position. 161. _Q._--Is a furnace with a revolving grate applicable to a steam vessel? _A._--I see nothing to prevent its application. But the arrangement of the boiler would perhaps require to be changed, and it might be preferable to combine its use with the employment of vertical tubes, for the transmission of the smoke. The introduction of any effectual automatic contrivance for feeding the fire in steam vessels, would bring about an important economy, at the same time that it would give the assurance of the work being better done. It is very difficult to fire furnaces by hand effectually at sea, especially in rough weather and in tropical climates; whereas machinery would be unaffected by any such disturbing causes, and would perform with little expense the work of many men. 162. _Q._--The introduction of some mechanical method of feeding the fire with coals would enable a double tier of furnaces to be adopted in steam vessels without inconvenience? _A._--Yes, it would have at least that tendency; and as the space available for area of grate is limited in a steam vessel by the width of the vessel, it would be a great convenience if a double tier of furnaces could be employed without a diminished effect. It appears to me, however, that the objection would still remain of the steam raised by the lower furnace being cooled and deadened by the air entering the ash-pit of the upper fire, for it would strike upon the metal of the ash-pit bottom. 163. _Q._--Have any other plans been devised for feeding the fire by self-acting means besides that of a revolving grate? _A._--Yes, many plans, but none of them, perhaps, are free from an objectionable complication. In some arrangements the bars are made like screws, which being turned round slowly, gradually carry forward the coal; while in other arrangements the same object is sought to be attained by alternately lifting and depressing every second bar at the end nearest the mouth of the furnace. In Juckes' furnace, the fire bars are arranged in the manner of rows of endless chains working over a roller at the mouth of the furnace, and another roller at the farther end of the furnace. These rollers are put into slow revolution, and the coal which is deposited at the mouth of the furnace is gradually carried forward by the motion of the chains, which act like an endless web. The clinkers and ashes left after the combustion of the coal, are precipitated into the ash-pit, where the chain turns down over the roller at the extremity of the furnace. In Messrs. Maudslays' plan of a self-feeding furnace the fire bars are formed of round tubes, and are placed transversely across the furnace. The ends of the bars gear into endless screws running the whole length of the furnace, whereby motion is given to the bars, and the coal is thus carried gradually forward. It is very doubtful whether any of these contrivances satisfy all the conditions required in a plan for feeding furnaces of the ordinary form by self-acting means, but the problem of providing a suitable contrivance, does not seem difficult of accomplishment, and will no doubt be effected under adequate temptation. 164. _Q._--Have not many plans been already contrived which consume the smoke of furnaces very effectually? _A._--Yes, many plans; and besides those already mentioned there are Hall's, Coupland's, Godson's, Robinson's, Stevens's, Hazeldine's, Indie's, Bristow and Attwood's, and a great number of others. One plan, which promises well, consists in making the flame descend through the fire bars, and the fire bars are formed of tubes set on an incline and filled with water, which water will circulate with a rapidity proportionate to the intensity of the heat. After all, however, the best remedy for smoke appears to consist in removing from it those portions which form the smoke before the coal is brought into use. Many valuable products may be got from the coal by subjecting it to this treatment; and the residuum will be more valuable than before for the production of steam. STEAM. 165. _Q._--Have experiments been made to determine the elasticity of steam at different temperatures? _A._--Yes; very careful experiments. The following rule expresses the results obtained by Mr. Southern:--To the given temperature in degrees of Fahrenheit add 51.3 degrees; from the logarithm of the sum, subtract the logarithm of 135.767, which is 2.1327940; multiply the remainder by 5.13, and to the natural number answering to the sum, add the constant fraction .1, which will give the elastic force in inches of mercury. If the elastic force be known, and it is wanted to determine the corresponding temperature, the rule must be modified thus:--From the elastic force, in inches of mercury, subtract the decimal .1, divide the logarithm of the remainder by 5.13, and to the quotient add the logarithm 2.1327940; find the natural number answering to the sum, and subtract therefrom the constant 51.3; the remainder will be the temperature sought. The French Academy, and the Franklin Institute, have repeated Mr. Southern's experiments on a larger scale; the results obtained by them are not widely different, and are perhaps nearer the truth, but Mr. Southern's results are generally adopted by engineers, as sufficiently accurate for practical purposes. 166. _Q._--Have not some superior experiments upon this subject been lately made in France? _A._--Yes, the experiments of M. Regnault upon this subject have been very elaborate and very carefully conducted, and the results are probably more accurate than have been heretofore obtained. Nevertheless, it is questionable how far it is advisable to disturb the rules of Watt and Southern, with which the practice of engineers is very much identified, for the sake of emendations which are not of such magnitude as to influence materially the practical result. M. Regnault has shown that the total amount of heat, existing in a given weight of steam, increases slightly with the pressure, so that the sum of the latent and sensible heats do not form a constant quantity. Thus, in steam of the atmospheric pressure, or with 14.7 Lbs. upon the square inch, the sensible heat of the steam is 212 degrees, the latent heat 966.6 degrees, and the sum of the latent and sensible heats 1178.6 degrees; whereas in steam of 90 pounds upon the square inch the sensible heat is 320.2 degrees, the latent heat 891.4 degrees, and the sum of the latent and sensible heats 1211.0 degrees. There is, therefore, 33 degrees less of heat in any given weight of water, raised into steam of the atmospheric pressure, than if raised into steam of 90 Lbs.[1] pressure. 167. _Q._--What expansion does water undergo in its conversion into steam? _A._--A cubic inch of water makes about a cubic foot of steam of the atmospheric pressure. 168. _Q._--And how much at a higher pressure? _A._--That depends upon what the pressure is. But the proportion is easily ascertained, for the pressure and the bulk of a given quantity of steam, as of air or any other elastic fluid, are always inversely proportional to one another. Thus if a cubic inch of water makes a cubic foot of steam, with the pressure of one atmosphere, it will make half a cubic foot with the pressure of two atmospheres, a third of a cubic foot with the pressure of three atmospheres, and so on in all other proportions. High pressure steam indeed is just low pressure steam forced into a less space, and the pressure will always be great in the proportion in which the space is contracted. 169. _Q._--If this be so, the quantity of heat in a given weight of steam must be nearly the same, whether the steam is high or low pressure? _A._--Yes; the heat in steam is nearly a constant quantity, at all pressures, but not so precisely. Steam to which an additional quantity of heat has been imparted after leaving the boiler, or as it is called "surcharged steam," comes under a different law, for the elasticity of such steam may be increased without any addition being made to its weight; but surcharged steam is not at present employed for working engines, and it may therefore be considered in practice that a pound of steam contains very nearly the same quantity of heat at all pressures. 170. _Q._--Does not the quantity of heat in any body vary with the temperature? _A._--Other circumstances remaining the same the quantity of heat in a body increases with the temperatures. 171. _Q._--And is not high pressure steam hotter than low pressure steam? _A._--Yes, the temperature of steam rises with the pressure. 172. _Q._--How then comes it, that there is the same quantity of heat in the same weight of high and low pressure steam, when the high pressure steam has the highest temperature? _A._--Because although the temperature or sensible heat rises with the pressure, the latent heat becomes less in about the same proportion. And as has been already explained, the latent and sensible heats taken together make up nearly the same amount at all temperatures; but the amount is somewhat greater at the higher temperatures. As a damp sponge becomes wet when subjected to pressure, so warm vapor becomes hot when forced into less bulk, but in neither case does the quantity of moisture or the quantity of heat sustain any alteration. Common air becomes so hot by compression that tinder may be inflamed by it, as is seen in the instrument for producing instantaneous light by suddenly forcing air into a syringe. 173. _Q._--What law is followed by surcharged steam on the application of heat? _A._--The same as that followed by air, in which the increments in volume are very nearly in the same proportion as the increments in temperature; and the increment in volume for each degree of increased temperature is 1/490th part of the volume at 32°. A volume of air which, at the temperature of 32°, occupies 100 cubic feet, will at 212° fill a space of 136.73 cubic feet. The volume which air or steam--out of contact with water--of a given temperature acquires by being heated to a higher temperature, the pressure remaining the same, may be found by the following rule:--To each of the temperatures before and after expansion, add the constant number 458: divide the greater sum by the less, and multiply the quotient by the volume at the lower temperature; the product will give the expanded volume. 174. _Q._--If the relative volumes of steam and water are known, is it possible to tell the quantity of water which should be supplied to a boiler, when the quantity of steam expended is specified? _A._--Yes; at the atmospheric pressure, about a cubic inch of water has to be supplied to the boiler for every cubic foot of steam abstracted; at other pressures, the relative bulk of water and steam may be determined as follows:--To the temperature of steam in degrees of Fahrenheit, add the constant number 458, multiply the sum by 37.3, and divide the product by the elastic force of the steam in pounds per square inch; the quotient will give the volume required. 175. _Q._--Will this rule give the proper dimensions of the pump for feeding the boiler with water? _A._--No; it is necessary in practice that the feed pump should be able to supply the boiler with a much larger quantity of water than what is indicated by these proportions, from the risk of leaks, priming, or other disarrangements, and the feed pump is usually made capable of raising 3-1/2 times the water evaporated by the boiler. About 1/240th of the capacity of the cylinder answers very well for the capacity of the feed pump in the case of low pressure engines, supposing the cylinder to be double acting, and the pump single acting; but it is better to exceed this size. 176. _Q._--Is this rule for the size of the feed pump applicable to the case of high pressure engines? _A._--Clearly not; for since a cylinder full of high pressure steam, contains more water than the same cylinder full of low pressure steam, the size of the feed must vary in the same proportion as the density of the steam. In all pumps a good deal of the effect is lost from the imperfect action of the valves; and in engines travelling at a high rate of speed, in particular, a large part of the water is apt to return, through the suction valve of the pump, especially if much lift be permitted to that valve. In steam vessels moreover, where the boiler is fed with salt water, and where a certain quantity of supersalted water has to be blown out of the boiler from time to time, to prevent the water from reaching too high a degree of concentration, the feed pump requires to be of additional size to supply the extra quantity of water thus rendered necessary. When the feed water is boiling or very hot, as in some engines is the case, the feed pump will not draw from a depth, and will altogether act less efficiently, so that an extra size of pump has to be provided in consequence. These and other considerations which might be mentioned, show the propriety of making the feed pump very much larger than theory requires. The proper proportions of pumps, however, forms part of a subsequent chapter. [1] A table containing the results arrived at by M. Regnault is given in the Key. CHAPTER III. EXPANSION OF STEAM AND ACTION OF THE VALVES. 177. _Q._--What is meant by working engines expansively? _A._--Adjusting the valves, so that the steam is shut off from the cylinder before the end of the stroke, whereby the residue of the stroke is left to be completed by the expanding steam. 178. _Q._--And what is the benefit of that practice? _A._--It accomplishes an important saving of steam, or, what is the same thing, of fuel; but it diminishes the power of the engine, while increasing the power of the steam. A larger engine will be required to do the same work, but the work will be done with a smaller consumption of fuel. If, for example, the steam be shut off when only half the stroke is completed, there will only be half the quantity of steam used. But there will be more than half the power exerted; for although the pressure of the steam decreases after the supply entering from the boiler is shut off, yet it imparts, during its expansion, _some_ power, and that power, it is clear, is obtained without any expenditure of steam or fuel whatever. 179. _Q._--What will be the pressure of the steam, under such circumstances, at the end of the stroke? _A._--If the steam be shut off at half stroke, the pressure of the steam, reckoning the total pressure both below and above the atmosphere, will just be one-half of what it was at the beginning of the stroke. It is a well known law of pneumatics, that the pressure of elastic fluids varies inversely as the spaces into which they are expanded or compressed. For example, if a cubic foot of air of the atmospheric density be compressed into the compass of half a cubic foot, its elasticity will be increased from 15 lbs. on the square inch to 30 lbs. on the square inch; whereas, if its volume be enlarged to two cubic feet, its elasticity will be reduced to 7-1/2 lbs. on the square inch, being just half its original pressure. The same law holds in all other proportions, and with all other gases and vapors, provided their temperature remains unchanged; and if the steam valve of an engine be closed, when the piston has descended through one- fourth of the stroke, the steam within the cylinder will, at the end of the stroke, just exert one-fourth of its initial pressure. 180. _Q._--Then by computing the varying pressure at a number of stages, the average or mean pressure throughout the stroke may be approximately determined? [Illustration: Fig. 32. Diagram showing law of expansion of steam in a cylinder.] _A._--Precisely so. Thus in the accompanying figure, (fig. 32), let E be a cylinder, J the piston, _a_ the steam pipe, _c_ the upper port, _f_ the lower port, _d_ the steam pipe, prolonged to _e_ the equilibrium valve, _g_ the eduction valve, M the steam jacket, N the cylinder cover, O stuffing box, _n_ piston rod, P cylinder bottom; let the cylinder be supposed to be divided in the direction of its length into any number of equal parts, say twenty, and let the diameter of the cylinder represent the pressure of the steam, which, for the sake of simplicity, we may take at 10 lbs., so that we may divide the cylinder, in the direction of its diameter, into ten equal parts. If now the piston be supposed to descend through five of the divisions, and the steam valve then be shut, the pressure at each subsequent position of the piston will be represented by a series, computed according to the laws of pneumatics, and which, if the initial pressure be represented by 1, will give a pressure of .5 at the middle of the stroke, and .25 at the end of it. If this series be set off on the horizontal lines, it will mark out a hyperbolic curve--the area of the part exterior to which represents the total efficacy of the stroke, and the interior area, therefore, represents the diminution in the power of a stroke, when the steam is cut off at one- fourth of the descent. If the squares above the point, where the steam is cut off, be counted, they will be found to amount to 50; and if those beneath that point be counted or estimated, they will be found to amount to about 69. These squares are representative of the power exerted; so that while an amount of power represented by 50 has been obtained by the expenditure of a quarter of a cylinder full of steam, we get an amount of power represented by 69, without any expenditure of steam at all, merely by permitting the steam first used to expand into four times its original volume. 181. _Q._--Then by working an engine expansively, the power of the steam is increased, but the power of the engine is diminished? _A._--Yes. The efficacy of a given quantity of steam is more than doubled by expanding the steam four times, while the efficacy of each stroke is made nearly one-half less. And, therefore, to carry out the expansive principle in practice, the cylinder requires to be larger than usual, or the piston faster than usual, in the proportion in which the expansion is carried out. Every one who is acquainted with simple arithmetic, can compute the terminal pressure of steam in a cylinder, when he knows the initial pressure and the point at which the steam is cut off; and he can also find, by the same process, any pressure intermediate between the first and the last. By setting down these pressures in a table, and taking their mean, he can determine the effect, with tolerable accuracy, of any particular measure of expansion. It is necessary to remark, that it is the total pressure of the steam that he must take; not the pressure above the atmosphere, but the pressure above a perfect vacuum. 182. _Q._--Can you give any rule for ascertaining at one operation the amount of benefit derivable from expansion? _A._--Divide the length of stroke through which the steam expands, by the length of stroke performed with full pressure, which last call 1; the hyperbolic logarithm of the quotient is the increase of efficiency due to expansion. According to this rule it will be found, that if a given quantity of steam, the power of which working at full pressure is represented by 1, be admitted into a cylinder of such a size that its ingress is concluded when one-half the stroke has been performed, its efficacy will be raised by expansion to 1.69; if the admission of the steam be stopped at one-third of the stroke, the efficacy will be 2.10; at one- fourth, 2.39; at one-fifth, 2.61; at one-sixth, 2.79; at one-seventh, 2.95; at one-eighth, 3.08. The expansion, however, cannot be carried beneficially so far as one-eighth, unless the pressure of the steam in the boiler be very considerable, on account of the inconvenient size of cylinder or speed of piston which would require to be adopted, the friction of the engine, and the resistance of vapor in the condenser, which all become relatively greater with a smaller urging force. 183. _Q._--Is this amount of benefit actually realized in practice? _A._--Only in some cases. It appears to be indispensable to the realization of any large amount of benefit by expansion, that the cylinder should be enclosed in a steam jacket, or should in some other way be effectually protected from refrigeration. In some engines not so protected, it has been found experimentally that less benefit was obtained from the fuel by working expansively than by working without expansion--the whole benefit due to expansion being more than counteracted by the increased refrigeration due to the larger surface of the cylinder required to develop the power. In locomotive engines, with outside cylinders, this condition of the advantageous use of expansion has been made very conspicuous, as has also been the case in screw steamers with four cylinders, and in which the refrigerating surface of the cylinders was consequently large. 184. _Q._--The steam is admitted to and from the cylinder by means of a slide or sluice valve? [Illustration: Fig. 33.] _A._--Yes; and of the slide valve there are many varieties; but the kinds most in use are the D valve,--so called from its resemblance to a half cylinder or D in its cross section--and the three ported valve, shown in fig. 33, which consists of a brass or iron box set over the two ports or openings into the cylinder, and a central port which conducts away the steam to the atmosphere or condenser; but the length of the box is so adjusted that it can only cover one of the cylinder ports and the central or eduction port at the same time. The effect, therefore, of moving the valve up and down, as is done by the eccentric, is to establish a connection alternately between each cylinder port and the central passage whereby the steam escapes; and while the steam is escaping from beneath the piston, the position of the valve is such, that a free communication exists between the space above the piston and the steam in the boiler. The piston is thus urged alternately up and down--the valve so changing its position before the piston arrives at the end of the stroke, that the pressure is by that time thrown on the reverse side of the piston, so as to urge it into motion in the opposite direction. 185. _Q._--Is the motion of the valve, then, the reverse of that of the piston? _A._--No. The valve does not move down when the piston moves down, nor does it move down when the piston moves up; but it moves from its mid position, to the extremity of its throw, and back again to its mid position, while the piston makes an upward or downward movement, so that the motion is as it were at right angles to the motion of the piston; or it is the same motion that the piston of another engine, the crank of which is set at right angles with that of the first engine, would acquire. 186. _Q._--Then in a steam vessel the valve of one engine may be worked from the piston of the other? _A._--Yes, it may; or it may be worked from its own connecting rod; and in the case of locomotive engines, this has sometimes been done. 187. _Q._--What is meant by the lead of the valve? _A._--The amount of opening which the valve presents for the admission of the steam, when the piston is just beginning its stroke. It is found expedient that the valve should have opened a little to admit steam on the reverse side of the piston before the stroke terminates; and the amount of this opening, which is given by turning the eccentric more or less round upon the shaft, is what is termed the lead. 188. _Q._--And what is meant by the lap of the valve? _A._--It is an elongation of the valve face to a certain extent over the port, whereby the port is closed sooner than would otherwise be the case. This extension is chiefly effected at that part of the valve where the steam is admitted, or upon the _steam side_ of the valve, as the technical phrase is; and the intent of the extension is to close the steam passage before the end of the stroke, whereby the engine is made to operate to a certain extent expansively. In some cases, however, there is also a certain amount of lap given to the escape or eduction side, to prevent the eduction from being performed too soon when the lead is great; but in all cases there is far less lap on the eduction than on the steam side, very often there is none, and sometimes less than none, so that the valve is incapable of covering both the ports at once. 189. _Q._--What is the usual proportional length of stroke of the valve? _A._--The common stroke of the valve in rotative engines is twice the breadth or depth of the port, and the length of the valve face will then be just the breadth of the port when there is lap on neither the steam nor eduction side. Whatever lap is given, therefore, makes the valve face just so much longer. In some engines, however, the stroke of the valve is a good deal more than twice the breadth of the port; and it is to the stroke of the valve that the amount of lap should properly be referred. 190. _Q._--Can you tell what amount of lap will accomplish any given amount of expansion? _A._--Yes, when the stroke of the valve is known. From the length of the stroke of the piston subtract that part of the stroke which is intended to be accomplished before the steam is cut off; divide the remainder by the length of the stroke of the piston, and extract the square root of the quotient, which multiply by half the stroke of the valve, and from the product take half the lead; the remainder will be the lap required. 191. _Q._--Can you state how we may discover at what point of the stroke the eduction passage will be closed? _A._--To find how much before the end of the stroke the eduction passage will be closed:--to the lap on the steam side add the lead, and divide the sum by half the stroke of the valve; find the arc whose sine is equal to the quotient, and add 90° to it.; divide the lap on the eduction side by half the stroke of the valve, and find the arc whose cosine is equal to the quotient; subtract this arc from the one last obtained, and find the cosine of the remainder; subtract this cosine from 2, and multiply the remainder by half the stroke of the piston; the product is the distance of the piston from the end of the stroke when the eduction passage is closed. 192. _Q._--Can you explain how we may determine the distance of the piston from the end of the stroke, before the steam urging it onward is allowed to escape? _A._--To find how far the piston is from the end of its stroke when the steam that is propelling it by expansion is allowed to escape to the atmosphere or condenser--to the lap on the steam side add the lead; divide the sum by half the stroke of the valve, and find the arc whose sine is equal to the quotient; find the arc whose sine is equal to the lap on the eduction side, divided by half the stroke of the valve; add these two arcs together and subtract 90°; find the cosine of the residue, subtract it from 1, and multiply the remainder by half the stroke of the piston; the product is the distance of the piston from the end of its stroke when the steam that is propelling it is allowed to escape into the atmosphere or condenser. In using these rules, all the dimensions are to be taken in inches, and the answers will be found in inches also. 193. _Q._--Is it a benefit or a detriment to open the eduction passage before the end of the stroke? _A._--In engines working at a high rate of speed, such as locomotive engines, it is very important to open the exhaust passage for the escape of the steam before the end of the stroke, as an injurious amount of back pressure is thus prevented. In the earlier locomotives a great loss of effect was produced from inattention to this condition; and when lap was applied to the valves to enable the steam to be worked expansively, it was found that a still greater benefit was collaterally obtained by the earlier escape of the steam from the eduction passages, and which was incidental to the application of lap to the valves. The average consumption of coke per mile was reduced by Mr. Woods from 40 lbs. per mile to 15 lbs. per mile, chiefly by giving a free outlet to the escaping steam. 194. _Q._--To what extent can expansion be carried beneficially by means of lap upon the valve? _A._--To about one-third of the stroke; that is, the valve may be made with so much lap, that the steam will be cut off when two thirds of the stroke have been performed, leaving the residue to be accomplished by the agency of the expanding steam; but if more lap be put on than answers to this amount of expansion, a very distorted action of the valve will be produced, which may impair the efficiency of the engine. If a further amount of expansion than this is wanted, it may be accomplished by wire drawing the steam, or by so contracting the steam passage that the pressure within the cylinder must decline when the speed of the piston is accelerated, as it is about the middle of the stroke. 195. _Q._--Will you explain how this result ensues? _A._--If the valve be so made as to shut off the steam by the time two thirds of the stroke have been performed, and the steam be at the same time throttled in the steam pipe, the full pressure of the steam within the cylinder cannot be maintained except near the beginning of the stroke where the piston travels slowly; for, as the speed of the piston increases, the pressure necessarily subsides, until the piston approaches the other end of the cylinder, where the pressure would rise again but that the operation of the lap on the valve by this time has had the effect of closing the communication between the cylinder and steam pipe, so as to prevent more steam from entering. By throttling the steam, therefore, in the manner here indicated, the amount of expansion due to the lap may be doubled, so that an engine with lap enough upon the valve to cut off the steam at two-thirds of the stroke, may, by the aid of wire drawing, be virtually rendered capable of cutting off the steam at one-third of the stroke. 196. _Q._--Is this the usual way of cutting off the steam? _A._--No; the usual way of cutting off the steam is by means of a separate valve, termed an expansion valve; but such a device appears to be hardly necessary in ordinary engines. In the Cornish engines, where the steam is cut off in some cases at one-twelfth of the stroke, a separate valve for the admission of steam, other than that which permits its escape, is of course indispensable; but in common rotative engines, which may realize expansive efficacy by throttling, a separate expansion valve does not appear to be required. 197. _Q._--That is, where much expansion is required, an expansion valve is a proper appendage, but where not much is required, a separate expansion valve may be dispensed with? _A._--Precisely so. The wire drawing of the steam causes a loss of part of its power, and the result will not be quite so advantageous by throttling as by cutting off. But for moderate amounts of expansion it will suffice, provided there be lap upon the slide valve. 198. _Q._--Will you explain the structure or configuration of expansion apparatus of the usual construction? [Illustration: Fig 34.] _A._--The structure of expansion apparatus is very various; but all the kinds operate either on the principle of giving such a motion to the slide valve as will enable it to cut off the steam, at the desired point, or on the principle of shutting off the steam by a separate valve in the steam pipe or valve casing. The first class of apparatus has not been found so manageable, and is not in extensive use, except in that form known as the link motion. Of the second class, the most simple probably is the application of a cam giving motion to the throttle valve, or to a valve of the same construction, which either accurately fits the steam pipe, or which comes round to a face, which, however, it is restrained from touching by a suitable construction of the cam. A kind of expansion valve, often employed in marine engines of low speed, is the kind used in the Cornish engines, and known as the equilibrium valve. This valve is represented in fig. 34. It consists substantially of an annulus or bulging cylinder of brass, with a steam-tight face both at its upper and lower edges, at which points it fits accurately upon a stationary seat. This annulus may be raised or lowered without being resisted by the pressure of the steam, and in rotative engines it is usually worked by a cam on the shaft. The expansion cam is put on the shaft in two pieces, which are fastened to each other by means of four bolts passing through lugs, and is fixed to the shaft by keys. A roller at one end of a bell-crank lever, which is connected with the expansion valve, presses against the cam, so that the motion of the lever will work the valve. The roller is kept against the cam by a weight on a lever attached to the same shaft, but a spring is necessary for high speeds. If the cam were concentric with the shaft, the lever which presses upon it would remain stationary, and also the expansion valve; but by the projection of the cam, the end of the lever receives a reciprocating motion, which is communicated to the valve. 199. _Q._--The cam then works the valve? _A._--Yes. The position of the projection of the cam determines the point in relation to the stroke at which the valve is opened, and its circumferential length determines the length of the time during which the valve continues open. The time at which the valve should begin to open is the same under all circumstances, but the duration of its opening varies with the amount of expansion desired. In order to obtain this variable extent of expansion, there are several projections made upon the cam, each of which gives a different degree, or _grade_ as it is usually called, of expansion. These grades all begin at the same point on the cam, but are of different lengths, so that they begin to move the lever at the same time, but differ in the time of returning it to its original position. 200. _Q._--How is the degree of expansion changed? _A._--The change of expansion is effected by moving the roller on to the desired grade; which is done by slipping the lever carrying the roller endways on the shaft or pin sustaining it. 201. _Q._--Are such cams applicable in all cases? _A._--In engines moving at a high rate of speed the roller will be thrown back from the cam by its momentum, unless it be kept against it by means of springs. In some cases I have employed a spring formed of a great number of discs of India rubber to keep the roller against the cam, but a few brass discs require to be interposed to prevent the India rubber discs from being worn in the central hole. 202. _Q._--May not the percussion incident to the action of a cam at a high speed, when the roller is not kept up to the face by springs, be obviated by giving a suitable configuration to the cam itself? _A._--It may at all events be reduced. The outline of the cam should be a parabola, so that the valve may be set in motion precisely as a falling body would be; but it will, nevertheless, be necessary that the roller on which the cam presses should be forced upward by a spring rather than by a counterweight, as there will thus be less inertia or momentum in the mass that has to be moved. 203. _Q._--An additional slide valve is sometimes used for cutting off the steam? _A._--Yes, very frequently; and the slide valve is sometimes on the side or back of the valve casing, and sometimes on the back of the main or distributing valve, and moving with it. 204. _Q._--Are cams used in locomotive engines? _A._--In locomotive engines the use of cams is inadmissible, and other expedients are employed, of which those contrived by Stephenson and by Cabrey operate on the principle of accomplishing the requisite variations of expansion by altering the throw of the slide valve. 205. _Q._--What is Stephenson's arrangement? [Illustration: Fig. 35.] _A._--Stephenson connects the ends of the forward and backward eccentric rods by a link with a curved slot in which a pin upon the end of the valve rod works. By moving this link so as to bring the forward eccentric rod in the same line with the valve rod, the valve receives the motion due to that eccentric; whereas if the backward eccentric rod is brought in a line with the valve rod, the valve gets the motion proper for reversing, and if the link be so placed that the valve rod is midway between the two eccentric rods, the valve will remain nearly stationary. This arrangement, which is now employed extensively, is what is termed "the link motion." It is represented in the annexed figure, fig. 35, where _e_ is the valve rod, which is attached by a pin to an open curved link susceptible of being moved up and down by the bell-crank lever _f''_ _f''_, supported on the centre _g_, and acting on the links _f_, while the valve rod _e_ remains in the same horizontal plane; _d d'_ are the eccentric rods, and the link is represented in its lowest position. The dotted lines _h' h''_ show the position of the eccentric rods when the link is in its highest position, and _l l'_ when in mid position. 206. _Q._--What is Cabrey's arrangement? _A._--Mr. Cabrey makes his eccentric rod terminate in a pin which works into a straight slotted lever, furnished with jaws similar to the jaws on the eccentric rods of locomotives. By raising the pin of the eccentric rod in this slot, the travel of the valve will be varied, and expansive action will be the result. 207. _Q._--What other forms of apparatus are there for working steam expansively? _A._--They are too numerous for description here, but a few of them may be enumerated. Fenton seeks to accomplish the desired object by introducing a spiral feather on the crank axle, by moving the eccentric laterally against which the eccentric is partially turned round so as to cut off the steam at a different part of the stroke. Dodds seeks to attain the same end by corresponding mechanical arrangements. Farcot, Edwards, and Lavagrian cut off the steam by the application of a supplementary valve at the back of the ordinary valve, which supplementary valve is moved by tappets fixed to the valve casing. Bodmer, in 1841, and Meyer, in 1842, employed two slides or blocks fitted over apertures in the ordinary slide valve, and which blocks were approximated or set apart by a right and left handed screw passing through both.[1] Hawthorn, in 1843, employed as an expansion valve a species of frame lying on the ordinary cylinder face upon the outside of the valve, and working up against the steam side of the valve at each end so as to cut off the steam. In the same year Gonzenbach patented an arrangement which consists of an additional slide valve and valve casing placed on the back of the ordinary slide valve casing, and through this supplementary valve the steam must first pass. This supplementary valve is worked by a double ended lever, slotted at one end for the reception of a pin on the valve link, the position of which in the slot determines the throw of the supplementary valve, and the consequent degree of expansion. 208. _Q._--What is the arrangement of expansion valve used in the most approved modern engines? _A._--In modern engines, either marine or locomotive, it is found that if they are fitted with the link motion, as they nearly all are, a very good expansive action can be obtained by giving a suitable adjustment to it, without employing an expansion valve at all. Diagrams taken from engines worked in this manner show a very excellent result, and most of the modern engines trust for their expansive working to the link motion and the throttle valve. [1] In 1838 I patented an arrangement of expansion valve, consisting of two movable plates set upon the ordinary slide valve, and which might be drawn together or asunder by means of a right and left handed screw passing through both plates. The valve spindle was hollow, and a prolongation of the screw passed up through it, and was armed on the top with a small wheel, by means of which the plates might be adjusted while the engine was at work. In 1839 I fitted an expansion valve in a steam vessel, consisting of two plates, connected by a rod, and moved by tappets up against the steam edges of the valve. In another steam vessel I fitted the same species of valve, but the motion was not derived from tappets, but from a moving part of the engine, though at the moderate speed at which these engines worked I found tappets to operate well and make little noise. In 1837 I employed, as an expansion valve, a rectangular throttle valve, accurately fitting a bored out seat, in which it might be made to revolve, though it did not revolve in working. This valve was moved by a pin in a pinion, making two revolutions for every revolution of the engine, and the configuration of the seat determined the amount of the expansion. In 1855 I have again used expansion valves of this construction in engines making one hundred revolutions per minute, and with perfectly satisfactory results.-- J.B. CHAPTER IV. MODES OF ESTIMATING THE POWER AND PERFORMANCE OF ENGINES AND BOILERS. HORSES POWER. 209. _Q._--What do you understand by a horse power? _A._--An amount of mechanical force that will raise 33,000 lbs. one foot high in a minute. This standard was adopted by Mr. Watt, as the average force exerted by the strongest London horses; the object of his investigation being to enable him to determine the relation between the power of a certain size of engine and the power of a horse, so that when it was desired to supersede the use of horses by the erection of an engine, he might, from the number of horses employed, determine the size of engine that would be suitable for the work. 210. _Q._--Then when we talk of an engine of 200 horse power, it is meant that the impelling efficacy is equal to that of 200 horses, each lifting 33,000 lbs. one foot high in a minute? _A._--No, not now; such was the case in Watt's engines, but the capacity of cylinder answerable to a horse power has been increased by most engineers since his time, and the pressure on the piston has been increased also, so that what is now called a 200 horse power engine exerts, almost in every case, a greater power than was exerted in Watt's time, and a horse power, in the popular sense of the term, has become a mere conventional unit for expressing a certain size of engine, without reference to the power exerted. 211. _Q._--Then, each nominal horse power of a modern engine may raise much more than 33,000 lbs. one foot high in a minute? _A._--Yes; some raise 52,000 lbs., others 60,000 lbs., and others 66,000 lbs., one foot high in a minute by each nominal horse power. Some engines indeed work as high as five times above the nominal power, and therefore no comparison can be made between the performances of different engines, unless the power actually exerted be first discovered. 212. _Q._--How is the power actually exerted by engines ascertained? _A._--By means of an instrument called the indicator, which is a miniature cylinder and piston attached to the cylinder cover of the main engine, and which indicates, by the pressure exerted on a spring, the amount of pressure or vacuum existing within the cylinder. From this pressure, expressed in pounds per square inch, deduct a pound and a half of pressure for friction, the loss of power in working the air pump, &c.; multiply the area of the piston in square inches by this residual pressure, and by the motion of the piston, in feet per minute, and divide by 33,000; the quotient is the actual number of horses power of the engine. The same result is attained by squaring the diameter of the cylinder, multiplying by the pressure per square inch, as shown by the indicator, less a pound and a half, and by the motion of the piston, in feet per minute, and dividing by 42,017. 213. _Q._ How is the nominal power of an engine ascertained? _A._--Since the nominal power is a mere conventional expression, it is clear that it must be determined by a merely conventional process. The nominal power of ordinary condensing engines may be ascertained by the following rule: multiply the square of the diameter of the cylinder in inches, by the velocity of the piston in feet per minute, and divide the product by 6,000; the quotient is the number of nominal horses power. In using this rule, however, it is necessary to adopt the speed of piston prescribed by Mr. Watt, which varies with the length of the stroke. The speed of piston with a 2 feet stroke is, according to his system, 160 per minute; with a 2 ft. 6 in. stroke, 170; 3 ft., 180; 3 ft. 6 in., 189; 4 ft., 200; 5 ft., 215; 6 ft., 228; 7 ft., 245; 8 ft., 256 ft. 214. _Q._--Does not the speed of the piston increase with the length of the stroke? _A._--It does: the speed of the piston varies nearly as the cube root of the length of the stroke. 215. _Q._--And may not therefore some multiple of the cube root of the length of the stroke be substituted for the velocity of the piston in determining the nominal power? _A._--The substitution is quite practicable, and will accomplish some simplification, as the speed of piston proper for the different lengths of stroke cannot always be remembered. The rule for the nominal power of condensing engines when thus arranged, will be as follows: multiply the square of the diameter of the cylinder in inches by the cube root of the stroke in feet, and divide the product by 47; the quotient is the number of nominal horses power of the engine, supposing it to be of the ordinary condensing description. This rule assumes the existence of a uniform effective pressure upon the piston of 7 lbs. per square inch; Mr. Watt estimated the effective pressure upon the piston of his 4 horse power engines at 6-8 lbs. per square inch, and the pressure increased slightly with the power, and became 6.94 lbs. per square inch in engines of 100 horse power; but it appears to be more convenient to take a uniform pressure of 7 lbs. for all powers. Small engines, indeed, are somewhat less effective in proportion than large ones, but the difference can be made up by slightly increasing the pressure in the boiler; and small boilers will bear such an increase without inconvenience. 216. _Q._--How do you ascertain the power of high pressure engines? _A._--The actual power is readily ascertained by the indicator, by the same process by which the actual power of low pressure engines is ascertained. The friction of a locomotive engine when unloaded is found by experiment to be about 1 lb. per square inch on the surface of the pistons, and the additional friction caused by any additional resistance is estimated at about .14 of that resistance; but it will be a sufficiently near approximation to the power consumed by friction in high pressure engines, if we make a deduction of a pound and a half from the pressure on that account, as in the case of low pressure engines. High pressure engines, it is true, have no air pump to work; but the deduction of a pound and a half of pressure is relatively a much smaller one where the pressure is high, than where it does not much exceed the pressure of the atmosphere. The rule, therefore, for the actual horse power of a high pressure engine will stand thus: square the diameter of the cylinder in inches, multiply by the pressure of the steam in the cylinder per square inch less 1-1/2 lb., and by the speed of the piston in feet per minute, and divide by 42,017; the quotient is the actual horse power. 217. _Q._--But how do you ascertain the nominal horse power of high pressure engines? _A._--The nominal horse power of a high pressure engine has never been defined; but it should obviously hold the same relation to the actual power as that which obtains in the case of condensing engines, so that an engine of a given nominal power may be capable of performing the same work, whether high pressure or condensing. This relation is maintained in the following rule, which expresses the nominal horse power of high pressure engines: multiply the square of the diameter of the cylinder in inches by the cube root of the length of stroke in feet, and divide the product by 15.6. This rule gives the nominal power of a high pressure engine three times greater than that of a low pressure engine of the same dimensions; the average effective pressure being taken at 21 lbs. per square inch instead of 7 lbs., and the speed of the piston in feet per minute being in both rules 128 times the cube root of the length of stroke.[1] 218. _Q._--Is 128 times the cube root of the stroke in feet per minute the ordinary speed of all engines? _A._--Locomotive engines travel at a quicker speed--an innovation brought about not by any process of scientific deduction, but by the accidents and exigencies of railway transit. Most other engines, however, travel at about the speed of 128 times the cube root of the stroke in feet; but some marine condensing engines of recent construction travel at as high a rate as 700 feet per minute. To mitigate the shock of the air pump valves in cases in which a high speed has been desirable, as in the case of marine engines employed to drive the screw propeller without intermediate gearing, India rubber discs, resting on a perforated metal plate, are now generally adopted; but the India rubber should be very thick, and the guards employed to keep the discs down should be of the same diameter as the discs themselves. 219. _Q._--Can you suggest any eligible method of enabling condensing engines to work satisfactorily at a high rate of speed? _A._--The most feasible way of enabling condensing engines to work satisfactorily at a high speed, appears to lie in the application of balance weights to the engine, so as to balance the momentum of its moving parts, and the engine must also be made very strong and rigid. It appears to be advisable to perform the condensation partly in the air pump, instead of altogether in the condenser, as a better vacuum and a superior action of the air pump valves will thus be obtained. Engines constructed upon this plan may be driven at four times the speed of common engines, whereby an engine of large power may be purchased for a very moderate price, and be capable of being put into a very small compass; while the motion, from being more equable, will be better adapted for most purposes for which a rotary motion is required. Even for pumping mines and blowing iron furnaces, engines of this kind appear likely to come into use, for they are more suitable than other engines for driving the centrifugal pump, which in many cases appears likely to supersede other kinds of pumps for lifting water; and they are also conveniently applicable to the driving of fans, which, when so arranged that the air condensed by one fan is employed to feed another, and so on through a series of 4 or 5, have succeeded in forcing air into a furnace with a pressure of 2-1/2 lbs. on the square inch, and with a far steadier flow than can be obtained by a blast engine with any conceivable kind of compensating apparatus. They are equally applicable if blast cylinders be employed. 220. _Q._--Then, if by this modification of the engine you enable it to work at four times the speed, you also enable it to exert four times the power? _A._--Yes; always supposing it to be fully supplied with steam. The nominal power of this new species of engine can readily be ascertained by taking into account the speed of the piston, and this is taken into account by the Admiralty rule for power. 221. _Q._--What is the Admiralty rule for determining the power of an engine? _A._--Square the diameter of the cylinder in inches, which multiply by the speed of the piston in feet per minute, and divide by 6,000; the quotient is the power of the engine by the Admiralty rule.[2] 222. _Q._--The high speed engine does not require so heavy a fly wheel as common engines? _A._--No; the fly wheel will be lighter, both by virtue of its greater velocity of rotation, and because the impulse communicated by the piston is less in amount and more frequently repeated, so as to approach more nearly to the condition of a uniform pressure. 223. _Q._--Can nominal be transformed into actual horse power? _A._--No; that is not possible in the case of common condensing engines. The actual power exerted by an engine cannot be deduced from its nominal power, neither can the nominal power be deduced from the power actually exerted, or from anything else than the dimensions of the cylinder. The actual horse power being a dynamical unit, and the nominal horse power a measure of capacity of the cylinder, are obviously incomparable things. 224. _Q._--That is, the _nominal_ power is a commercial unit by which engines are bought and sold, and the _actual_ power a scientific unit by which the quality of their performance is determined? _A._--Yes; the nominal power is as much a commercial measure as a yard or a bushel, and is not a thing to be ascertained by any process of science, but to be fixed by authority in the same manner as other measures. The actual power, on the contrary, is a mechanical force or dynamical effort capable of raising a given weight through a given distance in a given time, and of which the amount is ascertainable by scientific investigation. 225. _Q._--Is there any other measure of an actual horse power than 33,000 lbs. raised one foot high in the minute? _A._--There cannot be any _different_ measure, but there are several equivalent measures. Thus the evaporation of a cubic foot of water in the hour, or the expenditure of 33 cubic feet of low pressure steam per minute, is reckoned equivalent to an actual horse power, or 528 cubic feet of water raised one foot high in the minute involves the same result. [1] Tables of the horse power of both high and low pressure engines are given in the Key. [2] Example.--What is the power of an engine of 42 inches diameter, 3-1/2 feet stroke, and making 85 strokes per minute? The speed of the piston will be 7 (the length of a double stroke) x 85 = 595 feet per minute. Now 42 x 42 = 1,764 x 595 = 1,049,580 / 6,000 = 175 horses power. DUTY OF ENGINES AND BOILERS. 226. _Q._--What is meant by the duty of a engine? _A._--The work done in relation to the fuel consumed. 227. _Q._--And how is the duty ascertained? _A._--In ordinary mill or marine engines it can only be ascertained by the indicator, as the load upon such engines is variable, and cannot readily be determined; but in the case of engines pumping water, where the load is constant, the number of strokes performed by the engine will represent the work done, and the amount of work done by a given quantity of coal represents the duty. In Cornwall the duty of an engine is expressed by the number of millions of pounds raised one foot high by a bushel, or 94 lbs. of Welsh coal. A bushel of Newcastle coal will only weigh 84 Lbs.; and in comparing the duty of a Cornish engine with the performance of an engine in some locality where a different kind of coal is used, it is necessary to pay regard to such variations. 228. _Q._--Can you tell the duty of an engine when you know its consumption of coal per horse power per hour? _A._--Yes, if the power given be the actual, and not the nominal, power. Divide 166.32 by the number of pounds of coal consumed per actual horse power per hour; the quotient is the duty in millions of pounds. If you already have the duty in millions of pounds, and wish to know the equivalent consumption in pounds per actual horse power per hour, divide 166.32 by the duty in millions of pounds; the quotient is the consumption per actual horse power per hour. The duty of a locomotive engine is expressed by the weight of coke it consumes in transporting a ton through the distance of one mile upon a railway; but this is a very imperfect method of representing the duty, as the tractive efficacy of a pound of coke becomes less as the speed of the locomotive becomes greater; and the law of variation is not accurately known. 229. _Q._--What amount of power is generated in good engines of the ordinary kind by a given weight of coal? _A._--The duty of different kinds of engines varies very much, and there are also great differences in the performance of different engines of the same class. In ordinary rotative condensing engines of good construction, 10 lbs. of coal per nominal horse power per hour is a common consumption; but such engines exert nearly twice their nominal power, so that the consumption per actual horse power per hour may be taken at from 5 to 6 lbs. Engines working very expansively, however, attain an economy much superior to this. The average duty of the pumping engines in Cornwall is about 60,000,000 lbs. raised 1 ft. high by a bushel of Welsh coals, which weighs 94 lbs. This is equivalent to a consumption of 3.1 lbs. of coal per actual horse power per hour; but some engines reach a duty of above 100,000,000, or 1.74 lbs. of coal per actual horse power per hour. Locomotives consume from 8 to 10 lbs. of coke in evaporating a cubic foot of water, and the evaporation of a cubic foot of water per hour may be set down as representing an actual horse power in locomotives as well as in condensing engines, if expansion be not employed. When the locomotive is worked expansively, however, there is of course a less consumption of water and fuel per horse power, or per ton per mile, than when the full pressure is used throughout the stroke; and most locomotives now operate with as much expansion as can be conveniently given by the slide valves. 230. _Q._--But is not the evaporative power of locomotives affected materially by the proportions of the boiler? _A._--Yes, but this may be said of all boilers; but in locomotive boilers, perhaps, the effect of any misproportion becomes more speedily manifest. A high temperature of the fire box is found to be conducive to economy of fuel; and this condition, in its turn, involves a small area of grate bars. The heating surface of locomotive boilers should be about 80 square feet for each square foot of grate bars, and upon each foot of grate bars about 1 cwt. of coke should be burnt in the hour. 231. _Q._--Probably the heat is more rapidly absorbed when the temperature of the furnace is high? _A._--That seems to be the explanation. The rapidity with which a hot body imparts heat to a colder, varies as the square of the difference of temperature; so that if the temperature of the furnace be very high, the larger part of the heat passes into the water at the furnace, thereby leaving little to be transmitted by the tubes. If, on the contrary, the temperature of the furnace be low, a large part of the heat will pass into the tubes, and more tube surface will be required to absorb it. About 16 cubic feet of water should be evaporated by a locomotive boiler for each, square foot of fire grate, which, with the proportion of heating surface already mentioned, leaves 5 square feet of heating surface to evaporate a cubic foot of water in the hour. This is only about half the amount of surface usual in land and marine boilers per cubic foot evaporated, and its small amount is due altogether to the high temperature of the furnace, which, by the rapidity of transmission it causes, is tantamount to an additional amount of heating surface. 232. _Q._--You have stated that the steam and vacuum gauges are generally glass tubes, up which mercury is forced by the steam or sucked by the vacuum? _A._--Vacuum gauges are very often of this construction, but steam gauges more frequently consist of a small iron tube, bent like the letter U, and into which mercury is poured. The one end of this tube communicates with the boiler, and the other end with the atmosphere; and when the pressure of the steam rises in the boiler, the mercury is forced down in the leg communicating with the boiler and rises in the other leg, and the difference of level in the legs denotes the pressure of the steam. In this gauge a rise of the mercury one inch in the one leg involves a difference of the level between the two legs of two inches, and an inch of rise is, therefore, equivalent to two inches of mercury, or a pound of pressure. A small float of wood is placed in the open leg to show the rise or fall of the mercury, and this leg is surmounted by a brass scale, graduated in inches, to the marks of which the float points. 233. _Q._--What other kinds of steam and vacuum gauges are there? _A._--There are many other kinds; but probably Bourdon's gauges are now in more extended use than, any other, and their operation has been found to be satisfactory in practice. The principle of their action may be explained to be, that a thin elliptical metal tube, if bent into a ring, will seek to coil or uncoil itself if subjected to external or internal pressure, and to an extent proportional to the pressure applied. The end of the tube is sharpened into an index, and moves to an extent corresponding to the pressure applied to the tube; but in the more recent forms of this apparatus, a dial and a hand, like those of a clock, are employed, and the hand is moved round by a toothed sector connected to the tube, and which sector acts on a pinion attached to the hand. Mr. Shank, of Paisley, has lately introduced a form of steam gauge like a thermometer, with a flattened bulb; and the pressure of the steam, by compressing the bulb, causes the mercury to rise to a point proportional to the pressure applied. THE INDICATOR. 234. _Q._--You have already stated that the actual power of an engine is ascertained by an instrument called the indicator, which consists of a small cylinder with a piston moving against a spring, and compressing it to an extent answerable to the pressure of the steam. Will you explain further the structure and mode of using that instrument? [Illustration: Fig. 36] _A._--The structure of the common form of indicator will be most readily apprehended by a reference to fig. 36, which is a McNaught's indicator. Upon a movable barrel A, a piece of paper is wound, the ends of which are secured by the slight brass clamps shown in the drawing. The barrel is supported by the bracket _b_, proceeding from the body of the indicator, and at the bottom of the barrel a watch spring is coiled with one end attached to the barrel and the other end to the bracket, so that when the barrel is drawn round by a string wound upon its lower end like a roller blind, the spring returns the barrel to its original position, when the string is relaxed. The string is attached to some suitable part of the engine, and at every stroke the string is drawn out, turning round the barrel, and the barrel is returned again by the spring on the return stroke. 235. _Q_--But in what way can these reciprocations of the barrel determine the power of the engine? _A._--They do not determine it of themselves, but are only part of the operation. In the inside of the cylinder _c_ there is a small piston moving steam tight in a cylinder of which _d_ is the piston rod, and _e_ a spiral spring of steel, which the piston, when forced upwards by the steam or sucked downwards by the vacuum, either compresses or extends; _f_ is a cock attached to the cylinder of the indicator, and which is screwed into the cylinder cover. It is obvious that, so soon as this cock is opened, the piston will be forced up when the space above the piston of the engine is opened to the boiler, and sucked down when that space is opened to the condenser--in each case to an extent proportionate to the pressure of the steam or the perfection of the vacuum, the top of the piston _c_ being open to the atmosphere. A pencil, _p_, with a knife hinge, is inserted into the piston rod, at _e_, and the point of the pencil bears upon the surface of the paper wound upon the drum A. If the drum A did not revolve, this pencil would merely trace on the paper a vertical line; but as the drum A moves round and back again every stroke of the engine, and as the pencil moves up and down again every stroke of the engine, the combined movements trace upon the paper a species of rectangle, which is called an indicator diagram; and the nature of this diagram determines the nature of the engine's performance. 236. _Q._--How does it do this? _A._--It is clear that if the pencil was moved up instantaneously to the top of its stroke, and was also moved down instantaneously to the bottom of its stroke, and if it remained without fluctuation while at the top and bottom, the figure described by the pencil would be a perfect rectangle, of which the vertical height would represent the total pressure of the steam and vacuum, and therefore the total pressure urging the piston of the engine. But in practice the pencil will neither rise nor fall instantaneously, nor will it remain at a uniform height throughout the stroke. If the steam be worked expansively the pressure will begin to fall so soon as the steam is cut off; and at the end of the stroke, when the steam comes to be discharged, the subsidence of pressure will not be instantaneous, but will occupy an appreciable time. It is clear, therefore, that in no engine can the diagram described by an indicator be a complete rectangle; but the more nearly it approaches to a rectangle, the larger will be the power produced at every stroke with any given pressure, and the area of the space included within the diagram will in every case accurately represent the power exerted by the engine during that stroke. 237. _Q._--And how is this area ascertained? _A._--It may be ascertained in various ways; but the usual mode is to take the vertical height of the diagram at a number of equidistant points on a base line, and then to take the mean of these several heights as representative of the mean pressure actually urging the piston. Now if you have the pressure on the piston per square inch, and if you know the number of square inches in its area, and the velocity with which it moves in feet per minute, you have obviously the dynamical effort of the engine, or, in other words, its actual power. 238. _Q._--How is the base line you have referred to obtained? _A._--In proceeding to take an indicator diagram, the first thing to be done is to allow the barrel to make two or three reciprocations with the pencil resting against it, before opening the cock attached to the cylinder. There will thus be traced a horizontal line, which is called the _atmospheric line_, and in condensing engines, a part of the diagram will be above and a part of it below this line; whereas, in high pressure engines the whole of the diagram will be above this line. Upon this line the vertical ordinates may be set off at equal distances, or upon any base line parallel to it; but the usual course is to erect the ordinates on the atmospheric line. 239. _Q._--Will you give an example of an indicator diagram? [Illustration: Fig. 37] _A._--Fig. 37 is an indicator diagram taken from a low pressure engine, and the waving line _a b c_, forming a sort of irregular parallelogram, is that which is described by the pencil. The atmospheric line is represented by the line o o. The scale at the side shows the pressure of the steam, which in this engine rose to about 9 lbs. per square inch, and the vacuum fell to 11 lbs. The steam begins to be cut off when, about one-fourth of the stroke has been performed, and the pressure consequently falls. 240. _Q._--Is this species of indicator which you have just described applicable to locomotive engines? _A._--It is no doubt applicable under suitable conditions; but another species of indicator has been applied by Mr. Gooch to locomotive engines, which presents several features of superiority for such a purpose. This indicator has its cylinder placed horizontally; and its piston compresses two elliptical springs; a slide valve is substituted for a cock, to open or close the communication with the engine. The top of the piston rod of this indicator is connected to the short arm of a smaller lever, to the longer arm of which the pencil is attached, and the pencil has thus a considerably larger amount of motion than the piston; but it moves in the arc of a circle instead of in a straight line. The pencil marks on a web of paper, which is unwound from one drum and wound on to another, so that a succession of diagrams are taken without the necessity of any intermediate manipulation. 241. _Q._--These diagrams being taken with a pencil moving in an arc, will be of a distorted form? _A._--They will not be of the usual form, but they may be easily translated into the usual form. It is undoubtedly preferable that the indicator should act immediately in the production of the final form of diagram. DYNAMOMETER, GAUGES, AND CATARACT. 242. _Q._--What other gauges or instruments are there for telling the state, or regulating the power of an engine? _A._--There is the counter for telling the number of strokes the engine makes, and the dynamometer for ascertaining the tractive power of steam vessels or locomotives; then there are the gauge cocks, and glass tubes, or floats, for telling the height of water in the boiler; and in pumping engines there is the cataract for regulating the speed of the engine. 243. _Q._--Will you describe the mechanism of the counter? _A._--The counter consists of a train of wheel work, so contrived that by every stroke of the engine an index hand is moved forward a certain space, whereby the number of strokes made by the engine in any given time is accurately recorded. In most cases the motion is communicated by means of a detent,--attached to some reciprocating part of the engine,--to a ratchet wheel which gives motion to the other wheels in its slow revolution; but it is preferable to derive the motion from some revolving part of the engine by means of an endless screw, as where the ratchet is used the detent will sometimes fail to carry it round the proper distance. In the counter contrived by Mr. Adie, an endless screw works into the rim of two small wheels situated on the same axis, but one wheel having a tooth more than the other, whereby a differential motion is obtained; and the difference in the velocity of the two wheels, or their motion upon one another, expresses the number of strokes performed. The endless screw is attached to some revolving part of the engine, whereby a rotatory motion is imparted to it; and the wheels into which the screws work hang down from it like a pendulum, and are kept stationary by the action of gravity. 244. _Q._--What is the nature of the dynamometer? _A._--The dynamometer employed for ascertaining the traction upon railways consists of two flat springs joined together at the ends by links, and the amount of separation of the springs at the centre indicates, by means of a suitable hand and dial, the force of traction. A cylinder of oil, with a small hole through its piston, is sometimes added to this instrument to prevent sudden fluctuations. In screw vessels the forward thrust of the screw is measured by a dynamometer constructed on the principle of a weighing machine, in which a small spring pressure at the index will balance a very great pressure where the thrust is employed; and in each case the variations of pressure are recorded by a pencil on a sheet of paper, carried forward by suitable mechanism, whereby the mean thrust is easily ascertained. The tractive force of paddle wheel steamers is ascertained by a dynamometer fixed on shore, to which the floating vessel is attached by a rope. Sometimes the power of an engine is ascertained by a friction break dynamometer applied to the shaft. 345. _Q._--What will determine the amount of thrust shown by the dynamometer? _A._--In locomotives and in paddle steamers it will be determined by the force turning the wheels, and by the smallness of the diameter of the wheels; for with small wheels the thrust will be greater than with large wheels. In screw vessels the thrust will be determined by the force turning round the screw, and by the smallness of the screw's pitch; for with any given force of torsion a fine pitch of screw will give a greater thrust than a coarse pitch of screw, just as is the case when a screw works in a solid nut. 246. _Q._--Will you explain the use of the glass gauges affixed to the boiler? _A._--The glass gauges are tubes affixed to the fronts of boilers, by the aid of which the height of the water within the boilers is readily ascertainable, for the water will stand at the same height in the tube as in the boiler, with which there is a communication maintained both at the top and bottom of the tube by suitable stopcocks. The cocks connecting the glass tube with the boiler should always be so constructed that the tube may be blown through with the steam, to clear it of any internal concretion that may impair its transparency; and the construction of the sockets in which the tube is inserted should be such, that, even when there is steam in the boiler, a broken tube may be replaced with facility. 247. _Q._--What then are the gauge cocks? _A._--The gauge cocks are cocks penetrating the boiler at different heights, and which, when opened, tell whether it is water or steam that exists at the level at which they are respectively inserted. It is unsafe to trust to the glass gauges altogether as a means of ascertaining the water level, as sometimes they become choked, and it is necessary, therefore, to have gauge cocks in addition; but if the boiler be short of steam, and a partial vacuum be produced within it, the glass gauges become of essential service, as the gauge cocks will not operate in such a case, for though opened, instead of steam and water escaping from them, the air will rush into the boiler. It is expedient to carry a pipe from the lower end of the glass tube downward into the water of the boiler, and a pipe from the upper end upward into the steam in the boiler, so as to prevent the water from boiling down through the tube, as it might otherwise do, and prevent the level of the water from being ascertainable. The average level of water in the boiler should be above the centre of the tube; and the lowest of the gauge cocks should always run water, and the highest should always blow steam. 248. _Q._--Is not a float sometimes employed to indicate the level of the water in the boiler? _A._--A float for telling the height of water in the boiler is employed only in the case of land boilers, and its action is like that of a buoy floating on the surface, which, by means of a light rod passing vertically through the boiler, shows at what height the water stands. The float is usually formed of stone or iron, and is so counterbalanced as to make its operation the same as if it were a buoy of timber; and it is generally put in connection with the feed valve, so that in proportion as the float rises, the supply of feed water is diminished. The feed water in land boilers is admitted from a small open cistern, situated at the top of an upright or stand pipe set upon the boiler, and in which there is a column of water sufficiently high to balance the pressure of the steam. 249. _Q._--What is the cataract which is employed to regulate the speed of pumping engines? [Illustration: Fig. 38. ] _A._--The cataract consists of a small pump-plunger _b_ and barrel, set in a cistern of water, the barrel being furnished on the one side with a valve, _c_, opening inwards, through which the water obtains admission to the pump chamber from the cistern, and on the other by a plug, _d_, through which, if the plunger be forced down, the water must pass out of the pump chamber. The engine in the upward stroke of the piston, which is accomplished by the preponderance of weight at the pump end of the beam, raises up the plunger of the cataract by means of a small rod,--the water entering readily through the valve already referred to; and when the engine reaches the top of the stroke, it liberates the rod by which the plunger has been drawn up, and the plunger then descends by gravity, forcing out the water through the cock, the orifice of which has previously been adjusted, and the plunger in its descent opens the injection valve, which causes the engine to make a stroke. 250. _Q._--Suppose the cock of the cataract be shut? _A._--If the cock of the cataract be shut, it is clear that the plunger cannot descend at all, and as in that case the injection valve cannot be opened, the engine must stand still; but if the cock be slightly opened, the plunger will descend slowly, the injection valve will slowly open, and the engine will make a gradual stroke as it obtains the water necessary for condensation. The extent to which the cock is open, therefore, will regulate the speed with which the engine works; so that, by the use of the cataract, the speed of the engine may be varied to suit the variations in the quantity of water requiring to be lifted from the mine. In some cases an air cylinder, and in other cases an oil cylinder, is employed instead of the apparatus just described; but the principle on which the whole of these contrivances operate is identical, and the only difference is in the detail. 251. _Q._--You have now shown that the performance of an engine is determinable by the indicator; but how do you determine the power of the boiler? _A._--By the quantity of water it evaporates. There is, however, no very convenient instrument for determining the quantity of water supplied to a boiler, and the consequence is that this element is seldom ascertained. CHAPTER V. PROPORTION OF BOILERS. HEATING AND FIRE GRATE SURFACE. 252. _Q._--What are the considerations which must chiefly be attended to in settling the proportions of boilers? _A._--In the first place there must be sufficient grate surface to enable the quantity of coal requisite for the production of the steam to be conveniently burnt, taking into account the intensity of the draught; and in the next place there must be a sufficient flue surface readily to absorb the heat thus produced, so that there may be no needless waste of heat by the chimney. The flues, moreover, must have such an area, and the chimney must be of such dimensions, as will enable a suitable draught through the fire to be maintained; and finally the boiler must be made capable of containing such supplies of water and steam as will obviate inconvenient fluctuations in the water level, and abate the risk of water being carried over into the engine with the steam. With all these conditions the boiler must be as light and compact as possible, and must be so contrived as to be capable of being cleaned and repaired with facility. 253. _Q._--Supposing, then, that you had to proportion a boiler, which should be capable of supplying steam sufficient to propel a steam vessel or railway train at a given speed, or to perform any other given work, how would you proceed? _A._--I would first ascertain the resistance which had to be overcome, and the velocity with which it was necessary to overcome it. I should then be in a position to know what pressure and volume of steam were required to overcome the resistance at the prescribed rate of motion; and, finally, I should allow a sufficient heating and fire grate surface in the boiler according to the kind of boiler it was, to furnish the requisite quantity of steam, or, in other words, to evaporate the requisite quantity of water. 254. _Q._--will you state the amount of heating surface and grate surface necessary to evaporate a given quantity of water? _A._--The number of square feet of heating or flue surface, required to evaporate a cubic foot of water per hour, is about 70 square feet in Cornish boilers, 8 to 11 square feet in land and marine boilers, and 5 or 6 square feet in locomotive boilers. The number of square feet of heating surface per square foot of fire grate, is from 13 to 15 square feet in wagon boilers; about 40 square feet in Cornish boilers; and from 50 to 90 square feet in locomotive boilers. About 80 square feet in locomotives is a very good proportion. 255. _Q._--What is the heating surface of boilers per horse power? _A._--About 9 square feet of flue and furnace surface per horse power is the usual proportion in wagon boilers, reckoning the total surface as effective surface, if the boilers be of a considerable size; but in the case of small boilers the proportion is larger. The total heating surface of a two horse power wagon boiler is, according to Boulton and Watt's proportions, 30 square feet, or 15 ft. per horse power; whereas, in the case of a 45 horse power boiler the total heating surface is 438 square feet, or 9.6 ft. per horse power. In marine boilers nearly the same proportions obtain. The original boilers of the Great Western steamer, by Messrs. Maudslay, were proportioned with about 10 square feet of flue and furnace surface per horse power, reckoning the total amount as effective; but in the boilers of the Retribution, by the same makers, but of larger size, a somewhat smaller proportion of heating surface was adopted. Boulton and Watt have found that in their marine flue boilers, 9 square feet of flue and furnace surface are requisite to boil off a cubic foot of water per hour, which is the proportion of heating surface that is allowed in their land boilers per horse power; but inasmuch as in most modern engines, and especially in marine engines, the nominal considerably exceeds the actual power, they allow 11 or 12 square feet of heating surface per nominal horse power in their marine boilers, and they reckon as effective heating surface the tops of the flues, and the whole of the sides of the flues, but hot the bottoms. For their land engines they still retain Mr. Watt's standard of power, which makes the actual and the nominal power identical; and an actual horse power is the equivalent of a cubic foot of water raised into steam every hour. 256. _Q._--What is the proper proportion of fire grate per horse power? _A._--Boulton and Watt allow 0.64 of a square foot area of grate bars per nominal horse power in their marine boilers, and a good effect arises from this proportion; but sometimes so large an area of fire grate cannot be conveniently got, and the proportion of half a square foot per horse power, which is the proportion adopted in the original boiler of the Great Western, seems to answer very well in engines working with a moderate pressure, and with some expansion; and this proportion is now very widely adopted. With this allowance, there will be 22 to 24 square feet of heating surface per square foot of fire grate; and if the consumption of fuel be taken at 6 lbs. per nominal horse power per hour, there will be about 12 lbs. of coal consumed per hour on each square foot of grate. The furnaces should not be more than 6 ft. long, as, if much longer than this, it will be impossible to work them properly for any considerable length of time, as they will become choked with clinker at the back ends. 257. _Q._--What quantity of fuel is usually consumed per hour on each square foot of fire grate? _A._--The quantity of fuel burned on each square foot of fire grate per hour, varies very much in different boilers; in wagon boilers it is from 10 to 13 lbs.; in Cornish boilers from 3-1/2 to 4 lbs.; and in locomotive boilers from 80 to 150 lbs.; but about 1 cwt. per hour is a good proportion in locomotives, as has been already explained. CALORIMETER AND VENT. 258. _Q._--In what manner are the proper sectional area and the proper capacity of the flue of a boiler determined? _A._--The proper collective area for the escape of the smoke and flame over the furnace bridges in marine boilers is 19 square inches per nominal horse power, according to Boulton and Watt's practice, and for the sectional area of the flue they allow 18 square inches per horse power. The sectional area of the flue in square inches is what is termed the _calorimeter_ of the boiler, and the calorimeter divided by the length of the flue in feet is what is termed the _vent_. In marine flue boilers of good construction the vent varies between the limits of 20 and 25, according to the size of the boiler and other circumstances--the largest boilers having generally the largest vents; and the calorimeter divided by the vent will give the length of the flue in feet. The flues of all flue boilers diminish in their calorimeter as they approach the chimney, as the smoke contracts in its volume in proportion as it parts with its heat. 259. _Q._--Is the method of determining the dimensions of a boiler flue, by a reference to its vent and calorimeter, the method generally pursued? _A._--It is Boulton and Watt's method; but some very satisfactory boilers have been made by allowing a proportion of 0.6 of a square foot of fire grate per nominal horse power, and making the sectional area of the flue at the largest part 1/7th of the area of fire grate, and at the smallest part, where it enters the chimney, 1/11th of the area of the fire grate. These proportions are retained whether the boiler is flue or tubular, and from 14 to 16 square feet of tube surface is allowed per nominal horse power. 260. _Q._--Are the proportions of vent and calorimeter, taken by Boulton and Watt for marine flue boilers, applicable also to wagon and tubular boilers? _A._--No. In wagon and tubular boilers very different proportions prevail, yet the proportions of every kind of boiler are determinable on the same general principle. In wagon boilers the proportion of the perimeter of the flue which is effective as heating surface, is to the total perimeter as 1 to 3, or, in some cases as 1 to 2.5; and with any given area of flue, therefore, the length of the flue must be from 3 to 2.5 times greater than would be necessary if the total surface were effective, else the requisite quantity of heating surface will not be obtained. If, then, the vent be the calorimeter, divided by the length, and the length be made 3 or 2.5 times greater, the vent must become 3 or 2.5 times less; and in wagon boilers accordingly, the vent varies from 8 to 11 instead of from 21 to 25, as in the case of marine flue boilers. In tubular marine boilers the calorimeter is usually made only about half the amount allowed by Boulton and Watt for marine flue boilers, or, in other words, the collective sectional area of the tubes, for the transmission of the smoke, is from 8 to 9 square inches per nominal horse power. It is better, however, to make the sectional area larger than this, and to work the boiler with the damper sufficiently closed to prevent the smoke and flame from rushing exclusively through a few of the tubes. 261. _Q._--What are the ordinary dimensions of the flue in wagon boilers? _A._--In Boulton and Watt's 45 horse wagon boiler the area of flue is 18 square inches per horse power, but the area per horse power increases very rapidly as the size of the boiler becomes less, and amounts to about 80 square inches per horse power in a boiler of 2 horse power. Some such increase is obviously inevitable, if a similar form of flue be retained in the larger and smaller powers, and at the same time the elongation of the flue in the same proportion as the increase of any other dimension is prevented; but in the smaller class of wagon boilers the consideration of facility of cleaning the flues is also operative in inducing a large proportion of sectional area. Boulton and Watt's 2 horse power wagon boiler has 30 square feet of surface, and the flue is 18 inches high above the level of the boiler bottom, by 9 inches wide; while their 12 horse wagon boiler has 118 square feet of heating surface, and the dimensions of the flue similarly measured are 36 inches by 13 inches. The width of the smaller flue, if similarly proportioned to the larger one, would be 6-1/2 inches, instead of 9 inches, and, by assuming this dimension, we should have the same proportion of sectional area per square foot of heating surface in both boilers. The length of flue in the 2 horse boiler is 19.5 ft., and in the 12 horse boiler 39 ft., so that the length and height of the flue are increased in the same proportion. 262. _Q._--Will you give an example of the proportions of a flue, in the case of a marine boiler? _A._--The Nile steamer, with engines of 110 horse power by Boulton and Watt, is supplied with steam by two boilers, which are, therefore, of 55 horses power each. The height of the flue winding within the boiler is 60 inches, and its mean width 16-1/2 inches, making a sectional area or calorimeter of 990 square inches, or 18 square inches per horse power of the boiler. The length of the flue is 39 ft., making the vent 25, which is the vent proper for large boilers. In the Dee and Solway steamers, by Scott and Sinclair, the calorimeter is only 9.72 square inches per horse power; in the Eagle, by Caird, 11.9; in the Thames and Medway, by Maudslay, 11.34, and in a great number of other cases it does not rise above 12 square inches per horse power; but the engines of most of these vessels are intended to operate to a certain extent expansively, and the boilers are less powerful in evaporating efficacy on that account. 263. _Q._--Then the chief difference in the proportions established by Boulton and Watt, and those followed by the other manufacturers you have mentioned is, that Boulton and Watt set a more powerful boiler to do the same work? _A._--That is the main difference. The proportion which one part of the boiler bears to another part is very similar in the cases cited, but the proportion of boiler relatively to the size of the engine varies very materially. Thus the calorimeter _of each boiler_ of the Dee and Solway is 1296 square inches; of the Eagle, 1548 square inches; and of the Thames and Medway, 1134 square inches; and the length of flue is 57, 60, and 52 ft. in the boilers respectively, which makes the respective vents 22-1/2, 25, and 21. Taking then the boiler of the Eagle for comparison with the boiler of the Nile, as it has the same vent, it will be seen that the proportions of the two are almost identical, for 990 is to 1548 as 39 is to 60, nearly; but Messrs. Boulton and Watt would not have set a boiler like that of the Eagle to do so much work. 264. _Q._--Then the evaporating power of the boiler varies as the sectional area of the flue? _A._--The evaporating power varies as the square root of the area of the flue, if the length of the flue remain the same; but it varies as the area simply, if the length of the flue be increased in the same proportion as its other dimensions. The evaporating power of a boiler is referable to the amount of its heating surface, and the amount of heating surface in any flue or tube is proportional to the product of the length of the tube and the square root of its sectional area, multiplied by a certain quantity that is constant for each particular form. But in similar tubes the length is proportional to the square root of the sectional area; therefore, in similar tubes, the amount of heating surface is proportional to the sectional area. On this area also depends the quantity of hot air passing through the flue, supposing the intensity of the draught to remain unaffected, and the quantity of hot air or smoke passing through the flue should vary in the same ratio as the quantity of surface. 265. _Q._--A boiler, therefore, to exert four times the power, should have four times the extent of heating surface, and four times the sectional area of flue for the transmission of the smoke? _A._--Yes; and if the same form of flue is to be retained, it should be of twice the diameter and twice the length; or twice the height and width if rectangular, and twice the length. As then the diameter or square root of the area increases in the same ratio as the length, the square root of the area divided by the length ought to be a constant quantity in each type of boiler, in order that the same proportions of flue may be retained; and in wagon boilers without an internal flue, the height in inches of the flue encircling the boiler divided by the length of the flue in feet will be 1 very nearly. Instead of the square root of the area, the effective perimeter, or outline of that part of the cross section of the flue which is effective in generating steam, may be taken; and the effective perimeter divided by the length ought to be a constant quantity in similar forms of flues and with the same velocity of draught, whatever the size of the flue may be. 266. _Q._--Will this proportion alter if the form of the flue be changed? _A._--It is clear, that with any given area of flue, to increase the perimeter by adopting a different shape is tantamount to a diminution of the length of the flue; and, if the perimeter be diminished, the length of the flue must at the same time be increased, else it will be impossible to obtain the necessary amount of heating surface. In Boulton and Watt's wagon boilers, the sectional area of the flue in square inches per square foot of heating surface is 5.4 in the two horse boiler; in the three horse it is 4.74; in the four horse, 4.35; six horse, 3.75; eight horse, 4.33; ten horse, 3.96; twelve horse, 3.63; eighteen horse, 3.17; thirty horse, 2.52; and in the forty-five horse boiler, 2.05 square inches. Taking the amount of heating surface in the 45 horse boiler at 9 square feet per horse power, we obtain 18 square inches of sectional area of flue per horse power, which is also Boulton and Watt's proportion of sectional area for marine boilers with internal flues. 267. _Q._--If to increase the perimeter of a flue is virtually to diminish the length, then a tubular boiler where the perimeter is in effect greatly extended ought to have but a short length of tube? _A._--The flue of the Nile steamer if reduced to the cylindrical form would be 35-1/2 inches in diameter to have the same area; but it would then require to be made 47-3/4 feet long, to have the same amount of heating surface, excluding the bottom as non-effective. Supposing that with these proportions the heat is sufficiently extracted from the smoke, then every tube of a tubular boiler in which the same draught existed ought to have very nearly the same proportions. 268. _Q._--But what are the best proportions of the parts of tubular boilers relatively with one another? _A._--The proper relative proportions of the parts of tubular boilers may easily be ascertained by a reference to the settled proportions of flue boilers; for the same general principles are operative in both cases. In the Nile steamer each boiler of 55 horse power has about 497 square feet of flue surface or 9 square feet per horse power, reckoning the total surface as effective. The area of the flue, which is rectangular is 990 square inches, therefore the area is equal to that of a tube 35-1/2 inches in diameter; and such a tube, to have a heating surface of 497 square feet, must be 53.4 feet or 640.8 inches in length. The length, therefore, of the tube, will be about 18 times its diameter, and with the same velocity of draught these proportions must obtain, whatever the absolute dimensions of the tube may be. With a calorimeter, therefore, of 18 square inches per horse power, the length of a tube 3 inches diameter must not exceed 4 feet 6 inches, since the heat will be sufficiently extracted from the smoke in this length, if the smoke only travels at the velocity due to a calorimeter of 18 square inches per horse power. 269. _Q._--Is this, then, the maximum length of flue which can be used in tubular boilers with advantage? _A._--By no means. The tubes of tubular boilers are almost always more than 4 feet 6 inches long, but then the calorimeter is almost always less than 18 square inches per horse power--generally about two thirds of this. Indeed, tubular boilers with a large calorimeter are not found to be so satisfactory as where the calorimeter is small, partly from the propensity of the smoke in such cases to pass through a few of the tubes instead of the whole of them, and partly from the deposit of soot which takes place when the draught is sluggish. It is a very confusing practice, however, to speak of nominal horse power in connection with boilers, since that is a quantity quite indeterminate. EVAPORATIVE POWER OF BOILERS. 270. _Q._--The main thing after all in boilers is their evaporative powers? _A._--The proportions of tubular boilers, as of all boilers, should obviously have reference to the evaporation required, whereas the demand upon the boiler for steam is very often reckoned contingent upon the nominal horse power of the engine; and as the nominal power of an engine is a conventional quantity by no means in uniform proportion to the actual quantity of steam consumed, perplexing complications as to the proper proportions of boilers have in consequence sprung up, to which most of the failures in that department of engineering may be imputed. It is highly expedient, therefore, in planning boilers for any particular engine, to consider exclusively the actual power required to be produced, and to apportion the capabilities of the boiler accordingly. 271. _Q._--In other words you would recommend the inquiry to be restricted to the mode of evaporating a given number of cubic feet of water in the hour, instead of embracing the problem how an engine of a given nominal power was to be supplied with steam? _A._--I would first, as I have already stated, consider the actual power required to be produced, and then fix the amount of expansion to be adopted. If the engine had to work up to three times its nominal power, as is now common in marine engines, I should either increase correspondingly the quantity of evaporating surface in the boiler, or adopt such an amount of expansion as would increase threefold the efficacy of the steam, or combine in a modified manner both of these arrangements. Reckoning the evaporation of a cubic foot of water in the hour as equivalent to an actual horse power, and allowing a square yard or 9 square feet as the proper proportion of flue surface to evaporate a cubic foot of water in the hour, it is clear that I must either give 27 square feet of heating surface in the boiler to have a trebled power without expansion, or I must cut off the steam at one seventh of the stroke to obtain a three-fold power without increasing the quantity of heating surface. By cutting off the steam, however, at one third of the stroke, a heating surface of 13-1/2 square feet will give a threefold power, and it will usually be the most judicious course to carry the expansion as far as possible, and then to add the proportion of heating surface necessary to make good the deficiency still found to exist. 272. _Q._--But is it certain that a cubic foot of water evaporated in the hour is equivalent to an actual horse power? _A._--An actual horse power as fixed by Watt is 33,000 lbs. raised one foot high in the minute; and in Watt's 40 horse power engine, with a 31-1/2 inch cylinder, 7 feet stroke, and making 17-1/2 strokes a minute, the effective pressure is 6.92 lbs. on the square inch clear of all deductions. Now, as a horse power is 33,000 lbs. raised one foot high, and as there are 6.92 lbs, on the square inch, it is clear that 33,000 divided by 6.92, on 4768 square inches with 6.92 lbs. on each if lifted 1 foot or 12 inches high, will also be equal to a horse power. But 4768 square inches multiplied by 12 inches in height is 57224.4 cubic inches, or 33.1 cubic feet, and this is the quantity of steam which must be expended per minute to produce an actual horse power. 273. _Q._--But are 33 cubic feet of steam expended per minute equivalent to a cubic foot of water expended in the hour? _A._.--Not precisely, but nearly so. A cubic foot of water produces 1669 cubic feet of steam of the atmospheric density of 15 lbs. per square inch, whereas a consumption of 33 cubic feet of steam in the minute is 1980 cubic feet in the hour. In Watt's engines about one tenth was reckoned as loss in filling the waste spaces at the top and bottom of the cylinder, making 1872 cubic feet as the quantity consumed per hour without this waste; and in modern engines the waste at the ends of the cylinder is inconsiderable. 274. _Q._--What power was generated by a cubic foot of water in the case of the Albion Mill engines when working without expansion? _A._--In the Albion Mill engines when working without expansion, it was found that 1 lb. of water in the shape of steam raised 28,489 lbs. 1 foot high. A cubic foot of water, therefore, or 62-1/2 lbs., if consumed in the hour, would raise 1780562.5 lbs. one foot high in the hour, or would raise 29,676 lbs. one foot high in a minute; and if to this we add one tenth for waste at the ends of the cylinder, a waste which hardly exists in modern engines, we have 32,643 lbs. raised one foot high in the minute, or a horse power very nearly. In some cases the approximation appears still nearer. Thus, in a 40 horse engine working without expansion, Watt found that .674 feet of water were evaporated from the boiler per minute, which is just a cubic foot per horse power per hour; but it is not certain in this case that the nominal and actual power were precisely identical. It will be quite safe, however, to reckon an actual horse power as producible by the evaporation of a cubic foot of water in the hour in the case of engines working without expansion; and for boiling off this quantity in flue or wagon boilers, about 8 lbs. of coal will be required and 9 square feet of flue surface. MODERN MARINE AND LOCOMOTIVE BOILERS. 275. _Q._--These proportions appear chiefly to refer to old boilers. I wish you to state what are the proportions of modern flue and tubular marine boilers. _A._--In modern marine boilers the area of fire grate is less than in Mr. Watt's original boilers, where it was one square foot to nine square feet of heating surface. The heat in the furnace is consequently more intense, and a somewhat less amount of surface suffices to evaporate a cubic foot of water. In Boulton and Watt's modern flue boilers they allow for the evaporation of a cubic foot of water 8 square feet of heating surface, 70 square inches of fire grate, 13 square inches sectional area of flues, 6 square inches sectional area of chimney, 14 square inches area over furnace bridges, ratio of area of flue to area of fire grate 1 to 5.4. To evaporate a cubic foot of water per hour in tubular boilers, the proportions are-- heating surface 9 square feet, fire grate 70 square inches, sectional area of tubes 10 square inches, sectional area of back uptake 12 square inches, sectional area of front uptake 10 square inches, sectional area of chimney 7 square inches, ratio of diameter of tube to length of tube 1/28th to 1/30th, cubical content of boiler exclusive of steam chest 6.5 cubic feet, cubical content of steam chest 1.5 cubic feet. 276. _Q._--These proportions do not apply to locomotive boilers? _A._--Not at all. In locomotive boilers the draught is maintained by the projection of the waste steam which escapes from the cylinders up the chimney, and the draught is much more powerful and the combustion much more rapid than in cases in which the combustion is maintained by the natural draught of a chimney, except indeed the chimney be of very unusual temperature and height. The proportions proper for locomotive boilers will be seen by the dimensions of a few locomotives of approved construction, which have been found to give satisfactory results in practice, and which are recorded in the following Table: Name of Engine Great Britain. Pallas. Snake. Sphinx. Diameter of cylinder 18 in. 15 in. 14-1/4 in. 18 in. Length of stroke 24 in. 20 in. 21 in. 24 in. Diameter of driving wheel 8 ft. 6 ft. 6-1/2 ft. 5 ft. Inside diameter of fire box 53 in. 55 in. 41-1/3 in. 44 in. Inside width of fire box 63 in. 42 in. 43-1/4 in. 39-1/2in. Height of fire box above bars 63 in. 52 in. 48-1/3 in. 55-1/2in. Number of fire bars 29 ... 32 16 Thickness of fire bars 3/4 in. 1-3/4 in. 5/8 in. 1 in. Number of Tubes 305 134 181 142 Outside diameter of tubes 2 in. 2 in. 1-7/8 in. 2-1/8 in. Length of tubes 11 ft 3 in 10 ft 6 in 10 ft 3-1/2 in. 14 ft 3-1/4 in. Space between tubes 1/2 in. 3/4 in. 1/2 in. Inside diameter of ferules 1-9/16 in. 1-1/2 in. 1-5/16 in. 1-5/8 in. Diameter of chimney 17 in. 15 in. 13 in. 15-1/2 in. Diameter of blast orifice 5-1/2 in. 4-5/8 in. 4-1/2 in. 4-3/4 in. Area of grate 21 sq. ft. 16.04 sqft 12.4 sq. ft. 10.56 sq. ft Area of air space of grate 11.4 sqft 4.08 sqft 5.54 sq. ft. 5 sq. ft. Area of tubes 5.46 sqft 2.40 sqft 2.8 sq. ft. 2.92 sq. ft. Area though ferules 4 sq. ft. 1.64 sqft 2 sq. ft. 2.04 sq. ft. Area of chimney 1.77 sqft 1.23 sqft .921 sq. ft. 1.31 sq. ft. Area of blast orifice 23.76 sqin 16.8 sqin 14.18 sq. in. 17.7 sq. in. Heating surface of tubes 1627 sqft 668.7 sqft 823 sq. ft. 864 sq. ft. THE BLAST IN LOCOMOTIVES. 277. _Q._--What is the amount of draught produced in locomotive boilers in comparison with that existing in other boilers? _A._--A good chimney of a land engine will produce a degree of exhaustion equal to from 1-1/2 to 2-1/2 inches of water. In locomotive boilers the exhaustion is in some cases equal to 12 or 13 inches of water, but from 3 to 6 inches is a more common proportion. 278. _Q._--And what force of blast is necessary to produce this exhaustion? _A._--The amount varies in different engines, depending on the sectional area of the tubes and other circumstances. But on the average, it may be asserted that such a pressure of blast as will support an inch of mercury, will maintain sufficient exhaustion in the smoke box to support an inch of water; and this ratio holds whether the exhaustion is little or great. To produce an exhaustion in the smoke box, therefore, of 6 inches of water, the waste steam would require to be of sufficient pressure to support a column of 6 inches of mercury, which is equivalent to a pressure of 3 lbs. on the square inch. 279. _Q._--How is the force of the blast determined? _A._--By the amount of contraction given to the mouth of the blast pipe, which is a pipe which conducts the waste steam from the cylinders and debouches at the foot of the chimney. If a strong blast be required, the mouth of this pipe requires to be correspondingly contracted, but such contraction throws a back pressure on the piston, and it is desirable to obtain the necessary draught with as little contraction of the blast pipe as possible. The blast pipe is generally a breeches pipe of which the legs join just before reaching the chimney; but it is better to join the two cylinders below, and to let a single pipe ascend to within 12 or 18 inches of the foot of the chimney. If made with too short a piece of pipe above the joining, the steam will be projected against each side of the chimney alternately, and the draught will be damaged and the chimney worn. The blast pipe should not be regularly tapered, but should be large in the body and gathered in at the mouth. 280. _Q._--Is a large and high chimney conducive to strength of draught in locomotives? _A._--It has not been found to be so. A chimney of three or four times its own diameter in height appears to answer fully as well as a longer one; and it was found that when in an engine with 17 inch cylinders a chimney of 15-1/4 inches was substituted for a chimney of 17-1/2 inches, a superior performance was the result. The chimney of a locomotive should have half the area of the tubes at the ferules, which is the most contracted part, and the blast orifice should have 1/10th of the area of the chimney. The sectional area of the tubes through the ferules should be as large as possible. Tubes without ferules it is found pass one fourth more air, and tubes with ferules only at the smoke box end pass one tenth more air than when there are ferules at both ends. 281. _Q._--Is the exhaustion produced by the blast as great in the fire box as in the smoke box? _A._--Experiments have been made to determine this, and in few cases has it been found to be more than about half as great as ordinary speeds; but much depends on the amount of contraction in the tubes. In an experiment made with an engine having 147 tubes of 1-3/4 inches external diameter, and 13 feet 10 inches long, and with a fire grate having an area of 9-1/2 square feet, the exhaustion at all speeds was found to be three times greater in the smoke box than in the fire box. The exhaustion in the smoke box was generally equivalent to 12 inches of water, while in the fire box it was equivalent to only 4 inches of water; showing that 4 inches were required to draw the air through the grate and 8 inches through the tubes. 282. _Q._--What will be the increase of evaporation in a locomotive from a given increase of exhaustion? _A._--The rate of evaporation in a locomotive or any other boiler will vary as the quantity of air passing through the fire, and the quantity of air passing through the fire will vary nearly as the square root of the exhaustion. With four times the exhaustion, therefore, there will be about twice the evaporation, and experiment shows that this theoretical law holds with tolerable accuracy in practice. 283. _Q._--But the same exhaustion will not be produced by a given strength of blast in all engines? _A._--No; engines with contracted fire grates and an inadequate sectional area of tubes, will require a stronger blast than engines of better proportions; but in any given engine the relations between the blast exhaustion and evaporation, hold which have been already defined. 284. _Q._--Is the intensity of the draught under easy regulation? _A._--The intensity of the draught may easily be diminished by partially closing the damper in the chimney, and it may be increased by contracting the orifice of the blast. A variable blast pipe, the orifice of which may be enlarged or contracted at pleasure, has been much used. There are various devices for this purpose, but the best appears to be that adopted in Stephenson's engine, where a conical nozzle is moved up or down within the blast pipe, which is made somewhat larger in diameter than the base of the cone, but with a ring projecting internally, against which the base of the cone abuts when the nozzle is pushed up. When the nozzle stands at the top of the pipe the whole of the steam has to pass through it, and the intensity of the blast is increased by the increased velocity thus given to the steam; whereas when the nozzle is moved downward the steam escapes through the annular opening left between the nozzle and the pipe, as well as through the nozzle itself, and the intensity of the blast is diminished by the enlargement of the opening for the escape of the steam thus made available. 285._Q._--What is the best diameter for the tubes of locomotive boilers? _A._--Bury's locomotive with 14 inch cylinders contains 92 tubes of 2-1/8th inches external diameter, and 10 feet 6 inches long; whereas Stephenson's locomotive with 15 inch cylinders contains 150 tubes of 1-5/8ths external diameter, 13 feet 6 inches long. In Stephenson's boiler, in order that the part of the tubes next the chimney may be of any avail for the generation of steam, the draught has to be very intense, which in its turn involves a considerable expenditure of power; and it is questionable whether the increased expenditure of power upon the blast, in Stephenson's long tubed locomotives, is compensated by the increased generation of steam consequent upon the extension of the heating surface. When the tubes are small in diameter they are apt to become partially choked with pieces of coke; but an internal diameter of 1-5/8ths may be employed without inconvenience if the draught be of medium intensity. 286. _Q._--Will you illustrate the relation between the length and diameter of locomotive tubes by a comparison with the proportion of flues in flue boilers? _A._--In most locomotives the velocity of the draught is such that it would require very long tubes to extract the heat from the products of combustion, if the heat were transmitted through the metal of the tubes with only the same facility as through the iron of ordinary flue boilers. The Nile steamer, with engines of 110 nominal horses power each, and with two boilers having two independent flues in each, of such dimensions as to make each flue equivalent to 55 nominal horses power, works at 62 per cent. above the nominal power, so that the actual evaporative efficacy of each flue would be equivalent to 89 actual horses power, supposing the engines to operate without expansion; but as the mean pressure in the cylinder is somewhat less than the initial pressure, the evaporative efficacy of each flue may be reckoned equivalent to 80 actual horses power. With this evaporative power there is a calorimeter of 990 square inches, or 12.3 square inches per actual horse power; whereas in Stephenson's locomotive with 150 tubes, if the evaporative power be taken at 200 cubic feet of water in the hour, which is a large supposition, the engine will be equal to 200 actual horses power. If the internal diameter of the tubes be taken at thirteen eighths of an inch, the calorimeter per actual horse power will only be 1.1136 square inches, or in other words the calorimeter in the locomotive boiler will be 11.11 times less than in the flue boiler for the same power, so that the draught in the locomotive must be 11.11 times stronger, and the ratio of the length of the tube to its diameter 11.11 times greater than in the flue boiler, supposing the heat to be transmitted with only the same facility. The flue of the Nile would require to be 35- 1/2 inches in diameter if made of the cylindrical form, and 47-3/4 feet long; the tubes of a locomotive if 1-3/8ths inch diameter would only require to be 22.19 inches long with the same velocity of draught; but as the draught is 11.11 times faster than in a flue boiler, the tubes ought to be 246.558 inches, or about 20-1/2 feet long according to this proportion. In practice, however, they are one third less than this, which reduces the heating surface from 9 to 6 square feet per actual horse power, and this length even is found to be inconvenient. It is greatly preferable therefore to increase the calorimeter, and diminish the intensity of the draught. BOILER CHIMNEYS. 287. _Q._--By what process do you ascertain the dimensions of the chimney of a land boiler? _A._--By a reference to the volume of air it is necessary in a given time to supply to the burning fuel, and to the velocity of motion produced by the rarefaction in the chimney; for the area of the chimney requires to be such, that with the velocity due to that rarefaction, the quantity of air requisite for the combustion of the fuel shall pass through the furnace in the specified time. Thus if 200 cubic feet of air of the atmospheric density are required for the combustion of a pound of coal,--though 250 lbs. is nearer the quantity generally required,--and 10 lbs. of coal per horse power per hour are consumed by an engine, then 2000 cubic feet of air must be supplied to the furnace per horse power per hour, and the area of the chimney must be such as to deliver this quantity at the increased bulk due to the high temperature of the chimney when moving with the velocity the rarefaction within the chimney occasions, and which, in small chimneys, is usually such as to support a column of half an inch of water. The velocity with which a denser fluid flows into a rarer one is equal to the velocity a heavy body acquires in falling through a height equal to the difference of altitude of two columns of the heavier fluid of such heights as will produce the respective pressures; and, therefore, when the difference of pressure or amount of rarefaction in the chimney is known, it is easy to tell the velocity of motion which ought to be produced by it. In practice, however, these theoretical results are not to be trusted, until they have received such modifications as will make them representative of the practice of the most experienced constructors. 288. _Q._--What then is the rule followed by the most experienced constructors? _A._--Boulton and Watt's rule for the dimensions of the chimney of a land engine is as follows:--multiply the number of pounds of coal consumed under the boiler per hour by 12, and divide the product by the square root of the height of the chimney in feet; the quotient is the area of the chimney in square inches in the smallest part. A factory chimney suitable for a 20 horse boiler is commonly made about 20 in. square inside, and 80 ft. high; and these dimensions are those which answer to a consumption of 15 lbs. of coal per horse power per hour, which is a very common consumption in factory engines. If 15 lbs. of coal be consumed per horse power per hour, the total consumption per hour in a 20 horse boiler will be 300 lbs., and 300 multiplied by 12 = 3600, and divided by 9 (the square root of the height) = 400, which is the area of the chimney in square inches. It will not answer well to increase the height of a chimney of this area to more than 40 or 50 yards, without also increasing the area, nor will it be of utility to increase the area much without also increasing the height. The quantity of coal consumed per hour in pounds, multiplied by 5, and divided by the square root of the height of the chimney, is the proper collective area of the openings between the bars of the grate for the admission of air to the fire. 289. _Q._--Is this rule applicable to the chimneys of steam vessels? _A._--In steam vessels Boulton and Watt have heretofore been in the habit of allowing 8-1/2 square inches of area of chimney per horse power, but they now allow 6 square inches to 7 square inches. In some steam vessels a steam blast like that of a locomotive, but of a smaller volume, is used in the chimney, and many of the evils of a boiler deficient in draught may be remedied by this expedient, but a steam blast in a low pressure engine occasions an obvious waste of steam; it also makes an unpleasant noise, and in steam vessels it frequently produces the inconvenience of carrying the smaller parts of the coal up the chimney, and scattering it over the deck among the passengers. It is advisable, therefore, to give a sufficient calorimeter in all low pressure boilers, and a sufficient height of chimney to enable the chimney to operate without a steam jet; but it is useful to know that a steam jet is a resource in the case of a defective boiler, or where the boiler has to be urged beyond its power. STEAM ROOM AND PRIMING. 290. _Q._--What is the capacity of steam room allowed in boilers per horse power? _A._--The capacity of steam room allowed by Boulton and Watt in their land wagon boilers is 8-3/4 cubic feet per horse power in the two horse power boiler, and 5-3/4 cubic feet in the 20 horse power boiler; and in the larger class of boilers, such as those suitable for 30 and 45 horse power engines, the capacity of the steam room does not fall below this amount, and, indeed, is nearer 6 than 5-3/4 cubic feet per horse power. The content of water is 18-1/2 cubic feet per horse power in the two horse power boiler, and 15 cubic feet per horse power in the 20 horse power boiler. 291. _Q._--Is this the proportion Boulton and Watt allow in their marine boilers? _A._--Boulton and Watt in their early steam vessels were in the habit of allowing for the capacity of the steam, space in marine boilers 16 times the content of the cylinder; but as there were two cylinders, this was equivalent to 8 times the content of both cylinders, which is the proportion commonly followed in land engines, and which agrees very nearly with the proportion of between 5 and 6 cubic feet of steam room per horse power already referred to. Taking for example an engine with 23 inches diameter of cylinder and 4 feet stroke, which will be 18.4 horse power--the area of the cylinder will be 415.476 square inches, which, multiplied by 48, the number of inches in the stroke, will give 19942.848 for the capacity of the cylinder in cubic inches; 8 times this is 159542.784 cubic inches, or 92.3 cubic feet; 92.3 divided by 18.4 is rather more than 5 cubic feet per horse power. 292. _Q._--Is the production of the steam in the boiler uniform throughout the stroke of the engine? _A._--It varies with the slight variations in the pressure within the boiler throughout the stroke. Usually the larger part of the steam is produced during the first part of the stroke of the engine, for there is then the largest demand for steam, as the steam being commonly cut off somewhat before the end of the stroke, the pressure rises somewhat in the boiler during that period, and little steam is then produced. There is less necessity that the steam space should be large when the flow of steam from the boiler is very uniform, as it will be where there are two engines attached to the boiler at right angles with one another, or where the engines work at a great speed, as in the case of locomotive engines. A high steam chest too, by rendering boiling over into the steam pipes, or priming as it is called, more difficult, obviates the necessity for so large a steam space; as does also a perforated steam pipe stretching through the length of the boiler, so as not to take the steam from one place. The use of steam of a high pressure, worked expansively, has the same operation; so that in modern marine boilers, of the tubular construction, where the whole or most of these modifying circumstances exist, there is no necessity for so large a proportion of steam room as 5 or 6 cubic feet per nominal horse power, and about one, 1-1/2, or 2 cubic feet of steam room per cubic foot of water evaporated, more nearly represents the general practice. 293. _Q._--Is this the proportion of steam room adopted in locomotive boilers? _A._--No; in locomotive boilers the proportion of steam room per cubic foot of water evaporated is considerably less even than this. It does not usually exceed 1/5 of a cubic foot per cubic foot of water evaporated; and with clean water, with a steam dome a few feet high set on the barrel of the boiler, or with a perforated pipe stretching from end to end of the barrel, and with the steam room divided about equally between the barrel and the fire box, very little priming is found to occur even with this small proportion of total steam room. About 3/4 the depth of the barrel is usually filled with water, and 1/4 with steam. 294. _Q._--What is priming? _A._--Priming is a violent agitation of the water within the boiler, in consequence of which a large quantity of water passes off with the steam in the shape of froth or spray. Such a result is injurious, both as regards the efficacy of the engine, and the safety of the engine and boiler; for the large volume of hot water carried by the steam into the condenser impairs the vacuum, and throws a great load upon the air pump, which diminishes the speed and available power of the engine; and the existence of water within the cylinder, unless there be safety valves upon the cylinder to permit its escape, will very probably cause some part of the machinery to break, by suddenly arresting the motion of the piston when it meets the surface of the water,--the slide valve being closed to the condenser before the termination of the stroke, in all engines with lap upon the valves, so that the water within the cylinder is prevented from escaping in that direction. At the same time the boiler is emptied of its water too rapidly for the feed pump to be able to maintain the supply, and the flues are in danger of being burnt from a deficiency of water above them. 295. _Q._--What are the causes of priming? _A._--The causes of priming are an insufficient amount of steam room, an inadequate area of water level, an insufficient width between the flues or tubes for the ascent of the steam and the descent of water to supply the vacuity the steam occasions, and the use of dirty water in the boiler. New boilers prime more than old boilers, and steamers entering rivers from the sea are more addicted to priming than if sea or river water had alone been used in the boilers--probably from the boiling point of salt water being higher than that of fresh, whereby the salt water acts like so much molten metal in raising the fresh water into steam. Opening the safety valve suddenly may make a boiler prime, and if the safety valve be situated near the mouth of the steam pipe, the spray or foam thus created may be mingled with the steam passing into the engine, and materially diminish its effective power; but if the safety valve be situated at a distance from the mouth of the steam pipe, the quantity of foam or spray passing into the engine may be diminished by opening the safety valve; and in locomotives, therefore, it is found beneficial to have a safety valve on the barrel of the boiler at a point remote from the steam chest, by partially opening which, any priming in that part of the boiler adjacent to the steam chest is checked, and a purer steam than before pusses to the engine. 296. _Q._--What is the proper remedy for priming? _A._--When a boiler primes, the engineer generally closes the throttle valve partially, turns off the injection water, and opens the furnace doors, whereby the generation of steam is checked, and a less violent ebullition in the boiler suffices. Where the priming arises from an insufficient amount of steam room, it may be mitigated by putting a higher pressure upon the boiler and working more expansively, or by the interposition of a perforated plate between the boiler and the steam chest, which breaks the ascending water and liberates the steam. In some cases, however, it may be necessary to set a second steam chest on the top of the existing one, and it will be preferable to establish a communication with this new chamber by means of a number of small holes, bored through the iron plate of the boiler, rather than by a single large orifice. Where priming arises from the existence of dirty water in the boiler, the evil may be remedied by the use of collecting vessels, or by blowing off largely from the surface; and where it arises from an insufficient area of water level, or an insufficient width between the flues for the free ascent of the steam and the descent of the superincumbent water, the evil may be abated by the addition of circulating pipes in some part of the boiler, which will allow the water to descend freely to the place from whence the steam rises, the width of the water spaces being virtually increased by restricting their function to the transmission of a current of steam and water to the surface. It is desirable to arrange the heating surface in such a way that the feed water entering the boiler at its lowest point is heated gradually as it ascends, until toward the superior part of the flues it is raised gradually into steam; but in all cases there will be currents in the boiler for which it is proper to provide. The steam pipe proceeding to the engine should obviously be attached to the highest point of the steam chest, in boilers of every construction. 297. _Q._--Having now stated the proportions proper to be adopted for evaporating any given quantity of water in steam boilers, will you proceed to show how you would proportion a boiler to do a given amount of work? say a locomotive boiler which will propel a train of 100 tons weight at a speed of 50 miles an hour. _A._--According to experiments on the resistance of railway trains at various rates of speed, made by Mr. Gooch, of the Great Western Railway, it appears that a train weighing, with locomotive, tender, and carriages, about 100 tons, experiences, at a speed of 50 miles an hour, a resistance of about 3,000 lbs., or about 30 lbs. per ton; which resistance includes the resistance of the engine as well as that of the train. This, therefore, is the force which must be imparted at the circumference of the driving wheels, except that small part intercepted by the engine itself, and the force exerted by the pistons must be greater than that at the circumference of the driving wheel, in the proportion of their slower motion, or in the proportion of the circumference of the driving wheel to the length of a double stroke of the engine. If the diameter of the driving wheel be 5-1/2 feet, its circumference will be 17.278 feet, and if the length of the stroke be 18 inches, the length of a double stroke will be 3 feet. The pressure on the pistons must therefore be greater than the traction at the circumference of the driving wheel, in the proportion of 17.278 to 3, or, in other words, the mean pressure on the pistons must be 17,278 lbs.; and the area of cylinders, and pressure of steam, must be such as to produce conjointly this total pressure. It thus becomes easy to tell the volume and pressure of steam required, which steam in its turn represents its equivalent of water which is to be evaporated from the boiler, and the boiler must be so proportioned, by the rules already given, as to evaporate this water freely. In the case of a steam vessel, the mode of procedure is the same, and when the resistance and speed are known, it is easy to tell the equivalent value of steam. STRENGTH OF BOILERS. 298. _Q._--What strain should the iron of boilers be subjected to in working? _A._--The iron of boilers, like the iron of machines or structures, is capable of withstanding a tensile strain of from 50,000 to 60,000 lbs. upon every square inch of section; but it will only bear a third of this strain without permanent derangement of structure, and it does not appear expedient in any boiler to let the strain exceed 4,000 lbs. upon the square inch of sectional area of metal, especially if it is liable to be weakened by corrosion. 299._Q._--Have any experiments been made to determine the strength of boilers? _A._--The question of the strength of boilers was investigated very elaborately a few years ago by a committee of the Franklin Institute, in America, and it was found that the tenacity of boiler plate increased with the temperature up to 550°, at which point the tenacity began to diminish. At 32°, the cohesive force of a square inch of section was 56,000 lbs.; at 570°, it was 66,500 lbs.; at 720°, 55,000 lbs.; at 1,050°, 32,000 lbs.; at 1,240°, 22,000 lbs.; and at 1,317°, 9,000 lbs. Copper follows a different law, and appears to be diminished in strength by every addition to the temperature. At 32° the cohesion of copper was found to be 32,800 lbs. per square inch of section, which exceeds the cohesive force at any higher temperature, and the square of the diminution of strength seems to keep pace with the cube of the increased temperature. Strips of iron cut in the direction of the fibre were found to be about 6 per cent. stronger than when cut across the grain. Repeated piling and welding was found to increase the tenacity of the iron, but the result of welding together different kinds of iron was not found to be favorable. The accidental overheating of a boiler was found to reduce the ultimate or maximum strength of the plates from 65,000 to 45,000 lbs. per square inch of section, and riveting the plates was found to occasion a diminution in their strength to the extent of one third. These results, however, are not precisely the same as those obtained by Mr. Fairbairn. 300. _Q._--What were the results obtained by him? _A._--He found that boiler plate bore a tensile strain of 23 tons per square inch before rupture, which was reduced to 16 tons per square inch when joined together by a double row of rivets, and 13 tons, or about 30,000, when joined together by a single row of rivets. A circular boiler, therefore, with the ends of its plates double riveted, will bear at the utmost about 36,000 lbs. per square inch of section, or about 12,000 lbs. per square inch of section without permanent derangement of structure. 301. _Q._--What pressure do cylindrical boilers sustain in practice? _A._--In some locomotive boilers, which are worked with a pressure of 80 lbs. upon the square inch, the thickness of the plates is only 5/16ths of an inch, while the barrel of the boiler is 39 inches in diameter. It will require a length of 3.2 inches of the boiler when the plates are 5/16ths thick to make up a sectional area of one square inch, and the separating force will be 39 times 3.2 multiplied by 80, which makes the separating force 9,984 lbs., sustained by two square inches of sectional area--one on each side; or the strain is 4,992 lbs. per square inch of sectional area, which is quite as great strain as is advisable. The accession of strength derived from the boiler ends is not here taken into account, but neither is the weakening effect counted that is caused by the rivet holes. Some locomotives of 4 feet diameter of barrel and of 3/8ths iron have been worked to as high a pressure as 200 lbs. on the inch; but such feats of daring are neither to be imitated nor commended. 302._Q._--Can you give a rule for the proper thickness of cylindrical boilers? _A._--The thickness proper for cylindrical boilers of wrought iron, exposed to an internal pressure, may be found by the following rule:--multiply 2.54 times the internal diameter of the cylinder in inches by the greatest pressure within the cylinder per circular inch, and divide by 17,800; the result is the thickness in inches. If we apply this rule to the example of the locomotive boiler just given, we have 39 x 2.54 x 62.832 (the pressure per circular inch corresponding to 80 lbs. per square inch) = 6224.1379, and this, divided by 17,800, gives 0.349 as the thickness in inches, instead of 0.3125, or 5/16ths, the actual thickness. If we take the pressure per square inch instead of per circular inch, we obtain the following rule, which is somewhat simpler:--multiply the internal diameter of the cylinder in inches by the pressure in pounds per square inch, and divide the product by 8,900; the result is the thickness in inches. Both these rules give the strain about one fourth of the elastic force, or 4,450 lbs. per square inch of sectional area of the iron; but 3,000 lbs. is enough when the flame impinges directly on the iron, as in some of the ordinary cylindrical boilers, and the rule may be adapted for that strain by taking 6,000 as a divisor instead of 8,900. 303. _Q._--In marine and wagon boilers, which are not of a cylindrical form, how do you procure the requisite strength? _A._--Where the sides of the boiler are flat, instead of being cylindrical, a sufficient number of stays must be introduced to withstand the pressure; and it is expedient not to let the strain upon these stays be more than 3,000 lbs. per square inch of section, as the strength of internal stays in boilers is generally soon diminished by corrosion. Indeed, a strain at all approaching that upon locomotive boilers would be very unsafe in the case of marine boilers, on account of the corrosion, both internal and external, to which marine boilers are subject. The stays should be small and numerous rather than large and few in number, as, when large stays are employed, it is difficult to keep them tight at the ends, and oxidation of the shell follows from leakage at the ends of the stays. All boilers should be proved, when new, to twice or three times the pressure they are intended to bear, and they should be proved occasionally by the hand pump when in use, to detect any weakness which corrosion may have occasioned. 304._ Q._--Will you describe the disposition of the stays in a marine boiler? _A._--If the pressure of steam be 20 lbs. on the square inch, which is a very common pressure in tubular boilers, there will be a pressure of 2,880 lbs. on every square foot of flat surface; so that if the strain upon the stays is not to exceed 3,000 lbs. on the square inch of section, there must be nearly a square inch of sectional area of stay for every square foot of flat surface on the top and bottom, sides, and ends of the boiler. This very much exceeds the proportion usually adopted; and in scarcely any instance are boilers stayed sufficiently to be safe when the shell is composed of flat surfaces. The furnaces should be stayed together with bolts of the best scrap iron, 1-1/4 inch in diameter, tapped through both plates of the water space with thin nuts in each furnace; and it is expedient to make the row of stays, running horizontally near the level of the bars, sufficiently low to come beneath the top of the bars, so as to be shielded from the action of the fire, with which view they should follow the inclination of the bars. The row of stays between the level of the bars and the top of the furnace should be as near the top of the furnace as will consist with the functions they have to perform, so as to be removed as far as possible from the action of the heat; and to support the furnace top, cross bars may either be adopted, to which the top is secured with bolts, as in the case of locomotives, or stays tapped into the furnace top, with a thin nut beneath, may be carried to the top of the boiler; but very little dependence can be put in such stays as stays for keeping down the top of the boiler; and the top of the boiler must, therefore, be stayed nearly as much as if the stays connecting it with the furnace crowns did not exist. The large rivets passing through thimbles, sometimes used as stays for water spaces or boiler shells, are objectionable; as, from the great amount of hammering such rivets have to receive to form the heads, the iron becomes crystalline, so that the heads are liable to come off, and, indeed, sometimes fly off in the act of being formed. If such a fracture occurs between the boilers after they are seated in their place, or in any position not accessible from the outside, it will in general be necessary to empty the faulty boiler, and repair the defect from the inside. 305. _Q._--What should be the pitch or numerical distribution of the stays? _A._--The stays, where the sides of the boiler are flat, and the pressure of the steam is from 20 to 30 lbs., should be pitched about a foot or 18 inches asunder; and in the wake of the tubes, where stays cannot be carried across to connect the boiler sides, angle iron ribs, like the ribs of a ship, should be riveted to the interior of the boiler, and stays of greater strength than the rest should pass across, above, and below the tubes, to which the angle irons would communicate the strain. The whole of the long stays within a boiler should be firmly riveted to the shell, as if built with and forming a part of it; as, by the common method of fixing them in by means of cutters, the decay or accidental detachment of a pin or cutter may endanger the safety of the boiler. Wherever a large perforation in the shell of any circular boiler occurs, a sufficient number of stays should be put across it to maintain the original strength; and where stays are intercepted by the root of the funnel, short stays in continuation of them should be placed inside. BOILER EXPLOSIONS. 306. _Q._--What is the chief cause of boiler explosions? _A._--The chief cause of boiler explosions is, undoubtedly, too great a pressure of steam, or an insufficient strength of boiler; but many explosions have also arisen from the flues having been suffered to become red hot. If the safety valve of a boiler be accidentally jammed, or if the plates or stays be much worn by corrosion, while a high pressure of steam is nevertheless maintained, the boiler necessarily bursts; and if, from an insufficiency of water in the boiler, or from any other cause, the flues become highly heated, they may be forced down by the pressure of the steam, and a partial explosion may be the result. The worst explosion is where the shell of the boiler bursts; but the collapse of a furnace or flue is also very disastrous generally to the persons in the engine room; and sometimes the shell bursts and the flues collapse at the same time; for if the flues get red hot, and water be thrown upon them either by the feed pump or otherwise, the generation of steam may be too rapid for the safety valve to permit its escape with sufficient facility, and the shell of the boiler may, in consequence, be rent asunder. Sometimes the iron of the flues becomes highly heated in consequence of the improper configuration of the parts, which, by retaining the steam in contact with the metal, prevents the access of the water: the bottoms of large flues, upon which the flame beats down, are very liable to injury from this cause; and the iron of flues thus acted upon may be so softened that the flues will collapse upward with the pressure of the steam. The flues of boilers may also become red hot in some parts from the attachment of scale, which, from its imperfect conducting power, will cause the iron to be unduly heated; and if the scale be accidentally detached, a partial explosion may occur in consequence. 307. _Q._--Does the contact of water with heated metal occasion an instantaneous generation of steam? _A._--It is found that a sudden disengagement of steam does not immediately follow the contact of water with the hot metal, for water thrown upon red hot iron is not immediately converted into steam, but assumes the spheroidal form and rolls about in globules over the surface. These globules, however high the temperature of the metal may be on which they are placed, never rise above the temperature of 205°, and give off but very little steam; but if the temperature of the metal be lowered, the water ceases to retain the spheroidal form, and comes into intimate contact with the metal, whereby a rapid disengagement of steam takes place. If water be poured into a very hot copper flask, the flask may be corked up, as there will be scarce any steam produced so long as the high temperature is maintained; but so soon as the temperature is suffered to fall below 350° or 400°, the spheroidal condition being no longer maintainable, steam is generated with rapidity, and the cork will be projected from the mouth of the flask with great force. 308. _Q._--What precautions can be taken to prevent boiler explosions? _A._--One useful precaution against the explosion of boilers from too great an internal pressure, consists in the application of a steam gauge to each boiler, which will make the existence of any undue pressure in any of the boilers immediately visible; and every boiler should have a safety valve of its own, the passage leading to which should have no connection with the passage leading to any of the stop valves used to cut off the connection between the boilers; so that the action of the safety valve may be made independent of the action of the stop valve. In some cases stop valves have jammed, or have been carried from their seats into the mouth of the pipe communicating between them, and the action of the safety valves should be rendered independent of all such accidents. Safety valves, themselves, sometimes stick fast from corrosion, from the spindles becoming bent, from a distortion of the boiler top with a high pressure, in consequence of which the spindles become jammed in the guides, and from various other causes which it would be tedious to enumerate; but the inaction of the safety valves is at once indicated by the steam gauge, and when discovered, the blow through valves of the engine and blow off cocks of the boiler should at once be opened, and the fires raked out. A cone in the ball of the waste steam pipe to send back the water carried upward by the steam, should never be inserted; as in some cases this cone has become loose, and closed up the mouth of the waste steam pipe, whereby the safety valves being rendered inoperative, the boiler was in danger of bursting. 309. _Q._--May not danger arise from excessive priming? _A._--If the water be carried out of the boiler so rapidly by priming that the level of the water cannot be maintained, and the flues or furnaces are in danger of becoming red hot, the best plan is to open every furnace door and throw in a few buckets full of water upon the fire, taking care to stand sufficiently to the one side to avoid being scalded by the rush of steam from the furnace. There is no time to begin drawing the fires in such an emergency, and by this treatment the fires, though not altogether extinguished, will be rendered incapable of doing harm. If the flues be already red hot, on no account must cold water be suffered to enter the boiler, but the heat should be maintained in the furnaces, and the blow off cocks be opened, or the mud hole doors loosened, so as to let all the water escape; but at the same time the pressure must be kept quite low in the boiler, so that there will be no danger of the hot flues collapsing with the pressure of the steam. 310. _Q._--Are plugs of fusible metal useful in preventing explosions? _A._--Plugs of fusible metal were at one time in much repute as a precaution against explosion, the metal being so compounded that it melted with the heat of high pressure steam; but the device, though ingenious, has not been found of any utility in practice. The basis of fusible metal is mercury, and it is found that the compound is not homogeneous, and that the mercury is forced by the pressure of the steam out of the interstices of the metal combined with it, leaving a porous metal which is not easily fusible, and which is, therefore, unable to perform its intended function. In locomotives, however, and also in some other boilers, a lead rivet is inserted with advantage in the crown of the fire box, which is melted out if the water becomes too low, and thus gives notice of the danger. 311. _Q._--May not explosion occur in marine boilers from the accumulation of salt on the flues? _A._--Yes, in marine boilers this is a constant source of danger, which is only to be met by attention on the part of the engineer. If the water in the boiler be suffered to become too salt, an incrustation of salt will take place on the furnaces, which may cause them to become red hot, and they may then be collapsed even by their own weight aided by a moderate pressure of steam. The expedients which should be adopted for preventing such an accumulation of salt from taking place within the boiler as will be injurious to it, properly fall under the head of the management of steam boilers, and will be explained in a subsequent chapter. CHAPTER VI. PROPORTIONS OF ENGINES. * * * * * STEAM PASSAGES. 312. _Q._--What size of orifice is commonly allowed for the escape of the steam through the safety valve in low pressure engines? _A._--About 0.8 of a circular inch per horse power, or a circular inch per 1-1/4 horse power. The following rule, however, will give the dimensions suitable for all kinds of engines, whether high or low pressure:--multiply the square of the diameter of the cylinder in inches by the speed of the piston in feet per minute, and divide the product by 375 times the pressure on the boiler per square inch; the quotient is the proper area of the safety valve in square inches. This rule of course supposes that the evaporating surface has been properly proportioned to the engine power. 313. _Q._--Is this rule applicable to locomotives? _A._--It is applicable to high pressure engines of every kind. The dimensions of safety valves, however, in practice are very variable, being in some cases greater, and in some cases less, than what the rule gives, the consideration being apparently as often what proportions will best prevent the valve from sticking in its seat, as what proportions will enable the steam to escape freely. In Bury's locomotives, the safety valve was generally 2-1/2 inches diameter for all sizes of boiler, and the valve was kept down by a lever formed in the proportion of 5 to 1, fitted at one end with a Salter's balance. As the area of the valve was 5 square inches, the number of pounds shown on the spring balance denoted the number of pounds pressure on each square inch of the boiler. 314. _Q._--Is there only one safety valve in a locomotive boiler? _A._--There are always two. 315. _Q._--And are they always pressed down by a spring balance, and never by weights? _A._--They are never pressed down by weights; in fact, weights would not answer on a locomotive at all, as they would jump up and down with the jerks or jolts of the train, and cause much of the steam to escape. In land and marine boilers, however, the safety valve is always kept down by weights; but in steam vessels a good deal of steam is lost in stormy weather by the opening of the valve, owing to the inertia of the weights when the ship sinks suddenly in the deep recess between the waves. 316. _Q._--What other sizes of safety valves are used in locomotives? _A._--Some are as large as 4 inches diameter, giving 12 square inches of area; and others are as small as 1-3/16 inch diameter, giving 1 square inch of area. 317. _Q._--And are these valves all pressed down by a Salter's spring balance? _A._--In the great majority of cases they are so, and the lever by which they are pressed down is generally graduated in the proportion of the area of the valve to unity; that is, in the case of a valve of 12 inches area, the long end of the lever to which the spring balance is attached is 12 times the length of the short end, so that the weight or pressure on the balance shows the pressure per square inch on the boiler. In some cases, however, a spiral spring, and in other cases a pile of elliptical springs, is placed directly upon the top of the valve, and it appears desirable that one of the valves at least should be loaded in this manner. It is difficult when the lever is divided in such a proportion as 12 to 1, to get sufficient lift of the valve without a large increase of pressure on the spring; and it appears expedient, therefore, to employ a shorter lever, which involves either a reduction in the area of the valve, or an increased strength in the spring. 318. _Q._--What are the proper dimensions of the steam passages? _A._--In slow working engines the common size of the cylinder passages is one twenty-fifth of the area of the cylinder, or one fifth of the diameter of the cylinder, which is the same thing. This proportion corresponds very nearly with one square inch per horse power when the length of the cylinder is about equal to its diameter; and one square inch of area per horse power for the cylinder ports and eduction passages answers very well in the case of engines working at the ordinary speed of 220 feet per minute. The area of the steam pipe is usually made less than the area of the eduction pipe, especially when the engine is worked expansively, and with a considerable pressure of steam. In the case of ordinary condensing engines, however, working with the usual pressure of from 4 to 8 lbs. above the atmosphere, the area of the steam pipe is not less than a circular inch per horse power. In such engines the diameter of the steam pipe may be found by the following rule: divide the number of nominal horse power by 0.8 and extract the square root of the quotient, which will be the internal diameter of the steam pipe. 319. _Q._--Will you explain by what process of computation these proportions are arrived at? _A._--The size of the steam pipe is so regulated that there will be no material disparity of pressure between the cylinder and boiler; and in fixing the size of the eduction passage the same object is kept in view. When the diameter of the cylinder and the velocity with which the piston travels are known, it is easy to tell what the velocity of the steam in the steam pipe will be; for if the area of the cylinder be 25 times greater than that of the steam pipe, the steam in the steam pipe must travel 25 times faster than the piston, and the difference of pressure requisite to produce this velocity of the steam can easily be ascertained, by finding what height a column of steam must be to give that velocity, and what the weight or pressure is of such a column. In practice, however, this proportion is always exceeded from the condensation of steam in the pipe. 320. _Q._--If the relation you have mentioned subsist between the area of the steam passages and the velocity of the piston, then the passages must be larger when the piston travels very rapidly? _A._--And they are so made. The area of the ports of locomotive engines is usually so proportioned as to be from 1/10th to 1/8th the area of the cylinder--in some cases even as much as 1/6th; and in all high speed engines the ports should be very large, and the valve should have a good deal of travel so as to open the port very quickly. The area of port which it appears advisable to give to modern engines of every description, is expressed by the following rule:--multiply the area of the cylinder in square inches by the speed of the piston in feet per minute, and divide the product by 4,000; the quotient is the area of each cylinder port in square inches. This rule gives rather more than a square inch of port per nominal horse power to condensing engines working at the ordinary speed; but the excess is but small, and is upon the right side. For engines travelling very fast it gives a good deal more area than the common proportion, which is too small in nearly every case. In locomotive engines the eduction pipe passes into the chimney and the force of the issuing steam has the effect of maintaining a rapid draught through the furnace as before explained. The orifice of the waste steam pipe, or the blast pipe as it is termed, is much contracted in some engines with the view of producing a fiercer draught, and an area of 1/22d of the cylinder is a common proportion; but this is as much contraction as should be allowed, and is greater than is advisable. 321. _Q._--In engines moving at a high rate of speed, you have stated that it is important to give the valve lead, or in other words to allow the steam to escape before the end of the stroke? _A._--Yes, this is very important, else the piston will have to force out the steam from the cylinder, and will be much resisted. Near the end of the stroke the piston begins to travel slowly, and if the steam be then permitted to escape, very little of the effective stroke is lost, and time is afforded to the steam, before the motion of the piston is again accelerated, to make its escape by the port. In some locomotives, from inattention to this adjustment, and from a contracted area of tube section, which involved a strong blast, about half the power of the engine has been lost; but in more recent engines, by using enlarged ports and by giving sufficient lead, this loss has been greatly diminished. 322. _Q._--What do you call sufficient lead? _A._--In fast going engines I would call it sufficient lead, when the eduction port was nearly open at the end of the stroke. 323. _Q._--Can you give any example of the benefit of increasing the lead? _A._--The early locomotives were made with very little lead, and the proportions were in fact very much the same as those previously existing in land engines. About 1832, the benefits of lap upon the valve, which had been employed by Boulton and Watt more than twenty years before, were beginning to be pretty generally apprehended; and, in the following year, this expedient of economy was applied to the steamer Manchester, in the Clyde, and to some other vessels, with very marked success. Shortly after this time, lap began to be applied to the valves of locomotives, and it was found that not only was there a benefit from the operation of expansion, but that there was a still greater benefit from the superior facility of escape given to the steam, inasmuch as the application of lap involved the necessity of turning the eccentric round upon the shaft, which caused the eduction to take place before the end of the stroke. In 1840, one of the engines of the Liverpool and Manchester Railway was altered so as to have 1 inch lap on the valve, and 1 inch opening on the eduction side at the end of the stroke, the valve having a total travel of 4-1/4 inches. The consumption of fuel per mile fell from 36.3 lbs. to 28.6 lbs, or about 25 per cent., and a softer blast sufficed. By using larger exhaust passages, larger tubes, and closer fire bars, the consumption was subsequently brought down to 15 lbs. per mile. AIR PUMP, CONDENSER, AND HOT AND COLD WATER PUMPS. 324. _Q._--Will you state the proper dimensions of the air pump and condenser in laud and marine engines? _A_--Mr. Watt made the air pump of his engine half the diameter of the cylinder and half the stroke, or one eighth of the capacity, and the condenser was usually made about the same size as the air pump; but as the pressure of the steam has been increased in all modern engines, it is better to make the air pump a little larger than this proportion. 0.6 of the diameter of the cylinder and half the stroke answers very well, and the condenser may be made as large as it can be got with convenience, though the same size as the air pump will suffice. 325. _Q._--Are air pumps now sometimes made double acting? _A._--Most of the recent direct acting marine engines for driving the screw are fitted with a double acting air pump, and when the air pump is double acting, it need only be about half the size that is necessary when it is single acting. It is single acting in nearly every case, except the case of direct acting screw engines of recent construction. 326. _Q._--What is the difference between a single and a double acting air pump? _A._--The single acting air pump expels the air and water from the condenser only in the upward stroke of the pump, whereas a double acting air pump expels the air and water both in the upward and downward stroke. It has, therefore, to be provided with inlet and outlet valves at both ends, whereas the single acting pump has only to be provided with an inlet or foot valve, as it is termed, at the bottom, and with an outlet or delivery valve, as it is termed, at the top. The single acting air pump requires to be provided with a valve or valves in the piston or bucket of the pump, to enable the air and water lying below the bucket when it begins to descend, and which have entered from the condenser during the upward stroke, to pass through the bucket into the space above it during the downward stroke, from whence they are expelled into the atmosphere on the upward stroke succeeding. But in the double acting air pump no valve is required in the piston or bucket of the pump, and all that is necessary is an inlet and outlet valve at each end. 337. _Q_--What are the dimensions of the foot and discharge valves of the air pump? _A._--The area through the foot and discharge valves is usually made equal to one fourth of the area of the air pump, and the diameter of the waste water pipe is made one fourth of the diameter of the cylinder, which gives an area somewhat less than that of the foot and discharge valve passages. But this proportion only applies in slow engines. In fast engines, with the air pump bucket moving as fast as the piston, the area through the foot and discharge valves should be equal to the area of the pump itself, and the waste water pipe should be of about the same dimensions. 328. _Q._--You have stated that double acting air pumps need only be of half the size of single acting ones. Does that relation hold at all speeds? _A._--It holds at all speeds if the velocity of the pump buckets are in each case the same; but it does not hold if the engine with the single acting pump works slowly, and the engine with the double acting pump moves rapidly, as in the case of direct acting screw engines. All pumps moving at a high rate of speed lose part of their efficiency, and such pumps should therefore be of extra size. 329. _Q._--How do you estimate the quantity of water requisite for condensation? _A._--Mr. Watt found that the most beneficial temperature of the hot well of his engines was 100 degrees. If, therefore, the temperature of the steam be 212°, and the latent heat 1,000°, then 1,212° may be taken to represent the heat contained in the steam, or 1,112° if we deduct the temperature of the hot well. If the temperature of the injection water be 50°, then 50 degrees of cold are available for the abstraction of heat; and as the total quantity of heat to be abstracted is that requisite to raise the quantity of water in the steam 1,112 degrees, or 1,112 times that quantity one degree, it would raise one fiftieth of this, or 22.24 times the quantity of water in the steam, 50 degrees. A cubic inch of water therefore raised into steam will require 22.24 cubic inches of water at 50 degrees for its condensation, and will form therewith 23.24 cubic inches of hot water at 100 degrees. Mr. Watt's practice was to allow about a wine pint (28.9 cubic inches) of injection water, for every cubic inch of water evaporated from the boiler. 330. _Q._--Is not a good vacuum in an engine conducive to increased power? _A._--It is. 331. _Q._--And is not the vacuum good in the proportion in which the temperature is low, supposing there to be no air leaks? _A._--Yes. 332. _Q._--Then how could Mr. Watt find a temperature of 100° in the water drawn from the condenser, to be more beneficial than a temperature of 70° or 80°, supposing there to be an abundant supply of cold water? 333. _A._--Because the superior vacuum due to a temperature of 70° or 80° involves the admission of so much cold water into the condenser, which has afterward to be pumped out in opposition to the pressure of the atmosphere, that the gain in the vacuum does not equal the loss of power occasioned by the additional load upon the pump, and there is therefore a clear loss by the reduction of the temperature below 100°, if such reduction be caused by the admission of an additional quantity of water. If the reduction of temperature, however, be caused by the use of colder water, there is a gain produced by it, though the gain will within certain limits be greater if advantage be taken of the lowness of the temperature to diminish the quantity of injection. 334. _Q._--How do you determine the proper area of the injection orifice? _A._--The area of the injection orifice proper for any engine can easily be told when the quantity of water requisite to condense the steam is known, and the pressure is specified under which the water enters the condenser. The vacuum in the condenser may be taken at 26 inches of mercury, which is equivalent to a column of water 29.4 ft. high, and the square root of 29.4 multiplied by 8.021 is 43.15, which is the velocity in feet per second that a heavy body would acquire in falling 29.4 ft., or with which the water would enter the condenser. Now, if a cubic foot of water evaporated per hour be equivalent to an actual horse power, and 28.9 cubic inches of water be requisite for the condensation of a cubic inch of water in the form of steam, 28.9 cubic feet of condensing water per horse power per hour, or 13.905 cubic inches per second, will be necessary for the engine, and the size of the injection orifice must be such that this quantity of water flowing with the velocity of 43.15 ft. per second, or 517.8 inches per second, will gain admission to the condenser. Dividing, therefore, 13.905, the number of cubic inches to be injected, by 517.8, the velocity of influx in inches per second, we get 0.02685 for the area of the orifice in square inches; but inasmuch as it has been found by experiment that the actual discharge of water through a hole in a thin plate is only six tenths of the theoretical discharge on account of the contracted vein, the area of the orifice must be increased in the proportion of such diminution of effect, or be made 0.04475, or 1/22d of a square inch per horse power. This, it will be remarked, is the theoretical area required per actual horse power; but as the friction and contractions in the pipe further reduce the discharge, the area is made 1/15th of a square inch per actual horse power, or rather per cubic foot of water evaporated from the boiler. 335. _Q._--Cannot the condensation of the steam be accomplished by any other means than by the admission of cold water into the condenser? _A._--It may be accomplished by the method of external cold, as it is called, which consists in the application of a large number of thin metallic surfaces to the condenser, on the one side of which the steam circulates, while on the other side there is a constant current of cold water, and the steam is condensed by coming into contact with the cold surfaces, without mingling with the water used for the purpose of refrigeration. The first kind of condenser employed by Mr. Watt was constructed after this fashion, but he found it in practice to be inconvenient from its size, and to become furred up or incrusted when the water was bad, whereby the conducting power of the metal was impaired. He therefore reverted to the use of the jet of cold water, as being upon the whole preferable. The jet entered the condenser instead of the cylinder as was the previous practice, and this method is now the one in common use. Some few years ago, a good number of steam vessels were fitted with Hall's condensers, which operated on the principle of external cold, and which consisted of a faggot of small copper tubes surrounded by water; but the use of those condensers has not been persisted in, and most of the vessels fitted with them have returned to the ordinary plan. 336. _Q._--You stated that the capacity of the feed pump was 1/240th of the capacity of the cylinder in the case of condensing engines,--the engine being double acting and the pump single acting,--and that in high pressure engines the capacity of the pump should be greater in proportion to the pressure of the steam. Can you give any rule that will express the proper capacity for the feed pump at all pressures? _A._--That will not be difficult. In low pressure engines the pressure in the boiler may be taken at 5 lbs. above the atmospheric pressure, or 20 lbs. altogether; and as high pressure steam is merely low pressure steam compressed into a smaller compass, the size of the feed pump in relation to the size of the cylinder must obviously vary in the direct proportion of the pressure; and if it be 1/240th of the capacity of the cylinder when the total pressure of the steam is 20 lbs., it must be 1/120th of the capacity of the cylinder when the pressure is 40 lbs. per square inch, or 25 lbs. per square inch above the atmospheric pressure. This law of variation is expressed by the following rule:--multiply the capacity of the cylinder in cubic inches by the total pressure of the steam in lbs. per square inch, or the pressure per square inch on the safety valve plus 15, and divide the product by 4,800; the quotient is the capacity of the feed pump in cubic inches, when the feed pump is single acting and the engine double acting. If the feed pump be double acting, or the engine single acting, the capacity of the pump must just be one half of what is given by this rule. 337. _Q._--But should not some addition be made to the size of pump thus obtained if the pump works at a high rate of speed? _A._--No; this rule makes allowance for defective action. All pumps lift much less water than is due to the size of their barrels and the number of their strokes. Moderately good pumps lose 50 per cent. of their theoretical effect, and bad pumps 80 per cent. 338. _Q._--To what is this loss of effect to be chiefly ascribed? _A._--Mainly to the inertia of the water, which, if the pump piston be drawn up very rapidly, cannot follow it with sufficient rapidity; so that there may be a vacant space between the piston and the water; and at the return stroke the momentum of the water in the pipe expends itself in giving a reverse motion to the column of water approaching the pump. Messrs. Kirchweger and Prusman, of Hanover, have investigated this subject by applying a revolving cock at the end of a pipe leading from an elevated cistern containing water, and the water escaped at every revolution of the cock in the same manner as if a pump were drawing it. With a column of water of 17 feet, they found that at 80 revolutions of the cock per minute, the water delivered per minute by the cock was 9.45 gallons; but with 140 revolutions of the cock per minute, the water delivered per minute by the cock was only 5.42 gallons. They subsequently applied an air vessel to the pipe beside the cock, when the discharge rose to 12.9 gallons per minute with 80 revolutions, and 18.28 gallons with 140 revolutions. Air vessels should therefore be applied to the suction side of fast moving pumps, and this is now done with good results. 339. _Q._--What are the usual dimensions of the cold water pump of land engines? _A._--If to condense a cubic inch of water raised into steam 28.9 cubic inches of condensing water are required, then the cold water pump ought to be 28.9 times larger than the feed pump, supposing that its losses were equally great. The feed pump, however, is made sufficiently large to compensate for leaks in the boiler and loss of steam through the safety valve, so that it will be sufficient if the cold water pump be 24 times larger than the feed pump. This ratio is preserved by the following rule:-- multiply the capacity of the cylinder in cubic inches by the total pressure of the steam per square inch, or the pressure on the safety valve plus 15, and divide the product by 200. The quotient is the proper capacity of the cold water pump in cubic inches when the engine is double acting, and the pump single acting. FLY WHEEL. 340. _Q._--By what considerations do you determine the dimensions of the fly wheel of an engine? _A._--By a reference to the power generated, each half stroke of the engine, and the number of half strokes that are necessary to give to the fly wheel its standard velocity, supposing the whole power devoted to that object. In practice the power resident in the fly varies from 2-1/2 to 6 times that generated each half stroke; and if the weight of the wheel be equal to the pressure on the piston, its velocity must be such as it would acquire by falling through a height equal to from 2-1/2 to 6 times the stroke, according to the purpose for which the engine is intended. If a very equable motion is required, a heavier or swifter fly wheel must be employed. 341. _Q._--What is Boulton and Watt's rule for fly wheels? _A._--Their rule is one which under any given circumstances fixes the sectional area of the fly wheel rim, and it is as follows:--multiply 44,000 times the square of the diameter of the cylinder in inches by the length of the stroke in feet, and divide this product by the product of the square of the number of revolutions of the fly wheel per minute, multiplied by the cube of its diameter in feet. The quotient is the area of section of the fly wheel rim in square inches. STRENGTHS OF LAND ENGINES. 342. _Q._--Can you give a rule for telling the proper thickness of the cylinders of steam engines? _A._--In low pressure engines the thickness of metal of the cylinder, in engines of a medium size, should be about 1/40th of the diameter of the cylinder, which, with a pressure of steam of 20 lbs. above the atmosphere, will occasion a strain of only 400 Lbs. per square inch of section of the metal; the thickness of the metal of the trunnion bearings of oscillating engines should be 1/32d of the diameter of the cylinder, and the breadth of the bearing should be about half its diameter. In high pressure engines the thickness of the cylinder should be about 1/16th its diameter, which, with a pressure of steam of 80 lbs. upon the square inch, will occasion a strain of 640 lbs. upon the square inch of section of the metal; and the thickness of the metal of the trunnion bearings of high pressure oscillating engines should be 1/13th of the diameter of the cylinder. The strength, however, is not the sole consideration in proportioning cylinders, for they must be made of a certain thickness, however small the pressure is within them, that they may not be too fragile, and will stand boring. While, also, an engine of 40 inches diameter would be about one inch thick, the thickness would not be quite two inches in an 80 inch cylinder. In fact there will be a small constant added to the thickness for all diameters, which will be relatively larger the smaller the cylinders become. In the cylinders of Penn's 12 horse power engines, the diameter of cylinder being 21-1/2 inches, the thickness of the metal is 9/16ths: in Penn's 40 inch cylinders, the thickness is 1 inch, and in the engines of the Ripon, Pottinger, and Indus, by Messrs. Miller, Ravenhill and Co., with cylinders 76 inches diameter, the thickness of the metal is 1-11/16. These are all oscillating engines. 343. _Q._--What is the proportion of the piston rod? _A._--The diameter of the piston rod is usually made 1/10th of the diameter of the cylinder, or the sectional area of the piston rod is 1/100th of the area of the cylinder. This proportion, however, is not applicable to locomotive, or even fast moving marine engines. In locomotive engines the piston rod is made 1/7th of the diameter of the cylinder, and it is obvious that where the pressure on the piston is great, the piston rod must be larger than when the pressure on the piston is small. 344. _Q._--What are the proper dimensions of the main links of a land beam engine? _A._--The sectional area of the main links in land beam engines is 1/113th of the area of the cylinder, and the length of the main links is usually half the length of the stroke. 345. _Q._--What are the dimensions of the connecting rod of a land engine? _A._--In land engines the connecting rod is usually of cast iron with a cruciform section: the breadth across the arms of the cross is about 1/20th of the length of the rod, the sectional area at the centre 1/28th of the area of the cylinder, and at the ends 1/35th of the area of the cylinder: the length of the rod is usually 3-1/2 times the length of the stroke. It is preferable, however, to make the connecting rod of malleable iron, and then the dimensions will be those proper for marine engines. 346. _Q._--What was Mr. Watt's rule for the connecting rod? _A._--Some of his connecting rods were of iron and some of wood. To determine the thickness when of wood, multiply the square of the diameter of the cylinder in inches by the length of the stroke in feet, and divide the product by 24. Extract the fourth root of the quotient, which is the thickness in inches. For iron the rule is the same, only the divisor was 57.6 instead of 24. 347. _Q._--What are the dimensions of the end studs of a land engine beam? _A._--In low pressure engines the diameter of the end studs of the engine beam are usually made 1/9th of the diameter of the cylinder when of cast iron, and 1/10th when of wrought iron, which gives a load with low steam of about 500 lbs. per circular inch of transverse section; but a larger size is preferable, as with large bearings the brasses do not wear so rapidly and the straps are not so likely to be burst by the bearings becoming oval. These sizes, as also those which immediately follow, suppose the pressure on the piston to be 18 lbs. per circular inch. 348. _Q._--How is the strength of a cast iron gudgeon computed? _A._--To find the proper size of a cast iron gudgeon adapted to sustain any given weight:--multiply the weight in lbs. by the intended length of bearing expressed in terms of the diameter; divide the product by 500, and extract the square root of the quotient, which is the diameter in inches. 349. _Q._--What was Mr. Watt's rule for the strength of gudgeons? _A._--Supposing the gudgeon to be square, then, to ascertain the thickness, multiply the weight resting on the gudgeon by the distance between the trunnions, and divide the product by 333. Extract the cube root of the quotient, which is the thickness in inches. 350. _Q._--How do you find the proper strength for the cast iron beam of a land engine? _A._--If the force acting at the end of an engine beam be taken at 18 lbs. per circular inch of the piston, then the force acting at the middle will be 36 lbs. per circular inch of the piston, and the proper strength of the beam at the centre will be found by the following rule:--divide the weight in lbs. acting at the centre by 250, and multiply the quotient by the distance between the extreme centres. To find the depth, the breadth being given:--divide this product by the breadth in inches, and extract the square root of the quotient, which is the depth. The depth of a land engine beam at the ends is usually made one third of the depth at the centre (the depth at the centre being equal to the diameter of the cylinder in the case of low pressure engines), while the length is made equal to three times the length of the stroke, and the mean thickness 1/108th of the length--the width of the edge bead being about three times the thickness of the web. In many modern engines the force acting at the end of the beam is more than 18 lbs. per circular inch of the piston, but the above rules are still applicable by taking an imaginary cylinder with an area larger in the proportion of the larger pressure. 351. _Q._--What was Mr. Watt's rule for the main beams of his engines? _A._--Some of those beams were of wood and some of cast iron. The wood beams were so proportioned that the thickness was 1/58th of the circumference, and the depth 1/375. The side of the beam, supposing it square, was found by multiplying the diameter of the cylinder by the length of the stroke, and extracting the cube root of the quotient, which will be the depth or thickness of the beam. This rule allows a beam 16 feet long to bend 1/8th of an inch, and a beam 32 feet long to bend 1/4 of an inch. For cast iron beams the square of the diameter of the cylinder, multiplied by the length between the centres, is equal to the square of the depth, multiplied by the thickness. 352. _Q._--What law does the strength of beams and shafts follow? _A._--In the case of beams subjected to a breaking force, the strength with any given cohesion of the material will be proportional to the breadth, multiplied by the square of the depth; and in the case of revolving shafts exposed to a twisting strain, the strength with any given cohesive power of the material will be as the cube of the diameter. 353. _Q._--How is the strength of a cast iron shaft to resist torsion determined? _A._--Experiments upon the force requisite to twist off cast iron necks show that if the cube of the diameter of neck in inches be multiplied by 880, the product will be the force of torsion which will twist them off when acting at 6 inches radius; on this fact the following rule is founded: To find the diameter of a cast iron fly wheel shaft:--multiply the square of the diameter of the cylinder in inches, by the length of the crank in inches, and extract the cube root of the product, which multiply by 0.3025, and the result will be the proper diameter of the shaft in inches at the smallest part, when of cast iron. 354. _Q._--What was Mr. Watt's rule for the necks of his crank shafts? _A._--Taking the pressure on the piston at 12 lbs. pressure on the square inch, and supposing this force to be applied at one foot radius, divide the total pressure of the piston reduced to 1 foot of radius by 31.4, and extract the cube root of the quotient, which is the diameter of the shaft: or extract the cube root of 13.7 times the number of cubic feet of steam required to make one revolution, which is also the diameter of the shaft. 355. _Q._--Can you give any rule for the strength of the teeth of wheels? _A._--To find the proper dimensions for the teeth of a cast iron wheel:-- multiply the diameter of the pitch circle in feet by the number of revolutions to be made per minute, and reserve the product for a divisor; multiply the number of _actual_ horses power to be transmitted by 240, and divide the product by the above divisor, which will give the strength. If the pitch be given to find the breadth, divide the above strength by the square of the pitch in inches; or if the breadth be given, then to find the pitch divide the strength by the breadth in inches, and extract the square root of the quotient, which is the proper pitch in inches. The length of the teeth is usually about 5/8ths of the pitch. Pinions to work satisfactorily should not have less than 30 or 40 teeth, and where the speed exceeds 220 feet in the minute, the teeth of the larger wheel should be of wood, made a little thicker, to keep the strength unimpaired. 356. _Q._--What was Mr. Watt's rule for the pitch of wheels? _A._--Multiply five times the diameter of the larger wheel by the diameter of the smaller, and extract the fourth root of the product, which is the pitch. STRENGTH OF MARINE AND LOCOMOTIVE ENGINES. 357. _Q._--Cannot you give some rules of strength which will be applicable whatever pressure may be employed? _A._--In the rules already given, the effective pressure may be reckoned at from 18 to 20 lbs. upon every square inch of the piston, as is usual in land engines; and if the pressure upon every square inch of the piston be made twice greater, the dimensions must just be those proper for an engine of twice the area of piston. It will not be difficult, however, to introduce the pressure into the rules as an element of the computation, whereby the result will be applicable both to high and low pressure engines. 358. _Q._--Will you apply this mode of computation to a marine engine, and first find the diameter of the piston rod? _A._--The diameter of the piston rod may be found by multiplying the diameter of the cylinder in inches, by the square root of the pressure on the piston in lbs. per square inch, and dividing by 50, which makes the strain 1/7th of the elastic force. 359. _Q._--What will be the rule for the connecting rod, supposing it to be of malleable iron? _A._--The diameter of the connecting rod at the ends, may be found by multiplying 0.019 times the square root of the pressure on the piston in lbs. per square inch by the diameter of the cylinder in inches; and the diameter of the connecting rod in the middle may be found by the following rule:--to 0.0035 times the length of the connecting rod in inches, add 1, and multiply the sum by 0.019 times the square root of the pressure on the piston in lbs. per square inch, multiplied by the diameter of the cylinder in inches. The strain is equal to 1/6th of the elastic force. 360. _Q._--How will you find the diameter of the cylinder side rods of a marine engine? _A._--The diameter of the cylinder side rods at the ends may be found by multiplying 0.0129 times the square root of the pressure on the piston in lbs. per square inch by the diameter of the cylinder; and the diameter of the cylinder side rods at the middle is found by the following rule:--to 0.0035 times the length of the rod in inches, add 1, and multiply the sum by 0.0129 times the square root of the pressure on the piston in lbs. per square inch, multiplied by the diameter of the cylinder in inches; the product is the diameter of each side rod at the centre in inches. The strain upon the side rods is by these rules equal to 1/6th of the elastic force. 361. _Q._--How do you determine the dimensions of the crank? _A._--To find the exterior diameter of the large eye of the crank when of malleable iron:--to 1.561 times the pressure of the steam upon the piston in lbs. per square inch, multiplied by the square of the length of the crank in inches, add 0.00494 times the square of the diameter of the cylinder in inches, multiplied by the square of the number of lbs. pressure per square inch on the piston; extract the square root of this quantity; divide the result by 75.59 times the square root of the length of the crank in inches, and multiply the quotient by the diameter of the cylinder in inches; square the product and extract the cube root of the square, to which add the diameter of the hole for the reception of the shaft, and the result will be the exterior diameter of the large eye of the crank when of malleable iron. The diameter of the small eye of the crank may be found by adding to the diameter of the crank pin 0.02521 times the square root of the pressure on the piston in lbs. per square inch, multiplied by the diameter of the cylinder in inches. 362. _Q._--What will be the thickness of the crank web? _A._--The thickness of the web of the crank, supposing it to be continued to the centre of the shaft, would at that point be represented by the following rule:--to 1.561 times the square of the length of the crank in inches, add 0.00494 times the square of the diameter of the cylinder in inches, multiplied by the pressure on the piston in lbs. per square inch; extract the square root of the sum, which multiply by the diameter of the cylinder squared in inches, and by the pressure on the piston in lbs. per square inch; divide the product by 9,000, and extract the cube root of the quotient, which will be the proper thickness of the web of the crank when of malleable iron, supposing the web to be continued to the centre of the shaft. The thickness of the web at the crank pin centre, supposing it to be continued thither, would be 0.022 times the square root of the pressure on the piston in lbs. per square inch, multiplied by the diameter of the cylinder. The breadth of the web of the crank at the shaft centre should be twice the thickness, and at the pin centre 1-1/2 times the thickness of the web; the length of the large eye of the crank would be equal to the diameter of the shaft, and of the small eye 0.0375 times the square root of the pressure on the piston in lbs. per square inch, multiplied by the diameter of the cylinder. 363. _Q._--Will you apply the same method of computation to find the dimensions of a malleable iron paddle shaft? _A._--The method of computation will be as follows:--to find the dimensions of a malleable iron paddle shaft, so that the strain shall not exceed 5/6ths of the elastic force, or 5/6ths of the force iron is capable of withstanding without permanent derangement of structure, which in tensile strains is taken at 17,800 lbs. per square inch: multiply the pressure in lbs. per square inch on the piston by the square of the diameter of the cylinder in inches, and the length of the crank in inches, and extract the cube root of the product, which, multiplied by 0.08264, will be the diameter of the paddle shaft journal in inches when of malleable iron, whatever the pressure of the steam may be. The length of the paddle shaft journal should be 1-1/4 times the diameter; and the diameter of the part where the crank is put on is often made equal to the diameter over the collars of the journal or bearing. 364. _Q._--How do you find the diameter of the crank pin? _A._--The diameter of the crank pin in inches may be found by multiplying 0.02836 times the square root of the pressure on the piston in lbs. per square inch, by the diameter of the cylinder in inches. The length of the pin is usually about 9/8th times its diameter, and the strain if all thrown upon the end of the pin will be equal to the elastic force; but in ordinary working, the strain will only be equal to 1/3d of the elastic force. 365. _Q._--What are the dimensions of the cross head? _A._--If the length of the cross head be taken at 1.4 times the diameter of the cylinder, the dimensions of the cross head will be as follows:--the exterior diameter of the eye in the cross head for the reception of the piston rod, will be equal to the diameter of the hole, plus 0.02827 times the cube root of the pressure on the piston in lbs. per square inch, multiplied by the diameter of the cylinder in inches; and the depth of the eye will be 0.0979 times the cube root of the pressure on the piston in lbs. per square inch, multiplied by the diameter of the cylinder in inches. The diameter of each cross head journal will be 0.01716 times the square root of the pressure on the piston in lbs. per square inch, multiplied by the diameter of the cylinder in inches--the length of the journal being 9/8ths its diameter. The thickness of the web at centre will be 0.0245 times the cube root of the pressure on the piston in lbs. per square inch, multiplied by the diameter of the cylinder in inches; and the depth of web at centre will be 0.09178 times the cube root of the pressure on the piston in lbs. per square inch, multiplied by the diameter of the cylinder in inches. The thickness of the web at journal will be 0.0122 times the square root of the pressure on the piston in lbs. per square inch, multiplied by the diameter of the cylinder in inches; and the depth of the web at journal will be 0.0203 times the square root of the pressure upon the piston in lbs. per square inch, multiplied by the diameter of the cylinder in inches. In these rules for the cross head, the strain upon the web is 1/2.225 times the elastic force; the strain upon the journal in ordinary working is 1/2.33 times the elastic force; and if the outer ends of the journals are the only bearing points, the strain is 1/1.165 times the elastic force, which is very little in excess of the elastic force. 366. _Q._--How do you find the diameter of the main centre when proportioned according to this rule? _A._--The diameter of the main centre may be found by multiplying 0.0367 times the square root of the pressure upon the piston in lbs. per square inch, by the diameter of the cylinder in inches, which will give the diameter of the main centre journal in inches when of malleable iron, and the length of the main centre journal should be 1-1/2 times its diameter; the strain upon the main centre journal in ordinary working will be about 1/2 the elastic force. 367. _Q._--What are the proper dimensions of the gibs and cutters of an engine? _A._--The depth of gibs and cutters for attaching the piston rod to the cross head, is 0.0358 times the cube root of the pressure of the steam on the piston in lbs. per square inch, multiplied by the diameter of the cylinder; and the thickness of the gibs and cutters is 0.007 times the cube root of the pressure on the piston in lbs. per square inch, multiplied by the diameter of its cylinder. The depth of the cutter through the piston is 0.017 times the square root of the pressure on the piston in lbs. per square inch, multiplied by the diameter of the cylinder in inches; and the thickness of the cutter through the piston is 0.007 times the square root of the pressure on the piston in lbs. per square inch, multiplied by the diameter of the cylinder. 368. _Q._--Are not some of the parts of an engine constructed according to these rules too weak, when compared with the other parts? _A._--It is obvious, from the varying proportions subsisting in the different parts of the engine between the strain and the elastic force, that in engines proportioned by these rules--which represent nevertheless the average practice of the best constructors--some of the parts must possess a considerable excess of strength over other parts, and it appears expedient that this disparity should be diminished, which may best be done by increasing the strength of the parts which are weakest; inasmuch as the frequent fracture of some of the parts shows that the dimensions at present adopted for those parts are scarcely sufficient, unless the iron of which they are made is of the best quality. At the same time it is quite certain, that engines proportioned by these rules will work satisfactorily where good materials are employed; but it is important to know in what parts good materials and larger dimensions are the most indispensable. In many of the parts, moreover, it is necessary that the dimensions should be proportioned to meet the wear and the tendency to heat, instead of being merely proportioned to obtain the necessary strength; and the crank pin is one of the parts which requires to be large in diameter, and as long as possible in the bearing, so as to distribute the pressure, and prevent the disposition to heat which would otherwise exist. The cross head journals also should be long and large; for as the tops of the side rods have little travel, the oil is less drawn into the bearings than if the travel was greater, and is being constantly pressed out by the punching strain. This strain should therefore be reduced as far as possible by its distribution over a large surface. In the rules which are contained in the answers to the ten preceding questions (358 to 367) the pressure on the piston in lbs. per square inch is taken as the sum of the pressure of steam in the boiler and of the vacuum; the latter being assumed to be 15 lbs. per square inch. CHAPTER VII. CONSTRUCTIVE DETAILS OF BOILERS. * * * * * LAND AND MARINE BOILERS. 369. _Q._--Will you explain the course of procedure in the construction and setting of wagon boilers? _A._--Most boilers are made of plates three eighths of an inch thick, and the rivets are from three eighths to three fourths of an inch in diameter. In the bottom and sides of a wagon boiler the heads of the rivets, or the ends formed on the rivets before they are inserted, should be large and placed next the fire, or on the outside; whereas on the top of the boiler the heads should be on the inside. The rivets should be placed about two inches distant from centre to centre, and the centre of the row of rivets should be about one inch from the edge of the plate. The edges of the plates should be truly cut, both inside and outside, and after the parts of the boiler have been riveted together, the edges of the plates should be set up or caulked with a blunt chisel about a quarter of an inch thick in the point, and struck by a hammer of about three or four pounds weight, one man holding the caulking tool while another strikes. 370. _Q._--Is this the usual mode of caulking? _A._--No, it is not the usual mode; but it is the best mode, and is the mode adopted by Mr. Watt. The usual mode now is for one man to caulk the seams with a hammer in one hand and a caulking chisel in the other, and in some of the difficult corners of marine flue boilers it is not easy for two men to get in. A good deal of the caulking has also sometimes to be done with the left hand. 371. _Q._--Should the boiler be proved after caulking? _A._--The boiler should be filled with water and caulked afresh in any leaky part. When emptied again, all the joints should be painted with a solution of sal ammoniac in urine, and so soon as the seams are well rusted they should be dried with a gentle fire, and then be painted over with a thin putty formed of whiting and linseed oil, the heat being continued until the putty becomes so hard that it cannot be readily scratched with the nail, and care must be taken neither to burn the putty nor to discontinue the fire until it has become quite dry. 372. _Q._--How should the brickwork setting of a wagon boiler be built? _A._--In building the brickwork for the setting of the boiler, the part upon which the heat acts with most intensity is to be built with clay instead of mortar, but mortar is to be used on the outside of the work. Old bars of flat iron may be laid under the boiler chime to prevent that part of the boiler from being burned out, and bars of iron should also run through the brickwork to prevent it from splitting. The top of the boiler is to be covered with brickwork laid in the best lime, and if the lime be not of the hydraulic kind, it should be mixed with Dutch terrass, to make it impenetrable to water. The top of the boiler should be well plastered with this lime, which will greatly conduce to the tightness of the seams. Openings into the flues must be left in convenient situations to enable the flues to be swept out when required, and these openings may be closed with cast iron doors jointed with clay or mortar, which may be easily removed when required. Adjacent to the chimney a slit must be left in the top of the flue with a groove in the brickwork to enable the sliding door or damper to be fixed in that situation, which by being lowered into the flue will obstruct the passage of the smoke and moderate the draught, whereby the chimney will be prevented from drawing the flame into it before the heat has acted sufficiently upon the boiler. 373. _Q._--Are marine constructed in the same way as land boilers? _A._--There is very little difference in the two cases: the whole of the shells of marine boilers, however, should be double riveted with rivets 11/16ths of an inch in diameter, and 2-3/8th inches from centre to centre, the weakening effect of double riveting being much less than that of single riveting. The furnaces above the line of bars should be of the best Lowmoor, Bowling, or Staffordshire scrap plates, and the portion of each furnace above the bars should consist only of three plates, one for the top and one for each side, the lower seam of the side plates being situated beneath the level of the bars, so as not to be exposed to the heat of the furnace. The tube plates of tubular boilers should be of the best Lowmoor, or Bowling iron, seven eighths to one inch thick: the shells should be of the best Staffordshire, or Thornycroft S crown iron, 7/16ths of an inch thick. 374. _Q._--Of what kind of iron should the angle iron or corner iron be composed? _A._--Angle iron should not be used in the construction of boilers, as in the manufacture it becomes reedy, and is apt to split up in the direction of its length: it is much the safer practice to bend the plates at the corners of the boiler; but this must be carefully done, without introducing any more sharp bends than can be avoided, and plates which require to be bent much should be of Lowmoor iron. It will usually be found expedient to introduce a ring of angle iron around the furnace mouths, though it is discarded in the other parts of the boiler; but it should be used as sparingly as possible, and any that is used should be of the best quality. 375. _Q._--Is it not important to have the holes in the plates opposite to one another? _A._--The whole of the plates of a boiler should have the holes for the rivets punched, and the edges cut straight, by means of self-acting machinery, in which a travelling table carries forward the plate with an equal progression every stroke of the punch or shears; and machinery of this kind is now extensively employed. The practice of forcing the parts of boilers together with violence, by means of screw-jacks, and drifts through the holes, should not be permitted; as a great strain may thus be thrown upon the rivets, even when there is no steam in the boiler. All rivets should be of the best Lowmoor iron. The work should be caulked both within and without wherever it is accessible, but in the more confined situations within the flues the caulking will in many cases have to be done with the hand or chipping hammer, instead of the heavy hammer previously prescribed. 376. _Q._--How is the setting of marine boilers with internal furnaces effected? _A._--In the setting of marine boilers care must be taken that no copper bolts or nails project above the wooden platform upon which they rest, and also that no projecting copper bolts in the sides of the ship touch the boiler, as the galvanic action in such a case would probably soon wear the points of contact into holes. The platform may consist of three inch planking laid across the keelsons nailed with iron, nails, the heads of which are well punched down, and caulked and puttied like a deck. The surface may then be painted over with thin putty, and fore and aft boards of half the thickness may then be laid down and nailed securely with iron nails, having the heads well punched down. This platform must then be covered thinly and evenly with mastic cement and the boiler be set down upon it, and the cement must be caulked beneath the boiler by means of wooden caulking tools, so as completely to fill every vacuity. Coomings of wood sloped on the top must next be set round the boiler, and the space between the coomings and the boiler must be caulked full of cement, and be smoothed off on the top to the slope of the coomings, so as to throw off any water that might be disposed to enter between the coomings and the boiler. 377. _Q._--How is the cement used for setting marine boilers compounded? _A._--Mastic cement proper for the setting of boilers is sold in many places ready made. Hamelin's mastic is compounded as follows:--to any given weight of sand or pulverized earthenware add two thirds such given weight of powdered Bath, Portland, or other similar stone, and to every 560 lbs. weight of the mixture add 40 lbs. weight of litharge, 2 lbs. of powdered glass or flint, 1 lb. of minium, and 2 lbs. of gray oxide of lead; pass the mixture through a sieve, and keep it in a powder for use. When wanted for use, a sufficient quantity of the powder is mixed with some vegetable oil upon a board or in a trough in the manner of mortar, in the proportion of 605 lbs. of the powder to 5 gallons of linseed, walnut, or pink oil, and the mixture is stirred and trodden upon until it assumes the appearance of moistened sand, when it is ready for use. The cement should be used on the same day as the oil is added, else it will be set into a solid mass. 378. _Q._--What is the best length of the furnaces of marine boilers? _A._--It has already been stated that furnace bars should not much exceed six feet in length, as it is difficult to manage long furnaces; but it is a frequent practice to make the furnaces long and narrow, the consequence of which is, that it is impossible to fire them effectually at the after end, especially upon long voyages and in stormy weather, and air escapes into the flues at the after end of the bars, whereby the efficacy of the boiler is diminished. Where the bars are very long it will generally be found that an increased supply of steam and a diminished consumption of coal will be the consequence of shortening them, and the bars should always lie with a considerable inclination to facilitate the distribution of the fuel over the after part of the furnace. When there are two lengths of bars in the furnace, it is expedient to make the central cross bar for bearing up the ends double, and to leave a space between the ends of the bars so that the ashes may fall through between them. The space thus left enables the bars to expand without injury on the application of heat, whereas without some such provision the bars are very liable to get burned out by bending up in the centre, or at the ends, as they must do if the elongation of the bars on the application of heat be prevented; and this must be the effect of permitting the spaces at the ends of the bars to be filled up with ashes. At each end of each bed of bars it is expedient to leave a space which the ashes cannot fill up so as to cause the bars to jam; and care must be taken that the heels of the bars do not come against any of the furnace bearers, whereby the room left at the end of the bars to permit the expansion would be rendered of no avail. 379. _Q._--Have you any remarks to offer respecting the construction and arrangement of the furnace bridges and dampers of marine boilers? _A._--The furnace bridges of marine boilers are walls or partitions built up at the ends of the furnaces to narrow the opening for the escape of heat into the flues. They are either made of fire brick or of plate iron containing water: in the case of water bridges, the top part of the bridge should be made with a large amount of slant so as to enable the steam to escape freely, but notwithstanding this precaution the plates of water bridges are apt to crack at the bend, so that fire brick bridges appear on the whole to be preferable. In shallow furnaces the bridges often come too near the furnace top to enable a man to pass over them; and it will save expense if in such bridges the upper portion is constructed of two or three fire blocks, which may be lifted off where a person requires to enter the flues to sweep or repair them, whereby the perpetual demolition and reconstruction of the upper part of the bridge will be prevented. 380. _Q._--What is the benefit of bridges? _A._--Bridges are found in practice to have a very sensible operation in increasing the production of steam, and in some boilers in which the brick bridges have been accidentally knocked down by the firemen, a very considerable diminution in the supply of steam has been experienced. Their chief operation seems to lie in concentrating the heat within the furnace to a higher temperature, whereby the heat is more rapidly transmitted from the furnace to the water, and less heat has consequently to be absorbed by the flues. In this way the bridges render the heating surface of a boiler more effective, or enable a smaller amount of heating surface to suffice. 381. _Q._--Are the bridges behind the furnaces the only bridges used in steam boilers? _A._--It is not an uncommon practice to place a hanging bridge, consisting of a plate of iron descending a certain distance into the flue, at that part of the flue where it enters the chimney, whereby the stratum of hot air which occupies the highest part of the flue is kept in protracted contact with the boiler, and the cooler air occupying the lower part of the flue is that which alone escapes. The practice of introducing a hanging bridge is a beneficial one in the case of some boilers, but is not applicable universally, as boilers with a small calorimeter cannot be further contracted in the flue without a diminution in their evaporating power. In tubular boilers a hanging bridge is not applicable, but in some cases a perforated plate is placed against the ends of the tubes, which by suitable connections is made to operate as a sliding damper which partially or totally closes up the end of every tube, and at other times a damper constructed in the manner of a venetian blind is employed in the same situation. These varieties of damper, however, have only yet been used in locomotive boilers, though applicable to tubular boilers of every description. 382. _Q._--Is it a benefit to keep the flues or tubes appertaining to each furnace distinct? _A._--In a flue boiler this cannot be done, but in a tubular boiler it is an advantage that there should be a division between the tubes pertaining to each furnace, so that the smoke of each furnace may be kept apart from the smoke of the furnace adjoining it until the smoke of both enters the chimney, as by this arrangement a furnace only will be rendered inoperative in cleaning the fires instead of a boiler, and the tubes belonging to one furnace may be swept if necessary at sea without interfering injuriously with the action of the rest. In a steam vessel it is necessary at intervals to empty out one or more furnaces every watch to get rid of the clinkers which would otherwise accumulate in them; and it is advisable that the connection between the furnaces should be such that this operation, when being performed on one furnace, shall injure the action of the rest as little as possible. 383. _Q._--Can any constructive precautions be taken to prevent the furnaces and tube plates of the boiler from being burned by the intensity of the heat? _A._--The sides of the internal furnaces or flues in all boilers should be so constructed that the steam may readily escape from their surfaces, with which view it is expedient to make the bottom of the flue somewhat wider than the top, or slightly conical in the cross section; and the upper plates should always be overlapped by the plates beneath, so that the steam cannot be retained in the overlap, but will escape as soon as it is generated. If the sides of the furnace be made high and perfectly vertical, they will speedily be buckled and cracked by the heat, as a film of steam in such a case will remain in contact with the iron which will prevent the access of the water, and the iron of the boiler will be injured by the high temperature it must in that case acquire. To moderate the intensity of the heat acting upon the furnace sides, it is expedient to bring the outside fire bars into close contact with the sides of the furnace, so as to prevent the entrance of air through the fire in that situation, by which the intensity of the heat would be increased. The tube plate nearest the furnace in tubular boilers should also be so inclined as to facilitate the escape of the steam; and the short bent plate or flange of the tube plate, connecting the tube plate with the top of the furnace, should be made with a gradual bend, as, if the bend be sudden, the iron will be apt to crack or burn away from the concretion of salt. Where the furnace mouths are contracted by bending in the sides and top of the furnace, as is the general practice, the bends should be gradual, as salt is apt to accumulate in the pockets made by a sudden bend, and the plates will then burn into holes. 384. _Q._--In what manner is the tubing of boilers performed? _A._--The tubes of marine boilers are generally iron tubes, three inches in diameter, and between six and seven feet long; but sometimes brass tubes of similar dimensions are employed. When brass tubes are employed, the use of ferules driven into the ends of the tubes is sometimes employed to keep them tight; but when the tubes are of malleable iron, of the thickness of Russell's boiler tubes, they may be made tight merely by firmly driving them into the tube plates, and the same may be done with thick brass tubes. The holes in the tube plate next the front of the boiler are just sensibly larger in diameter than the holes in the other tube plate, and the holes upon the outer surfaces of both tube plates are very slightly countersunk. The whole of the tubes are driven through both tube plates from the front of the boiler,--the precaution, however, being taken to drive them in gently at first with a light hand hammer, until the whole of the tubes have been inserted to an equal depth, and then they may be driven up by degrees with a heavy hammer, whereby any distortion of the holes from unequal driving will be prevented. Finally, the ends of the tubes should be riveted up so as to fill the countersink; the tubes should be left a little longer than the distance between the outer surfaces of the tube plates, so that the countersink at the ends may be filled by staving up the end of the tube rather than by riveting it over; and the staving will be best accomplished by means of a mandril with a collar upon it, which is driven into the tube so that the collar rests upon the end of the tube to be riveted; or a tool like a blunt chisel with a recess in its point may be used, as is the more usual practice. 385. _Q._--Should not stays be introduced in substitution of some of the tubes? _A._--It appears expedient in all cases that some of the tubes should be screwed at the ends, so as to serve as stays if the riveting at the tube ends happens to be burned away, and also to act as abutments to the riveted tube--or else to introduce very strong rods of about the same diameter as a tube, in substitution of some of the tubes; and these stays should have nuts at each end both within and without the tube plates, which nuts should be screwed up, with white lead interposed, before the tubes are inserted. If the tubes are long, their expansion when the boiler is being blown off will be apt to start them at the ends, unless very securely fixed; and it is difficult to prevent brass tubes of large diameter and proportionate length from being started at the ends, even when secured by ferules; but the brass tubes commonly employed are so small as to be susceptible of sufficient compression endways by the adhesion due to the ferules to compensate for the expansion, whereby they are prevented from starting at the ends. In some, of the early marine boilers fitted with brass tubes, a galvanic action at the ends of the tubes was found to take place, and the iron of the tube plates was wasted away in consequence, with rapidity; but further experience proved the injury to be attributable chiefly to imperfect fitting, whereby a leakage was caused that induced oxidation, and when, the tubes were well fitted any injurious action at the ends of the tubes was found to cease. 386. _Q._--What is the best mode of constructing the chimney and the parts in connection therewith? _A._--In sea-going steamers the funnel plates are usually about nine feet long and 3/16ths thick; and where different flues or boilers have their debouch in the same chimney, it is expedient to run division plates up the chimney for a considerable distance, to keep the draughts distinct. The dampers should not be in the chimney but at the end of the boiler flue, so that they may be available for use if the funnel by accident be carried away. The waste steam pipe should be of the same height as the funnel, so as to carry the waste steam clear of it, for if the waste steam strikes the funnel it will wear the iron into holes; and the waste steam pipes should be made at the bottom with a faucet joint, to prevent the working of the funnel, when the vessel rolls, from breaking the pipe at the neck. There should be two hoops round the funnel, for the attachment of the funnel shrouds, instead of one, so that the funnel may not be carried overboard if one hoop breaks, or if the funnel breaks at the upper hoop from the corrosive action of the waste steam, as sometimes happens. The deck over the steam chest should be formed of an iron plate supported by angle iron beams, and there should be a high angle iron cooming round the hole in the deck through which the chimney ascends, to prevent any water upon the deck from leaking down upon the boiler. Around the lower part of the funnel there should be a sheet iron casing to prevent any inconvenient dispersion of heat in that situation, and another short piece of casing, of a somewhat larger diameter, and riveted to the chimney, should descend over the first casing, so as to prevent the rain or spray which may beat against the chimney from being poured down within the casing upon the top of the boiler. The pipe for conducting away the waste water from the top of the safety valve should lead overboard, and not into the bilge of the ship, as inconvenience arises from the steam occasionally passing through it, if it has its termination in the engine room. 387. _Q._--Are not the chimneys of some vessels made so that they may be lowered when required? _A._--The chimneys of small river vessels which have to pass under bridges are generally formed with a hinge, so that they may be lowered backward when passing under a bridge; and the chimneys of some screw vessels are made so as to shut up like a spyglass when the fires are put out and the vessel is navigated under sails. In smaller vessels, however, two lengths of chimney suffice; and in that case there is a standing piece on deck, which, however, does not project above the bulwarks. 388. _Q._--Will you explain any further details in the construction of marine boilers which occur to you as important? _A._--The man-hole and mud-hole doors, unless put on from the outside, like a cylinder cover, with a great number of bolts, should be put on from the inside with cross bars on the outside, and the bolts should be strong, and have coarse threads and square nuts, so that the threads may not be overrun, nor the nuts become round, by the unskilful manipulations of the firemen, by whom these doors are removed or replaced. It is very expedient that sufficient space should be left between the furnace and the tubes in all tubular boilers to permit a boy to go in to clear away any scale that may have formed, and to hold on the rivets in the event of repair being wanted; and it is also expedient that a vertical row of tubes should be left out opposite to each water space to allow the ascent of the steam and descent of the water, as it has been found that the removal of the tubes in that position, even in a boiler with deficient heating surface, has increased the production of steam, and diminished the consumption of fuel. The tubes should all be kept in the same vertical line, so as to permit the introduction of an instrument to scrape them; but they may be zig-zagged in the horizontal line, whereby a greater strength of metal will be obtained around the holes in the tube plates, and the tubes should not be placed too close together, else their heating efficacy will be impaired. INCRUSTATION AND CORROSION OF BOILERS. 389. _Q._--What is the cause of the formation of scale in marine boilers? _A._--Scale is formed in all boilers which contain earthy or saline matters, just in the way in which a scaly deposit, or rock, as it is sometimes termed, is formed in a tea kettle. In sea water the chief ingredient is common salt, which exists in solution: the water admitted to the boiler is taken away in the shape of steam, and the saline matter which is not vaporizable accumulates in process of time in the boiler, until its amount is so great that the water is saturated, or unable to hold any more in solution; the salt is then precipitated and forms a deposit which hardens by heat. The formation of scale, therefore, is similar to the process of making salt from sea water by evaporation, the boiler being, in fact, a large salt pan. 390. _Q._--But is the scale soluble in fresh water like the salt in a salt pan? _A._--No, it is not; or if soluble at all, is only so to a very limited extent. The several ingredients in sea water begin to be precipitated from solution at different degrees of concentration; and the sulphate and carbonate of lime, which begin to be precipitated when a certain state of concentration is reached, enter largely into the composition of scale, and give it its insoluble character. Pieces of waste or other similar objects left within a marine boiler appear, when taken out, as if they had been petrified; and the scale deposited upon the flues of a marine boiler resembles layers of stone. 391. _Q/_--Is much inconvenience experienced in marine boilers from these incrustations upon the flues? _A._--Incrustation in boilers at one time caused much more perplexity than it does at present, as it was supposed that in some seas it was impossible to prevent the boilers of a steamer from becoming salted up; but it has now been satisfactorily ascertained that there is very little difference in the saltness of different seas, and that however salt the water may be, the boiler will be preserved from any injurious amount of incrustation by blowing off, as it is called, very frequently, or by permitting a considerable portion of the supersalted water to escape at short intervals into the sea. If blowing off be sufficiently practised, the scale upon the flues will never be much thicker than a sheet of writing paper, and _no excuse_ should be accepted from engineers for permitting a boiler to be damaged by the accumulation of calcareous deposit. 392. _Q._--What is the temperature at which sea water boils in a steam boiler? _A._--Sea water contains about 1/33rd its weight of salt, and in the open air it boils at the temperature of 213.2°; if the proportion of salt be increased to 2/33rds of the weight of the water, the boiling point will rise to 214.4°; with 3/33rds of salt the boiling point will be 215.5°; 4/33rds, 216.7°; 5/33rds, 217.9°; 6/33rds, 219°; 7/33rds, 220.2°; 8/33rds, 221.4°; 9/33rds, 222.5°; 10/33rds, 223.7°; 11/33rds, 224.9°; and 12/33rds, which is the point of saturation, 226°. In a steam boiler the boiling points of water containing these proportions of salt must be higher, as the elevation of temperature due to the pressure of the steam has to be added to that due to the saltness of the water; the temperature of steam at the atmospheric pressure being 212°, its temperature, at a pressure of 15 lbs. per square inch above the atmosphere, will be 250°, and adding to this 4.7° as the increased temperature due to the saltness of the water when it contains 4/33rds of salt, we have 254.7° as the temperature of the water in the boiler, when it contains 4/33rds of salt and the pressure of the steam is 15 lbs. on the square inch. 393. _Q._--What degree of concentration of the salt water may be safely permitted in a boiler? _A._--It is found by experience that when the concentration of the salt water in a boiler is prevented from exceeding that point at which it contains 2/33rds its weight of salt, no injurious incrustation will take place, and as sea water contains only 1/33rd of its weight of salt, it is clear that it must be reduced by evaporation to one half of its bulk before it can contain 2/33rds of salt; or, in other words, a boiler must blow out into the sea one half of the water it receives as feed, in order to prevent the water from rising above 2/33rds of concentration, or 8 ounces of salt to the gallon. 394. _Q._--How do you determine 8 ounces to the gallon to be equivalent to twice the density of salt water, or "two salt waters" as it is sometimes called? _A._--The density of the water of different seas varies somewhat. A gallon of fresh water weighs 10 lbs.; a gallon of salt water from the Baltic weighs 10.15 lbs.; a gallon of salt water from the Irish Channel weighs 10.28 lbs.; and a gallon of salt water from the Mediterranean 10.29 lbs. If we take an average saltness represented by a weight of 10.25 lbs., then a gallon of water concentrated to twice this saltness will weigh 10.5 lbs., or the salt in it will weigh .5 lbs or 8 oz., which is the proportion of 8 oz. to the gallon. However, the proportion of 2/33rds gives a greater proportion than 8 oz. to the gallon, for 2/33 = 1/16 nearly, and 1/16 of 10 lbs. = 10 oz. By keeping the density of the water in a marine boiler at the proportion of 8 or 10 oz. to the gallon, no inconvenient amount of scale will be deposited on the flues or tubes. The bulk of water, it may be remarked, is not increased by putting salt in it up to the point of saturation, but only its density is increased. 395. _Q._--Is there not a great loss of heat by blowing off so large a proportion of the heated water from the boiler? _A._--The loss is not very great. Boilers are sometimes worked at a saltness of 4/33rds, and taking this saltness and supposing the latent heat of steam to be at 1000° at the temperature of 212°, and reckoning the sum of the latent and sensible heats as forming a constant quantity, the latent heat of steam at the temperature of 250° will be 962°, and the total heat of the steam will be 1212° in the case of fresh water; but as the feed water is sent into the boiler at the temperature of 100°, the accession of heat it receives from the fuel will be 1112° in the case of fresh water, or 1112° increased by 3.98° in the case of water containing 4/33ds of salt-- the 3.98° being the 4.7° increase of temperature due to the presence of 4/33rds of salt, multiplied by 0.847 the specific heat of steam. This makes the total accession of heat received by the steam in the boiler equal to 1115.98°, or say 1116°, which multiplied by 3, as 3 parts of the water are raised into steam, gives us 3348° for the heat in the steam, while the accession of heat received in the boiler by the 1 part of residual brine will be 154.7°, multiplied by 0.85, the specific heat of the brine, or 130.495°; and 3348° divided by 130.495° is about 1/26th. It appears, therefore, that by blowing off the boiler to such an extent that the saltness shall not rise above what answers to 4/33rds of salt, about 1/25th of the heat is blown into the sea; this is but a small proportion, and as there will be a greater waste of heat, if from the existence of scale upon the flues the heat can be only imperfectly transmitted to the water, there cannot be even an economy of fuel in niggard blowing off, while it involves the introduction of other evils. The proportion of 4/33rds of saltness, however, or 16 oz. to the gallon, is larger than is advisable, especially as it is difficult to keep the saltness at a perfectly uniform point, and the working point should, therefore, be 2/33rds as before prescribed. 396. _Q._--Have no means been devised for turning to account the heat contained in the brine which is expelled from the boiler? _A._--To save a part of the heat lost by the operation of blowing off, the hot brine is sometimes passed through a number of small tubes surrounded by the feed water; but there is no very great gain from the use of such apparatus, and the tubes are apt to become choked up, whereby the safety of the boiler may be endangered by the injurious concentration of its contents. Pumps, worked by the engine for the extraction of the brine, are generally used in connection with the small tubes for the extraction of the heat from the supersalted water; and if the tubes become choked the pumps will cease to eject the water, while the engineer may consider them to be all the while in operation. 397._Q._--What is the usual mode of blowing off the supersalted water from the boiler? _A._--The general mode of blowing off the boiler is to allow the water to rise gradually for an hour or two above the lowest Working level, and then to open the cock communicating with the sea, and keep it open until the surface of the water within the boiler has fallen several inches; but in some cases a cock of smaller size is allowed to run water continuously, and in other cases brine pumps are used as already mentioned. In every case in which the supersalted water is discharged from the boiler in a continuous stream, a hydrometer or salt gauge of some convenient construction should be applied to the boiler, so that the density of the water may at all times be visible, and immediate notice be given of any interruption of the operation. Various contrivances have been devised for this purpose, the most of which operate on the principle of a hydrometer; but perhaps a more satisfactory principle would be that of a differential steam gauge, which would indicate the difference of pressure between the steam in the boiler and the steam of a small quantity of fresh water enclosed in a suitable vessel, and immerged in the water of the boiler. 398. _Q._--What is the advantage of blowing off from the surface of the water in the boiler? _A._--Blowing off from a point near the surface of the water is more beneficial than blowing off from the bottom of the boiler. Solid particles of any kind, it is well known, if introduced into boiling water, will lower the boiling point in a slight degree, and the steam will chiefly be generated on the surface of the particles, and indeed will have the appearance of coming out of them; if the particles be small the steam generated beneath and around them will balloon them to the surface of the water, where the steam will be liberated and the particles will descend; and the impalpable particles in a marine boiler, which by their subsidence upon the flues concrete into scale, are carried in the first instance to the surface of the water, so that if they be caught there and ejected from the boiler, the formation of scale will be prevented. 399. _Q._--Are there any plans in operation for taking advantage of this property of particles rising to the surface? _A._--Advantage is taken of this property in Lamb's Scale Preventer, which is substantially a contrivance for blowing off from the surface of the water that in practice is found to be very effectual; but a float in connection with a valve at the mouth of the discharging pipe is there introduced, so as to regulate the quantity of water blown out by the height of the water level, or by the extent of opening given to the feed cock. The operation, however, of the contrivance would be much the same if the float were dispensed with; but the float acts advantageously in hindering the water from rising too high in the boiler, should too much feed be admitted, and thereby obviates the risk of the water running over into the cylinder. In some boilers sheet iron vessels, called sediment collectors, are employed, which collect into them the impalpable matter, which in Lamb's apparatus is ejected from the boiler at once. One of these vessels, of about the size and shape of a loaf of sugar, is put into each boiler with the apex of the cone turned downwards into a pipe leading overboard, for conducting the sediment away from the boiler. The base of the cone stands some distance above the water line, and in its sides conical slits are cut, so as to establish a free communication between the water within the conical vessel and the water outside it. The particles of stony matter which are ballooned to the surface by the steam in every other part of the boiler, subside within the cone, where, no steam being generated, the water is consequently tranquil; and the deposit is discharged overboard by means of a pipe communicating with the sea. By blowing off from the surface of the water, the requisite cleansing action is obtained with less waste of heat; and where the water is muddy, the foam upon the surface of the water is ejected from the boiler--thereby removing one of the chief causes of priming. 400. _Q._--What is the cause of the rapid corrosion of marine boilers? _A._--Marine boilers are corroded externally in the region of the steam chest by the dripping of water from the deck; the bottom of the boiler is corroded by the action of the bilge water, and the ash pits by the practice of quenching the ashes with, salt water. These sources of injury, however, admit of easy remedy; the top of the boiler may be preserved from external corrosion by covering it with felt upon which is laid sheet lead soldered at every joint so as to be impenetrable to water; the ash pits may be shielded by guard plates which are plates fitting into the ash pits and attached to the boiler by a few bolts, so that when worn they may be removed and new ones substituted, whereby any wear upon the boiler in that part will be prevented; and there will be very little wear upon the bottom of a boiler if it be imbedded in mastic cement laid upon a suitable platform. 401. _Q._--Are not marine boilers subject to internal corrosion? _A._--Yes; the greatest part of the corrosion of a boiler takes place in the inside of the steam chest, and the origin of this corrosion is one of the obscurest subjects in the whole range of engineering. It cannot be from the chemical action of the salt water upon the iron, for the flues and other parts of the boiler beneath the water suffer very little from corrosion, and in steam vessels provided with Hall's condensers, which supply the boiler with fresh water, not much increased durability of the boiler has been experienced. Nevertheless, marine boilers seldom last more than for 5 or 6 years, whereas land boilers made of the same quality of iron often last 18 or 20 years, and it does not appear probable that land boilers would last a very much shorter time if salt water were used in them. The thin film of scale spread over the parts of a marine boiler situated beneath the water, effectually protect them from corrosion; and when the other parts are completely worn out the flues generally remain so perfect, that the hammer marks upon them are as conspicuous as at their first formation. The operation of the steam in corroding the interior of the boiler is most capricious--the parts which are most rapidly worn away in one boiler being untouched in another; and in some cases one side of a steam chest will be very much wasted away while the opposite side remains uninjured. Sometimes the iron exfoliates in the shape of a black oxide which comes away in flakes like the leaves of a book, while in other cases the iron appears as if eaten away by a strong acid which had a solvent action upon it. The application of felt to the outside of a boiler, has in several cases been found to accelerate sensibly its internal corrosion; boilers in which there is a large accumulation of scale appear to be more corroded than where there is no such deposit; and where the funnel passes through the steam chest the iron of the steam chest is invariably much more corroded than where the funnel does not pass through it. 402. _Q._--Can you suggest no reason for the rapid internal corrosion of marine boilers? _A._--The facts which I have enumerated appear to indicate that the internal corrosion of marine boilers is attributable chiefly to the existence of surcharged steam within them, which is steam to which an additional quantity of heat has been communicated subsequently to its generation, so that its temperature is greater than is due to its elastic force; and on this hypothesis the observed facts relative to corrosion become to some extent explicable. Felt, applied to the outside of a boiler, may accelerate its internal corrosion by keeping the steam in a surcharged state, when by the dispersion of a part of the heat it would cease to be in that state; boilers in which there is a large accumulation of scale must have worked with the water very salt, which necessarily produces surcharged steam; for the temperature of steam cannot be less than that of the water from which it is generated, and inasmuch as the boiling point of water, under any given pressure, rises with the saltness of the water, the temperature of the steam must rise with the saltness of the water, the pressure remaining the same; or, in other words, the steam must have a higher temperature than is due to its elastic force, or be in the state of surcharged steam. The circumstance of the chimney flue passing through the steam will manifestly surcharge the steam with heat, so that all the circumstances which are found to accelerate corrosion, are it appears such as would also induce the formation of surcharged steam. 403. _Q._--Is it the natural effect of surcharged steam to waste away iron? _A._--It is the natural effect of surcharged steam to oxidate the iron with which it is in contact, as is illustrated by the familiar process for making hydrogen gas by sending steam through a red hot tube filled with pieces of iron; and although the action of the surcharged steam in a boiler is necessarily very much weaker than where the iron is red hot, it manifestly must have _some_ oxidizing effect, and the amount of corrosion produced may be very material where the action is perpetual. Boilers with a large extent of heating surface, or with descending flues circulating through the cooler water in the bottom of the boiler before ascending the chimney, will be less corroded internally than boilers in which a large quantity of the heat passes away in the smoke; and the corrosion of the boiler will be diminished if the interior of any flue passing through the steam be coated with fire brick, so as to present the transmission of the heat in that situation. The best practice, however, appears to consist in the transmission of the smoke through a suitable passage on the outside of the boiler, so as to supersede the necessity of carrying any flue through the steam at all; or a column of water may be carried round the chimney, into which as much of the feed water may be introduced as the heat of the chimney is capable of raising to the boiling point, as under this limitation the presence of feed water around the chimney in the steam chest will fail to condense the steam. 404. _Q._--In steam vessels there are usually several boilers? _A._--Yes, in steam vessels of considerable power and size. 405. _Q._--Are these boilers generally so constructed, that any one of them may be thrown out of use? _A._--Marine boilers are now generally supplied with stop valves, whereby one boiler may be thrown out of use without impairing the efficacy of the remainder. These stop valves are usually spindle valves of large size, and they are for the most part set in a pipe which runs across the steam chests, connecting the several boilers together. The spindles of these valves should project through stuffing boxes in the covers of the valve chests, and they should be balanced by a weighted lever, and kept in continual action by the steam. If the valves be lifted up, and be suffered to remain up, as is the usual practice, they will become fixed by corrosion in that position, and it will be impossible after some time to shut them on an emergency. These valves should always be easily accessible from the engine room; and it ought not to be necessary for the coal boxes to be empty to gain access to them. 406. _Q._--Should each boiler have at least one safety valve for itself? _A._--Yes; it would be quite unsafe without this provision, as the stop valve might possibly jam. Sometimes valves jam from a distortion in the shape of the boiler when a considerable pressure is put upon it. 407. _Q._--How is the admission of the water into the boiler regulated? _A._--The admission of feed water into the boiler is regulated by hand by the engineer by means of cocks, and sometimes by spindle valves raised and lowered by a screw. Cocks appear to be the preferable expedient, as they are less liable to accident or derangement than screw valves, and in modern steam vessels they are generally employed. 408. _Q._--At what point of the boiler is the feed introduced? _A._--The feed water is usually conducted from the feed cock to a point near the bottom of the boiler by means of an internal pipe, the object of this arrangement being to prevent the rising steam from being condensed by the entering water. By being introduced near the bottom of the boiler, the water comes into contact in the first place with the bottoms of the furnaces and flues, and extracts heat from them which could not be extracted by water of a higher temperature, whereby a saving of fuel is accomplished. In some cases the feed water is introduced into a casing around the chimney, from whence it descends into the boiler. This plan appears to be an expedient one when the boiler is short of heating surface, and more than a usual quantity of heat ascends the chimney; but in well proportioned boilers a water casing round the chimney is superfluous. When a water casing is used the boiler is generally fed by a head of water, the feed water being forced up into a small tank, from whence it descends into the boiler by the force of gravity, while the surplus runs to waste, as in the feeding apparatus of land engines. 409. _Q._--Suppose that the engineer should shut off the feed water from the boilers while the engine was working, what would be the result? _A._--The result would be to burst the feed pipes, except for a safety valve placed on the feed pipe between the engine and the boilers, which safety valve opens when any undue pressure comes upon the pipes, and allows the water to escape. There is, however, generally a cock on the suction side of the feed pump, which regulates the quantity of water drawn into the pump. But there must be cocks on the boilers also to determine into which boiler the water shall be chiefly discharged, and these cocks are sometimes all shut accidentally at the same time. 410. _Q._--Is there no expedient in use in steam vessels for enabling the position of the water level in the boiler to determine the quantity of feed water admitted? _A._--In some steam vessels floats have been introduced to regulate the feed, but their action cannot be depended on in agitated water, if applied after the common fashion. Floats would probably answer if placed in a cylinder which communicates with the water in the boiler by means of small holes; and a disc of metal might be attached to the end of a rod extending beneath the water level, so as to resist irregular movements from the motion of the ship at sea, which would otherwise impair the action of the apparatus. 411. _Q._--How is the proper level of the water in the boiler of a steam vessel maintained when, the engine is stopped for some time, and the boiler is blowing off steam? _A._--By means of a separate pump worked sometimes by hand, but usually by a small separate engine called the Donkey engine. This pump, by the aid of suitable cocks, will pump from the sea into the boiler; from the sea upon deck either to wash decks or to extinguish fire; and from the bilge overboard, through a suitable orifice in the side of the ship. LOCOMOTIVE BOILERS. 412. _Q._--Will you recapitulate the general features of locomotive boilers? _A._--Locomotive boilers consist of three portions (see fig. 29): the barrel E, E, containing the tubes, the fire box B, and the smoke box F; of which the barrel smoke box, and external fire box are always of iron, but the internal fire box is generally made of copper, though sometimes also it is made of iron. The tubes are sometimes of iron, but generally of brass fixed in by ferules. The whole of the iron plates of a locomotive boiler Which are subjected to the pressure of steam, should be Lowmoor or Bowling plates of the best quality; and the copper should be coarse grained, rather than rich or soft, and be perfectly free from irregularities of structure and lamination. 413. _Q._--What are the usual dimensions of the barrel? _A._--The thickness of the plates composing the barrel of the boiler varies generally from 5/16ths to 3/8ths of an inch, and the plates should run in the direction of the circumference, so that the fibres of the iron may be in the direction of the strain. The diameter of the barrel commonly varies from 3 ft. to 3 ft. 6 inches; the diameter of the rivets should be from 11/16ths to 3/4ths of an inch, and the pitch of the rivets or distance between their centres should be from 17/8th to 2 inches. 414. _Q._--How are the fire boxes of a locomotive constructed? _A._--The space between the external and internal fire boxes forms a water space, which must be stayed every 4-1/2 or 5 inches by means of copper or iron stay bolts, screwed through the outer fire box into the metal of the inner fire box, and securely riveted within it: iron stay bolts are as durable as copper, and their superior tenacity gives them an advantage. Sometimes tubes are employed as stays. The internal and external fire boxes are joined together at the bottom by a N-shaped iron, and round the fire door they are connected by means of a copper ring 1-1/4 in. thick, and 2 in. broad,--the inner fire box being dished sufficiently outward at that point, and the outer fire box sufficiently inward, to enable a circle of rivets 3/4 of an inch in diameter passing through the copper ring and the two thicknesses of iron, to make a water-tight joint. The thickness of the plates composing the external fire box is in general 3/8ths of an inch if the fire box is circular, and from 3/8ths to 1/2 inch if the fire box is square; and the thickness of the internal fire box is in most cases 7/16ths if copper, and from 3/8ths to 7/16ths of an inch if of iron. Circular internal fire boxes, if made of iron, should be welded rather than riveted, as the rivet heads are liable to be burnt away by the action of the fire; and when the fire boxes are square each side should consist of a single plate, turned over at the edges with a radius of 3 inches, for the introduction of the rivets. 415. _Q._--Is there any provision for stiffening the crown of the furnace in a locomotive? _A._--The roof of the internal fire box, whether flat as in Stephenson's engines, or dome shaped as in Bury's, requires to be stiffened with cross stay bars, but the bars require to be stronger and more numerous when applied to a flat surface. The ends of these stay bars rest above the vertical sides of the fire box; and to the stay bars thus extending across the crown, the crown is attached at intervals by means of stay bolts. There are projecting bosses upon the stay bars encircling the bolts at every point where a bolt goes through, but in the other parts they are kept clear of the fire box crown so as to permit the access of water to the metal; and, with the view of facilitating the ascent of the steam, the bottom of each stay bar should be sharpened away in those parts where it does not touch the boiler. 416. _Q._--Is any inconvenience experienced from the intense heat in a locomotive furnace? _A._--The fire bars in locomotives have always been a source of trouble, as from the intensity of the heat in the furnace they become so hot as to throw off a scale, and to bend under the weight of the fuel. The best alleviation of these evils lies in making the bars deep and thin: 4 or 5 inches deep by five eighths of an inch thick on the upper side, and three eighths of an inch on the under side, are found in practice to be good dimensions. In some locomotives a frame carrying a number of fire bars is made so that it may be dropped suddenly by loosening a catch; but it is found that any such mechanism can rarely be long kept in working order, as the molten clinker by running down between the frame and the boiler will generally glue the frame into its place. It is therefore found preferable to fix the frame, and to lift up the bars by the dart used by the stoker, when any cause requires the fire to be withdrawn. The furnace bars of locomotives are always made of malleable iron, and indeed for every species of boiler malleable iron bars are to be preferred to bars of cast iron, as they are more durable, and may if thin be set closer together, whereby the small coal or coke is saved that would otherwise fall into the ash pit. The ash box of locomotives is made of plate iron, a quarter thick: it should not be less than 10 in. deep, and its bottom should be about 9 in. above the level of the rails. The chimney of a locomotive is made of plate iron one eighth of an inch thick: it is usually of the same diameter as the cylinder, but is better smaller, and must not stand more than 14 ft. high above the level of the rails. 417. _Q._--Are locomotive boilers provided with a steam chest? _A._--The upper portion of the external fire box is usually formed into a steam chest, which is sometimes dome shaped, sometimes semicircular, and sometimes of a pyramidical form, and from this steam chest the steam is conducted away by an internal pipe to the cylinders; but in other cases an independent steam chest is set upon the barrel of the boiler, consisting of a plate iron cylinder, 20 inches in diameter, 2 feet high, and three eighths of an inch thick, with a dome shaped top, and with the seam welded and the edge turned over to form a flange of attachment to the boiler. The pyramidical dome, of the form employed in Stephenson's locomotives, presents a considerable extent of flat surface to the pressure of the steam, and this flat surface requires to be very strongly stayed with angle irons and tension rods; whereas the semiglobular dome of the kind employed in Bury's engines requires no staying whatever. Latterly, however, these domes over the fire box have been either much reduced in size or abandoned altogether. 418. _Q._--Is any beneficial use made of the surplus steam of a locomotive? _A._--To save the steam which is formed when the engine is stationary, a pipe is usually fitted to the boiler, which on a cock being turned conducts the steam into the water in the tender, whereby the feed water is heated, and less fuel is subsequently required. This method of disposing of the surplus steam may be adopted when the locomotive is descending inclines, or on any occasion where more steam is produced than the engine can consume. 419._Q._--What means are provided to facilitate the inspection and cleaning of locomotive boilers? _A._--The man hole, or entrance into the boiler, consists of a circular or oval aperture of about 15 in. diameter, placed in Bury's locomotive at the apex of the dome, and in Stephenson's upon the front of the boiler, a few inches below the level of the rounded part; and the cover of the man hole in Bury's engine contains the safety valve seats. In whatever situation this man hole is placed, the surfaces of the ring encircling the hole, and of the internal part of the door or cover, should be accurately fitted together by scraping or grinding, so that they need only the interposition of a little red lead to make them quite tight when screwed together. Lead or canvas joints, if of any considerable thickness, will not long withstand the action of high pressure steam; and the whole of the joints about a locomotive should be such that they require nothing more than a little paint or putty, or a ring of wire gauze smeared with white or red lead to make them perfectly tight. There must be a mud hole opposite the edge of each water space, if the fire box be square, to enable the boiler to be easily cleaned out, and these holes are most conveniently closed by screwed plugs made slightly taper. A cock for emptying the boiler is usually fixed at the bottom of the fire box, and it should be so placed as to be accessible when the engine is at work, in order that the engine driver may blow off some water if necessary; but it must not be in such a position as to send the water blown off among the machinery, as it might carry sand or grit into the bearings, to their manifest injury. 420. _Q._--Will you state the dimensions of the tube plate, and the means of securing the tubes in it? _A._--The tube plates are generally made from five eighths to three fourths of an inch thick, but seven eighths of an inch thick appears to be preferable, as when the plate is thick the holes will not be so liable to change their figure during the process of feruling the tubes: the distance between the tubes should never be made less than three fourths of an inch, and the holes should be slightly tapered so as to enable the tubes to hold the tube plates together. The tubes are secured in the tube plates by means of taper ferules driven into the ends of the tubes. The ferules are for the most part made of steel at the fire box end, and of wrought iron at the smoke box end, though ferules of malleable cast iron have in some cases been used with advantage: malleable cast iron ferules are almost as easily expanded when hammered cold upon a mandrel, as the common wrought iron ones are at a working heat. Spring steel, rolled with a feather edge, to facilitate its conversion into ferules, is supplied by some of the steel-makers of Sheffield, and it appears expedient to make use of steel thus prepared when steel ferules are employed. In cases where ferules are not employed, it may be advisable to set out the tube behind the tube plate by means of an expanding mandrel. There are various forms of this instrument. One form is that known as Prosser's expanding mandrel, in which there are six or eight segments, which are forced out by means of a hexagonal or octagonal wedge, which is forced forward by a screw. When the wedge is withdrawn, the segments collapse sufficiently to enable them to enter the tube, and there is an annular protuberance on the exterior circle of the segments, which protuberance, when the mandrel is put into the tube, just comes behind the inner edge of the tube plate. When the wedge is tightened up by the screw, the protuberance on the exterior of the segments composing the mandrel causes a corresponding bulge to take place in the tube, at the back of the tube plate, and the tube is thereby brought into more intimate contact with the tube plate than would otherwise be the case. There is a steel ring indented into the segments of Prosser's mandrel, to contract the segments when the central wedge is withdrawn. A more convenient form of the instrument, however, is obtained by placing the segments in a circular box, with one end projecting; and supporting each segment in the box by a tenon, which fits into a mortise in the cylindrical box. To expand the segments, a round tapered piece of steel, like a drift, is forced into a central hole, round which the segments are arranged. A piece of steel tube, also slit up to enable a central drift to expand it, answers very well; but the thickness of that part of the tube in which there requires to be spring enough to let the mandrel expand, requires to be sufficiently reduced to prevent the pieces from cracking when the central drift is driven in by a hammer. The drift is better when made with a globular head, so that it may be struck back by the hammer, as well as be driven in. An expanding mandrel, with a central drift, is more rapid in its operation than when the expansion is produced by means of a screw. 421. _Q._--Will you explain the means that are adopted to regulate the admission of steam to the cylinders? _A._--In locomotives, the admission of the steam from the boiler to the cylinders is regulated by a valve called the regulator, which is generally placed immediately above the internal fire box, and is connected with two copper pipes;--one conducting steam from the highest point of the dome down to it, and the other conducting the steam that has passed through it along the boiler to the upper part of the smoke box. Regulators may be divided into two sorts, viz., those with, sliding valves and steam ports, and those with conical valves and seats, of which the latter kind are the best. The former kind have for the most part consisted of a circular valve and face, with radial apertures, the valve resembling the outstretched wings of a butterfly, and being made to revolve on its central pivot by connecting links between its outer edges, or by its central spindle. In some of Stephenson's engines the regulator consists of a slide valve covering a port on the top of the valve chests. A rod passes from this valve through the smoke box below the boiler, and by means of a lever parallel to the starting lever, is brought up to the engineer's reach. Cocks were at first used as regulators, but were given up, as they were found liable to stick fast. A gridiron slide valve has been used by Stephenson, which consists of a perforated square moving upon a face with an equal number of holes. This plan of a valve gives, with a small movement, a large area of opening. In Bury's engines a sort of conical plug is used, which is withdrawn by turning the handle in front of the fire box: a spiral grove of a very large pitch is made in the valve spindle, in which fits a pin fixed to the boiler, and by turning the spindle an end motion is given to it, which either shuts or opens the steam passage according to the direction in which it is turned. The best regulator would probably be a valve of the equilibrium description, such as is used in the Cornish engine: there would be no friction in such a regulator, and it could be opened or shut with a small amount of force. Such valves, indeed, are now sometimes employed for regulators in locomotives. CHAPTER VIII. CONSTRUCTIVE DETAILS OF ENGINES. PUMPING ENGINES. 422. _Q._--Will you explain the course of procedure in the erection of a pumping engine, such as Boulton and Watt introduced into Cornwall? _A._--The best instructions on this subject are those of Mr. Watt himself, which are as follows:--Having fixed on the proper situation of the pump in the pit, from its centre measure out the distance to the centre of the cylinder, from which set off all the other dimensions of the house, including the thickness of the walls, and dig out the whole of the included ground to the depth of the bottom of the cellar, so that the bottom of the cylinder may stand on a level with the natural ground of the place, or lower, if convenient, for the less the height of the house above the ground, the firmer it will be. The foundations of the walls must be laid at least two feet lower than the bottom of the cellar, unless the foundation be firm rock; and care must be taken to leave a small drain into the pit quite through the lowest part of the foundation of the lever wall, to let off any water that may be spilt in the engine house, or may naturally come into the cellar. If the foundation at that depth does not prove good, you must either go down to a better if in your reach, or make it good by a platform of wood or piles, or both. 423. _Q._--These directions refer to the foundations? _A._.--Yes; but I will now proceed to the other parts. Within the house, low walls must be built to carry the cylinder beams, so as to leave sufficient room to come at the holding down bolts, and the ends of these beams must also be lodged in the wall The lever wall must be built in the firmest manner, and run solid, course by course, with thin lime mortar, care being taken that the lime has not been long slaked. If the house be built of stone, let the stones be large and long, and let many headers be laid through the wall: it should also be a rule, that every stone be laid on the broadest bed it has, and never set on its edge. A course or two above the lintel of the door that leads to the condenser, build into the wall two parallel flat thin bars of iron equally distant from each other, and from the outside and inside of the wall, and reaching the whole breadth of the lever wall. About a foot higher in the wall, lay at every four feet of the breadth of the front, other bars of the same kind at right angles to the former course, and reaching quite through the thickness of the wall; and at each front corner lay a long bar in the middle of the side walls, and reaching quite through the front wall; if these bars are 10 feet or 12 feet long it will be sufficient. When the house is built up nearly to the bottom of the opening under the great beam another double course of bars is to be built in, as has been directed. At the level of the upper cylinder beams, holes must be left in the walls for their ends, with room to move them laterally, so that the cylinder may be got in; and smaller holes must be left quite through the walls for the introduction of iron bars, which being firmly fastened to the cylinder beams at one end, and screwed at the other or outer end, will serve, by their going through both the front and back walls, to bind the house more firmly together. The spring beams or iron bars fastened to them must reach quite through the back wall, and be keyed or screwed up tight; and they must be firmly fastened to the lever wall on each side, either by iron bars, firm pieces of wood, or long strong stones, reaching far back into the wall. They must also be bedded solidly, and the residue of the opening must be built up in the firmest manner. 424. _Q._--If there be a deficiency of water for the purpose of condensation, what course should be pursued? _A._--If there be no water in the neighborhood that can be employed for the purpose of condensation, it will be necessary to make a pond, dug in the earth, for the reception of the water delivered by the air pump, to the end that it may be cooled and used again for the engine. The pond may be three or four feet deep, and lined with turf, puddled, or otherwise made water tight. Throwing up the water into the air in the form of a jet to cool it, has been found detrimental; as the water is then charged with air which vitiates the vacuum. 425. _Q._--How is the piston of a pumping engine packed? _A._--To pack the piston, take sixty common-sized white or untarred rope-yarns, and with them plait a gasket or flat rope as close and firm as possible, tapering for eighteen inches at each end, and long enough to go round the piston, and overlapped for that length; coil this rope the thin way as hard as possible, and beat it with a sledge hammer until its breadth answers the place; put it in and beat it down with a wooden drift and a hand mallet, pour some melted tallow all around, then pack in a layer of white oakum half an inch thick, so that the whole packing may have the depth of five to six inches, depending on the size of the engine; finally, screw down the junk ring. The packing should be beat solid, but not too hard, otherwise it will create so great a friction as to prevent the easy going of the engine. Abundance of tallow should be allowed, especially at first; the quantity required will be less as the cylinder grows smooth. In some of the more modern pumping engines, the piston is provided with metallic packing, consisting for the most part of a single ring with a tongue piece to break the joint, and packed behind with hemp. The upper edge of the metallic ring is sharpened away from the inside so as to permit more conveniently the application of hemp packing behind it; and the junk ring is made much the same as if no metallic packing were employed. 426. _Q._--Will you explain the mode of putting the engine into operation? _A._--To set the engine going, the steam must be raised until the pressure in the steam pipe is at least equal to three pounds on the square inch; and when the cylinder jacket is fully warmed, and steam issues freely from the jacket cock, open all the valves or regulators; the steam will then forcibly blow out the air or water contained in the eduction pipe, and to get rid of the air in the cylinder, shut the steam valve after having blown through the engine for a few minutes. The cold water round the condenser will condense some of the steam contained in the eduction pipe, and its place will be supplied by some of the air from the cylinder. The steam valve must again be opened to blow out that air, and the operation is to be repeated until the air is all drawn out of the cylinder. When that is the case shut all the valves, and observe if the vacuum gauge shows a vacuum in the condenser; when there is a vacuum equivalent to three inches of mercury, open the injection a very little, and shut it again immediately; and if this produces any considerable vacuum, open the exhausting valve a very little way, and the injection at the same time. If the engine does not now commence its motion, it must be blown through again until it moves. If the engine be lightly loaded, or if there be no water in the pumps, the throttle valve must be kept nearly closed, and the top and exhaustion regulators must be opened only a very little way, else the engine will make its stroke with violence, and perhaps do mischief. If there is much unbalanced weight on the pump end, the plug which opens the steam valve must be so regulated, that the valve will only be opened very slightly; and if after a few strokes it is found that the engine goes out too slowly, the valve may be then so adjusted as to open wider. The engine should always be made to work full stroke, that is, until the catch pins be made to come within half an inch of the springs at each end, and the piston should stand high enough in the cylinder when the engine is at rest, to spill over into the perpendicular steam pipe any water which may be condensed above it; for if water remain upon the piston, it will increase the consumption of steam. When the engine is to be stopped, shut the injection valve and secure it, and adjust the tappets so as to prevent the exhausting valve from opening and to allow the steam valve to open and remain open, otherwise a partial vacuum may arise in the cylinder, and it may be filled with water from the injection or from leaks. A single acting engine, when it is in good order, ought to be capable of going as slow as one stroke in ten minutes, and as fast as ten strokes in one minute; and if it does not fulfil these conditions, there is some fault which should be ascertained and remedied. 427. _Q._--Your explanation has reference to the pumping engine as introduced into Cornwall by Watt: have any modifications been since made upon it? _A._--In the modern Cornish engines the steam is used very expansively, and a high pressure of steam is employed. In some cases a double cylinder engine is used, in which the steam, after having given motion to a small piston on the principle of a high pressure engine, passes into a larger cylinder, where it operates on the principle of a condensing engine; but there is no superior effect gained by the use of two cylinders, and there is greater complexity in the apparatus. Instead of the lever walls, cast iron columns are now frequently used for supporting the main beam in pumping engines, and the cylinder end of the main beam is generally made longer than the pump end in engines made in Cornwall, so as to enable the cylinder to have a long stroke, and the piston to move quickly, without communicating such a velocity to the pump buckets as will make them work with such a shock as to wear themselves out quickly. A high pressure of steam, too, can be employed where the stroke is long, without involving the necessity of making the working parts of such large dimensions as would otherwise be necessary; for the strength of the parts of a single acting engine will require to be much the same, whatever the length of the stroke may be. 428. _Q._--What kind of pump is mostly used in draining deep mines? _A._--The pump now universally preferred is the plunger pump, which admits of being packed or tightened while the engine is at work; but the lowest lift of a mine is generally supplied with a pump on the suction principle, both with the view of enabling the lowest pipe to follow the water with facility as the shaft is sunk deeper, and to obviate the inconvenience of the valves of the pump being rendered inaccessible by any flooding in the mine. The pump valves of deep mines are a perpetual source of expense and trouble, as from the pressure of water upon them it is difficult to prevent them from closing with violence; and many expedients have been contrived to mitigate the evil, of which the valve known as Harvey and West's valve has perhaps gained the widest acceptation. 429. _Q._--Will you describe Harvey and West's pump valve? _A._--This valve is a compromise between the equilibrium valve, of the kind employed for admitting the steam to and from the cylinder in single acting engines, and the common spindle valve formerly used for that purpose; and to comprehend its action, it is necessary that the action of the equilibrium valve, which has been already represented fig. 34, should first be understood. This valve consists substantially of a cylinder open at both ends, and capable of sliding upon a stationary piston fixed upon a rod the length of the cylinder, which proceeds from the centre of the orifice the valve is intended to close. It is clear, that when the cylinder is pressed down until its edge rests upon the bottom of the box containing it, the orifice of the pipe must be closed, as the steam can neither escape past the edge of the cylinder nor between the cylinder and the piston; and it is equally clear, that as the pressure upon the cylinder is equal all around it, and the whole of the downward pressure is maintained by the stationary piston, the cylinder can be raised or lowered without any further exertion of force than is necessary to overcome the friction of the piston and of the rod by which the cylinder is raised. Instead of the rubbing surface of a piston, however, a conical valve face between the cylinder and piston is employed, which is tight only when the cylinder is in its lowest position; and there is a similar face between, the edge of the cylinder and the bottom of the box in which it is placed. The moving part of the valve, too, instead of being a perfect cylinder, is bulged outward in the middle, so as to permit the steam to escape past the stationary piston when the cylindrical part of the valve is raised. It is clear, that if such a valve were applied to a pump, no pressure of water within the pump would suffice to open it, neither would any pressure of water above the valve cause it to shut with violence; and if an equilibrium valve, therefore, be used as a pump valve at all, it must be opened and shut by mechanical means. In Harvey and West's valves, however, the equilibrium principle is only partially adopted; the lower face is considerably larger in diameter than the upper face, and the difference constitutes an annulus of pressure, which will cause the valve to open or shut with the same force as a spindle valve of the area of the annulus. To deaden the shock still more effectually, the lower face of the valve is made to strike upon end wood driven into an annular recess in the pump bucket; and valves thus constructed work with very little noise or tremor; but it is found in practice, that the use of Harvey and West's valve, or any contrivance of a similar kind, adds materially to the load upon the pump, especially in low lifts where the addition of a load, to the valve makes a material addition to the total resistance which the engine has to overcome. Instead of end wood driven into a recess for the valve to strike upon, a mixture of tin and lead cast in a recess is now frequently used, and is found to be preferable to the wood. 430. _Q._--Is there any other kind of pump valve which is free from the shocks incidental to the working of common valves? _A._--In some cases canvass valves are used for pumps, with the effect of materially mitigating the shock; but they require frequent renewal, and are of inferior eligibility in their action to the slide valve, which might in many cases be applied to pumps without inconvenience. 431. _Q._--Could not a form of pump be devised capable of working without valves at all? _A._.--It appears probable, that by working a common reciprocating pump at a high speed, a continuous flow of water might be maintained through the pipes in such a way as to render the existence of any valves superfluous after once the action was begun, the momentum of the moving water acting in fact as valves. The centrifugal pump, however, threatens to supersede pumps of every other kind; and if the centrifugal pump be employed there will be no necessity for pump valves at all. There is less loss of effect by the centrifugal pump than by the common pump. 432. _Q._--What is the best form of the centrifugal pump? _A._--There are two forms in which the centrifugal pump may be applied to mines;--that in which the arms diverge from the bottom, like the letter V; and that in which revolving arms are set in a tight case near the bottom of the mine, and are turned by a shaft from the surface. Such pumps both draw and force; and either by arranging them in a succession of lifts in the shaft of the mine, or otherwise, the water may be drawn without inconvenience from any depth. The introduction of the centrifugal pump would obviously extinguish the single acting engine, as rotative engines working at a high speed would be the most appropriate form of engine where the centrifugal pump was employed. 433. _Q._--This would not be a heavy deprivation? _A._--The single acting engine is a remnant of engineering barbarism which must now be superseded by more compendious contrivances. The Cornish engines, though rudely manufactured, are very expensive in production, as a large engine does but little work; whereas by employing a smaller engine, moving with a high speed, the dimensions may be so far diminished that the most refined machinery may be obtained at less than the present cost. 434. _Q._--Are not the Cornish engines more economical in fuel than other engines? _A._--It is a mistake to suppose that there is any peculiar virtue in the existing form of Cornish engine to make it economical in fuel, or that a less lethargic engine would necessarily be less efficient. The large duty of the engines in Cornwall is traceable to the large employment of the principle of expansion, and to a few other causes which may be made of quite as decisive efficacy in smaller engines working with a quicker speed; and there is therefore no argument in the performance of the present engines against the proposed substitution. VARIOUS FORMS OF MARINE ENGINES. 435. _Q._--What species of paddle engine do you consider to be the best? _A._--The oscillating engine. 436. _Q._--Will you explain the grounds of that preference? _A._--The engine occupies little space, consists of few parts, is easily accessible for repairs, and may be both light and strong at the same time. In the case of large engines the crank in the intermediate shaft is a disadvantage, as it is difficult to obtain such a forging quite sound. But by forging it in three cranked flat bars, which are then laid together and welded into a square shaft, a sound forging will be more probable, and the bars should be rounded a little on the sides which are welded to allow the scoriae to escape during that operation. It is important in so large a forging not to let the fire be too fierce, else the surface of the iron will be burnt before the heart is brought to a welding heat. In some cases in oscillating engines the air pump has been wrought by an eccentric, and that may at any time be done where doubt of obtaining a sound intermediate shaft is entertained; but the precaution must be taken to make the eccentric very wide so as to distribute the pressure over a large surface, else the eccentric will be apt to heat. 437. _Q._--Have not objections been brought against the oscillating engine? _A._--In common with every other improvement, the oscillating engine, at the time of its introduction, encountered much opposition. The cylinder, it was said, would become oval, the trunnion bearings would be liable to heat and the trunnion joints to leak, the strain upon the trunnions would be apt to bend in or bend out the sides of the cylinder; and the circumstance of the cylinder being fixed across its centre, while the shaft requires to accommodate itself to the working of the ship, might, it was thought, be the occasion of such a strain upon the trunnions as would either break them or bend the piston rod. It is a sufficient reply to these objections to say that they are all hypothetical, and that none of them in practice have been found to exist--to such an extent at least as to occasion any inconvenience; but it is not difficult to show that they are altogether unsubstantial, even without a recourse to the disproofs afforded by experience. 438. _Q._--Is there not a liability in the cylinder to become oval from the strain thrown on it by the piston? _A._--There is, no doubt, a tendency in oscillating engines for the cylinder and the stuffing box to become oval, but after a number of years' wear it is found that the amount of ellipticity is less than that which is found to exist in the cylinders of side lever engines after a similar trial. The resistance opposed by friction to the oscillation of the cylinder is so small, that a man is capable of moving a large cylinder with one hand; whereas in the side lever engine, if the parallel motion be in the least untrue, which is, at some time or other, an almost inevitable condition, the piston is pushed with great force against the side of the cylinder, whereby a large amount of wear and friction is occasioned. The trunnion bearings, instead of being liable to heat like other journals, are kept down to the temperature of the steam by the flow of steam passing through them; and the trunnion packings are not liable to leak when the packings, before being introduced, are squeezed in a cylindrical mould. 439. _Q._--Might not the eduction trunnions be immersed in water? _A._--In some cases a hollow, or lantern brass, about one third or one fourth the length of the packing space, and supplied with steam or water by a pipe, is introduced in the middle of the packing, so that if there be any leakage through the trunnion, it will be a leakage of steam or water, which will not vitiate the vacuum; but in ordinary cases this device will not be necessary, and it is not commonly employed. It is clear that there can be no buckling of the sides of the cylinder by the strain upon the trunnions, if the cylinder be made strong enough, and in cylinders of the ordinary thickness such an action has never been experienced; nor is it the fact, that the intermediate shaft of steam vessels, to which part alone the motion is communicated by the engine, requires to adapt itself to the altering forms of the vessel, as the engine and intermediate shaft are rigidly connected, although the paddle shaft requires to be capable of such an adaptation. Even if this objection existed, however, it could easily be met by making the crank pin of the ball and socket fashion, which would permit the position of the intermediate shaft, relatively with that of the cylinder, to be slightly changed, without throwing an undue strain upon any of the working parts. 440. _Q._--Is the trunk engine inferior to the oscillating? _A._--A very elegant and efficient arrangement of trunk engine suitable for paddle vessels has latterly been employed by Messrs. Rennie, of which all the parts resemble those of Penn's oscillating engine except that the cylinders are stationary instead of being movable; and a round trunk or pipe set upon the piston, and moving steam tight through the cylinder cover, enables the connecting rod which is fixed to the piston to vibrate within it to the requisite extent. But the vice of all trunk engines is that they are necessarily more wasteful of steam, as the large mass of metal entering into the composition of the trunk, moving as it does alternately into the atmosphere and the steam, must cool and condense a part of the steam. The radiation of heat from the interior of the trunk will have the same operation, though in vertical trunk engines the loss from this cause might probably be reduced by filling the trunk with oil, so far as this could be done without the oil being spilt over the edge. 441. _Q._--What species of screw engine do you consider the best? _A._--I am inclined to give the preference to a variety of the horizontal steeple engine, such as was first used in H.M.S. Amphion. In this engine the cylinders lie on their sides, and they are placed near the side of the vessel with their mouths pointing to the keel. From each cylinder two long piston rods proceed across the vessel to a cross head working in guides; and from this cross head a connecting rod returns back to the centre of the vessel and gives motion to the crank. The piston rods are so placed in the piston that one of them passes above the crank shaft, and the other below the crank shaft. The cross head lies in the same horizontal plane as the centre of the cylinder, and a lug projects upwards from the cross head to engage one piston rod, and downwards from the cross head to engage the other piston rod. The air pump is double acting, and its piston or bucket has the same stroke as the piston of the engine. The air pump bucket derives its motion from an arm on the cross head, and a similar arm is usually employed in engines of this class to work the feed and bilge pumps. 442. _Q._--Is not inconvenience experienced in direct acting screw engines from the great velocity of their motion? _A._--Not if they are properly constructed; but they require to be much stronger, to be fitted with more care, and to have the bearing surfaces much larger than is necessary in engines moving slowly. The momentum of the reciprocating parts should also be balanced by a weight applied to the crank or crank shaft, as is done in locomotives. A very convenient arrangement for obtaining surface is to form the crank of each engine of two cast iron discs cast with heavy sides, the excess of weight upon the heavy sides being nearly equal to that of the piston and its connections. When the piston is travelling in one direction the weights are travelling in the opposite; and the momentum of the piston and its attachments, which is arrested at each reciprocation, is just balanced by the equal and opposite momentum of the weights. One advantage of the horizontal engine is, that a single engine may be employed, whereby greater simplicity of the machinery and greater economy of fuel will be obtained, since there will be less radiating surface in one cylinder than in two. CYLINDERS, PISTONS, AND VALVES, 443. _Q._--Is it a beneficial practice to make cylinders with steam jackets? _A._--In Cornwall, where great attention is paid to economy of fuel, all the engines are made with steam jackets, and in some cases a flue winds spirally round the cylinder, for keeping the steam hot. Mr. Watt, in his early practice, discarded the steam jacket for a time, but resumed it again, as he found its discontinuance occasioned a perceptible waste of fuel; and in modern engines it has been found that where a jacket is used less coal is consumed than where the use of a jacket is rejected. The cause of this diminished effect is not of very easy perception, for the jacket exposes a larger radiating surface for the escape of the heat than the cylinder; nevertheless, the fact has been established beyond doubt by repeated trials, that engines provided with a jacket are more economical than engines without one. The exterior of the cylinder, or jacket, should be covered with several plies of felt, and then be cased in timber, which must be very narrow, the boards being first dried in a stove, and then bound round the cylinder with hoops, like the staves of a cask. In many of the Cornish engines the steam is let into casings formed in the cylinder cover and cylinder bottom, for the further economisation of the heat, and the cylinder stuffing box is made very deep, and a lantern or hollow brass is introduced into the centre of the packing, into which brass the steam gains admission by a pipe provided for the purpose; so that in the event of the packing becoming leaky, it will be steam that will be leaked into the cylinder instead of air, which, being incondensable, would impair the efficiency of the engine. A lantern brass, of a similar kind, is sometimes introduced into the stuffing boxes of oscillating engines, but its use there is to receive the lateral pressure of the piston rod, and thus take any strain off the packing. 444. _Q._--Will you explain the proper course to pursue in the production of cylinders? _A._--In all engines the valve casing, if made in a separate piece from the cylinder, should be attached by means of a metallic joint, as such a barbarism as a rust joint in such situations is no longer permissible. In the case of large engines with valve casings suitable for long slides, an expansion joint in the valve casing should invariably be inserted, otherwise the steam, by gaining admission to the valve casing before it can enter the cylinder, expands the casing while the cylinder remains unaltered in its dimensions, and the joints are damaged, and in some cases the cylinder is cracked by the great strain thus introduced. The chest of the blow-through valve is very commonly cast upon the valve casing; and in engines where the cylinders are stationary this is the most convenient practice. All engines, where the valve is not of such a construction as to leave the face when a pressure exceeding that of the steam is created in the cylinder by priming or otherwise, should be provided with an escape valve to let out the water, and such valve should be so constructed that the water cannot fly out with violence over the attendants; but it should be conducted away by a suitable pipe, to a place where its discharge can occasion no inconvenience. The stuffing boxes of all engines which cannot be stopped frequently to be repacked, should be made very deep; metallic packing in the stuffing box has been used in some engines, consisting in most instances of one or more rings, cut, sprung, and slipped upon the piston rod before the cross head is put on, and packed with hemp behind. This species of packing answers very well when the parallel motion is true, and the piston rod free from scratches, and it accomplishes a material saving of tallow. In some cases a piece of sheet brass, packed behind with hemp, has been introduced with good effect, a flange being turned over on the under edge of the brass to prevent it from slipping up or down with the motion of the rod. The sheet brass speedily puts an excellent polish upon the rod, and such a packing is more easily kept, and requires less tallow than where hemp alone is employed. In side lever marine engines the attachments of the cylinder to the diagonal stay are generally made of too small an area, and the flanges are made too thick. A very thick flange cast on any part of a cylinder endangers the soundness of the cylinder, by inducing an unequal contraction of the metal; and it is a preferable course to make the flange for the attachment or the framing thin, and the surface large--the bolts being turned bolts and nicely fitted. If from malformation in this part the framing works to an inconvenient extent, the best expedient appears to be the introduction of a number of steel tapered bolts, the holes having been previously bored out; and if the flanges be thick enough, square keys may also be introduced, half into one flange and half into the other, so as to receive the strain. If the jaw cracks or breaks away, however, it will be best to apply a malleable iron hoop around the cylinder to take the strain, and this will in all cases be the preferable expedient, where from any peculiarities of structure there is a difficulty in introducing bolts and keys of sufficient strength. 445. _Q._--Which is the most eligible species of piston? _A._--For large engines, pistons with a metallic packing, consisting of a single ring, with the ends morticed into one another, and a piece of metal let in flush over the joint and riveted to one end of the ring, appears to be the best species of piston; and if the cylinder be oscillating, it will be expedient to chamfer off the upper edge of the ring on the inner side, and to pack it at the back with hemp. If the cylinder be a stationary one, springs may be substituted for the hemp packing, but in any case it will be expedient to make the vertical joints of the ends of the ring run a little obliquely, so as to prevent the joint forming a ridge in the cylinder. For small pistons two rings may be employed, made somewhat eccentric internally to give a greater thickness of metal in the centre of the ring; these rings must be set one above the other in the cylinder, and the joints, which are oblique, must be set at right angles with one another, so as to obviate any disposition of the rings, in their expansion, to wear the cylinder oval. The rings must first be turned a little larger than the diameter of the cylinder, and a piece is then to be cut out, so that when the ends are brought together the ring will just enter within the cylinder. The ring, while retained in a state of compression, is then to be put in the lathe and turned very truly, and finally it is to be hammered on the inside with the small end of the hammer, to expand the metal, and thus increase the elasticity. 446. _Q._--The rings should be carefully fitted to one another laterally? _A._--The rings are to be fitted laterally to the piston, and to one another, by scraping--a steady pin being fixed upon the flange of the piston, and fitting into a corresponding hole in the lower ring, to keep the lower ring from turning round; and a similar pin being fixed into the top edge of the lower ring to prevent the upper ring from turning round; but the holes into which these pins fit must be made oblong, to enable the rings to press outward as the rubbing surfaces wear. In most cases it will be expedient to press the packing rings out with springs where they are not packed behind with hemp, and the springs should be made very strong, as the prevailing fault of springs is their weakness. Sometimes short bent springs, set round at regular intervals between the packing rings and body of the piston, are employed, the centre of each spring being secured by a steady pin or bolt screwed into the side of the piston; but it will not signify much what kind of springs is used, provided they have sufficient tension. When pistons are made of a single ring, or of a succession of single rings, the strength of each ring should be tested previously to its introduction into the piston, by means of a lever loaded by a heavy weight. 447. _Q._--What kind of piston is employed by Messrs. Penn? _A._--Messrs. Penn's piston for oscillating engines has a single packing ring, with a tongue piece, or mortice end, made in the manner already described. The ring is packed behind with hemp packing, and the piece of metal which covers the joint is a piece of thick sheet copper or brass, and is indented into the iron of the ring, so as to offer no obstruction to the application of the hemp. The ring is fitted to the piston only on the under edge; the top edge is rounded to a point from the inside, and the junk ring does not bear upon it, but the junk ring squeezes down the hemp packing between the packing ring and the body of the piston. 448. _Q._--How should the piston rod be secured to the piston? _A._--The piston rod, where it fits into the piston, should have a good deal of taper; for if the taper be too small the rod will be drawn through the hole, and the piston will be split asunder. Small grooves are sometimes turned out of the piston rod above and below the cutter hole, and hemp is introduced in order to make the piston eye tight. Most piston rods are fixed to the piston by means of a gib and cutter, but in some cases the upper portion of the rod within the eye is screwed, and it is fixed into the piston by means of an indented nut. This nut is in some cases hexagonal, and in other cases the exterior forms a portion of a cone which completely fills a corresponding recess in the piston; but nuts made in this way become rusted into their seat after some time, and cannot be started again without much difficulty. Messrs. Miller, Ravenhill & Co. fix in their piston rods by means of an indented hexagonal nut, which may be started by means of an open box key. The thread of the screw is made flat upon the one side and much slanted on the other, whereby a greater strength is secured, without creating any disposition to split the nut. In side lever engines it is a judicious practice to add a nut to the top of the piston rod, in addition to the cutter for securing the piston rod to the cross head. In a good example of an engine thus provided, the piston rod is 7 in. in diameter, and the screw 5 in.; the part of the rod which fits into the cross head eye is 1 ft. 5-1/2 in. long, and tapers from 6-1/2 in. to 6-13/16 in. diameter. This proportion of taper is a good one; if the taper be less, or if a portion of the piston rod within the cross head eye be left untapered, as is sometimes the case, it is very difficult to detach the parts from one another. 449. _Q._--Which is the most beneficial construction of slide valve? _A._--The best construction of slide valve appears to be that adopted by Messrs. Penn for their larger engines, and which consists of a three ported valve, to the back of which a ring is applied of an area equal to that of exhaustion port, and which, by bearing steam tight against the back of the casing, so that a vacuum may be maintained within the ring, puts the valve in equilibrium, so that it may be moved with an inconsiderable exercise of force. The back of the valve casing is put on like a door, and its internal surface is made very true by scraping. There is a hole through the valve so as to conduct away any steam which may enter within the ring by leakage, and the ring is kept tight against the back of the casing by means of a ring situated beneath the bearing ring, provided with four lugs, through which bolts pass tapped into bosses on the back of the valve; and, by unscrewing these bolts,--which may be done by means of a box key which passes through holes in the casing closed with screwed plugs,--the lower ring is raised upwards, carrying the bearing ring before it. The rings must obviously be fitted over a boss upon the back of the valve; and between the rings, which are of brass, a gasket ring is interposed to compensate by its compressibility for any irregularity of pressure, and each of the bolts is provided with a ratchet collar to prevent it from turning back, so that the engineer, in tightening these bolts, will have no difficulty in tightening them equally, if he counts the number of clicks made by the ratchet. Where this species of valve is used, it is indispensable that large escape valves be applied to the cylinder, as a valve on this construction is unable to leave the face. In locomotive engines, the valve universally employed is the common three ported valve. 450. _Q._--Might not an equilibrium valve be so constructed by the interposition of springs, as to enable it to leave the cylinder face when an internal force is applied? _A._--That can no doubt be done, and in some engines has been done. In the screw steamer Azof, the valve is of the equilibrium construction, but the plate which carries the packing on which the top ring rests, is an octagon, and fits into an octagonal recess on the back of the valve. Below each side of the octagon there is a bent flat spring, which lifts up the octagonal plate, and with it the packing ring against the back of the valve casing; and should water get into the cylinder, it escapes by lifting the valve, which is rendered possible by the compressibility of the springs. An equivalent arrangement is shown in figs. 39 and 40, where the ring is lifted by spiral springs. [Illustration: Fig. 39. EQUILIBRIUM GRIDIRON SLIDE VALVE. Longitudinal Section. Scale 3/4 inch = 1 foot.] 451. _Q._--What species of valve is that shown in figs. 39 and 40? [Illustration: Fig. 40. EQUILIBRIUM GRIDIRON SLIDE VALVE. Back View with Ring removed. Scale 3/4 inch = 1 foot.] _A._--It is an equilibrium gridiron valve; so called because it lets the steam in and out by more than one port. A A are the ordinary steam passages to the top and bottom of the cylinder; B B is the ring which rubs against the back of the valve casing, and D is the eduction passage, S S S S shows the limits of the steam space, for the steam penetrates to the central chamber S S by the sides of the valve. When the valve is opened upon the steam side, the cylinder receives steam through both ports at that end of the cylinder, and both ports at the other end of the cylinder are at the same time open to the eduction. The benefit of this species of valve is, that it gives the same opening of the valve that is given in ordinary engines, with half the amount of travel; or if three ports were made instead of two, then it would give the same area of opening that is given in common engines with one third the amount of travel. For direct acting screw engines this species of valve is now extensively used. 452. _Q._--Will you describe the configuration and mode of attachment of the eccentric by which the valve is moved? _A._--In marine engines, whether paddle or screw, if moving at a slow rate of speed, the eccentric is generally loose upon the shaft, for the purpose of backing, and is furnished with a back balance and catches, so that it may stand either in the position for going ahead, or in that for going astern. The body of the eccentric is of cast iron, and it is put on the shaft in two pieces. The halves are put together with rebated joints to keep them from separating laterally, and they are prevented from sliding out by round steel pins, each ground into both halves; square keys would probably be preferable to round pins in this arrangement, as the pins tend to wedge the jaws of the eccentric asunder. In some cases the halves of the eccentric are bolted together by means of flanges, which is, perhaps, the preferable practice. The eccentric hoop in marine and land engines is generally of brass; it is expedient to cast an oil cup on the eccentric hoop, and, where practicable, a pan should be placed beneath the eccentric for the reception of the oil droppings. The notch of the eccentric rod for the reception of the pin of the valve shaft is usually steeled, to prevent inconvenient wear; for when the sides of the notch wear, the valve movement is not only disturbed, but it is very difficult to throw the eccentric rod out of gear. It is found to be preferable, however, to fit this notch with a brass bush, for the wear is then less rapid, and it is an easy thing to replace this bush with another when it becomes worn. The eccentric catches of the kind usually employed in marine engines, sometimes break off at the first bolt hole, and it is preferable to have a bolt in advance of the catch face, or to have a hoop encircling the shaft with the catches welded on it, the hoop itself being fixed by bolts or a key. This hoop may either be put on before the cranks in one piece or afterwards in two pieces. 453. _Q._--Are such eccentrics used in direct acting screw engines? _A._--No; direct acting screw engines are usually fitted with the link motion and two fixed eccentrics. AIR PUMP AND CONDENSER. 454. _Q._--What are the details of the air pump? _A._--The air pump bucket and valves are all of brass in modern marine engines, and the chamber of the pump is lined with copper, or made wholly of brass, whereby a single boring suffices. When a copper lining is used, the pump is first bored out, and a bent sheet of copper is introduced, which is made accurately to fill the place, by hammering the copper on the inside. Air pump rods of Muntz's metal or copper are much used. Iron rods covered with brass are generally wasted away where the bottom cone fits into the bucket eye, and if the casing be at all porous, the water will insinuate itself between the casing and the rod and eat away the iron. If iron rods covered with brass be used, the brass casing should come some distance into the bucket eye; the cutter should be of brass, and a brass washer should cover the under side of the eye, so as to defend the end of the rod from the salt water. Rods of Muntz's metal are probably on the whole to be preferred. It is a good practice to put a nut on the top of the rod, to secure it more firmly in the cross head eye, where that plan can be conveniently adopted. The part of the rod which fits into the cross head eye should have more taper when made of copper or brass, than when made of iron; as, if the taper be small, the rod may get staved into the eye, whereby its detachment will be difficult. 455. _Q._--What species of packing is used in air pumps? _A._--Metallic packing has in some instances been employed in air pump buckets, but its success has not been such as to lead to its further adoption. The packing commonly employed is hemp. A deep solid block of metal, however, without any packing, is often employed with a satisfactory result; but this block should have circular grooves cut round its edge to hold water. Where ordinary packing is employed, the bucket should always be made with a junk ring, whereby the packing may be easily screwed down at any time with facility. In slow moving engines the bucket valve is generally of the spindle or pot-lid kind, but butterfly valves are sometimes used. The foot and delivery valves are for the most part of the flap or hanging kind. These valves all make a considerable noise in working, and are objectionable in many ways. Valves on Belidor's construction, which is in effect that of a throttle valve hung off the centre, were some years ago proposed for the delivery and foot valves; and it appears probable that their operation would be more satisfactory than that of the valves usually employed. 456. _Q._--Where is the delivery valve usually situated? _A._--Some delivery valve seats are bolted into the mouth of the air pump, whereby access to the pump bucket is rendered difficult: but more commonly the delivery valve is a flap valve exterior to the pump. If delivery valve seats be put in the mouth of the air pump at all, the best mode of fixing them appears to be that adopted by Messrs. Maudslay. The top of the pump barrel is made quite fair across, and upon this flat surface a plate containing the delivery valve is set, there being a small ledge all round to keep it steady. Between the bottom of the stuffing box of the pump cover and the eye of the valve seat a short pipe extends encircling the pump rod, its lower end checked into the eye of the valve seat, and its upper end widening out to form the bottom of the stuffing box of the pump cover. Upon the top of this pipe some screws press, which are accessible from the top of the stuffing box gland, and the packing also aids in keeping down the pipe, the function of which is to retain the valve seat in its place. When the pump bucket has to be examined the valve seat may be slung with the cover, so as to come up with the same purchase. For the bucket valves of such pumps Messrs. Maudslay employ two or more concentric ring valves with a small lift. These valves have given a good deal of trouble in some cases, in consequence of the frequent fracture of the bolts which guide and confine the rings; but this is only a fault of detail which is easily remedied, and the principle appears to be superior to that of any of the other metallic air pump valves at present in common use. [Illustration: Fig. 41. TRUNK AIR PUMP. Scale 3/4 inch to 1 foot.] 457. _Q._--Are not air pump valves now very generally made of india rubber? _A._--They are almost invariably so made if the engines are travelling fast, as in the case of direct acting screw engines, and they are very often made of large discs or rings of india rubber, even when the engines travel slowly. A very usual and eligible arrangement for many purposes is that shown in fig. 41, where both foot and delivery valves are situated in the ends of the pump, and they, as well as the valve in the bucket are made of india rubber rings closing on a grating. The trunk in the air pump enables guide rods to be dispensed with. [Illustration: Fig. 42. PENN'S DISK VALVE FOR AIR PUMP. Section.] [Illustration: Fig. 43. PENN'S DISK VALVE FOR AIR PUMP. Ground Plan.] [Illustration: Fig. 44. MAUDSLAY'S DISC VALVE FOR AIR PUMP. Section.] 458. _Q._--The air pump, when double acting, has of course inlet and outlet valves at each end? _A._--Yes; and the general arrangement of the valves of double acting air pumps, such as are usual in direct acting screw engines, is that represented in the figure of Penn's trunk engine already described in Chapter I. Each inlet and outlet valve consists of a number of india rubber discs set over a perforated brass plate, and each disc is bound down by a bolt in the middle, which bolt also secures a brass guard set above the disc to prevent it from rising too high. The usual configuration of those valves is that represented in figs. 42, 43, and 44; figs. 42 and 43 being a section and ground plan of the species of valve used by Messrs. Penn, and fig. 44 being a section of that used by Messrs. Maudslay. It is important in these valves to have the india rubber thick,--say about an inch thick for valves eight inches in diameter. It is also advisable to make the central bolts with a nut above and a nut below, and to form the bolt with a counter sunk neck, so that it will not fall down when the top nut is removed. The lower point of the bolt should be riveted over on the nut to prevent it from unscrewing, and the top end should have a split pin through the point for the same purpose. The hole through which the bolt passes should be tapped, though the bolt is not screwed into it, so that if a bolt breaks, a temporary stud may be screwed into the hole without the necessity of taking out the whole plate. The guard should be large, else the disc may stretch in the central hole until it comes over it; but the guard should not permit too much lift of the valve, else a good deal of the water and air will return into the pump at the return stroke before the valve shuts. Penn's guard is rather small, and Maudslay's permits too much lift. 459. _Q._--What is the proper area through the valve gratings? _A._--The collective area should be at least equal to the area of the pump piston, and the lower edges of the perforations should be rounded off to afford more free ingress or egress to the water. 460. _Q._--Is there much strain thrown on the plates in which the valves are set? _A._--A good deal of strain; and in the earlier direct acting screw engines these plates were nearly in every case made too light. They should be made thick, have strong feathers upon them, and be very securely bolted down with split pins at the points of the bolts, to prevent them from unscrewing. The plate will be very apt to be broken should some of the bolts become loose. Of course all the bolts and split pins, as well as the plates and guards, must be of brass. 461. _Q._--How are the plates to be taken out should that become necessary? _A._--They are usually taken out through a door in the top of the hot well provided for that purpose, which door should be as large as the plates themselves; and it is a good precaution to cast upon this door--which will be of cast iron--six or eight stout projecting feet which will press upon the top of the outlet or delivery valve plate when the door is screwed down. The upper or delivery valve plate and the lower or foot valve plate should have similar feet. A large part of the strain will thus be transferred from the plates to the door, which can easily be made strong enough to sustain it. It is advisable that the plates should lie at an angle so that the shock of the water may not come upon the whole surface at once. 462. _Q._--Does the double acting air pump usual in direct acting screw engines, produce as good a vacuum as the single acting air pump usual in paddle engines? _A._--It will do so if properly constructed; but I do not know of any case of a double acting air pump, with india rubber valves, which has been properly constructed. 463. _Q._--What is the fault of such pumps? _A._--The pump frequently works by starts, as if at times it did not draw at all, and then again on a sudden gorged itself with water, so as to throw a great strain upon the working parts. The vacuum, moreover, is by no means so good as it should be, and it is a universal vice of direct acting screw engines that the vacuum is defective. I have been at some pains to investigate the causes of this imperfection; and in a sugar house engine fitted with pumps like those of a direct acting screw engine to maintain a vacuum in the pans, I found that a better vacuum was produced when the engine was going slowly than when it was going fast; which is quite the reverse of what was to have been expected, as the hot water which had to be removed by the condensation of the steam proceeding from the pan, was a constant quantity. In this engine, too, which was a high pressure one, the irregularities of the engine consequent upon the fitful catching of the water by the pump, was more conspicuous, as the working of this vacuum pump was the only work that the engine had to perform. 464. _Q._--And were you able to discover the cause of these irregularities? _A._--The main cause of them I found to be the largeness of the space left between the valve plates in this class of pumps, and out of which there is nothing to press the air or water which may be lying there. It consequently happens, that if there be the slightest leakage of air into the pump, this air is merely compressed, and not expelled, by the advance of the air pump piston. It expands again to its former bulk on the return of the pump piston, and prevents the water from entering until there is such an accumulation of pressure in the condenser as forces the water into the pump, when the air being expelled by the water, causes a good vacuum to be momentarily formed in the pump when it gorges itself by taking a sudden gulp of water. So soon, however, as the pressure falls in the condenser and some more air leaks into the pump, the former imperfect action recurs and is again redressed in the same violent manner. 465. _Q._--Is this irregular action of the pump the cause of the imperfect vacuum? _A._--It is one cause. Sometimes one end of the pump will alone draw and the other end will be inoperative, although it is equally open to the condenser, and this will chiefly take place at the stuffing box end, where a leakage of air is more likely to occur. I find, however, that even when both ends of the pump are acting equally and there is no leakage of air at all, the vacuum maintained by a double acting horizontal pump with india rubber valves, is not so good as that maintained by a single acting pump of the kind usual in old engines. 466. _Q._--Will you specify more precisely what were the results you obtained? _A._--When the vacuum pan was exhausted by the pumps without any boiling being carried on in the pan, but only a little cold water being let into it, and also into the pumps to enable them to act in their best manner, it was found that whereas with the old pump a vacuum of 114 on the sugar boiler's gauge could be readily obtained, equal to about 29-1/2 inches of mercury, the lowest that could possibly be got with the new horizontal pump was 122 degrees of the sugar boiler's gauge, or 29 inches of mercury, and to get that the engine must not go faster than 10 or 12 strokes per minute. The proper speed of the engine was 75 strokes per minute, but if allowed to go at that speed the vacuum fell to 130 of the sugar maker's gauge, or 28-1/2 inches of mercury. When the steam was let into the worms of the pan so as to boil the water in it, the vacuum was 134 at 75 revolutions of the engine, and went down to 132 at 40 revolutions, but rose again to 135, equal to about 28-1/4 inches of mercury, at 20 revolutions. 467. _Q._--To what do you attribute the circumstance of a better vacuum being got at low speeds than at high speeds? _A._--It is difficult to assign the precise reason, but it appears to be a consequence of the largeness of the vacant space between the valve plates. When the piston of the air pump is drawn back, the air contained in this large collection of water will cause it to boil up like soda water; and when the piston of the pump is forced forward, this air, instead of being expelled, will be again driven into the water. There will consequently be a quantity of air in the pump which cannot be got rid of at all, and which will impair the vacuum as a matter of course. 468. _Q._--What expedient did you adopt to improve the vacuum in the engine to which you have referred? _A._--I put blocks of wood on the air pump piston, which at the end of its stroke projected between the valve plates and forced the water out. I also introduced a cock of water at each end of the pump between the valve plates, to insure the presence of water at each end of the pump to force the air out. With these ameliorations the pump worked steadily, and the vacuum obtained became as good as in the old pump. I had previously introduced an injection cock into each end of the air pump in steam vessels, from which I had obtained advantageous results; and in all horizontal air pumps I would recommend the piston and valve plates to be so constructed that the whole of the water will be expressed by the piston. I would also recommend an injection cock to be introduced at each end of the pump. PUMPS, COCKS, AND PIPES. 469. _Q._--Will you explain the arrangement of the feed pump? _A._--In steam vessels, the feed pump plunger is generally of brass, and the barrel of the pump is sometimes of brass, but generally of cast iron. There should be a considerable clearance between the bottom of the plunger and the bottom of the barrel, as otherwise the bottom of the barrel may be knocked out, should coal dust or any other foreign substance gain admission, as it probably would do if the injection water were drawn at any time from the bilge of the vessel, as is usually done if the vessel springs a leak. The valves of the feed pump in marine engines are generally of the spindle kind, and are most conveniently arranged in a chest, which may be attached in any accessible position to the side of the hot well. There are two nozzles upon this chest, of which the lower one leads to the pump, and the upper one to the boiler. The pipe leading to the pump is a suction pipe when the plunger ascends, and a forcing pipe when the plunger descends. The plunger in ascending draws the water out of the hot well through the lowest of the valves, and in descending forces it through the centre valve into the space above it, which communicates with the feed pipe. Should the feed cock be shut so as to prevent any feed water from passing through it, the water will raise the topmost valve, which is loaded to a pressure considerably above the pressure of the steam, and escape into the hot well. This arrangement is neater and less expensive than that of having a separate loaded valve on the feed pipe with an overflow through the ship's side, as is the more usual practice. 470. _Q._--Will you describe what precautions are to be observed in the construction of the cocks used in engines? _A._--All the cocks about an engine should be provided with bottoms and stuffing boxes, and reliance should never be placed upon a single bolt passing through a bottom washer for keeping the plug in its place, in the case of any cock communicating with the boiler; for a great strain is thrown upon that bolt if the pressure of the steam be high, and if the plug be made with much taper; and should the bolt break, or the threads strip, the plug will fly out, and persons standing near may be scalded to death. In large cocks, it appears the preferable plan to cast the bottoms in; and the metal of which all the cocks about a marine engine are made, should be of the same quality as that used in the composition of the brasses, and should be without lead, or other deteriorating material. In some cases the bottoms of cocks are burnt in with hard solder, but this method cannot be depended upon, as the solder is softened and wasted away by the hot salt water, and in time the bottom leaks, or is forced out. The stuffing box of cocks should be made of adequate depth, and the gland should be secured by means of four strong copper bolts. The taper of blow-off cocks is an important element in their construction; as, if the taper be too great, the plugs will have a continual tendency to rise, which, if the packing be slack, will enable grit to get between the faces, while, if the taper be too little, the plug will be liable to jam, and a few times grinding will sink it so far through the shell that the waterways will no longer correspond. One eighth of an inch deviation from the perpendicular for every inch in height, is a common angle for the side of the cock, which corresponds with one quarter of an inch difference of diameter in an inch of height; but perhaps a somewhat greater taper than this, or one third of an inch difference in diameter for every inch of height, is a preferable proportion. The bottom of the plug must be always kept a small distance above the bottom of the shell, and an adequate surface must be left above and below the waterway to prevent leakage. Cocks formed according to these directions will be found to operate satisfactorily in practice, while they will occasion perpetual trouble if there be any malformation. 471. _Q._--What is the best arrangement and configuration of the blow-off cocks? _A._--The blow-off cocks of a boiler are generally placed some distance from the boiler; but it appears preferable that they should be placed quite close to it, as there are no means of shutting off the water from the pipe between the blow-off cock and the boiler, should fracture or leakage there arise. Every boiler must be furnished with a blow-off cock of its own, independently of the main blow-off cocks on the ship's sides, so that the boilers may be blown off separately, and may be shut off from one another. The preferable arrangement appears to be, to cast upon each blow-off cock a bend for attaching the cock to the bottom of the boiler, and the plug should stand about an inch in advance of the front of the boiler, so that it may be removed, or re-ground, with facility. The general arrangement of the blow-off pipes is to run a main blow-off pipe beneath the floor plates, across the ship, at the end of the engines, and into this pipe to lead a separate pipe, furnished with a cock, from each boiler. The main blow-off pipe, where it penetrates the ship's side, is furnished with a cock: and in modern steam vessels Kingston's valves are also used, which consist of a spindle or plate valve, fitted to the exterior of the ship, so that if the internal pipe or cock breaks, the external valve will still be operative. Some expedient of this kind is almost necessary, as the blow-off cocks require occasional regrinding, and the sea cocks cannot be re-ground without putting the vessel into dock, except by the use of Kingston's valves, or some equivalent expedient. 472. Q.--What is the proper construction and situation of the injection cocks, and waste water valves? A.--The sea injection cocks are usually made in the same fashion as the sea blow-off cocks, and of about the same size, or rather larger. The injection water is generally admitted to the condenser by means of a slide valve, but a cock appears to be preferable, as it is more easily opened, and has not any disposition to shut of its own accord. In paddle vessels the sea injection pipes should be put through the ship's sides in advance of the paddles, so that the water drawn in may not be injuriously charged with air. The waste water pipe passing from the hot well through the vessel's side is provided with a stop valve, called the discharge valve, which is usually made of the spindle kind, so as to open when the water coming from the air pump presses against it. In some cases this valve is a sluice valve, but the hot well is then almost sure to be split, if the engine be set on without the valve having been opened. The opening of the waste water pipe should always be above the load water line, as it will otherwise be difficult to prevent leakage through the engine into the ship when the vessel is lying in harbor. 473. Q.--What is the best arrangement of gauge cocks and glass gauges? A.--Gauge cocks are generally very inartificially made, and occasion needless annoyance. They are rarely made with bottoms, or with stuffing boxes, and are consequently, for the most part, adorned with stalactites of salt after a short period of service. The water discharged from them, too, from the want of a proper conduit, disfigures the front of the boiler, and adds to the corrosion in the ash pits. It would be preferable to combine the gauge cocks appertaining to each boiler into a single upright tube, connected suitably with the boiler, and the water flowing from them could be directed downward into a funnel tube communicating with the bilge. The cocks of the glass tubes, as well as of the gauge cocks, should be furnished with stuffing boxes and with bottoms, unless the water enters through the bottom of the plug, which in gauge cocks is sometimes the case. The glass gauge tubes should always be fitted with a cock at each neck communicating with the boiler, so that the water and steam may be shut off if the tube breaks; and the cocks should be so made as to admit of the tubes being blown through with steam to clear them, as in muddy water they will become so soiled that the water cannot be seen. The gauge cocks frequently have pipes running up within the boiler, to the end that a high water level may be made consistent with an easily accessible position of the gauge cocks themselves. With the glass tubes, however, this species of arrangement is not possible, and the glass tubes must always be placed in the position of the water level. 474. Q.--What is the proper material of the pipes in steam vessels? A.--Most of the pipes of marine engines should be made of copper. The steam pipes may be of cast iron, if made very strong, but the waste water pipes should be of copper. Cast iron blow-off pipes have in some cases been employed, but they are liable to fracture, and are dangerous. The blow-off and feed pipes should be of copper, but the waste steam pipe may be of galvanized iron. Every pipe passing through the ship's side, and every pipe fixed at both ends, and liable to be heated and cooled, should be furnished with a faucet or expansive joint; and in the case of the cast iron pipes, the part of the pipe fitting into the faucet should be turned. In the distribution of the faucets of the pipes exposed to pressure, care must be taken that they be so placed that the parts of the pipe cannot be forced asunder, or turned round by the strain, as serious accidents have occurred from the neglect of this precaution. 475. _Q._--What is the best mode of making pipes tight where they penetrate the ship's side? _A._--In wooden vessels the pipes where they pierce the ship's side, should be made tight, as follows:--the hole being cut, a short piece of lead pipe, with a broad flange at one end, should be fitted into it, the place having been previously smeared with white lead, and the pipe should then be beaten on the inside, until it comes into close contact all around with the wood. A loose flange should next be slipped over the projecting end of the lead pipe, to which it should be soldered, and the flanges should both be nailed to the timber with scupper nails, white lead having been previously spread underneath. This method of procedure, it is clear, prevents the possibility of leakage down through the timbers; and all, therefore, that has to be guarded against after this precaution, is to prevent leakage into the ship. To accomplish this object, let the pipe which it is desired to attach be put through the leaden hause, and let the space between the pipe and the lead be packed with gasket and white lead, to which a little olive oil has been added. The pipe must have a flange upon it to close the hole in the ship's side; the packing must then be driven in from the outside, and be kept in by means of a gland secured with bolts passing through the ship's side. If the pipe is below the water line the gland must be of brass, but for the waste water pipe a cast iron gland will answer. This method of securing pipes penetrating the side, however, though the best for wooden vessels, will, it is clear, fail to apply to iron ones. In the case of iron vessels, it appears to be the best practice to attach a short iron nozzle, projecting inward from the skin, for the attachment of every pipe below the water line, as the copper or brass would waste the iron of the skin if the attachment were made in the usual way. DETAILS OF THE SCREW AND SCREW SHAFT. 476. _Q._--What is the best method of fixing the screw upon the shaft? _A._--The best way is to cut two large grooves in the shaft coming up to a square end, and two corresponding grooves or key seats in the screw boss opposite the arms. Fit into the grooves on the shaft keys with heads, the length of which is equal to half the depth of the boss, and with the ends of the keys bearing against the ends of the grooves in the shaft. Then ship on the propeller, and drive other keys of an equal length from the other side of the boss, so that the points of the keys will nearly meet in the middle; next burr up the edge of the grooves upon the heads of the keys, to prevent them from working back; and finally tap a bolt into the side of the boss to penetrate the shaft. Propellers so fitted will never get slack. 477. _Q._--What is the best way of fitting in the screw pipe at the stern? _A._--It should have projecting rings, which should be turned; and cast iron pieces with holes in them, bored out to the sizes of these rings, should be secured to the stern frames, and the pipe be then shipped through all. Before this is done, however, the stern post must be bored out by a template to fit the pipe, and the pipe is to be secured at the end to the stern post either by a great external nut of cast iron, or by bolts passing through the stern post and through lugs on the pipe. The pipe should be bored throughout its entire length, and the shaft should be turned so as to afford a very long bearing which will prevent rapid wear. 478. _Q._--How is the hole formed in the deadwood of the ship in which the screw works? _A._--A great frame of malleable iron, the size of the hole, is first set up, and the plating of the ship is brought to the edge of this hole, and is riveted through the frame. It is important to secure this frame very firmly to the rest of the ship, with which view it is advisable to form a great palm, like the palm of a vice, on its inner superior corner, which, projecting into the ship, may be secured by breast-hook plates to the sides, whereby the strain which the screw causes will be distributed over the stern, instead of being concentrated on the rivets of the frame. 479. _Q._--Are there several lengths of screw shaft? _A._--There are. 480. _Q._--How then are these secured to one another? _A._--The best mode of securing the several lengths of shaft together is by forging the shafts with flanges at the ends, which are connected together by bolts, say six strong bolts in each, accurately fitted to the holes. [Illustration: Fig 44. End of the Screw Shaft of Correo, showing the mode of receiving the Thrust. A, discs; B, tightening wedge.] 481. _Q._--How is the thrust of the shaft usually received? _A._--In some cases it is received on a number of metal discs set in a box containing oil; and should one of these discs stick fast from friction, the others will be free to revolve. This arrangement, which is represented in fig. 44, is used pretty extensively and answers the purpose perfectly. It is of course necessary that the box in which the discs A are set, shall be strong enough to withstand the thrust which the screw occasions. Another arrangement still more generally used, is that represented in figs. 55 and 56, p. 331. It is a good practice to make the thrust plummer block with a very long sole in the direction of the shaft, so as to obviate any risk of canting or springing forward when the strain is applied, as such a circumstance, if occurring even to a slight extent, would be very likely to cause the bearing to heat. 482. _Q._--Are there not arrangements existing in some vessels for enabling the screw to be lifted out of the water while the vessel is at sea? _A._--There are; but such arrangements are not usual in merchant vessels. In one form of apparatus the screw is set on a short shaft in the middle of a sliding frame, which can be raised or lowered in grooves like a window and the screw shaft within the ship can be protruded or withdrawn by appropriate mechanism, so as to engage or leave free this short shaft as may be required. When the screw has to be lifted, the screw shaft is drawn into the vessel, leaving the short shaft free to be raised up by the sliding frame, and the frame is raised by long screws turned round by a winch purchase on deck. A chain or rope, however, is better for the purpose of raising this frame, than long screws; but the frame should in such case be provided with pall catches like those of a windlass, which, if the rope should break, will prevent the screw from falling. DETAILS OF THE PADDLES AND PADDLE SHAFT. 483. _Q._--What are the most important details of the construction of paddle wheels? _A._--The structure of the feathering wheel will be hereafter described in connection with an account of the oscillating engine; and it will be expedient now to restrict any account of the details to the common radial paddle, as applied to ocean steamers. The best plan of making the paddle centres is with square eyes, and each centre should be secured in its place by means of eight thick keys. The shaft should be burred up against the head of these keys with a chisel, so as to prevent the keys from coming back of their own accord. If the keys are wanted to be driven back, this burr must be cut off, and if made thick, and of the right taper, they may then be started without difficulty. The shaft must of course be forged with square projections on it, so as to be suitable for the application of centres with square eyes. Messrs. Maudslay & Co. bore out their paddle centres, and turn a seat for them on the shaft, afterward fixing them on the shaft with a single key. This plan is objectionable for the two reasons, that it is insecure when new, and when old is irremovable. The general practice among the London engineers is to fix the paddle arms at the centre to a plate by means of bolts, a projection being placed upon the plates on each side of the arm, to prevent lateral motion; but this method is inferior in durability to that adopted in the Clyde, in which each arm is fitted into a socket by means of a cutter--a small hole being left opposite to the end of each arm, whereby the arm may be forced back by a drift. 484. _Q._--How are the arms attached to the outside rings? _A._--Some engineers join the paddle arms to the outer ring by means of bolts; but unless very carefully fitted, those bolts after a time become slack sideways, and a constant working of the parts of the wheel goes on in consequence. Sometimes the part of the other ring opposite the arm is formed into a mortise, and the arms are wedged tight in these holes by wedges driven in on each side; but the plan is an expensive one, and not satisfactory, as the wedges work loose even though riveted over at the point. The best mode of making a secure attachment of the arms to the ring, consists in making the arms with long T heads, and riveting the cross piece to the outer ring with a number of rivets, not of the largest size, which would weaken the outer ring too much. The best way of securing the inner rings to the arms is by means of lugs welded on the arms, and to which the rings are riveted. 485. _Q._--What are the scantlings of the paddle floats? _A._--The paddle floats are usually made either of elm or pine; if of the former, the common thickness for large sea-going vessels is about 2-1/2 inches; if of the latter, 3 inches. The floats should have plates on both sides, else the paddle arms will be very liable to cut into the wood, and the iron of the arms will be very rapidly wasted. When the floats have been fresh put on they must be screwed up several times before they come to a bearing. If this be not done, the bolts will be sure to get slack at sea, and all the floats on the weather side may be washed off. The bolts for holding on the paddle floats are made extra strong, on account of the corrosion to which they are subject; and the nuts should be made large, and should be square, so that they may be effectually tightened up, even though their corners be worn away by corrosion. It is a good plan to give the thread of the paddle bolts a nick with a chisel, after the nut has been screwed up, which will prevent the nut from turning back. Paddle floats, when consisting of more than one board, should be bolted together edgeways, by means of bolts running through their whole breadth. The floats should not be notched to allow of their projection beyond the outer ring, as, if the sides of the notch be in contact with the outer ring, the ring is soon eaten away in that part, and the projecting part of the float, being unsupported, is liable to be broken off. 486. _Q._--Do not the wheels jolt sideways when the vessel rolls? _A._--It is usual to put a steel plate at each end of the paddle shafts tightened with a key, to prevent end play when the vessel rolls, but the arrangement is precarious and insufficient. Messrs. Maudslay make their paddle shaft bearings with very large fillets in the corner, with the view of diminishing the evil; but it would be preferable to make the bearings of the crank shafts spheroidal; and, indeed, it would probably be an improvement if most of the bearings about the engine were to be made in the same fashion. The loose end of the crank pin should be made not spheroidal, but consisting of a portion of a sphere; and a brass bush might then be fitted into the crank eye, that would completely encase the ball of the pin, and yet permit the outer end of the paddle shaft to fall without straining the pin, the bush being at the same time susceptible of a slight end motion. The paddle shaft, where it passes through the vessel's side, is usually surrounded by a lead stuffing box, which will yield if the end of the shaft falls; this stuffing box prevents leakage into the ship from the paddle wheels: but it is expedient, as a further precaution, to have a small tank on the ship's side immediately beneath the stuffing box, with a pipe leading down to the bilge to catch and conduct away any water that may enter around the shaft. 487. _Q._--How is the outer bearing of the paddle wheels supplied with tallow? _A._--The bearing at the outer end of the paddle shaft is sometimes supplied with tallow, forced into a hole in the plummer block cover, as in the case of water wheels; but for vessels intended to perform long voyages, it is preferable to have a pipe leading down to the oil cup above the journal from the top of the paddle box, through which pipe oil may at any time be supplied. 488. _Q._--Will you explain the method of putting engines into a steam vessel? _A._--As an illustration of this operation it may be advisable to take the case of a side lever engine, and the method of proceeding is as follows:-- First measure across from the inside of paddle bearers to the centre of the ship, to make sure that the central line, running in a fore and aft direction on the deck or beams, usually drawn by the carpenter, is really in the centre. Stretch a line across between the paddle bearers in the direction of the shaft; to this line, in the centre of the ship where the fore and aft mark has been made, apply a square with arms six or eight feet long, and bring a line stretched perpendicularly from the deck to the keelson, accurately to the edge of the square: the lower point of the line where it touches the keelson will be immediately beneath the marks made upon the deck. If this point does not come in the centre of the keelson, it will be better to shift it a little, so as to bring it to the centre, altering the mark upon the deck correspondingly, provided either paddle shaft will admit of this being done--one of the paddle brackets being packed behind with wood, to give it an additional projection from the side of the paddle bearer. Continue the line fore and aft upon the keelson as nearly as can be judged in the centre of the ship; stretch another line fore and aft through the mark upon the deck, and look it out of winding with the line upon the keelson. Fix upon any two points equally distant from the centre, in the line stretched transversely in the direction of the shaft; and from those points, as centres, and with any convenient radius, sweep across the fore and aft line to see that the two are at right angles; and, if not, shift the transverse line a little to make them so. From the transverse line next let fall a line upon each outside keelson, bringing the edge of the square to the line, the other edge resting on the keelson. A point will thus be got on each outside keelson, perpendicularly beneath the transverse line running in the direction of the shaft, and a line drawn between those two points will be directly below the shaft. To this line the line of the shaft marked on the sole plate has to be brought, care being taken, at the same time, that the right distance is preserved between the fore and aft line upon the sole plate, and the fore and aft line upon the central keelson. 489. _Q._--Of course the keelsons have first to be properly prepared? _A._--In a wooden vessel, before any part of the machinery is put in, the keelsons should be dubbed fair and straight, and be looked out of winding by means of two straight edges. The art of placing engines in a ship is more a piece of plain common sense than any other feat in engineering, and every man of intelligence may easily settle a method of procedure for himself. Plumb lines and spirit levels, it is obvious, cannot be employed on board a vessel, and the problem consists in so placing the sole plates, without these aids, that the paddle shaft will not stand awry across the vessel, nor be carried forward beyond its place by the framing shouldering up more than was expected. As a plumb line cannot be used, recourse must be had to a square; and it will signify nothing at what angle with the deck the keelsons run, so long as the line of the shaft across the keelsons is square down from the shaft centre. The sole plates being fixed, there is no difficulty in setting the other parts of the engine in their proper places upon them. The paddle wheels must be hung from the top of the paddle box to enable the shaft to be rove through them, and the cross stays between the engines should be fixed in when the vessel is afloat. To try whether the shafts are in a line, turn the paddle wheels, and try if the distance between the cranks is the same at the upper and under, and the two horizontal centres; if not, move the end of the paddle shaft up or down, backward or forward, until the distance between the cranks at all the four centres is the same. 490. _Q._--In what manner are the engines of a steam vessel secured to the hull? _A._--The engines of a steamer are secured to the hull by means of bolts called holding down bolts, and in wooden vessels a good deal of trouble is caused by these bolts, which are generally made of iron. Sometimes they go through the bottom of the ship, and at other times they merely go through the keelson,--a recess being made in the floor or timbers to admit of the introduction of a nut. The iron, however, wears rapidly away in both cases, even though the bolts are tinned; and it has been found the preferable method to make such of the bolts as pass through the bottom, or enter the bilge, of Muntz's metal, or of copper. In a side lever engine, four Muntz's metal bolts may be put through the bottom at the crank end of the framing of each engine, four more at the main centre, and four more at the cylinder, making twelve through bolts to each engine; and it is more convenient to make these bolts with a nut at each end, as in that case the bolts may be dropped down from the inside, and the necessity is obviated of putting the vessel on very high blocks in the dock, in order to give room to put the bolts up from the bottom. The remainder of the holding down bolts may be of iron, and may, by means of a square neck, be screwed into the timber of the keelsons as wood screws--the upper part being furnished with a nut which may be screwed down upon the sole plate, so soon as the wood screw portion is in its place. If the cylinder be a fixed one it should be bolted down to the sole plate by as many bolts as are employed to attach the cylinder cover, and they should be of copper or brass, in any situation that is not easily accessible. 491. _Q._--If the engines become loose, how do you refix them? _A._--It is difficult to fix engines effectually which have once begun to work in the ship, for in time the surface of the keelsons on which the engines bear becomes worn uneven, and the engines necessarily rock upon it. As a general rule, the bolts attaching the engines to the keelsons are too few and of too large a diameter: it would be preferable to have smaller bolts, and a greater number of them. In addition to the bolts going through the keelsons or the vessel's bottom, there should be a large number of wood screws securing the sole plate to the keelson, and a large number of bolts securing the various parts of the engine to the sole plate. In iron vessels, holding down bolts passing through the bottom are not expedient; and there the engine has merely to be secured to the iron plate of the keelsons, which are made hollow to admit of a more effectual attachment. 492. _Q._--What are the proper proportions of bolts? _A._--In well formed bolts, the spiral groove penetrates about one twelfth of the diameter of the cylinder round which it winds, so that the diameter of the solid cylinder which remains is five sixths of the diameter over the thread. If the strain to which iron may be safely subjected in machinery is one fifteenth of its utmost strength, or 4,000 lbs. on the square inch, then 2,180 lbs. may be sustained by a screw an inch in diameter, at the outside of the threads. The strength of the holding down bolts may easily be computed, when the elevating force of the piston or main centre is known; but it is expedient very much to exceed this strength in practice, on account of the elasticity of the keelsons, the liability to corrosion, and other causes. THE LOCOMOTIVE ENGINE. 493. _Q._--What is the amount of tractive force requisite to draw carriages on railways? _A._--Upon well formed railways with carriages of good construction, the average tractive force required for low speeds is about 7-1/2 lbs. per ton, or 1/300th of the load, though in some experimental cases, where particular care was taken to obtain a favorable result, the tractive force has been reduced as low as 1/500th of the load. At low speeds the whole of the tractive force is expended in overcoming the friction, which is made up partly of the friction of attrition in the axles, and partly of the rolling friction, or the obstruction to the rolling of the wheels upon the rail. The rolling friction is very small when the surfaces are smooth, and in the case of railway carriages does not exceed 1/1000th. of the load; whereas the draught on common roads of good construction, which is chiefly made up of the rolling friction, is as much as 1/36th of the load. 494._Q._--In reference to friction you have already stated that the friction of iron sliding upon brass, which has been oiled and then wiped dry, so that no film of oil is interposed, is about 1/11th of the pressure, but that in machines in actual operation, where there is a film of oil between the rubbing surfaces, the friction is only about one third of this amount, or 1/33d of the weight. How then can the tractive resistance of locomotives at low speeds, which you say is entirely made up of friction, be so little as 1/500th. of the weight? _A._--I did not state that the resistance to traction was 1/500th of the weight upon an average--to which condition the answer given to a previous question must be understood to apply--but I stated that the average traction was about 1/300th of the load, which nearly agrees with my former statement. If the total friction be 1/300th of the load, and the rolling friction be 1/1000th of the load, then the friction of attrition must be 1/429th of the load; and if the diameter of the wheels be 36 in., and the diameter of the axles be 3 in., which are common proportions, the friction of attrition must be increased in the proportion of 36 to 3, or 12 times, to represent the friction of the rubbing surface when moving with the velocity of the carriage, 12/429ths are about 1/35th of the load, which does not differ much from the proportion of 1/33d as previously determined. 495. _Q._--What is the amount of adhesion of the wheels upon the rails? _A._--The adhesion of the wheels upon the rails is about 1/5th of the weight when the rails are clean, or either perfectly wet or perfectly dry; but when the rails are half wet or greasy, the adhesion is not more than 1/10th or 1/12th of the weight or pressure upon the wheels. The weight of a locomotive of modern construction varies from 20 to 25 tons. 496. _Q._--And what is its cost and average performance? _A._--The cost of a common narrow gauge locomotive, of average power, varies from £1,900 to £2,200; it will run on an average 130 miles per day, at a cost for repairs of 2-1/2d. per mile; and the cost of locomotive power, including repairs, wages, oil, and coke, does not much exceed 6d. per mile run, on economically managed railways. This does not include a sinking fund for the renewal of the engines when worn out, which may be taken as equivalent to 10 per cent. on their original cost. 497. _Q._--Does the expense of traction increase much with an increased speed? _A._--Yes; it increases very rapidly, partly from the undulation of the earth when a heavy train passes over it at a high velocity, but chiefly from the resistance of the atmosphere and blast pipe, which constitute the greatest of the impediments to motion at high speeds. At a speed of 30 miles an hour, the atmospheric resistance has been found in some cases to amount to about 12 lbs. a ton; and in side winds the resistance even exceeds this amount, partly in consequence of the additional friction caused from the flanges of the wheels being forced against the rails, and partly because the wind catches to a certain extent the front of every carriage, whereby the efficient breadth of each carriage, in giving motion to the air in the direction of the train, is very much increased. At a speed of 30 miles an hour, an engine evaporating 200 cubic feet of water in the hour, and therefore exerting about 200 horses power, will draw a load of 110 tons. Taking the friction of the train at 7-1/2 lbs. per ton, or 825 lbs. operating at the circumference of the driving wheel--which, with 5 ft. 6 in. wheels, and 18 in. stroke, is equivalent to 4,757 lbs. upon the piston--and taking the resistance of the blast pipe at 6 lbs. per square inch of the pistons, and the friction of the engine unloaded at 1 lb. per square inch, which, with pistons 12 in. in diameter, amount together to 1,582 lbs., and reckoning the increased friction of the engine due to the load at 1/7th of the load, as in some cases it has been found experimentally to be, though a much less proportion than this would probably be a nearer average, we have 7018.4 lbs. for the total load upon the pistons. At 30 miles an hour the speed of the pistons will be 457.8 feet per minute, and 7018.4 lbs. multiplied by 457.8 ft. per minute, are equal to 3213023.5 lbs. raised one foot high in the minute, which, divided by 33,000, gives 97.3 horses power as the power which would draw 110 tons upon a railway at a speed of 30 miles an hour, if there were no atmospheric resistance. The atmospheric resistance is at the rate of 12 lbs. a ton, with a load of 110 tons, equal to 1,320 lbs., moving at a speed of 30 miles an hour, which, when reduced, becomes 105.8 horses power, and this, added to 97.3, makes 203.1, instead of 200 horses power, as ascertained by a reference to the evaporative power of the boiler. This amount of atmospheric resistance, however, exceeds the average, and in some of the experiments for ascertaining the atmospheric resistance, a part of the resistance due to the curves and irregularities of the line has been counted as part of the atmospheric resistance. 498. _Q._--Is the resistance per ton of the engine the same as the resistance per ton of the train? _A._--No; it is more, since the engine has not merely the resistance of the atmosphere and of the wheels to encounter, but the resistance of the machinery besides. According to Mr. Gooch's experiments upon a train weighing 100 tons, the resistance of the engine and tender at 13.1 miles per hour was found by the indicator to be 12.38 lbs.; the resistance per ton of the train, as ascertained by the dynamometer, was at the same speed 7.58 lbs., and the average resistance of locomotive and train was 9.04 lbs. At 20.2 miles per hour these resistances respectively became 19.0, 8.19, and 12.2 lbs. At 441 miles per hour the resistances became 34.0, 21.10, and 25.5 lbs., and at 57.4 miles an hour they became 35.5, 17.81, and 23.8 lbs. 499. _Q._--Is it not maintained that the resistance of the atmosphere to the progress of railway trains increases as the square of the velocity? _A._--The atmospheric resistance, no doubt, increases as the square of the velocity, and the power, therefore, necessary to overcome it will increase as the cube of the velocity, since in doubling the speed four times, the power must be expended in overcoming the atmospheric resistance in half the time. At low speeds, the resistance does not increase very rapidly; but at high speeds, as the rapid increase in the atmospheric resistance causes the main resistance to be that arising from the atmosphere, the total resistance will vary nearly as the square of the velocity. Thus the resistance of a train, including locomotive and tender, will, at 15 miles an hour, be about 9.3 lbs. per ton; at 30 miles an hour it will be 13.2 lbs. per ton; and at 60 miles an hour, 29 lbs. per ton. If we suppose the same law of progression to continue up to 120 miles an hour, the resistance at that speed will be 92.2 lbs. per ton, and at 240 miles an hour the resistance will be 344.8 lbs. per ton. Thus, in doubling the speed from 60 to 120 miles per hour, the resistance does not fall much short of being increased fourfold, and the same remark applies to the increase of the speed from 120 to 240 miles an hour. These deductions and other deductions from Mr. Gooch's experiments on the resistance of railway trains, are fully discussed by Mr. Clark, in his Treatise on railway machinery, who gives the following rule for ascertaining the resistance of a train, supposing the line to be in good order, and free from curves:--To find the total resistance of the engine, tender, and train in pounds per ton, at any given speed. Square the speed in miles per hour; divide it by 171, and add 8 to the quotient. The result is the total resistance at the rails in lbs. per ton. 500._Q._--How comes it, that the resistance of fluids increases as the square of the velocity, instead of the velocity simply? _A._--Because the height necessary to generate the velocity with which the moving object strikes the fluid, or the fluid strikes the object, increases as the _square_ of the velocity, and the resistance or the weight of a column of any fluid varies as the height. A falling body, as has been already explained, to have acquired twice the velocity, must have fallen through four times the height; the velocity generated by a column of any fluid is equal to that acquired by a body falling through the height of the column; and it is therefore clear, that the pressure due to any given velocity must be as the square of that velocity, the pressure being in every case as twice the altitude of the column. The work done, however, by a stream of air or other fluid in a given time, will vary as the cube of the velocity; for if the velocity of a stream of air be doubled, there will not only be four times the pressure exerted per square foot, but twice the quantity of air will be employed; and in windmills, accordingly, it is found, that the work done varies nearly as the cube of the velocity of the wind. If, however, the work done by _a given quantity_ of air moving at different speeds be considered, it will vary as the squares of the speeds. 501. _Q._--But in a case where there is no work done, and the resistance varies as the square of the speed, should not the power requisite to overcome that resistance vary as the square of the speed? _A._--It should if you consider the resistance over a given distance, and not the resistance during a given time. Supposing the resistance of a railway train to increase as the square of the speed, it would take four times the power, so far as atmospheric resistance is concerned, to accomplish a mile at the rate of 60 miles an hour, that it would take to accomplish a mile at 30 miles an hour; but in the former case there would be twice the number of miles accomplished in the same time, so that when the velocity of the train was doubled, we should require an engine that was capable of overcoming four times the resistance at twice the speed, or in other words, that was capable of exerting eight times the power, so far as regards the element of atmospheric resistance. We know by experience, however, that it is easier to attain high speeds on railways than in steam vessels, where the resistance does increase nearly as the square of the speed. 502. _Q._--Will you describe generally the arrangement of a locomotive engine? _A._--The boiler and engine are hung upon a framework set on wheels, and, together with this frame or carriage, constitute what is commonly called the locomotive. Behind the locomotive runs another carriage, called the tender, for holding coke and water. A common mode of connecting the engine and tender is by means of a rigid bar, with an eye at each end through which pins are passed. Between the engine and tender, however, buffers should always be interposed, as their pressure contributes greatly to prevent oscillation and other irregular motions of the engine. 503. _Q._--How is the framing of a locomotive usually constructed? _A._--All locomotives are now made with the framing which supports the machinery situated within the wheels; but for some years a vehement controversy was maintained respecting the relative merits of outside and inside framing, which has terminated, however, in the universal adoption of the inside framing. It is difficult, in engines intended for the narrow gauge, to get cylinders within the framing of sufficient diameter to meet the exigencies of railway locomotion; by casting both cylinders in a piece, however, a considerable amount of room may be made available to increase their diameters. It is very desirable that the cylinders of locomotives should be as large as possible, so that expansion may be adopted to a large extent; and with any given speed of piston, the power of an engine either to draw heavy loads, or achieve high velocities, will be increased with every increase of the dimensions of the cylinder. The framing of locomotives, to which the boiler and machinery are attached, and which rests upon the springs situated above the axles, is formed generally of malleable iron, but in some engines the side frames consist of oak with iron plates riveted on each side. The guard plates are in these cases generally of equal length, the frames being curved upward to pass over the driving axle. Hard cast iron blocks are riveted between the guard plates to serve as guides for the axle bushes. The side frames are connected across the ends, and cross stays are introduced beneath the boiler to stiffen the frame sideways, and prevent the ends of the connecting or eccentric rods from falling down if they should be broken. 504. _Q._--What is the nature and arrangement of the springs of locomotives? _A._--The springs are of the ordinary carriage kind, with plates connected at the centre, and allowed to slide on each other at their ends. The upper plate terminates in two eyes, through each of which passes a pin, which also passes through the jaws of the bridle, connected by a double threaded screw to another bridle, which is jointed to the framing; the centre of the spring rests upon the axle box. Sometimes the springs are placed between the guard plates, and below the framing which rests upon their extremities. One species of springs which has gained a considerable introduction, consists of a number of flat steel plates with a piece of metal or other substance interposed between them at the centre, leaving the ends standing apart. It would be preferable, perhaps, to make the plates of a common spring with different curves, so that the leaves, though in contact at the centre, would not be in contact with the ends with light loads, but would be brought into contact gradually, as the strain conies on: a spring would thus be obtained that was suitable for all loads. 505. _Q._--What is the difference between inside and outside cylinder engines? _A._--Outside cylinders are so designated when placed upon the outside of the framing, with their connecting rods operating upon pins in the driving wheels; while the inside cylinders are situated within the framing, and the connecting rods attach themselves to cranks in the driving axle. 506. _Q._--Whether are inside or outside cylinder engines to be preferred? _A._--A diversity of opinion obtains as to the relative merits of outside and inside cylinders. The chief objection to outside cylinders is, that they occasion a sinuous motion in the engine which is apt to send the train off the rails; but this action may be made less perceptible or be remedied altogether, by placing a weight upon one side of the wheels, the momentum of which will just balance the momentum of the piston and its connections. The sinuous or rocking motion of locomotives is traceable to the arrested momentum of the piston and its attachments at every stroke of the engine, and the effect of the pressure thus created will be more operative in inducing oscillation the farther it is exerted from the central line of the engine. If both cylinders were set at right angles in the centre of the carriage, and the pistons were both attached to a central crank, there would be no oscillation produced; or the same effect would be realized by placing one cylinder in the centre of the carriage, and two at the sides-- the pistons of the side cylinders moving simultaneously: but it is impossible to couple the piston of an upright cylinder direct to the axle of a locomotive, without causing the springs to work up and down with every stroke of the engine: and the use of three cylinders, though adopted in some of Stephenson's engines, involves too much complication to be a beneficial innovation. 507. _Q._--Whether are four-wheeled or six-wheeled engines preferable? _A._--Much controversial ingenuity has been expended upon the question of the relative merits of the four and six-wheeled engines; one party maintaining that four-wheeled engines are most unsafe, and the other that six-wheeled engines are unmechanical, and are more likely to occasion accidents. The four-wheeled engines, however, appear to have been charged with faults that do not really attach to them when properly constructed; for it by no means follows that if the axle of a four-wheeled engine breaks, or even altogether comes away, that the engine must fall down or run off the line; inasmuch as, if the engine be properly coupled with the tender, it has the tender to sustain it. It is obvious enough, that such a connection may be made between the tender and the engine, that either the fore or hind axle of the engine may be taken away, and yet the engine will not fall down, but will be kept up by the support which the tender affords; and the arguments hitherto paraded against the four-wheeled engines are, so far as regards the question of safety, nothing more than arguments against the existence of the suggested connection. It is no doubt the fact, that locomotive engines are now becoming too heavy to be capable of being borne on four wheels at high speeds without injury to the rails; but the objection of damage to the rails applies with at least equal force to most of the six-wheeled engines hitherto constructed, as in those engines the engineer has the power of putting nearly all the weight upon the driving wheels; and if the rail be wet or greasy, there is a great temptation to increase the bite of those wheels by screwing them down more firmly upon the rails. A greater strain is thus thrown upon the rail than can exist in the case of any equally heavy four-wheeled engine; and the engine is made very unsafe, as a pitching motion will inevitably be induced at high speeds, when an engine is thus poised upon the central driving wheels, and there will also be more of the rocking or sinuous motion. Locomotives, however, intended to achieve high speeds or to draw heavy loads, are now generally made with eight wheels, and in some cases the driving wheels are placed at the end of the engine instead of in the middle. 508. _Q._--As the question of the locomotive boiler has been already disposed of in discussing the question of boilers in general, it now only remains to inquire into the subject of the engine, and we may commence with the cylinders. Will you state the arrangement and construction of the cylinders of a locomotive and their connections? _A._--The cylinders are placed in the same horizontal plane as the axle of the driving wheels, and the connecting rod which is attached to the piston rod engages either a crank in the driving axle or a pin in the driving wheel, according as the cylinders are inside or outside of the framework. The cylinders are generally made an inch longer than the stroke, or there is half an inch of clearance at each end of the cylinder, to permit the springs of the vehicle to act without causing the piston to strike the top or bottom of the cylinder. The thickness of metal of the cylinder ends is usually about a third more than the thickness of the cylinder itself, and both ends are generally made removable. The priming of the boiler, when it occurs, is very injurious to the cylinders and valves of locomotives, especially if the water be sandy, as the grit carried over by the steam wears the rubbing surfaces rapidly away. The face of the cylinder on which the valve works is raised a little above the metal around it, both to facilitate the operation of forming the face and with the view of enabling any foreign substance deposited on the face to be pushed aside by the valve into the less elevated part, where it may lie without occasioning any further disturbance. The valve casing is sometimes cast upon the cylinder, and it is generally covered with a door which may be removed to permit the inspection of the faces. In some valve casings the top as well as the back is removable, which admits of the valve and valve bridle being removed with greater facility. A cock is placed at each end of locomotive cylinders, to allow the water to be discharged which accumulates in the cylinder from priming or condensation; and the four cocks of the two cylinders are usually connected together, so that by turning a handle the whole are opened at once. In Stephenson's engines, however, with variable expansion, there is but one cock provided for this purpose, which is on the bottom of the valve chest. 509. _Q._--What kind of piston is used in locomotives? _A._--The variety of pistons employed in locomotives is very great, and sometimes even the more complicated kinds are found to work very satisfactorily; but, in general, those pistons which consist of a single ring and tongue piece, or of two single rings set one above the other, so as to break joint, are preferable to those which consist of many pieces. In Stephenson's pistons the screws were at one time liable to work slack, and the springs to break. 510. _Q._--Will you explain the connection of the piston rod with the connecting rod? _A._--The piston rods of all engines are now generally either case hardened very deeply, or are made of steel; and in locomotive engines the diameter of the piston rod is about one seventh of the diameter of the cylinder, and it is formed of tilted steel. The cone of the piston rod, by which it is attached to the piston, is turned the reverse way to that which is adopted in common engines, with the view of making the cutter more accessible from the bottom of the cylinder, which is made to come off like a door. The top of the piston rod is secured with a cutter into a socket with jaws, through the holes of which a cross head passes, which is embraced between the jaws by the small end of the connecting rod, while the ends of the cross head move in guides. Between the piston rod clutch and the guide blocks, the feed pump rod joins the cross head in some engines. 511. _Q._--What kind of guides is employed for the end of the piston rod? _A._--The guides are formed of steel plates attached to the framing, between which work the guide blocks, fixed on the ends of the cross head, which have flanges bearing against the inner edges of the guides. Steel or brass guides are better than iron ones: Stephenson and Hawthorn attach their guides at one end to a cross stay, at the other to lugs on the cylinder cover; and they are made stronger in the middle than at the ends. Stout guide rods of steel, encircled by stuffing boxes on the ends of the cross head, would probably be found superior to any other arrangement. The stuffing boxes might contain conical bushes, cut spirally, in addition to the packing, and a ring, cut spirally, might be sprung upon the rod and fixed in advance of the stuffing box, with lateral play to wipe the rod before entering the stuffing box, to prevent it from being scratched by the adhesion of dust. 512. _Q._--Is any provision made for keeping the connecting rod always of the same length? _A._--In every kind of locomotive it is very desirable that the length of the connecting rod should remain invariable, in spite of the wear of the brasses, for there is a danger of the piston striking against the cover of the cylinder if it be shortened, as the clearance is left as small as possible in order to economize steam. In some engines the strap encircling the crank pin is fixed immovably to the connecting rod by dovetailed keys, and a bolt passes through the keys, rod, and strap, to prevent the dovetailed keys from working out. The brass is tightened by a gib and cutter, which is kept from working loose by three pinching screws and a cross pin or cutter through the point. The effect of this arrangement is to lengthen the rod, but at the cross head end of the rod the elongation is neutralized by making the strap loose, so that in tightening the brass the rod is shortened by an amount equal to its elongation at the crank pin end. The tightening here is also effected by a gib and cutter, which is kept from working loose by two pinching screws pressing on the side of the cutter. Both journals of the connecting rod are furnished with oil cups, having a small tube in the centre with siphon wicks. The connecting rod is a thick flat bar, with its edges rounded. 513. _Q._--How is the cranked axle of locomotives constructed? _A._--The cranked axle of locomotives is always made of wrought iron, with two cranks forged upon it toward the middle of its length, at a distance from each other answerable to the distance between the cylinders. Bosses are made on the axle for the wheels to be keyed upon, and bearings for the support of the framing. The axle is usually forged in two pieces, which are afterward welded together. Sometimes the pieces for the cranks are put on separately, but the cranks so made are liable to give way. In engines with outside cylinders the axles are made straight-the crank pins being inserted in the naves of the wheels. The bearings to which the connecting rods are attached are made with very large fillets in the corners, so as to strengthen the axle in that part, and to obviate side play in the connecting rod. In engines which, have been in use for some time, however, there is generally a good deal of end play in the bearings of the axles themselves, and this slackness contributes to make the oscillation of the engine more violent; but this evil may be remedied by making the bearings spheroidal, whereby end play becomes impossible. 514. _Q._--How are the bearings of the axles arranged? _A._--The axles bear only against the top of the axle boxes, which are generally of brass; but a plate extends underneath the bearing, to prevent sand from being thrown upon it. The upper part of the box in most engines has a reservoir of oil, which is supplied to the journal by tubes with siphon wicks. Stephenson uses cast iron axle boxes with brasses, and grease instead of oil; and the grease is fed upon the journal by the heat of the bearing melting it, whereby it is made to flow down through a hole in the brass. Any engines constructed with outside bearings have inside bearings also, which are supported by longitudinal bars, which serve also in some cases to support the piston guides; these bearings are sometimes made so as not to touch the shafts unless they break. 515. _Q._--How are the eccentrics of a locomotive constructed? _A._--In locomotives the body of the eccentric is of cast iron, in inside cylinder engines the eccentrics are set on the axle between the cranks, and they are put on in two pieces held together by bolts; but in straight axle engines the eccentrics are cast in a piece, and are secured on the shaft by means of a key. The eccentric, when in two pieces, is retained at its proper angle on the shaft by a pinching screw, which is provided with a jam nut to prevent it from working loose. A piece is left out of the eccentric in casting it to allow of the screw being inserted, and the void is afterward filled by inserting a dovetailed piece of metal. Stephenson and Hawthorn leave holes in their eccentrics on each side of the central arm, and they apply pinching screws in each of these holes. The method of fixing the eccentric to the shaft by a pinching screw is scarcely sufficiently substantial; and cases are perpetually occurring, when this method of attachment is adopted, of eccentrics shifting from their place. In the modern engines the eccentrics are forged on the axles. 516. _Q._--How are the eccentric straps constructed? _A._--The eccentric hoops are generally of wrought iron, as brass hoops are found liable to break. When formed of malleable iron, one half of the strap is forged with the rod, the other half being secured to it by bolts, nuts, and jam nuts. Pieces of brass are, in some cases, pinned within the malleable iron hoop; but it appears to be preferable to put brasses within the hoop to encircle the eccentric, as in the case of any other bearing. When the brass straps are used, the lugs have generally nuts on both sides, so that the length of the eccentric rod may be adjusted by their means to the proper length; but it is better for the lugs of the hoops to abut against the necks of the screws, and, if any adjustment be necessary from the wear of the straps, washers can be interposed. In some engines the adjustment is effected by screwing the valve rod, and the cross head through which it passes has a nut on either side of it, by which its position upon the valve rod is determined. 517. _Q._--Will you describe the eccentric rod and valve levers? _A._--In the engines in use before the introduction of the link motion, the forks of the eccentric rod were of steel, and the length of the eccentric rod was the distance between the centre of the crank axle and the centre of the valve shaft; but in modern engines the use of the link motion is universal. The valve lever in locomotives is usually longer than the eccentric lever, to increase the travel of the valve, if levers are employed; but it is better to connect the valve rod to the link of the link motion without the intervention of levers. The pins of the eccentric lever in the old engines used to wear quickly; Stephenson used to put a ferule of brass on these pins, which being loose, and acting like a roller, facilitated the throwing in and out of gear, and when worn could easily be replaced, so that there was no material derangement of the motion of the valve from play in this situation. 518. _Q._--What is the arrangement of a starting lever? _A._--The starting lever travels between two iron segments, and can be fixed in any desired position. This is done by a small catch or bell crank, jointed to the bottom of the handle at the end of the lever, and coming up by the side of the handle, but pressed out from it by a spring. The smaller arm of this bell crank is jointed to a bolt, which shoots into notches, made in one of the segments between which the lever moves. By pressing the bell crank against the handle of the lever the bolt is withdrawn, and the lever may be shifted to any other point, when, the spring being released, the bolt flies into the nearest notch. 519. _Q._--In what way does the starting handle act on the machinery of the engine to set it in motion? _A._--Its whole action lies in raising or depressing the link of the link motion relatively with the valve rod. If the valve rod be attached to the middle of the link, the valve will derive no motion from, it at all, and the engine will stop. If the attachment be slipped to one end of the link the engine will go ahead, and if slipped to the other end it will go astern. The starting handle merely achieves this change of position. 520. _Q._--Will you explain the operation of setting the valve of a locomotive? _A._--In setting the valves of locomotives, place the crank in the position answerable to the end of the stroke of the piston, and draw a straight line, representing the centre line of the cylinder, through the centres of the crank shaft and crank pin. From the centre of the shaft describe a circle with the diameter equal to the throw of the valve; another circle to represent the crank shaft; and a third circle to represent the path of the crank pin. From the centre of the crank shaft, draw a line perpendicular to the centre line of the cylinder and crank shaft, and draw another perpendicular at a distance from the first equal to the amount of the lap and the lead of the valve: the points in which this line intersects the circle of the eccentric are the points in which the centre of the eccentric should be placed for the forward and reverse motions. When the eccentric rod is attached directly to the valve, the radius of the eccentric, which precedes the crank in its revolution, forms with the crank an obtuse angle; but when, by the intervention of levers, the valve has a motion, opposed to that of the eccentric rod, the angle contained by the crank and the radius of the eccentric must be acute, and the eccentric must follow the crank: in other words, with a direct attachment to the valve the eccentric is set _more_ than one fourth of a revolution in advance of the crank, and with an indirect attachment the eccentric is set _less_ than one fourth of a circle behind the crank. If the valve were without lead or lap the eccentric would be exactly one fourth of a circle in advance of the crank or behind the crank, according to the nature of the valve connection; but as the valve would thus cover the port by the amount of the lap and lead, the eccentric must be set forward so as to open the port to the extent of the lap and lead, and this is effected by the plan just described. 521. _Q._--In the event of the eccentrics slipping round upon the shaft, which you stated sometimes happens, is it necessary to perform the operation of setting the valve as you have just described it? _A._--If the eccentrics shift upon the shaft, they may be easily refixed by setting the valve open the amount of the lead, setting the crank at the end of the stroke, and bringing round the eccentric upon the shaft till the eccentric rod gears with the valve. It would often be troublesome in practice to get access to the valve for the purpose of setting it, and this may be dispensed with if the amount of lap on the valve and the length of the eccentric rod be known. To this end draw upon a board two straight lines at right angles to one another, and from their point of intersection as a centre describe two circles, one representing the circle of the eccentric, the other the crank shaft; draw a straight line parallel to one of the diameters, and distant from it the amount of the lap and the lead: the points in which his parallel intersects the circle of the eccentric are the positions of the forward and backward eccentrics. Through these points draw straight lines from the centre of the circle, and mark the intersection of these lines with the circle of the crank shaft; measure with a pair of compasses the chord of the arc intercepted between either of these points, and the diameter which is at right angles with the crank, and the diameters being first marked on the shaft itself, then by transferring with the compasses the distance found in the diagram, and marking the point, the eccentric may at any time be adjusted without difficulty. [Illustration: Fig. 45.] 522. _Q._--Will you describe the structure and arrangement of the feed pumps of locomotive engines? _A._--The feed pumps of locomotives are generally made of brass, but the plungers are sometimes made of iron, and are generally attached to the piston, cross head, though in Stephenson's engines they are worked by rods attached to eyes on the eccentric hoops. There is a ball valve, fig. 45, between the pump and the tender, and two usually in the pipe leading from the pump to the boiler, besides a cock close to the boiler, by which the pump may be shut off from the boiler in case of any accident to the valves. The ball valves are guided by four branches, which rise vertically, and join together at the top in a hemispherical form. The shocks of the ball against this cap have in some cases broken it after one week's work, from the top of the cage having been flat, and the branches not having had their junction at the top properly filleted. These valve guards are attached in different ways to the pipes; when one occurs at the junction of two pieces of pipe it has a flange, which along with the flanges of the pipes and that of the valve seat are held together by a union joint. It is sometimes formed with a thread at the under end, and screwed into the pipe. The balls are cast hollow to lessen the shock, as well as to save the metal. In some cases where the feed pump plunger has been attached to the cross head, the piston rod has been bent by the strain; and that must in all cases occur, if the communication between the pump and boiler be closed when the engine is started, and there be no escape valve for the water. 523. _Q._--Are none but ball valves used in the feed pump? _A._--Spindle valves have in some cases been used instead of ball valves, but they are more subject to derangement; but piston valves, so contrived as to shut a portion of water in the cage when about to close, might be adopted with a great diminution of the shock. Slide valves might be applied, and would probably be found preferable to any of the expedients at present in use. In all spindle valves opened and shut rapidly, it is advisable to have the lower surface conical, to take off the shock of the water; and a large lift of the valve should be prevented, else much of the water during the return stroke of the pump will flow out before the valve shuts. 524. _Q._--At what part of the boiler is the feed water admitted? _A._--The feed pipe of most locomotive engines enters the boiler near the bottom and about the middle of its length. In Stephenson's engine the water is let in at the smoke box end of the boiler, a little below the water level; by this means the heat is more fully extracted from the escaping smoke, but the arrangement is of questionable applicability to engines of which the steam dome and steam pipe are at the smoke box end, as in that case the entering cold water would condense the steam. 525. _Q._--How are the pipes connecting the tender and locomotive constructed, so as to allow of play between the engine and tender without leakage? _A._--The pipes connecting the tender with the pumps should allow access to the valves and free motion to the engine and tender. This end is attained by the use of ball and socket joints; and, to allow some end play, one piece of the pipe slides into the other like a telescope, and is kept tight by means of a stuffing box. Any pipe joint between the engine and tender must be made in this fashion. 526. _Q._--Have you any suggestion to make respecting the arrangement of the feed pump? _A._--It would be a material improvement if a feed pump was to be set in the tender and worked by means of a small engine, such as that now used in steam vessels for feeding the boilers. The present action of the feed pumps of locomotives is precarious, as, if the valves leak in the slightest degree, the steam or boiling water from the boiler will prevent the pumps from drawing. It appears expedient, therefore, that at least one pump should be far from the boiler and should be set among the feed water, so that it will only have to force. If a pump was arranged in the manner suggested, the boiler could still be fed regularly, though the locomotive was standing still; but it would be prudent to have the existing pumps still wrought in the usual way by the engine, in case of derangement of the other, or in case the pump in the tender might freeze. 527. _Q._--Will you explain the construction of locomotive wheels? _A._--The wheels of a locomotive are always made of malleable iron. The driving wheels are made larger to increase the speed; the bearing wheels also are easier on the road when large. In the goods engines the driving wheels are smaller than in the passenger engines, and are generally coupled together. Wheels are made with much variety in their constructive details: sometimes they are made with cast iron naves, with the spokes and rim of wrought iron; but in the best modern wheels the nave is formed of the ends of the spokes welded together at the centre. When cast iron naves are adopted, the spokes are forged out of flat bars with T-formed heads, and are arranged radially in the founder's mould, the cast iron, when fluid, being poured among them. The ends of the T heads are then welded together to constitute the periphery of the wheel or inner tire; and little wedge-form pieces are inserted where there is any deficiency of iron. In some cases the arms are hollow, though of wrought iron; the tire of wrought iron, and the nave of cast iron; and the spokes are turned where they are fitted into the nave, and are secured in their sockets by means of cutters. Hawthorn makes his wheels with cast iron naves and wrought iron rims and arms; but instead of welding the arms together, he makes palms on their outer end, which are attached by rivets to the rim. These rivets, however, unless very carefully formed, are apt to work loose; and it would probably be found an improvement if the palms were to be slightly indented into the rim, in cases in which the palms do not meet each other at the ends. When the rim is turned it is ready for the tire, which is now made of steel. 528. _Q._--How do you find the length of bar necessary for forming a tire? _A._--To find the proper length of bar requisite for the formation of a hoop of any given diameter, add the thickness of the bar to the required diameter, and the corresponding circumference in the table of circumferences of circles is the length of the bar. If the iron be bent edgewise the breadth of the bar must be added to the diameter, for it is the thickness of the bar measured radially that is to be taken into consideration. In the tires of railway wheels, which have a flange on one edge, it is necessary to add not only the thickness of the tire, but also two thirds of the depth of the flange; generally, however, the tire bars are sent from the forge so curved that the plain edge of the tire is concave, and the flange edge convex, while the side which is afterward to be bent into contact with the cylindrical surface of the wheel is a plane. In this case the addition of the diameter of two thirds of the depth of the flange is unnecessary, for the curving of the flange edge has the effect of increasing the real length of the bar. When the tire is thus curved, it is only necessary to add the thickness of the hoop to the diameter, and then to find the circumference from a table; or the same result will be obtained by multiplying the diameter thus increased by the thickness of the hoop by 3.1416. 529. _Q._--How are the tires attached to the wheels? _A._--The materials for wheel tires are first swaged separately, and then welded together under the heavy hammer at the steel works; after which they are bent to the circle, welded, and turned to certain gauges. The tire is now heated to redness in a circular furnace; during the time it is getting hot, the iron wheel, turned to the right diameter, is bolted down upon a face plate or surface; the tire expands with the heat, and when at a cherry red, it is dropped over the wheel, for which it was previously too small, and it is also hastily bolted down to the surface plate; the whole mass is then quickly immersed by a swing crane in a tank of water five feet deep, and hauled up and down till nearly cold; the tires are not afterward tempered. The tire is attached to the rim with rivets having countersunk heads, and the wheel is then fixed on its axle. 530. _Q._--Is it necessary to have the whole tire of steel? _A._--It is not indispensable that the whole tire should be of steel; but a dovetail groove, turned out of the tire at the place where it bears most on the rail, and fitted with a band of steel, will suffice. This band may be put in in pieces, and the expedient appears to be the best way of repairing a worn tire; but particular care must be taken to attach these pieces very securely to the tire by rivets, else in the rapid revolution of the wheel the steel may be thrown out by the centrifugal force. In aid of such attachment the steel, after being introduced, is well hammered, which expands it sideways until it fills the dovetail groove. 531. _Q._--Is any arrangement adopted to facilitate the passage of the locomotive round curves? _A._--The tire is turned somewhat conical, to facilitate the passage of the engine round curves--the diameter of the outer wheel being virtually increased by the centrifugal force of the engine, and that of the inner wheel being correspondingly diminished, whereby the curve is passed without the resistance which would otherwise arise from the inequality of the spaces passed over by wheels of the same diameter fixed upon the same axle. The rails, moreover, are not set quite upright, but are slightly inclined inward, in consequence of which the wheels must be either conical or slightly dished, to bear fairly upon the rails. One benefit of inclining the rails in this way, and coning the tires, is that the flange of the wheels is less liable to bear against the sides of the rail, and with the same view the flanges of all the wheels are made with large fillets in the corners. Wheels have been placed loose upon the axle, but they have less stability, and are not now much used. Nevertheless this plan appears to be a good one if properly worked out. 532. _Q._--Are any precautions taken to prevent engines from being thrown off the rails by obstructions left upon the line? _A_.--In most engines a bar is strongly attached to the front of the carriage on each side, and projects perpendicularly downward to within a short distance of the rail, to clear away stones or other obstructions that might occasion accidents if the engine ran over them. CHAPTER IX. STEAM NAVIGATION. * * * * * RESISTANCE OF VESSELS IN WATER. 533. _Q._--How do you determine the resistance encountered by a vessel moving in water? _A._--The resistance experienced by vessels moving in water varies as the square of the velocity of their motion, or nearly so; and the power necessary to impart an increased velocity varies nearly as the cube of such increased velocity. To double the velocity of a steam vessel, therefore, will require four times the amount of tractive force, and as that quadrupled force must act through twice the distance in the same time, an engine capable of exerting eight times the original power will be required.[1] 534. _Q._--In the case of a board moving in water in the manner of a paddle float, or in the case of moving water impinging on a stationary board, what will be the pressure produced by the impact? _A._--The pressure produced upon a flat board, by striking water at right angles to the surface of the board, will be equal to the weight of a column of water having the surface struck as a base, and for its altitude twice the height due to the velocity with which the board moves through the water. If the board strike the water obliquely, the resistance will be less, but no very reliable law has yet been discovered to determine its amount. 535. _Q._--Will not the resistance of a vessel in moving through the water be much less than that of a flat board of the area of the cross section? _A._--It will be very much less, as is manifest from the comparatively small area of paddle board, and the small area of the circle described by the screw, relatively with the area of the immersed midship section of the vessel. The absolute speed of a vessel, with any given amount of power, will depend very much upon her shape. 536. _Q._--In what way is it that the shape of a vessel influences her speed, since the vessels of the same sectional area must manifestly put in motion a column of water of the same magnitude, and with the same velocity? _A._--A vessel will not strike the water with the same velocity when the bow lines are sharp as when they are otherwise; for a very sharp bow has the effect of enabling the vessel to move through a great distance, while the particles of water are moved aside but a small distance, or in other words, it causes the velocity with which the water is moved to be very small relatively with the velocity of the vessel; and as the resistance increases as the square of the velocity with which the water is moved, it is conceivable enough in what way a sharp bow may diminish the resistance. 537. _Q._--Is the whole power expended in the propulsion of a vessel consumed in moving aside the water to enable the vessel to pass? _A._--By no means; only a portion, and in well-formed vessels only a small portion, of the power is thus consumed. In the majority of cases, the greater part of the power is expended in overcoming the friction of the water upon the bottom of the vessel; and the problem chiefly claiming consideration is, in what way we may diminish the friction. 538. _Q._--Does the resistance produced by this friction increase with the velocity? _A._--It increases nearly as the square of the velocity. At two nautical miles per hour, the thrust necessary to overcome the friction varies as the 1.823 power of the velocity; and at eight nautical miles per hour, the thrust necessary to overcome the friction varies as the 1.713 power of the velocity. It is hardly proper, perhaps, to call this resistance by the name of friction; it is partly, perhaps mainly, due to the viscidity or adhesion of the water. 539. _Q._--Perhaps at high velocities this resistance may become less? _A_.--That appears very probable. It may happen that at high velocities the adhesion is overcome, so that the water is dragged off the vessel, and the friction thereafter follows the law which obtains in the case of solid bodies. But any such conclusion is mere speculation, since no experiments illustrative of this question have yet been made. 540. _Q._--Will a vessel experience more resistance in moving in salt water than in moving in fresh? _A._--If the immersion be the same in both cases a vessel will experience more resistance in moving in salt water than in moving in fresh, on account of the greater density of salt water; but as the notation is proportionably greater in the salt water the resistance will be the same with the same weight carried. 541. _Q._--Discarding for the present the subject of friction, and looking merely to the question of bow and stern resistance, in what manner should the hull of a vessel be formed so as to make these resistances a minimum? _A._--The hull should be so formed that the water, instead of being away driven forcibly from the bow, is opened gradually, so that every particle of water may be moved aside slowly at first, and then faster, like the ball of a pendulum, until it reaches the position of the midship frame, at which point it will have come to a state of rest, and then again, like a returning pendulum, vibrate back in the same way, until it comes to rest at the stern. It is not difficult to describe mechanically the line which the water should pursue. If an endless web of paper be put into uniform motion, and a pendulum carrying a pencil or brush be hung in front of it, then such pendulum will trace on the paper the proper water line of the ship, or the line which the water should pursue in order that no power may be lost except that which is lost in friction. It is found, however, in practice, that vessels formed with water lines on this principle are not much superior to ordinary vessels in the facility with which they pass through the water: and this points to the conclusion that in ordinary vessels of good form, the amount of power consumed in overcoming the resistance due to the wave at the bow and the partial vacuity at the stern is not so great as has heretofore been supposed, and that, in fact, the main resistance is that due to the friction. [1] This statement supposes that there is no difference of level between the water at the bow and the water at the stern. In the experiments on the steamer Pelican, the resistance was found to vary, as the 2.28th power of the velocity, but the deviation from the recognized law was imputed to a difference in the level of the water at the bow and stern. EXPERIMENTS ON THE RESISTANCE OF VESSELS. 542. _Q._--Have experiments been made to determine the resistance which steam vessels experience in moving through the waters? _A._--Experiments have been made both to determine the relative resistance of different classes of vessels, and also the absolute resistance in pounds or tons. The first experiments made upon this subject were conducted by Messrs. Boulton and Watt, and they have been numerous, long continued, and carefully performed. These experiments were made upon paddle vessels. 543. _Q._--Will you recount the chief results of these experiments? _A._--The purpose of the experiments was to establish a coefficient of performance, which with any given class of vessel would enable the speed, which would be obtained with any given power, to be readily predicted. This coefficient was obtained by multiplying the cube of the velocity of the vessels experimented upon, in miles per hour, by the sectional area of the immersed midship section in square feet, and dividing by the numbers of nominal horses power, and this coefficient will be large in the proportion of the goodness of the shape of the vessel. 544. _Q._--How many experiments were made altogether? _A._--There were five different sets of experiments on five different classes of vessels. The first set of experiments was made in 1828, upon the vessels Caledonia, Diana, Eclipse, Kingshead, Moordyke, and Eagle-vessels of a similar form and all with square bilges and flat floors; and the result was to establish the number 925 as the coefficient of performance of such vessels. The second set of experiments was made upon the superior vessels Venus, Swiftsure, Dasher, Arrow, Spitfire, Fury, Albion, Queen, Dart, Hawk, Margaret, and Hero-all vessels having flat floors and round bilges, where the coefficient became 1160. The third set of experiments was made upon the vessels Lightning, Meteor, James Watt, Cinderella, Navy Meteor, Crocodile, Watersprite, Thetis, Dolphin, Wizard, Escape, and Dragon-all vessels with rising floors and round bilges, and the coefficient of performance was found to be 1430. The fourth set of experiments was made in 1834, upon the vessels Magnet, Dart, Eclipse, Flamer, Firefly, Ferret, and Monarch, when the coefficient of performance was found to be 1580. The fifth set of experiments was made upon the Red Rover, City of Canterbury, Herne, Queen, and Prince of Wales, and in the case of those vessels the coefficient rose to 2550. The velocity of any of these vessels, with any power or sectional area, may be ascertained by multiplying the coefficient of its class by the nominal horse power, dividing by the sectional area in square feet, and extracting the cube root of the quotient, which will be the velocity in miles per hour; or the number of nominal horse power requisite for the accomplishment of any required speed may be ascertained by multiplying the cube of the required velocity in miles per hour, by the sectional area in square feet, and dividing by the coefficient: the quotient is the number of nominal horse power requisite to realize the speed. 545. _Q._--Seeing, however, that the nominal power does not represent an invariable amount of dynamical efficiency, would it not be better to make the comparison with reference to the actual power? _A._--In the whole of the experiments recited, except in the case of one or two of the last, the pressure of steam in the boiler varied between 2-3/4 lbs. and 4 lbs. per square inch, and the effective pressure on the piston varied between 11 lbs. and 13 lbs. per square inch, so that the average ratio of the nominal to the actual power may be easily computed; but it will be preferable to state the nominal power of some of the vessels, and their actual power as ascertained by experiment. 546. _Q._--Then state this. _A._--Of the Eclipse, the nominal power was 76, and the actual power 144.4 horses; of the Arrow, the nominal power was 60, and the actual 119.5; Spitfire, nominal 40, actual 64; Fury, nominal 40, actual 65.6; Albion, nominal 80, actual 135.4; Dart, nominal 100, actual 152.4; Hawk, nominal 40, actual 73; Hero, nominal 100, actual 171.4; Meteor, nominal 100, actual 160; James Watt, nominal 120, actual 204; Watersprite, nominal 76, actual 157.6; Dolphin, nominal 140, actual 238; Dragon, nominal 80, actual 131; Magnet, nominal 140, actual 238; Dart, nominal 120, actual 237; Flamer, nominal 120, actual 234; Firefly, nominal 52, actual 86.6; Ferret, nominal 52, actual 88; Monarch, nominal 200, actual 378. In the case of swift vessels of modern construction, such as the Red Rover, Herne, Queen, and Prince of Wales, the coefficient appears to be about 2550; but in these vessels there is a still greater excess of the actual over the nominal power than in the case of the vessels previously enumerated, and the increase in the coefficient is consequent upon the increased pressure of the steam in the boiler, as well as the superior form of the ship. The nominal power of the Red Rover, Herne, and City of Canterbury is, in each case, 120 horses, but the actual power of the Red Rover is 294, of the Herne 354, and of the City of Canterbury 306, and in some vessels the excess is still greater; so that with such variations it becomes necessary to adopt a coefficient derived from the introduction of the actual instead of the nominal power. 547. _Q._--What will be the average difference between the nominal and actual powers in the several classes of vessels you have mentioned and the respective coefficients when corrected for the actual power? _A._--In the first class of vessels experimented upon, the actual power was about 1.6 times greater than the nominal power; in the second class, 1.67 times greater; in the third class, 1.7 times greater; and in the fourth, 1.96 times greater; while in such vessels as the Red Rover and City of Canterbury, it is 2.65 times greater; so that if we adopt the actual instead of the nominal power in fixing the coefficients, we shall have 554 as the first coefficient, 694 as the second, 832 for the third, and 806 for the fourth, instead of 925, 1160, 1430, and 1580 as previously specified; while for such vessels as the Red Rover, Herne, Queen, and Prince of Wales, we shall have 962 instead of 2550. These smaller coefficients, then, express the relative merits of the different vessels without reference to any difference of efficacy in the engines, and it appears preferable, with such a variable excess of the actual over the nominal power, to employ them instead of those first referred to. From the circumstance of the third of the new coefficients being greater than the fourth, it appears that the superior result in the fourth set of experiments arose altogether from a greater excess of the actual over the nominal power. 548. _Q._--These experiments, you have already stated, were all made on paddle vessels. Have similar coefficients of performance been obtained in the case of screw vessels? _A._--The coefficients of a greater number of screw vessels have been obtained and recorded, but it would occupy too much time to enumerate them here. The coefficient of performance of the Fairy is 464.8; of the Rattler 676.8; and of the Frankfort 792.3. This coefficient, however, refers to nautical and not to statute miles. If reduced to statute miles for the purpose of comparison with the previous experiments, the coefficients will respectively become 703, 1033, and 1212; which indicate that the performance of screw vessels is equal to the performance of paddle vessels, but some of the superiority of the result may be imputed to the superior size of the screw vessels. INFLUENCE OF THE SIZE OF VESSELS UPON THEIR SPEED. 549. _Q._--Will large vessels attain a greater speed than small, supposing each to be furnished with the same proportionate power? _A._--It is well known that large vessels furnished with the same proportionate power, will attain a greater speed than small vessels, as appears from the rule usual in yacht races of allowing a certain part of the distance to be run to vessels which are of inferior size. The velocity attained by a large vessel will be greater than the velocity attained by a small vessel of the same mould and the same proportionate power, in the proportion of the square roots of the linear dimensions of the vessels. A vessel therefore with four times the sectional area and four times the power of a smaller symmetrical vessel, and consequently of twice the length, will have its speed increased in the proportion of the square root of 1 to the square root of 2, or 1.4 times. 550. _Q._--Will you further illustrate this doctrine by an example? _A._--The screw steamer Fairy, if enlarged to three times the size while retaining the same form, would have twenty-seven times the capacity, nine times the sectional area, and nine times the power. The length of such a vessel would be 434 feet; her breadth 63 feet 4-1/2 inches; her draught of water 16-1/2 feet; her area of immersed section 729 square feet; and her nominal power 1080 horses. Now as the lengths of the Fairy and of the new vessel are in the proportion of 1 to 3, the speeds will be in the proportion of the square root of 1 to the square root of 3; or, in other words, the speed of the large vessel will be 1.73 times greater than the speed of the small vessel. If therefore the speed of the Fairy be 13 knots, the speed of the new vessel will be 22.49 knots, although the proportion of power to sectional area, which is supposed to be the measure of the resistance, is in both cases precisely the same. If the speed of the Fairy herself had to be increased to 22.29 knots, the power would have to be increased in the proportion of the cube of 13 to the cube of 22.49, or 5.2 times, which makes the power necessary to propel the Fairy at that speed equal to 624 nominal horses power. STRUCTURE AND OPERATION OF PADDLE WHEELS. 551. _Q._--Will you describe the configuration and mode of action of the paddle wheels in general use? _A._--There are two kinds of paddle wheels in extensive use, the one being the ordinary radial wheel, in which the floats are fixed on arms radiating from the centre; and the other the feathering wheel, in which each float is hung upon a centre, and is so governed by suitable mechanism as to be always kept in nearly the vertical position. In the radial wheel there is some loss of power from oblique action, whereas in the feathering wheel there is little or no loss from this cause; but in every kind of paddle there is a loss of power from the recession of the water from the float boards, or the _slip_ as it is commonly called; and this loss is the necessary condition of the resistance for the propulsion of the vessel being created in a fluid. The slip is expressed by the difference between the speed of the wheel and the speed of the vessel, and the larger this difference is the greater the loss of power from slip must be--the consumption of steam in the engine being proportionate to the velocity of the wheel, and the useful effect being proportionate to the speed of the ship. 552. _Q._--The resistance necessary for propulsion will not be situated at the circumference of the wheel? _A._--In the feathering wheel, where every part of any one immerged float moves forward with the same horizontal velocity, the pressure or resistance may be supposed to be concentrated in the centre of the float; whereas, in the common radial wheel this cannot be the case, for as the outer edge of the float moves more rapidly than the edge nearest the centre of the wheel, the outer part of the float is the most effectual in propulsion. The point at which the outer and inner portions of the float just balance one another in propelling effect, is called the _centre of pressure_; and if all the resistances were concentrated in this point, they would have the same effect as before in resisting the rotation of the wheel. The resistance upon any one moving float board totally immersed in the water will, when the vessel is at rest, obviously vary as the square of its distance from the centre of motion--the resistance of a fluid varying with the square of the velocity; but, except when the wheel is sunk to the axle or altogether immersed in the water, it is impossible, under ordinary circumstances, for one float to be totally immersed without others being immersed partially, whereby the arc described by the extremity of the paddle arm will become greater than the arc described by the inner edge of the float; and consequently the resistance upon any part of the float will increase in a higher ratio than the square of its distance from the centre of motion--the position of the centre of pressure being at the same time correspondingly affected. In the feathering wheel the position of the centre of pressure of the entering and emerging floats is continually changing from the lower edge of the float--where it is when the float is entering or leaving the water--to the centre of the float, which is its position when the float is wholly immerged; but in the radial wheel the centre of pressure can never rise so high as the centre of the float. 553. _Q._--All this relates to the action of the paddle when the vessel is at rest: will you explain its action when the vessel is in motion? _A._--When the wheel of a coach rolls along the ground, any point of its periphery describes in the air a curve which is termed a cycloid; any point within the periphery traces a prolate or protracted cycloid, and any point exterior to the periphery traces a curtate or contracted cycloid--the prolate cycloid partaking more of the nature of a straight line, and the curtate cycloid more of the nature of a circle. The action of a paddle wheel in the water resembles in this respect that of the wheel of a carriage running along the ground: that point in the radius of the paddle of which the rotative speed is just equal to the velocity of the vessel will describe a cycloid; points nearer the centre, prolate cycloids, and points further from the centre, curtate cycloids. The circle described by the point whose velocity equals the velocity of the ship, is called the _rolling circle_, and the resistance due to the difference of velocity of the rolling circle and centre of pressure is that which operates in the propulsion of the vessel. The resistance upon any part of the float, therefore, will vary as the square of its distance from the rolling circle, supposing the float to be totally immerged; but, taking into account the greater length of time during which the extremity of the paddle acts, whereby the resistance will be made greater, we shall not err far in estimating the resistance upon any point at the third power of its distance from the rolling circle in the case of light immersions, and the 2.5 power in the case of deep immersions. 554. _Q._--How is the position of the centre of pressure to be determined? _A._--With the foregoing assumption, which accords sufficiently with experiment to justify its acceptation, the position of the centre of pressure may be found by the following rule:--from the radius of the wheel substract the radius of the rolling circle; to the remainder add the depth of the paddle board, and divide the fourth power of the sum by four times the depth; from the cube root of the quotient subtract the difference between the radii of the wheel and rolling circle, and the remainder will be the distance of the centre of pressure from the upper edge of the paddle. 555. _Q._--How do you find the diameter of the rolling circle? _A._--The diameter of the rolling circle is very easily found, for we have only to divide 5,280 times the number of miles per hour, by 60 times the number of strokes per minute, to get an expression for the circumference of the rolling circle, or the following rule may be adopted:--divide 88 times the speed of the vessel in statute miles per hour, by 3.1416 times the number of strokes per minute; the quotient will be the diameter in feet of the rolling circle. The diameter of the circle in which the centre of pressure moves or the effective diameter of the wheel being known, and also the diameter of the rolling circle, we at once find the excess of the velocity of the wheel over the vessel. 556. _Q._--Will you illustrate these rules by an example? _A._--A steam vessel of moderately good shape, and with engines of 200 horses power, realises, with 22 strokes per minute, a speed of 10.62 miles per hour. To find the diameter of the rolling circle, we have 88 times 10.62, equal to 934.66, and 22 times 3.1416, equal to 69.1152; then 934.66 divided by 69.1152 is equal to 13.52 feet, which is the diameter of the rolling circle. The diameter of the wheel is 19 ft. 4 in., so that the diameter of the rolling circle is about 2/3ds of the diameter of the wheel, and this is a frequent proportion. The depth of the paddle board is 2 feet, and the difference between the diameters of the wheel and rolling circle will be 5.8133, which will make the difference of their radii 2.9067; and adding to this the depth of the paddle board, we have 4.9067, the fourth power of which is 579.64, which, divided by four times the depth of the paddle board, gives us 72.455, the cube root of which is 4.1689, which, diminished by the difference of the radii of the wheel and rolling circle, leaves 1.2622 feet for the distance of the centre of pressure from the upper edge of the paddle board in the case of light immersions. The radius of the wheel being 9.6667, the distance from the centre of the wheel to the upper edge of the float is 7.6667, and adding to this 1.2622, we get 8.9299 feet as the radius, or 17.8598 feet as the diameter of the circle in which the centre of pressure revolves. With 22 strokes per minute, the velocity of the centre of pressure will be 20.573 feet per second, and with 10.62 miles per hour for the speed of the vessel, the velocity of the rolling circle will be 15.576 feet per second. The effective velocity will be the difference between these quantities, or 4.997 feet per second. Now the height from which a body must fall by gravity, to acquire a velocity of 4.997 feet per second, is about .62 feet; and twice this height, or 1.24 feet, multiplied by 62-1/2, which is the number of Lbs. weight in a cubic foot of water, gives 77-1/2 Lbs. as the pressure on each square foot of the vertical paddle boards. As each board is of 20 square feet of area, and there is a vertical board on each side of the ship, the total pressure on the vertical paddle boards will be 2900 Lbs. 557. _Q._--What pressure is this equivalent to on each square inch of the pistons? _A._--A vessel of 200 horses power will have two cylinders, each 50 inches diameter, and 5 feet stroke, or thereabout. The area of a piston of 50 inches diameter is 1963.5 square inches, so that the area of the two pistons is 3927 square inches, and the piston will move through 10 feet every revolution; and with 22 strokes per minute this will be 220 feet per minute, or 3.66 feet per second. Now, if the effective velocity of the centre of pressure and the velocity of the pistons had been the same, then a pressure of 2900 Lbs. upon the vertical paddles would have been balanced by an equal pressure on the pistons, which would have been in this case about .75 Lbs. per square inch; but as the effective velocity of the centre of pressure is 4.997 feet per second, while that of the pistons is only 3.66 feet per second, the pressure must be increased in the proportion of 4.997 to 3.66 to establish an equilibrium of pressure, or, in other words, it must be 1.02 Lbs. per square inch. It follows from this investigation, that, in radial wheels, the greater part of the engine power is distributed among the oblique floats. 558. _Q._--How comes this to be the case? _A._--To understand how it happens that more power is expended upon the oblique than upon the vertical floats, it is necessary to remember that the only resistance upon the vertical paddle is that due to the difference of velocity of the wheel and the ship; but if the wheel be supposed to be immersed to its axle, so that the entering float strikes the water horizontally, it is clear that the resistance on such float is that due to the whole velocity of rotation; and that the resistance to the entering float will be the same whether the vessel is in motion or not. The resistance opposed to the rotation of any float increases from the position of the vertical float-where the resistance is that due to the difference of velocity of the wheel and vessel--until it reaches the plane of the axis, supposing the wheel to be immersed so far, where the resistance is that due to the whole velocity of rotation; and although in any oblique float the total resistance cannot be considered operative in a horizontal direction, yet the total resistance increases so rapidly on each side of the vertical float, that the portion of it which is operative in the horizontal direction, is in all ordinary cases of immersion very considerable. In the feathering wheel, where there is little of this oblique action, the resistance will be in the proportion of the square of the horizontal velocities of the several floats, which may be represented by the horizontal distances between them; and in the feathering wheel, the vertical float having the greatest horizontal velocity will have the greatest propelling effect. 559. _Q._--Should the floats in feathering wheels enter and leave the water vertically? _A._--The floats should be so governed by the central crank or eccentric, that the entering and emerging floats have a direction intermediate between a radius and a vertical line. 560. _Q._--Can you give any practical rules for proportioning paddle wheels? _A._--A common rule for the pitch of the floats is to allow one float for every foot of diameter of the wheel; but in the case of fast vessels a pitch of 2-1/2 feet, or even less, appears preferable, as a close pitch occasions less vibration. If the floats be put too close, however, the water will not escape freely from between them, and if set too far apart the stroke of the entering paddle will occasion an inconvenient amount of vibratory motion, and there will also be some loss of power. To find the proper area of a single float:--divide the number of actual horses power of both engines by the diameter of the wheel in feet; the quotient is the area of one paddle board in square feet proper for sea going vessels, and the area multiplied by 0.6 will give the length of the float in feet. In very sharp vessels, which offer less resistance in passing through the water, the area of paddle board is usually one-fourth less than the above proportion, and the proper length of the float may in such case be found by multiplying the area by 0.7. In sea going vessels about four floats are usually immersed, and in river steamers only one or two floats. There is more slip in the latter case, but there is also more engine power exerted in the propulsion of the ship, from the greater speed of engine thus rendered possible. 561. _Q._--Then is it beneficial to use small floats? _A._--Quite the contrary. If to permit a greater speed of the engine the floats be diminished in area instead of being raised out of the water, no appreciable accession to the speed of the vessel will be obtained; whereas there will be an increased speed of vessel if the accelerated speed of the engine be caused by diminishing the diameter of the wheels. In vessels intended to be fast, therefore, it is expedient to make the wheels small, so as to enable the engine to work with a high velocity; and it is expedient to make such wheels of the feathering kind, to obviate loss of power from oblique action. In no wheel must the rolling circle fall below the water line, else the entering and emerging floats will carry masses of water before them. The slip is usually equal to about one-fourth of the velocity of the centre of pressure in well proportioned wheels; but it is desirable to have the slip as small as is possible consistently with the observance of other necessary conditions. The speed of the engine and also the speed of the vessel being fixed, the diameter of the rolling circle becomes at once ascertainable, and adding to this the slip, we have the diameter of the wheel. CONFIGURATION AND ACTION OF THE SCREW. 562. _Q._--Will you describe more in detail than you have yet done, the configuration and mode of action of the screw propeller? _A._--The ordinary form of screw propeller is represented in figs. 46 and 47; fig. 46 being a perspective view, and fig. 47 an end view, or view such as is seen when looking upon the end of the shaft. The screw here represented is one with two arms or blades. Some screws have three arms, some four and some six; but the screw with two arms is the most usual, and screws with more than three arms are not now much employed in this country. The screw on being put into revolution by the engine, preserves a spiral path in the water, in which it draws itself forward in the same way as a screw nail does when turned round in a piece of wood, whereas the paddle wheel more resembles the action of a cog wheel working in a rack. [Illustration: Fig. 46. Fig. 47. ORDINARY FORM OF SCREW PROPELLER.] 563. _Q._--But the screw of a steam vessel has no resemblance to a screw nail? _A._--It has in fact a very close resemblance if you suppose only a very short piece of the screw nail to be employed, and if you suppose, moreover, the thread of the screw to be cut nearly into the centre to prevent the wood from stripping. The original screw propellers were made with several convolutions of screw, but it was found advantageous to shorten them, until they are now only made one-sixth of a convolution in length. 564. _Q._--And the pitch you have already explained to be the distance in the line of the shaft from one convolution to the next, supposing the screw to consist of two or more convolutions? _A._--Yes, that is what is meant by the pitch. If a thread be wound upon a cylinder with an equal distance between the convolutions, it will trace a screw of a uniform pitch; and if the thread be wound upon the cylinder with an increasing distance between each convolution, it will trace a screw of an increasing pitch. But two or more threads may be wound upon the cylinder at the same time, instead of a single thread. If two threads be wound upon it they will trace a double-threaded screw; if three threads be wound upon it they will trace a treble-threaded screw; and so of any other number. Now if the thread be supposed to be raised up into a very deep and thin spiral feather, and the cylinder be supposed to become very small, like the newel of a spiral stair, then a screw will be obtained of the kind proper for propelling vessels, except that only a very short piece of such screw must be employed. Whatever be the number of threads wound upon a cylinder, if the cylinder be cut across all the threads will be cut. A slice cut out of the cylinder will therefore contain a piece of each thread. But the threads, in the case of a screw propeller, answer to the arms, so that in every screw propeller the number of threads entering into the composition of the screw will be the same as the number of arms. An ordinary screw with two blades is a short piece of a screw of two threads. 565. _Q._--In what part of the ship is the screw usually placed? [Illustration: Fig. 48] _A._--In that part of the run of the ship called the dead wood, which is a thin and unused part of the vessel just in advance of the rudder. The usual arrangement is shown in fig. 48, which represents the application to a vessel of a species of screw which has the arms bent backwards, to counteract the centrifugal motion given to the water when there is a considerable amount of slip. 566. _Q._--How is the slip in a screw vessel determined? _A._--By comparing the actual speed of the vessel with the speed due to the pitch and number of revolutions of the screw, or, what is the same thing, the speed which the vessel would attain if the screw worked in a solid nut. The difference between the actual speed and this hypothetical speed, is the slip. 567. _Q._--In well formed screw propellers what is the amount of slip found to be? _A._--If the screw be properly proportioned to the resistance that the vessel has to overcome, the slip will not be more than 10 per cent., but in some cases it amounts to 30 per cent., or even more than this. In other cases, however, the slip is nothing at all, and even less than nothing; or, in other words the vessel passes through the water with a greater velocity than if the screw were working in a solid nut. 568. _Q._--Then it must be by the aid of the wind or some other extraneous force? _A._--No; by the action of the screw alone. 569. _Q._--But how is such a result possible? _A._--It appears to be mainly owing to the centrifugal action of the screw, which interposes a film or wedge of water between the screw itself and the water on which the screw reacts. This negative slip, as it is called, chiefly occurs when the pitch of the screw is less than its diameter, and when, consequently, the velocity of rotation is greater than if a coarser pitch had been employed. There is, moreover, in all vessels passing through the water with any considerable velocity, a current of water following the vessel, in which current, in the case of a screw vessel, the screw will revolve; and in certain cases the phenomenon of negative slip may be imputable in part to the existence of this current. 570. _Q._--Is the screw propeller as effectual an instrument of propulsion as the radial or feathering paddle? _A._--In all cases of deep immersion it appears to be quite as effectual as the radial paddle, indeed, more so; but it is scarcely as effectual as the feathering paddle, with any amount of immersion, and scarcely as effectual as the common paddle in the case of light immersions. COMPARATIVE ADVANTAGES OF PADDLE AND SCREW VESSELS. 571. _Q._--Whether do you consider paddle or screw vessels to be on the whole the most advantageous? _A._--That is a large question, and can only receive a qualified answer. In some cases the use of paddles is indispensable, as, for example, in the case of river vessels of a limited draught of water, where it would not be possible to get sufficient depth below the water surface to enable a screw of a proper diameter to be got in. 572. _Q._--But how does the matter stand in the case of ocean vessels? _A._--In the case of ocean vessels, it is found that paddle vessels fitted with the ordinary radial wheels, and screw vessels fitted with the ordinary screw, are about equally efficient in calms and in fair or beam winds with light and medium immersions. If the vessels are loaded deeply, however, as vessels starting on a long voyage and carrying much coal must almost necessarily be, then the screw has an advantage, since the screw acts in its best manner when deeply immersed, and the paddles in their worst. When a screw and paddle vessel, however, of the same model and power are set to encounter head winds, the paddle vessel it is found has in all cases an advantage, not in speed, but in economy of fuel. For whereas in a paddle vessel, when her progress is resisted, the speed of the engine diminishes nearly in the proportion of the diminished speed of ship, it happens that in a screw vessel this is not so,--at least to an equal extent,--but the engines work with nearly the same rate of speed as if no increase of resistance had been encountered by the ship. It follows from this circumstance, that whereas in paddle vessels the consumption of steam, and therefore of fuel, per hour is materially diminished when head winds occur, in screw vessels a similar diminution in the consumption of steam and fuel does not take place. 573. _Q._--But perhaps under such circumstances the speed of the screw vessel will be the greater of the two? _A._--No; the speed of the two vessels will be the same, unless the strength of the head wind be so great as to bring the vessels nearly to a state of rest, and on that supposition the screw vessel will have the advantage. Such cases occur very rarely in practice; and in the case of the ordinary resistances imposed by head winds, the speed of the screw and paddle vessel will be the same, but the screw vessel will consume most coals. 574. _Q._--What is the cause of this peculiarity? _A._--The cause is, that when the screw is so proportioned in its length as to be most suitable for propelling vessels in calms, it is too short to be suitable for propelling vessels which encounter a very heavy resistance. It follows, therefore, that if it is prevented from pursuing its spiral course in the water, it will displace the water to a certain extent laterally, in the manner it does if the engine be set on when the vessel is at anchor; and a part of the engine power is thus wasted in producing a useless disturbance of the water, which in paddle vessels is not expended at all. 575. _Q._--If a screw and paddle vessel of the same mould and power be tied stern to stern, will not the screw vessel preponderate and tow the paddle vessel astern against the whole force of her engines? _A._--Yes, that will be so. 576. _Q._--And seeing that the vessels are of the same mould and power, so that neither can derive an advantage from a variation in that condition, does not the preponderance of the screw vessel show that the screw must be the most powerful propeller? _A._---No, it does not. 577. _Q._--Seeing that the vessels are the same in all respects except as regards the propellers, and that one of them exhibits a superiority, does not this circumstance show that one propeller must be more powerful than the other? _A._--That does not follow necessarily, nor is it the fact in this particular case. All steam vessels when set into motion, will force themselves forward with an amount of thrust which, setting aside the loss from friction and from other causes, will just balance the pressure on the pistons. In a paddle vessel, as has already been explained, it is easy to tell the tractive force exerted at the centre of pressure of the paddle wheels, when the pressure urging the pistons, the dimensions of the wheels and the speed of the vessel are known; and that force, whatever be its amount, must always continue the same with any constant pressure on the pistons. In a screw vessel the same law applies, so that with any given pressure on the pistons and discarding the consideration of friction, it will follow that whatever be the thrust exerted by a paddle or a screw vessel, it must remain uniform whether the vessel is in motion or at rest, and whether moving at a high or a low velocity through the water. Now to achieve an equal speed during calms in two vessels of the same model, there must be the same amount of propelling thrust in each; and this thrust, whatever be its amount, cannot afterward vary if a uniform pressure of steam be maintained. The thrusts, therefore, caused by their respective propelling instruments, when a screw and paddle vessel are tied stern to stern, must be the same as at other times; and as at other times those thrusts are equal, so must they be when the vessels are set in the antagonism supposed. 578. _Q._--How comes it then that the screw vessel preponderates? _A._--Not by virtue of a larger thrust exerted by the screw in pressing forward the shaft and with it the vessel, but by the gravitation against the stern of the wave of water which the screw raises by its rapid rotation. This wave will only be raised very high when the progress of the vessel through the water is nearly arrested, at which time the centrifugal action of the screw is very great; and the vessel under such circumstances is forced forward partly by the thrust of the screw, and partly by the hydrostatic pressure of the protuberance of water which the centrifugal action of the screw raises up at the stern. 579. _Q._--Can you state any facts in corroboration of this view? _A._--The screw vessel will not preponderate if a screw and paddle vessel be tied bow to bow and the engines of each be then reversed. In, some screw vessels the amount of thrust actually exerted by the screw under all its varying circumstances, has been ascertained by the application of a dynamometer to the end of the shaft. By this instrument--which is formed by a combination of levers like a weighing machine for carts--a thrust or pressure of several tons can be measured by the application of a small weight; and it has been found, by repeated experiment with the dynamometer, that the thrust of the screw in a screw vessel when towing a paddle vessel against the whole force of her engines, is just the same as it is when the two vessels are maintaining an equal speed in calms. The preponderance of the screw vessel must, therefore, be imputable to some other agency than to a superior thrust of the screw, which is found by experiment not to exist. 580. _Q._--Has the dynamometer been applied to paddle vessels? _A._--It has not been applied to the vessels themselves, as in the case of screw vessels, but it has been employed on shore to ascertain the amount of tractive force that a paddle vessel can exert on a rope. 581. _Q._--Have any experiments been made to determine the comparative performances of screw and paddle vessels at sea? _A._--Yes, numerous experiments; of which the best known are probably those made on the screw steamer Rattler and the paddle steamer Alecto, each vessel of the same model, size, and power,--each vessel being of about 800 tons burden and 200 horses power. Subsequently another set of experiments with the same object was made with the Niger screw steamer and the Basilisk paddle steamer, both vessels being of about 1000 tons burden and 400 horses power. The general results which were obtained in the course of these experiments are those which have been already recited. 582. _Q._--Will you recapitulate some of the main incidents of these trials? _A._--I may first state some of the chief dimensions of the vessels. The Rattler is 176 feet 6 inches long, 32 feet 8-1/2 inches broad, 888 tons burden, 200 horses power, and has an area of immersed midship section of 380 square feet at a draught of water of 11 feet 5-1/2 inches. The Alecto is of the same dimensions in every respect, except that she is only of 800 tons burden, the difference in this particular being wholly owing to the Rattler having been drawn out about 15 feet at the stern, to leave abundant room for the application of the screw. The Rattler was fitted with a dynamometer, which enabled the actual propelling thrust of the screw shaft to be measured; and the amount of this thrust, multiplied by the distance through which the vessel passed in a given time, would determine the amount of power actually utilized in propelling the ship. Both vessels were fitted with indicators applied to the cylinders, so as to determine the amount of power exerted by the engines. 583. _Q._--How many trials of the vessels were made on this occasion? _A._--Twelve trials in all; but I need not refer to those in which similar or identical results were only repeated. The first trial was made under steam only, the weather was calm and the water smooth. At 54 minutes past 4 in the morning both vessels left the Nore, and at 30-1/2 minutes past 2 the Rattler stopped her engines in Yarmouth Roads, where in 20-1/2 minutes afterward she was joined by the Alecto. The mean speed achieved by the Rattler during this trial was 9.2 knots per hour; the mean speed of the Alecto was 8.8 knots per hour. The slip of the screw was 10.2 per cent. The actual power exerted by the engines, as shown by the indicator, was in the case of the Rattler 334.6 horses, and in the case of the Alecto 281.2 horses; being a difference of 53.4 horses in favor of the Rattler. The forward thrust upon the screw shaft was 3 tons, 17 cwt., 3 qrs., and 14 lbs. The horse power of the shaft--or power actually utilized--ascertained by multiplying the thrust in pounds by the space passed through by the vessel in feet per minute, and dividing by 33,000, was 247.8 horses power. This makes the ratio of the shaft to the engine power as 1 to 1.3, or, in other words, it shows that the amount of engine power utilized in propulsion was 77 per cent. In a subsequent trial made with the vessels running before the wind, but with no sails set and the masts struck, the speed realized by the Rattler was 10 knots per hour. The slip of the screw was 11.2 per cent. The actual power exerted by the engines of the Rattler was 368.8 horses. The actual power exerted by the engines of the Alecto was 291.7 horses. The thrust of the shaft was equal to a weight of 4 tons, 4 cwt., 1 qr., 1 lb. The horse power of the shaft was 290.2 horses, and the ratio of the shaft to the engine power was 1 to 1.2. Here, therefore, the amount of the engine power utilized was 84 per cent. 584. _Q._--If in any screw vessel the power of the engine be diminished by shutting off the steam or otherwise, you will then have a larger screw relatively with the power of the engine than before? _A._--Yes. 585. _Q._--Was any experiment made to ascertain the effect of this modification? _A._--There was; but the result was not found to be better than before. The experiment was made by shutting off the steam from the engines of the Rattler until the number of strokes was reduced to 17 in the minute. The actual power was then 126.7 horses; thrust upon the shaft 2 tons, 2 cwt., 3 qrs., 14 lbs; horse power of shaft 88.4 horses; ratio of shaft to engine power 1 to 1.4; slip of the screw 18.7 per cent. In this experiment the power utilized was 71 per cent. 586. _Q._--Was any experiment made to determine the relative performances in head winds? _A._--The trial in which this relation was best determined lasted for seven hours, and was made against a strong head wind and heavy head sea. The speed of the Rattler by patent log was 4.2 knots; and at the conclusion of the trial the Alecto had the advantage by about half a mile. Owing to an accidental injury to the indicator, the power exerted by the engines of the Rattler in this trial could not be ascertained; but judging from the power exerted in other experiments with the same number of revolutions, it appears probable that the power actually exerted by the Rattler was about 300 horses. The number of strokes per minute made by the engines of the Rattler was 22, whereas in the Alecto the number of strokes per minute was only 12; so that while the engines of the Alecto were reduced, by the resistance occasioned by a strong head wind, to nearly half their usual speed, the engines of the Rattler were only lessened about one twelfth of their usual speed. The mean thrust upon the screw shaft during this experiment, was 4 tons, 7 cwt., 0 qr., 16 lbs. The horse power of the shaft was 125.9 horses, and the slip of the screw was 56 per cent. Taking the power actually exerted by the Rattler at 300 horses, the power utilized in this experiment is only 42 per cent. 587. _Q._--What are the dimensions of the screw in the Rattler? _A._--Diameter 10 feet, length 1 foot 3 inches, pitch 11 feet. The foregoing experiments show that with a larger screw a better average performance would be obtained. The best result arrived at, was when the vessel was somewhat assisted by the wind, which is equivalent to a reduction of the resistance of the hull, or to a smaller hull, which is only another expression for a larger proportionate screw. 588. _Q._--When you speak of a larger screw, what increase of dimension do you mean to express? _A._--An increase of the diameter. The amount of reacting power of the screw upon the water is hot measured by the number of square feet of surface of the arms, but by the area of the disc or circle in which the screw revolves. The diameter of the screw of the Rattler being 10 feet, the area of its disc is 78.5 square feet; and with the amount of thrust already mentioned as existing in the first experiment, viz. 8722 lbs., the reacting pressure on each square foot of the screw's disc will be 108-1/2 lbs. The immersed midship section being 380 square feet, this is equivalent to 23 lbs. per square foot of immersed midship section at a speed of 9.2 knots per hour. 589. _Q._--In smaller vessels of similar form, will the resistance per square foot of midship section be more than this? _A._--It will be considerably more. In the Pelican, a vessel of 109-3/4 square feet of midship section, I estimate the resistance per square foot of midship section at 30 lbs., when the speed of the vessel is 9.7 knots per hour. In the Minx with an immersed midship section of 82 square feet, the resistance per square foot of immersed midship section was found by the dynamometer to be 41 lbs. at a speed of 8-1/2 knots; and in the Dwarf, a vessel with 60 square feet of midship section, I estimate the resistance per square foot of midship section at 46 lbs. at a speed of 9 knots per hour, which is just double the resistance per square foot of the Rattler. The diameter of the screw of the Minx is 4-1/2 feet, so that the area of its disc is 15.9 square feet, and the area of immersed midship section is about 5 times greater than that of the screw's disc. The diameter of the screw of the Dwarf is 5 feet 8 inches, so that the area of its disc is 25.22 square feet, and the area of immersed midship section is 2.4 times greater than that of the screw's disc. The pressure per square foot of the screw's disc is 214 lbs. in the case of the Minx, and 109-1/2 lbs. in the case of the Dwarf. 590. _Q._--From the greater proportionate resistance of small vessels, will not they require larger proportionate screws than large vessels? _A._--They will. 591. _Q._--Is there any ready means of predicting what the amount of thrust of a screw will be? _A._--When we know the amount of pressure on the pistons, and the velocity of their motion relatively with the velocity of advance made by the screw, supposing it to work in a solid nut, it is easy to tell what the thrust of the screw would be if it were cleared of the effects of friction and other irregular sources of disturbance. The thrust, in fact, would be at once found by the principle of virtual velocities; and if we take this theoretical thrust and diminish it by one fourth to compensate for friction and lateral slip, we shall have a near approximation to the amount of thrust that will be actually exerted.[1] [1] See Treatise on the Screw Propeller, by J. Bourne, C. E. COMPARATIVE ADVANTAGES OF DIFFERENT SCREWS. 592. _Q._--What species of screw do you consider the best? _A._--In cases in which a large diameter of screw can be employed, the ordinary screw or helix with two blades seems to be as effective as any other, and it is the most easily constructed. If, however, the screw is restricted in diameter, or if the vessel is required to tow, or will have to encounter habitually strong head winds, it will be preferable to employ a screw with an increasing pitch, and also of such other configuration that it will recover from the water some portion of the power that has been expended in slip. 593. _Q._--How can this be done? _A._--There are screws which are intended to accomplish, this object already in actual use. When there is much slip a centrifugal velocity is given to the water, and the screw, indeed, if the engine be set on when the vessel is at rest, acts very much as a centrifugal fan would do if placed in the same situation. The water projected outward by the centrifugal force escapes in the line of least resistance, which is to the surface; and if there be a high column of water over the screw, or, in other words, if the screw is deeply immersed, then the centrifugal action is resisted to a greater extent, and there will be less slip produced. The easiest expedient, therefore, for obviating loss by slip is to sink the screw deeply in the water; but as there are obvious limits to the application of this remedy, the next best device is to recover and render available for propulsion some part of the power which has been expended in giving motion to the water. One device for doing this consists in placing the screw well forward in the dead wood, so that it shall be overhung by the stern of the ship. The water forced upward by the centrifugal action of the screw will, by impinging on the overhanging stern, press the vessel forward in the water, just in the same way as is done by the wind when acting on an oblique sail. I believe, the two revolving vanes without any twist or obliquity on them at all, would propel a vessel if set well forward in the dead wood or beneath the bottom, merely by the ascent of the water up the inclined plane of the vessel's run; and, at all events, a screw so placed would, in my judgment, aid materially in propelling the vessel when her progress was resisted by head winds. 594. _Q._--But you said there are some kinds of screws which profess to accomplish this? [Illustration: Fig. 49. THE EARL OF DUNDONALD'S PROPELLER.] _A._--There are screws which profess to counteract the centrifugal velocity given to the water by imparting to it an equal centripetal force, the consequence of which will be, that the water projected backward by the screw, instead of taking the form of the frustum of a cone, with its small end next the screw, will take the form of a cylinder. One of these forms of screw is that patented by the Earl of Dundonald in 1843, and which is represented in fig. 49. Another is the form of screw already represented in fig. 48, and which was patented by Mr. Hodgson in 1844. Mr. Hodgson bends the arms of his propellers backward, not into the form of a triangle, but into the form of a parabola, to the end that the impact of the screw on the particles of the water may cause them to converge to a focus, as the rays of light would do in a parabolic reflector. But this particular configuration is not important, seeing that the same convergence which is given to the particles of the water, with a screw of uniform pitch bent back into the form of a parabola, will be given with a screw bent back into the form of a triangle, if the pitch be suitably varied between the centre and the circumference. 595. _Q._--Then the pitch may be varied in two ways? _A._--Yes: a screw may have a pitch increasing in the direction of the length, as would happen in the case of a spiral stair, if every successive step in the ascent was thicker than the one below it; or it may increase from the centre to the circumference, as would happen in the case of a spiral stair, if every step were thinner at the centre of the lower than at its outer wall. When the pitch of a screw increases in the direction of its length, the leading edge of the screw enters the water without shock or impact, as the advance of the leading edge per revolution will not be greater than the advance of the vessel. When the pitch of a screw increases in the direction of its diameter, the central part of the screw will advance with only the same velocity as the water, so that it cannot communicate any centrifugal velocity to the water; and the whole slip, as well as the whole propelling pressure, will occur at the outer part of the screw blades. 596. _Q._--Is there any advantage derived from these forms of screws? _A._--There is a slight advantage, but it is so slight as hardly to balance the increased trouble of manufacture, and, consequently, they are not generally or widely adopted. 597. _Q._--What other kinds of screw are there proposing to themselves the same or similar objects? _A._--There is the corrugated screw, the arms of which are corrugated, so as it were to gear with the water during its revolution, and thereby prevent it from acquiring a centrifugal velocity. Then there is Griffith's screw, which has a large ball at its centre, which, by the suction it creates at its hinder part, in passing through the water, produces a converging force, which partly counteracts the divergent action of the arms. Finally, there is Holm's screw, which has now been applied to a good number of vessels with success. 598. _Q._--Will you describe the configuration and action of Holm's screw? _A._--First, then, the screw increases in the direction of its length, and this increase is very rapid at the following edge, so that, in fact, the following edge stands in the plane of the shaft, or in the vertical longitudinal plane of the vessel. Then the ends of the arms are bent over into a curved flange, the edge of which points astern, and the point where this curved flange joins the following edge of the screw is formed, not into an angle, but into a portion of a sphere, so that this corner resembles the bowl of a spoon. When the screw is put into revolution, the water is encountered by the leading edge of the screw without shock, as its advance is only equal to the advance of the vessel, and before the screw leaves the water it is projected directly astern. At the same time, the curved flange at the rim of the screw prevents the dispersion of the water in a radial direction, and it consequently assumes the form of a column or cylinder of water, projected backward from the ship. 599. _Q._--What is the nature of Beattle's screw? _A._--Beattie's screw is an arrangement of the screw propeller whereby it is projected beyond the rudder, and the main object of the arrangement is to take away the vibratory motion at the stern,--an intention which it accomplishes in practice. There is an oval eye in the rudder, to permit the screw shaft to pass through it. 600. _Q._--When the diameter of the cylinder of water projected backward by a screw, and the force urging it into motion are known, may not the velocity it will acquire be approximately determined? _A._--That will not be very difficult; and I will take for illustration the case of the Minx, already referred to, which will show how such a computation is to be conducted. The speed of this vessel, in one of the experiments made with her, was 8.445 knots; the number of revolutions of the screw per minute, 231.32; and the pressure on each square foot of area of the screw's disc, 214 lbs. If a knot be taken to be 6075.6 feet, then the distance advanced by the vessel, when the speed is 8.445 knots, will be 3.7 feet per revolution, and this advance will be made in about .26 of a second of time. Now the distance which a body will fall by gravity, in .26 of a second, is 1.087 feet; and a weight of 214 lbs. put into motion by gravity, or by a pressure of 214 lbs., would, therefore, acquire a velocity of 1.087 feet during the time one revolution of the screw is being performed. The weight to be moved, however, is 3.7 cubic feet of water, that being the new water seized by the screw each revolution for every square foot of surface in the screw's disc; and 3.7 cubic feet of water weigh 231.5 lbs., so that the urging force of 214 lbs. is somewhat less than the force of gravity, and the velocity of motion communicated to the water will be somewhat under 1.087 feet per revolution, or we may say it will be in round numbers 1 foot per revolution. This, added to the progress of the vessel, will make the distance advanced by the screw through the water 4.7 feet per revolution, leaving the difference between this and the pitch, namely 1.13 feet, to be accounted for on the supposition that the screw blades had broken laterally through the water to that extent. It would be proper to apply some correction to this computation, which would represent the increased resistance due to the immersion of the screw in the water; for a column of water cannot be moved in the direction of its axis beneath the surface, without giving motion to the superincumbent water, and the inertia of this superincumbent water must, therefore, be taken into the account. In the experiment upon the Minx, the depth of this superincumbent column was but small. The total amount of the slip was 36.53 per cent.; and there will not be much error in setting down about one half of this as due to the recession of the water in the direction of the vessel's track, and the other half as due to the lateral penetration of the screw blades. 601. _Q._--Is it not important to make the stern of screw vessels very fine, with the view of diminishing the slip, and increasing the speed? _A._--It is most important. The Rifleman, a vessel of 486 tons, had originally engines of 200 horses power, which propelled her at a speed of 8 knots an hour. The Teazer, a vessel of 296 tons, had originally engines of 100 horses power, which propelled her at a speed of 6-1/2 knots an hour. The engines of the Teazer were subsequently transferred to the Rifleman, and new engines of 40 horse power were put into the Teazer. Both vessels were simultaneously sharpened at the stern, and the result was, that the 100 horse engines drove the Rifleman, when sharpened, as fast as she had previously been driven by the 200 horse engines; and the 40 horse engines drove the Teazer, when sharpened, a knot an hour faster than she had previously been driven by the 100 horse engines. The immersion of both vessels was kept unchanged in each case; and the 100 horse engines of the Teazer, when transferred to the Rifleman, drove that vessel, after she had been sharpened, 2 knots an hour faster than they had previously driven a vessel not much more than half the size. These are important facts for every one to be acquainted with who is interested in the success of screw vessels, and who seeks to obtain the maximum of efficiency with the minimum of expense.[1] [1] See Treatise on the Screw Propeller, by John Bourne, C. E. PROPORTIONS OF SCREWS. 602. _Q._--In fixing upon the proportions of a screw proper to propel any given vessel, how would you proceed? _A._--I would first compute the probable resistance of the vessel, and I would be able to find the relative resistances of the screw and hull, and in every case it is advisable to make the screw as large in diameter as possible. The larger the screw is, the greater will be the efficiency of the engine in propelling the vessel; the larger will be the ratio of the pitch to the diameter, which produces a maximum effect; and the smaller will be the length of the screw or the fraction of a convolution to produce a maximum effect. 603. _Q._--Will you illustrate this doctrine by a practical example? _A._--The French screw steamer Pelican was fitted successively with two screws of four blades, but the diameter of the first screw was 98.42 inches, and the diameter of the second 54 inches. If the efficiency of the first screw by represented by 1, that of the second screw will be represented by .823, or, in other words, if the first screw would give a speed of 10 knots, the second would give little more than 8. The most advantageous ratio of pitch to diameter was found to be 2.2 in the case of the large screw, and 1.384 in the case of the small. The fraction of a convolution which was found to be most advantageous was .281 in the case of the large screw, and .450 in the case of the small screw. 604. _Q_--Were screws of four blades found to be more efficient than screws with two? _A_--They were found to have less slip, but not to be more efficient, the increased slip in those of two blades being balanced by the increased friction in those of four. Screws of two blades, to secure a maximum efficiency, must have a finer pitch than screws of four. 605. _Q._--Are the proportions found to be most suitable in the case of the Pelican applicable to the screws of other vessels? _A._--Only to those which have the same relative resistance of screw and hull. Taking the relative resistance to be the area of immersed midship section, divided by the square of the screw's diameter, it will in the case of the Rattler be 380/100 or 3.8. From the experiments made by MM. Bourgois and Moll on the screw steamer Pelican, they have deduced the proportions of screws proper for all other classes of vessels, whether the screws are of two, four, or six blades. 606. _Q._--Will you specify the nature of their deductions? _A._--I will first enumerate those which bear upon screws with two blades. When the relative resistance is 5.5 the ratio of pitch to diameter should be 1.006, and the fraction of the pitch or proportion of one entire convolution should be 0.454. When the relative resistance is 5, the ratio of pitch to diameter should be 1.069, and fraction of pitch 0.428; relative resistance 4.5, pitch 1.135, fraction 0.402; relative resistance 4, pitch 1.205, fraction 0.378; relative resistance 3.5, pitch 1.279, fraction 0.355; relative resistance 3, pitch 1.357, fraction 0.334; relative resistance 2.5, pitch 1.450, fraction 0.313; relative resistance 2, pitch 1.560, fraction 0.294; relative resistance 1.5, pitch 1.682, fraction 0.275. The relative resistance of 4 is that which is usual in an auxiliary line of battle ship, 3.5 in an auxiliary frigate, 3 in a high speed line of battle ship, 2.5 in a high speed frigate, 2 in a high speed corvette, and 1.5 in a high speed despatch boat. 607. _Q._--What are the corresponding proportions of screws of four blades? _A._--The ratios of the pitches to the diameter being for each of the relative resistances enumerated above, 1.342, 1.425, 1.513, 1.607, 1.705, 1.810, 1.933, 2.080, and 2.243, the respective fractions of pitch or fractions of a whole convolution will be 0.455, 0.428, 0.402, 0.378, 0.355, 0.334, 0.313, 0.294, and 0.275. 608. _Q._--And what are the corresponding proportions proper for screws of six blades? _A._--Beginning with the relative resistance of 5.5 as before, the proper ratio of pitch to diameter for that and each of the successive resistances in the case of screws with six blades, will be 1.677, 1.771, 1.891, 1.2009, 2.131, 2.262, 2.416, 2.600, 2.804; and the respective fractions of pitch will be 0.794, 0.749, 0.703, 0.661, 0.621, 0.585, 0.548, 0.515, and 0.481. These are the proportions which will give a maximum performance in every case.[1] [1] In my Treatise on the Screw Propeller I have gone into these various questions more fully than would consort with the limits of this publication. SCREW VESSELS WITH FULL AND AUXILIARY POWER. 609. _Q._--Do you consider that the screw propeller is best adapted for vessels of full power, or for vessels with auxiliary power? _A._--It is, in my opinion, best adapted for vessels with auxiliary power, and it is a worse propeller than paddle wheels for vessels which have habitually to encounter strong head winds. Screw vessels are but ill calculated--at least as constructed heretofore--to encounter head winds, and the legitimate sphere of the screw is in propelling vessels with auxiliary power. 610. _Q._--Does the screw act well in conjunction with sails? _A._--I cannot say it acts better than paddles, except in so far as it is less in the way and is less affected by the listing or heeling over of the ship. A small steam power, however, acts very advantageously in aid of sails, for not only does the operation of the sails in reducing the resistance of the hull virtually increase the screw's diameter, but the screw, by reducing the resistance which has to be overcome by the sails and by increasing the speed of the vessel, enables the sails to act with greater efficiency, as the wind will not rebound from them with as great a velocity as it would otherwise do, and a larger proportion of the power of the wind will also be used up. In the case of beam winds, moreover, the action of the screw, by the larger advance it gives to the vessel will enable the sails to intercept a larger column of wind in a given time. It appears, therefore, that the sails add to the efficiency of the screw, and that the screw also adds to the efficiency of the sails. 611. _Q._--What is the comparative cost of transporting merchandise in paddle steamers of full power, in screw steamers of auxiliary power, and in sailing ships? _A._--That will depend very much upon the locality where the comparison is made. In the case of vessels performing distant ocean voyages, in which they may reckon upon the aid of uniform and constant winds, such as the trade winds or the monsoon, sailing ships of large size will be able to carry more cheaply than any other species of vessel. But where the winds are irregular and there is not much sea room, or for such circumstances as exist in the Channel or Mediterranean trades, screw vessels with auxiliary power will constitute the cheapest instrument of conveyance. 612. _Q._--Are there any facts recorded illustrative of the accuracy of this conclusion? _A._--A full paddle vessel of 1000 tons burden and 350 horses power, will carry about 400 tons of cargo, besides coal for a voyage of 500 miles, and the expense of such a voyage, including wear and tear, depreciation, &c., will be about 190_l_. The duration of the voyage will be about 45-1/2 hours. A screw vessel of 400 tons burden and 100 horses power, will carry the same amount of cargo, besides her coals, on the same voyage, and the expense of the voyage, including wear and tear, depreciation, &c., will be not much more than 60_l_. An auxiliary screw vessel, therefore, can carry merchandise at one third of the cost of a full-powered paddle vessel. By similar comparisons made between the expense of conveying merchandise in auxiliary screw steamers and sailing ships on coasting voyages, it appears that the cost in screw steamers is about one third less than in the sailing ships; the greater expedition of the screw steamers much more than compensating for the expense which the maintenance of the machinery involves. SCREW AND PADDLES COMBINED. 613. _Q._--Would not a screw combined with paddles act in a similarly advantageous way as a screw or paddles when aided by the wind? _A._--If in any given paddle vessel a supplementary screw be added to increase her power and speed, the screw will act in a more beneficial manner than if it had the whole vessel to propel itself, and for a like reason the paddles will act in a more beneficial manner. There will be less slip both upon the paddles and upon the screw than if either had been employed alone; but the same object would be attained by giving the vessel larger paddles or a larger screw. 614. _Q._--Have any vessels been constructed with combined screw and paddles? _A._--Not any that I know of, except the great vessel built under the direction of Mr. Brunel. The Bee many years since was fitted with both screw and paddles, but this was for the purpose of ascertaining the relative efficiency of the two modes of propulsion, and not for the purpose of using both together. 615. _Q._--What would be the best means of accelerating the speed of a paddle vessel by the introduction of a supplementary screw? _A._--If the vessel requires new boilers, the best course of procedure would be to work a single engine giving motion to the screw with high pressure steam, and to let the waste steam from the high pressure engine work the paddle engines. In this way the power might be doubled without any increased expenditure of fuel per hour, and there would be a diminished expenditure per voyage in the proportion of the increased speed. 616. _Q._--What would the increased speed be by doubling the power? _A._--The increase would be in the proportion of the cube root of 1 to the cube root of 2, or it would be 1.25 times greater. If, therefore, the existing speed were 10 miles, it would be increased to 12-1/2 miles by doubling the power, and the vessel would ply with about a fourth less coals by increasing the power in the manner suggested. 617. _Q._--Is not high pressure steam dangerous in steam vessels? _A._--Not necessarily so, and it has now been introduced into a good number of steam vessels with satisfactory results. In the case of locomotive engines, where it is used so widely, very few accidents have occurred; and in steam vessels the only additional source of danger is the salting of the boiler. This may be prevented either by the use of fresh water in the boiler, or by practising a larger amount of blowing off, to insure which it should be impossible to diminish the amount of water sent into the boiler by the feed pump, and the excess should be discharged overboard through a valve near the water level of the boiler, which valve is governed by a float that will rise or fall with the fluctuating level of the water. If the float be a copper ball, a little water should be introduced into it before it is soldered or brazed up, which will insure an equality of pressure within and without the ball, and a leakage of water into it will then be less likely to take place. A stone float, however, is cheaper, and if properly balanced will be equally effective. All steam vessels should have a large excess of boiling feed water constantly flowing into the boiler, and a large quantity of water constantly blowing off through the surface valves, which being governed by floats will open and let the superfluous water escape whenever the water level rises too high. In this way the boiler will be kept from salting, and priming will be much less likely to occur. The great problem of steam navigation is the economy of fuel, since the quantity of fuel consumed by a vessel will very much determine whether she is profitable or otherwise. Notwithstanding the momentous nature of this condition, however, the consumption of fuel in steam vessels is a point to which very little attention has been paid, and no efficient means have yet been adopted in steam vessels to insure that measure of economy which is known to be attainable, and which has been attained already in other departments of engineering in which the benefits of such economy are of less weighty import. It needs nothing more than the establishment of an efficient system of registration in steam vessels, to insure a large and rapid economy in the consumption of fuel, as this quality would then become the test of an engineer's proficiency, and would determine the measure of his fame. In the case of the Cornish engines, a saving of more than half the fuel was speedily effected by the introduction of the simple expedient of registration. In agricultural engines a like economy has speedily followed from a like arrangement; yet in both of these cases the benefits of a large saving are less eminent than they would be in the case of steam navigation; and it is to be hoped that this expedient of improvement will now be speedily adopted. CHAPTER X. EXAMPLES OF ENGINES. * * * * * OSCILLATING PADDLE ENGINES. 618. _Q._--Will you describe the structure of an oscillating engine as made by Messrs. Penn? _A._--To do this it will be expedient to take an engine of a given power, and then the sizes may be given as well as an account of the configuration of the parts: we may take for an example a pair of engines of 21-1/2 inches diameter of cylinder, and 22 inches stroke, rated by Messrs. Penn at 12 horses power each. The cylinders of this oscillating engine are placed beneath the cranks, and, as in all Messrs. Penn's smaller engines, the piston rod is connected to the crank pin by means of a brass cap, provided with a socket, by means of which it is cuttered to the piston rod. There is but one air pump, which is situated within the condenser between the cylinders, and it is wrought by means of a crank in the intermediate shaft--this crank being cut out of a solid piece of metal as in the formation of the cranked axles of locomotive engines. The steam enters the cylinder through the outer trunnions, or the trunnions adjacent to the ship's sides, and enters the condenser through the two midship trunnions--a short three ported valve being placed on the front of the cylinder to regulate the flow of steam to and from the cylinder in the proper manner. The weight of this valve on one side of the cylinder is balanced by a weight hung upon the other side of the cylinder; but in the most recent engines this weight is discarded, and two valves are used, which balance one another. The framing consists of an upper and lower frame of cast iron, bound together by eight malleable iron columns: upon the lower frame the pillow blocks rest which carry the cylinder trunnions, and the condenser and the bottom frame are cast in the same piece. The upper frame supports the paddle shaft pillow blocks; and pieces are bolted on in continuation of the upper frame to carry the paddle wheels, which are overhung from the journal. 619. _Q._--What are the dimensions and arrangement of the framing? _A._--The web, or base plate of the lower frame is 3/4 of an Inch thick, and a cooming is earned all round the cylinder, leaving an opening of sufficient size to permit the necessary oscillation. The cross section of the upper frame is that of a hollow beam 6 inches deep, and about 3-1/2 inches wide, with holes at the sides to take out the core; and the thickness of the metal is 13/16ths of an inch. Both the upper and the lower frame is cast in a single piece, with the exception of the continuations of the upper frame, which support the paddle wheels. An oval ring 3 inches wide is formed in the upper frame, of sufficient size to permit the working of the air pump crank; and from this ring feathers run to the ends of the cross portions of the frame which supports the intermediate shaft journals. The columns are 1-1/2 inches in diameter; they are provided with collars at the lower ends, which rest upon bosses in the lower frame, and with collars at the upper ends for supporting the upper frame; but the upper collars of two of the corner columns are screwed on, so as to enable the columns to be drawn up when it is required to get the cylinders out. The cross section of the bottom frame is also of the form of a hollow beam, 7 inches deep, except in the region of the condenser, where it is, of course, of a different form. The depth of the boss for the reception of the columns is a little more than 7 inches deep on the lower frame, and a little more than 6 inches deep on the upper frame; and the holes through them are so cored out, that the columns only bear at the upper and lower edges of the hole, instead of all through it--a formation by which the fitting of the columns is facilitated. 620. _Q._--What are the dimensions of the condenser? _A._--The condenser, which is cast upon the lower frame, consists of an oval vessel 22-1/2 inches wide, by 2 feet 4-1/4 inches long, and 1 foot 10-1/2 inches deep; it stands 9 inches above the upper face of the bottom frame, the rest projecting beneath it; and it is enlarged at the sides by being carried beneath the trunnions. 621. _Q._--What are the dimensions of the air pump? _A._--The air pump, which is set in the centre of the condenser, is 15-1/4 inches in diameter, and has a stroke of 11 inches. The foot valve is situated in the bottom of the air pump, and its seat consists of a disc of brass, in which there is a rectangular flap valve, opening upwards, but rounded on one side to the circle of the pump, and so balanced as to enable the valve to open with facility. The balance weight, which is formed of brass cast in the same piece as the valve itself, operates as a stop, by coming into contact with the disc which constitutes the bottom of the pump; the disc being recessed opposite to the stop to enable the valve to open sufficiently. This disc is bolted to the barrel of the pump by means of an internal flange, and before it can be removed the pump must be lifted out of its place. The air pump barrel is of brass to which is bolted a cast iron mouth piece, with a port for carrying the water to the hot well; within the hot well the delivery valve, which consists of a common flap valve, is situated. The mouth piece and the air pump barrel are made tight to the condenser, and to one another, by means of metallic joints carefully scraped to a true surface, so that a little white or red lead interposed makes an air tight joint. The air pump bucket is of brass, and the valve of the bucket is of the common pot lid or spindle kind. The injection water enters through a single cock in front of the condenser--the jet striking against the barrel of the air pump. The air pump rod is maintained in its vertical position by means of guides, the lower ends of which are bolted to the mouth of the pump, and the upper to the oval in the top frame, within which the air pump crank works; and the motion is communicated from this crank to the pump rod by means of a short connected rod. The lower frame is not set immediately below the top frame, but 2-1/2 inches behind it, and the air pump and condenser are 2-1/2 inches nearer one edge of the lower frame than the other. 622. _Q._--What are the dimensions of the cylinder? _A._--The thickness of the metal of the cylinder is 9/16ths of an inch; the depth of the belt of the cylinder is 9-1/2 inches, and its greatest projection from the cylinder is 2-1/2 inches. The distance from the lower edge of the belt to the bottom of the cylinder is 11-1/2 inches, and from the upper edge of the belt to the top flange of the cylinder is 9 inches. The trunnions are 7-1/4 inches diameter in the bearings, and 3-1/2 inches in width; and the flanges to which the glands are attached for screwing in the trunnion packings are 1-1/2 inch thick, and have 7/8ths of an inch of projection. The width of the packing space round the trunnions is 5/8ths of an inch, and the diameter of the pipe passing through the trunnion 4-5/8ths, which leaves 11/16ths for the thickness of the metal of the bearing. Above and below each trunnion a feather runs from the edge of the belt or bracket between 3 and 4 inches along the cylinder, for the sake of additional support; and in large engines the feather is continued through the interior of the belt, and cruciform feathers are added for the sake of greater stiffness. The projection of the outer face of the trunnion flange from the side of the cylinder is 6-1/2 inches; the thickness of the flange round the mouth of the cylinder is 3/4 of an inch, and its projection 1-3/8 inch; the height of the cylinder stuffing box above the cylinder cover is 4-1/8 inches, and its external diameter 4-3/8 inches--the diameter of the piston rod being 2-1/8 inches. The thickness of the stuffing box flange is 1-1/8 inch. 623. _Q._--Will you describe the nature of the communication between the cylinder and condenser? _A._--The pipe leading to the condenser from the cylinder is made somewhat bell mouthed where it joins the condenser, and the gland for compressing the packing is made of a larger internal diameter in every part except at the point at which the pipe emerges from it, where it accurately fits the pipe so as to enable the gland to squeeze the packing. By this construction the gland may be drawn back without being jammed upon the enlarged part of the pipe; and the enlargement of the pipe toward the condenser prevents the air pump barrel from offering any impediment to the free egress of the steam. The gland is made altogether in four pieces: the ring which presses the packing is made distinct from the flange to which the bolts are attached which force the gland against the packing, and both ring and flange are made in two pieces, to enable them to be got over the pipe. The ring is half checked in the direction of its depth, and is introduced without any other support to keep the halves together, than what is afforded by the interior of the stuffing box; and the flange is half checked in the direction of its thickness, so that the bolts which press down the ring by passing through this half-checked part, also keep the segments of the flange together. The bottom of the trunnion packing space is contracted to the diameter of the eduction pipe, so as to prevent the packing from being squeezed into the jacket; but the eduction pipe does not fit quite tight into this contracted part, but, while in close contact on the lower side, has about 1/32nd of an inch of space between the top of the pipe and the cylinder, so as to permit the trunnions to wear to that extent without throwing a strain upon the pipe. The eduction pipe is attached to the condenser by a flange joint, and the bolt holes are all made somewhat oblong in the perpendicular direction, so as to permit the pipe to be slightly lowered, should such an operation be rendered necessary by the wear of the trunnion bearings; but in practice the wear of the trunnion bearings is found to be so small as to be almost inappreciable. 624. _Q._--Will you describe the valve and valve casing? _A._--The length of the valve casing is 16-1/2 inches, and its projection from the cylinder is 3-1/2 inches at the top, 4-1/4 inches at the centre, and 2-1/2 inches at the bottom, so that the back of the valve casing is not made flat, but is formed in a curve. The width of the valve casing is 9 inches, but there is a portion of the depth of the belt 1-1/2 inch wider, to permit the steam to enter from the belt into the casing. The valve casing is attached to the cylinder by a metallic joint; the width of the flange of this joint is 1-1/4 inch, the thickness of the flange on the casing 1/2 inch, and the thickness of the flange on the cylinder 5/8ths of an inch. The projection from the cylinder of the passage for carrying the steam upwards, and downwards, from the valve to the top and bottom of the cylinder, is 2-1/4 inches, and its width externally 8-5/8 inches. The valve is of the ordinary three ported description, and both cylinder and valve faces are of cast iron. 625. _Q._--What description of piston is used? _A._--The piston is packed with hemp, but the junk ring is made of malleable iron, as cast iron junk rings have been found liable to break: there are four plugs screwed into the cylinder cover, which, when removed, permit a box key to be introduced, to screw down the piston packing. The screws in the junk ring are each provided with a small ratchet, cut in a washer fixed upon the head, to prevent the screw from turning back; and the number of clicks given by these ratchets, in tightening up the bolts, enables the engineer to know when they have all been tightened equally. In more recent engines, and especially in those of large size, Messrs. Penn employ for the piston packing a single metallic ring with tongue piece and indented plate behind the joint; and this ring is packed behind with hemp squeezed by the junk ring as in ordinary hemp-packed pistons. 626. _Q._--Will you describe the construction of the cap for connecting the piston rod with the crank pin? _A._--The cap for attaching the piston rod to the crank pin, is formed altogether of brass, which brass serves to form the bearing of the crank pin. The external diameter of the socket by which this cap is attached to the piston rod is 3-5/16 inches. The diameter of the crank pin is 3 inches, and the length of the crank pin bearing 3-7/8 inches. The thickness of the brass around the crank pin bearing is 1 inch, and the upper portion of the brass is secured to the lower portion, by means of lugs, which are of such a depth that the perpendicular section through the centre of the bearing has a square outline measuring 7 inches in the horizontal direction, 3-7/8 inches from the centre of the pin to the level of the top of the lugs, and 2-1/2 inches from the centre of the pin to the level of the bottom of the lugs. The width of the lugs is 2 inches, and the bolts passing through them are 1-1/4 inch in diameter. The bolts are tapped into the lower portion of the cap, and are fitted very accurately by scraping where they pass through the upper portion, so as to act as steady pins in preventing the cover of the crank pin bearing from being worked sideways by the alternate thrust on each side. The distance between the centres of the bolts is 5 inches, and in the centre of the cover, where the lugs, continued in the form of a web, meet one another, an oil cup 1-5/8 inch in diameter, 1-1/8 inch high, and provided with an internal pipe, is cast upon the cover, to contain oil for the lubrication of the crank pin bearing. The depth of the cutter for attaching the cap to the piston rod is 1-1/4 inch and its thickness is 3/8ths of an inch. 627. _Q._--Will you describe the means by which the air pump rod is connected with the crank which works the air pump? [Illustration: Fig. 50. AIR PUMP CONNECTING ROD AND CROSS HEAD. Messrs. Penn.] _A._--A similar cap to that of the piston rod attaches the air pump crank to the connecting rod by which the air pump rod is moved, but in this instance the diameter of the bearing is 5 inches, and the length of the bearing is about 3 inches. The air pump connecting rod and cross head are shown in perspective in fig. 50. The thickness of the brass encircling the bearing of the shaft is three fourths of an inch upon the edge, and 1-1/8 inch in the centre, the back being slightly rounded; the width of the lugs is 1-5/8 inch, and the depth of the lugs is 2 inches upon the upper brass, and 2 inches upon the lower brass, making a total depth of 4 inches. The diameter of the bolts passing through the lugs is 1 inch, and the bolts are tapped into the lower brass, and accurately fitted into the upper one, so as to act as steady pins, as in the previous instance. The lower eye of the connecting rod is forked, so as to admit the eye of the air pump rod; and the pin which connects the two together is prolonged into a cross head, as shown in fig. 50. The ends of this cross head move in guides. The forked end of the connecting rod is fixed upon the cross head by means of a feather, so that the cross head partakes of the motion of the connecting rod, and a cap, similar to that attached to the piston rod, is attached to the air pump rod, for connecting it with the cross head. The diameter of the air pump rod is 1-1/2 inch, the external diameter of the socket encircling the rod is 2-1/8 inches, and the depth of the socket 4-1/2 inches from the centre of the cross head. The depth of the cutter for attaching the socket to the rod is 1 inch, and its thickness 5/16 inch. The breadth of the lugs is 1-3/8 inch, the depth 1-1/4 inch, making a total depth of 2-1/2 inches; and the diameter of the bolts seven eighths of an inch. The diameter of the cross head at the centre is 2 inches, the thickness of each jaw around the bearing 1 inch, and the breadth of each 9/16 inch. 628. _Q._--What are the dimensions of the crank shaft and cranks? _A._--The diameter of the intermediate shaft journal is 4-3/16 inches, and of the paddle shaft journal 4-3/8 inches; the length of the journal in each case is 5 inches. The diameter of the large eye of the crank is 7 inches, and the diameter of the hole through it is 4-3/8 inches; the diameter of the small eye of the crank is 5-1/4 inches, the diameter of the hole through it being 3 inches. The depth of the large eye is 4-1/4 inches, and of the small eye 3-3/4 inches; the breadth of the web is 4 inches at the shaft end, and 3 inches at the pin end, and the thickness of the web is 2-5/8 inches. The width of the notch forming the crank in the intermediate shaft for working the air pump is 3-1/2 inches, and the width of each of the arms of this crank is 3-15/16 inches. Both the outer and inner corners of the crank are chamfered away, until the square part of the crank meets the round of the shaft. The method of securing the cranks pins into the crank eyes of the intermediate shaft consists in the application of a nut to the end of each pin, where it passes through the eye, the projecting end of the pin being formed with a thread upon which the nut is screwed. 629. _Q._--Will you describe the eccentric and eccentric rod? [Illustration: Fig. 51. ECCENTRIC AND ROD. Messrs. Penn.] _A._--The eccentric and eccentric rod are shown in fig. 51. The eccentric is put on the crank shaft in two halves, joined in the diameter of largest eccentricity by means of a single bolt passing through lugs on the central eye, and the back balance is made in a separate piece five eighths of an inch thick, and is attached by means of two bolts, which also help to bind the halves of the eccentric together. The eccentric strap is half an inch thick, and 1-1/4 inch broad, and the flanges of the eccentric, within which the strap works, are each three eighths of an inch thick. The eccentric rod is attached to the eccentric hoop by means of two bolts passing through lugs upon the rod, and tapped into a square boss upon the hoop; and pieces of iron, of a greater or less thickness, are interposed between the surfaces in setting the valve, to make the eccentric rod of the right length. The eccentric rod is kept in gear by the push of a small horizontal rod, attached to a vertical blade spring, and it is thrown out of gear by means of the ordinary disengaging apparatus, which acts in opposition to the spring, as, in cases where the eccentric rod is not vertical, it acts in opposition to the gravity of the rod. 630. _Q._--Will you explain in detail the construction of the valve gearing, or such parts of it as are peculiar to the oscillating engine? _A._--The eccentric rod is attached by a pin, 1 inch in diameter, to an open curved link or sector with a tail projecting upward and passing through an eye to guide the link in a vertical motion. The link is formed of iron case-hardened, and is 2-3/4 inches deep at the middle, and 2-3/8 inches deep at the ends, and 1 inch broad. The opening in the link, which extends nearly its entire length, is 1-5/16 inch broad; and into this opening a brass block 2 inches long is truly fitted, there being a hole through the block 3/4 inch diameter, for the reception of the pin of the valve shaft lever. The valve shaft is 1-3/4 inch diameter at the end next the link or segment, and diminishes regularly to the other end, but its cross section assumes the form of an octagon in its passage round the cylinder, measuring mid-way 1-1/4 inch deep, by about 3/4 inch thick, and the greatest depth of the finger for moving the valve is about 1 inch. The depth of the lever for moving the valve shaft is 2 inches at the broad, and 1-1/4 inch at the narrow end. The internal breadth of the mortice in which the valve finger moves is 5/16 inch, and its external depth is 1-3/4 inch, which leaves three eighths of an inch as the thickness of metal round the hole; and the breadth, measuring in the direction of the hole, is 1-1/2 inch. The valve rod is three fourths of an inch in diameter, and the mortice is connected to the valve rod by a socket 1 inch long, and 1-1/8 inch diameter, through which a small cutter passes. A continuation of the rod, eleven sixteenths of an inch diameter, passes upward from the mortice, and works through an eye, which serves the purpose of a guide. In addition to the guide afforded to the segment by the ascending tail, it is guided at the ends upon the columns of the framing by means of thin semicircular brasses, 4 inches deep, passing round the columns, and attached to the segment by two 3/8 inch bolts at each end, passing through projecting feathers upon the brasses and segment, three eighths of an inch in thickness. The curvature of the segment is such as to correspond with the arc swept from the centre of the trunnion to the centre of the valve lever pin when the valve is at half stroke as a radius; and the operation of the segment is to prevent the valve from being affected by the oscillation of the cylinder, but the same action, would be obtained by the employment of a smaller eccentric with more lead. In some engines the segment is not formed in a single piece, but of two curved blades, with blocks interposed at the ends, which may be filed down a little, to enable the sides of the slot to be brought nearer, as the metal wears away. 631. _Q._--What kind of plummer blocks are used for the paddle shaft bearings? _A._--The paddle shaft plummer blocks are altogether of brass, and are formed in much the same manner as the cap of the piston rod, only that the sole is flat, as in ordinary plummer blocks, and is fitted between projecting lugs of the framing, to prevent side motion. In the bearings fitted on this plan, however, the upper brass will generally acquire a good deal of play after some amount of wear. The bolts are worked slack in the holes, though accurately fitted at first; and it appears expedient, therefore, either to make the bolts very large, and the sockets through which they pass very deep, or to let one brass fit into the other. 632. _Q._--How are the trunnion plummer blocks made? _A._--The trunnion plummer blocks are formed in the same manner as the crank shaft plummer blocks; the nuts are kept from turning back by means of a pinching screw passing through a stationary washer. It is not expedient to cast the trunnion plummer blocks upon the lower frame, as is sometimes done; for the cylinders, being pressed from the steam trunnions by the steam, and drawn in the direction of the condenser by the vacuum, have a continual tendency to approach one another; and as they wear slightly toward midships, there would be no power of readjustment unless the plummer blocks were movable. The flanges of the trunnions should always fit tight against the plummer block sides, but there should be a little play sideways at the necks of the trunnions, so that the cylinder may be enabled to expand when heated, without throwing an undue strain upon the trunnion supports. 633. _Q._--What kind of paddle wheel is supplied with these oscillating engines? _A._--The wheels are of the feathering kind, 9 feet 8 inches in diameter, measuring to the edges of the floats; and there are 10 floats upon each wheel, measuring 4 feet 6 inches long each, and 18-1/2 inches broad. There are two sets of arms to the wheel, which converge to a cast iron centre, formed like a short pipe with large flanges, to which the arms are affixed. The diameter of the shaft, where the centre is put on, is 4-1/2 inches, the external diameter of the pipe is 8 inches, and the diameter of the flanges is 20 inches, and their thickness 1-1/4 inch. The flanges are 12 inches asunder at the outer edge, and they partake of the converging direction of the arms. The arms are 2-1/4 inches broad and half an inch thick; the heads are made conical, and each is secured into a recess upon the side of the flange by means of three bolts. The ring which connects together the arms, runs round at a distance of 3 feet 6 inches from the centre, and the projecting ends of the arms are bent backward the length of the lever which moves the floats, and are made very wide and strong at the point where they cross the ring, to which they are attached by four rivets. The feathering action of the floats is accomplished by means of a pin fixed to the interior of the paddle box, set 3 inches in advance of the centre of the shaft, and in the same horizontal line. This pin is encircled by a cast iron collar, to which rods are attached 1-3/8 inch diameter in the centre, proceeding to the levers, 7 inches long, fixed on the back of the floats in the line of the outer arms. One of these rods, however, is formed of nearly the same dimensions as one of the arms of the wheel, and is called the driving arm, as it causes the cast iron collar to turn round with the revolution of the wheel, and this collar, by means of its attachments to the floats, accomplishes the feathering action. The eccentricity in this wheel is not sufficient to keep the floats in the vertical position, but in the position between the vertical and the radial. The diameter of the pins upon which the floats turn is 1-3/8 inch, and between the pins and paddle ring two stud rods are set between each of the projecting ends of the arms, so as to prevent the two sets of arms from being forced nearer or further apart; and thus prevent the ends of the arms from hindering the action of the floats, by being accidentally jammed upon the sides of the joints. Stays, crossing one another, proceed from the inner flange of the centre to the outer ring of the wheel, and from the outer flange of the centre to the inner ring of the wheel, with the view of obtaining greater stiffness. The floats are formed of plate iron, and the whole of the joints and joint pins are steeled, or formed of steel. For sea-going vessels the most approved practice is to make the joint pins of brass, and also to bush the eyes of the joints with brass; and the surface should be large to diminish wear. 634. _Q._--Can you give the dimensions of any other oscillating engines? _A._--In Messrs. Penn's 50 horse power oscillating engine, the diameter of the cylinder is 3 feet 4 inches, and the length of the stroke 3 feet. The thickness of the metal of the cylinder is 1 inch, and the thickness of the cylinder bottom is 1-3/4 inch, crossed with feathers, to give it additional stiffness. The diameter of the trunnion bearings is 1 foot 2 inches, and the breadth of the trunnion bearings 5-1/2 inches. Messrs. Penn, in their larger engines, generally make the area of the steam trunnion less than that of the eduction trunnion, in the proportion of 32 to 37; and the diameter of the eduction trunnion is regulated by the internal diameter of the eduction pipe, which is about 1/5th of the diameter of the cylinder. But a somewhat larger proportion than this appears to be expedient: Messrs. Rennie make the area of their eduction pipes, in oscillating engines, 1/22d of the area of the cylinder. In the oscillating engines of the Oberon, by Messrs. Rennie, the cylinder is 61 inches diameter, and 1-1/2 inch thick above and below the belt, but in the wake of the belt it is 1-1/4 inch thick, which is also the thickness of metal of the belt itself. The internal depth of the belt is 2 feet 6 inches, and its internal breadth is 4 inches. The piston rod is 6-3/4 inches in diameter, and the total depth of the cylinder stuffing box is 2 feet 4 inches, of which 18 inches consists of a brass bush--this depth of bearing being employed to prevent the stuffing box or cylinder from wearing oval. 635. _Q._--Can you give any other examples? _A._--The diameter of cylinder of the oscillating engines of the steamers Pottinger, Ripon, and Indus, by Miller & Ravenhill, is 76 inches, and the length of the stroke 7 feet. The thickness of the metal of the cylinder is 1-11/16 inch; diameter of the piston rod 8-3/4 inches; total depth of cylinder stuffing box 3 feet; depth of bush in stuffing box 4 inches; the rest of the depth, with the exception of the space for packing, being occupied with a very deep gland, bushed with brass. The internal diameter of the steam pipe is 13 inches; diameter of steam trunnion journal 25 inches; diameter of eduction trunnion journal 25 inches; thickness of metal of trunnions 2-1/4 inches; length of trunnion bearings 11 inches; projection of cylinder jacket, 8 inches; depth of packing space in trunnions, 10 inches; width of packing space in trunnions, or space round the pipes, 1-1/2 inch; diameter of crank pin 10-1/4 inches; length of bearing of crank pin 15-1/2, inches. There are six boilers on the tubular plan in each of these vessels; the length of each boiler is 10 feet 6 inches, and the breadth 8 feet; and each boiler contains 62 tubes 3 inches in diameter, and 6 feet 6 inches long, and two furnaces 6 feet 4-1/2 inches long, and 3 feet 1-1/2 inch broad. 636. _Q._--Is it the invariable practice to make the piston rod cap of brass in the way you have described? _A._--In all oscillating engines of any considerable size, the cover of the connecting brass, which attaches the crank pin to the connecting rod, is formed of malleable iron; and the socket also, which is cuttered to the end of the piston rod, is of malleable iron, and is formed with a T head, through which bolts pass up through the brass, to keep the cover of the brass in its place. 637. _Q._--Is the piston of an oscillating engine made deeper than in common engines? _A._--It is expedient, in oscillating engines, to form the piston with a projecting rim round the edge above and below, and a corresponding recess in the cylinder cover and cylinder bottom, whereby the breadth of bearing of the solid part of the metal will be increased, and in many engines this is now done. 638. _Q._--Would any difficulty be experienced in keeping the trunnions tight in a high pressure oscillating engine? _A._--It is very doubtful whether the steam trunnions of a high pressure oscillating engine will continue long tight if the packing consists of hemp; and it appears preferable to introduce a brass ring, to embrace the pipe, cut spirally, with an overlap piece to cover the cut, and packed behind with hemp. 639. _Q._--How is the packing of the trunnions usually effected? _A._--The packing of the trunnions, after being plaited as hard as possible, and cut to the length to form one turn round the pipe, is dipped into boiling tallow, and is then compressed in a mould, consisting of two concentric cylinders, with a gland forced down into the annular space by three to six screws in the case of large diameters, and one central screw in the case of small diameters. Unless the trunnion packings be well compressed, they will be likely to leak air, and it is, therefore, necessary to pay particular attention to this condition. It is also very important that the trunnions be accurately fitted into their brasses by scraping, so that there may not be the smallest amount of play left upon them; for if any upward motion is permitted, it will be impossible to prevent the trunnion packings from leaking. DIRECT ACTING SCREW ENGINE. 640. _Q._--Will you describe the configuration and construction of a direct acting screw engine? _A._--I will take as an example of this species of engine, the engine constructed by Messrs. John Bourne & Co., for the screw steamer Alma, a vessel of 500 tons burden. This engine is a single steeple engine laid on its side, and in its general features it resembles the engines of the Amphion already described, only that there is one cylinder instead of two. The cylinder is of 42 inches diameter and 42 inches stroke, and the vessel has been propelled by this single engine at the rate of fourteen miles an hour. 641. _Q._--Is not a single engine liable to stick upon the centre so that it cannot be started or reversed with facility? _A._--A single engine is no doubt more liable to stick upon the centre than two engines, the cranks of which are set at right angles with one another; but numerous paddle vessels are plying successfully that are propelled by a single engine, and the screw offers still greater facility than paddles for such a mode of construction. In the screw engine referred to, as the cylinder is laid upon its side, there is no unbalanced weight to be lifted up every stroke, and the crank, whereby the screw shaft is turned round, consists of two discs with a heavy side intended to balance the momentum of the piston and its connections; but these counter-weights by their gravitation also prevent the connecting rod and crank from continuing in the same line when the engine is stopped, and in fact they place the crank in the most advantageous position for starting again when it has to be set on. 642. _Q._--Will you explain the general arrangement of the parts of this engine? _A._--The cylinder lies on its side near one side of the vessel, and from the end of the cylinder two piston rods extend to a cross head sliding athwartships, in guides, near the other side of the vessel. To this cross head the connecting rod is attached, and one end of it partakes of the motion of the cross head or piston, while the other end is free to follow the revolution of the crank on the screw shaft. 643. _Q._--What is the advantage of two discs entering into the composition of the crank instead of one? _A._--A double crank, such as two discs form with the crank pin, is a much steadier combination than would result if only one disc were employed with an over-hung pin. Then the friction on the neck of the shaft is made one half less by being divided between the two bearings, and the short prolongation of the shaft beyond the journal is convenient for the attachment of the eccentrics to work the valves. 644. _Q._--Will you enumerate some of the principal dimensions of this engine? _A._--The bottom frame, on which also the condenser is cast, forms the base of the engine: on one end of it the cylinder is set; on the other end are the guides for the cross head, and in the middle are the bearings for the crank shaft. The part where the cylinder stands is two feet high above the engine platform, and the elevation to the centre of the guides or the centre of the shaft is 10 inches higher than this. The metal both of the side frames and bottom flange is 1-1/4 inch thick. The cylinder has flanges cast on its sides, upon which it rests on the bottom frame, and it is sunk between the sides of the frame so as to bring the centre of the cylinder in the same plane as the centre of the screw shaft. The opening left at the guides for the reception of the guide blocks is 6 inches deep, and the breadth of the bearing surface is 11 inches. The cover of the guides is 8 inches deep at the middle, and about half the depth at the ends, and holes are cored through the central web for two oil cups on each guide. The brass for each of the crank shaft bearings is cut into four pieces so that it may be tightened in the up and down direction by the bolts, which secure the plummer block cap, and tightened in the athwartship direction, which is the direction of the strain, by screwing up a wedge-formed plate against the side of the brass, a parallel plate being applied to the other side of the brass, which may be withdrawn to get out the wedge piece when the shaft requires to be lifted out of its place. The air pump is bolted to one side of the bottom frame, and a passage is cast on it conducting from the condenser to the air pump. In this passage the inlet and outlet valves at each end of the air pump are situated, and appropriate doors are formed above them to make them easily accessible. The outlet passage leading from the air pump communicates with the waste water pipe, through which the water expelled by the air pump is discharged overboard. 645. _Q._--Is the cylinder of the usual strength and configuration? _A._--The cylinder is formed of cast iron in the usual way, and is 1-1/8 inch thick in the barrel. The ends are of the same thickness, but are each stiffened with six strong feathers. The piston is cast open. The bottom of it is 5/8ths of an inch thick, and it is stiffened by six feathers 3/4 of an inch thick; but the feather connecting the piston rod eyes is 1-1/4 inch thick, and the metal round the eyes is 2 inches thick. The piston is closed by a disc or cover 5/8ths of an inch thick, secured by 15 bolts, and this cover answers also the purpose of a junk ring. The piston packing consists of a single cast iron ring 3-1/2 inches broad, and 1/2 inch thick, packed behind with hemp. This ring is formed with a tongue piece, with an indented plate behind the cut; and the cut is oblique to prevent a ridge forming in the cylinder. The total thickness of the piston is 5-1/2 inches. The piston rods are formed with conical ends for fitting into the piston, but are coned the reverse way as in locomotives, and are secured in the piston by nuts on the ends of the rods, these nuts being provided with ratchets to prevent them from unscrewing accidentally. 646. _Q._--What species of slide valve is employed? _A._--The ordinary three ported valve, and it is set on the top of the cylinder. The cylinder ports are 4-1/2 inches broad by 24 inches long; and to relieve the valve from the great friction due to the pressure on so large a surface, a balance piston is placed over the back of the valve, to which it is connected by a strong link; and the upward pressure on this piston being nearly the same as the downward pressure on the valve, it follows that the friction is extinguished, and the valve can be moved with great case with one hand. The balance piston is 21 inches in diameter. In the original construction of this balance piston two faults were committed. The passage communicating between the condenser and the top of the balance piston was too small, and the pins at the ends of the link connecting the valve and balance piston were formed with an inadequate amount of bearing surface. It followed from this misproportion that the balance piston, being adjusted to take off nearly the whole of the pressure, lifted the valve off the face at the beginning of each stroke. For the escape of the steam into the eduction passage momentarily impaired the vacuum subsisting there, and owing to the smallness of the passage leading to the space above the balance piston, the vacuum subsisting in that space could not be impaired with equal rapidity. The balance piston, therefore, rose by the upward pressure upon it momentarily predominating over the downward pressure on the valve; but this fault was corrected by enlarging the communicating passage between the top of the balance piston and the eduction pipe. The smallness of the pins at the ends of the link connecting the valve and balance piston, caused the surfaces to cut into one another, and to wear very rapidly, and the pins and eyes in this situation should be large in diameter, and as long as they can be got, as they are not so easily lubricated as the other bearings about the engine, and are moreover kept at a high temperature by the steam. The balance piston is packed in the same way as the main piston of the engine. Its cylinder, which is only a few inches in length, is set on the top of the valve casing, and a trunk projects upwards from its centre to enable the connecting link to rise up in it to attain the necessary length. [Illustration: Fig 52. CONNECTING ROD. Messrs. Bourne & Co.] 647. _Q._--What is the diameter of the piston rods and connecting rod? _A._--The piston rods, which are two in number, are 3 inches diameter, and 12 feet 10 inches long over all. They were, however, found to be rather small, and have since been made half an inch thicker. The connecting rod consists of two rods, which are prolongations of the bolts that connect the sides of the brass bushes which encircle the crank pin and cross head. The connecting rod is shown in perspective in fig. 52. The rods composing it are each 2-3/4 inches in diameter. 648. _Q._--Will you describe the configuration of the cross head. _A._--The cross head, exhibited in fig. 53, is a round piece of iron like a short shaft, with two unequal arms keyed upon it, the longer of which _b_ works the air pump, and the shorter _c_ works the feed pump. The piston rods enter these arms at _a A._ The cross head is 8 inches diameter where it is embraced by the connecting rod at _e_, and 7 inches diameter where the air pump and feed pump arms are fixed on. The ends of the cross head _d d_, for a length of 12 inches, are reduced to 3 inches diameter where they fit into round holes in the centre of the guide blocks. Those blocks are of cast iron 6 inches deep, 11 inches wide, and 14 inches long, and they are formed with flanges 1 inch thick on the inner sides of the blocks. The projection of the air pump lever from the centre of the cross head is 1 foot 9 inches, and it is bent 5-3/4 inches to one side to enable it to engage the air pump rod. The eye of this arm is 6 inches broad and about 2 inches thick. At the part where one of the piston rods passes through it, the arm is 8 inches deep and 6 inches wide; but the width thereafter narrows to 3 inches, and finally to 2 inches; and the depth of the web of the arm reduces from 8 inches at the piston rod, to 4 inches at the eye, which receives the end of the air pump rod. The feed pump arm is only 3 inches thick, and has 9 inches of projection from the centre of the cross head; but the eye attached to it on the opposite side of the cross head for the reception of the other piston rod is of the same length as that part of the air pump arm which one of the piston rods passes through. The piston rods have strong nuts on each side of each of these arms to attach them to the arms, and also to enable the length of the piston rods to be suitably adjusted, to leave equal clearance between the piston and each end of the cylinder at the termination of the stroke. [Illustration: Fig. 53. CROSS HEAD AND PUMP ARMS. Messrs. Bourne & Co.] 649. _Q._--Will you recapitulate the main particulars of the air pump? _A._--The air pump is made of brass 12-1/2 inches diameter and 42 inches stroke, and the metal of the barrel is 9/16ths of an inch thick. The air pump bucket is a solid piston of brass, 6-1/2 inches deep at the edge, and 7 inches deep at the eye; and in the edge three grooves are turned to hold water which answers the purpose of packing. The inlet and outlet valves of the air pump consist of brass plates 1/2 inch with strong feathers across them, and in each plate there are six grated perforations covered by india rubber discs 7 inches in diameter. These six perforations afford collectively an area for the passage of the water equal to the area of the pump. The air pump rod is of brass, 2-1/2 inches diameter. 650. _Q._--What are the constructive peculiarities of the discs and crank pin? _A._--The discs, which are 64 inches diameter, are formed of cast iron, and are 2-1/2 inches thick in the body, and 5 inches broad at the rim. The crank shaft is 8-1/2 inches diameter, and the central boss of the disc which receives the shaft measures 10 inches through the eye, and the metal of the eye is 3 inches thick. In the part of the disc opposite to the crank pin, the web is thickened to 10 inches for nearly the whole semicircle, with the view of making that side of the disc heavier than the other side; and when the engine is stopped, the gravitation of this heavy side raises the crank pin to the highest point it can attain, whereby it is placed in mid stroke, and cannot rest with the piston rods and connecting rod in a horizontal line. The crank pin is 8-1/2 inches diameter, and the length of the bearing or rubbing part of it is 16 inches. It is secured at the ends to the discs by flanges 18 inches diameter, and 2 inches thick. These flanges are indented into thickened parts of the discs, and are each attached to its corresponding disc by six bolts 2 inches diameter, countersunk in the back of the disc, and tapped into the malleable iron flange. Besides this attachment, each end of the pin, reduced to 4-1/2 inches diameter, passes through a hole in its corresponding disc, and the ends of the pin are then riveted over. The crank pin is perforated through the centre by a small hole about 3/4 of an inch in diameter, and three perforations proceed from this central hole to the surface of the pin. Each crank shaft bearing is similarly perforated, and pipes are cast in the discs connecting these perforations together. The result of this arrangement is, that a large part of the oil or water fed into the bearings of the shaft is driven by the centrifugal action of the discs to the surface of the crank pin, and in this way the crank pin may be oiled or cooled with water in a very effectual manner. To intercept the water or oil which the discs thus drive out by their centrifugal action, a light paddle box or splash board of thin sheet brass is made to cover the upper part of each of the discs, and an oil cup with depending wick is supported by the tops of these paddle boxes, which wick is touched at each revolution of the crank by a bridge standing in the middle of an oil cup attached to the crank pin. The oil is wiped from the wick by the projecting bridge at each revolution, and subsides into the cup from whence it proceeds to lubricate the crank pin bearing. This is the expedient commonly employed to oil the crank pins of direct acting engines; but in the engine now described, there are over and above this expedient, the communicating passages from the shaft bearings to the surface of the pin, by which means any amount of cooling or lubrication can be administered to the crank pin bearing, without the necessity of stopping or slowing the engine. [Illustration: Fig. 54. DOUBLE DISC CRANK. Messrs. Bourne & Co.] 651. _Q._--What is the diameter of the screw shaft? _A._--The screw shaft is 7-1/2 inches diameter, but the bearings on each side of the disc are 8-1/2 inches diameter, and 16 inches long. Between the side of the disc and the side of the contiguous bearings there is a short neck extending 4-3/4 inches in the length of the shaft, and hollowed out somewhat to permit the passage of the piston rod; for one piston rod passes immediately above the shaft on the one side of the discs, and the other piston rod passes immediately below the shaft on the other side of the discs. A short piece of one piston rod is shown in fig. 54. [Illustration: Fig. 55. THRUST BEARING. Messers. Bourne & Co.] [Illustration: Fig. 56. COUPLING CRANKS. Messers. Bourne & Co.] 652. _Q._--How is the thrust of the screw shaft received? _A._--The thrust of the screw shaft is received upon 7 collars, each 1 inch thick, and with 1 inch of projection above the shaft. The plummer block for receiving the thrust of the shaft is shown in fig. 55, and the coupling to enable the screw propeller to be disconnected from the engine, so that it may revolve freely when the vessel is under sail, is shown in fig. 56. When it is required to disengage the propeller from the engine, the pins passing through the opposite eyes shown fig. 56, are withdrawn by means of screws provided for that purpose, and the propeller and the engine are thenceforth independent of one another. [Illustration: Fig. 57. LINK MOTION. Messrs. Bourne & Co.] 653. _Q._--Will you describe the arrangement of the valve gearing? _A._--The end of the screw shaft, after emerging from the bearing beside the disc, is reduced to a diameter of 4 inches, and is prolonged for 4-1/2 inches to give attachment to the cam or curved plate which gives motion to the expansion valve. This plate is 3-1/2 inches thick, and a stud 3-1/2 inches diameter is fixed in the plate at a distance of 5 inches from the centre of the shaft. To this stud an arm is attached which extends to a distance of 2 inches from the centre of the shaft in the opposite direction, and the end of this arm carries a pin of 2-1/2 inches diameter. From the pin most remote from the centre of the shaft, a rod 2-1/2 inches broad and 1 inch thick extends to the upper end of the link of the link motion; and from the pin least remote from the centre of the shaft, a similar rod extends to the lower end of the link of the link motion. This link, which is represented in fig. 57, is 2-1/4 inches broad, 1 inch thick, and is capable of being raised or lowered 25 inches in all. In the open part of the link is a brass block, which, by raising or lowering the link, takes either the position in which it is represented at the centre of the link, or a position at either end of it. Through the hole in the brass block a pin passes to attach the brass to the end of a lever fixed on the valve shaft; so that whatever motion is imparted to the brass block is communicated to the valve through the medium of this lever. If the brass block be set in the middle of the link, no motion is communicated to it, and the valve being consequently kept stationary and covering both ports, the engine stops. If the link be lowered until the brass block comes to the upper end of the link, the valve receives the motion of the eccentric for going ahead, and the engine moves ahead; whereas if the link be raised until the brass block comes to the lower end of the link, the valve receives the motion of the backing eccentric, and the engine moves astern. Instead of eccentrics, however, pins at the end of the shaft are employed in this engine, the arrangement partaking of the nature of a double crank; but the backing pin has less throw than the going ahead pin, whereby the efficient length of the link for going ahead is increased; and the operation of backing, which does not require to be performed at the highest rate of speed, is sufficiently accommodated by about half the throw being given to the valve that is given in going ahead. A valve shaft extends across the end of the cylinder with two levers standing up, which engage horizontal side rods extending from a small cross head on the end of the valve rod. A lever extends downwards from the end of the valve shaft, which is connected by a pin to the brass block within the link; and the link is moved up or down by the starting handle, which, by means of a spring bolt shooting into a quadrant, holds the starting handle at any position in which it may be set. 654. _Q._--What is the diameter and pitch of the screw propeller? _A._--The diameter is 7 feet and the pitch 14 feet. The propeller is Holm's conchoidal propeller. Its diameter is smaller than is advisable, being limited by the draught of water of the vessel; and the vessel was required to have a small draught of water to go over a bar. This engine makes, under favorable circumstances, 100 strokes per minute. The speed of piston with this number of strokes is 700 feet per minute, and the engine works steadily at this speed, the shock and tremor arising from the arrested momentum of the moving parts being taken away by the counterbalance applied at the discs. LOCOMOTIVE ENGINE. 655. _Q._--Will you describe the principal features of a modern locomotive engine? _A._--I will take for this purpose the locomotive Snake, constructed by John V. Gooch for the London and South Western Railway, as an example of a modern locomotive of good construction, adapted for the narrow gauge. The length of the wheel base of this engine is 12 feet 8-1/2 inches. There are two cylinders, each 14-1/4 inches diameter and 21 inches stroke. The total weight of the engine is 19 tons; and this weight is so distributed on the wheels as to throw 8 tons on the leading wheels, 6 tons on the driving wheels, and 5 tons on the hind wheels. The engine is made with outside cylinders, and the cylinders are raised somewhat out of the horizontal line to enable them better to clear the leading wheels. 656. _Q._--What are the dimensions of the boiler? _A._--The interior of the fire box is 3 feet 7-1/4 inches wide by 3 feet 5-1/2 inches long, measuring in the direction of the rails. The area of the fire grate is consequently 12.4 square feet. The bars are somewhat lower on the side next the fire door than at the side next the tubes, and the mean height of the crown of the fire box above the bars is 3 feet 10 inches. The top edge of the fire door is about 7 inches lower than the crown of the fire box. The fire box is divided transversely by a corrugated feather or bridge of plate iron, containing water, about 3-1/2 inches wide, and of about one-third of the height of the fire box in the centre of the feather, and about two-thirds the height of the fire box at the sides where it joins the sides of the fire box. The internal shell of the fire box tapers somewhat upwards to facilitate the disengagement of the steam. It is about 2 inches narrower and shorter at the top than at the bottom; the water space between the external and internal shell of the fire box being 2 inches at the bottom and 3 inches at the top. 657. _Q._--Of what material is the fire box composed? _A._--The external shell of the fire box is formed of iron plates 3/8ths of an inch thick, and the internal shell is formed of copper plates 1/4 inch thick, but the tube plate is 3/4 inch thick. The fire grate is rectangular, and the internal and external shells are tied together by iron stay bolts 3/4 inch diameter, and pitched about 4 inches apart. The roof of the fire box is stiffened by six strong bars extending from side to side of the fire box like beams, and the top of the fire box is secured to these bars, so that it cannot be forced down without breaking or bending them. 658. _Q._--What are the dimensions of the barrel of the boiler? _A._--The barrel of the boiler is 3 feet 7-1/2 inches in diameter, and 10 feet long. It is formed of iron plates 3/8ths of an inch thick, riveted together. It is furnished with 181 brass tubes 1-7/8 inch diameter and 10 feet long, secured at the ends by ferules. The tube plate at the smoke box end is 5/8ths of an inch thick, and the tube plates above the tubes are tied together by eight iron rods 7/8ths of an inch thick, extending from end to end of the boiler. The metal of the tubes is somewhat thicker at the end next the fire, being 13 wire gauge at fire box end, and 14 wire gauge at smoke box end. The rivets of the boiler are 3/4 inch diameter and 1-1/2 inch pitch. The plating of the ash pan is 5/16ths of an inch thick, and the plating of the smoke box is 3/16ths of an inch thick. 659. _Q._--Will you describe the structure of the framework on which the boiler and its attachments rest, and in which the wheels are set? _A._--The framework or framing consists of a rectangular structure of plate iron circumscribing the boiler, with projecting lugs or arms for the reception of the axles of the wheels. In this engine the sides of the rectangle are double, or, as far as regards the sides, there are virtually two framings, one for the reception of the driving axles, and the other for the reception of the axles not connected with the engine. The whole of the parts of the outer and inner framings are connected together by knees at the corners, and the double sides are elsewhere connected by intervening brackets and stays, so as to constitute the whole into one rigid structure. The whole of the plating of the inside frame is 3/4 inch thick and 9 inches deep. The plating of the outside frame is of the same thickness and depth at the fore part, until it reaches abaft the position of the cylinders and guides, where it reduces to 1/2 inch thick. The axle guard of the leading wheels is formed of 3/4 plate bolted to the frame with angle iron guides. The axle guards of the trailing wheels are formed of two 1/2 inch plates, with cast iron blocks between them to serve as guides. The ends of the rectangular frame are formed of plates 3/4 thick, and at the front end there is a buffer beam of oak 4-1/2 inches thick and 15 inches deep. The draw bolt is 2 inches diameter. There are two strong stays on each side, joining the barrel of the boiler to the inside framing, and one angle iron on each side joining the bottom of the smoke box to the inside framing. 660. _Q._--Of what construction are the wheels? _A._--The wheels and axles are of wrought iron, and the tires of the wheels are of steel. The driving wheels are 6 feet 6-1/2 inches in diameter, and the diameter of crank pin is 3-1/2 inches. The diameter of the smaller wheels is 48-1/2 inches. The axle boxes are of cast iron with bushes of Fenton's metal, and the leading axle has four bearings. The springs are formed of steel plates, 3 feet long, 4 inches broad, and 1\2 inch thick. The axle of the driving wheel has two eccentrics, forged solid upon it, for working the pumps. 661. _Q._--Will you specify the dimensions of the principal parts of the engine? _A._--Each of the cylinders which is 14-1/4 inches diameter, has the valve casing cast upon it. The steam ports are 13 inches long and 1-5/8 inches broad, and the exhaust port is 2-1/2 inches broad. The travel of the valve is 4-1/8 inches, the lap 1 inch, and the lead 1/4 inch. The piston is 4 inches thick: its body is formed of brass with a cover of cast iron, and between the body and the cover two flanges, forged on the piston rod, are introduced to communicate the push and pull of the piston to the rod. The piston rod is of iron, 2-1/2 inches diameter. The guide bars for guiding the top of the piston rod are of steel, 4 inches broad, fixed to rib iron bearers, with hard wood 1/4 of an inch thick, interposed. The connecting rod is 6 feet long between the centres, and is fitted with bushes of white metal. The eccentrics are formed of wrought iron, and have 4-1/8 inches of throw. The link of the link motion is formed of wrought iron. It is hung by a link from a pin attached to the framing; and instead of being susceptible of upward and downward motion, as in the case of the link represented in fig. 57 a rod connecting the valve rod with the movable block in the link, is susceptible of this motion, whereby the same result is arrived at as if the link were moved and the block was stationary. One or the other expedient is preferable, according to the general nature of the arrangements adopted. The slide valve is of brass, and the regulator consists of two brass slide valves worked over ports in a chest in the steam pipe, set in the smoke box. The steam pipe is of brass, No. 14. wire gauge, perforated within the boiler barrel with holes 1/12th of an inch in diameter along its upper side. The blast pipe, which is of copper, has an orifice of 4-1/4 inches diameter. There is a damper, formed like a Venetian blind, with the plates running athwartships at the end of the tubes. [Illustration: Fig. 58. SAFETY VALVE. Gooch.] 662. _Q._--Of what construction is the safety valve? _A._--There are two safety valves, consisting of pistons 1-3/16 inch in diameter, and which are kept down by spiral springs placed immediately over them. A section of this valve is given in fig. 58. 663. _Q._--What are the dimensions of the feed pumps? _A._--The feed pumps are of brass, with plungers 4 inches diameter and 3-1/4 inches stroke. The feed pipe is of copper, 2 inches diameter. A good deal of trouble has been experienced in locomotives from the defective action of the feed pump, partly caused by the leakage of steam into the pumps, which prevented the water from entering them, and partly from the return of a large part of the water through the valves at the return stroke of the pump, in consequence of the valve lifting too high. The pet cock--a small cock communicating with the interior of the pump--will allow any steam to escape which gains admission, and the air which enters by the cock cools down the barrel of the pump, so that in a short time it will be in a condition to draw. The most ordinary species of valve in the feed pumps of locomotives, is the ball valve. Notwithstanding the excellent performance of the best examples of locomotive engines, it is quite certain that there is still much room for improvement; and indeed various sources of economy are at present visible, which, if properly developed, would materially reduce the expense of the locomotive power. In all engines the great source of expense is the fuel; and although the consumption of fuel has been greatly reduced within the last ten or fifteen years, it is capable of being still further reduced by certain easy expedients of improvement, which therefore it is important should be universally applied. One of these expedients consists in heating the feed water by the waste steam; and the feed water should in every case be sent into the boiler _boiling hot_, instead of being quite cold, as is at present generally the case. The ports of the cylinders should be as large as possible; the expansion of the steam should be carried to a greater extent; and in the case of engines with outside cylinders, the waste steam should circulate entirely round the cylinders before escaping by the blast pipe. The escape of heat from the boiler should be more carefully prevented; and the engine should be balanced by weights on the wheels to obviate a waste of power by yawing on the rails. The most important expedient of all, however, lies in the establishment of a system of registering the performance of all new engines, in order that competition may stimulate the different constructors to the attainment of the utmost possible economy; and under the stimulus of comparison and notoriety, a large measure of improvement would speedily ensue. The benefits consequent on public competition are abundantly illustrated by the rapid diminution of the consumption of fuel in the case of agricultural engines, when this stimulus was presented. CHAPTER XI OF VARIOUS FORMS, APPLICATIONS, AND APPLIANCES OF THE STEAM ENGINE. In the English edition of this work, the first part of this chapter is devoted to examples of Portable and fixed Agricultural engines, of different makers and styles of workmanship, but not in sufficient detail, nor illustrated on large enough scale to be of practical value as models, forming rather in fact an illustrated catalogue of the manufacturer, than a study for the mechanic. On this account, they have been entirely omitted, and their place supplied by a few illustrations from American workmanship, not only of Steam Engines, of various forms and applications, but also of various machines, or appliances, connected with the working of engines, as for the determination, or regulation of pressure, of the boilers; for the supply or feed of the boilers, the regulation of the speed of the engine, and the like. The Gauges used in this country to show the pressures of steam in boilers are of various constructions, but perhaps the most common is the Bourdon, or, as it is known here, the Ashcroft gauge, from the party introducing it, and holding the patent. Fig. 59 represents its interior construction. It consists of a thin metallic tube, _a_, bent into nearly a complete circle closed at one end, the steam being introduced at the other, at _b_. The effect of the pressure of the steam on the interior of the tube is to expand the circle, more or less according to the pressure, the elasticity of the metal returning the circle to its original position, when the pressure is removed. The free or closed end of the tube is connected by a link _c_ with a lever _d_, at the opposite end of which is segmental gear, in gear with a pinion, on which is a hand, which marks the pressure on a dial. The dial and hand are not shown on the cut, but are on the exterior case removed to show the construction. [Illustration: Fig. 59.] [Illustration: Fig. 60.] Fig. 60 is an elevation of a boiler with Clark's Patent Steam and Fire Regulator attached, for the control of the draft of the chimney by the pressure of steam in the boiler. It consists of a chamber, _a_, with a flexible diaphragm or cover on top, in communication with the boiler. On this diaphragm rests a plunger or piston, which is held down like a safety valve, by a lever and weight, _b_. The end of the lever is connected with a balanced damper, _c_, in the chimney. The weight, _b_, is placed at any required position on the lever, and when the pressure of steam in the boiler, exerted on the diaphragm, becomes sufficient to raise the weight, the lever rises, and the damper begins to close, and to check the draft in the chimney. When properly adjusted, the machine works on a variation of from, one to two pounds between the extremes of motion. When the dampers are very large, say 3 feet or over, they should be set on rollers, like common grindstone rollers; the regulator should be attached directly to the damper, the length of the pipe connecting the regulator with the boiler being of no account. [Illustration: Fig. 61.] Porter's Patent Governor, fig. 61, is a modification of the ordinary centrifugal governor. Very small balls are employed, from 2-1/4 to 2-5/8 inches in diameter. These swing from a single joint at the axis of the spindle, which is the most sensitive arrangement, and make from 300 to 350 revolutions per minute, at which speed their centrifugal force lifts the counterpoise. The lower arms are jointed to the upper ones at the centres of the balls, and connect with the slide by joints about two inches apart. The counterpoise may be attached to the slide in any manner; for the sake of elegance, it is put in the form of a vase rising between the arms, its stem forming the slide. The vase is hollow and filled with lead, and weighs from 60 lbs. to 175 lbs. It moves freely on the spindle, through nearly twice the vertical distances traversed by the balls, and is capable of rising from 2-1/2 to 3 inches, before its rim will touch the arms. It is represented in the figure as lifted through about one half of its range of action. The standard is bored out of the solid, forming a long and perfect bearing for the spindle; the arms and balls are of gun metal, the joint pins of steel; every part of the governor is finished bright, except the bracket carrying the lever, and the square base of the standard, which are painted. The pulley is from 3 to 10 inches in diameter, and makes in the larger sizes about 125 revolutions, and in the smaller 230 revolutions per minute; the higher speed of the governor being got up by gearing. Mr. Porter warrants the following action in this governor, operating any regulating valve or cut-off which is in reasonably good order. The engine should be run with the stop-valve wide open, and, except the usual oiling, will require no attention from the engineer, under any circumstances, after it is started, until it is to be stopped. No increase in the pressure of steam will affect its motion perceptibly. The extreme possible variation in the speed, between that at which the regulating valve will be held wide open, and that at which it will be closed, is from 3 to 5 per cent., being least in the largest governors. This is less than 1/6 of the variation required by the average of ordinary governors, and is with difficulty detected by the senses. The entire load which the engine is capable of driving may be thrown on or off at once, and one watching the revolutions cannot tell when it is done. The governor will be sensibly affected by a variation in the motion of the engine of 1 revolution in 800. Notwithstanding this extreme sensitiveness, or rather by reason of it, it will not oscillate, but when the load is uniform will stand quite, or nearly, motionless. For the supply of the water to the boiler, in many positions, it is very convenient to have a pump unconnected with the engine. On this account it is very usual in this country to have what are called donkey pumps or engines independent of the main engines, which can be used to feed the boilers, or for supplying water for many other purposes. Fig. 62 is a longitudinal section of the Worthington Steam Pump, the first of its kind, and for many years in successful operation. The general arrangement is that of a Steam Cylinder, the piston rod of which, carried through into the water cylinder and attached directly to the water plunger, works back and forth without rotary motion, and of course without using either crank or fly wheel. [Illustration: Fig. 62.] In the figures, _a_ is the Steam Cylinder--_b_, the Steam Chest--_d_, a handle for regulating the steam valve--_f_, the starting bar _g, g_, tappets attached to the valve rod, which is moved by the contact of the arm _e_, on the piston rod with said tappets--_h_, the double-acting water plunger working through a packing ring--_o, o_, force valves--_o', o'_, suction valves. The pump piston is represented as moving from right to left, the arrows indicating the course of the water through the passages. The suction valves _o'_, on the right side, and the force valves _o_, on the left side, are show open; _x_, is an air chamber made of copper; _s_, the suction pipe terminating in a vacuum chamber; made by prolonging the suction pipe, and closing it perfectly tight at the top, the connection being made to the pump by a branch as shown; _m, m_, are hand-hole plates, affording easy access to the water valves; _n, n_, small holes through the plunger, which relieve the pressure near the end of the stroke, to give momentum to throw the valves when working at slow speed. [Illustration: Fig. 63.] Fig. 63 is a perspective view of H.R. Worthington's Duplex Steam Pump. The prominent peculiarity of this pump is its valve motion. As seen in the cut, two steam pumps are placed side by side (or end to end, if desired). Each pump, by a rock shaft connected with its piston rod, gives a constant and easy motion to the steam valve of the other. Each pump therefore gives steam to and starts its neighbor, and then finishes its own stroke, pausing an instant till its own steam valve, being opened by the other pump, allows it to make the return stroke. This combined action produces a perfectly positive valve motion without dead points, great regularity and ease of motion, and entire absence of noise or shock of any kind. Both kinds of pumps are made by Mr. Worthington, of various size according to the requirements, the duplex being used for boiler feed and for the supply of cities with water. Fig. 64 is a side elevation of the Woodward Steam Pump. The pump is direct acting. The steam and water piston being on the same rod, but momentum is obtained to throw the valves by means of a fly wheel, placed beyond the pump, and connected with the piston rod by a cross head and a yoke. The machine is simple in its construction and action, and is extensively used. Giffard's Injector, both in Europe and this country, is quite extensively used to supply the place of a pump, as independent feed for all classes of boilers. It is represented in elevation and section, figs. 65 and 66. [Illustration: Fig. 64.] [Illustration: Fig. 65.] [Illustration: Fig. 66.] _A_, steam pipe leading from the boiler. _B_, a perforated tube or cylinder, through which the steam passes into the space _b_. _C_ screwed rod for regulating the passage of steam through the annular conical space _c_, and worked by the handle _d/_. _E_, suction pipe, leading from the tank or hot well to small chamber _m_. _F_, annular conical opening or discharge pipe, the size of which is regulated by the movement of the tube or cylinder _B_. _G_, hand wheel for actuating the cylinder _B_. _H_, opening, in connection with the atmosphere, intervening between discharge pipe _F_ and the receiving pipe through which the water is forced. _I_, tube through which the water passes to the boiler. _K_, valve for preventing the return of the water from the boiler when the injector is not working. _L_, waste or overflow pipe. _M_, nut to tighten the packing rings _g_ and upper packing _i_ in cylinder _B_. _N_, lock nut to hold _M_. The pipe _A_ is connected with the steam space of the boiler at its highest part, to obtain as dry steam as possible. The passage of the steam into _A_ is controlled by a cock, as is also the feed pipe to the boiler. In working, both are opened, the steam passes through _A_ into the space _b_, and issuing through the nozzle _c_ with the pressure due to its head, and a partial vacuum by its contact with the feed water, it drives this water in connection with the jet through the pipe _F_ into the pipe _I_ in connection with the water space of the boiler. _Method of Working._--Turn the wheel so as to permit a small quantity of water to flow to the instrument. Open the steam cock connecting the apparatus with the boiler. Turn slightly the handle, which will admit a small quantity of steam to the apparatus; a partial vacuum is thus produced, causing the water to enter through the supply pipe. As soon as this happens, which can be observed at the overflow pipe, the supply of steam or water may be increased as required, up to the capacity of the instrument, regulating either by means of the wheel and handle, so as to prevent any overflow. The quantity of water delivered into the boiler, may be varied by means of the stop cocks on the steam and water pipes, without altering the handles on the injector; a graduated cock on the water supply pipe is very convenient for this purpose. The machines are manufactured by Wm. Sellers & Co. Philadelphia. As an example of Portable Steam Engines, of which there are large numbers in this country of different manufacturers, we give the representation (fig. 67) of one made by J.C. Hoadley, of Lawrence, Mass. [Illustration: Fig. 67.] In these machines, the rules and proportions of the locomotive engine are adapted to the requirements of stationary power, for all purposes under forty horse power. The leading ideas are: high velocity, high pressure, good valve motion, large fire-box, numerous and short flues, and steam blast. The characteristic features are: great strength of boiler, fully adequate to bear with safety 200. lbs. pressure per sq. in., great compactness and simplicity, large and adjustable wearing surfaces, and the entire absence of all finish, or polish, for mere show. The cylinder is placed over the centre of the boiler, at the fire-box end, so that the strain due to the engine is central to the boiler (which serves as bed plate); the starting valve is under the hand of the engineer when at the fire door; and both ends of the crank shaft are available for driving pulleys. For the sake of compactness, the cylinders are set low, by means of a depression in the boiler between the stands of the crank shaft, to admit of the play of the crank and connecting rod. All the parts are attached to the boiler, which is made of sufficient strength to bear all extra strain due to the working of the engine. They have feed water heater, force pumps, Jackson's governor and valve, belt for governor, belt pulley, turned on the face, steam gauge; everything, in short, necessary to the convenient working of a steam engine. All engines are fired up and tried before they leave the shop, and they are warranted tight, safe, and complete. A strong and convenient running gear, so arranged as to be easily attached and detached at pleasure, is furnished, if desired; forming, when separate, a useful wagon. [Illustration: Fig. 68.] Fig. 68 is a compact vertical engine, as built by R. Hoe & Co., of this city. It is intended to drive printing presses, but is adapted to any kind of work, and is especially suited to such places as require economy of space. Although the value of expansion has been called in question by some of the engineers of the United States Navy, and under an appropriation from Congress is now to be made the subject of experiment; yet, in almost all the manufactories and workshops of the United States, no matter what the form of steam engine, or the purposes to which it is applied, whether stationary, locomotive, or marine, some form of cut-off, by which expansion of the steam can be availed of, is considered indispensable. Many varieties are in use, but those engines are most popular in which the cut-off is applied directly to the valves on the cylinder, opening them quickly and shutting off almost instantly, avoiding all wire drawing of the steam at the ports, and regulating the speed of the engine promptly. Of this class of engines, those manufactured by the Corliss Steam Engine Company, of Providence, R.I., are perhaps the widest known, not only for their extensive introduction, but also from having, by a long and successful litigation, established the claims of the patentee, Mr. George H. Corliss. [Illustration: Fig. 70.] Fig. 70 is a section of the cylinder and valve chests of a horizontal Corliss engine. _S_ is the steam connection, and _E_ the exhaust; there are two distinct sets of valves, the steam _s, s'_, and the exhaust _e, e'_, operated independently of each other. In their construction the valves may be considered cylindrical plugs, of which portions near the ports are cut away to admit the steam and reduce the bearing surface; the valves are fitted on the lathe and the seats by boring. The motion given to the valves is rocking, but it will be observed that the valves are not firmly connected to the rocking shaft or cylinder; in the figure the valves are shown shade lined, and the shaft or stem plain; in this way the valves are not affected by the packing of the valve stem, but always rest upon the face of the ports. In the figure the piston is just about to commence its outstroke, the movement of the steam is supposed to be represented by the arrows; the inner steam valve _s_, and the outer exhaust _e'_, are just beginning to open. It will be observed that the outer steam _s'_ is fully closed, whilst the inner exhaust valve _e_ is but barely so, showing that there has been a cut-off on the steam valve, but no lead to the exhaust, that it was left fully open till the completion of the stroke. [Illustration: Fig. 71.] Fig. 71 is a side elevation of the cylinder, with the valve connections with the governor. _S_ is the steam pipe; _s, s'_ handles to the steam valves, and _e, e'_ to the exhaust valves, shown in dotted line in fig. 70. The handles to the exhaust valves are connected directly to a rocking plate _R_, to which motion is given by a connection _x_, with an eccentric on the engine shaft. When once set, therefore the movement of the exhaust valves is constant, and they will always be opened and closed at the same point of the stroke. Connected with the rocking plate _R_, and on opposite sides of its centre, the same as the exhaust valve connections, there are two levers, vibrating on a centre _c_, of which one only is shown, as it covers the other; to the upper ends of these levers pawls are attached, one end of which rests on the stems or rods connected with the handles _s, s'_, of the steam valves; on these stems there are notches against which the pawls strike, and as the levers vibrate inward they push back the stems and thereby open the valves, and this continues for the whole length of the inward motion of the levers, or till the outer extremities of the pawls come in contact with the end of the short lever _l_, which, pushing down the outer end of the pawls, relieves the stems at the other ends, and the valve stem returns to its place through the force of springs attached to the outer extremities of the valve stems _a_, are cylindrical guides to the valve stems, at the inner extremities of which are air cushions. The lever _l_ is connected directly with the governor. As the balls rise, they depress the extremity, which comes in contact with the pawls sooner, and thereby shut the valves earlier; and on the contrary when the balls are depressed, the valves remain open longer; as the pawls come in contact with the stems always at one point, the steam valves open constantly, but are closed at any point by the relief of the pawls, according to the speed of the governor. Fig. 71 represents, partly in section and partly in plan, the cylinder, steam chests, valves, &c., of one of the Woodruff & Beach high pressure Engines, Wright's patent. Fig. 72 represents, in elevation, the cam shaft, to the upper end of which, not shown in the drawing, is attached the ordinary centrifugal governor. The cylinder, steam chests, valves, &c., being similar to those of other engines, need no special notice; but the cam for opening and closing the steam valves, fig. 72, requires particular attention, as it embodies a beautiful and simple device for cutting off the steam with certainty at any part of the stroke, the motion being produced automatically by the action of the governor on this cam, throwing it more or less out of centre with the spindle of the governor, as the rotation of the balls is less or more rapid, the eccentricity of the cam determining the amount of steam admitted to the working cylinder of the engine. To produce this effect the cam is made as follows: _C_ is a hollow cylinder or shell, with a part of one end formed into a cam proper. Throughout the whole length of this piece, upon the inside, there is a spiral groove cut to receive one end of a feather, by which its pitch or eccentricity is regulated. _C'_ is also a hollow cylinder or shell, of the same length and diameter as _C_, with a similar spiral groove cut on the inside, the outside being perfectly smooth and plain, upon which the toe (_t_) for closing the valves is fastened. The inside piece consists of two hubs _D, D'_, eccentric with each other, and made in one piece, _D_ being turned to exactly fit the inside of the shell _C_, and _D'_ to fit the shell _C'_, the hub _D'_ having a socket (_c_) into which the spindle (_s_) of the governor is screwed; the end (_d_) of the hub _D_ forming a journal or bearing, with a bevel wheel on its extremity to convey motion from the crank-shaft gearing to the governor and cut-off. There is a hole throughout the length of the inside hubs _D_ and _D'_, which is continued through the spindle of the governor, and contains the rod (_r_) that connects the cam with the governor. This hole is eccentric to the outside surface of the hub _D_, as well as to the shell _C_, and concentric with the hub _D'_ and shell _C'_, and with the governor rod (_r_). The shell _C_ and hub _D_, and shell _C'_ and hub _D'_, are connected together by feathers; one piece of each feather is of a spiral form, and the other a straight or rectangular piece, the two being connected together by a stub on the rectangular piece, which fits into a hole or bearing in the other or spiral piece, so that the latter can turn on the stub and accommodate itself to the groove in which it has to work. The spiral part of each feather works in the spiral groove on the inside of its corresponding shell _C_ and _C'_ respectively, and the rectangular pieces work in a straight groove cut in the hubs _D_ and _D'_, the inner parts of the rectangular pieces being fastened to the governor rod (_r_), so that the feathers are permanently connected with the governor. The shell _C'_ revolves inside of two yokes (_y_) and (_y'_), one attached to each steam-valve toe, (_a_) and (_a'_) respectively. On the inside of each yoke, and opposite to its valve-toe, is a raised piece, against which the closing piece (_t_) on the shell (_C'_) acts to close the valves. This shell (_C'_), as before noticed, has a spiral groove on its inside, similar in all respects to that in the cam-shell (_C_); and being acted upon in the same manner and through the same rod by the governor, it is evident that the closing piece (_t_) on its outside will always hold the same relation to the opening toe on the lower or cam-shell (_C_); and whatever alteration is made in the one, a corresponding alteration takes place in the other, thereby insuring the closing of the valves at the proper time at every point of the variation of the cut-off. When the several pieces above described are put together, the apparatus for opening and closing the valves and producing the cut-off is complete, as shown in fig. 72, and it operates as follows: [Illustration: Fig. 71.] [Illustration: Fig. 72.] Motion is communicated by gearing from the crank-shaft to the bevel wheel on the piece (_d_) on the end of the hub _D_, and is communicated to the spindle of the governor, which is screwed into the socket on _D'_. As the balls rise or fall, through change of centrifugal force due to the variation in the speed of rotation, they raise or depress the governor-rod, which passes through the spindle and the hubs _D'_ and _D_, and is attached to the feathers, thereby raising or depressing the feathers, which, acting on their respective spiral grooves, instantly alters the lift of the cam on the shell (_C_), and brings the closing toe (_t_) on the shell (_C'_) into proper position for closing, and so regulates the amount of steam admitted to the cylinder. [Illustration: Fig. 71.] Consequently, any speed may be selected at which the load of the engine is to move, and any variation from that will be instantly felt by the governor, and corrected by this simple and beautiful device. There is no jar in the working of the parts; the feathers move noiselessly in their grooves; the governor rod moves up and down through the spindle and the hubs _D_ and _D'_, and can be regulated by hand to give any required opening of the steam ports to suit the work to be done. Any change in the amount of work will then alter the speed of the engine, and so affect the governor and cam, as before said. It is unnecessary to insist on the great economy attained by using steam with a well-regulated cut-off, for practical men know now that the essential points of excellence in the steam engine are a good boiler, which generates the greatest quantity of steam for the least consumption of fuel; and, secondly, a reliable cut-off, which uses the steam to the best advantage, by admitting the proper quantity for the work required. STEAM FIRE ENGINES.--Portable engines for the extinguishment of fires, are an American invention, and to Messrs. A.B. & E. Latta, of Cincinnati, working on the right principles, is due the credit which they claim in their circular, as follows: "We claim to be the _original_ and first _projectors_ of the _first successful steam fire engine_ in the world's history. There have been many attempts at making a machine of such construction as would answer to extinguish fires; but none of them proved to be available in a sufficiently short space of time to warrant their use as a fire apparatus. We hold that a steam fire engine should be of such nature as to be brought into requisition in as short a space of time as is necessary to get the machine on the ground, and the hose laid and ready to work: that is, supposing the fire to be within one square of the place where the steamer is located. The object in locating a machine at any point is to protect that immediate vicinity; and it is therefore absolutely necessary to have it available in the shortest space of time, and that with unerring certainty. We think that reliability is of the greatest importance to the protection of a city from fire, as everything is dependent on the _working_ of such apparatus in time; and for this reason no expense should be spared on this kind of machinery." Fig. 73 is a representation of one of the Messrs. Latta's fire engines, of which there are many of different classes, according to the requirements; they say that they can furnish engines as low as $1,000, and have made some for $10,000. The first peculiar feature of this engine is the boiler; it differs entirely from all boilers now in use. [Illustration: Fig. 73.] The fire box or furnace is simply a square box or furnace of any required dimensions; it is nothing more than a water space surrounding the fire, stay-bolted as all water spaces are. It is made of boiler plate in the usual manner. The water space extends only 2/3 of the height, the balance being a single sheet. The bottom of this fire box is crossed by grate bars to support the fuel; in its rear side are fire doors, inserted for firing. The internal arrangements of the boiler are composed of a large number of tubes, lying across in a horizontal position, put together in sections with return bends resembling the coils for heating buildings. These coils are of small pipe (say one inch in diameter), and as numerous as may be necessary. They give the required amount of steam. They are secured to wrought-iron plates at each end by rivets. These plates lie close to the box, and are secured to it, top and bottom. These tubes are wrought iron, firmly screwed into the bends, so as to prevent any possible breaking. The box has a hole through both sheets, in the same manner as a hollow stay-bolt, through which the coil pipe passes, having no connection with the box. After passing into the box it divides into two pipes, then subdivides into four, and so on, until its numbers equal the number of coils in the box, and to which each limb is attached. The upper ends of these coils are the same in number, and are carried through at the top or nearly the top of the box. They then run down outside to the steam chamber, or rather water space, as the box is both steam chamber and water space. These pipes empty their contents into the box, steam and water, as it may come, all together. It will be observed that these coils of tube are sufficiently separated to allow the fire to pass between them freely, and cover their whole surface. The mode of operation of this boiler is this: The fire box is filled 2/3 full of water. The coils are dry at starting; the space for fuel being filled with good wood, the fire is lighted, and in a few moments the engineer moves his hand pump, which takes its water from the box to which it is attached, and forces it through the coils. By this means steam is generated in from 3 to 5 minutes, so as to start the engine. It will be seen that the water performs a complete circuit; it is taken from the box and passed through the coils; what is steam remains in the steam chamber, and what is not (if any) drops back into the box from where it started. Hence it will be seen that a large surface is exposed to a small quantity of water, and in a way that it is entirely controllable. All the engineer has to do to surcharge his steam, is to reduce the speed of the pump (which is independent of the main engine). By raising the heat and quantity of water, any degree of elasticity can be given to the steam, and that, too, with the least amount of waste heat in giving a natural draft. Hence the great economy of this boiler. The next feature of this engine is, it has no wood work about it to perish with the heat and roughness of the streets. All the wheels are wrought iron; and, as yet, these are the only ones that have stood a steam fire engine. The frame is wrought iron; truck, on which the front wheel is hung, wrought iron. The axles are cast steel. The engine and pump is a double-acting piston pump direct, without any rotary motion; with a perfect balance valve, it is balanced at all times, and hence the engine remains quiet without blocking, when at work. The engine is mounted on three wheels, which enables it to be turned in a very short space. Many engines have been constructed by the Messrs. Latta for the fire companies, of different cities, and have been in successful competition with other engines; the farthest throw ever made by one of their first-class engines was 310 feet from a 1-5/8 inch nozzle; steaming time, starting from cold water, 3-1/2 minutes. [Illustration: Fig. 74 AMOSKEAG STEAM FIRE ENGINE.] Fig. 74 is a representation of one class of steam fire engine, as built by the Amoskeag Manufacturing Company, at Manchester, N.H. The boiler is an upright tubular boiler, of a peculiar construction, the patent right to which is vested in the Amoskeag Manufacturing Company. This boiler is very simple in its combination, and for safety, strength, durability, and capacity for generating steam is unsurpassed. No fan or artificial blower is ever used or needed, the natural draft of the boiler being always sufficient. Starting with cold water in the boiler, a working head of steam can be generated in _less than five minutes_ from the time of kindling the fire. The engine "Amoskeag," owned by the city of Manchester, has played two streams in _three minutes and forty seconds_ after touching the match, at the same time drawing her own water. The boilers are made and proved so as to be safely run at a steam pressure of 140 to 150 lbs. to the square inch; but the engines are constructed so as to give the best streams at a pressure of about 100 lbs. to the square inch, and for service at fires a steam pressure of about 60 lbs. to the square inch is all that is required. The various styles of engine are all _vertical_ in their action, and in all the pumps and steam cylinders are firmly and directly fastened to the boiler, the steam cylinders being attached directly to the steam dome. This arrangement obviates the necessity of carrying steam to the cylinders through pipes of considerable length, and the machine has very little vibratory motion when in operation--so little that it is not necessary to block its wheels to keep it in its place, or to take the weight off the springs before commencing work. The pumps are placed on the engines as near the ground as they can be with safety, and are arranged so as to attach the suction and leading hose to either or both sides of the machine, as may be most convenient or desirable, so that less difficulty will be found in placing an engine for work, and when required to draw its own water, it has only to draw it the shortest possible distance. Each engine has two "feed pumps" for supplying the boiler, and also a connection between the main forcing pumps and the boiler, so that it can be supplied from that source if desirable. The tank which carries the water for supplying the boiler is so placed that the water in it is always above the "feed pumps," an advantage that insures the almost certain working of these pumps. These pumps are of brass, the best locomotive pattern, and one of them running with the engine, when at work, furnishes an ample supply of water to the boiler. [Illustration: Fig. 75.] The engines are exceedingly portable; they can be turned about or placed for service in as contracted a space as any hand engine, and two good horses will draw a first-class engine with the greatest ease, carrying at the same time water for the boiler, a supply of fuel sufficient to run the engine two hours, the driver, the engineer, and the fireman. Fig. 75 is a representation of the class of steam fire engine built by Silsbee, Mynderse & Co., Seneca Falls, N. Y. under Holly's patent. The boiler is vertical, with vertical water tubes passing directly through the fire. These tubes are closed at the bottom and open at the top, where they pass through a water-tight plate, and communicate with the water in the boiler. The arrangement of the tubes causes a constant current, the water rising on the outside of the tubes as they are heated, and its place being supplied by a current flowing downward through the tube to the boiler. The smoke and flame pass among the tubes up through flues. Both engine and pump are rotary, and of the same type. They consist essentially of two elliptical rotary pistons, cogged and working into one another in an air-tight case. The pistons fit close to the inside of the case, and gear into each on the line of their conjugate diameters. The action is somewhat similar to the old-fashioned rotary pump, consisting of two cog wheels in gear with, each other, the spaces at the side of the case being filled with water, which at the centre are occupied by the teeth in gear. In Holly's pump, instead of uniform teeth, and depending on the fit of the teeth with the side of the case and with each other for the packing, there are two large teeth in each piston opposite each other, which have slide pistons, and intermediate with these large teeth are small cogs, which continue the motion of the rotary pistons. The machine works very smoothly, and performs the work necessary, in ordinary service, under a pressure of 50 to 60 lbs. There are many other makers of fire engines in this country; but sufficient examples are given to illustrate the class; so successful have they been, that they are fast superseding hand engines, even in the smaller cities. Under a paid department, the following is, in the city of Boston, Mass., the comparative cost of running the two kinds of engines, viz.: STEAM FIRE ENGINE. 1 engineer........................................... $720 00 1 fireman............................................ 600 00 1 driver............................................. 600 00 1 foreman of hose.................................... 150 00 8 hosemen, at $125 each.............................. 375 00 -- -------- 7 men................................................ $2,445 00 Keeping of 2 horses.................................. 315 00 -------- Total......................................... $2,760 00 HAND ENGINE. 1 foreman............................................ $150 00 1 assistant foreman.................................. 125 00 1 clerk.............................................. 125 00 1 steward............................................ 125 00 3 leading hosemen, at $125 each...................... 375 00 33 men, at $100 each................................. 3,300 00 -- --------- 40 men............................................... $4,200 00 Here the engineer, fireman, and driver are constantly employed, the hosemen have other employment in the neighborhood, but all the company sleep in the engine house. In the city of Manchester, N.H., a steam fire engine company is composed of fourteen men, all told, one of whom, acting as driver and steward, is constantly employed, remaining at the engine house with a pair of horses always ready to run out with the engine in case of an alarm of fire. The other members of the company have other employments, and turn out only on an alarm of fire. STEAM FIRE ENGINES. "Amoskcag," Expenditures..................... $864 32 "Fire King," " ..................... 855 78 "E.W. Harrington," " ..................... 496 09 The above expense includes pay of members, team expenses, cost of gas, wood, coal, and all necessities incident to service. The "E.W. Harrington" is a second-class engine, stationed in the outskirts of the city, and was run cheaper from the fact that no horses were kept for it by the city. A first-class hand-engine company is allowed to number, all told, fifty men, and the members of the company are paid as follows: FIRST-CLASS HAND-ENGINE COMPANY. 1 foreman.......................................... $35 00 1 assistant foreman............................... 28 00 1 clerk........................................... 28 00 1 steward........................................ 68 00 46 men, at $18 each................................ 828 00 -------- 50 men. Total.............................. $987 00 By this it will be seen, that in a city like Manchester, with from twenty to twenty-five thousand inhabitants, a first-class steam fire engine can be run at an expense not to exceed that of a first-class hand engine, while in service it will do at least _four times_ the work. The cost of repairs is found by experience to be no greater on the steam fire engines than on hand engines. The Excavator, fig. 76, is the invention of the late Mr. Otis, an application of the spoon dredging machine of the docks to railway purposes, with very important modifications. The machine consists of a strong truck, _A_, _A_, mounted on railway wheels, on which is placed the boiler _C_, the crane _E_, and the requisite gearing. The excavator or shovel, _D_, is a box of wrought iron, with strong points in front to act as picks in loosening the earth, and its bottom hung by a hinge at _d_, so that, by detaching a catch, it may fly open and discharge the material raised. To operate the machine, suppose the shovel _D_ to be in the position shown in the cut; it is lowered by the chains _o_, _o_, and thrown forward or backward, if necessary, by the drum _B_, and handle _S_, till the picks in the front of the shovel are brought in proper contact with the face of the cut; motion forward is now given to the shovel by the drum _B_ and handle _S_, and at the same time it is raised by the chains _o_, _o_. These two motions can be so adjusted to each other, as to give movement to the shovel to enable it to loosen and scrape up a shovelful of earth. The handle _S_ is now left free, and the shovel _D_ is raised vertically by the chains _o_, _o_. The crane is now turned round, till the shovel comes over a rail car on a side track; the bottom of the shovel is opened, and the dirt deposited in the car. All these motions are performed by the aid of a steam engine, and are controlled by a man who stands on a platform at _f_. [Illustration: Fig 76.] 692. _Q._--Having now described the most usual and approved forms of engines applicable to numerous miscellaneous purposes for which a moderate amount of steam power is required, will you briefly recapitulate what amount of work of different kinds an engine of a given power will perform, so that any one desiring to employ an engine to perform a given amount of work, will be able to tell what the power of such engine should be? _A._--It will of course be impossible to recapitulate all the purposes to which engines are applicable, or to specify for every case the amount of power necessary for the accomplishment of a given amount of work; but some examples may be given which will be applicable to the bulk of the cases occurring in practice. 693. _Q._--Beginning, then, with the power necessary for threshing,--a 4 horse power engine, with cylinder 6 inches diameter, pressure of steam 45 lbs., per square inch, and making 140 revolutions per minute, will thresh out 40 quarters of wheat in 10 hours with a consumption of 3 cwt. of coals. _A._--Although this may be done, it is probably too much to say that it can be done on an average, and about three fourths of a quarter of wheat per horse power would probably be a nearer average. The amount of power consumed varies with the yield. Messrs. Barrett, Exall, and Andrewes give the following table as illustrative of the work done, and the fuel consumed by their portable engines; but this must be regarded as a maximum performance:-- Number of | Weight of | Quarters of | Quantity of | Quantity of Horse Power.| Engine. | Corn thrashed| Coals consumed| Water required | | in 10 Hours. | in 10 Hours. | for 10 Hours | | | | in Gallons. ------------|-----------|--------------|---------------|--------------- |Tons. Cwts.| | Cwts. | 4 | 2 0 | 40 | 3 | 360 5 | 2 5 | 50 | 4 | 380 6 | 2 10 | 60 | 5 | 460 7 | 2 15 | 70 | 6 | 540 8 | 3 0 | 80 | 7 | 620 10 | 3 10 | 100 | 9 | 780 ----------------------------------------------------------------------- 694. _Q._--In speaking of horses power, I suppose you mean indicator horse power? _A._--Yes; or rather the dynamometer horse power, which is the same, barring the friction of the engine. At the shows of the Royal Agricultural Society, the power actually exerted by the different engines is ascertained by the application of a friction wheel or dynamometer. 695. _Q._--Can you give any other examples of the power necessary for grinding corn? _A._--An engine exerting 23-1/3 horses power by the indicator works two pairs of flour stones of 4 feet 8 inches diameter, two pairs of stones grinding oatmeal of 4 feet 8 inches diameter, one dressing machine, one pair of fanners, one dust screen, and one sifting machine. One of the flour stones makes 85, and the other 90 revolutions in the minute. One of the oatmeal stones makes 120, and the other 140 revolutions in the minute. To take another case:--An engine exerting 26-1/2 indicator horses power works two pairs of flour stones, one dressing machine, two pairs of stones grinding oatmeal, and one pair of shelling stones. The flour stones, one pair of the oatmeal stones, and shelling stones, are 4 feet 8 inches diameter. The diameter of the other pair of oatmeal stones is 3 feet 8 inches. The length of the cylinder of the dressing machine is 7 feet 6 inches. The flour stones make 87 revolutions in the minute, and the larger oatmeal stone 111 revolutions, but the smaller oatmeal stone and the shelling stone revolve faster than this. At the time the indicator diagram was taken, each pair of flour stones was grinding at the rate of 5 bushels an hour; each pair of oatmeal stones about 24 bushels an hour; and the shelling stones were shelling at the rate of about 54 bushels an hour. The fanners and screen were also in operation. 696. _Q._--Have you any other case to enumerate? _A._--I may mention one in which the power of the same engine was increased by giving it a larger supply of steam. The engine when working with 8.65 horses power, gives motion to one pair of oatmeal stones of 4 feet 6 inches diameter, and one pair of flour stones 4 feet 8 inches diameter. The oatmeal stone makes 100 revolutions in the minute, and the flour stone 89. The oatmeal stones grind about 36 bushels in the hour, and the flour stones 5 bushels in the hour. The engine when working to 12 horses power drives one pair of flour stones, 4 feet 8 inches diameter, at 89 revolutions per minute and one pair of stones of the same diameter at 105 revolutions, grinding beans for cattle. The flour mill stones with this proportion of power, being more largely fed, ground 6 bushels per hour, and the other stones also ground 6 bushels per hour. When the power was increased to 18 horses, and the engine was burdened in addition with a dressing machine having a cylinder of 19 inches diameter, the speed of the flour stone fell to 85, and of the beans stone to 100 revolutions per minute, and the yield was also reduced. The dressing machine dressed 24 bushels per hour. 697. _Q._--What is the power necessary to work a sugar mill such as is used to press the juice from canes in the West Indies? _A._--Twenty horses power will work a sugar mill having rollers about 5 feet long and 28 inches diameter; the rollers making 2-1/3 turns in a minute. If the rollers be 26 inches diameter and 4-1/2 feet long, 18 horses power will suffice to work them at the same speed, and 16 horses power if the length be reduced to 3 feet 8 inches. 12 horses power will be required to work a sugar mill with rollers 24 inches diameter and 4 feet 2 inches long; and 10 horses power will suffice if the rollers be 3 feet 10 inches long and 23 inches diameter. The speed of the surface of sugar mill rollers should not be greater than 16 feet per minute, to allow time for the canes to part with their juice. In the old mills the speed was invariably too great. The quantity of juice expressed will not be increased by increasing the speed of the rollers, but more of the juice will pass away in the begass or woody refuse of the cane. 698. _Q._--What is the amount of power necessary to drive cotton mills? _A._--An indicator or actual horse power will drive 305 hand mule spindles, with proportion of preparing machinery for the same; or 230 self-acting mule spindles with preparation; or 104 throstle spindles with preparation; or 10-1/2 power looms with common sizing. The throstles referred to are the common throstles spinning 34's twist for power loom weaving, and the spindles make 4000 turns per minute. The self-acting mules are Robert's, about one half spinning 36's weft, and spindles revolving 4800 turns per minute; and the other half spinning 36's twist, with the spindles revolving 5200 times per minute. Half the hand mules were spinning 36's weft, at 4700 revolutions, and the other half 36's twist at 5000 revolutions per minute. The average breadth of the looms was 37 inches, weaving 37 inch cloth, making 123 picks per minute,--all common calicoes about 60 reed, Stockport count, and 68 picks to the inch. To take another example in the case of a mill for twisting cotton yarn into thread:--In this mill there are 27 frames with 96 common throstle spindles in each, making in all 2592 spindles. The spindles turn 2200 times in a minute; the bobbins are 1-7/8 inches diameter, and the part which holds the thread is 2-3/16 inches long. In addition to the twisting frames the steam engine works 4 turning lathes, 3 polishing lathes, 2 American machines for turning small bobbins, two circular saws, one of 22 and the other of 14 inches diameter, and 24 bobbin heads or machines for filling the bobbins with finished thread. The power required to drive the whole of this machinery is 28-1/2 horses. When all the machinery except the spindles is thrown off, the power required is 21 horses, so that 2592, the total number of spindles, divided by 21, the total power, is the number of twisting spindles worked by each actual horse power. The number is 122.84. 699. _Q._--What work will be done by a given engine in sawing timber, pressing cotton, blowing furnaces, driving piles, and dredging earth out of rivers? _A._--A high pressure cylinder 10 inches diameter, 4 feet stroke, making 35 revolutions with steam of 90 to 100 lbs. on the square inch, supplied by three cylindrical boilers 30 inches diameter and 20 feet long, works two vertical saws of 34 inches stroke, which are capable of cutting 30 feet of yellow pine, 18 inches deep, in the minute. A high pressure cylinder 14 inches diameter and 4 feet stroke, making 60 strokes per minute with steam of 40 lbs. on the square inch, supplied by three cylindrical boilers without flues, 30 inches diameter and 26 feet long, with 32 square feet of grate surface, works four cotton presses geared 6 to 1, with two screws in each, of 7-1/2 inches diameter and 1-5/8 pitch, which presses will screw 1000 bales of cotton in the twelve hours. Also one high pressure cylinder of 10 inches diameter and 3 feet stroke, making 45 to 60 revolutions per minute, with steam of 45 to 50 lbs. per square inch, with two hydraulic presses having 13 inch rams of 41 feet stroke, and force pumps 2 inches diameter and 6 inches stroke, presses 30 bales of cotton per hour. One condensing engine with cylinder 56 inches diameter, 10 feet stroke, and making 15 strokes per minute with steam of 60 lbs. pressure per square inch, cut off at 1/4th of the stroke, supplied by six boilers, each 5 feet diameter, and 24 feet long, with a 22-inch double-return flue in each, and 198 square feet of fire grate, works a blast cylinder of 126 inches diameter, and 10 feet stroke, at 15 strokes per minute. The pressure of the blast is 4 to 5 lbs. per square inch; the area of pipes 2300 square inches, and the engine blows four furnaces of 14 feet diameter, each making 100 tons of pig iron per week. Two high pressure cylinders, each of 6 inches diameter and 18 inches stroke, making 60 to 80 strokes per minute, with steam of 60 Lbs. per square inch, lift two rams, each weighing 1000 lbs., five times in a minute, the leaders for the lift being 24 feet long. One high pressure cylinder of 12 inches diameter and 5 feet stroke, making 20 strokes per minute, with steam of 60 to 70 lbs. pressure per square inch, lifts 6 buckets full of dredging per minute from a depth of 30 feet below the water, or lifts 10 buckets full of mud per minute from a depth of 18 feet below the water. CHAPTER XII. MANUFACTURE AND MANAGEMENT OF STEAM ENGINES. CONSTRUCTION OF ENGINES. 700. _Q._--What are the qualities which should be possessed by the iron of which the cylinder of steam engines are made? _A._--The general ambition in making cylinders is to make them sound and hard; but it is expedient also to make them tough, so as to approach as nearly as possible to the state of malleable iron. This may be done by mixing in the furnace as many different kinds of iron as possible; and it may be set down as a general rule in iron founding, that the greater the number of the kinds of metal entering into the composition of any casting, the denser and tougher it will be. The constituent atoms of the different kinds of iron appear to be of different sizes, and the mixture of different kinds maintains the toughness, while it adds to the density and cohesive power. Hot blast iron was at one time generally believed to be weaker than cold blast iron, but it is now questioned whether it is not the stronger of the two. The cohesive strength of unmixed iron is not in proportion to its specific gravity, and its elasticity and power to resist shocks appear to become greater as the specific gravity becomes less. Nos. 3 and 4 are the strongest irons. In most cases, iron melted in a cupola is not so strong as when remelted in an air furnace, and when run into green sand it is not reckoned so strong as when run into dry sand, or loam. The quality of the fuel, and even the state of the weather, exerts an influence on the quality of the iron: smelting furnaces, on the cold blast principle, have long been known to yield better iron in winter than in summer, probably from the existence of less moisture in the air; and it would probably be found to accomplish an improvement in the quality of the iron if the blast were made to pass through a vessel containing muriate of lime, by which the moisture of the air would be extracted. The expense of such a preparation would not be considerable, as, by subsequent evaporation, the salt might be used over and over again for the same purpose. 701. _Q._--Will you explain the process of casting cylinders? _A._--The mould into which the metal is poured is built up of bricks and loam, the loam being clay and sand ground together in a mill, with the addition of a little horse-dung to give it a fibrous structure and prevent cracks. The loam board, by which the circle of the cylinder is to be swept, is attached to an upright iron bar, at the distance of the radius of the cylinder, and a cylindrical shell of brick is built up, which is plastered on the inside with loam, and made quite smooth by traversing the perpendicular loam board round it. A core is then formed in a similar manner, but so much smaller as to leave a space between the shell and the core equal to the thickness of the cylinder, and into this space the melted metal is poured. Whatever nozzles or projections are required upon the cylinder, must be formed by means of wooden patterns, which are built into the shell, and subsequently withdrawn; but where a number of cylinders of the same kind are required, it is advisable to make these patterns of iron, which will not be liable to warp or twist while the loam is being dried. Before the iron is cast into the mould, the interior of the mould must be covered with finely powdered charcoal--or blackening, as it is technically termed; and the secret of making finely skinned castings lies in using plenty of blackening. In loam and dry sand castings the charcoal should be mixed with thick clay water, and applied until it is an eighth of an inch thick, or more; the surface should be then very carefully smoothed or sleeked, and if the metal has been judiciously mixed, and the mould thoroughly dried, the casting is sure to be a fine one. Dry sand and loam castings should be, as much as possible, made in boxes; the moulds may thereby be more rapidly and more effectually dried, and better castings will be got with a less expense. 702. _Q._--Will you explain the next operation which a cylinder undergoes? _A._--The next stage is the boring; and in boring cylinders of 74 inches diameter, the boring bar must move so as to make one revolution in about 4-1/2 minutes, at which speed the cutters will move at the rate of about 5 feet per minute. In boring brass, the speed must be slower; the common rate at which the tool moves in boring brass air pumps is about 3 feet per minute. If this speed be materially exceeded the tool will be spoiled, and the pump made taper. The speed proper for boring a cylinder will answer for boring the brass air pump of the same engine. A brass air pump of 36-1/2 inches diameter requires the bar to make one turn in about three minutes, which is also the speed proper for a cylinder 60 inches in diameter. To bore a brass air pump 36-1/2 inches in diameter requires a week, an iron one requires 48 hours, and a copper one 24 hours. In turning a malleable iron shaft 12-3/4 inches in diameter, the shaft should make about five turns per minute, which is equivalent to a speed in the tool of about 16 feet per minute; but this speed may be exceeded if soap and water be plentifully run on the point of the tool. A boring mill, of which the speed may be varied from one turn in six minutes to twenty-five turns in one minute, will be suitable for all ordinary wants that can occur in practice. 703. _Q._--Are there any precautions necessary to be observed in order that the boring may be truly effected? _A._--In fixing a cylinder into the boring mill, great care must be taken that it is not screwed down unequally; and indeed it will be impossible to bore a large cylinder in a horizontal mill without being oval, unless the cylinder be carefully gauged when standing on end, and be set up by screws when laid in the mill until it again assumes its original form. A large cylinder will inevitably become oval if laid upon its side; and if while under the tension due to its own weight it be bored round, it will become oval again when set upon end. If the bottom be cast in, the cylinder will be probably found to be round at one end and oval at the other, unless a vertical boring mill be employed, or the precautions here suggested be adopted. 704. _Q._--Does the boring tool make the cylinder sufficiently smooth for the reception of the piston? _A._--Many engine makers give no other finish to their cylinders; but Messrs. Penn grind their cylinders after they are bored, by laying them on their side, and rubbing a piece of lead, with a cross iron handle like that of a rolling stone, and smeared with emery and oil, backward and forward-- the cylinder being gradually turned round so as to subject every part successively to the operation. The lead by which this grinding is accomplished is cast in the Cylinder, whereby it is formed of the right curve; but the part of the cylinder in which it is cast should be previously heated by a hot iron, else the metal may be cracked by the sudden heat. 705. _Q._--How are the parts of a piston fitted together so as to be perfectly steam tight? _A._--The old practice was to depend chiefly upon grinding as the means of making the rings tight upon the piston or upon one another; but scraping is now chiefly relied on. Some makers, however, finish their steam surfaces by grinding them with powdered Turkey stone and oil. A slight grinding, or polishing, with powdered Turkey stone and oil, appears to be expedient in ordinary cases, and may be conveniently accomplished by setting the piston on a revolving table, and holding the ring stationary by a cross piece of wood while the table turns round. Pieces of wood may be interposed between the ring and the body of the piston, to keep the ring nearly in its right position; but these pieces of wood should be fitted so loosely as to give some side play, else the disposition would arise to wear the flange of the piston into a groove. 706. _Q._--What kind of tool is used for finishing surfaces by scraping? _A._--A flat file bent, and sharpened at the end, makes an eligible scraper for the first stages; or a flat file sharpened at the end and used like a chisel for wood. A three-cornered file, sharpened at all the corners, is the best instrument for finishing the operation. The scraping tool should be of the best steel, and should be carefully sharpened at short intervals on a Turkey stone, so as to maintain a fine edge. 707. _Q._--Will you explain the method of fitting together the valve and cylinder faces? _A._--Both faces must first be planed, then filed according to the indications of a metallic straight edge, and subsequently of a thick metallic face plate, and finally scraped very carefully until the face plate bears equally all over the surface. In planing any surface, the catches which retain the surface on the planing machine should be relaxed previously to the last cut, to obviate distortion from springing. To ascertain, whether the face plate bears equally, smear it over with a little red ochre and oil, and move the face plate slightly, which will fix the color upon the prominent points. This operation is to be repeated frequently; and as the work advances, the quantity of coloring matter is to be diminished, until finally it is spread over the face plate in a thin film, which only dims the brightness of the plate. The surfaces at this stage must be rubbed firmly together to make the points of contact visible, and the higher points will become slightly clouded, while the other parts are left more or less in shade. If too small a quantity of coloring matter be used at first, it will be difficult to form a just conception of the general state of the surface, as the prominent points will alone be indicated, whereas the use of a large quantity of coloring matter in the latter stages would destroy the delicacy of the test the face plate affords. The number of bearing points which it is desirable to establish on the surface of the work, depends on the use to which the surface is to be applied; but whether it is to be finished with great elaboration, or otherwise, the bearing points should be distributed equally over the surface. Face plates, or planometers, as they are sometimes termed, are supplied by most of the makers of engineering tools. Every factory should be abundantly supplied with them, and also with steel straight edges; and there should be a master face plate, and a master straight edge, for the sole purpose of testing, from time to time, the accuracy of those in use. 708. _Q._--Is the operation of surfacing, which you have described, necessary in the case of all slide valves? _A._--Yes; and in fitting the faces of a D valve, great care must, in addition, be taken that the valve is not made conical; for unless the back be exactly parallel with the face, it will be impossible to keep the packing from being rapidly cut away. When the valve is laid upon the face plate, the back must be made quite fair along the whole length, by draw filing, according to the indications of a straight edge; and the distance from the face to the extreme height of the back must be made identical at each extremity. 709. _Q._--When you described the operation of boring the cylinder, you stated that the cylinder, when laid upon its side, became oval; will not this change of figure distort the cylinder face? _A._--It is not only in the boring of the cylinder that it is necessary to be careful that there is no change of figure, for it will be impossible to face the valves truly in the case of large cylinders, unless the cylinder be placed on end, or internal props be introduced to prevent the collapse due to the cylinder's weight. It may be added, that the change of figure is not instantaneous, but becomes greater after some continuance of the strain than it was at first, so that in gauging a cylinder to ascertain the difference of diameter when it is placed on its side, it should have lain some days upon its side to ensure the accuracy of the operation. 710. _Q._--How is any flaw in the valve or cylinder face remedied? _A._--Should a hole occur either in the valve, in the cylinder, or any other part where the surface requires to be smooth, it may be plugged up with a piece of cast iron, as nearly as possible of the same texture. Bore out the faulty part, and afterward widen the hole with an eccentric drill, so that it will be of the least diameter at the mouth. The hole may go more than half through the iron: fit then a plug of cast iron roughly by filing, and hammer it into the hole, whereby the plug will become riveted in it, and its surface may then be filed smooth. Square pieces may be let in after the same fashion, the hole being made dovetailed, and the pieces thus fitted will never come out. 711. _Q._--When cylinders are faced with brass, how is the face attached to the cylinder? _A._--Brass faces are put upon valves or cylinders by means of small brass screws tapped into the iron, with conical necks for the retention of the brass: they are screwed by means of a square head, which, when the screw is in its place, is cut off and filed smooth. In some cases the face is made of extra thickness, and a rim not so thick runs round it, forming a step or recess for the reception of brass rivets, the heads of which are clear of the face. 712. _Q._--What is the best material for valve faces? _A._--Much trouble is experienced with every modification of valve face; but cast iron working upon cast iron is, perhaps, the best combination yet introduced. A usual practice is to pin brass faces on the cylinder, allowing the valve to retain its cast iron face. Some makers employ brass valves, and others pin brass on the valves, leaving the cylinder with a cast iron face. If brass valves are used, it is advisable to plane out two grooves across the face, and to fill them up with hard cast iron to prevent rutting. Speculum metal and steel have been tried for the cylinder faces, but only with moderate success. In some cases the brass gets into ruts; but the most prevalent affection is a degradation of the iron, owing to the action of the steam, and the face assuming a granular appearance, something like loaf sugar. This action shows itself only at particular spots, and chiefly about the angles of the port or valve face. At first the action is slow; but when once the steam has worked a passage for itself, the cutting away becomes very rapid, and, in a short time, it will be impossible to prevent the engine from heating when stopped, owing to the leakage of steam through the valve into the condenser. Copper steam pipes seem to have some galvanic action on valve faces, and malleable iron pipes have sometimes been substituted; but they are speedily worn out by oxidation, and the scales of rust which are carried on by the steam scratch the valves and cylinders, so that the use of copper pipes is the least evil. 713. _Q._--Will you explain in what manner the joints of an engine are made? _A._--Rust joints are not now much used in engines of any kind, yet it is necessary that the engineer should be acquainted with the manner of their formation. One ounce of sal-ammoniac in powder is mingled with 18 ounces or a pound of borings of cast iron, and a sufficiency of water is added to wet the mixture thoroughly, which should be done some hours before it is wanted for use. Some persons add about half an ounce of flowers of brimstone to the above proportions, and a little sludge from the grindstone trough. This cement is caulked into the joints with a caulking iron, about three quarters of an inch wide and one quarter of an inch thick, and after the caulking is finished the bolts of the joints may be tried to see if they cannot be further tightened. The skin of the iron must, in all cases, be broken where a rust joint is to be made; and, if the place be greasy, the surface must be well rubbed over with nitric acid, and then washed with water, till no grease remains. The oil about engines has a tendency to damage rust joints by recovering the oxide. Coppersmiths staunch the edges of their plates and rivets by means of a cement formed of pounded quicklime, with serum of blood, or white of egg; and in copper boilers such a substance may be useful in stopping the impalpable leaks which sometimes occur, though Roman, cement appears to be nearly as effectual. 714. _Q._--Will you explain the method of case hardening the parts of engines? _A._--The most common plan for case hardening consists in the insertion of the articles to be operated upon among horn or leather cuttings, hone dust, or animal charcoal, in an iron box provided with a tight lid, which is then put into a furnace for a period answerable to the depth of steel required. In some cases the plan pursued by the gunsmiths may be employed with convenience. The article is inserted in a sheet iron case amid bone dust, often not burned; the lid of the box is tied on with wire, and the joint luted with clay; the box is heated to redness as quickly as possible and kept half an hour at a uniform heat: its contents are then suddenly immersed in cold water. The more unwieldy portions of an engine may be case hardened by prussiate of potash--a salt made from animal substances, composed of two atoms of carbon and one of nitrogen, and which operates on the same principle as the charcoal. The iron is heated in the fire to a dull red heat, and the salt is either sprinkled upon it or rubbed on in a lump, or the iron is rubbed in the salt in powder. The iron is then returned to the fire for a few minutes, and finally immersed in water. By some persons the salt is supposed to act unequally, as if there were greasy spots upon the iron which the salt refused to touch, and the effect under any circumstances is exceedingly superficial; nevertheless, upon all parts not exposed to wear, a sufficient coating of steel may be obtained by this process. 715. _Q._--What kind of iron is most suitable for the working parts of an engine? _A._--In the malleable iron work of engines scrap iron has long been used, and considered preferable to other kinds; but if the parts are to be case hardened, as is now the usual practice, the use of scrap iron is to be reprehended, as it is almost sure to make the parts twist in the case hardening process. In case hardening, iron absorbs carbon, which causes it to swell; and as some kinds of iron have a greater capacity for carbon than other kinds, in case hardening they will swell more, and any such unequal enlargement in the constituent portions of a piece of iron will cause it to change its figure. In some cases, case hardening has caused such a twisting of the parts of an engine, that they could not afterward be fitted together; it is preferable, therefore, to make such parts as are to be case hardened to any considerable depth of Lowmoor, Bowling, or Indian iron, which being homogeneous will absorb carbon equally, and will not twist. 716. _Q._--What is the composition of the brass used for engine bearings? _A._--The brass bearings of an engine are composed principally of copper and tin. A very good brass for steam engine bearings consists of old copper 112 lbs., tin 12-1/2 lbs., zinc 2 or 3 oz.; and if new tile copper be used, there should be 13 lbs. of tin instead of 12-1/2 lbs. A tough brass for engine work consists of 1-1/2 lb. tin, 1-1/2 lb. zinc, and 10 lbs. copper; a brass for heavy bearings, 2-1/2 oz. tin, 1/2 oz. zinc, and 1 lb. copper. There is a great difference in the length of time brasses wear, as made by different manufacturers; but the difference arises as much from a different quantity of surface, as from a varying composition of the metal. Brasses should always be made strong and thick, as when thin they collapse upon the bearing and increase the friction and the wear. 717. _Q._--How is Babbitt's metal for lining the bushes of machinery compounded? _A._--Babbitt's patent lining metal for bushes has been largely employed in the bushes of locomotive axles and other machinery: it is composed of 1 lb. of copper, 1 lb. regulus of antimony, and 10 lbs. of tin, or other similar proportions, the presence of tin being the only material condition. The copper is first melted, then the antimony is added, with a small proportion of tin-charcoal being strewed over the surface of the metal in the crucible to prevent oxidation. The bush or article to be lined, having been cast with a recess for the soft metal, is to be fitted to an iron mould, formed of the shape and size of the bearing or journal, allowing a little in size for the shrinkage. Drill a hole for the reception of the soft metal, say 1/2 to 3/4 inch diameter, wash the parts not to be tinned with a clay wash to prevent the adhesion of the tin, wet the part to be tinned with alcohol, and sprinkle fine sal-ammoniac upon it; heat the article until fumes arise from the ammonia, and immerse it in a kettle of Banca tin, care being taken to prevent oxidation. When sufficiently tinned, the bush should be soaked in water, to take off any particles of ammonia that may remain upon it, as the ammonia would cause the metal to blow. Wash with pipe clay, and dry; then heat the bush to the melting point of tin, wipe it clean, and pour in the metal, giving it sufficient head as it cools; the bush should then be scoured with fine sand, to take off any dirt that may remain upon it, and it is then fit for use. This metal wears for a longer time than ordinary gun metal, and its use is attended with very little friction. If the bearing heats, however, from the stopping of the oil hole or otherwise, the metal will be melted out. A metallic grease, containing particles of tin in the state of an impalpable powder, would probably be preferable to the lining of metal just described. 718. _Q._--Can you state the composition of any other alloys that are used in engine work? _A._--The ordinary range of good yellow brass that files and turns well, is about 4-1/2 to 9 ounces of zinc to the pound of copper. Flanges to stand brazing may be made of copper 1 lb., zinc 1/2 oz., lead 3/8 oz. Brazing solders when stated in the order of their hardness are:-three parts copper and one part zinc (very hard), eight parts brass and one part zinc (hard), six parts brass, one part tin, and one part zinc (soft); a very common solder for iron, copper, and brass, consists of nearly equal parts of copper and zinc. Muntz's metal consists of forty parts zinc and sixty of copper; any proportions between the extremes of fifty parts of zinc and fifty parts copper, and thirty-seven zinc and sixty-three copper, will roll and work at a red heat, but forty zinc to sixty copper are the proportions preferred. Bell metal, such as is used for large bells, consists of 4-1/2 ounces to 5 ounces of tin to the pound of copper; speculum metal consists of from 7-1/2 ounces to 8-1/2 ounces of tin to the pound of copper. ERECTION OF ENGINES. 719. _Q._--Will you explain the operation of erecting a pair of side lever engines in the workshop? A.--In beginning the erection of side lever marine engines in the workshop, the first step is to level the bed plate lengthways and across, and strike a line up the centre, as near as possible in the middle, which indent with a chisel in various places, so that it may at any time be easily found again. Strike another line at right angles with this, either at the cylinder or crank centre, by drawing a perpendicular in the usual manner. Lay the other sole plate alongside at the right distance, and strike a line at the cylinder or crank centre of it also, shifting either sole plate a little endways until these two transverse lines come into the same line, which may be ascertained by applying a straight edge across the two sole plates. Strike the rest of the centres across, and drive a pin into each corner of each sole plate, which file down level, so as to serve for points of reference at any future stage; next, try the cylinder, or plumb it on the inside roughly, and see how it is for height, in order to ascertain whether much will be required to be chipped off the bottom, or whether more requires to be chipped off the one side than the other. Chip the cylinder bottom fair; set it in its place, plumb the cylinder very carefully with a straight edge and silk thread, and scribe it so as to bring the cylinder mouth to the right height, then chip the sole plate to suit that height. The cylinder must then be tried on again, and the parts filed wherever they bear hard, until the whole surface is well fitted. Next, chip the place for the framing; set up the framing, and scribe the horizontal part of the jaw with the scriber used for the bottom of the cylinder, the upright part being set to suit the shaft centres, and the angular flange of cylinder, where the stay is attached, having been previously chipped plumb and level. The stake wedges with which the framing is set up preparatorily to the operation of scribing, must be set so as to support equally the superincumbent weight, else the framing will spring from resting unequally, and it will be altogether impossible to fit it well. These directions obviously refer exclusively to the old description of side lever engine with cast iron framing; but there is more art in erecting an engine of that kind with accuracy, than in erecting one of the direct action engines, where it is chiefly turned or bored surfaces that have to be dealt with. 720. _Q._--How do you lay out the positions of the centres of a side lever engine? _A._--In fixing the positions of the centres in side lever engines, it appears to be the most convenient way to begin with the main centre. The height of the centre of the cross head at half stroke above the plane of the main centre is fixed by the drawing of the engine, which gives the distance from the centre of cross head at half stroke to the flange of the cylinder; and from thence it is easy to find the perpendicular distance from the cylinder flange to the plane of the main centre, merely by putting a straight edge along level, from the position of the main centre to the cylinder, and measuring from the cylinder flauge down to it, raising or lowering the straight edge until it rests at the proper measurement. The main centre is in that plane, and the fore and aft position is to be found by plumbing up from the centre line on the sole plate. To find the paddle shaft centre, plumb up from the centre line marked on the edge of the sole plate, and on this line lay off from the plane of the main centre the length of the connecting rod, if that length be already fixed, or otherwise the height fixed in the drawing of the paddle shaft above the main centre. To fix the centre for the parallel motion shaft, when the parallel bars are connected with the cross head, lay off from the plane of main centre the length of the parallel bar from the centre of the cylinder, deduct the length of the radius crank, and plumb up the central line of motion shaft; lay off on this line, measuring from the plane of main centre, the length of the side rod; this gives the centre of parallel motion shaft when the radius bars join the cross head, as is the preferable practice where parallel motions are used. The length of the connecting rod is the distance from the centre of the beam when level, or the plane of the main centre, to the centre of the paddle shaft. The length of the side rods is the distance from the centre line of the beam when level, to the centre of the cross head when the piston is at half stroke. The length of the radius rods of the parallel motion is the distance from the point of attachment on the cross head or side rod, when the piston is at half stroke, to the extremity of the radius crank when the crank is horizontal; or in engines with the parallel motion attached to the cross head, it is the distance from the centre of the pin of the radius crank when horizontal to the centre of the cylinder. Having fixed the centre of the parallel motion shaft in the manner just described, it only remains to put the parts together when the motion is attached to the cross head; but when the motion is attached to the side rod, the end of the parallel bar must not move in a perpendicular line, but in an arc, the versed sine of which bears the same ratio to that of the side lever, that the distance from the top of the side rod to the point of attachment bears to the total length of the side rod. 721. _Q._--How do you ascertain the accuracy of the parallel motion? _A._--The parallel motion when put in its place should be tested by raising and lowering the piston by means of the crane. First, set the beams level, and shift in or out the motion shaft plummer blocks or bearings, until the piston rod is upright. Then move the piston to the two extremes of its motion. If at both ends the cross head is thrown too much out, the stud in the beam to which the motion side rod is attached is too far out, and must be shifted nearer to the main centre; if at the extremities the cross head is thrown too far in, the stud in the beam is not out far enough. If the cross head be thrown in at the one end, and out equally at the other, the fault is in the motion side rod, which must be lengthened or shortened to remedy the defect. 722. _Q._--Will you describe the method pursued in erecting oscillating engines? _A._--The columns here are of wrought iron, and in the case of small engines there is a template made of wood and sheet iron, in which the holes are set in the proper positions, by which the upper and lower frames are adjusted; but in the case of large engines, the holes are set off by means of trammels. The holes for the reception of the columns are cast in the frames, and are recessed out internally: the bosses encircling the holes are made quite level across, and made very true with a face plate, and the pillars which have been turned to a gauge are then inserted. The top frame is next put on, and must bear upon the collars of the columns so evenly, that one of the columns will not be bound by it harder than another. If this point be not attained, the surfaces must be further scraped, until a perfect fit is established. The whole of the bearings in the best oscillating engines are fitted by means of scraping, and on no other mode of fitting can the same reliance be placed for exactitude. 723. _Q._--How do you set out the trunnions of oscillating engines, so that they shall be at right angles with the interior of the cylinder? _A._--Having bored the cylinder, faced the flange, and bored out the hole through which the boring bar passes, put a piece of wood across the mouth of the cylinder, and jam it in, and put a similar piece in the hole through the bottom of the cylinder. Mark the centre of the cylinder upon each of these pieces, and put into the bore of each trunnion an iron plate, with a small indentation in the middle to receive the centre of a lathe, and adjusting screws to bring the centre into any required position. The cylinder must then be set in a lathe, and hung by the centres of the trunnions, and a straight edge must be put across the cylinder mouth and levelled, so as to pass through the line in which the centre of the cylinder lies. Another similar straight edge, and similarly levelled, must be similarly placed across the cylinder bottom, so as to pass through the central line of the cylinder; and the cylinder is then to be turned round in the trunnion centres-the straight edges remaining stationary, which will at once show whether the trunnions are in the same horizontal plane as the centre of the cylinder, and if not, the screws of the plates in the trunnions must be adjusted until the central point of the cylinder just comes to the straight edge, whichever end of the cylinder is presented. To ascertain whether the trunnions stand in a transverse plane, parallel to the cylinder flange, it is only necessary to measure down from the flange to each trunnion centre; and if both these conditions are satisfied, the position of the centres may be supposed to be right. The trunnion bearings are then turned, and are fitted into blocks of wood, in which they run while the packing space is being turned out. Where many oscillating engines are made, a lathe with four centres is used, which makes the use of straight edges in setting out the trunnions superfluous. 724. _Q._--Will you explain how the slide valve of a marine engine is set? _A._--Place the crank in the position corresponding to the end of the stroke, which can easily be done in the shop with a level, or plumb line; but in a steam vessel another method becomes necessary. Draw the transverse centre line, answering to the centre line of the crank shaft, on the sole plate of the engine, or on the cylinder mouth if the engine be of the direct action kind; describe a circle of the diameter of the crank pin upon the large eye of the crank, and mark off on either side of the transverse centre line a distance equal to the semi-diameter of the crank pin. From the point thus found, stretch a line to the edge of the circle described on the large eye of the crank, and bring round the crank shaft till the crank pin touches the stretched line; the crank may thus be set at either end of its stroke. When the crank is thus placed at the end of the stroke, the valve must be adjusted so as to have the amount of lead, or opening on the steam side, which it is intended to give at the beginning of the stroke; the eccentric must then be turned round upon the shaft until the notch in the eccentric rod comes opposite the pin on the valve lever, and falls into gear: mark upon the shaft the situation of the eccentric, and put on the catches in the usual way. The same process must be repeated for going astern, shifting round the eccentric to the opposite side of the shaft, until the rod again falls into gear. In setting valves, regard must of course be had to the kind of engine, the arrangements of the levers, and the kind of valve employed; and in any general instructions it is impossible to specify every modification in the procedure that circumstances may render advisable. 725. _Q._--Is a similar method of setting the valve adopted when the link motion is employed. _A._--Each end of the link of the link motion has the kind of motion communicated to it that is due to the action of the particular eccentric with which that end is in connection. In that form of the link motion in which the link itself is moved up or down, there is a different amount of lead for each different position of the link, since to raise or lower the link is tantamount to turning the eccentric round on the shaft. In that form of the link motion in which the link itself is not raised or lowered, but is susceptible of a motion round a centre in the manner of a double ended lever, the lead continues uniform. In both forms of the link motion, as the stroke of the valve may be varied to any required extent while the lap is a constant quantity, the proportion of the lap relatively to the stroke of the valve may also be varied to any required extent, and the amount of the lap relatively with the stroke of the valve determines the amount of the expansion. In setting the valve when fitted with the link motion, the mode of procedure is much the same as when it is moved by a simple eccentric. The first thing is to determine if the eccentric rods are of the proper length, and this is done by setting the valve at half stroke and turning round the eccentric, marking each extremity of the travel of the end of the rod. The valve attachment should be midway between these extremes; and if it is not so, it must be made so by lengthening or shortening the rod. The forward and backward eccentric rods are to be adjusted in this way, and this being done, the engine is to be put to the end of the stroke, and the eccentric is to be turned round until the amount of lead has been given that is desired. The valve must be tried by turning the engine round to see that it is right at both centres, for going ahead and also for going astern. In some examples of the link motion, one of the eccentric rods is made a little longer than the other, and the position of the point of suspension or point of support powerfully influences the action of the link in certain cases, especially if the link and this point are not in the same vertical line. To reconcile all the conditions proper to the satisfactory operation of the valve in the construction of the link motion, is a problem requiring a good deal of attention and care for its satisfactory solution; and to make sure that this result is attained, the engine must be turned round a sufficient number of times to enable us to ascertain if the valve occupies the desired position, both at the top and bottom centres, whether the engine is going ahead or astern. This should also be tried with the starting handle in the different notches, or, in other words, with the sliding block in the slot or opening of the link in different positions. MANAGEMENT OF MARINE BOILERS. 726. _Q._--You have already stated that the formation of salt or scale in marine boilers is to be prevented by blowing out into the sea at frequent intervals a portion of the concentrated water. Will you now explain how the proper quantity of water to be blown out is determined? _A._--By means of the salinometer, which is an instrument for determining the density of the water, constructed on the principle of the hydrometer for telling the strength of spirits. Some of the water is drawn off from the boiler from time to time, and the salinometer is immersed in it after it has been cooled. By the graduations of the salinometer the saltness of this water is at once discovered; and if the saltness exceeds 8 ounces of salt in the gallon, more water should be blown out of the boiler to be replenished with fresher water from the sea, until the prescribed limit of freshness is attained. Should the salinometer be accidentally broken, a temporary one may be constructed of a phial weighted with a few grains of shot or other convenient weight. The weighted phial is first to be floated in fresh water, and its line of floatation marked; then to be floated in salt water, and its line of floatation marked; and another mark of an equal height above the salt water mark will be the blow off point. 727. _Q._--HOW often should boilers be blown off in order to keep them free from incrustation? _A._--Flue boilers generally require to be blown off about twice every watch, or about twice in the four hours; but tubular boilers may require to be blown off once every twenty minutes, and such an amount of blowing off should in every case be adopted, as will effectually prevent any injurious amount of incrustation. 728. _Q._--In the event of scale accumulating on the flues of a boiler, what is the best way of removing it? _A._--If the boilers require to be scaled, the best method of performing the operation appears to be the following:--Lay a train of shavings along the flues, open the safety valve to prevent the existence of any pressure within the boiler, and light the train of shavings, which, by expanding rapidly the metal of the flues, while the scale, from its imperfect conducting power, can only expand slowly, will crack off the scale; by washing down the flues with a hose, the scale will be carried to the bottom of the boiler, or issue, with the water, from the mud-hole doors. This method of scaling must be practised only by the engineer himself, and must not be intrusted to the firemen who, in their ignorance, might damage the boiler by overheating the plates. It is only where the incrustation upon the flues is considerable that this method of removing it need be practised; in partial cases the scale may be chipped off by a hatched faced hammer, and the flues may then be washed down with the hose in the manner before described. 729. _Q._--Should the steam be let out of the boiler, after it has blown out the water, when the engine is stopped? _A._--No; it is better to retain the steam in the boiler, as the heat and moisture it occasions soften any scale adhering to the boiler, and cause it to peel off. Care must, however, be taken not to form a vacuum in the boiler; and the gauge cocks, if opened, will prevent this. 730. _Q._--Are tubular boilers liable to the formation of scale in certain places, though generally free from it? _A._--In tubular boilers a good deal of care is required to prevent the ends of the tubes next the furnace from becoming coated with scale. Even when the boiler is tolerably clean in other places the scale will collect here; and in many cases where the amount of blowing off previously found to suffice for flue boilers has been adopted, an incrustation five eighths of an inch in thickness has formed in twelve months round the furnace ends of the tubes, and the stony husks enveloping them have actually grown together in some parts so as totally to exclude the water. 731. _Q._--When a tubular boiler gets incrusted in the manner you have described, what is the best course to be adopted for the removal of the scale? _A._--When a boiler gets into this state the whole of the tubes must be pulled out, which may be done by a Spanish windlass combined with a pair of blocks; and three men, when thus provided, will be able to draw out from 50 to 70 tubes per day,--those tubes with the thickest and firmest incrustations being, of course, the most difficult to remove. The act of drawing out the tubes removes the incrustation; but the tubes should afterward be scraped by drawing them backward and forward between the old files, fixed in a vice, in the form of the letter V. The ends of the tube should then be heated and dressed with the hammer, and plunged while at a blood heat into a bed of sawdust to make them cool soft, so that they may be riveted again with facility. A few of the tubes will be so far damaged at the ends by the act of drawing them out, as to be too short for reinsertion: this result might be to a considerable extent obviated by setting the tube plates at different angles, so that the several horizontal rows of tubes would not be originally of the same length, and the damaged tubes of the long rows would serve to replace the short ones; but the practice would be attended with other inconveniences. 732. _Q._--Is there no other means of keeping boilers free from scale than by blowing off? _A._--Muriatic acid, or muriate of ammonia, commonly called sal-ammoniac, introduced into a boiler, prevents scale to a great extent; but it is liable to corrode the boiler internally, and also to damage the engine, by being carried over with the steam; and the use of such intermixtures does not appear to be necessary, if blowing off from the surface of the water is largely practised. In old boilers, however, already incrusted with scale, the use of muriate of ammonia may sometimes be advantageous. 733. _Q._--Are not the tubes of tubular boilers liable to be choked up by deposits of soot? _A._--The soot which collects in the inside of the tubes of tubular boilers is removed by means of a brush, like a large bottle brush; and the carbonaceous scale, which remains adhering to the interior of the tubes, is removed by a circular scraper. Ferules in the tubes interfere with the action of this scraper, and in the case of iron tubes ferules are now generally discarded; but it will sometimes be necessary to use ferules for iron tubes, where the tubes have been drawn and reinserted, as it may be difficult to refix the tubes without such an auxiliary. Tubes one tenth of an inch in thickness are too thin: one eighth of an inch is a better thickness, and such tubes will better dispense with the use of ferules, and will not so soon wear into holes. 734. _Q._--If the furnace or flue of a boiler be injured, how do you proceed to repair it? _A._--If from any imperfection in the roof of a furnace or flue a patch requires to be put upon it, it will be better to let the patch be applied upon the upper, rather than upon the lower, surface of the plate; as if applied within the furnace a recess will be formed for the lodgment of deposit, which will prevent the rapid transmission of the heat in that part; and the iron will be very liable to be again burned away. A crack in a plate may be closed by boring holes in the direction of the crack, and inserting rivets with large heads, so as to cover up the imperfection. If the top of the furnace be bent down, from the boiler having been accidentally allowed to get short of water, it may be set up again by a screw jack,--a fire of wood having been previously made beneath the injured plate; but it will in general be nearly as expeditious a course to remove the plate and introduce a new one, and the result will be more satisfactory. 735. _Q._--In the case of the chimney being carried away by shot or otherwise, what course would you pursue? _A._--In some cases of collision, the funnel is carried away and lost overboard, and such cases are among the most difficult for which a remedy can be sought. If flame come out of the chimney when the funnel is knocked away, so as to incur the risk of setting the ship on fire, the uptake of the boiler must be covered over with an iron plate, or be sufficiently covered to prevent such injury. A temporary chimney must then be made of such materials as are on board the ship. If there are bricks and clay or lime on board, a square chimney may be built with them, or, if there be sheet iron plates on board, a square chimney may be constructed of them. In the absence of such materials, the awning stanchions may be set up round the chimney, and chain rove in through among them in the manner of wicker work, so as to make an iron wicker chimney, which may then be plastered outside with wet ashes mixed with clay, flour, or any other material that will give the ashes cohesion. War steamers should carry short spare funnels, which may easily be set up should the original funnel be shot away; and if a jet of steam be let into the chimney, a very short and small funnel will suffice for the purpose of draught. MANAGEMENT OF MARINE ENGINES. 736. _Q._--What are the most important of the points which suggest themselves to you in connection with the management of marine engines? _A._--The attendants upon engines should prepare themselves for any casualty that may arise, by considering possible cases of derangement, and deciding In what way they would act should certain accidents occur. The course to be pursued must have reference to particular engines, and no general rules can therefore be given; but every marine engineer should be prepared with the measures to be pursued in the emergencies in which he may be called upon to act, and where everything may depend upon his energy and decision. 737. _Q._--What is the first point of a marine engineer's duty? _A._--The safe custody of the boiler. He must see that the feed is maintained, being neither too high nor too low, and that blowing out the supersalted water is practised sufficiently. The saltness of the water at every half hour should be entered in the log book, together with the pressure of steam, number of revolutions of the engine, and any other particulars which have to be recorded. The economical use of the fuel is another matter which should receive particular attention. If the coal is very small, it should be wetted before being put on the fire. Next to the safety of the boiler, the bearings of the engine are the most important consideration. These points, indeed, constitute the main parts of the duty of an engineer, supposing no accident to the machinery to have taken place. 738. _Q._--If the eccentric catches or hoops were disabled, how would you work the valve? _A._--If the eccentric catches or hoops break or come off, and the damage cannot readily be repaired, the valve may be worked by attaching the end of the starting handle to any convenient part of the other engine, or to some part in connection with the connecting rod of the same engine. In side lever engines, with the starting bar hanging from the top of the diagonal stay, as is a very common arrangement, the valve might be wrought by leading a rope from the side lever of the other engine through blocks so as to give a horizontal pull to the hanging starting bar, and the bar could be brought back by a weight. Another plan would be, to lash a piece of wood to the cross tail butt of the damaged engine, so as to obtain a sufficient throw for working the valve, and then to lead a piece of wood or iron, from a suitable point in the piece of wood attached to the cross tail, to the starting handle, whereby the valve would receive its proper motion. In oscillating engines it is easy to give the required motion to the valve, by deriving it from the oscillation of the cylinder. 739. _Q._--What would you do if a crank pin broke? _A._--If the crank pin breaks in a paddle vessel with two engines, the other engine must be made to work one wheel. In a screw vessel the same course may be pursued, provided the broken crank is not the one through which the force of the other engine is communicated to the screw. In such a case the vessel will be as much disabled as if she broke the screw shaft or screw. 740. _Q._--Will the unbroken engine, in the case of disarrangement of one of the two engines of a screw or paddle vessel, be able of itself to turn the centre? _A._--It will sometimes happen, when there is much lead upon the slide valve, that the single engine, on being started, cannot be got to turn the centre if there be a strong opposing wind and sea; the piston going up to near the end of the stroke, and then coming down again without the crank being able to turn the centre. In such cases, it will be necessary to turn the vessel's head sufficiently from the wind to enable some sail to be set; and if once there is weigh got upon the vessel the engine will begin to work properly, and will continue to do so though the vessel be put head to wind as before. 741. _Q._--What should be done if a crack shows itself in any of the shafts or cranks? _A._--If the shafts or cranks crack, the engine may nevertheless be worked with moderate pressure to bring the vessel into port; but if the crack be very bad, it will be expedient to fit strong blocks of wood under the ends of the side levers, or other suitable part, to prevent the cylinder bottom or cover from being knocked out, should the damaged part give way. The same remark is applicable when flaws are discovered in any of the main parts of the engine, whether they be malleable or cast iron; but they must be carefully watched, so that the engines may be stopped if the crack is extending further. Should fracture occur, the first thing obviously to be done is to throw the engines out of gear; and should there be much weigh on the vessel, the steam should at once be thrown on the reverse side of the piston, so as to counteract the pressure of the paddle wheel. 742. _Q._--Have you any information to offer relative to the lubrication of engine bearings? _A._--A very useful species of oil cup is now employed in a number of steam vessels, and which, it is said, accomplishes a considerable saving of oil, at the same time that it more effectually lubricates the bearings. A ratchet wheel is fixed upon a little shaft which passes through the side of the oil cup, and is put into slow revolution by a pendulum attached to its outside and in revolving it lifts up little buckets of oil and empties them down a funnel upon the centre of the bearing. Instead of buckets a few short pieces of wire are sometimes hung on the internal revolving wheel, the drops of oil which adhere on rising from the liquid being deposited. upon a high part set upon the funnel, and which, in their revolution, the hanging wires touch. By this plan, however, the oil is not well supplied at slow speeds, as the drops fall before the wires are in proper position for feeding the journal. Another lubricator consists of a cock or plug inserted in the neck of the oil cup, and set in revolution by a pendulum and ratchet wheel, or any other means. There is a small cavity in one side of the plug, which is filled with oil when that side is uppermost, and delivers the oil through the bottom pipe when it comes opposite to it. 743. _Q._--What are the prevailing causes of the heating of bearings? _A._--Bad fitting, deficient surface, and too tight screwing down. Sometimes the oil hole will choke, or the syphon wick for conducting the oil from the oil cup into the central pipe leading to the bearing will become clogged with mucilage from the oil. In some cases bearings heat from the existence of a cruciform groove on the top brass for the distribution of the oil, the effect of which is to leave the top of the bearings dry. In the case of revolving journals the plan for cutting a cruciform channel for the distribution of the oil does not do much damage; but in other cases, as in beam journals, for instance, it is most injurious, and the brasses cannot wear well wherever the plan is pursued. The right way is to make a horizontal groove along the brass where it meets the upper surface of the bearing, so that the oil may be all deposited on the highest point of the journal, leaving the force of gravity to send it downward. This channel should, of course, stop short a small distance from each flange of the brass, otherwise the oil would run out at the ends. 744. _Q._--If a bearing heats, what is to be done? _A._--The first thing is to relax the screws, slow or stop the engine, and cool the bearing with water, and if it is very hot, then hot water may be first employed to cool it, and then cold. Oil with sulphur intermingled is then to be administered, and as the parts cool down, the screws may be again cautiously tightened, so as to take any jump off the engine from the bearing being too slack. The bearings of direct acting screw engines require constant watching, as, if there be any disposition to heat manifested by them, they will probably heat with great rapidity from the high velocity at which the engines work. Every bearing of a direct acting screw engine should have a cock of water laid on to it, which may be immediately opened wide should heating occur; and it is advisable to work the engine constantly, partly with water, and partly with oil applied to the bearings. The water and oil are mixed by the friction into a species of soap which both cools and lubricates, and less oil moreover is used than if water were not employed. It is proper to turn off the water some time before the engine is stopped, so as to prevent the rusting of the bearings. MANAGEMENT OF LOCOMOTIVES. 745. _Q._--What are the chief duties of the engine driver of a locomotive? _A._--His first duties are those which concern the safety of the train; his next those which concern the safety and right management of the engine and boiler. The engine driver's first solicitude should be relative to the observation and right interpretation of the signals; and it is only after these demands upon his attention have been satisfied, that he can look to the state of his engine. 746. _Q._--As regards the engine and boiler, what should his main duties be? _A._--The engineer of a locomotive should constantly be upon the foot board of the engine, so that the regulator, the whistle or the reversing handle may be used instantly, if necessary; he must see that the level of the water in the boiler is duly maintained, and that the steam is kept at a uniform pressure. In feeding the boilers with water, and the furnaces with fuel, a good deal of care and some tact are necessary, as irregularity in the production of steam will often occasion priming, even though the water be maintained at a uniform level; and an excess of water will of itself occasion priming, while a deficiency is a source of obvious danger. The engine is generally furnished with three gauge cocks, and water should always come out of the second gauge cock, and steam out of the top one when the engine is running: but when the engine is at rest, the water in the boiler is lower than when in motion, so that when the engine is at rest, the water will be high enough if it just reaches to the middle gauge cock. In all boilers which generate steam rapidly, the volume of the water is increased by the mingled steam, and in feeding with cold water the level at first falls; but it rises on opening the safety valve, which causes the steam in the water to swell to a larger volume. In locomotive boilers, the rise of the water level due to the rapid generation of steam is termed "false water." To economize fuel, the variable expansion gear, if the engine has one, should be adjusted to the load, and the blast pipe should be worked with the least possible contraction; and at stations the damper should be closed to prevent the dissipation of heat. 747. _Q._--In starting from a station, what precautions should be observed with respect to the feed? _A._--In starting from a station, and also in ascending inclined planes, the feed water is generally shut off; and therefore before stopping or ascending inclined planes, the boiler should be well filled up with water. In descending inclined planes an extra supply of water may be introduced into the boiler, and the fire may be fed, as there, is at such times a superfluity of steam. In descending inclined planes the regulator must be partially closed, and it should be entirely closed if the plane be very steep. The same precaution should be observed in the case of curves, or rough places on the line, and in passing over points or crossings. 748. _Q._--In approaching a station, how should the supply of water and fuel be regulated? _A._--The boiler should be well filled with water on approaching a station, as there is then steam to spare, and additional water cannot be conveniently supplied when the engine is stationary. The furnace should be fed with small quantities of fuel at a time, and the feed should be turned off just before a fresh supply of fuel is introduced. The regulator may, at the same time, be partially closed; and if the blast pipe be a variable one, it will be expedient to open it widely while the fuel is being introduced, to check the rush of air in through the furnace door, and then to contract it very much so soon as the furnace door is closed, in order to recover the fire quickly. The proper thickness of coke upon the grate depends upon the intensity of the draught; but in heavily loaded engines it is usually kept up to the bottom of the fire door. Care, however, must be taken that the coke does not reach up to the bottom row of tubes so as to choke them up. The fuel is usually disposed on the grate like a vault; and if the fire box be a square one, it is heaped high in the corners, the better to maintain the combustion. 749. _Q._--How can you tell whether the feed pumps are operating properly? _A._--To ascertain whether the pumps are acting well, the pet cock must be turned, and if any of the valves stick they will sometimes be induced to act again by working with the pet cock open, or alternately open and shut. Should the defect arise from a leakage of steam into the pump, which prevents the pump from drawing, the pet cock remedies the evil by permitting the steam to escape. 750. _Q._--What precautions should be taken against priming in locomotives? _A._--Should priming occur from the water in the boiler being dirty, a portion of it may be blown out; and should there be much boiling down through the glass gauge tube, the stop cock may be partially closed. The water should be wholly blown out of locomotive boilers three times a week, and at those times two mud-hole doors at opposite corners of the boiler should be opened, and the boiler be washed internally by means of a hose. If the boiler be habitually fed with dirty water, the priming will be a constant source of trouble. 751. _Q._--What measures should the locomotive engineer take, to check the velocity of the train, on approaching a station where he has to stop? _A._--On approaching a station the regulator should be gradually closed, and it should be completely shut about half a mile from the station if the train be a very heavy one: the train may then be brought to rest by means of the breaks. Too much reliance, however, must not be put upon the breaks, as they sometimes give way, and in frosty weather are nearly inoperative. In cases of urgency the steam may be thrown upon the reverse side of the piston, but it is desirable to obviate this necessity as far as possible. At terminal stations the steam should be shut off earlier than at roadside stations, as a collision will take place at terminal stations if the train overshoots the place where it ought to stop. There should always be a good supply of water when the engine stops, but the fire may be suffered gradually to burn low toward the conclusion of the journey. 752. _Q._--What is the duty of an engine man on arriving at the end of his journey? _A._--So soon as the engine stops it should be wiped down, and be then carefully examined: the brasses should be tried, to see whether they are slack or have been heating; and, by the application of a gauge, it should be ascertained occasionally whether the wheels are square on their axles, and whether the axles have end play, which should be prevented. The stuffing boxes must be tightened, and the valve gear examined, and the eccentrics be occasionally looked at to see that they have not shifted on their axles, though this defect will be generally intimated by the irregular beating of the engines. The tubes should also be examined and cleaned out, and the ashes emptied out of the smoke box through the small ash door at the end. If the engine be a six-wheeled one, with the driving wheels in the middle, it will be liable to pitch, and oscillate if too much weight be thrown upon the driving wheels; and where such faults are found to exist, the weight upon the drivings wheels should be diminished. The practice of blowing off the boiler by the steam, as is always done in marine boilers, should not be permitted as a general rule in locomotive boilers, when the tubes are of brass and the fire box of copper; but when the tubes and fire boxes are of iron, there will not be an equal risk of injury. Before starting on a journey, the engine man should take a summary glance beneath the engine--but before doing so he ought to assure himself that no other engine is coming up at the time. The regulator, when the engine is standing, should be closed and locked, and the eccentric rod be fixed out of gear, and the tender break screwed down; the cocks of the oil vessels should at the same time be shut, but should all be opened a short time before the train starts. 753. _Q._--What should be done if a tube bursts in the boiler? _A._--When a tube bursts, a wooden or iron plug must be driven into each end of it, and if the water or steam be rushing out so fiercely that the exact position of the imperfection cannot be discovered, it will be advisable to diminish the pressure by increasing the supply of feed water. Should the leak be so great that the level of the water in the boiler cannot be maintained, it will be expedient to drop the bars and quench the fire, so as to preserve the tubes and fire box from injury. 754. _Q._--If any of the working parts of a locomotive break or become deranged, what should be done? _A._--Should the piston rod or connecting rod break, or the cutters fall out or be clipped off--as sometimes happens to the piston cutter when the engine is suddenly reversed upon a heavy train--the parts should be disconnected, if the connection cannot be restored, so as to enable one engine to work; and of course the valve of the faulty engine must be kept closed. If one engine has not power enough to enable the train to proceed with the blast pipe full open, the engine may perhaps be able to take on a part of the carriages, or it may run on by itself to fetch assistance. The same course must be pursued if any of the valve gearing becomes deranged, and the defects cannot be rectified upon the spot. 755. _Q._--What are the most usual causes of railway collisions? _A._--Probably fogs and inexactness in the time kept by the trains. Collisions have sometimes occurred from carriages having been blown from a siding on to the rails by a high wind; and the slippery state of the rails, or the fracture of a break, has sometimes occasioned collisions at terminal stations. Collision has also repeatedly taken place from one engine having overtaken another, from the failure of a tube in the first engine, or from some other slight disarrangement; and collision has also taken place from the switches having been accidentally so left as to direct the train into a siding, instead of continuing it on the main line. Every train now carries fog signals, which are detonating packets, which are fixed upon the rails in advance or in the rear of a train which, whether from getting off the rails or otherwise, is stopped upon the line, and which are exploded by the wheels of any approaching train. 756. _Q._--What other duties of an engine-driver are there deserving attention? _A._--They are too various to be all enumerated here, and they also vary somewhat with the nature of the service. One rule, however, of universal application, is for the driver to look after matters himself, and not delegate to the stoker the duties which the person in charge of the engine should properly perform. Before leaving a station, the engine-driver should assure himself that he has the requisite supply of coke and water. Besides the firing tools and rakes for clearing the tubes, he should have with him in the tender a set of signal lamps and, torches, for tunnels and for night, detonating signals, screw keys, a small tank of oil, a small cask of tallow, and a small box of waste, a coal hammer, a chipping hammer, some wooden and iron plugs for the tubes, and an iron tube holder for inserting them, one or two buckets, a screw jack, wooden and iron wedges, split wire for pins, spare cutters, some chisels and files, a pinch bar, oil cans and an oil syringe, a chain, some spare bolts, and some cord, spun yarn, and rope. INDEX. Accidents in steam vessels, proper preparation for. Admiralty rule for horse power. Adhesion of wheels of locomotives to rails. Air, velocity of, entering a vacuum, required for combustion of coal; law of expansion of, by heat; Air pump, description of, action of; proper dimensions of. Air pump of marine engines, details of. Air pump of oscillating engine. Air pump of direct acting screw engines. Air pumps made both single and double acting, difference of, explained. Air pumps, double acting valves of, bad vacuum in; causes and remedy. Air pump rods, brass or copper, in marine engines. Air pump bucket, valves of. Air pump, connecting rod and cross head of oscillating engine. Air pump rod of oscillating engine. Air pump arm. Air vessels applied to suction side of pumps. "Alma," engine of, by Messrs. John Bourne & Co. "Amphion," engines of. Amoskeag steam fire engine. Angle iron in boilers, precautions respecting. Apparatus for raising screw propeller. Atmospheric valve. Atmospheric resistance to railway trains. Auxiliary power, screw vessels with. Axle bearings of locomotives. Axle guards. Axles and wheels of modern locomotives. "Azof," slide valve of. Babbitt's metal, how to compound. Balance piston to take pressure off slide valve. Ball valves. Barrel of boiler of modern locomotives. Beam, working of land engine, main or working strength proper for. Bearings of engines or other machinery, rule for determining proper surface of. Bearings, heating of, how to prevent or remedy, journals should always bottom, as, if they grip on the sides, the pressure is infinite. Beattie's screw. Belidor's valves might be used for foot and delivery valves. Bell-metal, composition of. Blast pipe of locomotives, description of. Blast in locomotives, exhaustion produced by, proper construction of the blast pipe; the blast pipe should be set below the root of the chimney so much that the cone of escaping steam shall just fill the chimney. Blast pipe with variable orifice, at one time much used. Blow-off cock of locomotives. Blow-off cocks of marine boilers, proper construction of. Blow-off cocks, description of. Blowing off supersalted water from marine boilers. Blowing off, estimate of heat lost by, mode of. Blow through valve, description of. Blowing furnaces, power necessary for. Bodies, falling, laws of. Bodmer, expansion valve by. Boilers, general description of: the wagon boiler, the Cornish boiler; the marine flue boiler; the marine tubular boiler; locomotive boiler--_see_ Locomotives. Boilers proportions of: heating surface of, fire grate, surface of; consumption of fuel on each square foot of fire bars in wagon, Cornish, and locomotive boilers; calorimmeter and vent of boilers; comparison of proportions of wagon, flue, and tubular boilers; evaporative power of boilers; power generated by evaporation of a cubic foot of water; proper proportions of modern marine boilers both flue and tubular; modern locomotive boilers; exhaustion produced by blast in locomotives; increased evaporation from increased exhaustion; strength of boilers; experiments on, by Franklin Institute; by Mr. Fairbairn; mode of computing strength of boilers; staying of. Boilers, marine, prevented from salting by blowing off, early locomotive and contemporaneous marine boilers compared; chimneys of land; rules for proportions of chimneys; chimneys of marine boilers. Boilers, constructive details of: riveting and caulking of land boilers, proving of; seams payed with mixture of whiting and linseed oil; setting of wagon boilers; riveting of marine boilers; precautions respecting angle iron; how to punch the rivet holes and shear edges of plates; setting of marine boilers in wooden vessels; mastic cement for setting marine boilers; composition of mastic cement; best length of furnace; configuration of furnace bars; advantages and construction of furnace bridges; various forms of dampers; precautions against injury to boilers from intense heat; tubing of boilers; proper mode of staying tube plates; proper mode of constructing steamboat chimneys; waste steam-pipe and funnel casing; telescope chimneys; formation of scale in marine boilers; injury of such incrustations; amount of salt in sea water; saltness permissible in boilers; amount of heat lost by blowing off; mode of discharging the supersalted water; Lamb's scale preventer; internal corrosion of marine boilers; causes of internal corrosion; surcharged steam produced from salt water; stop valves between boilers; safety or escape valve on feed pipe; locomotive boilers consist of the fire box, barrel for holding tubes, and smoke box; dimensions of the barrel and thickness of plates; mode of staying fire box and furnace crown; fire bars, ash box, and chimney; steam dome used only in old engines; manhole, mudholes, and blow-oft cock; tube plate, and mode of securing tubes; expanding mandrels; various forms of regulator. Boilers of modern locomotives. Boiler, the, proper care of, the first duty of the engineer. Bolts, proper proportions of. Boring of cylinders. Boulton and Watt's rules for fly wheel, proportions of marine flue boilers; rule for proportions of chimneys of land boilers; of marine boilers; experiments on the resistance of vessels in water. Bourdon's steam and vacuum gauges. Bourne, expansion valves by. Bourne, Messrs. J. & Co., direct acting screw engines by. Brass for bearings, composition of. Brazing solders. Bridges in furnaces, benefits of. Burning of boilers, precautions against. Bursting velocity of fly wheel, and of railway wheels. Bursting of boilers, causes of; precautions against; may be caused by accumulations of salt. Butterfly valves of air pump. Cabrey, expansion valve by. Calorimeter of boilers, definition of. Cams, proper forms of. Cast iron, strength of, proportions of cast iron beams; effects of different kinds of strains on beams; strength to resist shocks not proportional to strength to resist strains; to attain maximum strength should be combined with wrought iron. Casting of cylinders. Case-hardening, how to accomplish. Cataract, explanation of nature and uses of. Caulking of land boilers. Cement, mastic, for setting marine boilers. Central forces. Centre of pressure of paddle wheels. Centres of gravity, gyration and oscillation. Centres for fixing arms of paddle wheel. Centres of an engine, how to lay off. Centrifugal force, nature of, rule for determining; bursting velocity of fly wheel; and of railway wheels. Centrifugal pump will supersede common pump. Centripetal force, nature of. Chimney of locomotives. Chimney of steam vessels, what to do if carried away. Chimneys of land boilers, Boulton and Watt's rule for proportions of; of marine boilers. Chimneys, exhaustion produced by, high and wide chimneys in locomotives injurious. Chimneys of steamboats, telescope. Clark's patent steam fire regulator. Coal, constituents of, combustion of air required for; evaporative efficacy of; of wood, turf, and coke. Cocks, proper construction of. Cog wheels for screw engines. Coke, evaporative efficacy of. Cold water pump, description of, rule for size of. Combustion, nature of. Combustion of coal, air required for. Combustion, slow and rapid, comparative merits of, rapid combustion necessary in steam vessels, and enables less heating, surface in the boiler to suffice. Conchoidal propeller. Condensation of steam, water required for. Condenser, description of, action of; proper dimensions of. Condenser of oscillating engine. Condenser of direct acting screw engine. Condensing engine, definition of. Condensing water, how to provide when deficient. Conical pendulum or governor. Connecting rod, description of, strength proper for. Connecting rod of direct acting screw engines, of locomotives. Consumption of fuel on each square foot of fire bars in wagon, Cornish, and locomotive boilers. Copper, strength of. Corliss's steam engine. Corrosion produced by surcharged steam. Corrosion of marine boilers, causes of. Cost of locomotives. Cotton spinning, power necessary for. Counter for counting strokes of an engine. Crank, description of, unequal leverage of, corrected by fly wheel; no power lost by; action of; strength proper for. Crank of direct acting screw engines. Crank pin, strength proper for. Crank pin of direct acting screw engines. Cranked axle of locomotives. Cross head, description of, strength proper for. Cross head of direct acting screw engines. Cross tail, description of. Cylinder, description of, strength proper for. Cylinder of oscillating engine, of direct acting screw engine. Cylinders should have a steam jacket, and be felted and planted, should have escape valves. Cylinders of locomotives should be large, proper arrangement of. Cylinders, how to cast, how to bore; how to grind. Cylinder jacket, advantages of. Damper. Dampers, various forms of. Deadwood, hole in, for screw. Delivery valve, description of. Delivery or discharge valves, proper dimensions of. Delivery valves might be made on Belidor's plan. Delivery valves in mouth of air pump, of india rubber. Direct acting screw engines should be balanced. Direct acting screw engine by Messrs. John Bourne &, Co., cylinder; discs; guides; screw shaft brasses; air pump; slide valve; balance piston; connecting rod; piston rods; cross head; air pump arm; feed pump; crank pin; screw shaft; thrust plummer block; link motion; screw propeller. Discharge valves. Disc valves of india rubber for air pumps. Discs of direct acting screw engine instead of crank. Dodds, expansion valve by. Double acting engines, definition of. Double acting air pumps, valves of; faults of. Draw bolt. Dredging earth out of rivers, power necessary for. Driving wheels of locomotives. Driving piles, power necessary for. Duplex pump, Worthington's. Dundonald, Earl of, screw by. Duty of engines and boilers, how the duty is ascertainable. Dynamometer, description of. Dynamometric power of screw vessels. Eccentric, description of, sometimes made loose for backing. Eccentric and eccentric rod of oscillating engine. Eccentric notch should be fitted with a brass bush. Eccentric straps of locomotives, rods of locomotives. Eccentrics of locomotives, how to readjust. Economy of fuel in steam vessels. Edwards, expansion valve by. Elasticity, limits of. Engine, high pressure, definition of, low pressure, definition of. Engines, classification of, rotative, definition of; rotatory, definition of; single acting, definition of; double acting, definition of; mode of erecting in a vessel; how to refix if they have become loose. Engineers of steam vessels should make proper preparation for accidents. Equilibrium slide valve, grid-iron valve. Erecting engines in a vessel. Erection of engines in the workshop. Escape valve on feed pipe. Escape valves for letting water out of cylinders. Evaporative efficacy of coal, of wood, turf, and coke. Evaporative power of boilers, power generated by evaporation of a cubic foot of water; increase of evaporation due to increased exhaustion in locomotives. Excavator, Otis's. Exhaustion produced by chimneys, by the blast in locomotives; increased evaporation from increased exhaustion. Expanding mandrels for tubing boilers. Expansion of air by heat. Expansion of surcharged steam by heat. Expansion of steam, pressure of steam inversely as the space occupied; law of expansion; rule for computing the increase of efficiency produced by working expansively; necessity of efficient provisions against refrigeration in working expansively; advantages of steam jacket; Forms of apparatus for working expansively: lap on the slide valve wire drawing the steam; Cornish expansion valve, in rotative engines worked by a cam; mode of varying the degree of expansion; proper forms of cams; the link motion; expansion valves, by Cabrey, Fenton, Dodds, Farcot, Edwards, Lavagrian, Bodmer, Meyer, Hawthorn, Gonzenbach, and Bourne. Expansion joint in valve casing. Expansion valves, Cornish, the link motion; by Cabrey, Fenton, Dodds, Farcot, Edwards, Lavagrian, Bodmer, Meyer, Hawthorn, Gouzenbach, and Bourne. Explosions of boilers, causes of explosions; precautions against; dangers of accumulations of salt. Face plates or planometers. Falling bodies, laws of. Farcot, expansion valve by. Feathering paddle wheels, description of, details of. Feed pump, description of, action of; proper dimensions of; rule for proportioning. Feed pump plunger, and valves. Feed pumps of locomotives, details of. Feed pumps of direct acting screw engines. Fenton, expansion valve by. Fire bars of locomotives. Fire box of locomotives, mode of staying. Fire box of modern locomotives. Fire engines, cost of running. Fire grate surface of boilers. Fire grate in locomotives should be of small area, coke proper to be burned per hour on each square foot of bars. Firing furnaces, proper mode of. Flaws in valves or cylinders, how to remedy. Float for regulating water level in boilers. Floats of paddle. Floats of paddle wheels, increased resistance of, if oblique, floats should be large. Fly wheel corrects unequal leverage of crank, proper energy for; Boulton and Watt's rule for; bursting velocity of; description of; action of, in redressing irregularities of motion. Foot valve, description of, proper dimensions of. Foot valves might be made on Belidor's plan, of india rubber. Frame at stern for holding screw propeller. Framing of locomotives. Framing of oscillating engine. Franklin Institute, experiments on steam by. French Academy, experiments on steam by. Friction, nature of, does not vary as the rubbing surfaces, but as the retaining pressure; does not increase with the velocity per unit of distance, but increases with the velocity per unit of time; measures of friction; effect of unguents; kind of unguent should vary with the pressure; Morin's experiments; rule for determining proper surfaces of bearings; friction of rough surfaces. Friction of the water the main cause of the resistance of vessels of good shape. Fuel burnt on each square foot of fire bars in wagon, Cornish, and locomotive boilers, economy of, in steam vessels. Funnel casing. Funnel, what to do if carried away. Funnels of steam boats. _See_ Chimneys. Furnaces, proper mode of firing, smoke burning: Williams's argand; Prideaux's; Boulton and Watt's dead plate; revolving crate; Juckes's; Maudslay's; Hull's, Coupland's, Godson's, Robinson's, Stevens's, Hazeldine's, &c.. Furnaces of marine boilers, proper length of. Furnace bridges, benefits of. Fusible metal plugs useless as antidotes to explosions. Gauges, vacuum, steam; gauge cocks and glass tubes for showing level of water in boiler, description of. Gauge cocks for showing level of water in boiler. Gearing for screw engines. Gibs and cutters, strengths proper for. Giffard's injector. Glass tubes for showing water level in boilers. Glass tube cocks. Gonzeubach, expansion valve by. Gooch's indicator. Gooch's locomotive. Governor or conical pendulum, description of. Governor, Porter's patent. Gravity, centre of. "Great Western," boilers of, by Messrs. Maudslay. Gridiron valve. Griffith's screw. Grinding corn, power necessary for. Grinding of cylinders. Gudgeons, strength proper for. Guides of locomotives. Guides of direct acting screw engine. Gun metal, strength of. Gyration, centre of. Harvey and West's pump valves. Hawthorn, expansion valve by. Heat, latent, definition of. Heat, specific, definition of. Heat, Regnault's experiments on. Heat, loss of, by blowing off marine boilers. Heating surface of boilers. Heating surface per square foot of fire bars in locomotives, a cubic foot of water evaporates by five square feet of heating surface. Heating of bearings, causes of, bearings should always be slack at the sides, else the pressure is infinite. High pressure engine, definition of. High pressure engines, power of. High speed engines, arrangements proper for high speeds. Hoadley's portable engine. Hodgson's screw. Hoe & Co.'s steam engine. Holding down bolts of marine engines, or bolts for securing engines to hull. Holms's screw propeller. Horses power, definition of, nominal horse power; actual power ascertained by the indictator; Admiralty rule for. Hot water or feed pump, description of. Hot well, description of. Increasing pitch of screw. Incrustation in boilers. _See_ also Salt. India rubber valves for air pump. Indicator, description of the, by McNaught, structure and mode of using; Gooch's continuous indicator. Injection cock. Injection cocks of marine engines at ship's sides. Injection orifice, proper area of. Injector, Giffard's. Injection valve. Inside cylinder locomotives. Iron, strength of, limits of elasticity of; proper strain to be put upon iron in engines and machines; aggravation of strain by being intermittent; increase of strain due to deflection; strength of pillars and tubes, combination of malleable and cast iron. Iron, cast, strength of, cast iron beams; may be strong to resist strains, but not strong to resist shocks; should be combined with wrought iron to obtain maximum strength. Iron, if to be case hardened, should be homogeneous. Jacket of cylinder, advantages of. Joints, rust, how to make. Kingston's valves. Lamb's scale preventer. Lantern brass in stuffing boxes. Lap and lead of the valve, meaning of. Large vessels have least proportionate resistance. Latent heat, definition of. Latta's steam fire engine. Lavagrian, expansion valve by. Lead and lap of the valve, meaning of. Lead of the valve, benefits of. Lever, futility of plans for deriving power from a lever. Lifting apparatus for screw propeller. Limits of elasticity. Links, main description of. Link motion of direct acting screw engine. Link motion, how to set. Locomotive engines, general description of the locomotive; Stephenson's locomotive; Gooch's locomotive for the wide gauge; Crampton's locomotive for the narrow gauge. Locomotives, adhesion of wheels of, cost and performance of; framing of; cylinders of; springs of; outside and inside cylinders; sinuous motion of; rocking motion of; pitching motion of; pistons; piston rods; guides; cranked axle; axle bearings; eccentrics; eccentric rod; starting handle; link motion; valves, how to set; eccentrics, how to readjust; feed pumps; connection of engine and tender, driving wheels; wheel tires. Locomotive engine of modern construction, example of, fire box; barrel of boiler; tubes; tube plate; framing; axle guards; draw bolt; wheels and axles; cylinders; valve; piston; piston rod; guides; connecting rod; eccentrics; link motion; regulator; blast pipe; safety valve; feed pump; tendencies of improvement in locomotives. Locomotives, management of. Locomotive boilers, examples of modern proportions. Locomotive boilers, details of. Low pressure or condensing engine, definition of. Lubrication of rubbing surfaces, the friction depends mainly on the nature of lubricant; oil forced out of bearings, if the pressure exceeds 800 lbs. per square inch longitudinal section; water a good lubricant if the surfaces are large enough. Lubrication of engine bearings. McNaught's indicator. Main beam, strength proper for. Main centre, description of, strength proper for. Main links, description of, strength proper for. Mandrels, expanding, for tubing boilers. Manhole door. Manhole of locomotives. Marine flue boilers, proportions of. _See_ also Boilers. Marine boilers of modern construction, proper proportions of. Marine engines. _See_ Steam Engines, marine. Mastic cement for setting marine boilers. Maudslay, Messrs., boilers of "Retribution" and "Great Western," by, Mechanical powers, misconceptions respecting. Mechanical power, definition of, indestructible and eternal; the sun the source of mechanical power. Metallic packing for pistons. Metallic packing for stuffing boxes. Meyer, expansion valve by. Miller, Ravenhill & Co.'s mode of fixing piston rod to piston. Modern locomotives. Momentum, or _vis viva_. Morin, experiments on friction by. Mudholes of locomotives. Muntz's metal, composition of. "Niger" and "Basilisk," trials of. "Nile," boilers of the, by Boulton and Watt. Notch of eccentric should be fitted with brass bush. Oils for lubrication. _See_ Lubrication. Oscillation, centre of. Oscillating paddle engine, description of. Oscillating engine, advantages of, futility of objections to; details of cylinder; framing; condenser; air pump; trunnions; valve and valve casing; piston; piston rod; air pump connecting rod and cross head; air pump rod; eccentric and eccentric rod; valve gear; valve sector; shaft plummer blocks; trunnion plummer blocks; feathering paddle wheels; packing of trunnions. Oscillating engines, how to erect. Otis's excavator. Outside and inside cylinder locomotives. Packing for stuffing box of Watt's engine. Packing of piston of pumping engines, how to accomplish. Packing of trunnions. Paddle bolts, proper mode of forming. Paddle centres. Paddle floats. Paddle shaft, description of. Paddle shaft, details of. Paddle shaft plummer blocks of oscillating engines. Paddle wheels, details of, structure and operation of; slip of; centre of pressure of; rolling circle; action of oblique floats; rule for proportioning paddle wheels; benefits of large floats. Paddle wheels, feathering, description of; details of. Paddles and screw combined. Parallel motion, description of, how to lay off centres of. Pendulum, cause of vibrations of; relation of vibrations of pendulum to velocity of falling bodies; conical pendulum or governor. Penn, Messrs., engines of "Great Britain," by, direct acting screw engines by; trunk engines by. Performance of locomotives. Pillars, hollow, strength of, law of strength varies with thickness of metal. Pipe for receiving screw shaft. Pipes of marine engines. Piston, description of, how to pack with hemp. Pistons, metallic packing for. Pistons for oscillating engines. Pistons, how to fit and finish. Pistons of locomotives. Piston rod, description of, strength proper for. Piston rods of locomotives. Piston rod of oscillating engine. Piston rods of direct acting screw engine. Pitch of the screw. Pitch, increasing or expanding. Pitching motion in locomotives. Planometers, or face plates. Plummer blocks of shafts and trunnions of oscillating engines. Plummer blocks for receiving thrust of screw propeller. Plunger of feed pump. Portable engine, Hoadley's. Porter's patent governor. Ports of the cylinder, area of. Pot-lid valves of air pump. Powers, mechanical, misconception respecting. Power, horses, definition of, nominal and actual power; power of high pressure engines. Power necessary for thrashing and grinding corn, working sugar mills, spinning cotton, sawing timber, grossing cotton, blowing furnaces, driving piles, and dredging earth out of rivers. Pressing cotton, power necessary for. Priming, nature and causes of. Priming, if excessive, may occasion explosion. Propeller, screw, description of. Proportions of screws with, two, four, and six blades. Proving of boilers. Prussiate of potash for case hardening. Pumping engines, mode of erecting, mode of starting. Pumps, loss of effect in, at high speed and with hot water, causes of this loss; remedy for. Pumps used for mines. Pump, air, description, of, action of. Pumps, air, proper proportions of, single and double acting. Pump, centrifugal, better than common pump. Pump, cold water, description of. Pump, feed, description of, action of; proper dimensions of; rule for proportioning; plunger of; valves of; independent. Pump valves for mines, &c. Punching and shearing boiler plates. Railway wheels, bursting velocity of. Railway trains, resistance of. Rarefaction or exhaustion produced by chimneys. "Rattler" and "Alecto," trials of. Registration, benefits of. Regnault, experiments on heat by. Regulator, a valve for regulating the admission of steam in locomotives, description of; various forms of. Regulator, Clark's, patent steam and fire. Rennie, experiments on friction by. Resistance, experienced by railway trains. Resistance of vessels in water, mainly made up of friction; experiments on. Resistance and speed of vessels influenced by their size. "Retribution," boilers of, by Messrs. Mandslay. Riveting and caulking of land boilers. Rocking motion of locomotives. Rolling circle of paddle wheels. Rotatory engines, definition of. Rotative engines, definition of. Rust joints, how to make. Safety valve, area of, in low pressure engines, in locomotives. Salinometer, or salt gauge, how to use, how to construct. Salt, accumulation of, prevented in marine boilers by blowing off, if allowed to accumulate in boilers may occasion explosion; amount of, in sea water. Salt water produces surcharged steam. Salting of boilers, what to do if this takes place. Sawing timber, power necessary for. Scale in marine boilers. _See_ also Salt. Scale preventer, Lamb's. Scrap iron, unsuitable for case hardening. Scraping tools for metal surfaces. Screw. Screw engine, geared oscillating, description of, direct acting, description of. Screw engine, direct acting, by Messrs. John Bourne & Co. Screw engines, best forms of. Screw frame in deadwood. Screw propeller, description of. Screw propeller, mode of fixing on shaft, modes of receiving thrust; apparatus for lifting; configuration of; action of; pitch of the screw; screws of increasing or expanding pitch; slip of the screw; positive and negative slip; screw and paddles compared; test of the dynamometer; trials of "Rattler" and "Alecto," and "Niger" and "Basilisk"; indicator and dynamometer power; loss of power in screw vessels in head winds; the screw should be deeply immersed; screws of the Earl of Dundonald, Hodgson, Griffith, Holm, and Beattie; lateral and retrogressive slip; sterns of screw vessels should be sharp; proportions of screws with two, four, and six blades; screw vessels with auxiliary power; screw and paddles combined; economy of fuel in steam vessels; benefits of registration. Screw propeller, Holm's conchoidal. Screw shaft, details of. Screw shaft pipe at stern. Screw shaft brasses of direct acting screw engines. Sea water, amount of salt in. Sea injection cocks. Setting of wagon boilers, of marine boilers. Setting the valves of locomotives. Shaft, paddle, details of. Shaft of screw propeller, details of. Shafts, strength of. Shank's steam gauge. Shocks may not be well resisted by iron that can well resist strains, effect of inertia in resisting shocks. Side levers or beams, description of. Side lever marine engines, description of. Side lever engines, how to erect. Side rods, description of, strength proper for. Silsbee, Mynderse & Co.'s steam fire engine. Single acting engines, definition of. Single acting or pumping engines, mode of erecting; mode of starting. Sinuous motion of locomotives. Slide valve, various forms of; long D and three ported valve, description of; action of the slide valve; lead and lap of the valve; rules for determining the proportions of valves; advantages of lead in swift moving engines. Slide valve, equilibrium. Slide valve with balance piston of direct acting screw engine. Slide valve, how to finish. Slide valves of marine engines, how to set. Slip of paddle wheels. Slip of the screw, positive and negative slip; lateral and retrogressive slip. Smoke, modes of consuming. Smoke burning furnaces, Williams's argand; Prideaux's; Boulton and Watt's dead plate; revolving grate; Juckes's; Maudslay's; Hall's, Coupland's, Godson's, Robinson's, Stevens's, Hazeldine's, &c. "Snake" locomotive. Southern, experiments on friction by; experiments on steam by. Specific heat, definition of. Speed of vessels influenced by their size. Spheroidal condition of water in boilers. Springs of locomotives. Stand pipe for low pressure boilers. Starting handle of locomotives. Staying of boilers. Staying tube plates, mode of. Staying fire boxes of locomotives. Steam, experiments on by Southern, French Academy, Franklin Institute, and M. Regnault. Steam pump, Worthington's; Woodward's. Steam and water, relative bulks of. Steam, expansion of; pressure of; inversely as space occupied; _See also_ Expansion of Steam. Steam engine, applications and appliances of the. Steam engine, general description of Watt's double acting engine; R. Hoe & Co.'s; Corliss's; Woodruff & Beach's. Steam engine, various forms of, for propelling vessels; paddle engines and screw engines; principal varieties of paddle engines; different kinds of paddle wheels; the side lever engine; description of the side lever engine; oscillating paddle engine; description of feathering paddle wheels; direct acting screw engine. Steam dome of locomotives. Steam fire engine, Latta's. Amoskeag. Silsbee, Mynderse & Co.'s. Steam gauge, Bourdon's; Shank's. Steam jacket, benefits of; Steam passages, area of; Steam room in boilers; Steam, surcharged, law of expansion by heat; Steel, strength of; Stephenson, link motion by; Stop valves between boilers; Straight edges; Strains subsisting in machines; Strain proper to be put upon iron in engines; Strains in machines, vary inversely as the velocity of the part to which the strain is applied. aggravated by being intermittent. increase of strain due to deflection. effects of alternate strains in opposite directions. Strength of materials. Strength of hollow pillars, law of; strength varies with thickness of metal. Strength of cast iron to resist shocks does not vary as the strength to resist strains, increase of strength by combination with cast iron. Strength of boilers, experiments on, by Franklin Institute; by Mr. Fairbairn; mode of computing; mode of staying for strength. Strength of engines: cylinder, trunnions; piston rod; main links; connecting rod; studs of the beam; gudgeons; working beam; cast iron shaft; malleable iron shaft; teeth of wheels; side rods; crank; crank pin; cross head; main centre; gibs and cutter. Studs, strength proper for. Stuffing box, description of. Stuffing boxes with metallic packing, with sheet brass packed behind with hemp; sometimes fitted with a lantern, brass. Sugar mills, power necessary to work. Summers' experiments on the friction of rough surfaces. Surcharged steam, law of expansion of, by heat. Surcharged steam produced by salt water, corrosive action of. Surfaces, how to make true. Sweeping the tubes of boilers clean of soot. Teeth of wheels. Telescope chimneys. Tender of a locomotive, description of, attachment of, to engine. Thrashing corn, power necessary for. Throttle valve, description of. Thrust of the screw propeller, modes of receiving. Thrust plummer block. Tires of locomotive wheels. Traction on railways. Trunk engine by Messrs. Rennie, disadvantages of. Trunk engines by Messrs. Penn. Trunnions of oscillating engines, description of, strength proper for; details of. Trunnion packing. Trunnion plummer blocks. Tube plates, mode of staying. Tube plates of modern locomotives. Tubes of modern locomotive boilers. Tubes of boilers, how to sweep clean of soot. Tubing of boilers. Tubing locomotive boilers. Valve, atmospheric. Valve casing, description of. Valve casing should have expansion joint. Valve and valve casing of oscillating engine. Valve delivery, description of, action of Valve, equilibrium slide. Valve, foot, description of, action of. Valve gear of Watt's engine, action of. Valve gear of oscillating engine. Valve, gridiron. Valve, slide. _See_ Slide Valve. Valve, slide, how to finish. Valves, ball, Belidor's might be used for foot and delivery valves; butterfly, of air pump; concentric ring, for air pump bucket. Valves, equilibrium. Valves, escape, for cylinders. Valves, expansion. _See_ Expansion Valves. Valves of feed pumps. Valves, india rubber, for air pump. Valves, Kingston's. Valves of locomotives, how to set. Valves, pot-lid, of air pump. Vacuum, meaning of, nature and uses of; how maintained in engines. Vacuum sometimes occurs in boilers, evils of a vacuum in boilers. Vacuum, velocity with which air rushes into a. Vacuum gauge, Bourdon's. Velocity of air entering a vacuum. Velocity of falling bodies. Vent of boilers, definition of. Vessels, resistance of, mainly made up of friction in good forms; experiments on; influence of size. _Vis viva_, or mechanical power. Waste steam pipe. Waste water pipe. Water required for condensation, pumps for supplying. Watt's double acting engine, description of. Wedge. Wheels, toothed, for screw engines. Wheels, teeth of. Wheels of locomotives, adhesion of. Wheels, driving, of locomotives. Wheel tires. Wheels and axles of modern locomotives. Wood, experiments on friction by. Wood, evaporative efficacy of. Woodman's steam pump. Woodruff & Beach's steam engine. Working beam of land engine, description of. Worthington's steam pump, duplex pump. THE END. 
35916	----	+-------------------------------------------------------------------+ | | | TRANSCRIBER'S NOTES: | | | | | |Formatting and coding information: | | - Text in italics is marked with underscores as in _text_. | | - Bold-face text is marked =text=. | | - Superscript x and subscript x are represented as ^{x} and _{x},| | respectively. | | - sqrt(x) represents the square root of x. | | - [oe] and [OE] represent the oe-ligatures. | | - Greek letters are written between square brackets, as in [tau] | | or [theta]. | | - Overlined 1 is represented as [=1]. | | - [<] represents a 'rotated [Delta]'. | | | |General remarks: | | - Footnotes have been moved to directly below the paragraph they | | refer to. | | - In-line multiple line formulas have been changed to in-line | | single-line formulas, with brackets added when needed. | | - The Table of Contents has been corrected to conform to the text| | rather than to the original Table of Contents. | | - The table on operating costs of trains gives 'Other expenses | | per square mile.' This has been changed to 'Per mile' the same | | as the other expenses. | | - The table on dimensions of farm and road locomotives gives the | | diameter of the boiler shell as 30 feet, which seems unlikely. | | - Feet are sometimes used as unit of area, both knots and knots | | per hour as unit of speed. | | | |Changes in text: | | - Reference letters in the text have in several cases been | | changed to conform to the letters used in the illustrations. | | - Minor typographical errors have been corrected. | | - Except when mentioned here, inconsistencies in spelling | | and hyphenation have not been corrected. Exceptions: | | 'Desagulier' to 'Desaguliers' | | 'Séguin' to 'Seguin' | | 'Goldworthy Gurney' to 'Goldsworthy Gurney' | | 'Ctesibus' to 'Ctesibius' | | 'i.e.' to 'i. e.' | | 'Warmetheorie' to 'Wärmetheorie' | | 'tour a tour' to 'tour à tour' | | 'the beam passes to the' to 'the steam passes to the' | | 'Desagulier' to 'Desaguliers' | | 'éléver' to 'élever'. | | - 'As early as 1743' moved to new paragraph. | | - 'A = 6.264035' changed to 'a = 6.264035.' | | | +-------------------------------------------------------------------+ THE INTERNATIONAL SCIENTIFIC SERIES. VOLUME XXIV. THE INTERNATIONAL SCIENTIFIC SERIES. EACH BOOK COMPLETE IN ONE VOLUME, 12MO, AND BOUND IN CLOTH. 1. FORMS OF WATER: A Familiar Exposition of the Origin and Phenomena of Glaciers. By J. TYNDALL, LL. D., F. R. S. With 25 Illustrations. $1.50. 2. PHYSICS AND POLITICS; Or, Thoughts on the Application of the Principles of "Natural Selection" and "Inheritance" to Political Society. By WALTER BAGEHOT. $1.50. 3. FOODS. 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By ALPHONSE DE CANDOLLE. $2.00. 49. JELLY-FISH, STAR-FISH, AND SEA-URCHINS. Being a Research on Primitive Nervous Systems. By GEORGE J. ROMANES. $1.75. 50. THE COMMON SENSE OF THE EXACT SCIENCES. By the late WILLIAM KINGDON CLIFFORD. $1.50. 51. PHYSICAL EXPRESSION: Its Modes and Principles. By FRANCIS WARNER, M. D., Assistant Physician, and Lecturer on Botany to the London Hospital, etc. With 51 Illustrations. $1.75. 52. ANTHROPOID APES. By ROBERT HARTMANN, Professor in the University of Berlin. With 63 Illustrations. $1.75. 53. THE MAMMALIA IN THEIR RELATION TO PRIMEVAL TIMES. By OSCAR SCHMIDT. $1.50. New York: D. APPLETON & CO., 1, 3, & 5 Bond Street. [Illustration: THE GRECIAN IDEA OF THE STEAM-ENGINE.] THE INTERNATIONAL SCIENTIFIC SERIES. A HISTORY OF THE GROWTH OF THE STEAM-ENGINE. BY ROBERT H. THURSTON, A. M., C. E., PROFESSOR OF ENGINEERING STEVENS INSTITUTE OF TECHNOLOGY, PAST PRESIDENT AMERICAN SOCIETY MECHANICAL ENGINEERS, MEMBER OF SOCIETY OF CIVIL ENGINEERS, SOCIÉTÉ DES INGÉNIEURS CIVILS, VEREIN DEUTSCHE INGENIEURE, OESTERREICHISCHER INGENIEUR- UND ARCHITEKTEN-VEREIN; ASSOCIATE BRITISH INSTITUTION OF NAVAL ARCHITECTS, ETC., ETC. _SECOND REVISED EDITION._ NEW YORK: D. APPLETON AND COMPANY, 1, 3, AND 5 BOND STREET. 1886. COPYRIGHT, 1878, 1884, BY ROBERT H. THURSTON. PREFACE. This little work embodies the more generally interesting portions of lectures first written for delivery at the STEVENS INSTITUTE OF TECHNOLOGY, in the winter of 1871-'72, to a mixed audience, composed, however, principally of engineers by profession, and of mechanics; it comprises, also, some material prepared for other occasions. These lectures have been rewritten and considerably extended, and have been given a form which is more appropriate to this method of presentation of the subject. The account of the gradual development of the philosophy of the steam-engine has been extended and considerably changed, both in arrangement and in method. That part in which the direction of improvement during the past history of the steam-engine, the course which it is to-day taking, and the direction and limitation of that improvement in the future, are traced, has been somewhat modified to accord with the character of the revised work. The author has consulted a large number of authors in the course of his work, and is very greatly indebted to several earlier writers. Of these, Stuart[1] is entitled to particular mention. His "History" is the earliest deserving the name; and his "Anecdotes" are of exceedingly great interest and of equally great historical value. The artistic and curious little sketches at the end of each chapter are from John Stuart, as are, usually, the drawings of the older forms of engines. [1] "History of the Steam-Engine," London, 1824. "Anecdotes of the Steam-Engine," London, 1829. Greenwood's excellent translation of Hero, as edited by Bennett Woodcroft (London, 1851), can be consulted by those who are curious to learn more of that interesting old Greek treatise. Some valuable matter is from Farey,[2] who gives the most extended account extant of Newcomen's and Watt's engines. The reader who desires to know more of the life of Worcester, and more of the details of his work, will find in the very complete biography of Dircks[3] all that he can wish to learn of that great but unfortunate inventor. Smiles's admirably written biography of Watt[4] gives an equally interesting and complete account of the great mechanic and of his partners; and Muirhead[5] furnishes us with a still more detailed account of his inventions. [2] "Treatise on the Steam-Engine," London, 1827. [3] "Life, Times, and Scientific Labors of the Second Marquis of Worcester," London, 1865. [4] "Lives of Boulton and Watt," London, 1865. [5] "Life of James Watt," D. Appleton & Co., New York, 1859. "Mechanical Inventions of James Watt," London, 1854. For an account of the life and work of John Elder, the great pioneer in the introduction of the now standard double-cylinder, or "compound," engine, the student can consult a little biographical sketch by Prof. Rankine, published soon after the death of Elder. The only published sketch of the history of the science of thermo-dynamics, which plays so large a part of the philosophy of the steam-engine, is that of Prof. Tait--a most valuable monograph. The section of this work which treats of the causes and the extent of losses of heat in the steam-engine, and of the methods available, or possibly available, to reduce the amount of this now immense waste of heat, is, in some respects, quite new, and is equally novel in the method of its presentation. The portraits with which the book is well furnished are believed to be authentic, and, it is hoped, will lend interest, if not adding to the real value of the work. Among other works which have been of great assistance to the author, and will be found, perhaps, equally valuable to some of the readers of this little treatise, are several to which reference has not been made in the text. Among them the following are deserving of special mention: Zeuner's "Wärmetheorie," the treatises of Stewart and of Maxwell, and McCulloch's "Mechanical Theory of Heat," a short but thoroughly logical and exact mathematical treatise; Cotterill's "Steam-Engine considered as a Heat-Engine," a more extended work on the same subject, which will be found an excellent companion to, and commentary upon, Rankine's "Steam-Engine and Prime Movers," which is the standard treatise on the theory of the steam-engine. The works of Bourne, of Holley, of Clarke, and of Forney, are standards on the practical every-day matters of steam-engine construction and management. The author is almost daily in receipt of inquiries which indicate that the above remarks will be of service to very many young engineers, as well as to many to whom the steam-engine is of interest from a more purely scientific point of view. CONTENTS. CHAPTER I. THE STEAM-ENGINE AS A SIMPLE MACHINE. PAGE SECTION I.--THE PERIOD OF SPECULATION--FROM HERO TO WORCESTER, B. C. 200 TO A. D. 1650 1 Introduction--the Importance of the Steam-Engine, 1; Hero and his Treatise on Pneumatics, 4; Hero's Engines, B. C. 200, 8; William of Malmesbury on Steam, A. D. 1150, 10; Hieronymus Cardan on Steam and the Vacuum, 10; Malthesius on the Power of Steam, A. D. 1571, 10; Jacob Besson on the Generation of Steam, A. D. 1578, 11; Ramelli's Work on Machines, A. D. 1588, 11; Leonardo da Vinci on the Steam-Gun, 12; Blasco de Garay's Steamer, A. D. 1543, 12; Battista della Porta's Steam-Engine, A. D. 1601, 13; Florence Rivault on the Force of Steam, A. D. 1608, 15; Solomon de Caus's Apparatus, A. D. 1615, 16; Giovanni Branca's Steam-Engine, A. D. 1629, 16; David Ramseye's Inventions, A. D. 1630, 17; Bishop John Wilkins's Schemes, A. D. 1648, 18; Kircher's Apparatus, 19. SECTION II.--THE PERIOD OF APPLICATION--WORCESTER, PAPIN, AND SAVERY 19 Edward Somerset, Marquis of Worcester, A. D. 1663, 19; Worcester's Steam Pumping-Engines, 21; Jean Hautefeuille's Alcohol and Gunpowder Engines, A. D. 1678, 24; Huyghens's Gunpowder-Engine, A. D. 1680, 25; Invention in Great Britain, 26; Sir Samuel Morland, A. D. 1683, 27; Thomas Savery and his Engine, A. D. 1698, 31; Desaguliers's Savery Engines, A. D. 1718, 41; Denys Papin and his Work, A. D. 1675, 45; Papin's Engines, A. D. 1685-1695, 50; Papin's Steam-Boilers, 51. CHAPTER II. THE STEAM-ENGINE AS A TRAIN OF MECHANISM. THE MODERN TYPE AS DEVELOPED BY NEWCOMEN, BEIGHTON, AND SMEATON 55 Defects of the Savery Engine, 55; Thomas Newcomen, A. D. 1705, 57; the Newcomen Steam Pumping-Engine, 59; Advantages of Newcomen's Engine, 60; Potter's and Beighton's Improvements, A. D. 1713-'18, 61; Smeaton's Newcomen Engines, A. D. 1775, 64; Operation of the Newcomen Engine, 65; Power and Economy of the Engine, 69; Introduction of the Newcomen Engine, 70. CHAPTER III. THE DEVELOPMENT OF THE MODERN STEAM-ENGINE. JAMES WATT AND HIS CONTEMPORARIES. SECTION I.--JAMES WATT AND HIS INVENTIONS 79 James Watt, his Birth and Parentage, 79; his Standing in School, 81; he learns his Trade in London, 81; Return to Scotland and Settlement in Glasgow, 82; the Newcomen Engine Model, 83; Discovery of Latent Heat, 84; Sources of Loss in the Newcomen Engine, 85; Facts experimentally determined by Watt, 86; Invention of the Separate Condenser, 87; the Steam-Jacket and other Improvements, 90; Connection with Dr. Roebuck, 91; Watt meets Boulton, 93; Matthew Boulton, 93; Boulton's Establishment at Soho, 95; the Partnership of Boulton and Watt, 97; the Kinneil Engine, 97; Watt's Patent of 1769, 98; Work of Boulton and Watt, 101; the Rotative Engine, 103; the Patent of 1781, 104; the Expansion of Steam--its Economy, 105; the Double-Acting Engine, 110; the "Compound" Engine, 110; the Steam-Hammer, 111; Parallel Motions, the Counter, 112; the Throttle-Valve and Governor, 114; Steam, Vacuum, and Water Gauges, 116; Boulton & Watt's Mill-Engine, 118; the Albion Mill and its Engine, 119; the Steam-Engine Indicator, 123; Watt in Social Life, 125; Discovery of the Composition of Water, 126; Death of James Watt, 128; Memorials and Souvenirs, 128. SECTION II.--THE CONTEMPORARIES OF JAMES WATT 132 William Murdoch and his Work, 132; Invention of Gas-Lighting, 134; Jonathan Hornblower and the Compound Engine, 135; Causes of the Failure of Hornblower, 137; William Bull and Richard Trevithick, 138; Edward Cartwright and his Engine, 140. CHAPTER IV. THE MODERN STEAM-ENGINE. THE SECOND PERIOD OF APPLICATION--1800-1850--STEAM-LOCOMOTION ON RAILROADS 144 Introduction, 144; the Non-Condensing Engine and the Locomotive, 147; Newton's Locomotive, 1680, 149; Nathan Read's Steam-Carriage, 150; Cugnot's Steam-Carriage, 1769, 151; the Model Steam-Carriage of Watt and Murdoch, 1784, 153; Oliver Evans and his Plans, 1786, 153; Evans's Oruktor Amphibolis, 1804, 157; Richard Trevithick's Steam-Carriage, 1802, 159; Steam-Carriages of Griffiths and others, 160; Steam-Carriages of Goldsworthy Gurney, 1827, 161; Steam-Carriages of Walter Hancock, 1831, 165; Reports to the House of Commons, 1831, 170; the Introduction of the Railroad, 172; Richard Trevithick's Locomotives, 1804, 174; John Stevens and the Railroad, 1812, 178; William Hedley's Locomotives, 1812, 181; George Stephenson, 183; Stephenson's Killingworth Engine, 1813, 186; Stephenson's Second Locomotive, 1815, 187; Stephenson's Safety-Lamp, 1815, 187; Robert Stephenson & Co., 1824, 190; the Stockton & Darlington Engine, 1825, 191; the Liverpool & Manchester Railroad, 1826, 193; Trial of Competing Engines at Rainhill, 1829, 195; the Rocket and the Novelty, 198; Atmospheric Railways, 201; Character of George Stephenson, 204; the Locomotive of 1833, 204; Introduction of Railroads in Europe, 206; Introduction of Railroads in the United States, 207; John Stevens's Experimental Railroad, 1825, 207; Horatio Allen and the "Stourbridge Lion," 1829, 208; Peter Cooper's Engine, 1829, 209; E. L. Miller and the S. C. Railroad, 1830, 210; the "American" Type of Engine of John B. Jervis, 1832, 212; Robert L. Stevens and the T-rail, 1830, 214; Matthias W. Baldwin and his Engine, 1831, 215; Robert Stephenson on the Growth of the Locomotive, 220. CHAPTER V. THE MODERN STEAM-ENGINE. THE SECOND PERIOD OF APPLICATION--1800-1850 (CONTINUED)--THE STEAM-ENGINE APPLIED TO SHIP-PROPULSION 221 Introduction, 221; Ancient Prophecies, 223; the Earliest Paddle-Wheel, 223; Blasco de Garay's Steam-Vessel, 1543, 224; Experiments of Dionysius Papin, 1707, 214; Jonathan Hulls's Steamer, 1736, 225; Bernouilli and Gauthier, 228; William Henry, 1782, 230; the Comte d'Auxiron, 1772, 232; the Marquis de Jouffroy, 1776, 233; James Rumsey, 1774, 234; John Fitch, 1785, 285; Fitch's Experiments on the Delaware, 1787, 237; Fitch's Experiments at New York, 1796, 240; the Prophecy of John Fitch, 241; Patrick Miller, 1786-'87, 241; Samuel Morey, 1793, 243; Nathan Read, 1788, 244; Dundas and Symmington, 1801, 246; Henry Bell and the Comet, 1811, 248; Nicholas Roosevelt, 1798, 250; Robert Fulton, 1802, 251; Fulton's Torpedo-Vessels, 1801, 252; Fulton's First Steamboat, 1803, 253; the Clermont, 1807, 257; Voyage of the Clermont to Albany, 259; Fulton's Later Steamboats, 260; Fulton's War-Steamer Fulton the First, 1815, 261; Oliver Evans, 1804, 263; John Stevens's Screw-Steamer, 1804, 264; Stevens's Steam-Boilers, 1804, 264; Stevens's Iron-Clad, 1812, 268; Robert L. Stevens's Improvements, 270; the "Stevens Cut-off," 1841, 276; the Stevens Iron-Clad, 1837, 277; Robert L. Thurston and John Babcock, 1821, 280; James P. Allaire and the Messrs. Copeland, 281; Erastus W. Smith's Compound Engine, 283; Steam-Navigation on Western Rivers, 1811, 283; Ocean Steam-Navigation, 1808, 285; the Savannah, 1819, 286; the Sirius and the Great Western, 1838, 289; the Cunard Line, 1840, 290; the Collins Line, 1851, 291; the Side-Lever Engine, 292; Introduction of Screw-Steamers, 293; John Ericsson's Screw-Vessels, 1836, 294; Francis Pettit Smith, 1837, 296; the Princeton, 1841, 297; Advantages of the Screw, 299; the Screw on the Ocean, 300; Obstacles to Improvement, 301; Changes in Engine-Construction, 302; Conclusion, 303. CHAPTER VI. THE STEAM-ENGINE OF TO-DAY. THE PERIOD OF REFINEMENT--1850 TO DATE 303 Condition of the Steam-Engine at this Time, 303; the Later Development of the Engine, 304; Stationary Steam-Engines, 307; the Steam-Engine for Small Powers, 307; the Horizontal Engine with Meyer Valve-Gear, 311; the Allen Engine, 314; its Performance, 316; the Detachable Valve-Gear, 316; the Sickels Cut-off, 317; Expansion adjusted by the Governor, 318; the Corliss Engine, 319; the Greene Engine, 321; Perkins's Experiments, 323; Dr. Alban's Work, 325; the Perkins Compound Engine, 327; the Modern Pumping-Engine, 328; the Cornish Engine, 328; the Steam-Pump, 331; the Worthington Pumping-Engine, 333; the Compound Beam and Crank Engine, 335; the Leavitt Pumping-Engine, 336; the Stationary Steam-Boiler, 338; "Sectional" Steam-Boilers, 343; "Performance" of Boilers, 344. SECTION II.--PORTABLE AND LOCOMOTIVE ENGINES. 347 The Semi-Portable Engine, 348; Performance of Portable Engines, 350; their Efficiency, 352; the Hoadley Engine, 354; the Mills Farm and Road Engine, 356; Fisher's Steam-Carriage, 356; Performance of Road-Engines, 357; Trial of Road-Locomotives by the Author, 358; Conclusions, 358; the Steam Fire-Engine, 360; the Rotary Steam-Engine and Pump, 365; the Modern Locomotive, 368; Dimensions and Performance, 373; Compound Engines for Locomotives, 376; Extent of Modern Railroads, 378; SECTION III.--MARINE ENGINES. 379 The Modern Marine Engine, 379; the American Beam Engine, 379; the Oscillating Engine and Feathering Wheel, 381; the two "Rhode Islands," 382; River-Boat Engines on the Mississippi, 384; Steam Launches and Yachts, 386; Marine Screw-Engines, 389; the Marine Compound Engine, 390; its Introduction by John Elder and others, 393; Comparison with the Single-Cylinder Engine, 395; its Advantages, 396; the Surface Condenser, 397; Weight of Machinery, 398; Marine Engine Performance, 398; Relative Economy of Simple and Compound Engines, 399; the Screw-Propeller, 399; Chain-Propulsion, or Wire-Rope Towage, 402; Marine Steam-Boilers, 403; the Modern Steamship, 405; Examples of Merchant Steamers, 406; Naval Steamers--Classification, 409; Examples of Iron-Clad Steamers, 412; Power of the Marine Engine, 415; Conclusion, 417. CHAPTER VII. THE PHILOSOPHY OF THE STEAM-ENGINE. THE HISTORY OF ITS GROWTH; ENERGETICS AND THERMO-DYNAMICS 419 General Outline, 419; Origin of its Power, 419; Scientific Principles involved in its Operation, 420; the Beginnings of Modern Science, 421; the Alexandrian Museum, 422; the Aristotelian Philosophy, 424; the Middle Ages, 426; Galileo's Work, 428; Da Vinci and Stevinus, 429; Kepler, Hooke, and Huyghens, 429; Newton and the New Mechanical Philosophy, 430; the Inception of the Science of Energetics, 483; the Persistence of Energy, 433; Rumford's Experiments, 434; Fourier, Carnot, Seguin, 437; Mayer and the Mechanical Equivalent of Heat, 438; Joule's Determination of its Value, 438; Prof. Rankine's Investigations, 442; Clausius-Thompson's Principles, 444; Experimental Work of Boyle, Black, and Watt, 446; Robison's, Dalton's, Ure's, and Biot's Study of Pressures and Temperatures of Steam, 447; Arago's and Dulong's Researches, 447; Franklin Institute Investigation, 447; Cagniard de la Tour--Faraday, 447; Dr. Andrews and the Critical Point, 448; Donny's and Dufour's Researches, 448; Regnault's Determination of Temperatures and Pressures of Steam, 449; Hirn's Experiments, 450; Résumé of the Philosophy of the Steam-Engine, 451; Energy--Definitions and Principles, 451; its Measure, 452; the Laws of Energetics, 453; Thermo-dynamics, 453; its Beginnings, 454; its Laws, 454; Rankine's General Equation, 455; Rankine's Treatise on the Theory of Heat-Engines, 456; Merits of the Great Philosopher, 456. CHAPTER VIII. THE PHILOSOPHY OF THE STEAM-ENGINE. ITS APPLICATION; ITS TEACHINGS RESPECTING THE CONSTRUCTION OF THE ENGINE AND ITS IMPROVEMENT 457 Origin of all Energy, 457; the Progress of Energy through Boiler and Engine, 458; Conditions of Heat-Development in the Boiler, 458; the Steam in the Engine, 458; the Expansion of Steam, 459; Conditions of Heat-Utilization, 460; Loss of Power in the Engine, 462; Conditions affecting the Design of the Steam-Engine, 466; the Problem stated, 466; Economy as affected by Pressure and Temperature, 467; Changes which have already occurred, 468; Direction of Changes now in Progress, 470; Summary of Facts, 471; Characteristics of a Good Steam-Engine, 473; Principles of Steam-Boiler Construction, 476. LIST OF ILLUSTRATIONS. FRONTISPIECE: The Grecian Idea of the Steam-Engine. FIG. PAGE 1. Opening Temple-Doors by Steam, B. C. 200 6 2. Steam Fountain, B. C. 200 7 3. Hero's Engine, B. C. 200 8 4. Porta's Apparatus, A. D. 1601 14 5. De Caus's Apparatus, A. D. 1605 15 6. Branca's Steam-Engine, A. D. 1629 17 7. Worcester's Steam-Fountain, A. D. 1650 21 8. Worcester's Engine, A. D. 1665 22 9. Wall of Raglan Castle 22 10. Huyghens's Engine, 1680 26 11. Savery's Model, 1698 34 12. Savery's Engine, 1698 35 13. Savery's Engine, A. D. 1702 37 14. Papin's Two-Way Cock 42 15. Engine Built by Desaguliers in 1718 43 16. Papin's Digester, 1680 48 17. Papin's Engine 50 18. Papin's Engine and Water-Wheel, A. D. 1707 53 19. Newcomen's Engine, A. D. 1705 59 20. Beighton's Valve-Gear, A. D. 1718 63 21. Smeaton's Newcomen Engine 65 22. Boiler of Newcomen Engine, 1763 67 23. Smeaton's Portable-Engine Boiler, 1765 73 24. The Newcomen Model 84 25. Watt's Experiment 89 26. Watt's Engine, 1774 98 27. Watt's Engine, 1781 104 28. Expansion of Steam 108 29. The Governor 115 30. Mercury Steam-Gauge and Glass Water-Gauge 117 31. Boulton & Watt's Double-Acting Engine, 1784 119 32. Valve-Gear of the Albion Mills Engine 121 33. Watt's Half-Trunk Engine, 1784 122 34. The Watt Hammer, 1784 123 35. James Watt's Workshop 129 36. Murdoch's Oscillating Engine, 1785 134 37. Hornblower's Compound Engine, 1781 136 38. Bull's Pumping-Engine, 1798 139 39. Cartwright's Engine, 1798 141 40. The First Railroad-Car, 1825 144 41. Leupold's Engine, 1720 148 42. Newton's Steam-Carriage, 1680 149 43. Read's Steam-Carriage, 1790 150 44. Cugnot's Steam-Carriage, 1770 151 45. Murdoch's Model, 1784 153 46. Evans's Non-Condensing Engine, 1800 156 47. Evans's "Oruktor Amphibolis," 1804 157 48. Gurney's Steam-Carriage 163 49. Hancock's "Autopsy", 1833 168 50. Trevithick's Locomotive, 1804 175 51. Stephenson's Locomotive of 1815. Section 187 52. Stephenson's No. 1 Engine, 1825 191 53. Opening of the Stockton and Darlington Railroad, 1815 192 54. The "Novelty," 1829 197 55. The "Rocket," 1829 198 56. The Atmospheric Railroad 202 57. Stephenson's Locomotive, 1833 203 58. The Stephenson Valve-Gear, 1833 206 59. The "Atlantic," 1832 210 60. The "Best Friend," 1830 211 61. The "West Point," 1831 212 62. The "South Carolina," 1831 213 63. The "Stevens" Rail and Enlarged Section 215 64. "Old Ironsides," 1832 216 65. The "E. L. Miller," 1834 217 66. Hulls's Steamboat, 1736 226 67. Fitch's Model, 1785 236 68. Fitch & Voight's Boiler, 1787 238 69. Fitch's First Boat, 1787 238 70. John Fitch, 1788 239 71. John Fitch, 1796 240 72. Miller, Taylor & Symmington, 1788 242 73. Read's Boiler in Section, 1788 245 74. Read's Multi-Tubular Boiler, 1788 245 75. The "Charlotte Dundas," 1801 247 76. The "Comet," 1812 248 77. Fulton's Experiments 253 78. Fulton's Table of Resistances 254 79. Barlow's Water-Tube Boiler, 1793 256 80. The "Clermont," 1807 258 81. Engine of the "Clermont," 1808 258 82. Launch of the "Fulton the First," 1804 262 83. Section of Steam-Boiler, 1804 264 84. Engine, Boiler, and Screw-Propellers used by Stevens, 1804 265 85. Stevens's Screw Steamer, 1804 265 86. John Stevens's Twin-Screw Steamer, 1805 269 87. The Feathering Paddle-Wheel 272 88. The "North America" and "Albany," 1827-'30 274 89. Stevens's Return Tubular Boiler, 1832 275 90. Stevens's Valve-Motion 276 91. The "Atlantic," 1851 290 92. The Side-Lever Engine, 1849 291 93. Vertical Stationary Steam-Engine 308 94. Vertical Stationary Steam-Engine. Section 309 95. Horizontal Stationary Steam-Engine 312 96. Horizontal Stationary Steam-Engine 313 97. Corliss Engine 319 98. Corliss Engine Valve-Motion 320 99. Greene Engine 321 100. Thurston's Greene-Engine Valve-Gear 322 101. Cornish Pumping-Engine, 1880 329 102. Steam-Pump 331 103. The Worthington Pumping-Engine, 1876. Section 333 104. The Worthington Pumping-Engine 334 105. Double-Cylinder Pumping-Engine, 1878 335 106. The Lawrence Water-Works Engine 336 107. The Leavitt Pumping-Engine 337 108. Babcock & Wilcox's Vertical Boiler 341 109. Stationary "Locomotive" Boiler 342 110. Galloway Tube 343 111. Harrison's Sectional Boiler 345 112. Babcock and Wilcox's Sectional Boiler 346 113. Root Sectional Boiler 347 114. Semi-Portable Engine, 1878 348 115. Semi-Portable Engine, 1878 349 116. The Portable Steam-Engine, 1878 354 117. The Thrashers' Road-Engine, 1878 355 118. Fisher's Steam-Carriage 356 119. Road and Farm Locomotive 357 120. The Latta Steam Fire-Engine 361 121. The Amoskeag Engine. Section 363 122. The Silsby Rotary Steam Fire-Engine 364 123. Rotary Steam-Engine 365 124. Rotary Pump 366 125. Tank Engine, New York Elevated Railroad 369 126. Forney's Tank-Locomotive 370 127. British Express Engine 371 128. The Baldwin Locomotive. Section 372 129. The American Type of Express Engine, 1878 374 130. Beam Engine 380 131. Oscillating Steam-Engine and Feathering Paddle-Wheel 381 132. The Two "Rhode Islands," 1836-1876 383 133. A Mississippi Steamboat 384 134. Steam-Launch, New York Steam-Power Company 386 135. Launch-Engine 387 136. Horizontal, Direct-acting Naval Screw Engine 389 137. Compound Marine Engine. Side Elevation 390 138. Compound Marine Engine. Front Elevation and Section 391 139. Screw-Propeller 400 140. Tug-Boat Screw 401 141. Hirsch Screw 401 142. Marine Fire-Tubular Boiler. Section 403 143. Marine High-Pressure Boiler. Section 404 144. The Modern Steamship 407 145. Modern Iron-Clads 410 146. The "Great Eastern" 415 147. The "Great Eastern" at Sea 416 PORTRAITS. NO. PAGE 1. Edward Somerset, the Second Marquis of Worcester 20 2. Thomas Savery 31 3. Denys Papin 46 4. James Watt 80 5. Matthew Boulton 94 6. Oliver Evans 154 7. Richard Trevithick 174 8. Colonel John Stevens 178 9. George Stephenson 183 10. Robert Fulton 251 11. Robert L. Stevens 270 12. John Elder 393 13. Benjamin Thompson, Count Rumford 434 14. James Prescott Joule 439 15. Prof. W. J. M. Rankine 443 ["A Machine, receiving at distant times and from many hands new combinations and improvements, and becoming at last of signal benefit to mankind, may be compared to a rivulet swelled in its course by tributary streams, until it rolls along a majestic river, enriching, in its progress, provinces and kingdoms. "In retracing the current, too, from where it mingles with the ocean, the pretensions of even ample subsidiary streams are merged in our admiration of the master-flood, glorying, as it were, in its expansion. But as we continue to ascend, those waters which, nearer the sea, would have been disregarded as unimportant, begin to rival in magnitude and share our attention with the parent stream; until, at length, on our approaching the fountains of the river, it appears trickling from the rock, or oozing from among the flowers of the valley. "So, also, in developing the rise of a machine, a coarse instrument or a toy may be recognized as the germ of that production of mechanical genius, whose power and usefulness have stimulated our curiosity to mark its changes and to trace its origin. The same feelings of reverential gratitude which attached holiness to the spot whence mighty rivers sprang, also clothed with divinity, and raised altars in honor of, inventors of the saw, the plough, the potter's wheel, and the loom."--STUART.] THE GROWTH OF THE STEAM-ENGINE. CHAPTER I. _THE STEAM-ENGINE AS A SIMPLE MACHINE._ SECTION I.--THE PERIOD OF SPECULATION--FROM HERO TO WORCESTER, B. C. 200 TO A. D. 1650. One of the greatest of modern philosophers--the founder of that system of scientific philosophy which traces the processes of evolution in every department, whether physical or intellectual--has devoted a chapter of his "First Principles" of the new system to the consideration of the multiplication of the effects of the various forces, social and other, which are continually modifying this wonderful and mysterious universe of which we form a part. Herbert Spencer, himself an engineer, there traces the wide-spreading, never-ceasing influences of new inventions, of the introduction of new forms of mechanism, and of the growth of industrial organization, with a clearness and a conciseness which are so eminently characteristic of his style. His illustration of this idea by reference to the manifold effects of the introduction of steam-power and its latest embodiment, the locomotive-engine, is one of the strongest passages in his work. The power of the steam-engine, and its inconceivable importance as an agent of civilization, has always been a favorite theme with philosophers and historians as well as poets. As Religion has always been, and still is, the great _moral_ agent in civilizing the world, and as Science is the great _intellectual_ promoter of civilization, so the Steam-Engine is, in modern times, the most important _physical_ agent in that great work. It would be superfluous to attempt to enumerate the benefits which it has conferred upon the human race, for such an enumeration would include an addition to every comfort and the creation of almost every luxury that we now enjoy. The wonderful progress of the present century is, in a very great degree, due to the invention and improvement of the steam-engine, and to the ingenious application of its power to kinds of work that formerly taxed the physical energies of the human race. We cannot examine the methods and processes of any branch of industry without discovering, somewhere, the assistance and support of this wonderful machine. Relieving mankind from manual toil, it has left to the intellect the privilege of directing the power, formerly absorbed in physical labor, into other and more profitable channels. The intelligence which has thus conquered the powers of Nature, now finds itself free to do head-work; the force formerly utilized in the carrying of water and the hewing of wood, is now expended in the God-like work of THOUGHT. What, then, can be more interesting than to trace the history of the growth of this wonderful machine?--the greatest among the many great creations of one of God's most beneficent gifts to man--the power of invention. While following the records and traditions which relate to the steam-engine, I propose to call attention to the fact that its history illustrates the very important truth: _Great inventions are never, and great discoveries are seldom, the work of any one mind_. Every great invention is really either an aggregation of minor inventions, or the final step of a progression. It is not a creation, but _a growth_--as truly so as is that of the trees in the forest. Hence, the same invention is frequently brought out in several countries, and by several individuals, simultaneously. Frequently an important invention is made before the world is ready to receive it, and the unhappy inventor is taught, by his failure, that it is as unfortunate to be in advance of his age as to be behind it. Inventions only become successful when they are not only needed, but when mankind is so far advanced in intelligence as to appreciate and to express the necessity for them, and to at once make use of them. More than half a century ago, an able New England writer, in a communication to an English engineering periodical, described the new machinery which was built at Newport, R. I., by John Babcock and Robert L. Thurston, for one of the first steamboats that ever ran between that city and New York. He prefaced his description with a frequently-quoted remark to the effect that, as Minerva sprang, mature in mind, in full stature of body, and completely armed, from the head of Jupiter, so the steam-engine came forth, perfect at its birth, from the brain of James Watt. But we shall see, as we examine the records of its history, that, although James Watt was _an_ inventor, and probably the greatest of the inventors of the steam-engine, he was still but one of the many men who have aided in perfecting it, and who have now made us so familiar with it, and its tremendous power and its facile adaptations, that we have almost ceased to admire it, or to wonder at the workings of the still more admirable intelligence that has so far perfected it. Twenty-one centuries ago, the political power of Greece was broken, although Grecian civilization had risen to its zenith. Rome, ruder than her polished neighbor, was growing continually stronger, and was rapidly gaining territory by absorbing weaker states. Egypt, older in civilization than either Greece or Rome, fell but two centuries later before the assault of the younger states, and became a Roman province. Her principal city was at this time Alexandria, founded by the great soldier whose name it bears, when in the full tide of his prosperity. It had now become a great and prosperous city, the centre of the commerce of the world, the home of students and of learned men, and its population was the wealthiest and most civilized of the then known world. It is among the relics of that ancient Egyptian civilization that we find the first records in the early history of the steam-engine. In Alexandria, the home of Euclid, the great geometrician, and possibly contemporary with that talented engineer and mathematician, Archimedes, a learned writer, called Hero, produced a manuscript which he entitled "Spiritalia seu Pneumatica." It is quite uncertain whether Hero was the inventor of any number of the contrivances described in his work. It is most probable that the apparatus described are principally devices which had either been long known, or which were invented by Ctesibius, an inventor who was famous for the number and ingenuity of the hydraulic and pneumatic machines that he devised. Hero states, in his Introduction, his intention to describe existing machines and earlier inventions, and to add his own. Nothing in the text, however, indicates to whom the several machines are to be ascribed.[6] [6] The British Museum contains four manuscript copies of Hero's "Pneumatics," which were written in the fifteenth and sixteenth centuries. These manuscripts have been examined with great care, and a translation from them prepared by Prof. J. G. Greenwood, and published at the desire of Mr. Bennett Woodcroft, the author of a valuable little treatise on "Steam Navigation." This is, so far as the author is aware, the only existing English translation of any portion of Hero's works. The first part of Hero's work is devoted to applications of the syphon. The 11th proposition is the first application of heat to produce motion of fluids. An altar and its pedestal are hollow and air-tight. A liquid is poured into the pedestal, and a pipe inserted, of which the lower end passes beneath the surface of the liquid, and the upper extremity leads through a figure standing at the altar, and terminates in a vessel inverted above this altar. When a fire is made on the altar, the heat produced expands the confined air, and the liquid is driven up the tube, issuing from the vessel in the hand of the figure standing by the altar, which thus seems to be offering a libation. This toy embodies the essential principle of all modern heat-engines--the change of energy from the form known as heat-energy into mechanical energy, or work. It is not at all improbable that this prototype of the modern wonder-working machine may have been known centuries before the time of Hero. Many forms of hydraulic apparatus, including the hand fire-engine, which is familiar to us, and is still used in many of our smaller cities, are described, the greater number of which are probably attributable to Ctesibius. They demand no description here. A hot-air engine, however, which is the subject of his 37th proposition, is of real interest. Hero sketches and describes a method of opening temple-doors by the action of fire on an altar, which is an ingenious device, and contains all the elements of the machine of the Marquis of Worcester, which is generally considered the first real steam-engine, with the single and vital defect that the expanding fluid is air instead of steam. The sketch, from Greenwood's translation, exhibits the device very plainly. Beneath the temple-doors, in the space _A B C D_, is placed a spherical vessel, _H_, containing water. A pipe, _F G_, connects the upper part of this sphere with the hollow and air-tight shell of the altar above, _D E_. Another pipe, _K L M_, leads from the bottom of the vessel, _H_, over, in syphon-shape, to the bottom of a suspended bucket, _N X_. The suspending cord is carried over a pulley and led around two vertical barrels, _O P_, turning on pivots at their feet, and carrying the doors above. Ropes led over a pulley, _R_, sustain a counterbalance, _W_. [Illustration: FIG. 1.--Opening Temple-Doors by Steam, B. C. 200.] On building a fire on the altar, the heated air within expands, passes through the pipe, _F G_, and drives the water contained in the vessel, _H_, through the syphon, _K L M_, into the bucket, _N X_. The weight of the bucket, which then descends, turns the barrels, _O P_, raises the counterbalance, and opens the doors of the temple. On extinguishing the fire, the air is condensed, the water returns through the syphon from the bucket to the sphere, the counterbalance falls, and the doors are closed. Another contrivance is next described, in which the bucket is replaced by an air-tight bag, which, expanding as the heated air enters it, contracts vertically and actuates the mechanism, which in other respects is similar to that just described. In these devices the spherical vessel is a perfect anticipation of the vessels used many centuries later by several so-called inventors of the steam-engine. Proposition 45 describes the familiar experiment of a ball supported aloft by a jet of fluid. In this example steam is generated in a close cauldron, and issues from a pipe inserted in the top, the ball dancing on the issuing jet. No. 47 is a device subsequently reproduced--perhaps reinvented by the second Marquis of Worcester. [Illustration: FIG. 2.--Steam Fountain, B. C. 200.] A strong, close vessel, _A B C D_, forms a pedestal, on which are mounted a spherical vessel, _E F_, and a basin. A pipe, _H K_, is led from the bottom of the larger vessel into the upper part of the sphere, and another pipe from the lower part of the latter, in the form of a syphon, over to the basin, _M_. A drain-pipe, _N O_, leads from the basin to the reservoir, _A D_. The whole contrivance is called "A fountain which is made to flow by the action of the sun's rays." It is operated thus: The vessel, _E F_, being filled nearly to the top with water, or other liquid, and exposed to the action of the sun's rays, the air above the water expands, and drives the liquid over, through the syphon, _G_, into the basin, _M_, and it will fall into the pedestal, _A B C D_. Hero goes on to state that, on the removal of the sun's rays, the air in the sphere will contract, and that the water will be returned to the sphere from the pedestal. This can, evidently, only occur when the pipe _G_ is closed previous to the commencement of this cooling. No such cock is mentioned, and it is not unlikely that the device only existed on paper. Several steam-boilers are described, usually simple pipes or cylindrical vessels, and the steam generated in them by the heat of the fire on the altar forms a steam-blast. This blast is either directed into the fire, or it "makes a blackbird sing," blows a horn for a triton, or does other equally useless work. In one device, No. 70, the steam issues from a reaction-wheel revolving in the horizontal plane, and causes dancing images to circle about the altar. A more mechanical and more generally-known form of this device is that which is frequently described as the "First Steam Engine." The sketch from Stuart is similar in general form, but more elaborate in detail, than that copied by Greenwood, which is here also reproduced, as representing more accurately the simple form which the mechanism of the "Æolipile," or Ball of Æolus, assumed in those early times. [Illustration: FIG. 3.--Hero's Engine, B. C. 200.] The cauldron, _A B_, contains water, and is covered by the steam-tight cover, _C D_. A globe is supported above the cauldron by a pair of tubes, terminating, the one, _C M_, in a pivot, _L_, and the other, _E F_, opening directly into the sphere at _G_. Short, bent pipes, _H_ and _K_, issue from points diametrically opposite each other, and are open at their extremities. A fire being made beneath the cauldron, steam is formed and finds exit through the pipe, _E F G_, into the globe, and thence rushes out of the pipes, _H K_, turning the globe on its axis, _G L_, by the unbalanced pressure thus produced. The more elaborate sketch which forms the frontispiece represents a machine of similar character. Its design and ornamentation illustrate well the characteristics of ancient art, and the Greek idea of the steam-engine. This "Æolipile" consisted of a globe, _X_, suspended between trunnions, _O S_, through one of which steam enters from the boiler, _P_, below. The hollow, bent arms, _W_ and _Z_, cause the vapor to issue in such directions that the reaction produces a rotary movement of the globe, just as the rotation of reaction water-wheels is produced by the outflowing water. It is quite uncertain whether this machine was ever more than a toy, although it has been supposed by some authorities that it was actually used by the Greek priests for the purpose of producing motion of apparatus in their temples. It seems sufficiently remarkable that, while the power of steam had been, during all the many centuries that man has existed upon the globe, so universally displayed in so many of the phenomena of natural change, that mankind lived almost up to the Christian era without making it useful in giving motion even to a toy; but it excites still greater surprise that, from the time of Hero, we meet with no good evidence of its application to practical purposes for many hundreds of years. Here and there in the pages of history, and in special treatises, we find a hint that the knowledge of the force of steam was not lost; but it is not at all to the credit of biographers and of historians, that they have devoted so little time to the task of seeking and recording information relating to the progress of this and other important inventions and improvements in the mechanic arts. Malmesbury states[7] that, in the year A. D. 1125, there existed at Rheims, in the church of that town, a clock designed or constructed by Gerbert, a professor in the schools there, and an organ blown by air escaping from a vessel in which it was compressed "by heated water." [7] Stuart's "Anecdotes." Hieronymus Cardan, a wonderful mathematical genius, a most eccentric philosopher, and a distinguished physician, about the middle of the sixteenth century called attention, in his writings, to the power of steam, and to the facility with which a vacuum can be obtained by its condensation. This Cardan was the author of "Cardan's Formula," or rule for the solution of cubic equations, and was the inventor of the "smoke-jack." He has been called a "philosopher, juggler, and madman." He was certainly a learned mathematician, a skillful physician, and a good mechanic. Many traces are found, in the history of the sixteenth century, of the existence of some knowledge of the properties of steam, and some anticipation of the advantages to follow its application. Matthesius, A. D. 1571, in one of his sermons describes a contrivance which may be termed a steam-engine, and enlarges on the "tremendous results which may follow the volcanic action of a small quantity of confined vapor;"[8] and another writer applied the steam æolipile of Hero to turn the spit, and thus rivaled and excelled Cardan, who was introducing his "smoke-jack." [8] "Berg-Postilla, oder Sarepta von Bergwerk und Metallen." Nuremberg, 1571. As Stuart says, the inventor enumerated its excellent qualities with great minuteness. He claimed that it would "eat nothing, and giving, withal, an assurance to those partaking of the feast, whose suspicious natures nurse queasy appetites, that the haunch has not been pawed by the turnspit in the absence of the housewife's eye, for the pleasure of licking his unclean fingers."[9] [9] "History of the Steam-Engine," 1825. Jacob Besson, a Professor of Mathematics and Natural Philosophy at Orleans, and who was in his time distinguished as a mechanician, and for his ingenuity in contriving illustrative models for use in his lecture-room, left evidence, which Beroaldus collected and published in 1578,[10] that he had found the spirit of his time sufficiently enlightened to encourage him to pay great attention to applied mechanics and to mechanism. There was at this time a marked awakening of the more intelligent men of the age to the value of practical mechanics. A scientific tract, published at Orleans in 1569, and probably written by Besson, describes very intelligently the generation of steam by the communication of heat to water, and its peculiar properties. [10] "Theatrum Instrumentorum et Machinarum, Jacobi Bessoni, cum Franc Beroaldus, figuarum declaratione demonstrativa." Lugduni, 1578. The French were now becoming more interested in mechanics and the allied sciences, and philosophers and literati, of native birth and imported by the court from other countries, were learning more of the nature and importance of such studies as have a bearing upon the work of the engineer and of the mechanic. Agostino Ramelli, an Italian of good family, a student and an artist when at leisure, a soldier and an engineer in busier times, was born and educated at Rome, but subsequently was induced to make his home in Paris. He published a book in 1588,[11] in which he described many machines, adapted to various purposes, with a skill that was only equaled by the accuracy and general excellence of his delineations. This work was produced while its author was residing at the French capital, supported by a pension which had been awarded him by Henry III. as a reward for long and faithful services. [11] "Le diverse et artificiose machine del Capitano Agostino Ramelli, del Ponte della Prefia." Paris, 1588. The books of Besson and of Ramelli are the first treatises of importance on general machinery, and were, for many years, at once the sources from which later writers drew the principal portion of their information in relation to machinery, and wholesome stimulants to the study of mechanism. These works contain descriptions of many machines subsequently reinvented and claimed as new by other mechanics. Leonardo da Vinci, well known as a mathematician, engineer, poet, and painter, of the sixteenth century, describes, it is said, a steam-gun, which he calls the "Architonnerre," and ascribes to Archimedes. It was a machine composed of copper, and seems to have had considerable power. It threw a ball weighing a talent. The steam was generated by permitting water in a closed vessel to fall on surfaces heated by a charcoal fire, and by its sudden expansion to eject the ball. In the year 1825, the superintendent of the royal Spanish archives at Simancas furnished an account which, it was said, had been there discovered of an attempt, made in 1543 by Blasco de Garay, a Spanish navy-officer under Charles V., to move a ship by paddle-wheels, driven, as was inferred from the account, by a steam-engine. It is impossible to say to how much credit the story is entitled, but, if true, it was the first attempt, so far as is now known, to make steam useful in developing power for practical purposes. Nothing is known of the form of the engine employed, it only having been stated that a "vessel of boiling water" formed a part of the apparatus. The account is, however, in other respects so circumstantial, that it has been credited by many; but it is regarded as apocryphal by the majority of writers upon the subject. It was published in 1826 by M. de Navarrete, in Zach's "Astronomical Correspondence," in the form of a letter from Thomas Gonzales, Director of the Royal Archives at Simancas, Spain. In 1601, Giovanni Battista della Porta, in a work called "Spiritali," described an apparatus by which the pressure of steam might be made to raise a column of water. It included the application of the condensation of steam to the production of a vacuum into which the water would flow. Porta is described as a mathematician, chemist, and physicist, a gentleman of fortune, and an enthusiastic student of science. His home in Naples was a rendezvous for students, artists, and men of science distinguished in every branch. He invented the magic lantern and the camera obscura, and described it in his commentary on the "Pneumatica." In his work,[12] he described this machine for raising water, as shown in Fig. 4, which differs from one shown by Hero in the use of steam pressure, instead of the pressure of heated air, for expelling the liquid. [12] "Pneumaticorum libri tres," etc., 4to. Naples, 1601. "I Tre Libri de' Spiritali." Napoli, 1606. The retort, or boiler, is fitted to a tank from which the bent pipe leads into the external air. A fire being kindled under the retort, the steam generated rises to the upper part of the tank, and its pressure on the surface of the water drives it out through the pipe, and it is then led to any desired height. This was called by Porta an improved "Hero's Fountain," and was named his "Steam Fountain." He described with perfect accuracy the action of condensation in producing a vacuum, and sketched an apparatus in which the vacuum thus secured was filled by water forced in by the pressure of the external atmosphere. His contrivances were not apparently ever applied to any practically useful purpose. We have not yet passed out of the age of speculation, and are just approaching the period of application. Porta is, nevertheless, entitled to credit as having proposed an essential change in this succession, which begins with Hero, and which did not end with Watt. [Illustration: FIG. 4.--Porta's Apparatus, A. D. 1601.] The use of steam in Hero's fountain was as necessary a step as, although less striking than, any of the subsequent modifications of the machine. In Porta's contrivance, too, we should note particularly the separation of the boiler from the "forcing vessel"--a plan often claimed as original with later inventors, and as constituting a fair ground for special distinction. The rude engraving (Fig. 4) above is copied from the book of Porta, and shows plainly the boiler mounted above a furnace, from the door of which the flame is seen issuing, and above is the tank containing water. The opening in the top is closed by the plug, as shown, and the steam issuing from the boiler into the tank near the top, the water is driven out through the pipe at the left, leading up from the bottom of the tank. [Illustration: FIG. 5.--De Caus's Apparatus, A. D. 1605.] Florence Rivault, a Gentleman of the Bedchamber to Henry IV., and a teacher of Louis XIII., is stated by M. Arago, the French philosopher, to have discovered, as early as 1605, that water confined in a bomb-shell and there heated would explode the shell, however thick its walls might be made. The fact was published in Rivault's treatise on artillery in 1608. He says: "The water is converted into air, and its vaporization is followed by violent explosion." In 1615, Salomon de Caus, who had been an engineer and architect under Louis XIII. of France, and later in the employ of the English Prince of Wales, published a work at Frankfort, entitled "Les Raisons des Forces Mouvantes, avec diverses machines tant utile que plaisante," in which he illustrated his proposition, "Water will, by the aid of fire, mount higher than its source," by describing a machine designed to raise water by the expanding power of steam. In the sketch here given (Fig. 5), and which is copied from the original in "Les Raisons des Forces Mouvantes," etc., _A_ is the copper ball containing water; _B_, the cock at the extremity of the pipe, taking water from the bottom, _C_, of the vessel; _D_, the cock through which the vessel is filled. The sketch was probably made by De Caus's own hand. The machine of De Caus, like that of Porta, thus consisted of a metal vessel partly filled with water, and in which a pipe was fitted, leading nearly to the bottom, and open at the top. Fire being applied, the steam formed by its elastic force drove the water out through the vertical pipe, raising it to a height limited only by either the desire of the builder or the strength of the vessel. In 1629, Giovanni Branca, of the Italian town of Loretto, described, in a work[13] published at Rome, a number of ingenious mechanical contrivances, among which was a steam-engine (Fig. 6), in which the steam, issuing from a boiler, impinged upon the vanes of a horizontal wheel. This it was proposed to apply to many useful purposes. [13] "Le Machine deverse del Signior Giovanni Branca, cittadino Romano, Ingegniero, Architetto della Sta. Casa di Loretto." Roma, MDCXXIX. At this time experiments were in progress in England which soon resulted in the useful application of steam-power to raising water. [Illustration: FIG. 6.--Branca's Steam-Engine, A. D. 1629.] A patent, dated January 21, 1630, was granted to David Ramseye[14] by Charles I., which covered a number of distinct inventions. These were: "1. To multiply and make saltpeter in any open field, in fower acres of ground, sufficient to serve all our dominions. 2. To raise water from low pitts by fire. 3. To make any sort of mills to goe on standing waters by continual motion, without help of wind, water, or horse. 4. To make all sortes of tapistrie without any weaving-loom, or waie ever yet in use in this kingdome. 5. To make boats, shippes, and barges to goe against strong wind and tide. 6. To make the earth more fertile than usual. 7. To raise water from low places and mynes, and coal pitts, by a new waie never yet in use. 8. To make hard iron soft, and likewise copper to be tuffe and soft, which is not in use in this kingdome. 9. To make yellow waxe white verie speedilie." [14] Rymer's "F[oe]dera," Sanderson. Ewbank's "Hydraulics," p. 419. This seems to have been the first authentic reference to the use of steam in the arts which has been found in English literature. The patentee held his grant fourteen years, on condition of paying an annual fee of £3 6_s._ 8_d._ to the Crown. The second claim is distinct as an application of steam, the language being that which was then, and for a century and a half subsequently, always employed in speaking of its use. The steam-engine, in all its forms, was at that time known as the "fire-engine." It would seem not at all improbable that the third, fifth, and seventh claims are also applications of steam-power. Thomas Grant, in 1632, and Edward Ford, in 1640, also patented schemes, which have not been described in detail, for moving ships against wind and tide by some new and great force. Dr. John Wilkins, Bishop of Chester, an eccentric but learned and acute scholar, described, in 1648, Cardan's smoke-jack, the earlier æolipiles, and the power of the confined steam, and suggested, in a humorous discourse, what he thought to be perfectly feasible--the construction of a flying-machine. He says: "Might not a 'high pressure' be applied with advantage to move wings as large as those of the 'ruck's' or the 'chariot'? The engineer might probably find a corner that would do for a coal-station near some of the 'castles'" (castles in the air). The reverend wit proposed the application of the smoke-jack to the chiming of bells, the reeling of yarn, and to rocking the cradle. Bishop Wilkins writes, in 1648 ("Mathematical Magic"), of æolipiles as familiar and useful pieces of apparatus, and describes them as consisting "of some such material as may endure the fire, having a small hole at which they are filled with water, and out of which (when the vessels are heated) the air doth issue forth with a strong and lasting violence." "They are," the bishop adds, "frequently used for the exciting and contracting of heat in the melting of glasses or metals. They may also be contrived to be serviceable for sundry other pleasant uses, as for the moving of sails in a chimney-corner, the motion of which sails may be applied to the turning of a spit, or the like." Kircher gives an engraving ("Mundus Subterraneus") showing the last-named application of the æolipile; and Erckern ("Aula Subterranea," 1672) gives a picture illustrating their application to the production of a blast in smelting ores. They seem to have been frequently used, and in all parts of Europe, during the seventeenth century, for blowing fires in houses, as well as in the practical work of the various trades, and for improving the draft of chimneys. The latter application is revived very frequently by the modern inventor. SECTION II.--THE PERIOD OF APPLICATION--WORCESTER, PAPIN, AND SAVERY. We next meet with the first instance in which the expansive force of steam is supposed to have actually been applied to do important and useful work. In 1663, Edward Somerset, second Marquis of Worcester, published a curious collection of descriptions of his inventions, couched in obscure and singular language, and called "A Century of the Names and Scantlings of Inventions by me already Practised." One of these inventions is an apparatus for raising water by steam. The description was not accompanied by a drawing, but the sketch here given (Fig. 7) is thought probably to resemble one of his earlier contrivances very closely. Steam is generated in the boiler _a_, and thence is led into the vessel _e_, already nearly filled with water, and fitted up like the apparatus of De Caus. It drives the water in a jet out through the pipe _f_. The vessel _e_ is then shut off from the boiler _a_, is again filled through the pipe _h_, and the operation is repeated. Stuart thinks it possible that the marquis may have even made an engine with a piston, and sketches it.[15] The instruments of Porta and of De Caus were "steam fountains," and were probably applied, if used at all, merely to ornamental purposes. That of the Marquis of Worcester was actually used for the purpose of elevating water for practical purposes at Vauxhall, near London. [15] "Anecdotes of the Steam-Engine," vol. i., p. 61. [Illustration: Edward Somerset, the Second Marquis of Worcester.] How early this invention was introduced at Raglan Castle by Worcester is not known, but it was probably not much later than 1628. In 1647 Dircks shows the marquis probably to have been engaged in getting out parts of the later engine which was erected at Vauxhall, obtaining his materials from William Lambert, a brass-founder. His patent was issued in June, 1663. [Illustration: FIG. 7.--Worcester's Steam Fountain, A. D. 1650.] We nowhere find an illustrated description of the machine, or such an account as would enable a mechanic to reproduce it in all its details. Fortunately, the cells and grooves (Fig. 9) remaining in the wall of the citadel of Raglan Castle indicate the general dimensions and arrangement of the engine; and Dircks, the biographer of the inventor, has suggested the form of apparatus shown in the sketch (Fig. 8) as most perfectly in accord with the evidence there found, and with the written specifications. The two vessels, _A A´_, are connected by a steam-pipe, _B B´_, with the boiler, _C_, behind them. _D_ is the furnace. A vertical water-pipe, _E_, is connected with the cold-water vessels, _A A´_, by the pipes, _F F´_, reaching nearly to the bottom. Water is supplied by the pipes, _G G´_, with valves, _a a´_, dipping into the well or ditch, _H_. Steam from the boiler being admitted to each vessel, _A_ and _A´_, alternately, and there condensing, the vacuum formed permits the pressure of the atmosphere to force the water from the well through the pipes, _G_ and _G´_. While one is filling, the steam is forcing the charge of water from the other up the discharge-pipe, _E_. As soon as each is emptied, the steam is shut off from it and turned into the other, and the condensation of the steam remaining in the vessel permits it to fill again. As will be seen presently, this is substantially, and almost precisely, the form of engine of which the invention is usually attributed to Savery, a later inventor. [Illustration: FIG. 8.--Worcester's Engine, A. D. 1665.] [Illustration: FIG. 9.--Wall of Raglan Castle.] Worcester never succeeded in forming the great company which he hoped would introduce his invention on a scale commensurate with its importance, and his fate was that of nearly all inventors. He died poor and unsuccessful. His widow, who lived until 1681, seemed to have become as confident as was Worcester himself that the invention had value, and, long after his death, was still endeavoring to secure its introduction, but with equal non-success. The steam-engine had taken a form which made it inconceivably valuable to the world, at a time when no more efficient means of raising water was available at the most valuable mines than horse-power; but the people, greatly as it was needed, were not yet sufficiently intelligent to avail themselves of the great boon, the acceptance of which was urged upon them with all the persistence and earnestness which characterizes every true inventor. Worcester is described by his biographer as having been a learned, thoughtful, studious, and good man--a Romanist without prejudice or bigotry, a loyal subject, free from partisan intolerance; as a public man, upright, honorable, and humane; as a scholar, learned without being pedantic; as a mechanic, patient, skillful, persevering, and of wonderful ingenuity, and of clear, almost intuitive, apprehension. Yet, with all these natural advantages, reinforced as they were by immense wealth and influence in his earlier life, and by hardly lessened social and political influence when a large fortune had been spent in experiment, and after misfortune had subdued his spirits and left him without money or a home, the inventor failed to secure the introduction of a device which was needed more than any other. Worcester had attained practical success; but the period of speculation was but just closing, and that of the application of steam had not quite yet arrived. The second Marquis of Worcester stands on the record as the first steam-engine builder, and his death marks the termination of the first of those periods into which we have divided the history of the growth of the steam-engine. The "water-commanding engine," as its inventor called it, was the first instance in the history of the steam-engine in which the inventor is known to have "reduced his invention to practice." It is evident, however, that the invention of the separate boiler, important as it was, had been anticipated by Porta, and does not entitle the marquis to the honor, claimed for him by many English authorities, of being _the_ inventor of the steam-engine. Somerset was simply _one_ of those whose works collectively made the steam-engine. After the time of Worcester, we enter upon a stage of history which may properly be termed a period of application; and from this time forward steam continued to play a more and more important part in social economy, and its influence on the welfare of mankind augmented with a rapidly-increasing growth. The knowledge then existing of the immense expansive force of steam, and the belief that it was destined to submit to the control of man and to lend its immense power in every department of industry, were evidently not confined to any one nation. From Italy to Northern Germany, and from France to Great Britain, the distances, measured in time, were vastly greater then than now, when this wonderful genius has helped us to reduce weeks to hours; but there existed, notwithstanding, a very perfect system of communication, and the learning of every centre was promptly radiated to every other. It thus happened that, at this time, the speculative study of the steam-engine was confined to no part of Europe; inventors and experimenters were busy everywhere developing this promising scheme. Jean Hautefeuille, the son of a French _boulanger_, born at Orleans, adopted by the Duchess of Bouillon at the suggestion of De Sourdis, profiting by the great opportunities offered him, entered the Church, and became one of the most learned men and greatest mechanicians of his time. He studied the many schemes then brought forward by inventors with the greatest interest, and was himself prolific of new ideas. In 1678, he proposed the use of alcohol in an engine, "in such a manner that the liquid should evaporate and be condensed, _tour à tour_, without being wasted"[16]--the first recorded plan, probably, for surface-condensation and complete retention of the working-fluid. He proposed a gunpowder-engine, of which[17] he described three varieties. [16] Stuart's "Anecdotes." [17] "Pendule Perpetuelle, avec la manière d'élever d'eau par le moyen de la poudre à canon," Paris, 1678. In one of these engines he displaced the atmosphere by the gases produced by the explosion, and the vacuum thus obtained was utilized in raising water by the pressure of the air. In the second machine, the pressure of the gases evolved by the combustion of the powder acted directly upon the water, forcing it upward; and in the third design, the pressure of the vapor drove a piston, and this engine was described as fitted to supply power for many purposes. There is no evidence that he constructed these machines, however, and they are here referred to simply as indicating that all the elements of the machine were becoming well known, and that an ingenious mechanic, combining known devices, could at this time have produced the steam-engine. Its early appearance should evidently have been anticipated. Hautefeuille, if we may judge from evidence at hand, was the first to propose the use of a piston in a heat-engine, and his gunpowder-engine seems to have been the first machine which would be called a heat-engine by the modern mechanic. The earlier "machines" or "engines," including that of Hero and those of the Marquis of Worcester, would rather be denominated "apparatus," as that term is used by the physicist or the chemist, than a machine or an engine, as the terms are used by the engineer. Huyghens, in 1680, in a memoir presented to the Academy of Sciences, speaks of the expansive force of gunpowder as capable of utilization as a convenient and portable mechanical power, and indicates that he had designed a machine in which it could be applied. This machine of Huyghens is of great interest, not simply because it was the first gas-engine and the prototype of the very successful modern explosive gas-engine of Otto and Langen, but principally as having been the first engine which consisted of a cylinder and piston. The sketch shows its form. It consisted of a cylinder, _A_, a piston, _B_, two relief-pipes, _C C_, fitted with check-valves and a system of pulleys, _F_, by which the weight is raised. The explosion of the powder at _H_ expels the air from the cylinder. When the products of combustion have cooled, the pressure of the atmosphere is no longer counterbalanced by that of air beneath, and the piston is forced down, raising the weight. The plan was never put in practice, although the invention was capable of being made a working and possibly useful machine. [Illustration: FIG. 10.--Huyghens's Engine, 1680.] At about this period the English attained some superiority over their neighbors on the Continent in the practical application of science and the development of the useful arts, and it has never since been lost. A sudden and great development of applied science and of the useful arts took place during the reign of Charles II., which is probably largely attributable to the interest taken by that monarch in many branches of construction and of science. He is said to have been very fond of mathematics, mechanics, chemistry, and natural history, and to have had a laboratory erected, and to have employed learned men to carry on experiments and lines of research for his satisfaction. He was especially fond of the study and investigation of the arts and sciences most closely related to naval architecture and navigation, and devoted much attention to the determination of the best forms of vessels, and to the discovery of the best kinds of ship-timber. His brother, the Duke of York, was equally fond of this study, and was his companion in some of his work. Great as is the influence of the monarch, to-day, in forming the tastes and habits and in determining the direction of the studies and labors of the people, his influence was vastly more potent in those earlier days; and it may well be believed that the rapid strides taken by Great Britain from that time were, in great degree, a consequence of the well-known habits of Charles II., and that the nation, which had an exceptional natural aptitude for mechanical pursuits, should have been prompted by the example of its king to enter upon such a course as resulted in the early attainment of an advanced position in all branches of applied science. The appointment, under Sir Robert Moray, the superintendent of the laboratory of the king, of Master Mechanic, was conferred upon Sir Samuel Morland, a nobleman who, in his practical knowledge of mechanics and in his ingenuity and fruitfulness of invention, was apparently almost equal to Worcester. He was the son of a Berkshire clergyman, was educated at Cambridge, where he studied mathematics with great interest, and entered public life soon after. He served the Parliament under Cromwell, and afterward went to Geneva. He was of a decidedly literary turn of mind, and wrote a history of the Piedmont churches, which gave him great repute with the Protestant party. He was induced subsequently, on the accession of Charles II., to take service under that monarch, whose gratitude he had earned by revealing a plot for his assassination. He received his appointment and a baronetcy in 1660, and immediately commenced making experiments, partly at his own expense and partly at the cost of the royal exchequer, which were usually not at all remunerative. He built hand fire-engines of various kinds, taking patents on them, which brought him as small profits as did his work for the king, and invented the speaking-trumpet, calculating machines, and a capstan. His house at Vauxhall was full of curious devices, the products of his own ingenuity. He devoted much attention to apparatus for raising water. His devices seem to have usually been modifications of the now familiar force-pump. They attracted much attention, and exhibitions were made of them before the king and queen and the court. He was sent to France on business relating to water-works erected for King Charles, and while in Paris he constructed pumps and pumping apparatus for the satisfaction of Louis XIV. In his book,[18] published in Paris in 1683, and presented to the king, and an earlier manuscript,[19] still preserved in the British Museum, Morland shows a perfect familiarity with the power of steam. He says, in the latter: "Water being evaporated by fire, the vapors require a greater space (about two thousand times) than that occupied by the water; and, rather than submit to imprisonment, it will burst a piece of ordnance. But, being controlled according to the laws of statics, and, by science, reduced to the measure of weight and balance, it bears its burden peaceably (like good horses), and thus may be of great use to mankind, especially for the raising of water, according to the following table, which indicates the number of pounds which may be raised six inches, 1,800 times an hour, by cylinders half-filled with water, and of the several diameters and depths of said cylinders." [18] "Elevation des Eaux par toute sorte de Machines réduite à la Mesure au Poids et à la Balance, présentée a Sa Majesté Très Chrétienne, par le Chevalier Morland, Gentilhomme Ordinaire de la Chambre Privée et Maistre de Mechaniques du Roy de la Grande Bretagne, 1683." [19] "Les Principes de la Nouvelle Force de Feu, inventée par le Chevalier Morland, l'an 1682, et présentée a Sa Majesté Très Chrétienne, 1683." He then gives the following table, a comparison of which with modern tables proves Morland to have acquired a very considerable and tolerably accurate knowledge of the volume and pressure of saturated steam: -------------------------+------------------------ CYLINDERS. | POUNDS. -----------+-------------+---------------------- Diameter | Depth | Weight in Feet. | in Feet. | to be Raised. -----------+-------------+---------------------- 1 | 2 | 15 2 | 4 | 120 3 | 6 | 405 4 | 8 | 960 5 | 10 | 1,876 6 | 10 | 3,240 -----------+-------------+---------------------- Number of cylinders having a diameter of 6 feet and a depth of 12 feet. | | 1 | 12 | 3,240 2 | 12 | 6,480 3 | 12 | 9,720 4 | 12 | 12,960 5 | 12 | 16,200 6 | 12 | 19,440 7 | 12 | 22,680 8 | 12 | 25,920 9 | 12 | 29,190 10 | 12 | 32,400 20 | 12 | 64,800 30 | 12 | 97,200 40 | 12 | 129,600 50 | 12 | 162,000 60 | 12 | 194,400 70 | 12 | 226,800 80 | 12 | 259,200 90 | 12 | 291,600 -----------+-------------+---------------------- The rate of enlargement of volume in the conversion of water into steam, as given in Morland's book, appears remarkably accurate when compared with statements made by other early experimenters. Desaguliers gave the ratio of volumes at 14,000, and this was accepted as correct for many years, and until Watt's experiments, which were quoted by Dr. Robison as giving the ratio at between 1,800 and 1,900. Morland also states the "duty" of his engines in the same manner in which it is stated by engineers to-day. Morland must undoubtedly have been acquainted with the work of his distinguished contemporary, Lord Worcester, and his apparatus seems most likely to have been a modification--perhaps improvement--of Worcester's engine. His house was at Vauxhall, and the establishment set up for the king was in the neighborhood. It may be that Morland is to be credited with greater success in the introduction of his predecessor's apparatus than the inventor himself. Dr. Hutton considered this book to have been the earliest account of the steam-engine, and accepts the date--1682--as that of the invention, and adds, that "the project seems to have remained obscure in both countries till 1699, when Savery, who probably knew more of Morland's invention than he owned, obtained a patent," etc. We have, however, scarcely more complete or accurate knowledge of the extent of Morland's work, and of its real value, than of that of Worcester. Morland died in 1696, at Hammersmith, not far from London, and his body lies in Fulham church. From this time forward the minds of many mechanicians were earnestly at work on this problem--the raising of water by aid of steam. Hitherto, although many ingenious toys, embodying the principles of the steam-engine separately, and sometimes to a certain extent collectively, had been proposed, and even occasionally constructed, the world was only just ready to profit by the labors of inventors in this direction. But, at the end of the seventeenth century, English miners were beginning to find the greatest difficulty in clearing their shafts of the vast quantities of water which they were meeting at the considerable depths to which they had penetrated, and it had become a matter of vital importance to them to find a more powerful aid in that work than was then available. They were, therefore, by their necessities stimulated to watch for, and to be prepared promptly to take advantage of, such an invention when it should be offered them. The experiments of Papin, and the practical application of known principles by Savery, placed the needed apparatus in their hands. [Illustration: Thomas Savery.] THOMAS SAVERY was a member of a well-known family of Devonshire, England, and was born at Shilston, about 1650. He was well educated, and became a military engineer. He exhibited great fondness for mechanics, and for mathematics and natural philosophy, and gave much time to experimenting, to the contriving of various kinds of apparatus, and to invention. He constructed a clock, which still remains in the family, and is considered an ingenious piece of mechanism, and is said to be of excellent workmanship. He invented and patented an arrangement of paddle-wheels, driven by a capstan[20] for propelling vessels in calm weather, and spent some time endeavoring to secure its adoption by the British Admiralty and the Navy Board, but met with no success. The principal objector was the Surveyor of the Navy, who dismissed Savery, with a remark which illustrates a spirit which, although not yet extinct, is less frequently met with in the public service now than then: "What have interloping people, that have no concern with us, to do to pretend to contrive or invent things for us?"[21] Savery then fitted his apparatus into a small vessel, and exhibited its operation on the Thames. The invention was never introduced into the navy, however. [20] Harris, "Lexicon Technicum," London, 1710. [21] "Navigation Improved; or, The Art of Rowing Ships of all rates in Calms, with a more Easy, Swift, and Steady Motion, than Oars can," etc., etc. By Thomas Savery, Gent. London, 1698. It was after this time that Savery became the inventor of a steam-engine. It is not known whether he was familiar with the work of Worcester, and of earlier inventors. Desaguliers[22] states that he had read the book of Worcester, and that he subsequently endeavored to destroy all evidence of the anticipation of his own invention by the marquis by buying up all copies of the century that he could find, and burning them. The story is scarcely credible. A comparison of the drawings given of the two engines exhibits, nevertheless, a striking resemblance; and, assuming that of the marquis's engine to be correct, Savery is to be given credit for the finally successful introduction of the "semi-omnipotent" "water-commanding" engine of Worcester. [22] "Experimental Philosophy," vol. ii., p. 465. The most important advance in actual construction, therefore, was made by Thomas Savery. The constant and embarrassing expense, and the engineering difficulties presented by the necessity of keeping the British mines, and particularly the deep pits of Cornwall, free from water, and the failure of every attempt previously made to provide effective and economical pumping-machinery, were noted by Savery, who, July 25, 1698, patented the design of the first engine which was ever actually employed in this work. A working-model was submitted to the Royal Society of London in 1699, and successful experiments were made with it. Savery spent a considerable time in planning his engine and in perfecting it, and states that he expended large sums of money upon it. Having finally succeeded in satisfying himself with its operation, he exhibited a model "Fire-Engine," as it was called in those days, before King William III. and his court, at Hampton Court, in 1698, and obtained his patent without delay. The title of the patent reads: "A grant to Thomas Savery, Gentl., of the sole exercise of a new invention by him invented, for raising of water, and occasioning motion to all sorts of mill-works, by the impellant force of fire, which will be of great use for draining mines, serving towns with water, and for the working of all sorts of mills, when they have not the benefit of water nor constant winds; to hold for 14 years; with usual clauses." Savery now went about the work of introducing his invention in a way which is in marked contrast with that usually adopted by the inventors of that time. He commenced a systematic and successful system of advertisement, and lost no opportunity of making his plans not merely known, but well understood, even in matters of detail. The Royal Society was then fully organized, and at one of its meetings he obtained permission to appear with his model "fire-engine" and to explain its operation; and, as the minutes read, "Mr. Savery entertained the Society with showing his engine to raise water by the force of fire. He was thanked for showing the experiment, which succeeded, according to expectation, and was approved of." He presented to the Society a drawing and specifications of his machine, and "The Transactions"[23] contain a copperplate engraving and the description of his model. It consisted of a furnace, _A_, heating a boiler, _B_, which was connected by pipes, _C C_, with two copper receivers, _D D_. There were led from the bottom of these receivers branch pipes, _F F_, which turned upward, and were united to form a rising main, or "forcing-pipe," _G_. From the top of each receiver was led a pipe, which was turned downward, and these pipes united to form a suction-pipe, which was led down to the bottom of the well or reservoir from which the water was to be drawn. The maximum lift allowable was stated at 24 feet. [23] "Philosophical Transactions, No. 252." Weld's "Royal Society," vol. i., p. 357. Lowthorp's "Abridgment," vol. i. [Illustration: FIG. 11.--Savery's Model, 1698.] The engine was worked as follows: Steam is raised in the boiler, _B_, and a cock, _C_, being opened, a receiver, _D_, is filled with steam. Closing the cock, _C_, the steam condensing in the receiver, a vacuum is created, and the pressure of the atmosphere forces the water up, through the supply-pipe, from the well into the receiver. Opening the cock, _C_, again, the check-valve in the suction-pipe at _E_ closes, the steam drives the water out through the forcing-pipe, _G_, the clack-valve, _E_, on that pipe opening before it, and the liquid is expelled from the top of the pipe. The valve, _C_, is again closed; the steam again condenses, and the engine is worked as before. While one of the two receivers is discharging, the other is filling, as in the machine of the Marquis of Worcester, and thus the steam is drawn from the boiler with tolerable regularity, and the expulsion of water takes place with similar uniformity, the two systems of receivers and pipes being worked alternately by the single boiler. In another and still simpler little machine,[24] which he erected at Kensington (Fig. 12), the same general plan was adopted, combining a suction-pipe, _A_, 16 feet long and 3 inches in diameter; a single receiver, _B_, capable of containing 13 gallons; a boiler, _C_, of about 40 gallons capacity; a forcing-pipe, _D_, 42 feet high, with the connecting pipe and cocks, _E F G_; and the method of operation was as already described, except that _surface-condensation_ was employed, the cock, _F_, being arranged to shower water from the rising main over the receiver, as shown. Of the first engine Switzer says: "I have heard him say myself, that the very first time he played, it was in a potter's house at Lambeth, where, though it was a small engine, yet it (the water) forced its way through the roof, and struck off the tiles in a manner that surprised all the spectators." [24] Bradley, "New Improvements of Planting and Gardening." Switzer, "Hydrostatics," 1729. [Illustration: FIG. 12.--Savery's Engine, 1698.] The Kensington engine cost £50, and raised 3,000 gallons per hour, filling the receiver four times a minute, and required a bushel of coal per day. Switzer remarks: "It must be noted that this engine is but a small one in comparison with many others that are made for coal-works; but this is sufficient for any reasonable family, and other uses required of it in watering all middling gardens." He cautions the operator: "When you have raised water enough, and you design to leave off working the engine, take away all the fire from under the boiler, and open the cock (connected to the funnel) to let out the steam, which would otherwise, were it to remain confined, perhaps burst the engine." With the intention of making his invention more generally known, and hoping to introduce it as a pumping-engine in the mining districts of Cornwall, Savery wrote a prospectus for general circulation, which contains the earliest account of the later and more effective form of engine. He entitled his pamphlet "The Miner's Friend; or, A Description of an Engine to raise Water by Fire described, and the Manner of fixing it in Mines, with an Account of the several Uses it is applicable to, and an Answer to the Objections against it." It was printed in London in 1702, for S. Crouch, and was distributed among the proprietors and managers of mines, who were then finding the flow of water at depths so great as, in some cases, to bar further progress. In many cases, the cost of drainage left no satisfactory margin of profit. In one mine, 500 horses were employed raising water, by the then usual method of using horse-gins and buckets. The approval of the King and of the Royal Society, and the countenance of the mine-adventurers of England, were acknowledged by the author, who addressed his pamphlet to them. The engraving of the engine was reproduced, with the description, in Harris's "Lexicon Technicum," 1704; in Switzer's "Hydrostatics," 1729; and in Desaguliers's "Experimental Philosophy," 1744. The sketch which here follows is a neater engraving of the same machine. Savery's engine is shown in Fig. 13, as described by Savery himself, in 1702, in "The Miner's Friend." _L_ is the boiler in which steam is raised, and through the pipes _O O_ it is alternately let into the vessels _P P_. [Illustration: FIG. 13.--Savery's Engine, A. D. 1702.] Suppose it to pass into the left-hand vessel first. The valve _M_ being closed, and _R_ being opened, the water contained in _P_ is driven out and up the pipe _S_ to the desired height, where it is discharged. The valve _R_ is then closed, and the valve in the pipe _O_; the valve _M_ is next opened, and condensing water is turned upon the exterior of _P_ by the cock _Y_, leading water from the cistern _X_. As the steam contained in _P_ is condensed, forming a vacuum there, a fresh charge of water is driven by atmospheric pressure up the pipe _T_. Meantime, steam from the boiler has been let into the right-hand vessel _P_, the cock _W_ having been first closed, and _R_ opened. The charge of water is driven out through the lower pipe and the cock _R_, and up the pipe _S_ as before, while the other vessel is refilling preparatory to acting in its turn. The two vessels are thus alternately charged and discharged, as long as is necessary. Savery's method of supplying his boiler with water was at once simple and ingenious. The small boiler, _D_, is filled with water from any convenient source, as from the stand-pipe, _S_. A fire is then built under it, and, when the pressure of steam in _D_ becomes greater than in the main boiler, _L_, a communication is opened between their lower ends, and the water passes, under pressure, from the smaller to the larger boiler, which is thus "fed" without interrupting the work. _G_ and _N_ are _gauge-cocks_, by which the height of water in the boilers is determined; they were first adopted by Savery. Here we find, therefore, the first really practicable and commercially valuable steam-engine. Thomas Savery is entitled to the credit of having been the first to introduce a machine in which the power of heat, acting through the medium of steam, was rendered generally useful. It will be noticed that Savery, like the Marquis of Worcester, used a boiler separate from the water-reservoir. He added to the "water-commanding engine" of the marquis the system of _surface-condensation_, by which he was enabled to charge his vessels when it became necessary to refill them; and added, also, the secondary boiler, which enabled him to supply the working-boiler with water without interrupting its work. The machine was thus made capable of working uninterruptedly for a period of time only limited by its own decay. Savery never fitted his boilers with safety-valves, although it was done earlier by Papin; and in deep mines he was compelled to make use of higher pressures than his rudely-constructed boilers could safely bear. Savery's engine was used at a number of mines, and also for supplying water to towns; some large estates, country houses, and other private establishments, employed them for the same purpose. They did not, however, come into general use among the mines, because, according to Desaguliers, they were apprehensive of danger from the explosion of the boilers or receivers. As Desaguliers wrote subsequently: "Savery made a great many experiments to bring this machine to perfection, and did erect several which raised water very well for gentlemen's seats, but could not succeed for mines, or supplying towns, where the water was to be raised very high and in great quantities; for then the steam required being boiled up to such a strength as to be ready to tear all the vessels to pieces." "I have known Captain Savery, at York's buildings, to make steam eight or ten times stronger than common air; and then its heat was so great that it would melt common soft solder, and its strength so great as to blow open several joints of the machine; so that he was forced to be at the pains and charge to have all his joints soldered with spelter or hard solder." Although there were other difficulties in the application of the Savery engine to many kinds of work, this was the most serious one, and explosions did occur with fatal results. The writer just quoted relates, in his "Experimental Philosophy," that a man who was ignorant of the nature of the engine undertook to work a machine which Desaguliers had provided with a safety-valve to avoid this very danger, "and, having hung the weight at the further end of the steelyard, in order to collect more steam in order to make his work the quicker, he hung also a very heavy plumber's iron upon the end of the steelyard; the consequence proved fatal; for, after some time, the steam, not being able, with the safety-cock, to raise up the steelyard loaded with all this unusual weight, burst the boiler with a great explosion, and killed the poor man." This is probably the earliest record of a steam-boiler explosion. Savery proposed to use his engine for driving mills; but there is no evidence that he actually made such an application of the machine, although it was afterward so applied by others. The engine was not well adapted to the drainage of surface-land, as the elevation of large quantities of water through small heights required great capacity of receivers, or compelled the use of several engines for each case. The filling of the receivers, in such cases, also compelled the heating of large areas of cold and wet metallic surfaces by the steam at each operation, and thus made the work comparatively wasteful of fuel. Where used in mines, they were necessarily placed within 30 feet or less of the lowest level, and were therefore exposed to danger of submergence whenever, by any accident, the water should rise above that level. In many cases this would result in the loss of the engine, and the mine would remain "drowned," unless another engine should be procured to pump it out. Where the mine was deep, the water was forced by the pressure of steam from the level of the engine-station to the top of the lift. This compelled the use of pressures of several atmospheres in many cases; and a pressure of three atmospheres, or about 45 pounds per square inch, was considered, in those days, as about the maximum pressure allowable. This difficulty was met by setting a separate engine at every 60 or 80 feet, and pumping the water from one to the other. If any one engine in the set became disabled, the pumping was interrupted until that one machine could be repaired. The size of Savery's largest boilers was not great, their maximum diameter not exceeding two and a half feet. This made it necessary to provide several of his engines, usually, for a single mine, and at each level. The first cost and the expense of repairs were exceedingly serious items. The expense and danger, either real or apparent, were thus sufficient to deter many from their use, and the old method of raising water by horse-power was adhered to. The consumption of fuel with these engines was very great. The steam was not generated economically, as the boilers used were of such simple forms as only could then be produced, and presented too little heating surface to secure a very complete transfer of heat from the gases of combustion to the water within the boiler. This waste in the generation of steam in these uneconomical boilers was followed by still more serious waste in its application, without expansion, to the expulsion of water from a metallic receiver, the cold and wet sides of which absorbed heat with the greatest avidity. The great mass of the liquid was not, however, heated by the steam, and was expelled at the temperature at which it was raised from below. Savery quaintly relates the action of his machine in "The Miner's Friend," and so exactly, that a better description could scarcely be asked: "The steam acts upon the surface of the water in the receiver, which surface only being heated by the steam, it does not condense, but the steam gravitates or presses with an elastic quality like air, and still increasing its elasticity or spring, until it counterpoises, or rather exceeds, the weight of the column of water in the force-pipe, which then it will necessarily drive up that pipe; the steam then takes some time to recover its power, but it will at last discharge the water out at the top of the pipe. You may see on the outside of the receiver how the water goes out, as well as if it were transparent; for, so far as the steam is contained within the vessel, it is dry without, and so hot as scarcely to endure the least touch of the hand; but so far as the water is inside the vessel, it will be cold and wet on the outside, where any water has fallen on it; which cold and moisture vanish as fast as the steam takes the place of the water in its descent." After Savery's death, in 1716, several of these engines were erected in which some improvements were introduced. Dr. Desaguliers, in 1718, built a Savery engine, in which he avoided some defects which he, with Dr. Gravesande, had noted two years earlier. They had then proposed to adopt the arrangement of a single receiver which had been used by Savery himself, as already described, finding, by experiment on a model which they had made for the purpose, that one could be discharged three times, while the same boiler would empty two receivers but once each. In their arrangement, the steam was shut back in the boiler while the receiver was filling with water, and a high pressure thus accumulated, instead of being turned into the second receiver, and the pressure thus kept comparatively low. [Illustration: FIG. 14.--Papin's Two-Way Cock.] In the engine built in 1718, Desaguliers used a spherical boiler, which he provided with the lever safety-valve already applied by Papin, and adopted a comparatively small receiver--one-fifth the capacity of the boiler--of slender cylindrical form, and attached a pipe leading the water for condensation into the vessel, and effected its distribution by means of the "rose," or a "sprinkling-plate," such as is still frequently used in modern engines having jet-condensers. This substitution of jet for surface-condensation was of very great advantage, securing great promptness in the formation of a vacuum and a rapid filling of the receiver. A "two-way cock" admitted steam to the receiver, or, being turned the other way, admitted the cold condensing water. The dispersion of the water in minute streams or drops was a very important detail, not only as securing great rapidity of condensation, but enabling the designer to employ a comparatively small receiver or condenser. The engine is shown in Fig. 15, which is copied from the "Experimental Philosophy" of Desaguliers. [Illustration: FIG. 15.--Engine built by Desaguliers in 1718.] The receiver, _A_, is connected to the boiler, _B_, by a steam-pipe, _C_, terminating at the two-way cock, _D_; the "forcing-pipe," _E_, has at its foot a check-valve, _F_, and the valve _G_ is a similar check at the head of the suction-pipe. _H_ is a strainer, to prevent the ingress of chips or other bodies carried to the pipe by the current; the cap above the valves is secured by a bridle, or stirrup, and screw, _I_, and may be readily removed to clear the valves or to renew them; _K_ is the handle of the two-way cock; _M_ is the injection-cock, and is kept open during the working of the engine; _L_ is the chimney-flue; _N_ and _O_ are gauge-cocks fitted to pipes leading to the proper depths within the boiler, the water-line being somewhere between the levels of their lower ends; _P_ is a lever safety-valve, as first used on the "Digester" of Papin; _R_ is the reservoir into which the water is pumped; _T_ is the flue, leading spirally about the boiler from the furnace, _V_, to the chimney; _Y_ is a cock fitted in a pipe through which the rising-main may be filled from the reservoir, should injection-water be needed when that pipe is empty. Seven of these engines were built, the first of which was made for the Czar of Russia. Its boiler had a capacity of "five or six hogsheads," and the receiver, "holding one hogshead," was filled and emptied four times a minute. The water was raised "by suction" 29 feet, and forced by steam pressure 11 feet higher. Another engine built at about this time, to raise water 29 feet "by suction," and to force it 24 feet higher, made 6 "strokes" per minute, and, when forcing water but 6 or 8 feet, made 8 or 9 strokes per minute. Twenty-five years later a workman overloaded the safety-valve of this engine, by placing the weight at the end and then adding "a very heavy plumber's iron." The boiler exploded, killing the attendant. Desaguliers says that one of these engines, capable of raising ten tons an hour 38 feet, in 1728 or 1729, cost £80, exclusive of the piping. Blakely, in 1766, patented an improved Savery engine, in which he endeavored to avoid the serious loss due to condensation of the steam by direct contact with the water, by interposing a cushion of oil, which floated upon the water and prevented the contact of the steam with the surface of the water beneath it. He also used air for the same purpose, sometimes in double receivers, one supported on the other. These plans did not, however, prove satisfactory. Rigley, of Manchester, England, soon after erected Savery engines, and applied them to the driving of mills, by pumping water into reservoirs, from whence it returned to the wells or ponds from which it had been raised, turning water-wheels as it descended. Such an arrangement was in operation many years at the works of a Mr. Kiers, St. Pancras, London. It is described in detail, and illustrated, in Nicholson's "Philosophical Journal," vol. i., p. 419. It had a "wagon-boiler" 7 feet long, 5 wide, and 5 deep; the wheel was 18 feet in diameter, and drove the lathes and other machinery of the works. In this engine Blakely's plan of injecting air was adopted. The injection-valve was a clack, which closed automatically when the vacuum was formed. The engine consumed 6 or 7 bushels of good coals, and made 10 strokes per minute, raising 70 cubic feet of water 14 feet, and developing nearly 3 horse-power. Many years after Savery's death, in 1774, Smeaton made the first duty-trials of engines of this kind. He found that an engine having a cylindrical receiver 16 inches in diameter and 22 feet high, discharging the water raised 14 feet above the surface of the water in the well, making 12 strokes, and raising 100 cubic feet per minute, developed 2-2/3 horse-power, and consumed 3 hundredweight of coals in four hours. Its duty was, therefore, 5,250,000 pounds raised one foot per bushel of 84 pounds of coals, or 62,500 "foot-pounds" of work per pound of fuel. An engine of slightly greater size gave a duty about 5 per cent. greater. When Louis XIV. revoked the edict of Nantes, by which Henry IV. had guaranteed protection to the Protestants of France, the terrible persecutions at once commenced drove from the kingdom some of its greatest men. Among these was Denys Papin. It was at about this time that the influence of the atmospheric pressure on the boiling-point began to be observed, Dr. Hooke having found that the boiling-point was a fixed temperature under the ordinary pressure of the atmosphere, and the increase in temperature and pressure of steam when confined having been shown by Papin with his "Digester." Denys Papin was of a family which had attached itself to the Protestant Church; but he was given his education in the school of the Jesuits at Blois, and there acquired his knowledge of mathematics. His medical education was given him at Paris, although he probably received his degree at Orleans. He settled in Paris in 1672, with the intention of practising his profession, and devoted all his spare time, apparently, to the study of physics. [Illustration: Denys Papin.] Meantime, that distinguished philosopher, Huyghens, the inventor of the clock and of the gunpowder-engine, had been induced by the linen-draper's apprentice, Colbert, now the most trusted adviser of the king, to take up his residence in Paris, and had been made one of the earliest members of the Academy of Science, which was founded at about that time. Papin became an assistant to Huyghens, and aided him in his experiments in mechanics, having been introduced by Madame Colbert, who was also a native of Blois. Here he devised several modifications of the instruments of Guericke, and printed a description of them.[25] This little book was presented to the Academy, and very favorably noticed. Papin now became well known among contemporary men of science at Paris, and was well received everywhere. Soon after, in the year 1675, as stated by the _Journal des Savants_, he left Paris and took up his residence in England, where he very soon made the acquaintance of Robert Boyle, the founder, and of the members of the Royal Society. Boyle speaks of Papin as having gone to England in the hope of finding a place in which he could satisfactorily pursue his favorite studies. [25] "Nouvelles Expériences du Vuide, avec la description des Machines qui servent à le faire." Paris, 1674. Boyle himself had already been long engaged in the study of pneumatics, and had been especially interested in the investigations which had been original with Guericke. He admitted young Papin into his laboratory, and the two philosophers worked together at these attractive problems. It was while working with Boyle that Papin invented the double air-pump and the air-gun. Papin and his work had now become so well known, and he had attained so high a position in science, that he was nominated for membership in the Royal Academy, and was elected December 16, 1680. He at once took his place among the most talented and distinguished of the great men of his time. He probably invented his "Digester" while in England, and it was first described in a brochure written in English, under the title, "The New Digester." It was subsequently published in Paris.[26] This was a vessel, _B_ (Fig. 16), capable of being tightly closed by a screw, _D_, and a lid, _C_, in which food could be cooked in water raised by a furnace, _A_, to the temperature due to any desired safe pressure of steam. The pressure was determined and limited by a weight, _W_, on the safety-valve lever, _G_. It is probable that this essential attachment to the steam-boiler had previously been used for other purposes; but Papin is given the credit of having first made use of it to control the pressure of steam. [26] "La manière d'amollir les os et de faire cuire toutes sortes de viandes," etc. [Illustration: FIG. 16.--Papin's Digester, 1680.] From England, Papin went to Italy, where he accepted membership and held official position in the Italian Academy of Science. Papin remained in Venice two years, and then returned to England. Here, in 1687, he announced one of his inventions, which is just becoming of great value in the arts. He proposed to transmit power from one point to another, over long distances, by the now well-known "pneumatic" method. At the point where power was available, he exhausted a chamber by means of an air-pump, and, leading a pipe to the distant point at which it was to be utilized, there withdrew the air from behind a piston, and the pressure of the air upon the latter caused it to recede into the cylinder, in which it was fitted, raising a weight, of which the magnitude was proportionate to the size of the piston and the degree of exhaustion. Papin was not satisfactorily successful in his experiments; but he had created the germ of the modern system of pneumatic transmission of power. His disappointment at the result of his efforts to utilize the system was very great, and he became despondent, and anxious to change his location again. In 1687 he was offered the chair of Mathematics at Marburg by Charles, the Landgrave of Upper Hesse, and, accepting the appointment, went to Germany. He remained in Germany many years, and continued his researches with renewed activity and interest. His papers were published in the "Acta Eruditorum" at Leipsic, and in the "Philosophical Transactions" at London. It was while at Marburg that his papers descriptive of his method of pneumatic transmission of power were printed.[27] [27] "Recueil des diverses Pieces touchant quelques Nouvelles Machines et autres Sujets Philosophiques," M. D. Papin. Cassel, 1695. In the "Acta Eruditorum" of 1688 he exhibited a practicable plan, in which he exhausted the air from a set of engines or pumps by means of pumps situated at a long distance from the point of application of the power, and at the place where the prime mover--which was in this case a water-wheel--was erected. After his arrival at the University of Marburg, Papin exhibited to his colleagues in the faculty a modification of Huyghens's gunpowder-engine, in which he had endeavored to obtain a more perfect vacuum than had Huyghens in the first of these machines. Disappointed in this, he finally adopted the expedient of employing steam to displace the air, and to produce, by its condensation, the perfect vacuum which he sought; and he thus produced _the first steam-engine with a piston_, and the first piston steam-engine, in which condensation was produced to secure a vacuum. It was described in the "Acta" of Leipsic,[28] in June, 1690, under the title, "Nova Methodus ad vires motrices validissimas leri pretio comparandeo" ("A New Method of securing cheaply Motive Power of considerable Magnitude"). He describes first the gunpowder-engine, and continues by stating that, "until now, all experiments have been unsuccessful; and after the combustion of the exploded powder, there always remains in the cylinder about one-fifth its volume of air." He says that he has endeavored to arrive by another route at the same end; and "as, by a natural property of water, a small quantity of this liquid, vaporized by the action of heat, acquires an elasticity like that of the air, and returns to the liquid state again on cooling, without retaining the least trace of its elastic force," he thought that it would be easy to construct machines in which, "by means of a moderate heat, and without much expense," a more perfect vacuum could be produced than could be secured by the use of gunpowder. [28] "Acta Eruditorum," Leipsic, 1690. [Illustration: FIG. 17.--Papin's Engine.] The first machine of Papin (Fig. 17) was very similar to the gunpowder-engine already described as the invention of Huyghens. In place of gunpowder, a small quantity of water is placed at the bottom of the cylinder, _A_; a fire is built beneath it, "the bottom being made of very thin metal," and the steam formed soon raises the piston, _B_, to the top, where a latch, _E_, engaging a notch in the piston-rod, _H_, holds it up until it is desired that it shall drop. The fire being removed, the steam condenses, and a vacuum is formed below the piston, and the latch, _E_, being disengaged, the piston is driven down by the superincumbent atmosphere and raises the weight which has been, meantime, attached to a rope, _L_, passing from the piston-rod over pulleys, _T T_. The machine had a cylinder two and a half inches in diameter, and raised 60 pounds once a minute; and Papin calculated that a machine of a little more than two feet diameter of cylinder and of four feet stroke would raise 8,000 pounds four feet per minute--i. e., that it would yield about one horse-power. The inventor claimed that this new machine would be found useful in relieving mines from water, in throwing bombs, in ship-propulsion, attaching revolving paddles--i. e., paddle-wheels--to the sides of the vessel, which wheels were to be driven by several of his engines, in order to secure continuous motion, the piston-rods being fitted with racks which were to engage ratchet-wheels on the paddle-shafts. "The principal difficulty," he says, answering anticipated objections, "is that of making these large cylinders." In a reprint describing his invention, in 1695, Papin gives a description of a "newly-invented furnace," a kind of fire-box steam-boiler, in which the fire, completely surrounded by water, makes steam so rapidly that his engine could be driven at the rate of four strokes per minute by the steam supplied by it. Papin also proposed the use of a peculiar form of furnace with this engine, which, embodying as it does some suggestions that very probably have since been attributed to later inventors, deserves special notice. In this furnace, Papin proposed to burn his fuel on a grate within a furnace arranged with a _down-draught_, the air entering above the grate, passing _down_ through the fire, and from the ash-pit through a side flue to the chimney. In starting the fire, the coal was laid on the grate, covered with wood, and the latter was ignited, the flame, passing downward through the coal, igniting that in turn, and, as claimed by Papin, the combustion was complete, and the formation of smoke was entirely prevented. He states, in "Acta Eruditorum," that the heat was intense, the saving of fuel very great, and that the only difficulty was to find a refractory material which would withstand the high temperature attained. This is the first fire-box and flue boiler of which we have record. The experiment is supposed to have led Papin to suggest the use of a hot-blast, as practised by Neilson more than a century later, for reducing metals from their ores. Papin made another boiler having a flue winding through the water-space, and presenting a heating surface of nearly 80 square feet. The flue had a length of 24 feet, and was about 10 inches square. It is not stated what were the maximum pressures carried on these boilers; but it is known that Papin had used very high pressures in his digesters--probably between 1,200 and 1,500 pounds per square inch. In the year 1705, Leibnitz, then visiting England, had seen a Savery engine, and, on his return, described it to Papin, sending him a sketch of the machine. Papin read the letter and exhibited the sketch to the Landgrave of Hesse, and Charles at once urged him to endeavor to perfect his own machine, and to continue the researches which he had been intermittently pursuing since the earlier machine had been exhibited in public. In a small pamphlet printed at Cassel in 1707,[29] Papin describes a new form of engine, in which he discards the original plan of a modified Huyghens engine, with tight-fitting piston and cylinder, raising its load by indirect action, and makes a modified Savery engine, which he calls the "Elector's Engine," in honor of his patron. This is the engine shown in the engraving, and as proposed to be used by him in turning a water-wheel. [29] "Nouvelle manière d'élever l'Eau par la Force du Feu, mis en Lumière," par D. Papin. Cassel, 1707. The sketch is that given by the inventor in his memoir. It consists (Fig. 18) of a steam-boiler, _a_, from which steam is led through the cock, _c_, to the working cylinder, _n n_. The water beneath the floating-piston, _h_, which latter serves simply as a cushion to protect the steam from sudden condensation or contact with the water, is forced into the vessel _r r_, which is a large air-chamber, and which serves to render the outflow of water comparatively uniform, and the discharge occurs by means of the pipe _q_, from which the water rises to the desired height. A fresh supply of water is introduced through the funnel _k_, after condensation of the steam in _n n_, and the operation of expulsion is repeated. [Illustration: FIG. 18.--Papin's Engine and Water-Wheel, A. D. 1707.] This machine is evidently a retrogression, and Papin, after having earned the honor of having invented the first steam-engine of the typical form which has since become so universally applied, forfeited that credit by his evident ignorance of its superiority over existing devices, and by attempting unsuccessfully to perfect the inferior device of another inventor. Subsequently, Papin made an attempt to apply the steam-engine to the propulsion of vessels, the account of which will be given in the chapter on Steam-Navigation. Again disappointed, Papin once more visited England, to renew his acquaintance with the _savans_ of the Royal Society; but Boyle had died during the period which Papin had spent in Germany, and the unhappy and disheartened inventor and philosopher died in 1810, without having seen any one of his many devices and ingenious inventions a practical success. [Illustration] CHAPTER II. _THE STEAM-ENGINE AS A TRAIN OF MECHANISM._ "The introduction of new Inventions seemeth to be the very chief of all human Actions. The Benefits of new Inventions may extend to all Mankind universally; but the Good of political Achievements can respect but some particular Cantons of Men; these latter do not endure above a few Ages, the former forever. Inventions make all Men happy, without either Injury or Damage to any one single Person. Furthermore, new Inventions are, as it were, new Erections and Imitations of God's own Works."--BACON. THE MODERN TYPE, AS DEVELOPED BY NEWCOMEN, BEIGHTON, AND SMEATON. At the beginning of the eighteenth century every element of the modern type of steam-engine had been separately invented and practically applied. The character of atmospheric pressure, and of the pressure of gases, had become understood. The nature of a vacuum was known, and the method of obtaining it by the displacement of the air by steam, and by the condensation of the vapor, was understood. The importance of utilizing the power of steam, and the application of condensation in the removal of atmospheric pressure, was not only recognized, but had been actually and successfully attempted by Morland, Papin, and Savery. Mechanicians had succeeded in making steam-boilers capable of sustaining any desired or any useful pressure, and Papin had shown how to make them comparatively safe by the attachment of the safety-valve. They had made steam-cylinders fitted with pistons, and had used such a combination in the development of power. It now only remained for the engineer to combine known forms of mechanism in a practical machine which should be capable of economically and conveniently utilizing the power of steam through the application of now well-understood principles, and by the intelligent combination of physical phenomena already familiar to scientific investigators. Every essential fact and every vital principle had been learned, and every one of the needed mechanical combinations had been successfully effected. It was only requisite that an inventor should appear, capable of perceiving that these known facts and combinations of mechanism, properly illustrated in a working machine, would present to the world its greatest physical blessing. The defects of the simple engines constructed up to this time have been noted as each has been described. None of them could be depended upon for safe, economical, and continuous work. Savery's was the most successful of all. But the engine of Savery, even with the improvements of Desaguliers, was unsafe where most needed, because of the high pressures necessarily carried in its boilers when pumping from considerable depths; it was uneconomical, in consequence of the great loss of heat in its forcing-cylinders when the hot steam was surrounded at its entrance by colder bodies; it was slow in operation, of great first cost, and expensive in first cost and in repairs, as well as in its operation. It could not be relied upon to do its work uninterruptedly, and was thus in many respects a very unsatisfactory machine. The man who finally effected a combination of the elements of the modern steam-engine, and produced a machine which is unmistakably a true engine--i. e., a train of mechanism consisting of several elementary pieces combined in a train capable of transmitting a force applied at one end and of communicating it to the resistance to be overcome at the other end--was THOMAS NEWCOMEN, an "iron-monger" and blacksmith of Dartmouth, England. The engine invented by him, and known as the "Atmospheric Steam-Engine," is the first of an entirely new type. The old type of engine--the steam-engine as a simple machine--had been given as great a degree of perfection, by the successive improvements of Worcester, Savery, and Desaguliers, as it was probably capable of attaining by any modification of its details. The next step was necessarily a complete change of type; and to effect such a change, it was only necessary to combine devices already known and successfully tried. But little is known of the personal history of Newcomen. His position in life was humble, and the inventor was not then looked upon as an individual of even possible importance in the community. He was considered as one of an eccentric class of schemers, and of an order which, concerning itself with mechanical matters, held the lowest position in the class. It is supposed that Savery's engine was perfectly well known to Newcomen, and that the latter may have visited Savery at his home in Modbury, which was but fifteen miles from the residence of Newcomen. It is thought, by some biographers of these inventors, that Newcomen was employed by Savery in making the more intricate forgings of his engine. Harris, in his "Lexicon Technicum," states that drawings of the engine of Savery came into the hands of Newcomen, who made a model of the machine, set it up in his garden, and then attempted its improvement; but Switzer says that Newcomen "was as early in his invention as Mr. Savery was in his." Newcomen was assisted in his experiments by John Calley, who, with him, took out the patent. It has been stated that a visit to Cornwall, where they witnessed the working of a Savery engine, first turned their attention to the subject; but a friend of Savery has stated that Newcomen was as early with his general plans as Savery. After some discussion with Calley, Newcomen entered into correspondence with Dr. Hooke, proposing a steam-engine to consist of a _steam-cylinder containing a piston similar to that of Papin's, and to drive a separate pump_, similar to those generally in use where water was raised by horse or wind power. Dr. Hooke advised and argued strongly against their plan, but, fortunately, the obstinate belief of the unlearned mechanics was not overpowered by the disquisitions of their distinguished correspondent, and Newcomen and Calley attempted an engine on their peculiar plan. This succeeded so well as to induce them to continue their labors, and, in 1705, to patent,[30] in combination with Savery--who held the exclusive right to practise surface-condensation, and who induced them to allow him an interest with them--an engine combining a steam-cylinder and piston, surface-condensation, a separate boiler, and separate pumps. [30] It has been denied that a patent was issued, but there is no doubt that Savery claimed and received an interest in the new engine. In the atmospheric-engine, as first designed, the slow process of condensation by the application of the condensing water to the exterior of the cylinder, to produce the vacuum, caused the strokes of the engine to take place at very long intervals. An improvement was, however, soon effected, which immensely increased the rapidity of condensation. A jet of water was thrown directly _into_ the cylinder, thus effecting for the Newcomen engine just what Desaguliers had done for the Savery engine previously. As thus improved, the Newcomen engine is shown in Fig. 19. Here _b_ is the boiler. Steam passes from it through the cock, _d_, and up into the cylinder, _a_, equilibrating the pressure of the atmosphere, and allowing the heavy pump-rod, _k_, to fall, and, by the greater weight acting through the beam, _i i_, to raise the piston, _s_, to the position shown. The rod _m_ carries a counterbalance, if needed. The cock _d_ being shut, _f_ is then opened, and a jet of water from the reservoir, _g_, enters the cylinder, producing a vacuum by the condensation of the steam. The pressure of the air above the piston now forces it down, again raising the pump-rods, and thus the engine works on indefinitely. [Illustration: FIG. 19.--Newcomen's Engine, A. D. 1705.] The pipe _h_ is used for the purpose of keeping the upper side of the piston covered with water, to prevent air-leaks--a device of Newcomen. Two gauge-cocks, _c c_, and a safety-valve, _N_, are represented in the figure, but it will be noticed that the latter is quite different from the now usual form. Here, the pressure used was hardly greater than that of the atmosphere, and the weight of the valve itself was ordinarily sufficient to keep it down. The condensing water, together with the water of condensation, flows off through the open pipe _p_. Newcomen's first engine made 6 or 8 strokes a minute; the later and improved engines made 10 or 12. The steam-engine has now assumed a form that somewhat resembles the modern machine. The Newcomen engine is seen at a glance to have been a combination of earlier ideas. It was the engine of Huyghens, with its cylinder and piston as improved by Papin, by the substitution of steam for the gases generated by the explosion of gunpowder; still further improved by Newcomen and Calley by the addition of the method of condensation used in the Savery engine. It was further modified, with the object of applying it directly to the working of the pumps of the mines by the introduction of the overhead beam, from which the piston was suspended at one end and the pump-rod at the other. The advantages secured by this combination of inventions were many and manifest. The piston not only gave economy by interposing itself between the impelling and the resisting fluid, but, by affording opportunity to make the area of piston as large as desired, it enabled Newcomen to use any convenient pressure and any desired proportions for any proposed lift. The removal of the water to be lifted from the steam-engine proper and handling it with pumps, was an evident cause of very great economy of steam. The disposal of the water to be raised in this way also permitted the operations of condensation of steam, and the renewal of pressure on the piston, to be made to succeed each other with rapidity, and enabled the inventor to choose, unhampered, the device for securing promptly the action of condensation. Desaguliers, in his account of the introduction of the engine of Newcomen, says that, with his coadjutor Calley, he "made several experiments in private about the year 1710, and in the latter end of the year 1711 made proposals to drain the water of a colliery at Griff, in Warwickshire, where the proprietors employed 500 horses, at an expense of £900 a year; but, their invention not meeting with the reception they expected, in March following, through the acquaintance of Mr. Potter, of Bromsgrove, in Worcestershire, they bargained to draw water for Mr. Back, of Wolverhampton, where, after a great many laborious attempts, they did make the engine work; but, not being either philosophers to understand the reason, or mathematicians enough to calculate the powers and proportions of the parts, they very luckily, by accident, found what they sought for. "They were at a loss about the pumps, but, being so near Birmingham, and having the assistance of so many admirable and ingenious workmen, they came, about 1712, to the method of making the pump-valves, clacks, and buckets, whereas they had but an imperfect notion of them before. One thing is very remarkable: as they were at first working, they were surprised to see the engine go several strokes, and very quick together, when, after a search, they found a hole in the piston, which let the cold water in to condense the steam in the inside of the cylinder, whereas, before, they had always done it on the outside. They used before to work with a buoy to the cylinder, inclosed in a pipe, which buoy rose when the steam was strong and opened the injection, and made a stroke; thereby they were only capable of giving 6, 8, or 10 strokes in a minute, till a boy, named Humphrey Potter, in 1713, who attended the engine, added (what he called a _scoggan_) a catch, that the beam always opened, and then it would go 15 or 16 strokes a minute. But, this being perplexed with catches and strings, Mr. Henry Beighton, in an engine he had built at Newcastle-upon-Tyne in 1718, took them all away but the beam itself, and supplied them in a much better manner." In illustration of the application of the Newcomen engine to the drainage of mines, Farey describes a small machine, of which the pump is 8 inches in diameter, and the lift 162 feet. The column of water to be raised weighed 3,535 pounds. The steam-piston was made 2 feet in diameter, giving an area of 452 square inches. The net working-pressure was assumed at 10-3/4 pounds per square inch; the temperature of the water of condensation and of uncondensed vapor after the entrance of the injection-water being usually about 150° Fahr. This gave an excess of pressure on the steam-side of 1,324 pounds, the total pressure on the piston being 4,859 pounds. One-half of this excess is counterweighted by the pump-rods, and by weight on that end of the beam; and the weight, 662 pounds, acting on each side alternately as a surplus, produced the requisite rapidity of movement of the machine. This engine was said to make 15 strokes per minute, giving a speed of piston of 75 feet per minute, and the power exerted usefully was equivalent to 265,125 pounds raised one foot high per minute. As the horse-power is equivalent to 33,000 "foot-pounds" per minute, the engine was of 265125/33000 = 8.034--almost exactly 8 horse-power. It is instructive to contrast this estimate with that made for a Savery engine doing the same work. The latter would have raised the water about 26 feet in its "suction-pipe," and would then have forced it, by the direct pressure of steam, the remaining distance of 136 feet; and the steam-pressure required would have been nearly 60 pounds per square inch. With this high temperature and pressure, the waste of steam by condensation in the forcing-vessels would have been so great that it would have compelled the adoption of two engines of considerable size, each lifting the water one-half the height, and using steam of about 25 pounds pressure. Potter's rude valve-gear was soon improved by Henry Beighton, in an engine which that talented engineer erected at Newcastle-upon-Tyne in 1718, and in which he substituted substantial materials for the cords, as in Fig. 20. In this sketch, _r_ is a plug-tree, plug-rod, or plug-frame, as it is variously called, suspended from the great beam, with which it rises and falls, bringing the pins _p_ and _k_, at the proper moment, in contact with the handles _k k_ and _n n_ of the valves, moving them in the proper direction and to the proper extent. A lever safety-valve is here used, at the suggestion, it is said, of Desaguliers. The piston was packed with leather or with rope, and lubricated with tallow. [Illustration: FIG. 20.--Beighton's Valve-Gear, A. D. 1718.] After the death of Beighton, the atmospheric engine of Newcomen retained its then standard form for many years, and came into extensive use in all the mining districts, particularly in Cornwall, and was also applied occasionally to the drainage of wet lands, to the supply of water to towns, and it was even proposed by Hulls to be used for ship-propulsion. The proportions of the engines had been determined in a hap-hazard way, and they were in many cases very unsafe. John Smeaton, the most distinguished engineer of his time, finally, in 1769, experimentally determined proper proportions, and built several of these engines of very considerable size. He built his engines with steam-cylinders of greater length of stroke than had been customary, and gave them such dimensions as, by giving a greater excess of pressure on the steam-side, enabled him to obtain a greatly-increased speed of piston. The first of his new style of engine was erected at Long Benton, near Newcastle-upon-Tyne, in 1774. Fig. 21[31] illustrates its principal characteristic features. The boiler is not shown. [31] A fac-simile of a sketch in Galloway's "On the Steam-Engine," etc. The steam is led to the engine through the pipe, _C_, and is regulated by turning the cock in the receiver, _D_, which connects with the steam-cylinder by the pipe, _E_, which latter pipe rises a little way above the bottom of the cylinder, _F_, in order that it may not drain off the injection-water into the steam-pipe and receiver. The steam-cylinder, about ten feet in length, is fitted with a carefully-made piston, _G_, having a flanch rising four or five inches and extending completely around its circumference, and nearly in contact with the interior surface of the cylinder. Between this flanch and the cylinder is driven a "packing" of oakum, which is held in place by weights; this prevents the leakage of air, water, or steam, past the piston, as it rises and falls in the cylinder at each stroke of the engine. The chain and piston-rod connect the piston to the beam, _I I_. The arch-heads at each end of the beam keep the chains of the piston-rod and the pump-rods perpendicular and in line. [Illustration: FIG. 21.--Smeaton's Newcomen Engine.] A "jack-head" pump, _N_, is driven by a small beam deriving its motion from the plug-rod at _g_, raises the water required for condensing the steam, and keeps the cistern, _O_, supplied. This "jack-head cistern" is sufficiently elevated to give the water entering the cylinder the velocity requisite to secure prompt condensation. A waste-pipe carries away any surplus water. The injection-water is led from the cistern by the pipe, _P P_, which is two or three inches in diameter, and the flow of water is regulated by the injection-cock, _r_. The cap at the end, _d_, is pierced with several holes, and the stream thus divided rises in jets when admitted, and, striking the lower side of the piston, the spray thus produced very rapidly condenses the steam, and produces a vacuum beneath the piston. The valve, _e_, on the upper end of the injection-pipe, is a check-valve, to prevent leakage into the engine when the latter is not in operation. The little pipe, _f_, supplies water to the upper side of the piston, and, keeping it flooded, prevents the entrance of air when the packing is not perfectly tight. The "working-plug," or plug-rod, _Q_, is a piece of timber slit vertically, and carrying pins which engage the handles of the valves, opening and closing them at the proper times. The steam-cock, or regulator, has a handle, _h_, by which it is moved. The iron rod, _i i_, or spanner, gives motion to the handle, _h_. The vibrating lever, _k l_, called the _Y_, or the "tumbling-bob," moves on the pins, _m n_, and is worked by the levers, _o p_, which in turn are moved by the plug-tree. When _o_ is depressed, the loaded end, _k_, is given the position seen in the sketch, and the leg _l_ of the _Y_ strikes the spanner, _i i_, and, opening the steam-valve, the piston at once rises as steam enters the cylinder, until another pin on the plug-rod raises the piece, _P_, and closes the regulator again. The lever, _q r_, connects with the injection-cock, and is moved, when, as the piston rises, the end, _q_, is struck by a pin on the plug-rod, and the cock is opened and a vacuum produced. The cock is closed on the descent of the plug-tree with the piston. An eduction-pipe, _R_, fitted with a clock, conveys away the water in the cylinder at the end of each down-stroke; the water thus removed is collected in the hot-well, _S_, and is used as feed-water for the boiler, to which it is conveyed by the pipe _T_. At each down-stroke, while the water passes out through _R_, the air which may have collected in the cylinder is driven out through the "snifting-valve," _s_. The steam-cylinder is supported on strong beams, _t t_; it has around its upper edge a guard, _v_, of lead, which prevents the overflow of the water on the top of the piston. The excess of this water flows away to the hot-well through the pipe _W_. Catch-pins, _x_, are provided, to prevent the beam descending too far should the engine make too long a stroke; two wooden springs, _y y_, receive the blow. The great beam is carried on sectors, _z z_, to diminish losses by friction. The boilers of Newcomen's earlier engines were made of copper where in contact with the products of combustion, and their upper parts were of lead. Subsequently, sheet-iron was substituted. The steam-space in the boiler was made of 8 or 10 times the capacity of the cylinder of the engine. Even in Smeaton's time, a chimney-damper was not used, and the supply of steam was consequently very variable. In the earlier engines, the cylinder was placed on the boiler; afterward, they were placed separately, and supported on a foundation of masonry. The injection or "jack-head" cistern was placed from 12 to 30 feet above the engine, the velocity due the greater altitude being found to give the most perfect distribution of the water and the promptest condensation. [Illustration: FIG. 22.--Boiler of Newcomen's Engine, 1768.] Smeaton covered the lower side of his steam-pistons with wooden plank about 2-1/4 inches thick, in order that it should absorb and waste less heat than when the iron was directly exposed to the steam. Mr. Beighton was the first to use the water of condensation for feeding the boiler, taking it directly from the eduction-pipe, or the "hot-well." Where only a sufficient amount of pure water could be obtained for feeding the boiler, and the injection-water was "hard," Mr. Smeaton applied a heater, immersed in the hot-well, through which the feed passed, absorbing heat from the water of condensation _en route_ to the boiler. Farey first proposed the use of the "coil-heater"--a pipe, or "worm," which, forming a part of the feed-pipe, was set in the hot-well. As early as 1743, the metal used for the cylinders was cast-iron. The earlier engines had been fitted with brass cylinders. Desaguliers recommended the iron cylinders, as being smoother, thinner, and as having less capacity for heat than those of brass. In a very few years after the invention of Newcomen's engine it had been introduced into nearly all large mines in Great Britain; and many new mines, which could not have been worked at all previously, were opened, when it was found that the new machine could be relied upon to raise the large quantities of water to be handled. The first engine in Scotland was erected in 1720 at Elphinstone, in Stirlingshire. One was put up in Hungary in 1723. The first mine-engine, erected in 1712 at Griff, was 22 inches in diameter, and the second and third engines were of similar size. That erected at Ansthorpe was 23 inches in diameter of cylinder, and it was a long time before much larger engines were constructed. Smeaton and others finally made them as large as 6 feet in diameter. In calculating the lifting-power of his engines, Newcomen's method was "to square the diameter of the cylinder in inches, and, cutting off the last figure, he called it 'long hundredweights;' then writing a cipher on the right hand, he called the number on that side 'odd pounds;' this he reckoned tolerably exact at a mean, or rather when the barometer was above 30 inches, and the air heavy." In allowing for frictional and other losses, he deducted from one-fourth to one-third. Desaguliers found the rule quite exact. The usual mean pressure resisting the motion of the piston averaged, in the best engines, about 8 pounds per square inch of its area. The speed of the piston was from 150 to 175 feet per minute. The temperature of the hot-well was from 145° to 175° Fahr. Smeaton made a number of test-trials of Newcomen engines to determine their "duty"--i. e., to ascertain the expenditure of fuel required to raise a definite quantity of water to a stated height. He found an engine 10 inches in diameter of cylinder, and of 3 feet stroke, could do work equal to raising 2,919,017 pounds of water one foot high, with a bushel of coals weighing 84 pounds. One of Smeaton's larger engines, erected at Long Benton, was 52 inches in diameter of cylinder and of 7 feet stroke of piston, and made 12 strokes per minute. Its load was equal to 7-1/2 pounds per square inch of piston-area, and its effective capacity about 40 horse-power. Its duty was 9-1/2 millions of pounds raised one foot high per bushel of coals. Its boiler evaporated 7.88 pounds of water per pound of fuel consumed. It had 35 square feet of grate-surface and 142 square feet of heating-surface beneath the boilers, and 317 square feet in the flues--a total of 459 square feet. The moving parts of this engine weighed 8-1/2 tons. Smeaton erected one of these engines at the Chasewater mine, in Cornwall, in 1775, which was of very considerable size. It was 6 feet in diameter of steam-cylinder, and had a maximum stroke of piston of 9-1/2 feet. It usually worked 9 feet. The pumps were in three lifts of about 100 feet each, and were 16-3/4 inches in diameter. Nine strokes were made per minute. This engine replaced two others, of 64 and of 62 inches diameter of cylinder respectively, and both of 6 feet stroke. One engine at the lower lift supplied the second, which was set above it. The lower one had pumps 18-1/2 inches in diameter, and raised the water 144 feet; the upper engine raised the water 156 feet, by pumps 17-1/2 inches in diameter. The later engine replacing them exerted 76-1/2 horse-power. There were three boilers, each 15 feet in diameter, and having each 23 square feet of grate-surface. The chimney was 22 feet high. The great beam, or "lever," of this engine was built up of 20 beams of fir in two sets, placed side by side, and ten deep, strongly bolted together. It was over 6 feet deep at the middle and 5 feet at the ends, and was 2 feet thick. The "main centres," or journals, on which it vibrated were 8-1/2 inches in diameter and 8-1/2 inches long. The cylinder weighed 6-1/2 tons, and was paid for at the rate of 28 shillings per hundredweight. By the end of the eighteenth century, therefore, the engine of Newcomen, perfected by the ingenuity of Potter and of Beighton, and by the systematic study and experimental research of Smeaton, had become a well-established form of steam-engine, and its application to raising water had become general. The coal-mines of Coventry and of Newcastle had adopted this method of drainage; and the tin and the copper mines of Cornwall had been deepened, using, for drainage, engines of the largest size. Some engines had been set up in and about London, the scene of Worcester's struggles and disappointments, where they were used to supply water to large houses. Others were in use in other large cities of England, where water-works had been erected. Some engines had also been erected to drive mills indirectly by raising water to turn water-wheels. This is said by Farey to have been first practised in 1752, at a mill near Bristol, and became common during the next quarter of a century. Many engines had been built in England and sent across the channel, to be applied to the drainage of mines on the Continent. Belidor[32] stated that the manufacture of these "fire-engines" was exclusively confined to England; and this remained true many years after his time. When used for the drainage of mines, the engine usually worked the ordinary lift or bucket pump; when employed for water-supply to cities, the force or plunger pump was often employed, the engine being placed below the level of the reservoir. Dr. Rees states that this engine was in common use among the collieries of England as early as 1725. [32] "Architecture Hydraulique," 1734. The Edmonstone colliery was licensed, in 1725, to erect an engine, not to exceed 28 inches diameter of cylinder and 9 feet stroke of piston, paying a royalty of £80 per annum for eight years. This engine was built in Scotland, by workmen sent from England, and cost about £1,200. Its "great cost" is attributed to an extensive use of brass. The workmen were paid their expenses and 15_s._ per week as wages. The builders were John and Abraham Potter, of Durham. An engine built in 1775, having a steam-cylinder 48 inches in diameter and of 7 feet stroke, cost about £2,000. Smeaton found 57 engines at work near Newcastle in 1767, ranging in size from 28 to 75 inches in diameter of cylinder, and of, collectively, about 1,200 horse-power. Fifteen of these engines gave an average of 98 square inches of piston to the horse-power, and the average duty was 5,590,000 pounds raised 1 foot high by 1 bushel (84 pounds) of coal. The highest duty noted was 7.44 millions; the lowest was 3.22 millions. The most efficient engine had a steam-cylinder 42 inches in diameter; the load was equivalent to 9-1/4 pounds per square inch of piston-area, and the horse-power developed was calculated to be 16.7. Price, writing in 1778, says, in the Appendix to his "Mineralogia Cornubiensis:" "Mr. Newcomen's invention of the fire-engine enabled us to sink our mines to twice the depth we could formerly do by any other machinery. Since this invention was completed, most other attempts at its improvement have been very unsuccessful; but the vast consumption of fuel in these engines is an immense drawback on the profit of our mines, for every fire-engine of magnitude consumes £3,000 worth of coals per annum. This heavy tax amounts almost to a prohibition." Smeaton was given the description, in 1773, of a _stone_ boiler, which was used with one of these engines at a copper mine at Camborne, in Cornwall. It contained three copper flues 22 inches in diameter. The gases were passed through these flues successively, finally passing off to the chimney. This boiler was cemented with hydraulic mortar. It was 20 feet long, 9 feet wide, and 8-1/2 feet deep. It was heated by the waste heat from the roasting-furnaces. This was one of the earliest flue-boilers ever made. In 1780, Smeaton had a list of 18 large engines working in Cornwall. The larger number of them were built by Jonathan Hornblower and John Nancarron. At this time, the largest and best-known pumping-engine for water-works was at York Buildings, in Villiers Street, Strand, London. It had been in operation since 1752, and was erected beside one of Savery's engines, built in 1710. It had a steam-cylinder 45 inches in diameter, and a stroke of piston of 8 feet, making 7-1/2 strokes per minute, and developing 35-1/2 horse-power. Its boiler was dome-shaped, of copper, and contained a large central fire-box and a spiral flue leading outward to the chimney. Another somewhat larger machine was built and placed beside this engine, some time previous to 1775. Its cylinder was 49 inches in diameter, and its stroke 9 feet. It raised water 102 feet. This engine was altered and improved by Smeaton in 1777, and continued in use until 1813. Smeaton, as early as 1765, designed a _portable_ engine,[33] in which he supported the machinery on a wooden frame mounted on short legs and strongly put together, so that the whole machine could be transported and set at work wherever convenient. [33] Smeaton's "Reports," vol. i., p. 223. [Illustration: FIG. 23.--Smeaton's Portable-Engine Boiler, 1765.] In place of the beam, a large pulley was used, over which a chain was carried, connecting the piston with the pump-rod, and the motion was similar to that given by the discarded beam. The wheel was supported on A-frames, resembling somewhat the "gallows-frames" still used with the beam-engines of American river-boats. The sills carrying the two A's supported the cylinder. The injection-cistern was supported above the great pulley-wheel. The valve-gearing and the injection-pump were worked by a smaller wheel, mounted on the same axis with the larger one. The boiler was placed apart from the engine, with which it was connected by a steam-pipe, in which was placed the "regulator," or throttle-valve. The boiler (Fig. 23) "was shaped like a large tea-kettle," and contained a fire-box, _B_, or internal furnace, of which the sides were made of cast-iron. The fire-door, _C_, was placed on one side and opposite the flue, _D_, through which the products of combustion were led to the chimney, _E_; a short, large pipe, _F_, leading downward from the furnace to the outside of the boiler, was the ash-pit. The shell of the boiler, _A_, was made of iron plate one-quarter of an inch thick. The steam-cylinder of the engine was 18 inches in diameter, the stroke of piston 6 feet, the great wheel 6-1/2 feet in diameter, and the A-frames 9 feet high. The boiler was made 6 feet, the furnace 34 inches, and the grate 18 inches in diameter. The piston was intended to make 10 strokes per minute, and the engine to develop 4-1/8 horse-power. In 1773, Smeaton prepared plans for a pumping-engine to be set up at Cronstadt, the port of St. Petersburg, to empty the great dry dock constructed by Peter the Great and Catherine, his successor. This great dock was begun in 1719. It was large enough to dock ten of the ships of that time, and had previously been imperfectly drained by two great windmills 100 feet high. So imperfectly did they do their work, that a _year_ was required to empty the dock, and it could therefore only be used once in each summer. The engine was built at the Carron Iron Works, in England. It had a cylinder 66 inches in diameter, and a stroke of piston of 8-1/2 feet. The lift varied from 33 feet when the dock was full to 53 feet when it was cleared of water. The load on the engine averaged about 8-1/3 pounds per square inch of piston-area. There were three boilers, each 10 feet in diameter, and 16 feet 4 inches high to the apex of its hemispherical dome. They contained internal fire-boxes with grates of 20 feet area, and were surrounded by flues helically traversing the masonry setting. The engine was started in 1777, and worked very successfully. The lowlands of Holland were, before the time of Smeaton, drained by means of windmills. The uncertainty and inefficiency of this method precluded its application to anything like the extent to which steam-power has since been utilized. In 1440, there were 150 inland lakes, or "_meers_," in that country, of which nearly 100, having an extent of over 200,000 acres, have since been drained. The "Haarlemmer Meer" alone covers nearly 50,000 acres, and forms the basin of a drainage-area of between 200,000 and 300,000 acres, receiving a rainfall of 54,000,000 tons, which must be raised 16 feet in discharging it. The beds of these lakes are from 10 to 20 feet lower than the water-level in the adjacent canals. In 1840, 12,000 windmills were still employed in this work. In the following year, William II., at the suggestion of a commission, decreed that only steam-engines should be employed to do this immense work. Up to this time the average consumption of fuel for the pumping-engines in use is said to have been 20 pounds per hour per horse-power. The first engine used was erected in 1777 and 1778, on the Newcomen plan, to assist the 34 windmills employed to drain a lake near Rotterdam. This lake covered 7,000 acres, and its bed was 12 feet below the surface of the river Meuse, which passes it, and empties into the sea in the immediate neighborhood. The iron parts of the engine were built in England, and the machine was put together in Holland. The steam-cylinder was 52 inches in diameter, and the stroke of piston 9 feet. The boiler was 18 feet in diameter, and contained a double flue. The main beam was 27 feet long. The pumps were 6 in number, 3 cylindrical and 3 having a square cross-section; 3 were of 6 feet and 3 of 2-1/2 feet stroke. Two pumps only were worked at high-tide, and the others were added one at a time, as the tide fell, until, at low-tide, all 6 were at work. The size of this engine, and the magnitude of its work, seem insignificant when compared with the machinery installed 60 years later to drain the Haarlemmer Meer, and with the work done by the last. These engines are 12 feet in diameter of cylinder and 10 feet stroke of piston, and work--they are 3 in number--the one 11 pumps of 63 inches diameter and 10 feet stroke, the others 8 pumps of 73 inches diameter and of the same length of stroke. The modern engines do a "duty" of 75,000,000 to 87,000,000 with 94 pounds of coal, consuming 2-1/4 pounds of coal per hour and per horse-power. The first steam-engine applied to working the blowing-machinery of a blast-furnace was erected at the Carron Iron-Works, in Scotland, near Falkirk, in 1765, and proved very unsatisfactory. Smeaton subsequently, in 1769 or 1770, introduced better machinery into these works and improved the old engine, and this use of the steam-engine soon became usual. This engine did its work indirectly, furnishing water, by pumping, to drive the water-wheels which worked the blowing-cylinders. Its steam-cylinder was 6 feet in diameter, and the pump-cylinder 52 inches. The stroke was 9 feet. A direct-acting engine, used as a blowing-engine, was not constructed until about 1784, at which time a single-acting blowing-cylinder, or air-pump, was placed at the "out-board" end of the beam, where the pump-rod had been attached. The piston of the air-cylinder was loaded with the weights needed to force it down, expelling the air, and the engine did its work in raising the loaded piston, the air-cylinder filling as the piston rose. A large "accumulator" was used to equalize the pressure of the expelled air. This consisted of another air-cylinder, having a loaded piston which was left free to rise and fall. At each expulsion of air by the blowing-engine this cylinder was filled, the loaded piston rising to the top. While the piston of the former was returning, and the air-cylinder was taking in its charge of air, the accumulator would gradually discharge the stored air, the piston slowly falling under its load. This piston was called the "floating piston," or "fly-piston," and its action was, in effect, precisely that of the upper portion of the common blacksmith's bellows. Dr. Robison, the author of "Mechanical Philosophy," one of the very few works even now existing deserving such a title, describes one of these engines[34] as working in Scotland in 1790. It had a steam-cylinder 40 or 44 inches in diameter, a blowing-cylinder 60 inches in diameter, and the stroke of piston was 6 feet. The air-pressure was 2.77 pounds per square inch as a maximum in the blowing-cylinder; and the floating piston in the regulating-cylinder was loaded with 2.63 pounds per square inch. Making 15 or 18 strokes per minute, this engine delivered about 1,600 cubic feet of air, or 120-1/2 pounds in weight, per minute, and developed 20 horse-power. [34] "Encyclopædia Britannica," 1st edition. At about the same date a change was made in the blowing-cylinder. The air entered at the bottom, as before, but was forced out at the top, the piston being fitted with valves, as in the common lifting-pump, and the engine thus being arranged to do the work of expulsion during the down-stroke of the steam-piston. Four years later, the regulating-cylinder, or accumulator, was given up, and the now familiar "water-regulator" was substituted for it. This consists of a tank, usually of sheet-iron, set open-end downward in a large vessel containing water. The lower edge of the inner tank is supported on piers a few inches above the bottom of the large one. The pipe carrying air from the blowing-engine passes above this water-regulator, and a branch-pipe is led down into the inner tank. As the air-pressure varies, the level of the water within the inverted tank changes, rising as pressure falls at the slowing of the motion of the piston, and falling as the pressure rises again while the piston is moving with an accelerated velocity. The regulator, thus receiving surplus air to be delivered when needed, greatly assists in regulating the pressure. The larger the regulator, the more perfectly uniform the pressure. The water-level outside the inner tank is usually five or six feet higher than within it. This apparatus was found much more satisfactory than the previously-used regulator, and, with its introduction, the establishment of the steam-engine as a blowing-engine for iron-works and at blast-furnaces may be considered as having been fully established. Thus, by the end of the third quarter of the eighteenth century, the steam-engine had become generally introduced, and had been applied to nearly all of the purposes for which a single-acting engine could be used. The path which had been opened by Worcester had been fairly laid out by Savery and his contemporaries, and the builders of the Newcomen engine, with such improvements as they had been able to effect, had followed it as far as they were able. The real and practical introduction of the steam-engine is as fairly attributable to Smeaton as to any one of the inventors whose names are more generally known in connection with it. As a mechanic, he was unrivaled; as an engineer, he was head and shoulders above any constructor of his time engaged in general practice. There were very few important public works built in Great Britain at that time in relation to which he was not consulted; and he was often visited by foreign engineers, who desired his advice with regard to works in progress on the Continent. [Illustration] CHAPTER III. _THE DEVELOPMENT OF THE MODERN STEAM-ENGINE. JAMES WATT AND HIS CONTEMPORARIES._ The world is now entering upon the Mechanical Epoch. There is nothing in the future more sure than the great triumphs which that epoch is to achieve. It has already advanced to some glorious conquests. What miracles of invention now crowd upon us! Look abroad, and contemplate the infinite achievements of the steam-power. And yet we have only begun--we are but on the threshold of this epoch.... What is it but the setting of the great distinctive seal upon the nineteenth century?--an advertisement of the fact that society has risen to occupy a higher platform than ever before?--a proclamation from the high places, announcing honor, honor immortal, to the workmen who fill this world with beauty, comfort, and power--honor to be forever embalmed in history, to be perpetuated in monuments, to be written in the hearts of this and succeeding generations!--KENNEDY. SECTION I.--JAMES WATT AND HIS INVENTIONS. The success of the Newcomen engine naturally attracted the attention of mechanics, and of scientific men as well, to the possibility of making other applications of steam-power. The best men of the time gave much attention to the subject, but, until James Watt began the work that has made him famous, nothing more was done than to improve the proportions and slightly alter the details of the Newcomen and Calley engine, even by such skillful engineers as Brindley and Smeaton. Of the personal history of the earlier inventors and improvers of the steam-engine, very little is ascertained; but that of Watt has become well known. [Illustration: James Watt.] JAMES WATT was of an humble lineage, and was born at Greenock, then a little Scotch fishing village, but now a considerable and a busy town, which annually launches upon the waters of the Clyde a fleet of steamships whose engines are probably, in the aggregate, far more powerful than were all the engines in the world at the date of Watt's birth, January 19, 1736. His grandfather, Thomas Watt, of Crawfordsdyke, near Greenock, was a well-known mathematician about the year 1700, and was for many years a schoolmaster at that place. His father was a prominent citizen of Greenock, and was at various times chief magistrate and treasurer of the town. James Watt was a bright boy, but exceedingly delicate in health, and quite unable to attend school regularly, or to apply himself closely to either study or play. His early education was given by his parents, who were respectable and intelligent people, and the tools borrowed from his father's carpenter-bench served at once to amuse him and to give him a dexterity and familiarity with their use that must undoubtedly have been of inestimable value to him in after-life. M. Arago, the eminent French philosopher, who wrote one of the earliest and most interesting biographies of Watt, relates anecdotes of him which, if correct, illustrate well his thoughtfulness and his intelligence, as well as the mechanical bent of the boy's mind. He is said, at the age of six years, to have occupied himself during leisure hours with the solution of geometrical problems; and Arago discovers, in a story in which he is described as experimenting with the tea-kettle,[35] his earliest investigations of the nature and properties of steam. [35] The same story is told of Savery and of Worcester. When finally sent to the village school, his ill health prevented his making rapid progress; and it was only when thirteen or fourteen years of age that he began to show that he was capable of taking the lead in his class, and to exhibit his ability in the study, particularly, of mathematics. His spare time was principally spent in sketching with his pencil, in carving, and in working at the bench, both in wood and metal. He made many ingenious pieces of mechanism, and some beautiful models. His favorite work seemed to be the repairing of nautical instruments. Among other pieces of apparatus made by the boy was a very fine barrel-organ. In boyhood, as in after-life, he was a diligent reader, and seemed to find something to interest him in every book that came into his hands. At the age of eighteen, Watt was sent to Glasgow, there to reside with his mother's relatives, and to learn the trade of a mathematical-instrument maker. The mechanic with whom he was placed was soon found too indolent, or was otherwise incapable of giving much aid in the project, and Dr. Dick, of the University of Glasgow, with whom Watt became acquainted, advised him to go to London. Accordingly, he set out in June, 1755, for the metropolis, where, on his arrival, he arranged with Mr. John Morgan, in Cornhill, to work a year at his chosen business, receiving as compensation 20 guineas. At the end of the year he was compelled, by serious ill-health, to return home. Having become restored to health, he went again to Glasgow in 1756, with the intention of pursuing his calling there. But, not being the son of a burgess, and not having served his apprenticeship in the town, he was forbidden by the guilds, or trades-unions, to open a shop in Glasgow. Dr. Dick came to his aid, and employed him to repair some apparatus which had been bequeathed to the college. He was finally allowed the use of three rooms in the University building, its authorities not being under the municipal rule. He remained here until 1760, when, the trades no longer objecting, he took a shop in the city; and in 1761 moved again, into a shop on the north side of the Trongate, where he earned a scanty living without molestation, and still kept up his connection with the college. He did some work as a civil engineer in the neighborhood of Glasgow, but soon gave up all other employment, and devoted himself entirely to mechanics. He spent much of his leisure time--of which he had, at first, more than was desirable--in making philosophical experiments and in the manufacture of musical instruments, in making himself familiar with the sciences, and in devising improvements in the construction of organs. In order to pursue his researches more satisfactorily, he studied German and Italian, and read Smith's "Harmonics," that he might become familiar with the principles of construction of musical instruments. His reading was still very desultory; but the introduction of the Newcomen engine in the neighborhood of Glasgow, and the presence of a model in the college collections, which was placed in his hands, in 1763, for repair, led him to study the history of the steam-engine, and to conduct for himself an experimental research into the properties of steam, with a set of improvised apparatus. Dr. Robison, then a student of the University, who found Watt's shop a pleasant place in which to spend his leisure, and whose tastes affiliated so strongly with those of Watt that they became friends immediately upon making acquaintance, called the attention of the instrument-maker to the steam-engine as early as 1759, and suggested that it might be applied to the propulsion of carriages. Watt was at once interested, and went to work on a little model, having tin steam-cylinders and pistons connected to the driving-wheels by an intermediate system of gearing. The scheme was afterwards given up, and was not revived by Watt for a quarter of a century. Watt studied chemistry, and was assisted by the advice and instruction of Dr. Black, who was then making the researches which resulted in the discovery of "latent heat." His proposal to repair the model Newcomen engine in the college collections led to his study of Desaguliers's treatise, and of the works of Switzer and others. He thus learned what had been done by Savery and by Newcomen, and by those who had improved the engine of the latter. In his own experiments he used, at first, apothecaries' phials and hollow canes for steam reservoirs and pipes, and later a Papin's digester and a common syringe. The latter combination made a non-condensing engine, in which he used steam at a pressure of 15 pounds per square inch. The valve was worked by hand, and Watt saw that an automatic valve-gear only was needed to make a working machine. This experiment, however, led to no practical result. He finally took hold of the Newcomen model, which had been obtained from London, where it had been sent for repairs, and, putting it in good working order, commenced experiments with that. The Newcomen model, as it happened, had a boiler which, although made to a scale from engines in actual use, was quite incapable of furnishing steam enough to work the engine. It was about nine inches in diameter; the steam-cylinder was two inches in diameter, and of six inches stroke of piston, arranged as in Fig. 24, which is a picture of the model as it now appears. It is retained among the most carefully-preserved treasures of the University of Glasgow. [Illustration: FIG. 24.--The Newcomen Model.] Watt made a new boiler for the experimental investigation on which he was about to enter, and arranged it in such a manner that he could measure the quantity of water evaporated and of steam used at every stroke of the engine. He soon discovered that it required but a very small quantity of steam to heat a very large quantity of water, and immediately attempted to determine with precision the relative weights of steam and water in the steam-cylinder when condensation took place at the down-stroke of the engine, and thus independently proved the existence of that "latent heat," the discovery of which constitutes, also, one of the greatest of Dr. Black's claims to distinction. Watt at once went to Dr. Black and related the remarkable fact which he had thus detected, and was, in turn, taught by Black the character of the phenomenon as it had been explained to his classes by the latter some little time previously. Watt found that, at the boiling-point, his steam, condensing, was capable of heating six times its weight of water such as was used for producing condensation. Perceiving that steam, weight for weight even, was a vastly greater absorbent and reservoir of heat than water, Watt saw plainly the importance of taking greater care to economize it than had previously been customary. He first attempted to economize in the boiler, and made boilers with wooden "shells," in order to prevent losses by conduction and radiation, and used a larger number of flues to secure more complete absorption of the heat from the furnace-gases. He also covered his steam-pipes with non-conducting materials, and took every precaution that his ingenuity could devise to secure complete utilization of the heat of combustion. He soon found, however, that he was not working at the most important point, and that the great source of loss was to be found in defects which he noted in the action of the steam in the cylinder. He soon concluded that the sources of loss of heat in the Newcomen engine--which would be greatly exaggerated in a small model--were: First, the dissipation of heat by the cylinder itself, which was of brass, and was both a good conductor and a good radiator. Secondly, the loss of heat consequent upon the necessity of cooling down the cylinder at every stroke, in producing the vacuum. Thirdly, the loss of power due to the pressure of vapor beneath the piston, which was a consequence of the imperfect method of condensation. He first made a cylinder of non-conducting material--wood soaked in oil and then baked--and obtained a decided advantage in economy of steam. He then conducted a series of very accurate experiments upon the temperature and pressure of steam at such points on the scale as he could readily reach, and, constructing a curve with his results, the abscesses representing temperatures and the pressures being represented by the ordinates, he ran the curve backward until he had obtained closely-approximate measures of temperatures less than 212°, and pressures less than atmospheric. He thus found that, with the amount of injection-water used in the Newcomen engine, bringing the temperature of the interior, as he found, down to from 140° to 175° Fahr., a very considerable back-pressure would be met with. Continuing his examination still further, he measured the amount of steam used at each stroke, and, comparing it with the quantity that would just fill the cylinder, he found that at least _three-fourths was wasted_. The quantity of cold water necessary to produce the condensation of a given weight of steam was next determined; and he found that one pound of steam contained enough heat to raise about six pounds of cold water, as used for condensation, from the temperature of 52° to the boiling-point; and, going still further, he found that he was compelled to use, at each stroke of the Newcomen engine, _four times as much injection-water as should suffice to condense a cylinder full of steam_. This confirmed his previous conclusion that three-fourths of the heat supplied to the engine was wasted. Watt had now, therefore, determined by his own researches, as he himself enumerates them,[36] the following facts: [36] Robison's "Mechanical Philosophy," edited by Brewster. "1. The capacities for heat of iron, copper, and of some sorts of wood, as compared with water. "2. The bulk of steam compared with that of water. "3. The quantity of water evaporated in a certain boiler by a pound of coal. "4. The elasticities of steam at various temperatures greater than that of boiling water, and an approximation to the law which it follows at other temperatures. "5. How much water in the form of steam was required every stroke by a small Newcomen engine, with a wooden cylinder 6 inches in diameter and 12 inches stroke. "6. The quantity of cold water required in every stroke to condense the steam in that cylinder, so as to give it a working-power of about 7 pounds on the square inch." After these well-devised and truly scientific investigations, Watt was enabled to enter upon his work of improving the steam-engine with an intelligent understanding of its existing defects, and with a knowledge of their cause. Watt soon saw that, in order to reduce the losses in the working of the steam in the steam-cylinder, it would be necessary to find some means, as he said, to keep the cylinder "always as hot as the steam that entered it," notwithstanding the great fluctuations of temperature and pressure of the steam during the up and the down strokes. He has told us how, finally, the happy thought occurred to him which relieved him of all difficulty, and led to the series of modifications which at last gave to the world the modern type of steam-engine. He says:[37] "I had gone to take a walk on a fine Sabbath afternoon. I had entered the Green by the gate at the foot of Charlotte street, and had passed the old washing-house. I was thinking upon the engine at the time, and had gone as far as the herd's house, when the idea came into my mind that, as steam was an elastic body, it would rush into a vacuum, and, if a communication were made between the cylinder and an exhausted vessel, it would rush into it, and might be there condensed without cooling the cylinder. I then saw that I must get rid of the condensed steam and injection-water if I used a jet, as in Newcomen's engine. Two ways of doing this occurred to me: First, the water might be run off by a descending pipe, if an offlet could be got at the depth of 35 or 36 feet, and any air might be extracted by a small pump. The second was, to make the pump large enough to extract both water and air." "I had not walked farther than the Golf-house, when the whole thing was arranged in my mind." [37] "Reminiscences of James Watt," Robert Hart; "Transactions of the Glasgow Archæological Society," 1859. Referring to this invention, Watt said to Prof. Jardine:[38] "When analyzed, the invention would not appear so great as it seemed to be. In the state in which I found the steam-engine, it was no great effort of mind to observe that the quantity of fuel necessary to make it work would forever prevent its extensive utility. The next step in my progress was equally easy--to inquire what was the cause of the great consumption of fuel. This, too, was readily suggested, viz., the waste of fuel which was necessary to bring the whole cylinder, piston, and adjacent parts from the coldness of water to the heat of steam, no fewer than from 15 to 20 times in a minute." It was by pursuing this train of thought that he was led to devise the separate condenser. [38] "Lives of Boulton and Watt," Smiles. On Monday morning Watt proceeded to make an experimental test of his new invention, using for his steam-cylinder and piston a large brass surgeon's-syringe, 1-3/4-inch diameter and 10 inches long. At each end was a pipe leading steam from the boiler, and fitted with a cock to act as a steam-valve. A pipe led also from the top of the cylinder to the condenser, the syringe being inverted and the piston-rod hanging downward for convenience. The condenser was made of two pipes of thin tin plate, 10 or 12 inches long, and about one-sixth of an inch in diameter, standing vertically, and having a connection at the top with a horizontal pipe of larger size, and fitted with a "snifting-valve." Another vertical pipe, about an inch in diameter, was connected to the condenser, and was fitted with a piston, with a view to using it as an "air-pump." The whole was set in a cistern of cold water. The piston-rod of the little steam-cylinder was drilled from end to end to permit the water to be removed from the cylinder. This little model (Fig. 25) worked very satisfactorily, and the perfection of the vacuum was such that the machine lifted a weight of 18 pounds hung upon the piston-rod, as in the sketch. A larger model was immediately afterward constructed, and the result of its test confirmed fully the anticipations which had been awakened by the first experiment. [Illustration: FIG. 25.--Watt's Experiment.] Having taken this first step and made such a radical improvement, the success of this invention was no sooner determined than others followed in rapid succession, as consequences of the exigencies arising from the first change in the old Newcomen engine. But in the working out of the forms and proportions of the details of the new engine, even Watt's powerful mind, stored as it was with happily-combined scientific and practical information, was occupied for years. In attaching the separate condenser, he first attempted surface-condensation; but this not succeeding well, he substituted the jet. Some provision became at once necessary for preventing the filling of the condenser with water. Watt at first intended adopting the expedient which had worked satisfactorily with the less effective condensation of Newcomen's engine--i. e., leading a pipe from the condenser to a depth greater than the height of a column of water which could be counterbalanced by the pressure of the atmosphere; but he subsequently employed the air-pump, which relieves the condenser not only of the water, but of the air which also usually collects in considerable volume in the condenser, and vitiates the vacuum. He next substituted oil and tallow for water in the lubrication of the piston and keeping it steam-tight, in order to avoid the cooling of the cylinder incident to the use of the latter. Another cause of refrigeration of the cylinder, and consequent waste of power in its operation, was seen to be the entrance of the atmosphere, which followed the piston down the cylinder at each stroke, cooling its interior by its contact. This the inventor concluded to prevent by covering the top of the cylinder, allowing the piston-rod to play through a "stuffing-box"--which device had long been known to mechanics. He accordingly not only covered the top, but surrounded the whole cylinder with an external casing, or "steam-jacket," and allowed the steam from the boiler to pass around the steam-cylinder and to press upon the upper surface of the piston, where its pressure was variable at pleasure, and therefore more manageable than that of the atmosphere. It also, besides keeping the cylinder hot, could do comparatively little harm should it leak by the piston, as it could be condensed, and thus readily disposed of. When he had concluded to build the larger experimental engine, Watt determined to give his whole time and attention to the work, and hired a room in an old deserted pottery near the Broomielaw. Here he worked with a mechanic--John Gardiner, whom he had taken into his employ--uninterruptedly for many weeks. Meantime, through his friend Dr. Black, probably, he had made the acquaintance of Dr. Roebuck, a wealthy physician, who had, with other Scotch capitalists, just founded the celebrated Carron Iron-Works, and had opened a correspondence with him, in which he kept that gentleman informed of the progress of his work on the new engine. This engine had a steam-cylinder, Watt tells us, of "five or six" inches diameter, and of two feet stroke. It was of copper, smooth-hammered, but not bored out, and "not very true." This was encased in another cylinder of wood. In August, 1765, he tried the small engine, and wrote Dr. Roebuck that he had had "good success," although the machine was very imperfect. "On turning the exhausting-cock, the piston, when not loaded, ascended as quick as the blow of a hammer, and as quick when loaded with 18 pounds (being 7 pounds on the inch) as it would have done if it had had an injection as usual." He then tells his correspondent that he was about to make the larger model. In October, 1765, he finished the latter. The engine, when ready for trial, was still very imperfect. It nevertheless did good work for so rude a machine. Watt was now reduced to poverty, and, after borrowing considerable sums from friends, he was finally compelled to give up his scheme for the time, and to seek employment in order to provide for his family. During an interval of about two years he supported himself by surveying, and by the work of exploring coal-fields in the neighborhood of Glasgow for the magistrates of the city. He did not, however, entirely give up his invention. In 1767, Dr. Roebuck assumed Watt's liabilities to the amount of £1,000, and agreed to provide capital for the prosecution of his experiments and to introduce his invention; and, on the other hand, Watt agreed to surrender to Dr. Roebuck two-thirds of the patent. Another engine was next built, having a steam-cylinder seven or eight inches in diameter, which was finished in 1768. This worked sufficiently well to induce the partners to ask for a patent, and the specifications and drawings were completed and presented in 1769. Watt also built and set up several Newcomen engines, partly, perhaps, to make himself thus thoroughly familiar with the practical details of engine-building. Meantime, also, he prepared the plans for, and finally had built, a moderately large engine of his own new type. Its steam-cylinder was 18 inches in diameter, and the stroke of piston was 5 feet. This engine was built at Kinneil, and was finished in September, 1769. It was not all satisfactory in either its construction or its operation. The condenser was a surface-condenser composed of pipes somewhat like that used in his first little model, and did not prove to be satisfactorily tight. The steam-piston leaked seriously, and repeated trials only served to make more evident its imperfections. He was assisted in this time of need by both Dr. Black and Dr. Roebuck; but he felt strongly the risks which he ran of involving his friends in serious losses, and became very despondent. Writing to Dr. Black, he says: "Of all things in life, there is nothing more foolish than inventing;" and probably the majority of inventors have been led to the same opinion by their own experiences. "Misfortunes never come singly;" and Watt was borne down by the greatest of all misfortunes--the loss of a faithful and affectionate wife--while still unable to see a successful issue of his schemes. Only less disheartening than this was the loss of fortune of his steadfast friend, Dr. Roebuck, and the consequent loss of his aid. It was at about this time, in the year 1769, that negotiations were commenced which resulted in the transfer of the capitalized interest in Watt's engine to the wealthy manufacturer whose name, coupled with that of Watt, afterward became known throughout the civilized world, as the steam-engine in its new form was pushed into use by his energy and business tact. Watt met Mr. Boulton, who next became his partner, in 1768, on his journey to London to procure his patent, and the latter had then examined Watt's designs, and, at once perceiving their value, proposed to purchase an interest. Watt was then unable to reply definitely to Boulton's proposition, pending his business arrangements with Dr. Roebuck; but, with Roebuck's consent, afterwards proposed that Boulton should take a one-third interest with himself and partner, paying Roebuck therefor one-half of all expenses previously incurred, and whatever he should choose to add to compensate "for the risk he had run." Subsequently, Dr. Roebuck proposed to transfer to Boulton and to Dr. Small, who was desirous of taking interest with Boulton, one-half of his proprietorship in Watt's inventions, on receiving "a sum not less than one thousand pounds," which should, after the experiments on the engine were completed, be deemed "just and reasonable." Twelve months were allowed for the adjustment of the account. This proposal was accepted in November, 1769. [Illustration: Matthew Boulton.] MATTHEW BOULTON, who now became a partner with James Watt, was the son of a Birmingham silver stamper and piecer, and succeeded to his father's business, building up a great establishment, which, as well as its proprietor, was well known in Watt's time. Watt, writing to Dr. Roebuck before the final arrangement had been made, urged him to close with Boulton for "the following considerations: "1st. From Mr. Boulton's own character as an ingenious, honest, and rich man. 2dly. From the difficulty and expense there would be of procuring accurate and honest workmen and providing them with proper utensils, and getting a proper overseer or overseers. If, to avoid this inconvenience, you were to contract for the work to be done by a master-workman, you must give up a great share of the profit. 3dly. The success of the engine is far from being verified. If Mr. Boulton takes his chance of success from the account I shall write Dr. Small, and pays you any adequate share of the money laid out, it lessens your risk, and in a greater proportion than I think it will lessen your profits. 4thly. The assistance of Mr. Boulton's and Dr. Small's ingenuity (if the latter engage in it) in improving and perfecting the machine may be very considerable, and may enable us to get the better of the difficulties that might otherwise damn it. Lastly, consider my uncertain health, my irresolute and inactive disposition, my inability to bargain and struggle for my own with mankind: all which disqualify me for any great undertaking. On our side, consider the first outlay and interest, the patent, the present engine, about £200 (though there would not be much loss in making it into a common engine), two years of my time, and the expense of models." Watt's estimate of the value of Boulton's ingenuity and talent was well-founded. Boulton had shown himself a good scholar, and had acquired considerable knowledge of the languages and of the sciences, particularly of mathematics, after leaving the school from which he graduated into the shop when still a boy. In the shop he soon introduced a number of valuable improvements, and he was always on the lookout for improvements made by others, with a view to their introduction in his business. He was a man of the modern style, and never permitted competitors to excel him in any respect, without the strongest efforts to retain his leading position. He always aimed to earn a reputation for good work, as well as to make money. His father's workshop was at Birmingham; but Boulton, after a time, found that his rapidly-increasing business would compel him to find room for the erection of a more extensive establishment, and he secured land at Soho, two miles distant from Birmingham, and there erected his new manufactory, about 1762. The business was, at first, the manufacture of ornamental metal-ware, such as metal buttons, buckles, watch-chains, and light filigree and inlaid work. The manufacture of gold and silver plated-ware was soon added, and this branch of business gradually developed into a very extensive manufacture of works of art. Boulton copied fine work wherever he could find it, and often borrowed vases, statuettes, and bronzes of all kinds from the nobility of England, and even from the queen, from which to make copies. The manufacture of inexpensive clocks, such as are now well known throughout the world as an article of American trade, was begun by Boulton. He made some fine astronomical and valuable ornamental clocks, which were better appreciated on the Continent than in England. The business of the Soho manufactory in a few years became so extensive, that its goods were known to every civilized nation, and its growth, under the management of the enterprising, conscientious, and ingenious Boulton, more than kept pace with the accumulation of capital; and the proprietor found himself, by his very prosperity, often driven to the most careful manipulation of his assets, and to making free use of his credit. Boulton had a remarkable talent for making valuable acquaintances, and for making the most of advantages accruing thereby. In 1758 he made the acquaintance of Benjamin Franklin, who then visited Soho; and in 1766 these distinguished men, who were then unaware of the existence of James Watt, were corresponding, and, in their letters, discussing the applicability of steam-power to various useful purposes. Between the two a new steam-engine was designed, and a model was constructed by Boulton, which was sent to Franklin and exhibited by him in London. Dr. Darwin seems to have had something to do with this scheme, and the enthusiasm awakened by the promise of success given by this model may have been the origin of the now celebrated prophetic rhymes so often quoted from the works of that eccentric physician and poet. Franklin contributed, as his share in the plan, an idea of so arranging the grate as to prevent the production of smoke. He says: "All that is necessary is to make the smoke of fresh coals pass descending through those that are already ignited." His idea has been, by more recent schemers, repeatedly brought forward as new. Nothing resulted from these experiments of Boulton, Franklin, and Darwin, and the plan of Watt soon superseded all less well-developed plans. In 1767, Watt visited Soho and carefully inspected Boulton's establishment. He was very favorably impressed by the admirable arrangement of the workshops and the completeness of their outfit, as well as by the perfection of the organization and administration of the business. In the following year he again visited Soho, and this time met Boulton, who had been absent at the previous visit. The two great mechanics were mutually gratified by the meeting, and each at once acquired for the other the greatest respect and esteem. They discussed Watt's plans, and Boulton then definitely decided not to continue his own experiments, although he had actually commenced the construction of a pumping-engine. With Dr. Small, who was also at Soho, Watt discussed the possibility of applying his engine to the propulsion of carriages, and to other purposes. On his return home, Watt continued his desultory labors on his engines, as already described; and the final completion of the arrangement with Boulton, which immediately followed the failure of Dr. Roebuck, took place some time later. Before Watt could leave Scotland to join his partner at Soho, it was necessary that he should finish the work which he had in hand, including the surveys of the Caledonian canal, and other smaller works, which he had had in progress some months. He reached Birmingham in the spring of 1774, and was at once domiciled at Soho, where he set at work upon the partly-made engines which had been sent from Scotland some time previously. They had laid, unused and exposed to the weather, at Kinneil three years, and were not in as good order as might have been desired. The _block-tin_ steam-cylinder was probably in good condition, but the iron parts were, as Watt said, "perishing," while he had been engaged in his civil engineering work. At leisure moments, during this period, Watt had not entirely neglected his plans for the utilization of steam. He had given much thought, and had expended some time, in experiments upon the plan of using it in a rotary or "wheel" engine. He did not succeed in contriving any plan which seemed to promise success. It was in November, 1774, that Watt finally announced to his old partner, Dr. Roebuck, the successful trial of the Kinneil engine. He did not write with the usual enthusiasm and extravagance of the inventor, for his frequent disappointments and prolonged suspense had very thoroughly extinguished his vivacity. He simply wrote: "The fire-engine I have invented is now going, and answers much better than any other that has yet been made; and I expect that the invention will be very beneficial to me." The change of the "atmospheric engine" of Newcomen into the modern steam-engine was now completed in its essential details. The first engine which was erected at Kinneil, near Boroughstoness, had a steam-cylinder 18 inches in diameter. It is seen in the accompanying sketch. [Illustration: FIG. 26.--Watt's Engine, 1774.] In Fig. 26, the steam passes from the boiler through the pipe _d_ and the valve _c_ to the cylinder-casing or steam-jacket, _Y Y_, and above the piston, _b_, which it follows in its descent in the cylinder, _a_, the valve _f_ being at this time open, to allow the exhaust into the condenser, _h_. The piston now being at the lower end of the cylinder, and the pump-rods at the opposite end of the beam, _y_, being thus raised and the pumps filled with water, the valves _c_ and _f_ close, while _e_ opens, allowing the steam which remains above the piston to flow beneath it, until, the pressures becoming equal above and below, the weight of the pump-rods overbalancing that of the piston, the latter is rapidly drawn to the top of the cylinder, while the steam is displaced above, passing to the under-side of the piston. The valve _e_ is next closed, and _c_ and _f_ are again opened; the down-stroke is repeated. The water and air entering the condenser are removed at each stroke by the air-pump, _i_, which communicates with the condenser by the passage _s_. The pump _q_ supplies condensing-water, and the pump _A_ takes away a part of the water of condensation, which is thrown by the air-pump into the "hot-well," _k_, and from it the feed-pump supplies the boiler. The valves are moved by valve-gear very similar to Beighton's and Smeaton's, by the pins, _m m_, in the "plug-frame" or "tappet-rod," _n n_. The engine is mounted upon a substantial foundation, _B B_. _F_ is an opening out of which, before starting the engine, the air is driven from the cylinder and condenser. The inventions covered by the patent of 1769 were described as follows: "My method of lessening the consumption of steam, and consequently fuel, in fire-engines, consists in the following principles: "1st. That the vessel in which the powers of steam are to be employed to work the engine--which is called 'the cylinder' in common fire-engines, and which I call 'the steam-vessel'--must, during the whole time that the engine is at work, be kept as hot as the steam which enters it; first, by inclosing it in a case of wood, or any other materials that transmit heat slowly; secondly, by surrounding it with steam or other heated bodies; and thirdly, by suffering neither water nor other substances colder than the steam to enter or touch it during that time. "2dly. In engines that are to be worked, wholly or partially, by condensation of steam, the steam is to be condensed in vessels distinct from the steam-vessel or cylinder, though occasionally communicating with them. These vessels I call condensers; and while the engines are working, these _condensers_ ought at least to be kept as cold as the air in the neighborhood of the engines, by application of water or other cold bodies. "3dly. Whatever air or other elastic vapor is not condensed by the cold of the condenser, and may impede the working of the engine, is to be drawn out of the steam-vessels or condensers by means of pumps, wrought by the engines themselves, or otherwise. "4thly. I intend in many cases to employ the expansive force of steam to press on the pistons, or whatever may be used instead of them, in the same manner as the pressure of the atmosphere is now employed in common fire-engines. In cases where cold water cannot be had in plenty, the engines may be wrought by this force of steam only, by discharging the steam into the open air after it has done its office. "5thly. Where motions round an axis are required, I make the steam-vessels in form of hollow rings or circular channels, with proper inlets and outlets for the steam, mounted on horizontal axles like the wheels of a water-mill. Within them are placed a number of valves that suffer any body to go round the channel in one direction only. In these steam-vessels are placed weights, so fitted to them as to fill up a part or portion of their channels, yet rendered capable of moving freely in them by the means hereinafter mentioned or specified. When the steam is admitted in these engines between these weights and the valves, it acts equally on both, so as to raise the weight on one side of the wheel, and, by the reaction of the valves successively, to give a circular motion to the wheel, the valves opening in the direction in which the weights are pressed, but not in the contrary. As the vessel moves round, it is supplied with steam from the boiler, and that which has performed its office may either be discharged by means of condensers, or into the open air. "6thly. I intend in some cases to apply a degree of cold not capable of reducing the steam to water, but of contracting it considerably, so that the engines shall be worked by the alternate expansion and contraction of the steam. "Lastly, instead of using water to render the piston or other parts of the engine air or steam-tight, I employ oils, wax, resinous bodies, fat of animals, quicksilver, and other metals, in their fluid state." In the construction and erection of his engines, Watt still had great difficulty in finding skillful workmen to make the parts with accuracy, to fit them with care, and to erect them properly when once finished. And the fact that both Newcomen and Watt met with such serious trouble, indicates that, even had the engine been designed earlier, it is quite unlikely that the world would have seen the steam-engine a success until this time, when mechanics were just acquiring the skill requisite for its construction. But, on the other hand, it is not at all improbable that, had the mechanics of an earlier period been as skillful and as well-educated in the manual niceties of their business, the steam-engine might have been much earlier brought into use. In the time of the Marquis of Worcester it would have probably been found impossible to obtain workmen to construct the steam-engine of Watt, had it been then invented. Indeed, Watt, upon one occasion, congratulated himself that one of his steam-cylinders only lacked _three-eighths_ of an inch of being truly cylindrical. The history of the steam-engine is from this time a history of the work of the firm of Boulton & Watt. Newcomen engines continued to be built for years after Watt went to Soho, and by many builders. A host of inventors still worked on the most attractive of all mechanical combinations, seeking to effect further improvements. Some inventions were made by contemporaries of Watt, as will be seen hereafter, which were important as being the germs of later growths; but these were nearly all too far in advance of the time, and nearly every successful and important invention which marked the history of steam-power for many years originated in the fertile brain of James Watt. The defects of the Newcomen engine were so serious, that it was no sooner known that Boulton of Soho had become interested in a new machine for raising water by steam-power, than inquiries came to him from all sides, from mine-owners who were on the point of being drowned out, and from proprietors whose profits were absorbed by the expense of pumping, and who were glad to pay the £5 per horse-power per year finally settled upon as royalty. The London municipal water-works authorities were also ready to negotiate for pumping-engines for raising water to supply the metropolis. The firm was therefore at once driven to make preparations for a large business. The first and most important matter, however, was to secure an extension of the patent, which was soon to expire. If not renewed, the 15 years of study and toil, of poverty and anxiety, through which Watt had toiled, would prove profitless to the inventor, and the fruits of his genius would have become the unearned property of others. Watt saw, at one time, little hope of securing the necessary act of Parliament, and was greatly tempted to accept a position tendered him by the Russian Government, upon the solicitation of his old friend, Dr. Robison, then a Professor of Mathematics at the Naval School at Cronstadt. The salary was £1,000--a princely income for a man in Watt's circumstances, and a peculiar temptation to the needy mechanic. Watt, however, went to London, and, with the help of his own and of Boulton's influential friends, succeeded in getting his bill through. His patent was extended 24 years, and Boulton & Watt set about the work of introducing their engines with the industry and enterprise which characterized their every act. In the new firm, Boulton took charge of the general business, and Watt superintended the design, construction, and erection of their engines. Boulton's business capacity, with Watt's wonderful mechanical ability--Boulton's physical health, and his vigor and courage, offsetting Watt's feeble health and depression of spirits--and, more than all, Boulton's pecuniary resources, both in his own purse and in those of his friends, enabled the firm to conquer all difficulties, whether in finance, in litigation, or in engineering. It was only after the successful erection and operation of several engines that Boulton and Watt became legally partners. The understood terms were explicitly stated by Watt to include an assignment to Boulton of two-thirds the patent-right; Boulton paying all expenses, advancing stock in trade at an appraised valuation, on which it was to draw interest; Watt making all drawings and designs, and drawing one-third net profits. As soon as Watt was relieved of the uncertainties regarding his business connections, he married a second wife, who, as Arago says, by "her various talent, soundness of judgment, and strength of character," made a worthy companion to the large-hearted and large-brained engineer. Thenceforward his cares were only such as every business-man expects to be compelled to sustain, and the next ten years were the most prolific in inventions of any period in Watt's life. From 1775 to 1785 the partners acquired five patents, covering a large number of valuable improvements upon the steam-engine, and several independent inventions. The first of these patents covered the now familiar and universally-used copying-press for letters, and a machine for drying cloth by passing it between copper rollers filled with steam of sufficiently high temperature to rapidly evaporate the moisture. This patent was issued February 14, 1780. [Illustration: FIG. 27.--Watt's Engine, 1781.] In the following year, October 25, 1781, Watt patented five devices by which he obtained the rotary motion of the engine-shaft without the use of a crank. One of these was the arrangement shown in Fig. 27, and known as the "sun-and-planet" wheels. The crank-shaft carries a gear-wheel, which is engaged by another securely fixed upon the end of the connecting-rod. As the latter is compelled to revolve about the axis of the shaft by a tie which confines the connecting-rod end at a fixed distance from the shaft, the shaft-gear is compelled to revolve, and the shaft with it. Any desired velocity-ratio was secured by giving the two gears the necessary relative diameters. A fly-wheel was used to regulate the motion of the shaft.[39] Boulton & Watt used the sun-and-planet device on many engines, but finally adopted the crank, when the expiration of the patent held by Matthew Wasborough, and which had earlier date than Watt's patent of 1781, permitted them. Watt had proposed the use of a crank, it is said, as early as 1771, but Wasborough anticipated him in securing the patent. Watt had made a model of an engine with a crank and fly-wheel, and he has stated that one of his workmen, who had seen the model, described it to Wasborough, thus enabling the latter to deprive Watt of his own property. The proceeding excited great indignation on the part of Watt; but no legal action was taken by Boulton & Watt, as the overthrow of the patent was thought likely to do them injury by permitting its use by more active competitors and more ingenious men. [39] For the privilege of using the fly-wheel to regulate the motion of the engine, Boulton & Watt paid a royalty to Matthew Wasborough, who had patented it, and who held also the patent for its combination with a crank, as invented by Pickard and Steed. The next patent issued to Watt was an exceedingly important one, and of especial interest in a history of the development of the economical application of steam. This patent included: 1. The expansion of steam, and six methods of applying the principle and of equalizing the expansive power. 2. The double-acting steam-engine, in which the steam acts on each side of the piston alternately, the opposite side being in communication with the condenser. 3. The double or coupled steam-engine--two engines capable of working together, or independently, as may be desired. 4. The use of a rack on the piston-rod, working into a sector on the end of the beam, thus securing a perfect rectilinear motion of the rod. 5. A rotary engine, or "steam-wheel." The efficiency to be secured by the expansion of steam had long been known to Watt, and he had conceived the idea of economizing some of that power, the waste of which was so plainly indicated by the violent rushing of the exhaust-steam into the condenser, as early as 1769. This was described in a letter to Dr. Small, of Birmingham, in May of that year. When experimenting at Kinneil, he had tried to determine the real value of the principle by trial on his small engine. Boulton had also recognized the importance of this improved method of working steam, and their earlier Soho engines were, as Watt said, made with cylinders "double the size wanted, and cut off the steam at half-stroke." But, though "this was a great saving of steam, so long as the valves remained as at first," the builders were so constantly annoyed by alterations of the valves by proprietors and their engineers, that they finally gave up that method of working, hoping ultimately to be able to resume it when workmen of greater intelligence and reliability could be found. The patent was issued July 17, 1782. Watt specified a cut-off at one-quarter stroke as usually best. Watt's explanation of the method of economizing by expansive working, as given to Dr. Small,[40] is worthy of reproduction. He says: "I mentioned to you a method of still doubling the effect of steam, and that tolerably easy, by using the power of steam rushing into a vacuum, at present lost. This would do a little more than double the effect, but it would too much enlarge the vessels to use it all. It is peculiarly applicable to wheel-engines, and may supply the want of a condenser where force of steam is only used; for, open one of the steam-valves and admit steam, until one-fourth of the distance between it and the next valve is filled with steam, shut the valve, and the steam will continue to expand and to pass round the wheel with a diminishing power, ending in one-fourth its first exertion. The sum of this series you will find greater than one-half, though only one-fourth steam was used. The power will indeed be unequal, but this can be remedied by a fly, or in several other ways." [40] "Lives of Boulton and Watt," Smiles. It will be noticed that Watt suggests, above, the now well-known non-condensing engine. He had already, as has been seen, described it in his patent of 1769, as also the rotary engine. Watt illustrates and explains his idea very neatly, by a sketch similar to that here given (Fig. 28). Steam, entering the cylinder at _a_, is admitted until one-fourth the stroke has been made, when the steam-valve is closed, and the remainder of the stroke is performed without further addition of steam. The variation of steam-pressure is approximately inversely proportional to the variation of its volume. Thus, at half-stroke, the pressure becomes one-half that at which the steam was supplied to the cylinder. At the end of the stroke it has fallen to one-fourth the initial pressure. The pressure is always nearly equal to the product of the initial pressure and volume divided by the volume at the given instant. In symbols, _PV_ _P´_ = ----. _V´_ It is true that the condensation of steam doing work changes this law in a marked manner; but the condensation and reëvaporation of steam, due to the transfer of heat to and from the metal of the cylinder, tends to compensate the first variation by a reverse change of pressure with change of volume. [Illustration: FIG. 28.--Expansion of Steam.] The sketch shows this progressive variation of pressure as expansion proceeds. It is seen that the work done per unit of volume of steam as taken from the boiler is much greater than when working without expansion. The product of the mean pressure by the volume of the cylinder is less, but the quotient obtained by dividing this quantity by the volume or weight of steam taken from the boiler, is much greater with than without expansion. For the case assumed and illustrated, the work done during expansion is one and two-fifths times that done previous to cutting off the steam, and the work done per pound of steam is 2.4 times that done without expansion. Were there no losses to be met with and to be exaggerated by the use of steam expansively, the gain would become very great with moderate expansion, amounting to twice the work done when "following" full stroke, when the steam is cut off at one-seventh. The estimated gain is, however, never realized. Losses by friction, by conduction and radiation of heat, and by condensation and reëvaporation in the cylinder--of which losses the latter are most serious--after passing a point which is variable, and which is determined by the special conditions in each case, augment with greater rapidity than the gain by expansion. In actual practice, it is rarely found, except where special precautions are taken to reduce these losses, that economy follows expansion to a greater number of volumes than about one-half the square root of the steam-pressure; i. e., about twice for 15 or 20 pounds pressure, three times for about 30 pounds, and four and five times for 60 or 65 and for 100 to 125 pounds respectively. Watt very soon learned this general principle; but neither he, nor even many modern engineers, seem to have learned that too great expansion often gives greatly-reduced economy. The inequality of pressure due to expansion, to which he refers, was a source of much perplexity to Watt, as he was for a long time convinced that he must find some method of "equalizing" the consequent irregular effort of the steam upon the piston. The several methods of "equalizing the expansive power" which are referred to in the patent were attempts to secure this result. By one method, he shifted the centre as the beam vibrated, thus changing the lengths of the arms of that great lever, to compensate the change of moment consequent upon the change of pressure. He finally concluded that a fly-wheel, as first proposed by Fitzgerald, who advised its use on Papin's engine, would be the best device on engines driving a crank, and trusted to the inertia of a balance-weight in his pumping-engines, or to the weight of the pump-rods, and permitted the piston to take its own speed so far as it was not thus controlled. The double-acting engine was a modification of the single-acting engine, and was very soon determined upon after the successful working of the latter had become assured. Watt had covered in the top of his single-acting engine, to prevent cooling the interior of the cylinder by contact with the comparatively cold atmosphere. When this had been done, there was but a single step required to convert the machine into the double-acting engine. This alteration, by which the steam was permitted to act upon the upper and the lower sides of the piston alternately, had been proposed by Watt as early as 1767, and a drawing of the engine was laid before a committee of the House of Commons in 1774-'75. By this simple change Watt doubled the power of his engine. Although invented much earlier, the plan was not patented until he was, as he states, driven to take out the patent by the "plagiarists and pirates" who were always ready to profit by his ingenuity. This form of engine is now almost universally used. The single-acting pumping-engine remains in use in Cornwall, and in a few other localities, and now and then an engine is built for other purposes, in which steam acts only on one side of the piston; but these are rare exceptions to the general rule. The subject of his next invention was not less interesting. The double-cylinder or "compound" engine has now, after the lapse of nearly a century, become an important and usual type of engine. It is impossible to determine precisely to whom to award the credit of its first conception. Dr. Falk, in 1779, had proposed a double-acting engine, in which there were two single-acting cylinders, acting in opposite directions and alternately on opposite sides of a wheel, with which a rack on the piston-rod of each geared. Watt claimed that Hornblower, the patentee of the "compound engine," was an infringer upon his patents; and, holding the patent on the separate condenser, he was able to prevent the engine of his competitor taking such form as to be successfully introduced. The Hornblower engine was soon given up. Watt stated that this form of engine had been invented by him as early as 1767, and that he had explained its peculiarities to Smeaton and others several years before Hornblower attempted to use it. He wrote to Boulton: "It is no less than our double-cylinder engine, worked upon our principle of expansion." He never made use of the plan, however; and the principal object sought, apparently, in patenting this, as well as many other devices, was to secure himself against competition. The rack and sector patented at this time was soon superseded by the parallel-motion; and the last claim, the "steam-wheel" or rotary engine, although one was built of considerable size, was not introduced. After the patent of 1782 had been secured, Watt turned his attention, when not too hard-pressed by business, to other schemes, and to experimenting with still other modifications and applications of his engine. He had, as early as 1777, proposed to make a steam-hammer for Wilkinson's forge; but he was too closely engaged with more important matters to take hold of the project with much earnestness until late in the year 1782, when, after some preliminary trials, he reported, December 13th: "We have tried our little tilting-forge hammer at Soho with success. The following are some of the particulars: Cylinder, 15 inches in diameter; 4 feet stroke; strokes per minute, 20. The hammer-head, 120 pounds weight, rises 8 inches, and strikes 240 blows per minute. The machine goes quite regularly, and can be managed as easily as a water-mill. It requires a very small quantity of steam--not above half the contents of the cylinder per stroke. The power employed is not more than one-fourth of what would be required to raise the quantity of water which would enable a water-wheel to work the same hammer with the same velocity." He immediately set about making a much heavier hammer, and on April 26, 1783, he wrote that he had done "a thing never done before"--making his hammer strike 300 blows a minute. This hammer weighed 7-1/2 hundredweight, and had a drop of 2 feet. The steam-cylinder had a diameter of 42 inches and 6 feet stroke of piston, and was calculated to have sufficient power to drive four hammers weighing 7 hundredweight each. The engine made 20 strokes per minute, the hammer giving 90 blows in the same time. This new application of steam-power proving successful, Watt next began to develop a series of minor inventions, which were finally secured by his patent of April 27, 1784, together with the steam tilt-hammer, and a steam-carriage, or "locomotive engine." The contrivance previously used for guiding the head of the piston-rod--the sectors and chains, or rack--had never given satisfaction. The rudeness of design of the contrivance was only equalled by its insecurity. Watt therefore contrived a number of methods of accomplishing the purpose, the most beautiful and widely-known of which is the "parallel-motion," although it has now been generally superseded by one of the other devices patented at the same time--the cross-head and guides. As originally proposed, a rod was attached to the head of the piston-rod, standing vertically when the latter was at quarter-stroke. The upper end of this rod was pivoted to the end of the beam, and the lower end to the extremity of a horizontal rod having a length equal to one-half the length of the beam. The other end of the horizontal rod was coupled to the frame of the engine. As the piston rose and fell, the upper and lower ends of the vertical rod were swayed in opposite directions, and to an equal extent, by the beam and the lower horizontal rod, the middle point at which the piston-rod was attached preserving its position in the vertical line. This form was objectionable, as the whole effort of the engine was transmitted through the parallel-motion rods. Another form is shown in the sketch given of the double-acting engine in Fig. 31, which was free from this defect. The head of the piston-rod, _g_, was guided by rods connecting it with the frame at _c_, and forming a "parallelogram," _g d e b_, with the beam. Many varieties of "parallel-motion" have been devised since Watt's invention was attached to his engines at Soho. They usually are more or less imperfect, guiding the piston-rod in a line only approximately straight. The cross-head and guides are now generally used, very much as described by Watt in this patent as his "second principle." This device will be seen in the engravings given hereafter of more modern engines. The head of the piston-rod is fitted into a transverse bar, or cross-head, which carries properly-shaped pieces at its extremities, to which are bolted "gibs," so made as to fit upon guides secured to the engine-frame. These guides are adjusted to precise parallelism with the centre line of the cylinder. The cross-head, sliding in or on these guides, moves in a perfectly straight line, and, compelling the piston-rod to move with it, the latter is even more perfectly guided than by a parallel-motion. This arrangement, where properly proportioned, is not necessarily subject to great friction, and is much more easily adjusted and kept in line than the parallel-motion when wear occurs or maladjustment takes place. By the same patent, Watt secured the now common "puppet-valve" with beveled seat, and the application of the steam-engine to driving rolling-mills and hammers for forges, and to "wheel-carriages for removing persons or goods, or other matters, from place to place." For the latter purpose he proposes to use boilers "of wood, or of thin metal, strongly secured by hoops or otherwise," and containing "internal fire-boxes." He proposed to use a condenser cooled by currents of air. It would require too much space to follow Watt in all his schemes for the improvement and for the application of the steam-engine. A few of the more important and more ingenious only can be described. Many of the contracts of Boulton & Watt gave them, as compensation for their engines, a fraction--usually one-third--of the value of the fuel saved by the use of the Watt engine in place of the engine of Newcomen, the amount due being paid annually or semiannually, with an option of redemption on the part of the purchaser at ten years' purchase. This form of agreement compelled a careful determination, often, of the work done and fuel consumed by both the engine taken out and that put in its place. It was impossible to rely upon any determination by personal observation of the number of strokes made by the engine. Watt therefore made a "counter," like that now familiar to every one as used on gas-meters. It consists of a train of wheels moving pointers on several dials, the first dial showing tens, the second hundreds, the third thousands, etc., strokes or revolutions. Motion was communicated to the train by means of a pendulum, the whole being mounted on the beam of the engine, where every vibration produced a swing of the pendulum. Eight dials were sometimes used, the counter being set and locked, and only opened once a year, when the time arrived for determining the work done during the preceding twelve-month. The application of his engine to purposes for which careful adjustment of speed was requisite, or where the load was subject to considerable variation, led to the use of a controlling-valve in the steam-pipe, called the "throttle-valve," which was adjustable by hand, and permitted the supply of steam to the engine to be adjusted at any instant and altered to any desired extent. It is now given many forms, but it still is most usually made just as originally designed by Watt. It consists of a circular disk, which just closes up the steam-pipe when set directly across it, or of an elliptical disk, which closes the pipe when standing at an angle of somewhat less than 90° with the line of the pipe. This disk is carried on a spindle extending through the pipe at one side, and carrying on its outer end an arm by means of which it may be turned into any position. When placed with its face in line with the pipe, it offers very little resistance to the flow of steam to the engine. When set in the other position, it shuts off steam entirely and stops the engine. It is placed in such position at any time, that the speed of the engine is just that required at the time. In the engraving of the double-acting engine with fly-wheel (Fig. 31), it is shown at _T_, as controlled by the governor. [Illustration: FIG. 29.--The Governor.] The governor, or "fly-ball governor," as it is often distinctively called, was another of Watt's minor but very essential inventions. Two heavy iron or brass balls, _B B´_, were suspended from pins, _C C´_, in a little cross-piece carried on the head of a vertical spindle, _A A´_, driven by the engine. The speed of the engine varying, that of the spindle changed correspondingly, and the faster the balls were swung the farther they separated. When the engine's speed decreased, the period of revolution of the balls was increased, and they fell back toward the spindle. Whenever the velocity of the engine was uniform, the balls preserved their distance from the spindle and remained at the same height, their altitude being determined by the relation existing between the force of gravity and centrifugal force in the temporary position of equilibrium. The distance from the point of suspension down to the level of the balls is always equal to 9.78 inches divided by the square of the number of revolutions per second--i. e., _h_ = 9.78 (1/_N_^2) = 0.248 (1/_N_^2) meters. The arms carrying the balls, or the balls themselves, are pinned to rods, _M M´_, which are connected to a piece, _N N´_, sliding loosely on the spindle. A score, _T_, cut in this piece engages a lever, _V_, and, as the balls rise and fall, a rod, _W_, is moved, closing and opening the throttle-valve, and thus adjusting the supply of steam in such a way as to preserve a nearly fixed speed of engine. The connection with the throttle-valve and with the cut-off valve-gear is seen not only in the engraving of the double-acting Watt engine, but also in those of the Greene and the Corliss engines. This contrivance had previously been used in regulating water-wheels and windmills. Watt's invention consisted in its application to the regulation of the steam-engine. Still another useful invention of Watt's was his "mercury steam-gauge"--a barometer in which the height of the mercury was determined by the pressure of the steam instead of that of the atmosphere. This simple instrument consisted merely of a bent tube containing a portion of mercury. One leg, _B D_, of this U-tube was connected with the steam-pipe, or with the boiler by a small steam-pipe; the other end, _C_, was open to the atmosphere. The pressure of the steam on the mercury in _B D_ caused it to rise in the other "leg" to a height exactly proportioned to the pressure, and causing very nearly two inches difference of level to the pound, or one inch to the pound actual rise in the outer leg. The rude sketch from Farey, here given (Fig. 30), indicates sufficiently well the form of this gauge. It is still considered by engineers the most reliable of all forms of steam-gauge. Unfortunately, it is not conveniently applicable at high pressure. The scale, _A_, is marked with numbers indicating the pressure, which numbers are indicated by the head of a rod floating up with the mercury. A similar gauge was used to determine the degree of perfection of vacuum attained in the condenser, the mercury falling in the outer leg as the vacuum became more complete. A perfect vacuum would cause a depression of level in that leg to 30 inches below the level of the mercury in the leg connected with the condenser. In a more usual form, it consisted of a simple glass tube having its lower end immersed in a cistern of mercury, as in the ordinary barometer, the top of the tube being connected with a pipe leading to the condenser. With a perfect vacuum in the condenser, the mercury would rise in the tube very nearly 30 inches. Ordinarily, the vacuum is not nearly perfect, and, a back pressure remaining in the condenser of one or two pounds per square inch, the atmospheric pressure remaining unbalanced is only sufficient to raise the mercury 26 or 28 inches above the level of the liquid metal in the cistern. [Illustration: FIG. 30. Mercury Steam Gauge. Glass Water Gauge.] To determine the height of water in his boiler, Watt added to the gauge-cocks already long in use the "glass water-gauge," which is still seen in nearly every well-arranged boiler. This was a glass tube, _a a´_ (Fig. 30), mounted on a standard attached to the front of the boiler, and at such a height that its middle point was very little below the proposed water-level. It was connected by a small pipe, _r_, at the top to the steam-space, and another little pipe, _r´_, led into the boiler from its lower end below the water-line. As the water rose and fell within the boiler, its level changed correspondingly in the glass. This little instrument is especially liked, because the position of the water is at all times shown to the eye of the attendant. If carefully protected against sudden changes of temperature, it answers perfectly well with even very high pressures. The engines built by Boulton & Watt were finally fitted with the crank and fly-wheel for application to the driving of mills and machinery. The accompanying engraving (Fig. 31) shows the engine as thus made, combining all of the essential improvements designed by its inventor. In the engraving, _C_ is the steam-cylinder, _P_ the piston, connected to the beam by the link, _g_, and guided by the parallel-motion, _g d c_. At the opposite end of the beam a connecting-rod, _O_, connects with the crank and fly-wheel shaft. _R_ is the rod of the air-pump, by means of which the condenser is kept from being flooded by the water used for condensation, which water-supply is regulated by an "injection-handle," _E_. A pump-rod, _N_, leads down from the beam to the cold-water pump, by which water is raised from the well or other source to supply the needed injection-water. The air-pump rod also serves as a "plug-rod," to work the valves, the pins at _m_ and _R_ striking the lever, _m_, at either end of the stroke. When the piston reaches the top of the cylinder, the lever, _m_, is raised, opening the steam-valve, _B_, at the top, and the exhaust-valve, _E_, at the bottom, and at the same time closing the exhaust at the top and the steam at the bottom. When the entrance of steam at the top and the removal of steam-pressure below the piston has driven the piston to the bottom, the pin, _R_, strikes the lever, _m_, opening the steam and closing the exhaust valve at the bottom, and similarly reversing the position of the valves at the top. The position of the valves is changed in this manner with every reversal of the motion of the piston as the crank "turns over the centre." [Illustration: FIG. 31.--Boulton & Watt's Double-Acting Engine, 1784.] The earliest engines of the double-acting kind, and of any considerable size, which were built to turn a shaft, were those which were set up in the Albion Mills, near Blackfriars' Bridge, London, in 1786, and destroyed when the mills burned down in 1791. There were a pair of these engines (shown in Fig. 27), of 50 horse-power each, and geared to drive 20 pairs of stones, making fine flour and meal. Previous to the erection of this mill the power in all such establishments had been derived from windmills and water-wheels. This mill was erected by Boulton & Watt, and capitalists working with them, not only to secure the profit anticipated from locating a flour-mill in the city of London, but also with a view to exhibiting the capacity of the new double-acting "rotating" engine. The plan was proposed in 1783, and work was commenced in 1784; but the mill was not set in operation until the spring of 1786. The capacity of the mill was, in ordinary work, 16,000 bushels of wheat ground into fine flour per week. On one occasion, the mill turned out 3,000 bushels in 24 hours. In the construction of the machinery of the mill, many improvements upon the then standard practice were introduced, including cast-iron gearing with carefully-formed teeth and iron framing. It was here that John Rennie commenced his work, after passing through his apprenticeship in Scotland, sending his chief assistant, Ewart, to superintend the erection of the milling machinery. The mill was a success as a piece of engineering, but a serious loss was incurred by the capitalists engaged in the enterprise, as it was set on fire a few years afterward and entirely destroyed. Boulton and Watt were the principal losers, the former losing £6,000, and the latter £3,000. The valve-gear of this engine, a view of which is given in Fig. 27, was quite similar to that used on the Watt pumping-engine. The accompanying illustration (Fig. 32) represents this valve-motion as attached to the Albion Mills engine. [Illustration: FIG. 32.--Valve-Gear of the Albion Mills Engine.] The steam-pipe, _a b d d e_, leads the steam from the boiler to the chambers, _b_ and _e_. The exhaust-pipe, _g g_, leads from _h_ and _i_ to the condenser. In the sketch, the upper steam and the lower exhaust valves, _b_ and _f_, are opened, and the steam-valve, _e_, and exhaust-valve, _c_, are closed, the piston being near the upper end of the cylinder and descending. _l_ represents the plug-frame, which carries tappets, 2 and 3, which engage the lever, _s_, at either end of its throw, and turn the shaft, _u_, thus opening and closing _c_ and _e_ simultaneously by means of the connecting-links, 13 and 14. A similar pair of tappets on the opposite side of the plug-rod move the valves, _b_ and _f_, by means of the rods, 10 and 11, the arm, _r_, when struck by those tappets, turning the shaft, _t_, and thus moving the arms to which those rods are attached. Counterbalance-weights, carried on the ends of the arms, 4 and 15, retain the valves on their seats when closed by the action of the tappets. When the piston nearly reaches the lower end of the cylinder, the tappet, 1, engages the arm, _r_, closing the steam-valve, _b_, and the next instant shutting the exhaust-valve, _f_. At the same time, the tappet, 3, by moving the arm, _s_, downward, opens the steam-valve, _e_, and the exhaust-valve, _c_. Steam now no longer issues from the steam-pipe into the space, _c_, and thence into the engine-cylinder (not shown in the sketch); but it now enters the engine through the valve, _e_, forcing the piston upwards. The exhaust is simultaneously made to occur at the upper end, the rejected steam passing from the engine into the space, _c_, and thence through _c_ and the pipe, _g_, into the condenser. This kind of valve-gear was subsequently greatly improved by Murdoch, Watt's ingenious and efficient foreman, but it is now entirely superseded on engines of this class by the eccentric, and the various forms of valve-gear driven by it. [Illustration: FIG. 33.--Watt's Half-Trunk Engine, 1784.] The "trunk-engine" was still another of the almost innumerable inventions of Watt. A half-trunk engine is described in his patent of 1784, as shown in the accompanying sketch (Fig. 33), in which _A_ is the cylinder, _B_ the piston, and _C_ its rod, encased in the half-trunk, _D_. The plug-rod, _G_, moves the single pair of valves by striking the catches, _E_ and _F_, as was usual with Watt's earlier engines. Watt's steam-hammer was patented at the same time. It is seen in Fig. 34, in which _A_ is the steam-cylinder and _B_ its rod, the engine being evidently of the form just described. It works a beam, _C C_, which in turn, by the rod, _M_, works the hammer-helve, _L J_, and the hammer, _L_. The beam, _F G_, is a spring, and the block, _N_, the anvil. [Illustration: FIG. 34.--The Watt Hammer, 1784.] Watt found it impossible to determine the duty of his engines at all times by measurement of the work itself, and endeavored to find a way of ascertaining the power produced, by ascertaining the pressure of steam within the cylinder. This pressure was so variable, and subject to such rapid as well as extreme fluctuations, that he found it impossible to make use of the steam-gauge constructed for use on the boiler. He was thus driven to invent a special instrument for this work, which he called the "steam-engine indicator." This consisted of a little steam-cylinder containing a nicely-fitting piston, which moved without noticeable friction through a range which was limited by the compression of a helical spring, by means of which the piston was secured to the top of its cylinder. The distance through which the piston rose was proportional to the pressure exerted upon it, and a pointer attached to its rod traversed a scale upon which the pressure per square inch could be read. The lower end of the instrument being connected with the steam-cylinder of the engine by a small pipe fitted with a cock, the opening of the latter permitted steam from the engine-cylinder to fill the indicator-cylinder, and the pressure of steam was always the same in both cylinders. The indicator-pointer therefore traversed the pressure-scale, always exhibiting the pressure existing at the instant in the cylinder of the engine. When the engine was at rest and steam off, the indicator-piston stood at the same level as when detached from the engine, and the pointer stood at 0 on the scale. When steam entered, the piston rose and fell with the fluctuations of pressure; and when the exhaust-valve opened, discharging the steam and producing a vacuum in the steam-cylinder, the pointer of the indicator dropped below 0, showing the degree of exhaustion. Mr. Southern, one of Watt's assistants, fitted the instrument with a sliding board, moved horizontally backward and forward by a cord or link-work connecting directly or indirectly with the engine-beam, and thus giving it a motion coincident with that of the piston. This board carried a piece of paper, upon which a pencil attached to the indicator piston-rod drew a curve. The vertical height of any point on this curve above the base-line measured the pressure in the cylinder at the moment when it was made, and the horizontal distance of the point from either end of the diagram determined the position, at the same moment, of the engine-piston. The curve thus inscribed, called the "indicator card," or indicator diagram, exhibiting every minute change in the pressure of steam in the engine, not only enabled the mean pressure and the power of the engine to be determined by its measurement, but, to the eye of the expert engineer, it was a perfectly legible statement of the position of the valves of the engine, and revealed almost every defect in the action of the engine which could not readily be detected by external examination. It has justly been called the "engineers' stethoscope," opening the otherwise inaccessible parts of the steam-engine to the inspection of the engineer even more satisfactorily than the stethoscope of the physician gives him a knowledge of the condition and working of organs contained within the human body. This indispensable and now familiar engineers' instrument has since been modified and greatly improved in detail. The Watt engine had, by the construction of the improvements described in the patents of 1782-'85, been given its distinctive form, and the great inventor subsequently did little more than improve it by altering the forms and proportions of its details. As thus practically completed, it embodied nearly all the essential features of the modern engine; and, as we have seen, the marked features of our latest practice--the use of the double cylinder for expansion, the cut-off valve-gear, and surface-condensation--had all been proposed, and to a limited extent introduced. The growth of the steam-engine has here ceased to be rapid, and the changes which followed the completion of the work of James Watt have been minor improvements, and rarely, if ever, real developments. Watt's mind lost none of its activity, however, for many years. He devised and patented a "smoke-consuming furnace," in which he led the gases produced on the introduction of fresh fuel over the already incandescent coal, and thus burned them completely. He used two fires, which were coaled alternately. Even when busiest, also, he found time to pursue more purely scientific studies. With Boulton, he induced a number of well-known scientific men living near Birmingham to join in the formation of a "Lunar Society," to meet monthly at the houses of its members, "at the full of the moon." The time was thus fixed in order that those members who came from a distance should be able to drive home, after the meetings, by moonlight. Many such societies were then in existence in England; but that at Birmingham was one of the largest and most distinguished of them all. Boulton, Watt, Drs. Small, Darwin, and Priestley, were the leaders, and among their occasional visitors were Herschel, Smeaton, and Banks. Watt called these meetings "Philosophers' meetings." It was during the period of most active discussion at the "philosophers' meetings" that Cavendish and Priestley were experimenting with mixtures of oxygen and hydrogen, to determine the nature of their combustion. Watt took much interest in the subject, and, when informed by Priestley that he and Cavendish had both noticed a deposit of moisture invariably succeeding the explosion of the mixed gases, when contained in a cold vessel, and that the weight of this water was approximately equal to the weight of the mixed gases, he at once came to the conclusion that the union of hydrogen with oxygen produced water, the latter being a chemical compound, of which the former were constituents. He communicated this reasoning, and the conclusions to which it had led him, to Boulton, in a letter written in December, 1782, and addressed a letter some time afterward to Priestley, which was to have been read before the Royal Society in April, 1783. The letter was not read, however, until a year later, and, three months after, a paper by Cavendish, making the same announcement, had been laid before the Society. Watt stated that both Cavendish and Lavoisier, to whom also the discovery is ascribed, received the idea from him. The action of chlorine in bleaching organic coloring-matters, by (as since shown) decomposing them and combining with their hydrogen, was made known to Watt by M. Berthollet, the distinguished French chemist, and the former immediately introduced its use into Great Britain, by inducing his father-in-law, Mr. Macgregor, to make a trial of it. The copartnership of Boulton & Watt terminated by limitation, and with the expiration of the patents under which they had been working, in the first year of the present century; and both partners, now old and feeble, withdrew from active business, leaving their sons to renew the agreement and to carry on the business under the same firm-style. Boulton, however, still interested himself in some branches of manufacture, especially in his mint, where he had coined many years and for several nations. Watt retired, a little later, to Heathfield, where he passed the remainder of his life in peaceful enjoyment of the society of his friends, in studies of all current matters of interest in science, as well as in engineering. One by one his old friends died--Black in 1799, Priestley, an exile to America, in 1803, and Robison a little later. Boulton died, at the age of eighty-one, August 17, 1809, and even the loss of this nearest and dearest of his friends outside the family was a less severe blow than that of his son Gregory, who died in 1804. Yet the great engineer and inventor was not depressed by the loneliness which was gradually coming upon him. He wrote: "I know that all men must die, and I submit to the decrees of Nature, I hope, with due reverence to the Disposer of events;" and neglected no opportunity to secure amusement or instruction, and kept body and mind constantly occupied. He still attended the weekly meetings of the club, meeting Rennie and Telford, and other distinguished men of his own and the succeeding generation. He lost nothing of his fondness for invention, and spent many months in devising a machine for copying statuary, which he had not perfected to his own satisfaction at the time of his death, ten years later. This machine was a kind of pentagraph, which could be worked in any plane, and in which the marking-pencil gave place to a cutting-tool. The tracing-point followed the surface of the pattern, while the cutting-point, following its motion precisely, formed a fac-simile in the material operated upon. In the year 1800 he invented the water-main which was laid down by the Glasgow Water-Works Company across the Clyde. The joints were spherical and articulated, like those of the lobster's tail. His workshop, of which a sketch is hereafter given, as drawn by the artist Skelton, was in the garret of his house, and was well supplied with tools and all kinds of laboratory material. His lathe and his copying-machine were placed before the window, and his writing-desk in the corner. Here he spent the greater part of his leisure time, often even taking his meals in the little shop, rather than go to the table for them. Even when very old, he occasionally made a journey to London or Glasgow, calling on his old friends and studying the latest engineering devices and inspecting public works, and was everywhere welcomed by young and old as the greatest living engineer, or as the kind and wise friend of earlier days. He died August 19, 1819, in the eighty-third year of his age, and was buried in Handsworth Church. The sculptor Chantrey was employed to place a fitting monument above his grave, and the nation erected a statue of the great man in Westminster Abbey. This sketch of the greatest of all the inventors of the steam-engine has been given no greater length than its subject justifies. Whether we consider Watt as the inventor of the standard steam-engine of the nineteenth century, as the scientific investigator of the physical principles upon which the invention is based, or as the builder and introducer of the most powerful known instrument by which the "great sources of power in Nature are converted, adapted, and applied for the use and convenience of man," he is fully entitled to preëminence. His character as a man was no less admirable than as an engineer. Smiles, Watt's most conscientious and indefatigable biographer, writes:[41] [41] "Life of Watt," p. 512. [Illustration: FIG. 35.--James Watt's Workshop. (From Smiles's "Lives of Boulton and Watt.")] "Some months since, we visited the little garret at Heathfield in which Watt pursued the investigations of his later years. The room had been carefully locked up since his death, and had only once been swept out. Everything lay very much as he left it. The piece of iron which he was last employed in turning, lay on the lathe. The ashes of the last fire were in the grate; the last bit of coal was in the scuttle. The Dutch oven was in its place over the stove, and the frying-pan in which he cooked his meals was hanging on its accustomed nail. Many objects lay about or in the drawers, indicating the pursuits which had been interrupted by death--busts, medallions, and figures, waiting to be copied by the copying-machine--many medallion-moulds, a store of plaster-of-Paris, and a box of plaster casts from London, the contents of which do not seem to have been disturbed. Here are Watt's ladles for melting lead, his foot-rule, his glue-pot, his hammer. Reflecting mirrors, an extemporized camera with the lenses mounted on pasteboard, and many camera-glasses laid about, indicate interrupted experiments in optics. There are quadrant-glasses, compasses, scales, weights, and sundry boxes of mathematical instruments, once doubtless highly prized. In one place a model of the governor, in another of the parallel-motion, and in a little box, fitted with wooden cylinders mounted with paper and covered with figures, is what we suppose to be a model of his calculating-machine. On the shelves are minerals and chemicals in pots and jars, on which the dust of nearly half a century has settled. The moist substances have long since dried up; the putty has been turned to stone, and the paste to dust. On one shelf we come upon a dish in which lies a withered bunch of grapes. On the floor, in a corner, near to where Watt sat and worked, is a hair-trunk--a touching memorial of a long-past love and a long-dead sorrow. It contains all poor Gregory's school-books, his first attempts at writing, his boy's drawings of battles, his first school-exercises down to his college-themes, his delectuses, his grammars, his dictionaries, and his class-books--brought into this retired room, where the father's eye could rest upon them. Near at hand is the sculpture-machine, on which he continued working to the last. Its wooden frame is worm-eaten, and dropping into dust, like the hands that made it. But though the great workman is gone to rest, with all his griefs and cares, and his handiwork is fast crumbling to decay, the spirit of his work, the thought which he put into his inventions, still survives, and will probably continue to influence the destinies of his race for all time to come." The visitor to Westminster Abbey will find neither monarch, nor warrior, nor statesman, nor poet, honored with a nobler epitaph than that which is inscribed on the pedestal of Chantrey's monument to Watt: NOT TO PERPETUATE A NAME, WHICH MUST ENDURE WHILE THE PEACEFUL ARTS FLOURISH, BUT TO SHOW THAT MANKIND HAVE LEARNT TO HONOR THOSE WHO BEST DESERVE THEIR GRATITUDE, THE KING, HIS MINISTERS, AND MANY OF THE NOBLES AND COMMONERS OF THE REALM, RAISED THIS MONUMENT TO JAMES WATT, WHO, DIRECTING THE FORCE OF AN ORIGINAL GENIUS, EARLY EXERCISED IN PHILOSOPHIC RESEARCH, TO THE IMPROVEMENT OF THE STEAM-ENGINE, ENLARGED THE RESOURCES OF HIS COUNTRY, INCREASED THE POWER OF MAN, AND ROSE TO AN EMINENT PLACE AMONG THE MOST ILLUSTRIOUS FOLLOWERS OF SCIENCE AND THE REAL BENEFACTORS OF THE WORLD. BORN AT GREENOCK, MDCCXXXVI. DIED AT HEATHFIELD, IN STAFFORDSHIRE, MDCCCXIX. [Illustration: Tomb of James Watt.] SECTION II.--THE CONTEMPORARIES OF JAMES WATT. In the chronology of the steam-engine, the contemporaries of Watt have been so completely overshadowed by the greater and more successful inventor, as to have been almost forgotten by the biographer and by the student of history. Yet, among the engineers and engine-builders, as well as among the inventors of his day, Watt found many enterprising rivals and keen competitors. Some of these men, had they not been so completely fettered by Watt's patents, would have probably done work which would have entitled them to far higher honor than has been accorded them. WILLIAM MURDOCH was one of the men to whom Watt, no less than the world, was greatly indebted. For many years he was the assistant, friend, and coadjutor of Watt; and it is to his ingenuity that we are to give credit for not only many independent inventions, but also for the suggestions and improvements which were often indispensable to the formation and perfection of some of Watt's own inventions. Murdoch was employed by Boulton & Watt in 1776, and was made superintendent of construction in the engine department, and given general charge of the erection of engines. He was sent into Cornwall, and spent in that district much of the time during which he served the firm, erecting pumping-engines, the construction of which for so many years constituted a large part of the business of the Soho establishment. He was looked upon by both Boulton and Watt as a sincere friend, as well as a loyal adherent, and from 1810 to 1830 was given a partner's share of the income of the firm, and a salary of £1,000. He retired from business at the last of the two dates named, and, dying in 1839, was buried near the two partners in Handsworth Church. Murdoch made a model, in 1784, of the locomotive patented by Watt in that year. He devised the arrangement of "sun-and-planet wheels," adopted for a time in all of Watt's "rotative" engines, and invented the oscillating steam-engine (Fig. 36) in 1785, using the "D-slide valves," _G_, moved by the gear, _E_, which was driven by an eccentric on the shaft, without regard to the oscillation of the cylinder, _A_. He was the inventor of a rotary engine and of many minor machines for special purposes, and of many machine-tools used at Soho in building engines and machines. He seems, like Watt, to have had special fondness for the worm-gear, and introduced it wherever it could properly take the place of ordinary gearing. Some of the machines designed by Watt and Murdoch, who always worked well together, were found still in use and in good working condition by the author when visiting the works at Soho in 1873. The old mint in which, from 1797 to 1805, Boulton had coined 4,000 tons of copper, had then been pulled down, and a new mint had been erected in 1860. Many old machines still remained about the establishment as souvenirs of the three great mechanics. [Illustration: FIG. 36.--Murdoch's Oscillating Engine, 1785.] Outside of Soho, Murdoch also found ample employment for his inventive talent. In 1792, while at Redruth, his residence before finally returning to Soho, he was led to speculate upon the possibility of utilizing the illuminating qualities of coal-gas, and, convinced of its practicability, he laid the subject before the Royal Society in 1808, and was awarded the Rumford gold medal. He had, ten years earlier, lighted a part of the Soho works with coal-gas, and in 1803 Watt authorized him to extend his pipes throughout all the buildings. Several manufacturers promptly introduced the new light, and its use extended very rapidly. Still another of Murdoch's favorite schemes was the transmission of power by the use of compressed air. He drove the pattern-shop engine at Soho by means of air from the blowing-engine in the foundery, and erected a pneumatic lift to elevate castings from the foundery-floor to the canal-bank. He made a steam-gun, introduced the heating of buildings by the circulation of hot water, and invented the method of transmitting packages through tubes by the impulse of compressed air, as now practised by the "pneumatic dispatch" companies. He died at the age of eighty-five years. Among the most active and formidable of Watt's business rivals was JONATHAN HORNBLOWER, the patentee of the "compound" or double-cylinder engine. A sketch of this engine, as patented by Hornblower in 1781, is here given (Fig. 37). It was first described by the inventor in the "Encyclopædia Britannica." It consists, as is seen by reference to the engraving, of two steam-cylinders, _A_ and _B_--_A_ being the low and _B_ the high pressure cylinder--the steam leaving the latter being exhausted into the former, and, after doing its work there, passing into the condenser, as already described. The piston-rods, _C_ and _D_, are both connected to the same part of the beam by chains, as in the other early engines. These rods pass through stuffing-boxes in the cylinder-heads, which are fitted up like those seen on the Watt engine. Steam is led to the engine through the pipe, _G Y_, and cocks, _a_, _b_, _c_, and _d_, are adjustable, as required, to lead steam into and from the cylinders, and are moved by the plug-rod, _W_, which actuates handles not shown. _K_ is the exhaust-pipe leading to the condenser. _V_ is the engine feed-pump rod, and _X_ the great rod carrying the pump-buckets at the bottom of the shaft. The cocks _c_ and _a_ being open and _b_ and _d_ shut, the steam passes from the boiler into the upper part of the steam-cylinder, _B_; and the communication between the lower part of _B_ and the top of _A_ is also open. Before starting, steam being shut off from the engine, the great weight of the pump-rod, _X_, causes that end of the beam to preponderate, the pistons standing, as shown, at the top of their respective steam-cylinders. The engine being freed from all air by opening all the valves and permitting the steam to drive it through the engine and out of the condenser through the "snifting-valve," _O_, the valves _b_ and _d_ are closed, and the cock in the exhaust-pipe opened. [Illustration: FIG. 37.--Hornblower's Compound Engine, 1781.] The steam beneath the piston of the large cylinder is immediately condensed, and the pressure on the upper side of that piston causes it to descend, carrying that end of the beam with it, and raising the opposite end with the pump-rods and their attachments. At the same time, the steam from the lower end of the small high-pressure cylinder being let into the upper end of the larger cylinder, the completion of the stroke finds a cylinder full of steam transferred from the one to the other with corresponding increase of volume and decrease of pressure. While expanding and diminishing in pressure as it passes from the smaller into the larger cylinder, this charge of steam gradually resists less and less the pressure of the steam from the boiler on the upper side of the piston of the small cylinder, _B_, and the net result is the movement of the engine by pressures exerted on the upper sides of both pistons and against pressures of less intensity on the under sides of both. The pressures in the lower part of the small cylinder, in the upper part of the large cylinder, and in the communicating passage, are evidently all equal at any given time. When the pistons have reached the bottoms of their respective cylinders, the valves at the top of the small cylinder, _B_, and at the bottom of the large cylinder, _A_, are closed, and the valves _c_ and _d_ are opened. Steam from the boiler now enters beneath the piston of the small cylinder; the steam in the larger cylinder is exhausted into the condenser, and the steam already in the small cylinder passes over into the large cylinder, following up the piston as it rises. Thus, at each stroke a small cylinder full of steam is taken from the boiler, and the same weight, occupying the volume of the larger cylinder, is exhausted into the condenser from the latter cylinder. Referring to the method of operation of this engine, Prof. Robison demonstrated that the effect produced was the same as in Watt's single-cylinder engine--a fact which is comprehended in the law enunciated many years later by Rankine, that, "so far as the theoretical action of the steam on the piston is concerned, it is immaterial whether the expansion takes place in one cylinder, or in two or more cylinders." It was found, in practice, that the Hornblower engine was no more economical than the Watt engine; and that erected at the Tin Croft Mine, Cornwall, in 1792, did even less work with the same fuel than the Watt engines. Hornblower was prosecuted by Boulton & Watt for infringement. The suit was decided against him, and he was imprisoned in default of payment of the royalty, and fine demanded. He died a disappointed and impoverished man. The plan thus unsuccessfully introduced by Hornblower was subsequently modified and adopted by others among the contemporaries of Watt; and, with higher steam and the use of the Watt condenser, the "compound" gradually became a standard type of steam-engine. Arthur Woolf, in 1804, re-introduced the Hornblower or Falck engine, with its two steam-cylinders, using steam of higher tension. His first engine was built for a brewery in London, and a considerable number were subsequently made. Woolf expanded his steam from six to nine times, and the pumping-engines built from his plans were said to have raised about 40,000,000 pounds one foot high per bushel of coals, when the Watt engine was raising but little more than 30,000,000. In one case, a duty of 57,000,000 was claimed. The most successful of those competitors of Watt who endeavored to devise a peculiar form of pumping-engine, which should have the efficiency of that of Boulton & Watt, and the necessary advantage in first cost, were WILLIAM BULL and RICHARD TREVITHICK.[42] The accompanying illustration shows the design, which was then known as the "Bull Cornish Engine." [42] For an exceedingly interesting and very faithful account of their work, _see_ "Life of Richard Trevithick," by F. Trevithick, London, 1872. [Illustration: FIG. 88.--Bull's Pumping-Engine, 1798.] The steam-cylinder, _a_, is carried on wooden beams, _b_, extending across the engine-house directly over the pump-well. The piston-rod, _c_, is secured to the pump-rods, _d d_, the cylinder being inverted, and the pumps, _e_, in the shaft, _f_, are thus operated without the intervention of the beam invariably seen in Watt's engines. A connecting-rod, _g_, attached to the pump-rod and to the end of a balance-beam, _h_, operates the latter, and is counterbalanced by a weight, _i_. The rod, _j_, serves both as a plug-rod and as an air-pump connecting-rod. A snifting-valve, _k_, opens when the engine is blown through, and relieves the condenser and air-pump, _l_, of all air. The rod, _m_, operates a solid air-pump piston, the valves of the pump being placed on either side at the base, instead of in the pump-bucket, as in Watt's engines. The condensing-water cistern was a wooden tank, _n_. A jet "pipe-condenser," _o_, was used instead of a jet condenser of the form adopted by other makers, and was supplied with water through the cock, _p_. The plug-rod, _q_, as it rises and falls with the pump-rods and balance-beam, operates the "gear-handles," _r r_, and opens and closes the valves, _s s_, at the required points in the stroke. The attendant works these valves by hand, in starting, from the floor, _t_. The operation of the engine is similar to that of a Watt engine. It is still in use, with a few modifications and improvements, and is a very economical and durable machine. It has not been as generally adopted, however, as it would probably have been had not the legal proscription of Watt's patents so seriously interfered with its introduction. Its simplicity and lightness are decided advantages, and its designers are entitled to great credit for their boldness and ingenuity, as displayed in their application of the minor devices which distinguish the engine. The design is probably to be credited to Bull originally; but Trevithick built some of these engines, and is supposed to have greatly improved them while working with Edward Bull, the son of the inventor, William Bull. One of these engines was erected by them at the Herland Mine, Cornwall, in 1798, which had a steam-cylinder 60 inches in diameter, and was built on the plan just described. Another of the contemporaries of James Watt was a clergyman, EDWARD CARTWRIGHT, the distinguished inventor of the power-loom, and of the first machine ever used in combing wool, who revived Watt's plan of surface-condensation in a somewhat modified form. Watt had made a "pipe-condenser," similar in plan to those now often used, but had simply immersed it in a tank of water, instead of in a constantly-flowing stream. Cartwright proposed to use two concentric cylinders or spheres, between which the steam entered when exhausted from the cylinder of the engine, and was condensed by contact with the metal surfaces. Cold water within the smaller and surrounding the exterior vessel kept the metal cold, and absorbed the heat discharged by the condensing vapor. Cartwright's engine is best described in the _Philosophical Magazine_ of June, 1798, from which the accompanying sketch is copied. [Illustration: FIG. 39.--Cartwright's Engine, 1798.] The object of the inventor is stated to have been to remedy the defects of the Watt engine--imperfect vacuum, friction, and complication. In the figure, the steam-cylinder takes steam through the pipe, _B_. The piston, _R_, has a rod extending downward to the smaller pump-piston, _G_, and upward to the cross-head, which, in turn, drives the cranks above, by means of connecting-rods. The shafts thus turned are connected by a pair of gears, _M L_, of which one drives a pinion on the shaft of the fly-wheel. _D_ is the exhaust-pipe leading to the condenser, _F_; and the pump, _G_, removes the air and water of condensation, forcing it into the hot-well, _H_, whence it is returned to the boiler through the pipe, _I_. A float in _H_ adjusts an air-valve, so as to keep a supply of air in the chamber, to serve as a cushion and to make an air-chamber of the reservoir, and permits the excess to escape. The large tank contains the water supplied for condensing the steam. The piston, _R_, is made of metal, and is packed with two sets of cut metal rings, forced out against the sides of the cylinder by steel springs, the rings being cut at three points in the circumference, and kept in place by the springs. The arrangement of the two cranks, with their shafts and gears, is intended to supersede Watt's plan for securing a perfectly rectilinear movement of the head of the piston-rod, without friction. In the accounts given of this engine, great stress is laid upon the supposed important advantage here offered, by the introduction of the surface-condenser, of permitting the employment of a working-fluid other than steam--as, for example, alcohol, which is too valuable to be lost. It was proposed to use the engine in connection with a still, and thus to effect great economy by making the fuel do double duty. The only part of the plan which proved both novel and valuable was the metallic packing and piston, which has not yet been superseded. The engine itself never came into use. At this point, the history of the steam-engine becomes the story of its applications in several different directions, the most important of which are the raising of water--which had hitherto been its only application--the locomotive-engine, the driving of mill-machinery, and steam-navigation. Here we take leave of James Watt and of his contemporaries, of the former of whom a French author[43] says: "The part which he played in the mechanical applications of the power of steam can only be compared to that of Newton in astronomy and of Shakespeare in poetry." Since the time of Watt, improvements have been made principally in matters of mere detail, and in the extension of the range of application of the steam-engine. [43] Bataille. "Traité des Machines à Vapeur," Paris, 1847. [Illustration] CHAPTER IV. _THE MODERN STEAM-ENGINE._ "Those projects which abridge distance have done most for the civilization and happiness of our species."--MACAULAY. THE SECOND PERIOD OF APPLICATION--1800-'40. STEAM-LOCOMOTION ON RAILROADS. [Illustration: FIG. 40.--The First Railroad-Car, 1825.] Introductory.--The commencement of the nineteenth century found the modern steam-engine fully developed in all its principal features, and fairly at work in many departments of industry. The genius of Worcester, and Morland, and Savery, and Desaguliers, had, in the first period of the application of the power of steam to useful work, effected a beginning which, looked upon from a point of view which exhibits its importance as the first step toward the wonderful results to-day familiar to every one, appears in its true light, and entitles those great men to even greater honor than has been accorded them. The results actually accomplished, however, were absolutely insignificant in comparison with those which marked the period of development just described. Yet even the work of Watt and of his contemporaries was but a mere prelude to the marvellous advances made in the succeeding period, to which we are now come, and, in extent and importance, was insignificant in comparison with that accomplished by their successors in the development of all mechanical industries by the application of the steam-engine to the movement of every kind of machine. The first of the two periods of application saw the steam-engine adapted simply to the elevation of water and the drainage of mines; during the second period it was adapted to every variety of useful work, and introduced wherever the muscular strength of men and animals, or the power of wind and of falling water, which had previously been the only motors, had found application. A history of the development of industries by the introduction of steam-power during this period, would be no less extended and hardly less interesting than that of the steam-engine itself. The way had been fairly opened by Boulton and Watt; and the year 1800 saw a crowd of engineers and manufacturers entering upon it, eager to reap the harvest of distinction and of pecuniary returns which seemed so promising to all. The last year of the eighteenth century was also the last of the twenty-five years of partnership of Boulton & Watt, and, with it, the patents under which that firm had held the great monopoly of steam-engine building expired. The right to manufacture the modern steam-engine was common to all. Watt had, at the commencement of the new century, retired from active business-life. Boulton remained in business; but he was not the inventor of the new engine, and could not retain, by the exercise of all his remaining power, the privileges previously held by legal authorization. The young Boulton and the young Watt were not the Boulton & Watt of earlier years; and, had they possessed all of the business talent and all of the inventive genius of their fathers, they could not have retained control of a business which was now growing far more rapidly than the facilities for manufacturing could be extended in any single establishment. All over the country, and even on the Continent of Europe, and in America, thousands of mechanics, and many men of mechanical tastes in other professions, were familiar with the principles of the new machine, and were speculating upon its value for all the purposes to which it has since been applied; and a multitude of enthusiastic mechanics, and a larger multitude of visionary and ignorant schemers, were experimenting with every imaginable device, in the vain hope of attaining perpetual motion, and other hardly less absurd results, by its modification and improvement. Steam-engine building establishments sprang up wherever a mechanic had succeeded in erecting a workshop and in acquiring a local reputation as a worker in metal, and many of Watt's workmen went out from Soho to take charge of the work done in these shops. Nearly all of the great establishments which are to-day most noted for their extent and for the importance and magnitude of the work done in them, not only in Great Britain, but in Europe and the United States, came into existence during this second period of the application of the steam-engine as a prime mover. The new establishments usually grew out of older shops of a less pretentious character, and were managed by men who had been trained by Watt, or who had had a still more awakening experience with those who vainly strove to make up, by their ingenuity and by great excellence of workmanship, the advantages possessed at Soho in a legal monopoly and greater experience in the business. It was exceedingly difficult to find expert and conscientious workmen, and machine-tools had not become as thoroughly perfected as had the steam-engine itself. These difficulties were gradually overcome, however, and thenceforward the growth of the business was increasingly rapid. Every important form of engine had now been invented. Watt had perfected, with the aid of Murdoch, both the pumping-engine and the rotative steam-engine for application to mills. He had invented the trunk engine, and Murdoch had devised the oscillating engine and the ordinary slide-valve, and had made a model locomotive-engine, while Hornblower had introduced the compound engine. The application of steam to navigation had been often proposed, and had sometimes been attempted, with sufficient success to indicate to the intelligent observer an ultimate triumph. It only remained to extend the use of steam as a motor into all known departments of industry, and to effect such improvements in details as experience should prove desirable. The engines of Hero, of Porta, and of Branca were, it will be remembered, non-condensing; but the first plan of a non-condensing engine that could be made of any really practical use is given in the "Theatrum Machinarum" of Leupold, published in 1720. This sketch is copied in Fig. 41. It is stated by Leupold that this plan was suggested by Papin. It consists of two single-acting cylinders, _r s_, receiving steam alternately from the same steam-pipe through a "four-way cock," _x_, and exhausting into the atmosphere. Steam is furnished by the boiler, _a_, and the pistons, _c d_, are alternately raised and depressed, depressing and raising the pump-rods, _k l_, to which they are attached by the beams, _h g_, vibrating on the centres, _i i_. The water from the pumps, _o p_, is forced up the stand-pipe, _q_, and discharged at its top. The alternate action of the steam-pistons is secured by turning the "four-way cock," _x_, first into the position shown, and then, at the completion of the stroke, into the reverse position, by which change the steam from the boiler is then led into the cylinder, _s_, and the steam in _r_ is discharged into the atmosphere.[44] [44] _Vide_ "Theatrum Machinarum," vol. iii., Tab. 30. [Illustration: FIG. 41.--Leupold's Engine, 1720.] Leupold states that he is indebted to Papin for the suggestion of the peculiar valve here used. He also proposed to use a Savery engine without condensation in raising water. We have no evidence that this engine was ever built. The first rude scheme for applying steam to locomotion on land was probably that of Isaac Newton, who, in 1680, proposed the machine shown in the accompanying figure (42), which will be recognized as representing the scientific toy which is found in nearly every collection of illustrative philosophical apparatus. As described in the "Explanation of the Newtonian Philosophy," it consists of a spherical boiler, _B_, mounted on a carriage. Steam issuing from the pipe, _C_, seen pointing directly backward, by its reaction upon the carriage, drives the latter ahead. The driver, sitting at _A_, controls the steam by the handle, _E_, and cock, _F_. The fire is seen at _D_. [Illustration: FIG. 42.--Newton's Steam-Carriage, 1680.] When, at the end of the eighteenth century, the steam-engine had been so far perfected that the possibility of its successful application to locomotion had become fully and very generally recognized, the problem of adapting it to locomotion on land was attacked by many inventors. Dr. Robison had, as far back as in 1759, proposed it to James Watt during one of their conferences, at a time when the latter was even more ignorant than the former of the principles which were involved in the construction of the steam-engine, and this suggestion may have had some influence in determining Watt to pursue his research; thus setting in operation that train of thoughtful investigation and experiment which finally earned for him his splendid fame. In 1765, that singular genius, Dr. Erasmus Darwin, whose celebrity was acquired by speculations in poetry and philosophy as well as in medicine, urged Matthew Boulton--subsequently Watt's partner, and just then corresponding with our own Franklin in relation to the use of steam-power--to construct a steam-carriage, or "fiery chariot," as he poetically styled it, and of which he sketched a set of plans. A young man named Edgeworth became interested in the scheme, and, in 1768, published a paper which had secured for him a gold medal from the Society of Arts. In this paper he proposed railroads on which the carriages were to be drawn by horses, _or by ropes from steam-winding engines_. [Illustration: FIG. 43.--Read's Steam-Carriage, 1790.] Nathan Read, of whom an account will be given hereafter, when describing his attempt to introduce steam-navigation, planned, and in 1790 obtained a patent for, a steam-carriage, of which the sketch seen in Fig. 43 is copied from the rough drawing accompanying his application. In the figure, _A A A A_ are the wheels; _B B_, pinions on the hubs of the rear wheels, which are driven by a ratchet arrangement on the racks, _G G_, connected with the piston-rods; _C o_ is the boiler; _D D_, the steam-pipes carrying steam to the steam-cylinder, _E E_; _F F_ are the engine-frames; _H_ is the "tongue" or "pole" of the carriage, and is turned by a horizontal steering-wheel, with which it is connected by the ropes or chains, _I K_, _I K_; _W W_ are the cocks, which serve to shut off steam from the engine when necessary, and to determine the amount of steam to be admitted. The pipes _a a_ are exhaust-pipes, which the inventor proposed to turn so that they should point backward, in order to secure the advantage of the effort of reaction of the expelled steam. (!) Read made a model steam-carriage, which he exhibited when endeavoring to secure assistance in furtherance of his schemes, but seems to have given more attention to steam-navigation, and nothing was ever accomplished by him in this direction. These were merely promising schemes, however. The first actual experiment was made, as is supposed, by a French army-officer, NICHOLAS JOSEPH CUGNOT, who in 1769 built a steam-carriage, which was set at work in presence of the French Minister of War, the Duke de Choiseul. The funds required by him were furnished by the Compte de Saxe. Encouraged by the partial success of the first locomotive, he, in 1770, constructed a second (Fig. 44), which is still preserved in the Conservatoire des Arts et Métiers, Paris. [Illustration: FIG. 44.--Cugnot's Steam-Carriage, 1770.] This machine, when recently examined by the author, was still in an excellent state of preservation. The carriage and its machinery are substantially built and well-finished, and exceedingly creditable pieces of work in every respect. It surprises the engineer to find such evidence of the high character of the work of the mechanic Brezin a century ago. The steam-cylinders were 13 inches in diameter, and the engine was evidently of considerable power. This locomotive was intended for the transportation of artillery. It consists of two beams of heavy timber extending from end to end, supported by two strong wheels behind, and one still heavier but smaller wheel in front. The latter carries on its rim blocks which cut into the soil as the wheel turns, and thus give greater holding power. The single wheel is turned by two single-acting engines, one on each side, supplied with steam by a boiler (seen in the sketch) suspended in front of the machine. The connection between the engines and the wheels was effected by means of pawls, as first proposed by Papin, which could be reversed when it was desired to drive the machine backward. A seat is mounted on the carriage-body for the driver, who steers the machine by a train of gearing, which turns the whole frame, carrying the machinery 15 or 20 degrees either way. This locomotive was found to have been built on a tolerably satisfactory general plan; but the boiler was too small, and the steering apparatus was incapable of handling the carriage with promptness. The death of one of Cugnot's patrons, and the exile of the other, put an end to Cugnot's experiments. Cugnot was a mechanic by choice, and exhibited great talent. He was a native of Vaud, in Lorraine, where he was born in 1725. He served both in the French and the German armies. While under the Maréchal de Saxe, he constructed his first steam locomotive-engine, which only disappointed him, as he stated, in consequence of the inefficiency of the feed-pumps. The second was that built under the authority of the Minister Choiseul, and cost 20,000 livres. Cugnot received from the French Government a pension of 600 livres. He died in 1804, at the age of seventy-nine years. Watt, at a very early period, proposed to apply his own engine to locomotion, and contemplated using either a non-condensing engine or an air-surface condenser. He actually included the locomotive-engine in his patent of 1784; and his assistant, Murdoch, in the same year, made a working-model locomotive (Fig. 45), which was capable of running at a rapid rate. This model, now deposited in the Patent Museum at South Kensington, London, had a flue-boiler, and its steam-cylinder was three-fourths of an inch in diameter, and the stroke of piston 2 inches. The driving-wheels were 9-1/2 inches diameter. [Illustration: FIG. 45.--Murdoch's Model, 1784.] Nothing was, however, done on a larger scale by either Watt or Murdoch, who both found more than enough to claim their attention in the construction and introduction of other engines. Murdoch's model is said to have run from 6 to 8 miles an hour, its little driving-wheels making from 200 to 275 revolutions per minute. As is seen in the sketch, this model was fitted with the same form of engine, known as the "grasshopper-engine," which was used in the United States by Oliver Evans. "To Oliver Evans," says Dr. Ernest Alban, the distinguished German engineer, "was it reserved to show the true value of a long-known principle, and to establish thereon a new and more simple method of applying the power of steam--a method that will remain an eternal memorial to its introducer." Dr. Alban here refers to the earliest permanently successful introduction of the non-condensing high-pressure steam-engine. OLIVER EVANS, one of the most ingenious mechanics that America has ever produced, was born at Newport, Del., in 1755 or 1756, the son of people in very humble circumstances. [Illustration: Oliver Evans.] He was, in his youth, apprenticed to a wheelwright, and soon exhibited great mechanical talent and a strong desire to acquire knowledge. His attention was, at an early period, drawn to the possible application of the power of steam to useful purposes by the boyish pranks of one of his comrades, who, placing a small quantity of water in a gun-barrel, and ramming down a tight wad, put the barrel in the fire of a blacksmith's forge. The loud report which accompanied the expulsion of the wad was an evidence to young Evans of great and (as he supposed) previously undiscovered power. Subsequently meeting with a description of a Newcomen engine, he at once noticed that the elastic force of confined steam was not there utilized. He then designed the non-condensing engine, in which the power was derived exclusively from the tension of high-pressure steam, and proposed its application to the propulsion of carriages. About the year 1780, Evans joined his brothers, who were millers by occupation, and at once employed his inventive talent in improving the details of mill-work, and with such success as to reduce the cost of attendance one-half, and also to increase the fineness of the flour made. He proved himself a very expert millwright. In 1786 he applied to the Pennsylvania Legislature for a patent for the application of the steam-engine to driving mills, and to the steam-carriage, but was refused it. In 1800 or 1801, Evans, after consultation with Professor Robert Patterson, of the University of Pennsylvania, and getting his approval of the plans, commenced the construction of a steam-carriage to be driven by a non-condensing engine. He soon concluded, however, that it would be a better scheme, pecuniarily, to adapt his engine, which was novel in form and of small first cost, to driving mills; and he accordingly changed his plans, and built an engine of 6 inches diameter of cylinder and 18 inches stroke of piston, which he applied with perfect success to driving a plaster-mill. This engine, which he called the "Columbian Engine," was of a peculiar form, as seen in Fig. 46. The beam is supported at one end by a rocking column; at the other, it is attached directly to the piston-rod, while the crank lies beneath the beam, the connecting-rod, 1, being attached to the latter at the extreme end. The head of the piston-rod is compelled to rise and fall in a vertical line by the "Evans's parallelogram"--a kind of parallel-motion very similar to one of those designed by Watt. In the sketch (Fig. 46), 2 is the crank, 3 the valve-motion, 4 the steam-pipe from the boiler, _E_, 5 6 7 the feed-pipe leading from the pump, _F_. _A_ is the boiler. The flame from the fire on the grate, _H_, passes under the boiler between brick walls, and back through a central flue to the chimney, _I_. [Illustration: FIG. 46.--Evans's Non-condensing Engine, 1800.] Subsequently, Evans continued to extend the applications of his engine and to perfect its details; and, others following in his track, the non-condensing engine is to-day fulfilling the predictions which he made 70 years ago, when he said: "I have no doubt that my engines will propel boats against the current of the Mississippi, and wagons on turnpike roads, with great profit...." "The time will come when people will travel in stages moved by steam-engines from one city to another, almost as fast as birds can fly, 15 or 20 miles an hour.... A carriage will start from Washington in the morning, the passengers will breakfast at Baltimore, dine at Philadelphia, and sup in New York the same day.... "Engines will drive boats 10 or 12 miles an hour, and there will be hundreds of steamers running on the Mississippi, as predicted years ago."[45] [45] Evans's prediction is less remarkable than that of Darwin, elsewhere quoted. In 1804, Evans applied one of his engines in the transportation of a large flat-bottomed craft, built on an order of the Board of Health of Philadelphia, for use in clearing some of the docks along the water-front of the city. Mounting it on wheels, he placed in it one of his 5-horse power engines, and named the odd machine (Fig. 47) "Oruktor Amphibolis." This steam dredging-machine, weighing about 40,000 pounds, was then propelled very slowly from the works, up Market Street, around to the Water-Works, and then launched into the Schuylkill. The engine was then applied to the paddle-wheel at the stern, and drove the craft down the river to its confluence with the Delaware. [Illustration: FIG. 47.--Evans's "Oruktor Amphibolis," 1804.] In September of the same year, Evans laid before the Lancaster Turnpike Company a statement of the estimated expenses and profits of steam-transportation on the common road, assuming the size of the carriage used to be sufficient for transporting 100 barrels of flour 50 miles in 24 hours, and placed in competition with 10 wagons drawn by 5 horses each. In the sketch above given of the "Oruktor Amphibolis," the engine is seen to resemble that previously described. The wheel, _A_, is driven by a rod depending from the end of a beam, _B´ B_, the other end of which is supported at _E_ by the frame, _E F G_. The body of the machine is carried on wheels, _K K_, driven by belts, _M M_, from the pulley on the shaft carrying _A_. The paddle-wheel is seen at _W_. Evans had some time previously sent Joseph Sampson to England with copies of his plans, and by him they were shown to Trevithick, Vivian, and other British engineers. Among other devices, the now familiar Cornish boiler, having a single internal flue, and the Lancashire boiler, having a pair of internal flues, were planned and used by Evans. At about the time that he was engaged on his steam dredging-machine, Evans communicated with Messrs. McKeever & Valcourt, who contracted with him to build an engine for a steam-vessel to ply between New Orleans and Natchez on the Mississippi, the hull of the vessel to be built on the river, and the machinery to be sent to the first-named city to be set up in the boat. Financial difficulties and low water combined to prevent the completion of the steamer, and the engine was set at work driving a saw-mill, where, until the mill was destroyed by fire, it sawed lumber at the rate of 250 feet of boards per hour. Evans never succeeded in accomplishing in America as great a success as had rewarded Watt in Great Britain; but he continued to build steam-engines to the end of his life, April 19, 1819, and was succeeded by his sons-in-law, James Rush and David Muhlenberg. He exhibited equal intelligence and ingenuity in perfecting the processes of milling, and in effecting improvements in his own business, that of the millwright. When but twenty-four years old, he invented a machine for making the wire teeth used in cotton and woolen cards, turning them out at the rate of 3,000 per minute. A little later he invented a card-setting machine, which cut the wire from the reel, bent the teeth, and inserted them. In milling, he invented a whole series of machines and attachments, including the elevator, the "conveyor," the "hopper-box," the "drill," and the "descender," and enabled the miller to make finer flour, gaining over 20 pounds to the barrel, and to do this at half the former cost of attendance. The introduction of his improvements into Ellicott's mills, near Baltimore, where 325 barrels of flour were made per day, was calculated to have saved nearly $5,000 per year in cost of labor, and over $30,000 by increasing the production. He wrote "The Young Steam-Engineer's Guide," and a work which remained standard many years after his death, "The Young Millwright's Guide." Less fortunate than his transatlantic rival, he was nevertheless equally deserving of fame. He has sometimes been called "The Watt of America." The application of steam to locomotion on the common road was much more successful in Great Britain than in the United States. As early as 1786, William Symmington, subsequently more successful in his efforts to introduce steam for marine propulsion, assisted by his father, made a working model of a steam-carriage, which did not, however, lead to important results. In 1802, Richard Trevithick, a pupil of Murdoch's, who afterward became well known in connection with the introduction of railroads, made a model steam-carriage, which was patented in the same year. The model may still be seen in the Patent Museum at South Kensington.[46] [46] _See_ "Life of Trevithick." In this engine, high-pressure steam was employed, and the condenser was dispensed with. The boiler was of the form devised by Evans, and was subsequently generally used in Cornwall, where it was called the "Trevithick Boiler." The engine had but one cylinder, and the piston-rod drove a "cross-tail," working in guides, which was connected with a "cross-head" on the opposite side of the shaft by two "side-rods." The connecting-rod was attached to the cross-head and the crank, "returning" toward the cylinder as the shaft lay between the latter and the cross-head. This was probably the first example of the now common "return connecting-rod engine." The connection between the crank-shaft and the wheels of the carriage was effected by gearing. The valve-gear and the feed-pumps were worked from the engine-shaft. The inventor proposed to secure his wheels against slipping by projecting bolts, when necessary, through the rim of the wheel into the ground. The first carriage of full size was built by Trevithick and Vivian at Camborne, in 1803, and, after trial, was taken to London, where it was exhibited to the public. _En route_, it was driven by its own engines to Plymouth, 90 miles from Camborne, and then shipped by water. It is not known whether the inventor lost faith in his invention; but he very soon dismantled the machine, sold the engine and carriage separately, and returned to Cornwall, where he soon began work on a railroad-locomotive. In 1821, Julius Griffiths, of Brompton, Middlesex, England, patented a steam-carriage for the transportation of passengers on the highway. His first road-locomotive was built in the same year by Joseph Bramah, one of the ablest mechanics of his time. The frame of the carriage carried a large double coach-body between the two axles, and the machinery was mounted over and behind the rear axle. One man was stationed on a rear platform, to manage the engine and to attend to the fire, and another, stationed in front of the body of the coach, handled the steering-wheel. The boiler was composed of horizontal water-tubes and steam-tubes, the latter being so situated as to receive heat from the furnace-gases _en route_ to the chimney, and thus to act as a superheater. The wheels were driven, by means of intermediate gearing, by two steam-engines, which, with their attachments, were suspended on helical springs, to prevent injury by jars and shocks. An air-surface condenser was used, consisting of flattened thin metal tubes, cooled by the contact of the external air, and discharging the water of condensation, as it accumulated within them, into a feed-pump, which, in turn, forced it into the lowest row of tubes in the boiler. The boiler did not prove large enough for continuous work; but the carriage was used experimentally, now and then, for a number of years. During the succeeding ten years the adaptation of the steam-engine to land-transportation continued to attract more and more attention, and experimental road-engines were built with steadily-increasing frequency. The defects of these engines revealing themselves on trial, they were one by one remedied, and the road-locomotive gradually assumed a shape which was mechanically satisfactory. Their final introduction into general use seemed at one time only a matter of time; their non-success was due to causes over which the legislator and the general public, and not the engineer, had control, as well as to the development of steam-transportation on a rival plan. In 1822, David Gordon patented a road-engine, but it is not known whether it was ever built. At about the same time, Mr. Goldsworthy Gurney, who subsequently took an active part in their introduction, stated, in his lectures, that "elementary power is capable of being applied to propel carriages along common roads with great political advantage, and the floating knowledge of the day places the object within reach." He made an ammonia-engine--probably the first ever made--and worked it so successfully, that he made use of it in driving a little locomotive. Two years later, Gordon patented a curious arrangement, which, however, had been proposed twelve years earlier by Brunton, and was again proposed afterward by Gurney, and others. This consisted in fitting to the engine a set of jointed legs, imitating, as nearly as the inventor could make them, the action of a horse's legs and feet. Such an arrangement was actually experimented with until it was found that they could not be made to work satisfactorily, when it was also found that they were not needed. During the same season, Burstall & Hill made a steam-carriage, and made many unsuccessful attempts to introduce their plan. The engine used was like that of Evans, except that the steam-cylinder was placed at the end of the beam, and the crank-shaft under the middle. The front and rear wheels were connected by a longitudinal shaft and bevel gearing. The boiler was found to have the usual defect, and would only supply steam for a speed of three or four miles an hour. The result was a costly failure. W. H. James, of London, in 1824-'25, proposed several devices for placing the working parts, as well as the body of the carriage, on springs, without interfering with their operation, and the Messrs. Seaward patented similar devices. Samuel Brown, in 1826, introduced a gas-engine, in which the piston was driven by the pressure produced by the combustion of gas, and a vacuum was secured by the condensation of the resulting vapor. Brown built a locomotive which he propelled by this engine. He ascended Shooter's Hill, near London, and the principal cause of his ultimate failure seems to have been the cost of operating the engine. From this date forward, during several years, a number of inventors and mechanics seem to have devoted their whole time to this promising scheme. Among them, Burstall & Hill, Gurney, Ogle & Summers, Sir Charles Dance, and Walter Hancock, were most successful. Gurney, in the year 1827, built a steam-carriage, which he kept at work nearly two years in and about London, and sometimes making long journeys. On one occasion he made the journey from Meksham to Cranford Bridge, a distance of 85 miles, in 10 hours, including all stops. He used the mechanical legs previously adopted by Brunton and by Gordon, but omitted this rude device in those engines subsequently built. Gurney's engine of 1828 is of interest to the engineer as exhibiting a very excellent arrangement of machinery, and as having one of the earliest of "sectional boilers." The latter was of peculiar form, and differed greatly in design from the sectional boiler invented a quarter of a century earlier by John Stevens, in the United States. [Illustration: FIG. 48.--Gurney's Steam-Carriage.] In the sketch (Fig. 48) this boiler is seen at the right. It was composed of bent [<]-shaped tubes, _a a_, connected to two cylinders, _b b_, the upper one of which was a steam-chamber. Vertical tubes connected these two chambers, and permitted a complete and regular circulation of the water. A separate reservoir, called a separator, _d_, was connected with these chambers by pipes, as shown. From the top of this separator a steam-pipe, _e e e_, conveyed steam to the engine-cylinders at _f_. The cranks, _g_, on the rear axle were turned by the engines, and the eccentric, _h_, on the axle drove the valve-gearing and the valve, _i_. The link, _k l_, being moved by a line, _l l_, led from the driver's seat, the carriage was started, stopped, or reversed, by throwing the upper end of the link into gear with the valve-stem, by setting the link midway between its upper and lower positions, or by raising it until the lower end, coming into action on the valve-stem, produced a reverse motion of the valve. The pin on which this link vibrated is seen at the centre of its elliptical strap. The throttle-valve, _o_, by which the supply of steam to the engine was adjusted, was worked by the lever, _n_. The exhaust-pipe, _p_, led to the tank, _q_, and the uncondensed vapor passed to the chimney, _s s_, by the pipe, _r r_. The force-pump, _u_, taking feed-water from the tank, _t_, supplied it to the boiler by the pipe, _x x x_, which, _en route_, was coiled up to form a "heater" directly above the boiler. The supply was regulated by the cock, _y_. The attendant had a seat at _z_. A blast-apparatus, 1, was driven by an independent engine, 2 3, and produced a forced blast, which was led to the boiler-furnace through the air-duct, 5 5; 4 4 represents the steam-pipe to the little blowing-engine. The steering-wheel, 6, was directed by a lever, 7, and the change of direction of the perch, 8, which turned about a king-bolt at 9, gave the desired direction to the forward wheels and to the carriage. This seems to have been one of the best designs brought out at that time. The boiler, built to carry 70 pounds, was safe and strong, and was tested up to 800 pounds pressure. A forced draught was provided. The engines were well placed, and of good design. The valve was arranged to work the steam with expansion from half-stroke. The feed-water was heated, and the steam slightly superheated. The boiler here used has been since reproduced under new names by later inventors, and is still used with satisfactory results. Modifications of the "pipe-boiler" were made by several other makers of steam-carriages also. Anderson & James made their boilers of lap-welded iron tubes of one inch internal diameter and one-fifth inch thick, and claimed for them perfect safety. Such tubes should have sufficient strength to sustain a pressure of 20,000 pounds per square inch. If made of such good iron as the makers claimed to have put into them, "which worked like lead," they would, as was also claimed, when ruptured, open by tearing, and discharge their contents without producing the usual disastrous consequences of boiler explosions. The primary principle of the sectional boiler was then well understood. The boilers of Ogle & Summers were made up of pairs of upright tubes, set one within the other, the intervening space being filled with water and steam, and the flame passing through the inner and around the outer tube of each pair. One of the engines of Sir James Anderson and W. H. James was built in 1829. It had two 3-1/2-inch steam-cylinders, driving the rear wheels independently. In James's earlier plan of 1824-'25, a pair of cylinders was attached to each of the two halves into which the rear axle was divided, and were arranged to drive cranks set at right-angles with each other. The later machine weighed 3 tons, and carried 15 passengers, on a rough graveled road across the Epping Forest, at the rate of from 12 to 15 miles per hour. Steam was carried at 300 pounds. Several tubes gave way in the welds, but the carriage returned, carrying 24 passengers at the rate of 7 miles per hour. On a later trial, with new boilers, the carriage again made 15 miles per hour. It was, however, subject to frequent accidents, and was finally withdrawn. WALTER HANCOCK was the most successful and persevering of all those who attempted the introduction of steam on the common road. He had, in 1827, patented a boiler of such peculiar form, that it deserves description. It consisted of a collection of flat chambers, of which the walls were of boiler-plate. These chambers were arranged side by side, and connected laterally by tubes and stays, and all were connected by short vertical tubes to a horizontal large pipe placed across the top of the boiler-casing, and serving as a steam-drum or separator. This earliest of "sheet flue-boilers" did excellent service on Hancock's steam-carriages, where experience showed that there was little or no danger of disruptive explosions. Hancock's first steam-carriage was mounted on three wheels, the leading-wheel arranged to swivel on a king-bolt, and driven by a pair of oscillating cylinders connected with its axle, which was "cranked" for the purpose. The engines turned with the steering-wheel. This carriage was by no means satisfactory, but it was used for a long time, and traveled many hundreds of miles without once failing to do the work assigned it. By this time there were a half-dozen steam-carriages under construction for Hancock, for Ogle & Summers, and for Sir Charles Dance. In 1831, Hancock placed a new carriage on a route between London and Stratford, where it ran regularly for hire. Dance, in the same season, started another on the line between Cheltenham and Gloucester, where it ran from February 21st to June 22d, traveling 3,500 miles and carrying 3,000 passengers, running the 9 miles in 55 minutes usually, and sometimes in three-quarters of an hour, and never meeting with an accident, except the breakage of an axle in running over heaps of stones which had been purposely placed on the road by enemies of the new system of transportation. Ogle & Summers's carriage attained a speed, as testified by Ogle before a committee of the House of Commons, of from 32 to 35 miles an hour, and on a rising grade, near Southampton, at 24-1/2 miles per hour. They carried 250 pounds of steam, ran 800 miles, and met with no accident. Colonel Macerone, in 1833, ran a steam-carriage of his own design from London to Windsor and back, with 11 passengers, a distance of 23-1/2 miles, in 2 hours. Sir Charles Dance, in the same year, ran his carriage 16 miles an hour, and made long excursions at the rate of 9 miles an hour. Still another experimenter, Heaton, ascended Lickey Hill, between Worcester and Birmingham, on gradients of one in eight and one in nine, in places; this was considered one of the worst pieces of road in England. The carriage towed a coach containing 20 passengers. Of all these, and many others, Hancock, however, had most marked success. His coach, called the "Infant," which was set at work in February, 1831, was, a year later, plying between London "City" and Paddington. Another, called the "Era," was built for the London and Greenwich Steam-Carriage Company, which was mechanically a success. The company, however, was financially unsuccessful. In October, 1832, the "Infant" ran to Brighton from London, carrying a party of 11, at the rate of 9 miles per hour, ascending Redhill at a speed of 5 miles. They steamed 38 miles the first day, stopping at night at Hazledean, and reached Brighton next day, running 11 miles per hour. Returning with 15 passengers, the coach ran 1 mile in less than 4 minutes, and made 10 miles in 55 minutes. A run from Stratford to Brighton was made in less than 10 hours, at an average speed of 12 miles an hour running time, the actual running time being less than 6 hours. The next year another carriage, the "Enterprise," was put on the road to Paddington by Hancock for another company, and ran regularly over two weeks; but this company was also unsuccessful. In the summer of 1833 he brought out still another steam-coach, the "Autopsy" (Fig. 49), which he ran to Brighton, and then, returning to London, man[oe]uvred the carriage in the crowded streets without difficulty or accident. He went about the streets of London at all times, and without hesitation. The coach next ran between Finsbury Square and Pentonville regularly for four weeks, without accident or delay. In the sketch, a part of the side is broken away to show the machinery. The boiler, _A B_, supplies steam through the steam-pipe, _H K_, to the steam-engine, _C D_, which is coupled to the crank-shaft, _F_. _E_ is the feed-pump. The rear axle is turned by the endless chain seen connecting it with the engine-shaft, and the rear wheels, _S_, are thus driven. A blower, _T_, gives a forced draught. The driver sits at _M_, steering by the wheel, _N_, which is coupled to the larger wheel, _P_, and thus turns the forward axle into any desired position. In 1834, Hancock built a steam "drag" on an Austrian order, which, carrying 10 persons and towing a coach containing 6 passengers, was driven through the city beyond Islington, making 14 miles an hour on a level, and 8 miles or more on rising ground. In the same year he built the "Era," and, in August, put the "Autopsy" on with it, to make a steam-line to Paddington. These coaches ran until the end of November, carrying 4,000 passengers, at a usual rate of speed of 12 miles per hour. He then sent the "Era" to Dublin, where, on one occasion, it ran 18 miles per hour. [Illustration: FIG. 49.--Hancock's "Autopsy," 1833.] In 1835 a large carriage, the "Erin," was completed, which was intended to carry 20 passengers. It towed three omnibuses and a stage-coach, with 50 passengers, on a level road, at the speed of 10 miles an hour. It drew an omnibus with 18 passengers through Whitehall, Charing Cross, and Regent Street, and out to Brentford, running 14 miles an hour. It ran also to Reading, making 38 miles, with the same load, in 3 hours and 8 minutes running time. The stops _en route_ occupied a half-hour. The same carriage made 75 miles to Marlborough in 7-1/2 hours running time, stopping 4-1/2 hours on the road, in consequence of having left the tender and supplies behind. In May, 1836, Hancock put all his carriages on the Paddington road, and ran regularly for over five months, running 4,200 miles in 525 trips to Islington, 143 to Paddington, and 44 to Stratford, passing through the city over 200 times. The carriages averaged 5 hours and 17 or 18 minutes daily running time. A light steam-phaeton, built in 1838, for his own use, made 20 miles an hour, and was driven about the city, and among horses and carriages, without causing annoyance or danger. Its usual speed was about 10 miles an hour. Altogether, Hancock built nine steam-carriages, capable of carrying 116 passengers in addition to the regular attendants.[47] [47] For a detailed account of the progress of steam on the highway, _see_ "Steam on Common Roads," etc., by Young, Holley, & Fisher, London, 1861. In December, 1833, about 20 steam-carriages and traction road-engines were running, or were in course of construction, in and near London. In our own country, the roughness of roads discouraged inventors; and in Great Britain even, the successful introduction of road-locomotives, which seemed at one time almost an accomplished fact, finally met with so many obstacles, that even Hancock, the most ingenious, persistent, and successful constructor, gave up in despair. Hostile legislation procured by opposing interests, and the rapid progress of steam-locomotion on railroads, caused this result. In consequence of this interruption of experiment, almost nothing was done during the succeeding quarter of a century, and it is only within a few years that anything like a business success has been founded upon the construction of road-locomotives, although the scheme seems to have been at no time entirely given up. The opposition of coach-proprietors, and of all classes having an interest in the old lines of coaches, was most determined, and the feeling evinced by them was intensely bitter; but the advocates of the new system of transportation were equally determined and persevering, and, having right on their side, and the pecuniary advantage of the public as their object, they would probably have succeeded ultimately, except for the introduction of the still better method of transportation by rail. In the summer of 1831, when the war between the two parties was at its height, a committee of the British House of Commons made a very complete investigation of the subject. This committee reported that they had become convinced that "the substitution of inanimate for animal power, in draught on common roads, is one of the most important improvements in the means of internal communication ever introduced." They considered its practicability to have been "fully established," and predicted that its introduction would "take place more or less rapidly, in proportion as the attention of scientific men shall be drawn, by public encouragement, to further improvement." The success of the system had, as they stated, been retarded by prejudice, adverse interests, and prohibitory tolls; and the committee remark: "When we consider that these trials have been made under the most unfavorable circumstances, at great expense, in total uncertainty, without any of those guides which experience has given to other branches of engineering; that those engaged in making them are persons looking solely to their own interests, and not theorists attempting the perfection of ingenious models; when we find them convinced, after long experience, that they are introducing such a mode of conveyance as shall tempt the public, by its superior advantages, from the use of the admirable lines of coaches which have been generally established, it surely cannot be contended that the introduction of steam-carriages on common roads is, as yet, an uncertain experiment, unworthy of legislative attention." Farey, one of the most distinguished mechanical engineers of the time, testified that he considered the practicability of such a system as fully established, and that the result would be its general adoption. Gurney had run his carriage between 20 and 30 miles an hour; Hancock could sustain a speed of 10 miles; Ogle had run his coach 32 to 35 miles an hour, and ascended a hill rising 1 in 6 at the speed of 24-1/2 miles. Summers had traveled up a hill having a gradient of 1 in 12, with 19 passengers, at the rate of speed of 15 miles per hour; he had run 4-1/2 hours at 30 miles an hour. Farey thought that steam-coaches would be found to cost one-third as much as the stage-coaches in use. The steam-carriages were reported to be safer than those drawn by horses, and far more manageable; and the construction of boilers adopted--the "sectional" boiler, as it is now called--completely insured against injury by explosion, and the dangers and inconveniences arising from the frightening of horses had proved to be largely imaginary. The wear and tear of roads were found to be less than with horses, while with broad wheel-tires the carriages acted beneficially as road-rollers. The committee finally concluded: "1. That carriages can be propelled by steam on common roads at an average rate of 10 miles per hour. "2. That at this rate they have conveyed upward of 14 passengers. "3. That their weight, including engine, fuel, water, and attendants, may be under three tons. "4. That they can ascend and descend hills of considerable inclination with facility and safety. "5. That they are perfectly safe for passengers. "6. That they are not (or need not be, if properly constructed) nuisances to the public. "7. That they will become a speedier and cheaper mode of conveyance than carriages drawn by horses. "8. That, as they admit of greater breadth of tire than other carriages, and as the roads are not acted on so injuriously as by the feet of horses in common draught, such carriages will cause less wear of roads than coaches drawn by horses. "9. That rates of toll have been imposed on steam-carriages, which would prohibit their being used on several lines of road, were such charges permitted to remain unaltered." THE RAILROAD, which now, by the adaptation of steam to the propulsion of its carriages, became the successful rival of the system of transportation of which an account has just been given, was not a new device. It, like all other important changes of method and great inventions, had been growing into form for ages. The ancients were accustomed to lay down blocks of stone as a way upon which their heavily-loaded wagons could be drawn with less resistance than on the common road. This practice was gradually so modified as to result in the adoption of the now universally-practised methods of paving and road-making. The old tracks, bearing the marks of heavy traffic, are still seen in the streets of the unearthed city of Pompeii. In the early days of mining in Great Britain, the coal or the ore was carried from the mine to the vessel in which it was to be embarked in sacks on the backs of horses. Later, the miners laid out wagon-roads, and used carts and wagons drawn by horses, and the roads were paved with stone along the lines traversed by the wheels of the vehicles. Still later (about 1630), heavy planks or squared timber took the place of the stone, and were introduced into the north of England by a gentleman of the name of Beaumont, who had transferred his property there from the south. A half century later, the system had become generally introduced. By the end of the eighteenth century the construction of these "tram-ways" had become well-understood, and the economy which justified the expenditure of considerable amounts of money in making cuts and in filling, to bring the road to a uniform grade, had become well-recognized. Arthur Young, writing at this time, says the coal wagon-roads were "great works, carried over all sorts of inequalities of ground, so far as the distance of nine or ten miles," and that, on these tram-ways of timber, "one horse is able to draw, and that with ease, fifty or sixty bushels of coals." The wagon-wheels were of cast-iron, and made with grooved rims, which fitted the rounded tops of the wooden rails. But these wooden rails were found subject to rapid decay, and at Whitehaven, in 1738, they were protected from wear by cast-iron plates laid upon them, and this improvement rapidly became known and adopted. A tram-road, laid down at Sheffield for the Duke of Norfolk, in 1776, was made by laying angle-bars of cast-iron on longitudinal sleepers of timber; another, built by William Jessup in Leicestershire, in 1789, had an edge-rail, and the wheels were made with flanges, like those used to-day. The coned "tread" of the wheel, which prevents wear of flanges and reduces resistance, was the invention of James Wright, of Columbia, Pa., 40 years later. The modern railroad was simply the result of this gradual improvement of the permanent way, and the adaptation of the steam-engine to the propulsion of its wagons. At the beginning of the nineteenth century, therefore, the steam-engine had been given a form which permitted its use, and the railroad had been so far perfected that there were no difficulties to be anticipated in the construction of the permanent way, and inventors were gradually preparing, as has been seen, to combine these two principal elements into one system. Railroads had been introduced in all parts of Great Britain, some of them of considerable length, and involving the interests of so many private individuals that they were necessarily constructed under the authorization of legal enactments. In the year 1805 the Merstham Railway was opened to traffic, and it is stated that on that occasion one horse drew a train of 12 wagons, carrying 38 tons of stone, on a "down gradient" of 1 in 120, at the rate of 6 miles per hour. [Illustration: Richard Trevithick.] [Illustration: FIG. 50.--Trevithick's Locomotive, 1804.] RICHARD TREVITHICK was the first engineer to apply steam-power to the haulage of loads on the railroad. Trevithick was a Cornishman by birth, a native of Redruth. He was naturally a skillful mechanic, and was placed by his father with Watt's assistant, Murdoch, who was superintending the erection of pumping-engines in Cornwall; and from that ingenious and accomplished engineer young Trevithick probably acquired both the skill and the knowledge which, with his native talent, enterprise, and industry, enabled him to accomplish the work which has made him famous. He was soon intrusted with the erection and management of large pumping-engines, and subsequently went into the business of constructing steam-engines with another engineer, Edward Bull, who took an active part, with the Hornblowers and others, in opposing the Boulton & Watt patents. The termination of the suits which established the validity of Watt's patent put an end to their business, and Trevithick looked about for other work, and, not long after, entered into partnership with a relative, Andrew Vivian, who was also a skillful mechanic; they together designed and patented the steam-carriage already referred to. Its success was sufficiently satisfactory to awaken strong confidence of a perfect success on the now common tram-roads; and Trevithick, in February, 1804, had completed a "locomotive" engine to work on the Welsh Pen-y-darran road. This engine (Fig. 50) had a cylindrical flue-boiler, _A_, like that designed by Oliver Evans, and a single steam-cylinder, _B_, set vertically into the steam-space of the boiler, and driving the outside cranks, _L_, on the rear axle of the engine by very long connecting-rods, _D_, attached to its cross-head at _E_. The guide-bars, _I_, were stayed by braces leading to the opposite end of the boiler. No attempt was made to condense the exhaust-steam, which was discharged into the smoke-pipe. The pressure of steam adopted was 40 pounds per square inch; but Trevithick had already made a number of non-condensing engines on which he carried from 50 to 145 pounds pressure. In the year 1808, Trevithick built a railroad in London, on what was known later as Torrington Square, or Euston Square, and set at work a steam-carriage, which he called "Catch-me-who-can." This was a very plain and simple machine. The steam-cylinder was set vertically in the after-end of the boiler, and the cross-head was connected to two rods, one on either side, driving the hind pair of wheels. The exhaust-steam entered the chimney, aiding the draught. This engine, weighing about 10 tons, made from 12 to 15 miles an hour on the circular railway in London, and was said by its builder to be capable of making 20 miles an hour. The engine was finally thrown from the track, after some weeks of work, by the breaking of a rail, and, Trevithick's funds having been expended, it was never replaced. This engine had a steam-cylinder 14-1/2 inches in diameter, and a stroke of piston of 4 feet. Trevithick used no device to aid the friction of the wheels on the rails in giving pulling-power, and seems to have understood that none was needed. This plan of working a locomotive-engine without such complications as had been proposed by other engineers was, however, subsequently patented, in 1813, by Blackett & Hedley. The latter was at one time Trevithick's agent, and was director of Wylam Colliery, of which Mr. Blackett was proprietor. Trevithick applied his high-pressure non-conducting engine not only to locomotives, but to every purpose that opportunity offered him. He put one into the Tredegar Iron-Works, to drive the puddle-train, in 1801. This engine had a steam-cylinder 28 inches in diameter, and 6 feet stroke of piston; a boiler of cast-iron, 6-3/4 feet in diameter and 20 feet long, with a wrought-iron internal tube, 3 feet in diameter at the furnace-end and 24 inches beyond the furnace. The steam-pressure ranged from 50 to 100 pounds per square inch. The valve was a four-way cock. The exhaust-steam was carried into the chimney, passing through a feed-water heater _en route_. This engine was taken down in 1856.[48] [48] "Life of Trevithick." In 1803, Trevithick applied his engine to driving rock-drills, and three years later made a large contract with the Trinity Board for dredging in the Thames, and constructed steam dredging-machines for the work, of the form which is still most generally used in Great Britain, although rarely seen in the United States--the "chain-and-bucket dredger." A little later, Trevithick was engaged upon the first and unsuccessful attempt to carry a tunnel under the Thames, at London; but no sooner had that costly scheme been given up, than he returned to his favorite pursuits, and continued his work on interrupted schemes for ship-propulsion. Trevithick at last left England, spent some years in South America, and finally returned home and died in extreme poverty, April, 1833, at the age of sixty-two, without having succeeded in accomplishing the general introduction of any of his inventions. Trevithick was characteristically an inventor of the typical sort. He invented many valuable devices, but brought but few into even experimental use, and reaped little advantage from any of them. He was ingenious, a thorough mechanic, bold, active, and indefatigable; but his lack of persistence made his whole life, as Smiles has said, "but a series of beginnings." It is at about this period that we find evidence of the intelligent labors of another of our own countrymen--one who, in consequence of the unobtrusive manner in which his work was done, has never received the full credit to which he is entitled. COLONEL JOHN STEVENS, of Hoboken, as he is generally called, was born in the city of New York, in 1749; but throughout his business-life he was a resident of New Jersey. [Illustration: Colonel John Stevens.] His attention is said to have been first called to the application of steam-power by seeing the experiments of John Fitch with his steamer on the Delaware, and he at once devoted himself to the introduction of steam-navigation with characteristic energy, and with a success that will be indicated when we come to the consideration of that subject. But this far-sighted engineer and statesman saw plainly the importance of applying the steam-engine to land-transportation as well as to navigation; and not only that, but he saw with equal distinctness the importance of a well-devised and carefully-prosecuted scheme of internal communication by a complete system of railroads. In 1812 he published a pamphlet containing "Documents tending to prove the superior advantages of Railways and Steam-Carriages over Canal-Navigation."[49] At this time, the only locomotive in the world was that of Trevithick and Vivian, at Merthyr Tydvil, and the railroad itself had not grown beyond the old wooden tram-roads of the collieries. Yet Colonel Stevens says, in this paper: "I can see nothing to hinder a steam-carriage moving on its ways with a velocity of 100 miles an hour;" adding, in a foot-note: "This astonishing velocity is considered here merely possible. It is probable that it may not, in practise, be convenient to exceed 20 or 30 miles per hour. Actual experiment can only determine this matter, and I should not be surprised at seeing steam-carriages propelled at the rate of 40 or 50 miles an hour." [49] Printed by T. & J. Swords, 160 Pearl Street, New York, 1812. At a yet earlier date he had addressed a memoir to the proper authorities, urging his plans for railroads. He proposed rails of timber, protected, when necessary, by iron plates, or to be made wholly of iron; the car-wheels were to be of cast-iron, with inside flanges to keep them on the track. The steam-engine was to be driven by steam of 50 pounds pressure and upward, and to be non-condensing. Answering the objections of Robert R. Livingston and of the State Commissioners of New York, he goes further into details. He gives 500 to 1,000 pounds as the maximum weight to be placed on each wheel; shows that the trains, or "suits of carriages," as he calls them, will make their journeys with as much certainty and celerity in the darkest night as in the light of day; shows that the grades of proposed roads would offer but little resistance; and places the whole subject before the public with such accuracy of statement and such evident appreciation of its true value, that every one who reads this remarkable document will agree fully with President Charles King, who said[50] that "whosoever shall attentively read this pamphlet, will perceive that the political, financial, commercial, and military aspects of this great question were all present to Colonel Stevens's mind, and that he felt that he was fulfilling a patriotic duty when he placed at the disposal of his native country these fruits of his genius. The offering was not then accepted. The 'Thinker' was ahead of his age; but it is grateful to know that he lived to see his projects carried out, though not by the Government, and that, before he finally, in 1838, closed his eyes in death, at the great age of eighty-nine, he could justly feel assured that the name of Stevens, in his own person and in that of his sons, was imperishably enrolled among those which a grateful country will cherish." [50] "Progress of the City of New York." Without having made any one superlatively great improvement in the mechanism of the steam-engine, like that which gave Watt his fame--without having the honor even of being the first to propose the propulsion of vessels by the modern steam-engine, or steam-transportation on land--he exhibited a far better knowledge of the science and the art of engineering than any man of his time; and he entertained and urged more advanced opinions and more statesmanlike views in relation to the economical importance of the improvement and the application of the steam-engine, both on land and water, than seem to be attributable to any other leading engineer of that time. Says Dr. King: "Who can estimate if, at that day, acting upon the well-considered suggestion of President Madison, 'of the signal advantages to be derived to the United States from a general system of internal communication and conveyance,' Congress had entertained Colonel Stevens's proposal, and, after verifying by actual experiment upon a small scale the accuracy of his plan, had organized such a 'general system of internal communication and conveyance;' who can begin to estimate the inappreciable benefits that would have resulted therefrom to the comfort, the wealth, the power, and, above all, to the absolutely impregnable union of our great Republic and all its component parts? All this Colonel Stevens embraced in his views, for he was a statesman as well as an experimental philosopher; and whoever shall attentively read his pamphlet, will perceive that the political, financial, commercial, and military aspects of this great question were all present to his mind, and he felt that he was fulfilling a patriotic duty when he placed at the disposal of his native country these fruits of his genius." WILLIAM HEDLEY, who has already been referred to, seems to have been the first to show, by carefully-conducted experiment, how far the adhesion of the wheels of the locomotive-engine could be relied upon for hauling-power in the transportation of loads. His employer, Blackett, had applied to Trevithick for a locomotive-engine to haul coal-trains at the Wylam collieries; but Trevithick was unable, or was disinclined, to build him one, and in October, 1812, Hedley was authorized to attempt the construction of an engine. It was at about this time that Blenkinsop (1811) was trying the toothed rail or rack, the Messrs. Chapman (December, 1812) were experimenting with a towing-chain, and (May, 1813) Brunton with movable legs. Hedley, who had known of the success met with in the experiments of Trevithick with smooth wheels hauling loads of considerable weight, in Cornwall, was confident that equal success might be expected in the north-country, and built a carriage to be moved by men stationed at four handles, by which its wheels were turned. This carriage was loaded with heavy masses of iron, and attached to trains of coal-wagons on the railway. By repeated experiment, varying the weight of the traction-carriage and the load hauled, Hedley ascertained the proportion of the weight required for adhesion to that of the loads drawn. It was thus conclusively proven that the weight of his proposed locomotive-engine would be sufficient to give the pulling-power necessary for the propulsion of the coal-trains which it was to haul. When the wheels slipped in consequence of the presence of grease, frost, or moisture on the rail, Hedley proposed to sprinkle ashes on the track, as sand is now distributed from the sand-box of the modern engine. This was in October, 1812. Hedley now went to work building an engine with smooth wheels, and patented his design March 13, 1813, a month after he had put his engine at work. The locomotive had a cast-iron boiler, and a single steam-cylinder 6 inches in diameter, with a small fly-wheel. This engine had too small a boiler, and he soon after built a larger engine, with a return-flue boiler made of wrought-iron. This hauled 8 loaded coal-wagons 5 miles an hour at first, and a little later 10, doing the work of 10 horses. The steam-pressure was carried at about 50 pounds, and the exhaust, led into the chimney, where the pipe was turned upward, thus secured a blast of considerable intensity in its small chimney. Hedley also contracted the opening of the exhaust-pipe to intensify the blast, and was subjected to some annoyance by proprietors of lands along his railway, who were irritated by the burning of their grass and hedges, which were set on fire by the sparks thrown out of the chimney of the locomotive. The cost of Hedley's experiment was defrayed by Mr. Blackett. Subsequently, Hedley mounted his engine on eight wheels, the four-wheeled engines having been frequently stopped by breaking the light rails then in use. Hedley's engines continued in use at the Wylam collieries many years. The second engine was removed in 1862, and is now preserved at the South Kensington Museum, London. GEORGE STEPHENSON, to whom is generally accorded the honor of having first made the locomotive-engine a success, built his first engine at Killingworth, England, in 1814. [Illustration: George Stephenson.] At this time Stephenson was by no means alone in the field, for the idea of applying the steam-engine to driving carriages on common roads and on railroads was beginning, as has been seen, to attract considerable attention. Stephenson, however, combined, in a very fortunate degree, the advantages of great natural inventive talent and an excellent mechanical training, reminding one strongly of James Watt. Indeed, Stephenson's portrait bears some resemblance to that of the earlier great inventor. George Stephenson was born June 9, 1781, at Wylam, near Newcastle-upon-Tyne, and was the son of a "north-country miner." When still a child, he exhibited great mechanical talent and unusual love of study. When set at work about the mines, his attention to duty and his intelligence obtained for him rapid promotion, until, when but seventeen years of age, he was made engineer, and took charge of the pumping-engine at which his father was fireman. When a mere child, and employed as a herd-boy, he amused himself making model engines in clay, and, as he grew older, never lost an opportunity to learn the construction and management of machinery. After having been employed at Newburn and Callerton, where he first became "engine-man," he began to study with greater interest than ever the various steam-engines which were then in use; and both the Newcomen engine and the Watt pumping-engine were soon thoroughly understood by him. After having become a brakeman, he removed to Willington Quay, where he married, and commenced his wedded life on 18 or 20 shillings per week. It was here that he became an intimate friend of the distinguished William Fairbairn, who was then working as an apprentice at the Percy Main Colliery, near by. The "father of the railroad" and the future President of the British Association were accustomed, at times, to "change works," and were frequently seen in consultation over their numerous projects. It was at Willington Quay that his son Robert, who afterward became a distinguished civil engineer, was born, October 16, 1803. In the following year Stephenson removed to Killingworth, and became brakeman at that colliery; but his wife soon died, and he gladly accepted an invitation to become engine-driver at a spinning-mill near Montrose, Scotland. At the end of a year he returned, on foot, to Killingworth with his savings (about £28), expended over one-half of the amount in paying his father's debts and in making his parents comfortable, and then returned to his old station as brakeman at the pit. Here he made some useful improvements in the arrangement of the machinery, and spent his spare hours in studying his engine and planning new machines. He a little later distinguished himself by altering and repairing an old Newcomen engine at the High Pit, which had failed to give satisfaction, making it thoroughly successful after three days' work. The engine cleared the pit, at which it had been vainly laboring a long time, in two days after Stephenson started it up. In the year 1812, Stephenson was made engine-wright of the Killingworth High Pit, receiving £100 a year, and it was made his duty to supervise the machinery of all the collieries under lease by the so-called "Grand Allies." It was here, and at this period, that he commenced a systematic course of self-improvement and the education of his son, and here he first began to be recognized as an inventor. He was full of life and something of a wag, and often made most amusing applications of his inventive powers: as when he placed the watch, which a comrade had brought him as out of repairs, in the oven "to cook," his quick eye having noted the fact that the difficulty arose simply from the clogging of the wheels by the oil, which had been congealed by cold. Smiles,[51] his biographer, describes his cottage as a perfect curiosity-shop, filled with models of engines, machines of various kinds, and novel apparatus. He connected the cradles of his neighbors' wives with the smoke-jacks in their chimneys, and thus relieved them from constant attendance upon their infants; he fished at night with a submarine lamp, which attracted the fish from all sides, and gave him wonderful luck; he also found time to give colloquial instruction to his fellow-workmen. [51] "Lives of George and Robert Stephenson," by Samuel Smiles. New York and London, 1868. He built a self-acting inclined plane for his pit, on which the wagons, descending loaded, drew up the empty trains; and made so many improvements at the Killingworth pit, that the number of horses employed underground was reduced from 100 to 16. Stephenson now had more liberty than when employed at the brakes, and, hearing of the experiments of Blackett and Hedley at Wylam, went over to their colliery to study their engine. He also went to Leeds to see the Blenkinsop engine draw, at a trial, 70 tons at the rate of 3 miles an hour, and expressed his opinion in the characteristic remark, "I think I could make a better engine than that to go upon legs." He very soon made the attempt. Having laid the subject before the proprietors of the lease under which the collieries were worked, and convinced Lord Ravensworth, the principal owner, of the advantages to be secured by the use of a "traveling engine," that nobleman advanced the money required. Stephenson at once commenced his first locomotive-engine, building it in the workshops at West Moor, assisted mainly by John Thirlwall, the colliery blacksmith, during the years 1813 and 1814, completing it in July of the latter year. This engine had a wrought-iron boiler 8 feet long and 2 feet 10 inches in diameter, with a single flue 20 inches in diameter. The cylinders were vertical, 8 inches in diameter and of 2 feet stroke of piston, set in the boiler, and driving a set of wheels which geared with each other and with other cogged wheels on the two driving-axles. A feed-water heater surrounded the base of the chimney. This engine drew 30 tons on a rising gradient of 10 or 12 feet to the mile at the rate of 4 miles an hour. This engine proved in many respects defective, and the cost of its operation was found to be about as great as that of employing horse-power. Stephenson determined to build another engine on a somewhat different plan, and patented its design in February, 1815. It proved a much more efficient machine than the "Blücher," the first engine. [Illustration: FIG. 51.--Stephenson's Locomotive of 1815. Section.] This second engine (Fig. 51) was also fitted with two vertical cylinders, _C c_, but the connecting-rods were attached directly to the four driving-wheels, _W W´_. To permit the necessary freedom of motion, "ball-and-socket" joints were adopted, to unite the rods with the cross-heads, _R r_, and with the cranks, _R´ Y´_; and the two driving-axles were connected by an endless chain, _T t´_. The cranked axle and the outside connection of the wheels, as specified in the patent, were not used until afterward, it having been found impossible to get the cranked axles made. In this engine the forced draught obtained by the impulse of the exhaust-steam was adopted, doubling the power of the machine and permitting the use of coke as a fuel, and making it possible to adopt the multi-tubular boiler. Small steam-cylinders, _S S S_, took the weight of the engine and served as springs. It was at about this time that George Stephenson and Sir Humphry Davy, independently and almost simultaneously, invented the "safety-lamp," without which few mines of bituminous coal could to-day be worked. The former used small tubes, the latter fine wire gauze, to intercept the flame. Stephenson proved the efficiency of his lamp by going with it directly into the inflammable atmosphere of a dangerous mine, and repeatedly permitting the light to be extinguished when the lamp became surcharged with the explosive mixture which had so frequently proved fatal to the miners. This was in October and November, 1815, and Stephenson's work antedates that of the great philosopher.[52] The controversy which arose between the supporters of the rival claims of the two inventors was very earnest, and sometimes bitter. The friends of the young engineer raised a subscription, amounting to above £1,000, and presented it to him as a token of their appreciation of the value of his simple yet important contrivance. Of the two forms of lamp, that of Stephenson is claimed to be safest, the Davy lamp being liable to produce explosions by igniting the explosive gas when, by its combustion within the gauze cylinder, the latter is made red-hot. Under similar conditions, the Stephenson lamp is simply extinguished, as was seen at Barnsley, in 1857, at the Oaks Colliery, where both kinds of lamp were in use, and elsewhere. [52] _Vide_ "A Description of the Safety-Lamp invented by George Stephenson," etc., London, 1817. Stephenson continued to study and experiment, with a view to the improvement of his locomotive and the railroad. He introduced better methods of track-laying and of jointing the rails, adopting a half-lap, or peculiar scarf-joint, in place of the then usual square-butt joint. He patented, with these modifications of the permanent way, several of his improvements of the engine. He had substituted forged for the rude cast wheels previously used,[53] and had made many minor changes of detail. The engines built at this time (1816) continued in use many years. Two years later, with a dynamometer which he designed for the purpose, he made experimental determinations of the resistance of trains, and showed that it was made up of several kinds, as the sliding friction of the axle-journals in their bearings, the rolling friction of the wheels on the rails, the resistance due to gravity on gradients, and that due to the resistance of the air. [53] The American chilled wheel of cast-iron, a better wheel than that above described, has never been generally and successfully introduced in Europe. These experiments seemed to him conclusive against the possibility of the competition of engines on the common highway with locomotives hauling trains on the rail. Finding that the resistance, with his rolling-stock, and at all the speeds at which he made his experiments, was approximately invariable, and equivalent to about 10 pounds per ton, and estimating that a gradient rising but 1 foot in 100 would decrease the hauling power of the engine 50 per cent., he saw at once the necessity of making all railroads as nearly absolutely level as possible, and, consequently, the radically distinctive character of this branch of civil engineering work. He persistently condemned the "folly" of attempting the general introduction of steam on the common road, where great changes of level and an impressible road-bed were certain to prove fatal to success, and was most strenuous in his advocacy of the policy of securing level tracks, even at very great expense. Taking part in the contest, which now became a serious one, between the advocates of steam on the common road and those urging the introduction of locomotives and their trains on an iron track, he calculated that a road-engine capable of carrying 20 or 30 passengers at 10 miles per hour, could, on the rail, carry ten times as many people at three or four times that speed. The railway-engine finally superseded its predecessor--the engine of the common road--almost completely. In 1817, Stephenson built an engine for the Duke of Portland, to haul coal from Kilmarnock to Troon, which cost £750, and, with some interruptions, this engine worked on that line until 1848, when it was broken up. On November 18, 1822, the Hetton Railway, near Sunderland, was opened. George Stephenson was the engineer of the line--a short track, 8 miles long, built from the Hetton Colliery to the docks on the bank of the river Wear. On this line he put in five of the "self-acting inclines"--two inclines worked by stationary engines, the gradients being too heavy for locomotives--and used five locomotive-engines of his own design, which were called by the people of the neighborhood, possibly for the first time, "the iron horses." These engines were quite similar to the Killingworth engine. They drew a train of 17 coal-cars--a total load of 64 tons--about 4 miles an hour. Meantime, also, in 1823, Stephenson had been made engineer of the Stockton & Darlington Railroad, which had been projected for the purpose of securing transportation to tide-water for the valuable coal-lands of Durham. This road was built without an expectation on the part of any of its promoters, Stephenson excepted, that steam would be used as a motor to the exclusion of horses. Mr. Edward Pearse, however, one of the largest holders of stock in the road, and one of its most earnest advocates, became so convinced, by an examination of the Killingworth engines and their work, of the immense advantage to be derived by their use, that he not only supported Stephenson's arguments, but, with Thomas Richardson, advanced £1,000 for the purpose of assisting Stephenson to commence the business of locomotive-engine construction at Newcastle. This workshop, which subsequently became a great and famous establishment, was commenced in 1824. For this road Stephenson recommended wrought-iron rails, which were then costing £12 per ton--double the price of cast rails. The directors, however, stipulated that he should only buy one-half the rails required from the dealers in "malleable" iron. These rails weighed 20 pounds to the yard. After long hesitation, in the face of a serious opposition, the directors finally concluded to order three locomotives of Stephenson. The first, or "No. 1," engine (Fig. 52) was delivered in time for the opening of the road, September 27, 1825. It weighed 8 tons. Its boiler contained a single straight flue, one end of which was the furnace. The cylinders were vertical, like those of the earlier engines, and coupled directly to the driving-wheels. The crank-pins were set in the wheels at right angles, in order that, while one engine was "turning the centre," the other might exert its maximum power. The two pairs of drivers were coupled by horizontal rods, as seen in the figure, which represents this engine as subsequently mounted on a pedestal at the Darlington station. A steam-blast in the chimney gave the requisite strength of draught. These engines were built for slow and heavy work, but were capable of making what was then thought the satisfactorily high speed of 16 miles per hour. The inclines on the road were worked by fixed engines. [Illustration: FIG. 52.--Stephenson's No. 1 Engine, 1825.] On the opening day, which was celebrated as a holiday by the people far and near, the No. 1 engine drew 90 tons at the rate of 12, and at times 15, miles an hour. [Illustration: FIG. 58.--Opening of the Stockton and Darlington Railroad, 1815. (After an old engraving.)] Stephenson's engines were kept at work hauling coal-trains, but the passenger-coaches were all drawn for some time by horses, and the latter system was a rude forerunner, in most respects, of modern street-railway transportation. Mixed passenger and freight trains were next introduced, and, soon after, separate passenger-trains drawn by faster engines were placed on the line, and the present system of railroad transportation was now fairly inaugurated. A railroad between Manchester and Liverpool had been projected at about the time that the Stockton & Darlington road was commenced. The preliminary surveys had been made in the face of strong opposition, which did not always stop at legal action and verbal attack, but in some instances led to the display of force. The surveyors were sometimes driven from their work by a mob armed with sticks and stones, urged on by land-proprietors and those interested in the lines of coaches on the highway. Before the opening of the Stockton & Darlington Railroad, the Liverpool & Manchester bill had been carried through Parliament, after a very determined effort on the part of coach-proprietors and landholders to defeat it, and Stephenson urged the adoption of the locomotive to the exclusion of horses. It was his assertion, made at this time, that he could build a locomotive to run 20 miles an hour, that provoked the celebrated rejoinder of a writer in the _Quarterly Review_, who was, however, in favor of the construction of the road and of the use of the locomotive upon it: "What can be more palpably absurd and ridiculous, than the prospect held out of locomotives traveling _twice as fast_ as stage-coaches? We would as soon expect the people of Woolwich to suffer themselves to be fired off upon one of Congreve's ricochet-rockets, as trust themselves to the mercy of such a machine going at such a rate." It was during his examination before a committee of the House of Commons, during this contest, that Stephenson, when asked, "Suppose, now, one of your engines to be going at the rate of 9 or 10 miles an hour, and that a cow were to stray upon the line and get in the way of the engine, would not that be a very awkward circumstance?" replied, "Yes, _very_ awkward--_for the coo!_" And when asked if men and animals would not be frightened by the red-hot smoke-pipe, answered, "But how would they know that it was not _painted?_" The line was finally built, with George Rennie as consulting, and Stephenson as principal constructing engineer. His work on this road became one of the important elements of the success, and one of the great causes of the distinction, which marked the life of these rising engineers. The successful construction of that part of the line which lay across "Chat Moss," an unfathomable swampy deposit of peat, extending over an area of 12 square miles, and the building of which had been repeatedly declared an impossibility, was in itself sufficient to prove that the engineer who had accomplished it was no common man. Stephenson adopted the very simple yet bold expedient of using, as a filling, compacted turf and peat, and building a road-bed of materials lighter than water, or the substance composing the bog, and thus forming a _floating_ embankment, on which he laid his rails. To the surprise of every one but Stephenson himself, the plan proved perfectly successful, and even surprisingly economical, costing but little more than one-tenth the estimate of at least one engineer. Among the other great works on this remarkable pioneer-line were the tunnel, a mile and a half long, from the station at Liverpool to Edgehill; the Olive Mount deep-cut, two miles long, and in some places 100 feet deep, through red sandstone, of which nearly 500,000 yards were removed; the Sankey Viaduct, a brick structure of nine arches, of 50 feet span each, costing £45,000; and a number of other pieces of work which are noteworthy in even these days of great works. Stephenson planned all details of the line, and even designed the bridges, machinery, engines, turn-tables, switches, and crossings, and was responsible for every part of the work of their construction. Finally, the work of building the line approached completion, and it became necessary promptly to settle the long-deferred question of a method of applying motive-power. Some of the directors and their advisers still advocated the use of horses; many thought stationary hauling-engines preferable; and the remainder were, almost to a man, undecided. The locomotive had no outspoken advocate, and few had the slightest faith in it. George Stephenson was almost alone, and the opponents of steam had secured a provision in the Newcastle & Carlisle Railroad concession, stipulating expressly that horses should there be exclusively employed. The directors did, however, in 1828, permit Stephenson to put on the line a locomotive, to be used, during its construction, in hauling gravel-trains. A committee was sent, at Stephenson's request, to see the Stockton & Darlington engines, but no decided expression of opinion seems to have been made by them. Two well-known professional engineers reported in favor of fixed engines, and advised the division of the line into 19 stages of about a mile and a half each, and the use of 21 fixed engines, although they admitted the excessive first-cost of that system. The board was naturally strongly inclined to adopt their plan. Stephenson, however, earnestly and persistently opposed such action, and, after long debate, it was finally determined "to give the traveling engine a chance." The board decided to offer a reward of £500 for the best locomotive-engine, and prescribed the following conditions: 1. The engine must consume its own smoke. 2. The engine, if of 6 tons weight, must be able to draw after it, day by day, 20 tons weight (including the tender and water-tank) at 10 miles an hour, with a pressure of steam on the boiler not exceeding 50 pounds to the square inch. 3. The boiler must have two safety-valves, neither of which must be fastened down, and one of them completely out of the control of the engine-man. 4. The engine and boiler must be supported on springs, and rest on 6 wheels, the height of the whole not exceeding 15 feet to the top of the chimney. 5. The engine, with water, must not weigh more than 6 tons; but an engine of less weight would be preferred, on its drawing a proportionate load behind it; if of only 4-1/2 tons, then it might be put only on 4 wheels. The company to be at liberty to test the boiler, etc., by a pressure of 150 pounds to the square inch. 6. A mercurial gauge must be affixed to the machine, showing the steam-pressure above 45 pounds to the square inch. 7. The engine must be delivered, complete and ready for trial, at the Liverpool end of the railway, not later than the 1st of October, 1829. 8. The price of the engine must not exceed £550. This circular was printed and published throughout the kingdom, and a considerable number of engines were constructed to compete at the trial, which was proposed to take place October 1, 1829, but which was deferred to the 6th of that month. Only four engines, however, were finally entered on the day of the trial. These were the "Novelty," constructed by Messrs. Braithwaite & Ericsson, the latter being the distinguished engineer who subsequently came to the United States to introduce screw-propulsion, and, later, the monitor system of iron-clads; the "Rocket," built from Stephenson's plans; and the "Sanspareil" and the "Perseverance," built by Hackworth and Burstall, respectively. The "Sanspareil," which was built under the direction of Timothy Hackworth, one of Stephenson's earlier foremen, resembled the engine built by the latter for the Stockton & Darlington road, but was heavier than had been stipulated, was not ready for work when called, and, when finally set at work, proved to be very extravagant in its use of fuel, partly in consequence of the extreme intensity of its blast, which caused the expulsion of unconsumed coals from the furnace. The "Perseverance" could not attain the specified speed, and was withdrawn. [Illustration: FIG. 54.--The "Novelty," 1829.] The "Novelty" was apparently a well-designed and for that time a remarkably well-proportioned machine. _A_, in Fig. 54, is the boiler, _D_ the steam-cylinders, _E_ a heater. Its weight but slightly exceeded three tons, and it was a "tank engine," carrying its own fuel and water at _B_. A forced draught was obtained by means of the bellows, _C_. This engine was run over the line at the rate of about 28 miles an hour at times, but its blowing apparatus failed, and the "Rocket" held the track alone. A later trial still left the "Rocket" alone in the field. The "Rocket" (Fig. 55) was built at the works of Robert Stephenson & Co., at Newcastle-upon-Tyne. The boiler was given considerable heating-surface by the introduction of 25 3-inch copper tubes, at the suggestion of Henry Booth, secretary of the railroad company. The blast was altered by gradually closing in the opening at the extremity of the exhaust-pipe, and thus "sharpening" it until it was found to have the requisite intensity. The effect of this modification of the shape of the pipe was observed carefully by means of syphon water-gauges attached to the chimney. The draft was finally given such an intensity as to raise the water 3 inches in the tube of the draught-gauge. The total length of the boiler was 6 feet, its diameter 40 inches. The fire-box was attached to the rear of the boiler, and was 3 feet high and 2 feet wide, with water-legs to protect its side-sheets from injury by overheating. The cylinders, as seen in the sketch, were inclined, and coupled to a single pair of driving-wheels. A tender, attached to the engine, carried the fuel and water. The engine weighed less than 4-1/2 tons. [Illustration: FIG. 55.--The "Rocket," 1829.] The little engine does not seem to have been very prepossessing in appearance, and the "Novelty" is said to have been the general favorite, the Stephenson engine having few, if any, backers among the spectators. On its first trial, it ran 12 miles in less than an hour. After the accident which disabled the "Novelty," the "Rocket" came forward again, and ran at the rate of from 25 to 30 miles an hour, drawing a single carriage carrying 30 passengers. Two days later, on the 8th of October, steam was raised in a little less than an hour from cold water, and it then, with 13 tons of freight in the train, ran 35 miles in 1 hour and 48 minutes, including stops, and attained a speed of 29 miles an hour. The average of all runs for the trial was 15 miles an hour. This success, far exceeding the expectation of the most sanguine of the advocates of the system, and greatly exceeding what had been asserted by opponents to be the bounds of possibility, settled completely the whole question, and the Manchester & Liverpool road was at once equipped with locomotive engines. The "Rocket" remained on the line until 1837, when it was sold, and set at work by the purchasers on the Midgeholme Railway, near Carlisle. On one occasion, on this road, it was driven 4 miles in 4-1/2 minutes. It is now in the Patent Museum at South Kensington, London. In January, 1830, a single line of rails had been carried across Chat Moss, and, six months later, the first train, drawn by the "Arrow," ran through, June 14th, from Liverpool to Manchester, making the trip in an hour and a half, and attaining a maximum speed of over 27 miles an hour. The line was formally opened to traffic September 15, 1830. This was one of the most notable occasions in the history of the railroad, and the successful termination of the great work was celebrated, as so important an event should be, by impressive ceremonies. Among the distinguished spectators were Sir Robert Peel and the Duke of Wellington. Mr. Huskisson, a Member of Parliament for Liverpool, was also present. There had been built for the line, by Robert Stephenson & Co., 7 locomotives besides the "Rocket," and a large number of carriages. These were all brought out in procession, and 600 passengers entered the train, which started for Manchester, and ran at times, on smooth portions of the road, at the rate of 20 and 25 miles an hour. Crowds of people along the line cheered at this strange and to them incomprehensible spectacle, and the story of the wonderful performances of that day on the new railroad was repeated in every corner of the land. A sad accident, the precursor of thousands to follow the introduction of the new method of transportation, while it repressed the rising enthusiasm of the people and dampened the ardor of the most earnest of the advocates of the railroad, occurring during this trip, assisted in making known the power of the new motor and the danger attending its use as well. The trains stopped for water at Parkside, and occasion was taken to send the "Northumbrian," an engine driven by George Stephenson himself, on a side track, with the carriage containing the Duke of Wellington, and the other engines and trains were all directed to be sent along the main track in view of the Duke and his party. While this movement was in process of execution, Mr. Huskisson, who had carelessly stood on the main line until the "Rocket," which led the column, had nearly reached him, attempted to enter the carriage of the Duke. He was too late, and was struck by the "Rocket," thrown down across the rail, and the advancing engine crushed a leg so seriously that he died the same evening. Immediately after the accident, he was placed on the "Northumbrian," and Stephenson made the 15 miles to the destination of the wounded man in 25 minutes--a speed of 36 miles an hour. The news of this accident, and the statement of the velocity of the engine, were published throughout the kingdom and Europe; and the misfortune of this first victim of a railroad accident was one of the causes of the immediate adoption and rapid spread of the modern railway system. This road, which was built in the hope of securing 400 passengers per day, almost immediately averaged 1,200, and in five years reported 500,000 passengers for the year.[54] The success of this road insured the general introduction of railroads, and from this time forward there was never a doubt of their ultimate adoption to the exclusion of every other system of general internal communication and transportation. [54] Smiles. For some years after this his first great triumph, George Stephenson gave his whole time to the building of railroads and the improvement of the engine. He was assisted by his son Robert, to whom he gradually surrendered his business, and retired to Tapton House, on the Midland Railway, and led a busy but pleasant life during the remaining years of his existence. Even as early as 1840, he seems to have projected many improvements which were only generally adopted many years later. He proposed self-acting and continuous systems of brake, and considered a good system of brake of so great importance, that he advocated their compulsory introduction by State legislation. He advised moderate speeds, from considerations both of safety and of expense. A few years after the opening of the Liverpool & Manchester road, great numbers of schemes were proposed by ignorant or designing men, which had for their object the filling of the pockets of their proposers rather than the benefit of the stockholders and the public; and the Stephensons were often called upon to combat these crude and ill-digested plans. Among these was the pneumatic system of propulsion, already referred to as first proposed by Papin, in combination with his double-acting air-pump, in 1687. It had been again proposed in the early part of the present century by Medhurst, who proposed a method of pneumatic transmission of small parcels and of letters, which is now in use, and, 15 years later, a railroad to take the place of that of Stephenson and his coadjutors. The most successful of several attempts to introduce this method was that of Clegg & Samuda, at West London, and on the London & Croydon road, and again in Ireland, between Kingstown and Dalkey. A line of pipe, _B B_, seen in Fig. 56, two feet in diameter, was laid between the rails, _A A_, of the road. This pipe was fitted with a nicely-packed piston, carrying a strong arm, which rose through a slit made along the top of the pipe, and covered by a flexible strip of leather, _E E_. This arm was attached to the carriage, _C C_, to be propelled. The pressure of the atmosphere being removed, by the action of a powerful pump, from the side toward which the train was to advance, the pressure of the atmosphere on the opposite side drove the piston forward, carrying the train with it. Stephenson was convinced, after examining the plans of the projectors, that the scheme would fail, and so expressed himself. Those who favored it, however, had sufficient influence with capitalists to secure repeated trials, although each was followed by failure, and it was several years before the last was heard of this system. [Illustration: FIG. 56.--The Atmospheric Railroad.] A considerable portion of several of the later years of Stephenson's life was spent in traveling in Europe, partly on business and partly for pleasure. During a visit to Belgium in 1845, he was received everywhere, and by all classes, from the king down to the humblest of his subjects, with such distinction as is rarely accorded even to the greatest men. He soon after visited Spain with Sir Joshua Walmsley, to report on a proposed railway from the capital to the Bay of Biscay. On this journey he was taken ill, and his health was permanently impaired. Thenceforward he devoted himself principally to the direction of his own property, which had become very considerable, and spent much of his time at the collieries and other works in which he had invested it. His son had now entirely relieved him of all business connected with railroads, and he had leisure to devote to self-improvement and social amusement. Among his friends he claimed Sir Robert Peel, his old acquaintance, now Sir William, Fairbairn, Dr. Buckland, and many others of the distinguished men of that time. In August, 1848, Stephenson was attacked with intermittent fever, succeeded by hæmorrhage from the lungs, and died on the 12th of that month, at the age of sixty-six years, honored of all men, and secure of an undying fame. Soon after his death, statues were erected at Liverpool, London, and Newcastle, the cost of the second of which was defrayed by private subscriptions, including a contribution of about $1,500 by 3,150 workingmen--one of the finest tributes ever offered to the memory of a great man. But the noblest monument is that which he himself erected by the establishment of a system of education and protection of his working-people at Clay Cross. He made it a condition of employment that every employé should contribute from five to twelve pence each fortnight to a fund, to which the works also made liberal contributions. From that fund it was directed that the expenses of free education of the children of the work-people, night-schools for those employed in the works, a reading-room and library, medical treatment, and a benevolent fund were to be defrayed. Music and cricket-clubs, and prize funds for the best garden, were also founded. The school, public hall, and the church of Clay Cross, and this noble system of support, are together a nobler monument than any statue or similar structure could be. The character of George Stephenson was in every way admirable. Simple, earnest, and honorable; courageous, indomitable, and industrious; humorous, kind, and philanthropic, his memory will long be cherished, and will long prove an incentive to earnest effort and to the pursuit of an honorable fame with hundreds of the youth who, reading his simple yet absorbing story, as told by his biographer, shall in later years learn to know him. [Illustration: FIG. 57.--Stephenson's Locomotive, 1833.] After the death of his father, Robert Stephenson continued, as he had already done for several years, to conduct the business of building locomotives, as well as of constructing railroads. The work of locomotive engine-building was done at Newcastle, and for many years those works were the principal engine-building establishment of the world. After their introduction on the Liverpool & Manchester road, the engines of the firm of Robert Stephenson & Co. were rapidly modified, until they assumed the form shown in Fig. 57, which remained standard until their gradual increase in weight compelled the builders to place a larger number of wheels beneath them, and make those other changes which finally resulted in the creation of distinct types for special kinds of work. In the engine of 1833, as shown above, the cylinders, _A_, are carried at the extreme forward end of the boiler, and the driving-wheels, _B_, are coupled directly to the connecting-rod of the engine and to each other. A buffer, _C_, extends in front, and the rear end of the boiler is formed into a rectangular fire-box, _D_, continuous with the shell, _E_, and the flame and gases pass to the connection and smoke-pipe, _F_, _G_, through a large number of small tubes, _a_. Steam is led to the cylinders by a steam-pipe, _H H_, to which it is admitted by the throttle-valve, _b_. A steam-dome, _I_, from which the steam is taken, assists by giving more steam-space far above the water-line, and thus furnishing dry steam. The exhaust steam issues with great velocity into the chimney from the pipe, _J_, giving great intensity of draught. The engine-driver stands on the platform, _K_, from which all the valves and handles are accessible. Feed-pumps, _L_, supply the boiler with water, which is drawn from the tender through the pipes, _e_, _f_. The valve-gear was then substantially what it is to-day, the "Stephenson link" (Fig. 58). On the driving-axle were keyed two eccentrics, _E_, so set that the motion of the one was adapted to driving the valve when the engine was moving forward, and the other was arranged to move the valve when running backward. The former was connected, through its strap and the rod, _B_, to the upper end of a "strap-link," _A_, while the second was similarly connected with the lower end. By means of a handle, _L_, and the link, _n_, and its connections, including the counterweighted bell-crank, _M_, this link could be raised or depressed, thus bringing the pin on the link-block, to which the valve-stem was connected, into action with either eccentric. Or, the link being set in mid-gear, the valve would cover both steam-ports of the cylinder, and the engine could move neither way. As shown, the engine is in position to run backward. A series of notches, _Z_, into either of which a catch on _L_ could be dropped, enabled the driver to place the link where he chose. In intermediate positions, between mid-gear and full-gear, the motion of the valve is such as to produce expansion of the steam, and some gain in economy of working, although reducing the power of the engine. [Illustration: FIG. 58.--The Stephenson Valve-Gear, 1833.] The success of the railroad and the locomotive in Great Britain led to its rapid introduction in other countries. In France, as early as 1823, M. Beaunier was authorized to construct a line of rails from the coal-mines of St. Étienne to the Loire, using horses for the traction of his trains; and in 1826, MM. Seguin began a road from St. Étienne to Lyons. In 1832, engines built at Lyons were substituted for horses on these roads, but internal agitations interrupted the progress of the new system in France, and, for 10 years after the opening of the Manchester & Liverpool road, France remained without steam-transportation on land. In Belgium the introduction of the locomotive was more promptly accomplished. Under the direction of Pierre Simon, an enterprising and well-informed young engineer, who had become known principally as an advocate of the even then familiar project of a canal across the Isthmus of Darien, very complete plans of railroad communication for the kingdom were prepared, in compliance with a decree dated July 31, 1834, and were promptly authorized. The road between Brussels and Mechlin was opened May 6, 1837, and other roads were soon built; and the railway system of Belgium was the first on the Continent of Europe. The first German railroad worked with locomotive steam-engines was that between Nuremberg and Fürth, built under the direction of M. Denis. The other European countries soon followed in this rapid march of improvement. In the United States, public attention had been directed to this subject, as has already been stated, very early in the present century, by Evans and Stevens. At that time the people of the United States, as was natural, closely watched every important series of events in the mother-country; and so remarkable and striking a change as that which was taking place in the time of Stephenson, in methods of communication and transportation, could not fail to attract general attention and awaken universal interest. Notwithstanding the success of the early experiments of Evans and others, and in spite of the statesmanlike arguments of Stevens and Dearborn, and the earnest advocacy of the plan by all who were familiar with the revelations which were daily made of the power and capabilities of the steam-engine, it was not until after the opening of the Manchester & Liverpool road that any action was taken looking to the introduction of the locomotive. Colonel John Stevens, in 1825, had built a small locomotive, which he had placed on a circular railway before his house--now Hudson Terrace--at Hoboken, to prove that his statements had a basis of fact. This engine had two "lantern" tubular boilers, each composed of small iron tubes, arranged vertically in circles about the furnaces.[55] This exhibition had no other effect, however, than to create some interest in the subject, which aided in securing a rapid adoption of the railroad when once introduced. [55] One of these sectional boilers is still preserved in the lecture-room of the author, at the Stevens Institute of Technology. The first line of rails in the New England States is said to have been laid down at Quincy, Mass., from the granite quarry to the Neponset River, three miles away, in 1826 and 1827. That between the coal-mines of Mauch Chunk, Pa., and the river Lehigh, nine miles distant, was built in 1827. In the following year the Delaware & Hudson Canal Company built a railroad from their mines to the termination of the canal at Honesdale. These roads were worked either by gravity or by horses and mules. The competition at Rainhill, on the Liverpool and Manchester Railroad, had been so widely advertised, and promised to afford such conclusive evidence relative to the value of the locomotive steam-engine and the railroad, that engineers and others interested in the subject came from all parts of the world to witness the trial. Among the strangers present were Mr. Horatio Allen, then chief-engineer of the Delaware & Hudson Canal Company, and Mr. E. L. Miller, a resident of Charleston, S. C., who went from the United States for the express purpose of seeing the new machines tested. Mr. Allen had been authorized to purchase, for the company with which he was connected, three locomotives and the iron for the road, and had already shipped one engine to the United States, and had set it at work on the road. This engine was received in New York in May, 1829, and its trial took place in August at Honesdale, Mr. Allen himself driving the engine. But the track proved too light for the locomotive, and it was laid up and never set at regular work. This engine was called the "Stourbridge Lion"; it was built by Foster, Rastrick & Co., of Stourbridge, England. During the summer of the next year, a small experimental engine, which was built in 1829 by Peter Cooper, of New York, was successfully tried on the Baltimore & Ohio Railroad, at Baltimore, making 13 miles in less than an hour, and moving, at some points on the road, at the rate of 18 miles an hour. One carriage carrying 36 passengers was attached. This was considered a working-model only, and was rated at one horse-power. Ross Winans, writing of this trial of Cooper's engine, makes a comparison with the work done by Stephenson's "Rocket," and claims a decided superiority for the former. He concluded that the trial established fully the practicability of using locomotives on the Baltimore & Ohio road at high speeds, and on all its curves and heavy gradients, without inconvenience or danger. This engine had a vertical tubular boiler, and the draught was urged, like that of the "Novelty" at Liverpool, by mechanical means--a revolving fan. The single steam-cylinder was 3-1/4 inches in diameter, and the stroke of piston 14-1/2 inches. The wheels were 30 inches in diameter, and connected to the crank-shaft by gearing. The engine, on the trial, worked up to 1.43 horse-power, and drew a gross weight of 4-1/2 tons. Mr. Cooper, unable to find such tubes as he needed for his boiler, used gun-barrels. The whole machine weighed less than a ton. Messrs. Davis & Gartner, a little later, built the "York" for this road--a locomotive having also a vertical boiler, of very similar form to the modern steam fire-engine boiler, 51 inches in diameter, and containing 282 fire-tubes, 16 inches long, and tapering from 1-1/2 inches diameter at the bottom to 1-1/4 at the top, where the gases were discharged through a combustion-chamber into a steam-chimney. This engine weighed 3-1/2 tons. They subsequently built several "grasshopper" engines (Fig. 59), some of which ran many years, doing good work, and one or two of which are still in existence. The first--the "Atlantic"--was set at work in September, 1832, and hauled 50 tons from Baltimore 40 miles, over gradients having a maximum rise of 37 feet to the mile, and on curves having a minimum radius of 400 feet, at the rate of 12 to 15 miles an hour. This engine weighed 6-1/2 tons, carried 50 pounds of steam--a pressure then common on both continents --and burned a ton of anthracite coal on the round trip. The blast was secured by a fan, and the valve-gear was worked by cams instead of eccentrics. This engine made the round trip at a cost of $16, doing the work of 42 horses, which had cost $33 per trip. The engine cost $4,500, and was designed by Phineas Davis, assisted by Ross Winans. [Illustration: FIG. 59.--The "Atlantic," 1882.] Mr. Miller, on his return from the Liverpool & Manchester trial, ordered a locomotive for the Charleston & Hamburg Railroad from the West Point Foundery. This engine was guaranteed by Mr. Miller to draw three times its weight at the rate of 10 miles an hour. It was built during the summer of 1830, from the plans of Mr. Miller, and reached Charleston in October. The trials were made in November and December. [Illustration: FIG. 60.--The "Best Friend," 1830.] This engine (Fig. 60) had a vertical tubular boiler, in which the gases rose through a very high fire-box, into which large numbers of rods projected from the sides and top, and passed out through tubes leading them laterally outward into an outside jacket, through which they rose to the chimney. The steam-cylinders were two in number, 8 inches in diameter and of 16 inches stroke, inclined so as to connect with the driving-axle. The four wheels were all of the same size, 4-1/2 feet in diameter, and connected by coupling-rods. The engine weighed 4-1/2 tons. The "Best Friend," as it was called, did excellent work until June, 1831, when the explosion of the boiler, in consequence of the recklessness of the fireman, unexpectedly closed its career. A second engine (Fig. 61) was built for this road, at the West Point Foundery, from plans furnished by Horatio Allen, and was received and set at work early in the spring of 1831. The engine, called the "West Point," had a horizontal tubular boiler, but was in other respects very similar to the "Best Friend." It is said to have done very good work. [Illustration: FIG. 61.--The "West Point," 1831.] The Mohawk & Hudson Railroad ordered an engine at about this time, also, of the West Point Foundery, and the trials, made in July and August, 1831, proved thoroughly successful. This engine, the "De Witt Clinton," was contracted for by John B. Jervis, and fitted up by David Matthew. It had two steam-cylinders, each 5-1/2 inches in diameter and 16 inches stroke of piston. The connecting-rods were directly attached to a cranked axle, and turned four coupled wheels 4-1/2 feet in diameter. These wheels had cast-iron hubs and wrought-iron spokes and tires. The tubes were of copper, 2-1/2 inches in diameter and 6 feet long. The engine weighed 3-1/2 tons, and hauled 5 cars at the rate of 30 miles an hour. Another engine, the "South Carolina" (Fig. 62), was designed by Horatio Allen for the South Carolina Railroad, and completed late in the year 1831. This was the first eight-wheeled engine, and the prototype, also, of a peculiar and lately-revived form of engine. In the summer of 1832, an engine built by Messrs. Davis & Gartner, of York, Pa., was put on the Baltimore & Ohio road, which at times attained a speed, unloaded, of 30 miles an hour. The engine weighed 3-1/2 tons, and drew, usually, 4 cars, weighing altogether 14 tons, from Baltimore to Ellicott's Mills, a distance of 13 miles, in the schedule-time, one hour. [Illustration: FIG. 62.--The "South Carolina," 1831.] Horatio Allen's engine on the South Carolina Railroad is said to have been the first eight-wheeled engine ever built. It was at about the time of which we are now writing that the first locomotive was built of what is now distinctively known as the American type--an engine with a "truck" or "bogie" under the forward end of the boiler. This was the "American" No. 1, built at the West Point Foundery, from plans furnished by John B. Jervis, Chief Engineer, for the Mohawk & Hudson Railroad. Ross Winans had already (1831) introduced the passenger-car with swiveling trucks.[56] It was completed in August, 1832, and is said by Mr. Matthew to have been an extremely fast and smooth-running engine. A mile a minute was repeatedly attained, and it is stated by the same authority,[57] that a speed of 80 miles an hour was sometimes made over a single mile. This engine had cylinders 9-1/2 inches diameter, 16 inches stroke of piston, two pairs of driving-wheels, coupled, 5 feet in diameter each; and the truck had four 33-inch wheels. The boiler contained tubes 3 inches in diameter, and its fire-box was 5 feet long and 2 feet 10 inches wide. Robert Stephenson & Co. subsequently built a similar engine, from the plans of Mr. Jervis, and for the same road. It was set at work in 1833. In both engines the driving-wheels were behind the fire-box. This engine is another illustration of the fact--shown by the description already given of other and earlier engines--that the independence of the American mechanic, and the boldness and self-confidence which have to the present time distinguished him, were among the earliest of the fruits of our political independence and freedom. [56] "History of the First Locomotives in America," Brown. [57] "Ross Winans _vs._ The Eastern Railroad Company--Evidence." Boston, 1854. These American engines were all designed to burn anthracite coal. The English locomotives all burned bituminous coal. Robert L. Stevens, the President and Engineer of the Camden & Amboy Railroad, and a distinguished son of Colonel John Stevens, of Hoboken, was engaged, at the time of the opening of the Liverpool & Manchester Railroad, in the construction of the Camden & Amboy Railroad. It was here that the first of the now standard form of _T_-rail was laid down. It was of malleable iron, and of the form shown in the accompanying figure. It was designed by Mr. Stevens, and is known in the United States as the "Stevens" rail. In Europe, where it was introduced some years afterward, it is sometimes called the "Vignolles" rail. He purchased an engine of the Stephensons soon after the trial at Rainhill, and this engine, the "John Bull," was set up on the then uncompleted road at Bordentown, in the year 1831. Its first public trial was made in November of that year. The road was opened for traffic, from end to end, two years later. This engine had steam-cylinders 9 inches in diameter, 2 feet stroke of piston, one pair of drivers 4-1/2 feet in diameter, and weighed 10 tons. This engine, and that built by Phineas Davis for the Baltimore & Ohio Railroad, were exhibited at the Centennial Exhibition at Philadelphia, in the year 1876. [Illustration: FIG. 63.--The "Stevens" Rail. Enlarged Section.] [Illustration: FIG. 64.--"Old Ironsides," 1832.] Engines supplied to the Camden & Amboy Railroad subsequent to 1831 were built from the designs of Robert L. Stevens, in the shop of the Messrs. Stevens, at Hoboken. The other principal roads of the country, at first, very generally purchased their engines of the Baldwin Locomotive Works, then a small shop owned by Matthias W. Baldwin. Baldwin's first engine was a little model built for Peale's Museum, to illustrate to the visitors of that then well-known place of entertainment the character of the new motor, the success of which, at Rainhill, had just then excited the attention of the world. This was in 1831, and the successful working of this little model led to his receiving an order for an engine from the Philadelphia & Germantown Railroad. Mr. Baldwin, after studying the new engine of the Camden & Amboy road, made his plans, and built an engine (Fig. 64), completing it in the autumn of 1832, and setting it in operation November 23d of that year. It was kept at work on that line of road for a period of 20 years or more. This engine was of Stephenson's "Planet" class, mounted on two driving-wheels 4-1/2 feet in diameter each, and two separate wheels of the same size, uncoupled. The steam-cylinders were 9-1/2 inches in diameter, 18 inches stroke of piston, and were placed horizontally on each side of the smoke-box. The boiler, 2-1/2 feet in diameter, contained 72 copper tubes 1-1/2 inches in diameter and 7 feet long. The engine cost the railroad company $3,500. On the trial, steam was raised in 20 minutes, and the maximum speed noted was 28 miles an hour. The engine subsequently attained a speed of over 30 miles. In 1834, Mr. Baldwin completed for Mr. E. L. Miller, of Charleston, a six-wheeled engine, the "E. L. Miller" (Fig. 65), with cylinders 10 inches in diameter and 16 inches stroke of piston. He made the boiler of this engine of a form which remained standard many years, with a high dome over the fire-box. At about the same time, he built the "Lancaster," an engine resembling the "Miller," for the State road to Columbia, and several others were soon contracted for and built. By the end of 1834, 5 engines had been built by him, and the construction of locomotive-engines had become one of the leading and most promising industries of the United States. Mr. William Norris established a shop in Philadelphia in 1832, which he gradually enlarged until it, like the Baldwin Works, became a large establishment. He usually built a six-wheeled engine, with a leading-truck or bogie, and placed his driving-wheels in front of the fire-box. [Illustration: FIG. 65.--The "E. L. Miller," 1834.] At this time the English locomotives were built to carry 60 pounds of steam. The American builders adopted pressures of 120 to 130 pounds per square inch, the now generally standard pressures throughout the world. In the years 1836 and 1837, Baldwin built 80 engines. They were of three classes: 1st, with cylinders 12-1/2 inches in diameter and of 16 inches stroke, weighing 12 tons; 2d, with cylinders 12 by 16, and a weight of 10-1/2 tons; and 3d, engines weighing 9 tons, and having steam-cylinders of 10-1/2 inches diameter and of the same stroke. The driving-wheels were usually 4-1/2 feet in diameter, and the cylinder "inside-connected" to cranked axles. A few "outside-connected" engines were made, this plan becoming generally adopted at a later period. The railroads of the United States were very soon supplied with locomotive-engines built in America. In the year 1836, William Norris, who had two years before purchased the interest of Colonel Stephen H. Long, an army-officer who patented and built locomotives of his own design, built the "George Washington," and set it at work. This engine, weighing 14,400 pounds, drew 19,200 pounds up an incline 2,800 feet long, rising 369 feet to the mile, at the speed of 15-1/2 miles an hour. This showed an adhesion not far from one-third the weight on the driving-wheels. This was considered a very wonderful performance, and it produced such an impression at the time, that several copies of the "George Washington" were made, on orders from British railroads, and the result was the establishment of the reputation of the locomotive-engine builders of the United States upon a foundation which has never since failed them. The engine had Jervis's forward-truck, now always seen under standard engines, which had already been placed under railroad-cars by Ross Winans. In New England, the Locks & Canals Company, of Lowell, began building engines as early as 1834, copying the Stephenson engine. Hinckley & Drury, of Boston, commenced building an outside-connected engine in 1840, and their successors, the Boston Locomotive Works, became the largest manufacturing establishment of the kind in New England. Two years later, Ross Winans, the Baltimore builder, introduced some of his engines upon Eastern railroads, fitting them with upright boilers, and burning anthracite coal. The changes which have been outlined produced the now typical American locomotive. It was necessarily given such form that it would work safely and efficiently on rough, ill-ballasted, and often sharply-winding tracks; and thus it soon became evident that the two pairs of coupled driving-wheels, carrying two-thirds the weight of the whole engine, the forward-truck, and the system of "equalizing" suspension-bars, by which the weight is distributed fairly among all the wheels, whatever the position of the engine, or whatever the irregularity of the track, made it the very best of all known types of locomotive for the railroads of a new country. Experience has shown it equally excellent on the smoothest and best of roads. The "cow-catcher," placed in front to remove obstacles from the track, the bell, and the heavy whistle, are characteristics of the American engine also. The severity of winter-storms compelled the adoption of the "cab," or house, and the use of wood for fuel led to the invention of the "spark-arrester" for that class of engines. The heavy grades on many roads led to the use of the "sand-box," from which sand was sprinkled on the track, to prevent the slipping of the wheels. In the year 1836, the now standard chilled wheel was introduced for cars and trucks; the single eccentric, which had been, until then, used on Baldwin engines, was displaced by the double eccentric, with hooks in place of the link; and, a year later, the iron frame took the place of the previously-used wooden frame on all engines. The year 1837 introduced a period of great depression in all branches of industry, which continued until the year 1840, or later, and seriously checked all kinds of manufacturing, including the building of locomotives. On the revival of business, numbers of new locomotive-works were started, and in these establishments originated many new types of engine, each of the more successful of which was adapted to some peculiar set of conditions. This variety of type is still seen on nearly all of the principal roads. The direction of change in the construction of locomotive-engines at the period at which this division of the subject terminates is very well indicated in a letter from Robert Stephenson to Robert L. Stevens, dated 1833, which is now preserved at the Stevens Institute of Technology. He writes: "I am sorry that the feeling in the United States in favor of light railways is so general. In England we are making every succeeding railway stronger and more substantial." He adds: "Small engines are losing ground, and large ones are daily demonstrating that powerful engines are the most economical." He gives a sketch of his latest engine, weighing _nine tons_, and capable, as he states, of "taking 100 tons, gross load, at the rate of 16 or 17 miles an hour on a level." To-day there are engines built weighing 70 tons, and our locomotive-builders have standard sizes guaranteed to draw over 2,000 tons on a good and level track. [Illustration] CHAPTER V. _THE MODERN STEAM-ENGINE._ "Voilà la plus merveilleuse de toutes les Machines; le Mécanisme ressemble à celui des animaux. La chaleur est le principe de son mouvement; il se fait dans ses différens tuyaux une circulation, comme celle du sang dans les veines, ayant des valvules qui s'ouvrent et se ferment à propos; elles se nourrit, s'évacue d'elle même dans les temps réglés, et tire de son travail tout ce qu'il lui faut pour subsister. Cette Machine a pris sa naissance en Angleterre, et toutes les Machines à feu qu'on a construites ailleurs que dans la Grande Brétagne ont été exécutées par des Anglais."--BELIDOR. THE SECOND PERIOD OF APPLICATION--1800-1850 (CONTINUED). THE STEAM-ENGINE APPLIED TO SHIP-PROPULSION. Among the most obviously important and most inconceivably fruitful of all the applications of steam which marked the period we are now studying, is that of the steam-engine to the propulsion of vessels. This direction of application has been that which has, from the earliest period in the history of the steam-engine, attracted the attention of the political economist and the historian, as well as the mechanician, whenever a new improvement, or the revival of an old device, has awakened a faint conception of the possibilities attendant upon the introduction of a machine capable of making so great a force available. The realization of the hopes, the prophecies, and the aspirations of earlier times, in the modern marine steam-engine, may be justly regarded as the greatest of all the triumphs of mechanical engineering. Although, as has already been stated, attempts were made at a very early period to effect this application of steam-power, they were not successful, and the steamship is a product of the present century. No such attempts were commercially successful until after the time of Newcomen and Watt, and at the commencement of the nineteenth century. It is, indeed, but a few years since the passage across the Atlantic was frequently made in sailing-vessels, and the dangers, the discomforts, and the irregularities of their trips were most serious. Now, hardly a day passes that does not see several large and powerful steamers leaving the ports of New York and Liverpool to make the same voyages, and their passages are made with such regularity and safety, that travelers can anticipate with confidence the time of their arrival at the termination of their voyage to a day, and can cross with safety and with comparative comfort even amid the storms of winter. Yet all that we to-day see of the extent and the efficiency of steam-navigation has been the work of the present century, and it may well excite our wonder and our admiration. The history of this development of the use of steam-power illustrates most perfectly that process of growth of this invention which has been already referred to; and we can here trace it, step by step, from the earliest and rudest devices up to those most recent and most perfect designs which represent the most successful existing types of the heat-engine--whether considered with reference to its design and construction, or as the highest application of known scientific principles--that have yet been seen in even the present advanced state of the mechanic arts. The paddle-wheel was used as a substitute for oars at a very early date, and a description of paddle-wheels applied to vessels, curiously illustrated by a large wood-cut, may be found in the work of Fammelli, "De l'artificioses machines," published in old French in 1588. Clark[58] quotes from Ogilby's edition of the "Odyssey" a stanza which reads like a prophecy, and almost awakens a belief that the great poet had a knowledge of steam-vessels in those early times--a thousand years before the Christian era. The prince thus addresses Ulysses: [58] "Steam and the Steam-Engine." "We use nor Helm nor Helms-man. Our tall ships Have Souls, and plow with Reason up the deeps; All cities, Countries know, and where they list, Through billows glide, veiled in obscuring Mist; Nor fear they Rocks, nor Dangers on the way." Pope's translation[59] furnishes the following rendering of Homer's prophecy: [59] "Odyssey," Book VIII., p. 175. "So shalt thou instant reach the realm assigned, In wondrous ships, self-moved, instinct with mind; ... Though clouds and darkness veil the encumbered sky, Fearless, through darkness and through clouds they fly. Though tempests rage, though rolls the swelling main, The seas may roll, the tempests swell in vain; E'en the stern god that o'er the waves presides, Safe as they pass and safe repass the tide, With fury burns; while, careless, they convey Promiscuous every guest to every bay." It is stated that the Roman army under Claudius Caudex was taken across to Sicily in boats propelled by paddle-wheels turned by oxen. Vulturius gives pictures of such vessels. This application of the force of steam was very possibly anticipated 600 years ago by Roger Bacon, the learned Franciscan monk, who, in an age of ignorance and intellectual torpor, wrote: "I will now mention some wonderful works of art and nature, in which there is nothing of magic, and which magic could not perform. Instruments may be made by which the largest ships, with only one man guiding them, will be carried with greater velocity than if they were full of sailors," etc., etc. Darwin's poetical prophecy was published long years before Watt's engine rendered its partial fulfillment a possibility; and thus, for many years before even the first promising effort had been made, the minds of the more intelligent had been prepared to appreciate the invention when it should finally be brought forward. The earliest attempt to propel a vessel by steam is claimed by Spanish authorities, as has been stated, to have been made by Blasco de Garay, in the harbor of Barcelona, Spain, in 1543. The record, claimed as having been extracted from the Spanish archives at Simancas, states the vessel to have been of 200 tons burden, and to have been moved by paddle-wheels; and it is added that the spectators saw, although not allowed closely to inspect the apparatus, that one part of it was a "vessel of boiling water"; and it is also stated that objection was made to the use of this part of the machine, because of the danger of explosion. The account seems somewhat apocryphal, and it certainly led to no useful results. In an anonymous English pamphlet, published in 1651, which is supposed by Stuart to have been written by the Marquis of Worcester, an indefinite reference to what may probably have been the steam-engine is made, and it is there stated to be capable of successful application to propelling boats. In 1690, Papin proposed to use his piston-engine to drive paddle-wheels to propel vessels; and in 1707 he applied the steam-engine, which he had proposed as a pumping-engine, to driving a model boat on the Fulda at Cassel. In this trial he used the arrangement of which a sketch has been shown, his pumping-engine forcing up water to turn a water-wheel, which, in turn, was made to drive the paddles. An account of his experiments is to be found in manuscript in the correspondence between Leibnitz and Papin, preserved in the Royal Library at Hanover. Professor Joy found there the following letter:[60] "Dionysius Papin, Councillor and Physician to his Royal Highness the Elector of Cassel, also Professor of Mathematics at Marburg, is about to dispatch a vessel of singular construction down the river Weser to Bremen. As he learns that all ships coming from Cassel, or any point on the Fulda, are not permitted to enter the Weser, but are required to unload at Münden, and as he anticipates some difficulty, although those vessels have a different object, his own not being intended for freight, he begs most humbly that a gracious order be granted that his ship may be allowed to pass unmolested through the Electoral domain; which petition I most humbly support. G. W. LEIBNITZ. "HANOVER, _July 13, 1707_." This letter was returned to Leibnitz, with the following indorsement: "The Electoral Councillors have found serious obstacles in the way of granting the above petition, and, without giving their reasons, have directed me to inform you of their decision, and that, in consequence, the request is not granted by his Electoral Highness. H. REICHE. "HANOVER, _July 25, 1707_." [60] _Scientific American_, February 24, 1877. This failure of Papin's petition was the death-blow to his effort to establish steam-navigation. A mob of boatmen, who thought they saw in the embryo steamship the ruin of their business, attacked the vessel at night, and utterly destroyed it. Papin narrowly escaped with his life, and fled to England. In the year 1736, Jonathan Hulls took out an English patent for the use of a steam-engine for ship-propulsion, proposing to employ his steamboat in towing. In 1737 he published a well-written pamphlet, describing this apparatus, which is shown in Fig. 66, a reduced fac-simile of the plate accompanying his paper. [Illustration: FIG. 66.--Hulls's Steamboat, 1736.] He proposed using the Newcomen engine, fitted with a counterpoise-weight and a system of ropes and grooved wheels, which, by a peculiar ratchet-like action, gave a continuous rotary motion. His vessel was to have been used as a tow-boat. He says, in his description: "In some convenient part of the Tow-boat there is placed a Vessel about two-3rds full of water, with the Top closed; and this Vessel being kept Boiling, rarifies the Water into a Steam, this Steam being convey'd thro' a large pipe into a cylindrical Vessel, and there condensed, makes a Vacuum, which causes the weight of the atmosphere to press down on this Vessel, and so presses down a Piston that is fitted into this Cylindrical Vessel, in the same manner as in Mr. Newcomen's Engine, with which he raises Water by Fire. "_P_, the Pipe coming from the Furnace to the Cylinder. _Q_, the Cylinder wherein the steam is condensed. _R_, the Valve that stops the Steam from coming into the Cylinder, whilst the Steam within the same is condensed. _S_, the Pipe to convey the condensing Water into the Cylinder. _T_, a cock to let in the condensing Water when the Cylinder is full of Steam and the Valve, _P_, is shut. _U_, a Rope fixed to the Piston that slides up and down in the Cylinder. "_Note._ This Rope, _U_, is the same Rope that goes round the wheel, _D_, in the machine." In the large division of his plate, _A_ is the chimney; _B_ is the tow-boat; _C C_ is the frame carrying the engine; _Da_, _D_, and _Db_ are three wheels carrying the ropes _M_, _Fb_, and _Fa_, _M_ being the rope _U_ of his smaller figure, 30. _Ha_ and _Hb_ are two wheels on the paddle-shafts, _I I_, arranged with pawls so that the paddle-wheel, _I I_, always turns the same way, though the wheels _Ha_ and _Hb_ are given a reciprocating motion; _Fb_ is a rope connecting the wheels in the vessel, _Db_, with the wheels at the stern. Hulls says: "When the Weight, _G_, is so raised, while the wheels _Da_, _D_, and _Db_ are moving backward, the Rope _Fa_ gives way, and the Power of the Weight, _G_, brings the Wheel _Ha_ forward, and the Fans with it, so that the Fans always keep going forward, notwithstanding the Wheels _Da_, _D_, and _Db_ move backward and forward as the Piston moves up and down in the Cylinder. _L L_ are Teeth for a Catch to drop in from the Axis, and are so contrived that they catch in an alternate manner, to cause the Fan to move always forward, for the Wheel _Ha_, by the power of the weight, _G_, is performing his Office while the other wheel, _Hb_, goes back in order to fetch another stroke. "_Note._ The weight, _G_, must contain but half the weight of the Pillar of Air pressing on the Piston, because the weight, _G_, is raised at the same time as the Wheel _Hb_ performs its Office, so that it is in effect two Machines acting alternately, by the weight of one Pillar of Air, of such a Diameter as the Diameter of the Cylinder is." The inventor suggests the use of timber guards to protect the wheels from injury, and, in shallow water, the attachment to the paddle-shafts of cranks "to strike a Shaft to the Bottom of the River, which will drive the Vessel forward with the greater Force." He concludes: "Thus I have endeavoured to give a clear and satisfactory Account of my New-invented Machine, for carrying Vessels out of and into any Port, Harbour, or River, against Wind and Tide, or in a Calm; and I doubt not but whoever shall give himself the Trouble to peruse this Essay, will be so candid as to excuse or overlook any Imperfections in the diction or manner of writing, considering the Hand it comes from, if what I have imagined may only appear as plain to others as it has done to me, viz., That the Scheme I now offer is Practicable, and if encouraged will be Useful." There is no positive evidence that Hulls ever put his scheme to the test of experiment, although tradition does say that he made a model, which he tried with such ill success as to prevent his prosecution of the experiment further; and doggerel rhymes are still extant which were sung by his neighbors in derision of his folly, as they considered it. A prize was awarded by the French Academy of Sciences, in 1752, for the best essay on the manner of impelling vessels without wind. It was given to Bernouilli, who, in his paper, proposed a set of vanes like those of a windmill--a screw, in fact--one to be placed on each side of the vessel, and two more behind. For a vessel of 100 tons, he proposed a shaft 14 feet long and 2 inches in diameter, carrying "eight wheels, for acting on the water, to each of which it" (the shaft) "is perpendicular, and forms an axis for them all; the wheels should be at equal distances from each other. Each wheel consists of 8 arms of iron, each 3 feet long, so that the whole diameter of the wheel is 6 feet. Each of these arms, at the distance of 20 inches from the centre, carries a sheet-iron plane (or paddle) 16 inches square, which is inclined so as to form an angle of 60 degrees, both with the arbor and keel of the vessel, to which the arbor is placed parallel. To sustain this arbor and the wheels, two strong bars of iron, between 2 and 3 inches thick, proceed from the side of the vessel at right angles to it, about 2-1/2 feet below the surface of the water." He proposed similar screw-propellers at the stern, and suggested that they could be driven by animal or by steam-power. But a more remarkable essay is quoted by Figuier[61]--the paper of l'Abbé Gauthier, published in the "Mémoires de la Société Royale des Sciences et Lettres de Nancy." Bernouilli had expressed the belief that the best steam-engine then known--that of Newcomen--was not superior to some other motors. Gauthier proposed to use that engine in the propulsion of paddle-wheels placed at the side of the vessel. His plan was not brought into use, but his paper embodied a glowing description of the advantages to be secured by its adoption. He states that a galley urged by 26 oars on a side made but 4,320 toises (8,420 meters), or about 5 miles, an hour, and required a crew of 260 men. A steam-engine, doing the same work, would be ready for action at all times, could be applied, when not driving the vessel, to raising the anchor, working the pumps, and to ventilating the ship, while the fire would also serve to cook with. The engine would occupy less space and weight than the men, would require less aliment, and that of a less expensive kind, etc. He would make the boiler safe against explosions by bands of iron; would make the fire-box of iron, with a water-filled ash-pit and base-plate. His injection-water was to come from the sea, and return by a delivery-pipe placed above the water-line. The chains, usually leading from the end of the beam to the pump-rods, were to be carried around wheels on the paddle-shaft, which were to be provided with pawls entering a ratchet, and thus the paddles, having been given several revolutions by the descent of the piston and the unwinding of the chain, were to revolve freely while the return-stroke was made, the chain being hauled down and rewound by the wheel on the shaft, the latter being moved by a weight. The engine was proposed to be of 6 feet stroke, and to make 15 strokes per minute, with a force of 11,000 pounds. [61] "Les Merveilles de la Science." A little later (1760), a Swiss clergyman, J. A. Genevois, published in London a paper relating to the improvement of navigation,[62] in which his plan was proposed of compressing springs by steam or other power, and applying their effort while recovering their form to ship-propulsion. [62] "Some New Enquiries tending to the Improvement of Navigation." London, 1760. It was at this time that the first attempts were made in the United States to solve this problem, which had begun to be recognized as one of the greatest which had presented itself to the mechanic and the engineer. WILLIAM HENRY was a prominent citizen of the then little village of Lancaster, Pa., and was noted as an ingenious and successful mechanic.[63] He was still living at the beginning of the present century. Mr. Henry was the first to make the "rag" carpet, and was the inventor of the screw-auger. He was of a Scotch and North-of-Ireland family, his father, John Henry, and his two older brothers, Robert and James, having come to the United States about 1720. Robert settled, finally, in Virginia, and it is said that Patrick Henry, the patriot and orator, was of his family. The others remained in Chester County, Pa., where William was born, in 1729. He learned the trade of a gunsmith, and, driven from his home during the Indian war (1755 to 1760), settled in Lancaster. [63] _Lancaster Daily Express_, December 10, 1872. This account is collated from various manuscripts and letters in the possession of the author. In the year 1760 he went to England on business, where his attention was attracted to the invention--then new, and the subject of discussion in every circle--of James Watt. He saw the possibility of its application to navigation and to driving carriages, and, on his return home, commenced the construction of a steam-engine, and finished it in 1763. Placing it in a boat fitted with paddle-wheels, he made a trial of the new machine on the Conestoga River, near Lancaster, where the craft, by some accident, sank,[64] and was lost. He was not discouraged by this failure, but made a second model, adding some improvements. Among the records of the Pennsylvania Philosophical Society is, or was, a design, presented by Henry in 1782, of one of his steamboats. The German traveler Schöpff visited the United States in 1783, and at Mr. Henry's house, at Lancaster, was shown "a machine by Mr. Henry, intended for the propelling of boats, etc.; 'but,' said Mr. Henry, 'I am doubtful whether such a machine would find favor with the public, as every one considers it impracticable against wind and tide;' but that such a Boat _will_ come into use and navigate on the waters of the Ohio and Mississippi, he had not the least doubt of, but the time had not yet arrived of its being appreciated and applied." [64] Bowen's "Sketches," p. 56. John Fitch, whose experiments will presently be referred to, was an acquaintance and frequent visitor to the house of Mr. Henry, and may probably have there received the earliest suggestions of the importance of this application of steam. About 1777, when Henry was engaged in making mathematical and philosophical instruments, and the screw-auger, which at that time could only be obtained of him, Robert Fulton, then twelve years old, visited him, to study the paintings of Benjamin West, who had long been a friend and protégé of Henry. He, too, not improbably received there the first suggestion which afterward led him to desert the art to which he at first devoted himself, and which made of the young portrait-painter a successful inventor and engineer. West's acquaintance with Henry had no such result. The young painter was led by his patron and friend to attempt historical pictures,[65] and probably owes his fame greatly to the kindly and discerning mechanic. Says Galt, in his "Memoirs of Sir Benjamin West" (London, 1816): "Towards his old friend, William Henry, of Lancaster City, he always cherished the most grateful affection; he was the first who urged him to attempt historical composition." [65] Some of West's portraits, including those of Mr. and Mrs. Henry, were lately in the possession of Mr. John Jordan, of Philadelphia. When, after the invention of Watt, the steam-engine had taken such shape that it could really work the propelling apparatus of a paddle or screw vessel, a new impetus was given to the work of its adaptation. In France, the Marquis de Jouffroy was one of the earliest to perceive that the improvements of Watt, rendering the engine more compact, more powerful, and, at the same time, more regular and positive in its action, had made it, at last, readily applicable to the propulsion of vessels. The brothers Périer had imported a Watt engine from Soho, and this was attentively studied by the marquis,[66] and its application to the paddle-wheels of a steam-vessel seemed to him a simple problem. Comte d'Auxiron and Chevalier Charles Mounin, of Follenai, friends and companions of Jouffroy, were similarly interested, and the three are said to have often discussed the scheme together, and to have united in devising methods of applying the new motor. [66] Figuier. In the year 1770, D'Auxiron determined to attempt the realization of the plans which he had conceived. He resigned his position in the army, prepared his plans and drawings, and presented them to M. Bertin, the Prime Minister, in the year 1771 or 1772. The Minister was favorably impressed, and the King (May 22, 1772) granted D'Auxiron a monopoly of the use of steam in river-navigation for 15 years, provided he should prove his plans practicable, and they should be so adjudged by the Academy. A company had been formed, the day previous, consisting of D'Auxiron, Jouffroy, Comte de Dijon, the Marquis d'Yonne, and Follenai, which advanced the requisite funds. The first vessel was commenced in December, 1772. When nearly completed, in September, 1774, the boat sprung a leak, and, one night, foundered at the wharf. After some angry discussion, during which D'Auxiron was rudely, and probably unjustly, accused of bad faith, the company declined to advance the money needed to recover and complete the vessel. They were, however, compelled by the court to furnish it; but, meantime, D'Auxiron died of apoplexy, the matter dropped, and the company dissolved. The cost of the experiment had been something more than 15,000 francs. The heirs of D'Auxiron turned the papers of the deceased inventor over to Jouffroy, and the King transferred to him the monopoly held by the former. Follenai retained all his interest in the project, and the two friends soon enlisted a powerful adherent and patron, the Marquis Ducrest, a well-known soldier, courtier, and member of the Academy, who took an active part in the prosecution of the scheme. M. Jacques Périer, the then distinguished mechanic, was consulted, and prepared plans, which were adopted in place of those of Jouffroy. The boat was built by Périer, and a trial took place in 1774, on the Seine. The result was unsatisfactory. The little craft could hardly stem the sluggish current of the river, and the failure caused the immediate abandonment of the scheme by Périer. Still undiscouraged, Jouffroy retired to his country home, at Baume-les-Dames, on the river Doubs. There he carried on his experiments, getting his work done as best he could, with the rude tools and insufficient apparatus of a village blacksmith. A Watt engine and a chain carrying "duck-foot" paddles were his propelling apparatus. The boat, which was about 14 feet long and 6 wide, was started in June, 1776. The duck's-foot system of paddles proved unsatisfactory, and Jouffroy gave it up, and renewed his experiments with a new arrangement. He placed on the paddle-wheel shaft a ratchet-wheel, and on the piston-rod of his engine, which was placed horizontally in the boat, a double rack, into the upper and the lower parts of which the ratchet-wheel geared. Thus the wheels turned in the same direction, whichever way the piston was moving. The new engine was built at Lyons in 1780, by Messrs. Frères-Jean. The new boat was about 140 feet long and 14 feet wide; the wheels were 14 feet in diameter, their floats 6 feet long, and the "dip," or depth to which they reached, was about 2 feet. The boat drew 3 feet of water, and had a total weight of about 150 tons. At a public trial of the vessel at Lyons, July 15, 1783, the little steamer was so successful as to justify the publication of the fact by a report and a proclamation. The fact that the experiment was not made at Paris was made an excuse on the part of the Academy for withholding its indorsement, and on the part of the Government for declining to confirm to Jouffroy the guaranteed monopoly. Impoverished and discouraged, Jouffroy gave up all hope of prosecuting his plans successfully, and reëntered the army. Thus France lost an honor which was already within her grasp, as she had already lost that of the introduction of the steam-engine, in the time of Papin. About 1785, John Fitch and James Rumsey were engaged in experiments having in view the application of steam to navigation. Rumsey's experiments began in 1774, and in 1786 he succeeded in driving a boat at the rate of four miles an hour against the current of the Potomac at Shepherdstown, W. Va., in presence of General Washington. His method of propulsion has often been reinvented since, and its adoption urged with that enthusiasm and persistence which is a peculiar characteristic of inventors. Rumsey employed his engine to drive a great pump which forced a stream of water aft, thus propelling the boat forward, as proposed earlier by Bernouilli. This same method has been recently tried again by the British Admiralty, in a gunboat of moderate size, using a centrifugal pump to set in motion the propelling stream, and with some other modifications which are decided improvements upon Rumsey's rude arrangements, but which have not done much more than his toward the introduction of "Hydraulic or Jet Propulsion," as it is now called. In 1787 he obtained a patent from the State of Virginia for steam-navigation. He wrote a treatise "On the Application of Steam," which was printed at Philadelphia, where a Rumsey society was organized for the encouragement of attempts at steam-navigation. Rumsey died of apoplexy, while explaining some of his schemes before a London society a short time later, December 23, 1793, at the age of fifty years. A boat, then in process of construction from his plans, was afterward tried on the Thames, in 1793, and steamed at the rate of four miles an hour. The State of Kentucky, in 1839, presented his son with a gold medal, commemorative of his father's services "in giving to the world the benefit of the steamboat." JOHN FITCH was an unfortunate and eccentric, but very ingenious, Connecticut mechanic. After roaming about until forty years of age, he finally settled on the banks of the Delaware, where he built his first steamboat. In April, 1785, as Fitch himself states, at Neshamony, Bucks County, Pa., he suddenly conceived the idea that a carriage might be driven by steam. After considering the subject a few days, his attention was led to the plan of using steam to propel vessels, and from that time to the day of his death he was a persistent advocate of the introduction of the steamboat. At this time, Fitch says, "I did not know that there was a steam-engine on the earth;" and he was somewhat disappointed when his friend, the Rev. Mr. Irwin, of Neshamony, showed him a sketch of one in "Martin's Philosophy." Fitch's first model was at once built, and was soon after tried on a small stream near Davisville. The machinery was made of brass, and the boat was impelled by paddle-wheels. A rough model of his steamboat was shown to Dr. John Ewing, Provost of the University of Pennsylvania, who, August 20, 1785, addressed a commendatory letter to an ex-Member of Congress, William C. Houston, asking him to assist Fitch in securing the aid of the General Government. The latter referred the inventor, by a letter of recommendation, to a delegate from New Jersey, Mr. Lambert Cadwalader. With this, and other letters, Fitch proceeded to New York, where Congress then met, and made his application in proper form. He was unsuccessful, and equally so in attempting to secure aid from the Spanish minister, who desired that the profits should be secured, by a monopoly of the invention, to the King of Spain. Fitch declined further negotiation, determined that, if successful at all, the benefit should accrue to his own countrymen. In September, 1785, Fitch presented to the American Philosophical Society, at Philadelphia, a model in which he had substituted an endless chain and floats for the paddle-wheels, with drawings and a descriptive account of his scheme. This model is shown in the accompanying figure. [Illustration: FIG. 67.--Fitch's Model, 1785.] In March, 1786, Fitch was granted a patent by the State of New Jersey, for the exclusive right to the navigation of the waters of the State by steam, for 14 years. A month later, he was in Philadelphia, seeking a similar patent from the State of Pennsylvania. He did not at once succeed, but in a few days he had formed a company, raised $300, and set about finding a place in which to construct his engine. Henry Voight, a Dutch watchmaker, a good mechanic, and a very ingenious man, took an interest in the company, and with him Fitch set about his work with great enthusiasm. After making a little model, having a steam-cylinder but one inch in diameter, they built a model boat and engine, the latter having a diameter of cylinder of three inches. They tried the endless chain, and other methods of propulsion, without success, and finally succeeded with a set of oars worked by the engine. In August, 1786, it was determined by the company to authorize the construction of a larger vessel; but the money was not readily obtained. Meantime, Fitch continued his efforts to secure a patent from the State, and was finally, March 28, 1787, successful. He also obtained a similar grant from the State of Delaware, in February of the same year, and from New York, March 19. Money was now subscribed more freely, and the work on the boat continued uninterruptedly until May, 1787, when a trial was made, which revealed many defects in the machinery. The cylinder-heads were of wood, and leaked badly; the piston leaked; the condenser was imperfect; the valves were not tight. All these defects were remedied, and a condenser invented by Voight--the "pipe-condenser"--was substituted for that defective detail as previously made. The steamboat was finally placed in working order, and was found capable, on trial, of making three or four miles an hour. But now the boiler proved to be too small to furnish steam steadily in sufficient quantity to sustain the higher speed. After some delay, and much distress on the part of the sanguine inventor, who feared that he might be at last defeated when on the very verge of success, the necessary changes were finally made, and a trial took place at Philadelphia, in presence of the members of the Convention--then in session at Philadelphia framing the Federal Constitution--August 22, 1787. Many of the distinguished spectators gave letters to Fitch certifying his success. Fitch now went to Virginia, where he succeeded in obtaining a patent, November 7, 1787, and then returned to ask a patent of the General Government. A controversy with Rumsey now followed, in which Fitch asserted his claims to the invention of the steamboat, and denied that Rumsey had done more than to revive the scheme which Bernouilli, Franklin, Henry, Paine, and others, had previously proposed, and that Rumsey's _steamboat_ was not made until 1786. The boiler adopted in Fitch's boat of 1787 was a "pipe-boiler," which he had described in a communication to the Philosophical Society, in September, 1785. It consisted (Fig. 68) of a small water-pipe, winding backward and forward in the furnace, and terminating at one end at the point at which the feed-water was introduced, and at the other uniting with the steam-pipe leading to the engine. Voight's condenser was similarly constructed. Rumsey claimed that this boiler was copied from his designs. Fitch brought evidence to prove that Rumsey had not built such a boiler until after his own. [Illustration: FIG. 68.--Fitch and Voight's Boiler, 1787.] [Illustration: FIG. 69.--Fitch's First Boat, 1787.] Fitch's first boat-engine had a steam-cylinder 12 inches in diameter. A second engine was now built (1788) with a cylinder 18 inches in diameter, and a new boat. The first vessel was 45 feet long and 12 feet wide; the new boat was 60 feet long and of but 8 feet breadth of beam. The first boat (Fig. 69) had paddles worked at the sides, with the motion given the Indian paddle in propelling a canoe; in the second boat (Fig. 70) they were similarly worked, but were placed at the stern. There were three of these paddles. The boat was finally finished in July, 1788, and made a trip to Burlington, 20 miles from Philadelphia. When just reaching their destination, their boiler gave out, and they made their return-trip to Philadelphia floating with the tide. Subsequently, the boat made a number of excursions on the Delaware River, making three or four miles an hour. [Illustration: FIG. 70.--John Fitch, 1788.] Another of Fitch's boats, in April, 1790, made seven miles an hour. Fitch, writing of this boat, says that "on the 16th of April we got our work completed, and tried our boat again; and, although the wind blew very fresh at the east, we reigned lord high admirals of the Delaware, and no boat on the river could hold way with us." In June of that year it was placed as a passenger-boat on a line from Philadelphia to Burlington, Bristol, Bordentown, and Trenton, occasionally leaving that route to take excursions to Wilmington and Chester. During this period, the boat probably ran between 2,000 and 3,000 miles,[67] and with no serious accident. During the winter of 1790-'91, Fitch commenced another steamboat, the "Perseverance," and gave considerable time to the prosecution of his claim for a patent from the United States. The boat was never completed, although he received his patent, after a long and spirited contest with other claimants, on the 26th of August, 1791, and Fitch lost all hope of success. He went to France in 1793, hoping to obtain the privilege of building steam-vessels there, but was again disappointed, and worked his passage home in the following year. [67] "Life of John Fitch," Westcott. [Illustration: FIG. 71.--John Fitch, 1796.] In the year 1796, Fitch was again in New York City, experimenting with a little _screw_ steamboat on the "Collect" Pond, which then covered that part of the city now occupied by the "Tombs," the city prison. This little boat was a ship's yawl fitted with a screw, like that adopted later by Woodcroft, and driven by a rudely-made engine. Fitch, while in the city of Philadelphia at about this time, met Oliver Evans, and discussed with him the probable future of steam-navigation, and proposed to form a company in the West, to promote the introduction of steam on the great rivers of that part of the country. He settled at last in Kentucky, on his land-grant, and there amused himself with a model steamboat, which he placed in a small stream near Bardstown. His death occurred there in July, 1798, and his body still lies in the village cemetery, with only a rough stone to mark the spot. Both Rumsey and Fitch endeavored to introduce their methods in Great Britain; and Fitch, while urging the importance and the advantages of his plan, confidently stated his belief that the ocean would soon be crossed by steam-vessels, and that the navigation of the Mississippi would also become exclusively a steam-navigation. His reiterated assertion, "The day will come when some more powerful man will get fame and riches from my invention; but no one will believe that poor John Fitch can do anything worthy of attention," now almost sounds like a prophecy. During this period, an interest which had never diminished in Great Britain had led to the introduction of experimental steamboats in that country. PATRICK MILLER, of Dalswinton, had commenced experimenting, in 1786-'87, with boats having double or triple hulls, and propelled by paddle-wheels placed between the parts of the compound vessel. James Taylor, a young man who had been engaged as tutor for Mr. Miller's sons, suggested, in 1787, the substitution of steam for the manual power which had been, up to that time, relied upon in their propulsion. Mr. Miller, in 1787, printed a description of his plan of propelling apparatus, and in it stated that he had "reason to believe that the power of the Steam-Engine may be applied to work the wheels." In the winter of 1787-'88, William Symmington, who had planned a new form of steam-engine, and made a successful working-model, was employed by Mr. Miller to construct an engine for a new boat. This was built; the little engine, having two cylinders of but four inches in diameter, was placed on board, and a trial was made October 14, 1788. The vessel (Fig. 72) was 25 feet long, of 7 feet beam, and made 5 miles an hour. [Illustration: FIG. 72.--Miller, Taylor, and Symmington, 1788.] In the year 1789, a large vessel was built, with an engine having a steam-cylinder 18 inches in diameter, and this vessel was ready for trial in November of that year. On the first trial, the paddle-wheels proved too slight, and broke down; they were replaced by stronger wheels, and, in December, the boat, on trial, made seven miles an hour. Miller, like many other inventors, seems to have lost his interest in the matter as soon as success seemed assured, and dropped it to take up other incomplete plans. More than a quarter of a century later, the British Government gave Taylor a pension of £50 per annum, and, in 1837, his four daughters were each given a similar annuity. Mr. Miller received no reward, although he is said to have expended over £30,000. The engine of Symmington was condemned by Miller as "the most improper of all steam-engines for giving motion to a vessel." Nothing more was done in Great Britain until early in the succeeding century. In the United States, several mechanics were now at work besides Fitch. Samuel Morey and Nathan Read were among these. Nicholas Roosevelt was another. It had just been found that American mechanics were able to do the required shop-work. The first experimental steam-engine built in America is stated to have been made in 1773 by Christopher Colles, a lecturer before the American Philosophical Society at Philadelphia. The first steam-cylinder of any considerable size is said[68] to have been made by Sharpe & Curtenius, of New York City. [68] _Rivington's Gazette_, February 16, 1775. SAMUEL MOREY was the son of one of the first settlers of Orford, N. H. He was naturally fond of science and mechanics, and became something of an inventor. He began experimenting with the steamboat in 1790 or earlier, building a small vessel, and fitting it with paddle-wheels driven by a steam-engine of his own design, and constructed by himself.[69] He made a trial-trip one Sunday morning in the summer of 1790, a friend to accompany him, from Oxford, up the Connecticut River, to Fairlee, Vt., a distance of several miles, and returned safely. He then went to New York, and spent the summer of each year until 1793 in experimenting with his boat and modifications of his engine. In 1793 he made a trip to Hartford, returning to New York the next summer. His boat was a "stern-wheeler," and is stated to have been capable of steaming five miles an hour. He next went to Bordentown, N. J., where he built a larger boat, which is said to have been a side-wheel boat, and to have worked satisfactorily. His funds finally gave out, and he gave up his project after having, in 1797, made a trip to Philadelphia. Fulton, Livingston, and Stevens met Morey at New York, inspected his boat, and made an excursion to Greenwich with him.[70] Livingston is said[71] to have offered to assist Morey if he should succeed in attaining a speed of eight miles an hour. [69] _Providence Journal_, May 7, 1874. Coll., N. H. Antiquar. Soc., No. 1; "Who invented the Steamboat?" William A. Mowry, 1874. [70] Rev. Cyrus Mann, in the _Boston Recorder_, 1858. [71] Westcott. Morey's experiments seem to have been conducted very quietly, however, and almost nothing is known of them. The author has not been able to learn any particulars of the engines used by him, and nothing definite is known of the dimensions of either boat or machinery. Morey never, like Fitch and Rumsey, sought publicity for his plans or notoriety for himself. NATHAN READ, who has already been mentioned, a native of Warren, Mass., where he was born in the year 1759, and a graduate of Harvard College, was a student of medicine, and subsequently a manufacturer of chain-cables and other iron-work for ships. He invented, and in 1798 patented, a nail-making machine. He was at one time (1800-1803) a Member of Congress, and, later, a Justice of the Court of Common Pleas, and Chief Justice in Hancock County, Me., after his removal to that State in 1807. He died in Belfast, Me., in 1849, at the age of ninety years. In the year 1788 he became interested in the problem of steam-navigation, and learned something of the work of Fitch. He first attempted to design a boiler that should be strong, light, and compact, as well as safe. His first plan was that of the "Portable Furnace-Boiler," as he called it; it was patented August 26, 1791. As designed, it consisted, as seen in Figs. 73 and 74, which are reduced from his patent drawings, of a shell of cylindrical form, like the now common vertical tubular boiler. _A_ is the furnace-door, _B_ a heater and feed-water reservoir, _D_ a pipe leading the feed-water into the boiler,[72] _E_ the smoke-pipe, and _F_ the steam-pipe leading to the engine. _G_ is the "shell" of the boiler, and _H_ the fire-box. The crown-sheet, _I I_, has depending from it, in the furnace, a set of water-tubes, _b b_, closed at their lower ends, and another set, _a a_, which connect the water-space above the furnace with the water-bottom, _K K_. _L_ is the furnace, and _M_ the draught-space between the boiler and the ash-pit, in which the grates are set. [72] This is substantially an arrangement that has recently become common. It has been repatented by later inventors. [Illustration: FIG. 73.--Read's Boiler in Section, 1788.] [Illustration: FIG. 74.--Read's Multi-Tubular Boiler, 1788.] This boiler was intended to be used in both steamboats and steam-carriages. The first drawings were made in 1788 or 1789, as were those of a peculiar form of steam-engine which also resembled very closely that afterward constructed in Great Britain by Trevithick.[73] He built a boat in 1789, which he fitted with paddle-wheels and a crank, which was turned by hand, and, by trial, satisfied himself that the system would work satisfactorily. [73] "Nathan Read and the Steam-Engine." He then applied for his patent, and spent the greater part of the winter of 1789-'90 in New York, where Congress then met, endeavoring to secure it. In January, 1791, Read withdrew his petitions for patents, proposing to incorporate accounts of new devices, and renewed them a few months later. His patents were finally issued, dated August 26, 1791. John Fitch, James Rumsey, and John Stevens, also, all received patents at the same date, for various methods of applying steam to the propulsion of vessels. Read appears to have never succeeded in even experimentally making his plans successful. He deserves credit for his early and intelligent perception of the importance of the subject, and for the ingenuity of his devices. As the inventor of the vertical multi-tubular fire-box boiler, he has also entitled himself to great distinction. This boiler is now in very general use, and is a standard form. In 1792, Elijah Ormsbee, a Rhode Island mechanic, assisted pecuniarily by David Wilkinson, built a small steamboat at Winsor's Cove, Narragansett Bay, and made a successful trial-trip on the Seekonk River. Ormsbee used an "atmospheric engine" and "duck's-foot" paddles. His boat attained a speed of from three to four miles an hour. In Great Britain, Lord Dundas and William Symmington, the former as the purveyor of funds and the latter as engineer, followed by Henry Bell, were the first to make the introduction of the steam-engine for the propulsion of ships so completely successful that no interruption subsequently took place in the growth of the new system of water-transportation. Thomas, Lord Dundas, of Kerse, had taken great interest in the experiments of Miller, and had hoped to be able to apply the new motor on the Forth and Clyde Canal, in which he held a large interest. After the failure of the earlier experiments, he did not forget the matter; but subsequently, meeting with Symmington, who had been Miller's constructing engineer, he engaged him to continue the experiments, and furnished all required capital, about £7,000. This was ten years after Miller had abandoned his scheme. Symmington commenced work in 1801. The first boat built for Lord Dundas, which has been claimed to have been the "first practical steamboat," was finished ready for trial early in 1802. The vessel was called the "Charlotte Dundas," in honor of a daughter of Lord Dundas, who became Lady Milton. [Illustration: FIG. 75.--The "Charlotte Dundas," 1801.] The vessel (Fig. 75) was driven by a Watt double-acting engine, turning a crank on the paddle-wheel shaft. The sectional sketch below exhibits the arrangement of the machinery. _A_ is the steam-cylinder, driving, by means of the connecting-rod, _B C_, a stern-wheel, _E E_. _F_ is the boiler, and _G_ the tall smoke-pipe. An air-pump and condenser, _H_, is seen under the steam-cylinder. In March, 1802, the boat was brought to Lock No. 20 on the Forth and Clyde Canal, and two vessels of 70 tons burden each taken in tow. Lord Dundas, William Symmington, and a party of invited guests, were taken on board, and the boat steamed down to Port Glasgow, a distance of about 20 miles, against a strong head-wind, in six hours. The proprietors of the canal were now urged to adopt the new plan of towing; but, fearing injury to the banks of the canal, they declined to do so. Lord Dundas then laid the matter before the Duke of Bridgewater, who gave Symmington an order for eight boats like the Charlotte Dundas, to be used on his canal. The death of the Duke, however, prevented the contract from being carried into effect, and Symmington again gave up the project in despair. A quarter of a century later, Symmington received from the British Government £100, and, a little later, £50 additional, as an acknowledgment of his services. The Charlotte Dundas was laid up, and we hear nothing more of that vessel. [Illustration: FIG. 76.--The "Comet," 1812.] Among those who saw the Charlotte Dundas, and who appreciated the importance of the success achieved by Symmington, was HENRY BELL, who, 10 years afterward, constructed the Comet (Fig. 76), the first passenger-vessel built in Europe. This vessel was built in 1811, and completed January 18, 1812. The craft was of 30 tons burden, 40 feet in length, and 10-1/2 feet breadth of beam. There were _two_ paddle-wheels on each side, driven by engines rated at three horse-power. Bell had, it is said, been an enthusiastic believer in the advantages to be secured by this application of steam, from about 1786. In 1800, and again in 1803, he applied to the British Admiralty for aid in securing those advantages by experimentally determining the proper form and proportions of machinery and vessel; but was not able to convince the Admiralty of "the practicability and great utility of applying steam to the propelling of vessels against winds and tides, and every obstruction on rivers and seas where there was depth of water." He also wrote to the United States Government, urging his views in a similar strain. Bell's boat was, when finished, advertised as a passenger-boat, to leave Greenock, where the vessel was built, on Mondays, Wednesdays, and Fridays, for Glasgow, 24 miles distant, returning Tuesdays, Thursdays, and Saturdays. The fare was made "four shillings for the best cabin, and three shillings for the second." It was some months before the vessel became considered a trustworthy means of conveyance. Bell, on the whole, was at first a heavy loser by his venture, although his boat proved itself a safe, stanch vessel. Bell constructed several other boats in 1815, and with his success steam-navigation in Great Britain was fairly inaugurated. In 1814 there were five steamers, all Scotch, regularly working in British waters; in 1820 there were 34, one-half of which were in England, 14 in Scotland, and the remainder in Ireland. Twenty years later, at the close of the period to which this chapter is especially devoted, there were about 1,325 steam-vessels in that kingdom, of which 1,000 were English and 250 Scotch. But we must return to America, to witness the first and most complete success, commercially, in the introduction of the steamboat. The Messrs. Stevens, Livingston, Fulton, and Roosevelt were there the most successful pioneers. The latter is said to have built the "Polacca," a small steamboat launched on the Passaic River in 1798. The vessel was 60 feet long, and had an engine of 20 inches diameter of cylinder and 2 feet stroke, which drove the boat 8 miles an hour, carrying a party of invited guests, which included the Spanish Minister. Livingston and John Stevens had induced Roosevelt to try their plans still earlier,[74] paying the expense of the experiments. The former adopted the plan of Bernouilli and Rumsey, using a centrifugal pump to force a jet of water from the stern; the latter used the screw. Livingston going to France as United States Minister, Barlow carried over the plans of the "Polacca," and Roosevelt's friends state that a boat built by them, in conjunction with Fulton, was a "sister-ship" to that vessel. In 1798, Roosevelt patented a double engine, having cranks set at right angles. As late as 1814 he received a patent for a steam-vessel, fitted with paddle-wheels having adjustable floats. His boat of 1798 is stated by some writers to have been made by him on joint account of himself, Livingston, and Stevens. Roosevelt, some years later, was again at work, associating himself with Fulton in the introduction of steam-navigation of the rivers of the West.[75] [74] "Encyclopædia Americana." [75] "A Lost Chapter in the History of the Steamboat," J. H. B. Latrobe, 1871. In 1798, the Legislature of New York passed a law giving Chancellor Livingston the exclusive right to steam-navigation in the waters of the State for a period of 20 years, _provided_ that he should succeed, within a twelve-month, in producing a boat that should steam four miles an hour. Livingston did not succeed in complying with the terms of the act, but, in 1803, he procured the reënactment of the law in favor of himself and Robert Fulton, who was then experimenting in France, after having, in England, watched the progress of steam-navigation there, and then taken a patent in this country. [Illustration: Robert Fulton.] ROBERT FULTON was a native of Little Britain, Lancaster County, Pa., born 1765. He commenced experimenting with paddle-wheels when a mere boy, in 1779, visiting an aunt living on the bank of the Conestoga.[76] During his youth he spent much of his time in the workshops of his neighborhood, and learned the trade of a watchmaker; but he adopted, finally, the profession of an artist, and exhibited great skill in portrait-painting. While his tastes were at this time taking a decided bent, he is said to have visited frequently the house of William Henry, already mentioned, to see the paintings of Benjamin West, who in his youth had been a kind of protégé of Mr. Henry; and he may probably have seen there the model steamboats which Mr. Henry exhibited, in 1783 or 1784, to the German traveler Schöpff. In later years, Thomas Paine, the author of "Common Sense," at one time lived with Mr. Henry, and afterward, in 1788, proposed that Congress take up the subject for the benefit of the country. [76] _Vide_ "Life of Fulton," Reigart. Fulton went to England when he came of age, and studied painting with Benjamin West. He afterward spent two years in Devonshire, where he met the Duke of Bridgewater, who afterward so promptly took advantage of the success of the "Charlotte Dundas." While in England and in France--where he went in 1797, and resided some time--he may have seen something of the attempts which were beginning to be made to introduce steam-navigation in both of those countries. At about this time--perhaps in 1793--Fulton gave up painting as a profession, and became a civil engineer. In 1797 he went to Paris, and commenced experimenting with submarine torpedoes and torpedo-boats. In 1801 he had succeeded so well with them as to create much anxiety in the minds of the English, then at war with France. He had, as early as 1793, proposed plans for steam-vessels, both to the United States and the British Governments, and seems never entirely to have lost sight of the subject.[77] While in France he lived with Joel Barlow, who subsequently became known as a poet, and as Embassador to France from the United States, but who was then engaged in business in Paris. [77] _Vide_ "Life of Fulton," Colden. When about leaving the country, Fulton met Robert Livingston (Chancellor Livingston, as he is often called), who was then (1801) Embassador of the United States at the court of France. Together they discussed the project of applying steam to navigation, and determined to attempt the construction of a steamboat on the Seine; and in the early spring of the year 1802, Fulton having attended Mrs. Barlow to Plombières, where she had been sent by her physician, he there made drawings and models, which were sent or described to Livingston. In the following winter Fulton completed a model side-wheel boat. [Illustration: FIG. 77.--Fulton's Experiments.] January 24, 1803, he delivered this model to MM. Molar, Bordel, and Montgolfier, with a descriptive memoir, in which he stated that he had, by experiment, proven that side-wheels were better than the "chaplet" (paddle-floats set on an endless chain).[78] These gentlemen were then building for Fulton and Livingston their first boat, on L'Isle des Cygnes, in the Seine. In planning this boat, Fulton had devised many different methods of applying steam to its propulsion, and had made some experiments to determine the resistance of fluids. He therefore had been able to calculate, more accurately than had any earlier inventor, the relative size and proportions of boat and machinery. [78] A French inventor, a watchmaker of Trévoux, named Desblancs, had already deposited at the Conservatoire a model fitted with "chaplets." [Illustration: FIG. 78.--Fulton's Table of Resistances.] The author has examined a large collection of Fulton's drawings, among which are sketches, very neatly executed, of many of these plans, including the chaplet, side-wheel, and stern-wheel boats, driven by various forms of steam-engine, some working direct, and some geared to the paddle-wheel shaft. Figs. 77 and 78 are engraved from two of these sheets. The first represents the method adopted by Fulton to determine the resistance of masses of wood of various forms and proportions, when towed through water. The other is "A Table of the resistance of bodies moved through water, taken from experiments made in England by a society for improving Naval architecture, between the years 1793 and 1798" (Fig. 78). This latter is from a certified copy of "The Original Drawing on file in the Office of the Clerk of the New York District, making a part of the Demonstration of the patent granted to Robert Fulton, Esqr., on the 11th day of February, 1809. Dated this 3rd March, 1814," and is signed by Theron Rudd, Clerk of the New York District. Resistances are given in pounds per square foot. Guided by these experiments and calculations, therefore, Fulton directed the construction of his vessel. It was completed in the spring of 1803. But, unfortunately, the hull of the little vessel was too weak for its heavy machinery, and it broke in two and sank to the bottom of the Seine. Undiscouraged, Fulton at once set about repairing damages. He was compelled to direct the rebuilding of the hull. The machinery was little injured. In June, 1803, the reconstruction was completed, and the vessel was set afloat in July. The hull was 66 feet long, of 8 feet beam, and of light draught. August 9, 1803, this boat was cast loose, and steamed up the Seine, in presence of an immense concourse of spectators. A committee of the National Academy, consisting of Bougainville, Bossuet, Carnot, and Périer, were present to witness the experiment. The boat moved but slowly, making only between 3 and 4 miles an hour against the current, the speed through the water being about 4-1/2 miles; but this was, all things considered, a great success. The experiment was successful, but it attracted little attention, notwithstanding the fact that its success had been witnessed by the committee of the Academy and by many well-known savants and mechanics, and by officers on Napoleon's staff. The boat remained a long time on the Seine, near the palace. The water-tube boiler of this vessel (Fig. 79) is still preserved at the Conservatoire des Arts et Métiers at Paris, where it is known as Barlow's boiler. Barlow patented it in France as early as 1793, as a steamboat-boiler, and states that the object of his construction was to obtain the greatest possible extent of heating-surface. Fulton endeavored to secure the pecuniary aid and the countenance of the First Consul, but in vain. Livingston wrote home, describing the trial of this steamboat and its results, and procured the passage of an act by the Legislature of the State of New York, extending a monopoly granted him in 1798 for the term of 20 years from April 5, 1803, the date of the new law, and extending the time allowed for proving the practicability of driving a boat four miles an hour by steam to two years from the same date. A later act further extended the time to April, 1807. [Illustration: FIG. 79.--Barlow's Water-Tube Boiler, 1793.] In May, 1804, Fulton went to England, giving up all hope of success in France with either his steamboats or his torpedoes. Fulton had already written to Boulton & Watt, ordering an engine to be built from plans which he furnished them; but he had not informed them of the purpose to which it was to be applied. This engine was to have a steam-cylinder 2 feet in diameter and of 4 feet stroke. The engine of the Charlotte Dundas was of very nearly the same size; and this fact, and the visit of Fulton to Symmington in 1801, as described by the latter, have been made the basis of a claim that Fulton was a copyist of the plans of others. The general accordance of the dimensions of his boat on the Seine with those of the "Polacca" of Roosevelt is also made the basis of similar claims by the friends of the latter. It would appear, however, that Symmington's statement is incorrect, as Fulton was in France, experimenting with torpedoes, at the time (July, 1801[79]) when he is accused of having obtained from the English engineer the dimensions and a statement of the performance of his vessel. Yet a fireman employed by Symmington has made an affidavit to the same statement. It is evident, however, from what has preceded, that those inventors and builders who were at that time working with the object of introducing the steamboat were usually well acquainted with what had been done by others, and with what was being done by their contemporaries; and it is undoubtedly the fact that each profited, so far as he was able, by the experience of others. [79] Woodcroft, p. 64. While in England, however, Fulton was certainly not so entirely absorbed in the torpedo experiments with which he was occupied in the years 1804-'6 as to forget his plans for a steamboat; and he saw the engine ordered by him in 1804 completed in the latter year, and preceded it to New York, sailing from Falmouth in October, 1806, and reaching the United States December 13, 1806. The engine was soon received, and Fulton immediately contracted for a hull in which to set it up. Meantime, Livingston had also returned to the United States, and the two enthusiasts worked together on a larger steamer than any which had yet been constructed. In the spring of 1807, the "Clermont" (Fig. 80), as the new boat was christened, was launched from the ship-yard of Charles Brown, on the East River, New York. In August the machinery was on board and in successful operation. The hull of this boat was 133 feet long, 18 wide, and 9 deep. The boat soon made a trip to Albany, running the distance of 150 miles in 32 hours running time, and returning in 30 hours. The sails were not used on either occasion. [Illustration: FIG. 80.--The Clermont, 1807.] This was the first voyage of considerable length ever made by a steam-vessel; and Fulton, though not to be classed with James Watt as an inventor, is entitled to the great honor of having been the first to make steam-navigation an every-day commercial success, and of having thus made the first application of the steam-engine to ship-propulsion, which was not followed by the retirement of the experimenter from the field of his labors before success was permanently insured. [Illustration: FIG. 81.--Engine of the Clermont, 1808.] The engine of the Clermont (Fig. 81) was of rather peculiar form, the piston, _E_, being coupled to the crank-shaft, _O_, by a bell-crank, _I H P_, and a connecting-rod, _P Q_, the paddle-wheel shaft, _M N_, being separate from the crank-shaft, and connected with the latter by gearing, _O O_. The cylinders were 24 inches in diameter by 4 feet stroke. The paddle-wheels had buckets 4 feet long, with a dip of 2 feet. Old drawings, made by Fulton's own hand, and showing the engine as it was in 1808, and the engine of a later steamer, the Chancellor Livingston, are in the lecture-room of the author at the Stevens Institute of Technology. The voyage of the Clermont to Albany was attended by some ludicrous incidents, which found their counterparts wherever, subsequently, steamers were for the first time introduced. Mr. Colden, the biographer of Fulton, says that she was described, by persons who had seen her passing by night, "as a monster moving on the waters, defying wind and tide, and breathing flames and smoke." This first steamboat used dry pine wood for fuel, and the flames rose to a considerable distance above the smoke-pipe. When the fires were disturbed, mingled smoke and sparks would rise high in the air. "This uncommon light," says Colden, "first attracted the attention of the crews of other vessels. Notwithstanding the wind and tide were averse to its approach, they saw with astonishment that it was rapidly coming toward them; and when it came so near that the noise of the machinery and paddles was heard, the crews (if what was said in the newspapers of the time be true), in some instances, shrank beneath their decks from the terrific sight, and left their vessels to go on shore; while others prostrated themselves, and besought Providence to protect them from the approach of the horrible monster which was marching on the tides, and lighting its path by the fires which it vomited." In the Clermont, Fulton used several of the now characteristic features of the American river steamboat, and subsequently introduced others. His most important and creditable work, aside from that of the introduction of the steamboat into every-day use, was the experimental determination of the magnitude and the laws of ship-resistance, and the systematic proportioning of vessel and machinery to the work to be done by them. The success of the Clermont on the trial-trip was such that Fulton soon after advertised the vessel as a regular passenger-boat between New York and Albany.[80] [80] A newspaper-slip in the scrap-book of the author has the following: "The traveler of today, as he goes on board the great steamboats St. John or Drew, can scarcely imagine the difference between such floating palaces and the wee-bit punts on which our fathers were wafted 60 years ago. We may, however, get some idea of the sort of thing then in use by a perusal of the steamboat announcements of that time, two of which are as follows: ["_Copy of an Advertisement taken from the Albany Gazette, dated September, 1807._] "The North River Steamboat will leave Pauler's Hook Ferry [now Jersey City] on Friday, the 4th of September, at 9 in the morning, and arrive at Albany on Saturday, at 9 in the afternoon. Provisions, good berths, and accommodations are provided. "The charge to each passenger is as follows: "To Newburg dols. 3, time 14 hours. " Poughkeepsie " 4, " 17 " " Esopus " 5, " 20 " " Hudson " 5-1/2, " 30 " " Albany " 7, " 36 " "For places, apply to William Vandervoort, No. 48 Courtlandt Street, on the corner of Greenwich Street. "_September 2, 1807._ ["_Extract from the New York Evening Post, dated October 2, 1807._] "Mr. Fulton's new-invented _Steamboat_, which is fitted up in a neat style for passengers, and is intended to run from New York to Albany as a Packet, left here this morning with 90 passengers, against a strong head-wind. Notwithstanding which, it was judged she moved through the waters at the rate of six miles an hour." During the next winter the Clermont was repaired and enlarged, and in the summer of 1808 was again on the route to Albany; and, meantime, two new steamboats--the Raritan and the Car of Neptune--had been built by Fulton. In the year 1811 he built the Paragon. Both of the two vessels last named were of nearly double the size of the Clermont. A steam ferry-boat was built to ply between New York and Jersey City in 1812, and the next year two others, to connect the metropolis with Brooklyn. These were "twin-boats," the two parallel hulls being connected by a "bridge" or deck common to both. The Jersey ferry was crossed in fifteen minutes, the distance being a mile and a half. To-day, the time occupied at the same ferry is about ten minutes. Fulton's ferry-boat carried, at one load, 8 carriages, and about 30 horses, and still had room for 300 or 400 foot-passengers. Fulton also designed steam-vessels for use on the Western rivers, and, in 1815, some of his boats were started as "packets" on the line between New York and Providence, R. I. Meantime, the War of 1812 was in progress, and Fulton designed a steam vessel-of-war, which was then considered a wonderfully formidable craft. His plans were submitted to a commission of experienced naval officers, among whom were Commodores Decatur and Perry, Captain John Paul Jones, Captain Evans, and others whose names are still familiar, and were favorably commended. Fulton proposed to build a steam-vessel capable of carrying a heavy battery, and of steaming four miles an hour. The ship was to be fitted with furnaces for red-hot shot. Some of her guns were to be discharged below the water-line. The estimated cost was $320,000. The construction of the vessel was authorized by Congress in March, 1814; the keel was laid June 20, 1814, and the vessel was launched October 29th of the same year. [Illustration: FIG. 82.--Launch of the "Fulton the First," 1804.] The "Fulton the First," as she was called, was considered an enormous vessel at that time. The hull was double, 156 feet long, 56 feet wide, and 20 feet deep, measuring 2,475 tons. In the following May the ship was ready for her engine, and in July was so far completed as to steam, on a trial-trip, to the ocean at Sandy Hook and back--53 miles--in 8 hours and 20 minutes. In September of the same year, with armament and stores on board, the same route was traversed again, the vessel making 5-1/2 miles an hour. The vessel, as thus completed, had a double hull, each about 20 feet longer than the Clermont, and separated by a space 15 feet across. Her engine, having a steam-cylinder 48 inches in diameter and of 5 feet stroke of piston, was furnished with steam by a copper boiler 22 feet long, 12 feet wide, and 8 feet high, and turned a wheel between the two hulls which was 16 feet in diameter, and carried "floats" or "buckets" 14 feet long, and with a dip of 4 feet. The engine was in one of the two hulls, and the boiler in the other. The sides, at the gun-deck, were 4 feet 10 inches thick, and her spar-deck was surrounded by heavy musket-proof bulwarks. The armament consisted of 30 32-pounders, which were intended to discharge red-hot shot. There was one heavy mast for each hull, fitted with large latteen sails. Each end of each hull was fitted with a rudder. Large pumps were carried, which were intended to throw heavy streams of water upon the decks of the enemy, with a view to disabling the foe by wetting his ordnance and ammunition. A submarine gun was to have been carried at each bow, to discharge shot weighing 100 pounds, at a depth of 10 feet below the water-line. This was the first application of the steam-engine to naval purposes, and, for the time, it was an exceedingly creditable one. Fulton, however, did not live to see the ship completed. He was engaged in a contest with Livingston, who was then endeavoring to obtain permission from the State of New Jersey to operate a line of steamboats in the waters of the Hudson River and New York Bay, and, while returning from attending a session of the Legislature at Trenton, in January, 1815, was exposed to the weather on the bay at a time when he was ill prepared to withstand it. He was taken ill, and died February 24th of that year. His death was mourned as a national calamity. From the above brief sketch of this distinguished man and his work, it is seen that, although Robert Fulton is not entitled to distinction as an inventor, he was one of the ablest, most persistent, and most successful of those who have done so much for the world by the introduction of the inventions of others. He was an intelligent engineer and an enterprising business-man, whose skill, acuteness, and energy have given the world the fruits of the inventive genius of all who preceded him, and have thus justly earned for him a fame that can never be lost. Fulton had some active and enterprising rivals. Oliver Evans had, in 1801 or 1802, sent one of his engines, of about 150 horse-power, to New Orleans, for the purpose of using it to propel a vessel owned by Messrs. McKeever and Valcourt, which was there awaiting it. The engine was actually set up in the boat, but at a low stage of the river, and no trial could be made until the river should again rise, some months later. Having no funds to carry them through so long a period, Evans's agents were induced to remove the engine again, and to set it up in a saw-mill, where it created great astonishment by its extraordinary performance in sawing lumber. Livingston and Roosevelt were also engaged in experiments quite as early as Fulton, and perhaps earlier. The prize gained by Fulton was, however, most closely contested by Colonel JOHN STEVENS, of Hoboken, who has been already mentioned in connection with the early history of railroads, and who had been since 1791 engaged in similar experiments. In 1789 he had petitioned the Legislature of the State of New York for a grant similar to that accorded to Livingston, and he then stated that his plans were complete, and on paper. [Illustration: FIG. 83.--Section of Steam-Boiler, 1804.] In 1804, while Fulton was in Europe, Stevens had completed a steamboat, 68 feet long and of 14 feet beam, which combined novelties and merits of design in a manner that exhibited the best possible evidence of remarkable inventive talent, as well as of the most perfect appreciation of the nature of the problem which he had proposed to himself to solve. Its boiler (Fig. 83) was of what is now known as the water-tubular variety. It was quite similar to some now known as sectional boilers, and contained 100 tubes 2 inches in diameter and 18 inches long, each fastened at one end to a central water-leg and steam-drum, and plugged at the other end. The flames from the furnace passed around and among the tubes, the water being inside them. The engine (Fig. 84) was a _direct-acting high-pressure_ condensing engine, having a 10-inch cylinder, 2 feet stroke of piston, and drove a _screw_ having four blades, and of a form which, even to-day, appears quite good. The whole is a most remarkable piece of early engineering. [Illustration: FIG. 84.--Engine, Boiler, and Screw-Propellers used by Stevens, 1804.] A model of this little steamer, built in 1804, is preserved in the lecture-room of the Department of Mechanical Engineering at the Stevens Institute of Technology; and the machinery itself, consisting of the high-pressure "sectional" or "safety" tubular boiler, as it would be called to-day, the high-pressure condensing engine, with rotating valves, and twin screw-propellers, as just described, is given a place of honor in the model-room, or museum, where it contrasts singularly with the mechanism contributed to the collection by manufacturers and inventors of our own time. The hub and blade of a single screw, also used with the same machinery, is likewise to be seen there. [Illustration: FIG. 85.--Stevens's Screw Steamer, 1804.] Stevens seems to have been the first to fully recognize the importance of the principle involved in the construction of the sectional steam-boiler. His eldest son, John Cox Stevens, was in Great Britain in the year 1805, and, while there, patented another modification of this type of boiler. In his specification, he details both the method of construction and the principles which determine its form. He says that he describes this invention as it was made known to him by his father, and adds: "From a series of experiments made in France, in 1790, by M. Belamour, under the auspices of the Royal Academy of Sciences, it has been found that, within a certain range the elasticity of steam is nearly doubled by every addition of temperature equal to 30° of Fahrenheit's thermometer. These experiments were carried no higher than 280°, at which temperature the elasticity of steam was found equal to about four times the pressure of the atmosphere. By experiments which have lately been made by myself, the elasticity of steam at the temperature of boiling oil, which has been estimated at about 600°, was found to equal 40 times the pressure of the atmosphere. "To the discovery of this principle or law, which obtains when water assumes a state of vapor, I certainly can lay no claim; but to the application of it, upon certain principles, to the improvement of the steam-engine, I do claim exclusive right. "It is obvious that, to derive advantage from an application of this principle, it is absolutely necessary that the vessel or vessels for generating steam should have strength sufficient to withstand the great pressure from an increase of elasticity in the steam; but this pressure is increased or diminished in proportion to the capacity of the containing vessel. The principle, then, of this invention consists in forming a boiler by means of a system, or combination of a number of small vessels, instead of using, as in the usual mode, one large one; the relative strength of the materials of which these vessels are composed increasing in proportion to the diminution of capacity. It will readily occur that there are an infinite variety of possible modes of effecting such combinations; but, from the nature of the case, there are certain limits beyond which it becomes impracticable to carry on improvement. In the boiler I am about to describe, I apprehend that the improvement is carried to the utmost extent of which the principle is capable. Suppose a plate of brass of one foot square, in which a number of holes are perforated; into each of which holes is fixed one end of a copper tube, of about an inch in diameter and two feet long; and the other ends of these tubes inserted in like manner into a similar piece of brass; the tubes, to insure their tightness, to be cast in the plates; these plates are to be inclosed at each end of the pipes by a strong cap of cast-iron or brass, so as to leave a space of an inch or two between the plates or ends of the pipes and the cast-iron cap at each end; the caps at each end are to be fastened by screw-bolts passing through them into the plates; the necessary supply of water is to be injected by means of a forcing-pump into the cap at one end, and through a tube inserted into the cap at the other end the steam is to be conveyed to the cylinder of the steam-engine; the whole is then to be encircled in brickwork or masonry in the usual manner, placed either horizontally or perpendicularly, at option. "I conceive that the boiler above described embraces the most eligible mode of applying the principle before mentioned, and that it is unnecessary to give descriptions of the variations in form and construction that may be adopted, especially as these forms may be diversified in many different modes." Boilers of the character of those described in the specification given above were used on the locomotive built by John Stevens in 1824-'25, and one of them remains in the collections of the Stevens Institute of Technology. The use of such a boiler 70 years ago is even more remarkable than the adoption of the screw-propeller, in such excellent proportions, 30 years before the labors of Smith and of Ericsson brought the screw into general use; and we have, in this strikingly original combination, as good evidence of the existence of unusual engineering talent in this great engineer as we found of his political and statesmanlike ability in his efforts to forward the introduction of railways. Colonel John Stevens designed a peculiar form of iron-clad in the year 1812, which has been since reproduced by no less distinguished and successful an engineer than the late John Elder, of Glasgow, Scotland. It consisted of a saucer-shaped hull, carrying a heavy battery, and plated with iron of ample thickness to resist the shot fired from the heaviest ordnance then known. This vessel was secured to a swivel, and was anchored in the channel to be defended. A set of screw-propellers, driven by steam-engines, and situated beneath the vessel, where they were safe against injury by shot, were so arranged as to permit the vessel to be rapidly revolved about its centre. As each gun was brought into line of fire, it was discharged, and was then reloaded before coming around again. This was probably the earliest embodiment of the now well-established "Monitor" principle. It was probably the first iron-clad ever designed. It has recently been again brought out and introduced into the Russian navy, and is there called the "Popoffka." The first of Stevens's boats performed so well, that he immediately built another one, using the same engine as before, but employing a larger boiler, and propelling the vessel by _twin screws_, the latter being another instance of his use of a device brought forward long afterward as new, and frequently adopted. This boat was sufficiently successful to prove the practicability of making steam-navigation a commercial success; and Stevens, assisted by his sons, built a boat which he named the "Ph[oe]nix," and made the first trial in 1807, but just too late to anticipate Fulton. This boat was driven by paddle-wheels. [Illustration: FIG. 86.--Stevens's Twin-Screw Steamer, 1805.] The Ph[oe]nix, being shut out of the waters of the State of New York by the monopoly held by Fulton and Livingston, was used for a time between New York and New Brunswick, and then, anticipating a better pecuniary return, it was concluded to send her to Philadelphia, to ply on the Delaware. At that time no canal offered the opportunity to make an inland passage; and in June, 1808, Robert L. Stevens, a son of John, started with her to make the passage by sea. Although meeting a gale of wind, he arrived at Philadelphia safely, having been the first to trust himself on the open sea in a vessel relying entirely upon steam-power. From this time forward the Stevenses, father and sons, continued to construct steam-vessels; and, after the breaking down of the Fulton monopoly by the courts, they built the most successful steamboats that ran on the Hudson River. After Fulton and Stevens had thus led the way, steam-navigation was introduced very rapidly on both sides of the ocean; and on the Mississippi the number of boats set afloat was soon large enough to fulfill Evans's prediction that the navigation of that river would ultimately be effected by steam-vessels. The changes and improvements which, during the 20 years succeeding the time of Fulton and of John Stevens, gradually led to the adoption of the now recognized type of "American river-boat" and its steam-engine, were principally made by that son of the senior Stevens, who has already been mentioned--ROBERT L. STEVENS--and who became known later as the designer and builder of the first well-planned iron-clad ever constructed, the Stevens Battery. Much of his best work was done during his father's lifetime. [Illustration: Robert L. Stevens.] He made many extended and most valuable, as well as interesting, experiments on ship-propulsion, expending much time and large sums of money upon them; and many years before they became generally understood, he had arrived at a knowledge not only of the laws governing the variation of resistance at excessive speeds, but he had determined, and had introduced into his practice, those forms of least resistance and those graceful water-lines which have only recently distinguished the practice of other successful naval architects. Referring to his invaluable services, President King, who seems to have been the first to thoroughly appreciate the immense amount of original invention and the surprising excellence of the engineering of this family, in a lecture delivered in New York in 1851, gave, for the first time, a connected and probably accurate description of their work, upon which nearly all later accounts have been based. Young Stevens began working in his father's machine-shop in 1804 or 1805, when a mere boy, and thus acquired at a very early age that familiarity with practical details of work and of business which is essential to perfect success. It was he who introduced the now common "hollow water-line" in the Ph[oe]nix, and thus anticipated the claims of the builders of the once famous "Baltimore clippers," and of the inventors of the "wave-line" form of vessels. In the same vessel he adopted a feathering paddle-wheel and the guard-beam now universally seen in our river steamboats. As usually constructed, this arrangement of float is as shown in Fig. 87. The rods, _F F_, connect the eccentrically-set collar, _G_, carried on _H_, a pin mounted on the paddle-beam outside the wheel, or an eccentric secured to the vessel, with the short arms, _D D_, by which the paddles are turned upon the pins, _E E_. _A_ is the centre of the paddle-wheel, and _C C_ are arms. Circular hoops, or bands, connect all of the arms, each of which carries a float. They are all thus tied together, forming a very firm and powerful combination to resist external forces. [Illustration: FIG. 87.--The Feathering Paddle-Wheel.] The steamboat Philadelphia was built in the year 1813, and the young naval architect took advantage of the opportunity to introduce several new devices, including screw-bolts in place of tree-nails, and diagonal knees of wood and of iron. Two years later he altered the engines of this boat, and arranged them to work steam expansively. A little later he commenced using anthracite coal, which had been discovered in 1791 by Philip Ginter, and introduced at Wilkesbarre, Pa., in the smith-shops, some years before the Revolution. It had been used in a peculiar grate devised by Judge Fell, of that town, in 1808. Oliver Evans also had used it in stoves even earlier than the latter date, and at about the same time it had been used in the blast-furnace[81] at Kingston. Stevens was the first of whom we have record who was thoroughly successful in using, as a steam-coal, the new and almost unmanageable fuel. He fitted up the boiler of the steamboat Passaic for it in 1818, and adopted anthracite as a steaming-coal. He used it in a cupola-furnace in the same year, and its use then rapidly became general in the Eastern States. [81] Bishop. Stevens continued his work of improving the beam-engine for many years. He designed the now universally-used "skeleton-beam," which is one of the characteristic features of the American engine, and placed the first example of this light and elegant, yet strong, construction on the steamer Hoboken in the year 1822. He built the Trenton, which was then considered an extraordinarily powerful, fast, and handsome vessel, two years afterward, and placed the two boilers on the guards--a custom which is still general on the river steamboats of the Eastern States. In this vessel he also adopted the plan of making the paddle-wheel floats in two parts, placing one above the other, and securing the upper half on the forward and the lower half on the after side of the arm, thus obtaining a smoother action of the wheel, and less loss by oblique pressures. In 1827 he built the North America (Fig. 88), one of his largest and most successful steamers, a vessel fitted with a pair of engines each 44-1/2 inches in diameter of cylinder and 8 feet stroke of piston, making 24 revolutions per minute, driving the boat 15 to 16 miles an hour. Anticipating difficulty in keeping the long, light, shallow vessel in shape when irregularly laden, and when steaming at the high speed expected to be obtained when her powerful engine was exerting its maximum effort, he adopted the expedient of stiffening the hull by means of a truss of simple form. This proved thoroughly satisfactory, and the "hog-frame," as it has since been inelegantly but universally called, is still one of the peculiar features of every American river-steamer of any considerable size. It was in the North America, also, that he first introduced the artificial blast for forcing the fires, which is still another detail of now usual practice. [Illustration: FIG. 88.--The North America and Albany, 1827-'30.] Stevens next turned his attention to the engine again, and adopted spring bearings under the paddle-shaft of the New Philadelphia in 1828, and fitted the steam-cylinder with the "double-poppet" valve, which is now universally used on beam-engines. This consists of two disk-valves, connected by the valve-spindle. The disks are of unequal sizes, the smaller passing through the seat of the larger. When seated, the pressure of the steam is, in the steam-valve, taken on the upper side of the larger and the lower side of the smaller disk, thus producing a partial balancing of the valve, and rendering it easy to work the heaviest engine by the hand-gear. The two valve-seats are formed in the top and the bottom, respectively, of the steam-passage leading to the cylinder; and when the valve is raised, the steam enters at the top and the bottom at the same time, and the two currents, uniting, flow together into the steam-cylinder. The same form of valve is used as an exhaust-valve. At about the same time he built the now standard form of return tubular boilers for moderate pressures. In the figure, _S_ is the steam and _W_ the water space, and _F_ the furnace. The direction of the currents of smoke and gas are shown by the arrows. [Illustration: FIG. 89.--Stevens's Return Tubular Boiler, 1832.] Some years later (1840), Stevens commenced using steam-packed pistons on the Trenton, in which steam was admitted by self-adjusting valves behind the metallic packing-rings, setting them out more effectively than did the steel springs then (and still) usually employed. His pistons, thus fitted, worked well for many years. A set of the small brass check-valves used in a piston of this kind, built by Stevens, and preserved in the cabinets of the Stevens Institute of Technology, are good evidence of the ingenuity and excellent workmanship which distinguished the machinery constructed under the direction of this great engineer. [Illustration: FIG. 90.--Stevens's Valve-Motion.] The now familiar "Stevens cut-off," a peculiar device for securing the expansion of steam in the steam-cylinder, was the invention (1841) of Robert L. Stevens and a nephew, who inherited the same constructive talent which distinguished the first of these great men--Mr. Francis B. Stevens. In this form of valve-gear, the steam and exhaust valves are independently worked by separate eccentrics, the latter being set in the usual manner, opening and closing the exhaust-passages just before the crank passes its centre. The steam-eccentric is so placed that the steam-valve is opened as usual, but closed when but about one-half the stroke has been made. This result is accomplished by giving the eccentric a greater throw than is required by the motion of the valve, and permitting it to move through a portion of its path without moving the valve. Thus, in Fig. 90, if _A B_ be the direction of motion of the eccentric-rod, the valve would ordinarily open the steam-port when the eccentric assumes the position _O C_, closing when the eccentric has passed around to _O D_. With the Stevens valve-gear, the valve is opened when the eccentric reaches _O E_, and closes when it arrives at _O F_. The steam-valve of the opposite end of the cylinder is open while the eccentric is moving from _O M_ to _O K_. Between _K_ and _E_, and between _F_ and _M_, both valves are seated. _H B_ is proportional to the lift of the valve, and _O H_ to the motion of the valve-gear when out of contact with the valve-lifters. While the crank is moving through an arc, _E F_, steam is entering the cylinder; from _F_ to _M_ the steam is expanding. At _M_ the stroke is completed, and the other steam-valve opens. The ratio (E M)/(E L) is the ratio of expansion. This form of cut-off motion is still a very usual one, and can be seen in nearly all steamers in the United States not using the device of Sickles. It was at about this time, also, that Stevens, having succeeded his father in the business of introducing the steam-engine in land-transportation, as well as on the water, adopted the use of steam expansively on the locomotives of the Camden & Amboy Railroad, which was controlled and built by capital furnished principally by the Messrs. Stevens. He at the same time constructed eight-wheeled engines for heavy work, and adopted anthracite coal as fuel. In the latter change he was thoroughly successful, and the same improvement was made with engines built for fast traffic in 1848. The most remarkable of all the applications of steam-power proposed by Robert L. Stevens was that known as the Stevens Steam Iron-Clad Battery. As has already been stated, Colonel John Stevens had proposed, as early as 1812, to build a circular or saucer-shaped iron-clad, like those built 60 years later for the Russian Navy. Nothing was done, however, although the son revived the idea in a modified form 20 years afterward. In the years 1813-'14, the war with England being then in progress, he invented, after numerous and hazardous experiments, an _elongated shell_, to be fired from ordinary smooth-bored cannon. Having perfected this invention, he sold the secret to the United States, after making experiments to prove their destructiveness so decisive as to leave no doubt of the efficacy of such projectiles. As early as 1837 he had perfected a plan of an iron-clad war-vessel, and in August, 1841, his brothers, James C. and Edwin A. Stevens, representing Robert L., addressed a letter to the Secretary of the Navy, proposing to build an iron-clad vessel of high speed, with all its machinery below the water-line, and having submerged screw-propellers. The armament was to consist of the most powerful rifled guns, loading at the breech, and provided with elongated shot and shell. In the year 1842, having contracted to build for the United States Government a large war-steamer on this plan, which should be shot and shell proof, Robert L. Stevens built a steamboat at Bordentown, for the sole purpose of experimenting on the forms and curves of propeller-blades, as compared with side-wheels, and continued his experiments for many months. After some delay, during which Mr. Stevens and his brothers were engaged with their experiments and in perfecting their plans, the keel of an iron-clad was laid down in a dry-dock which had been constructed for the purpose at great cost. This vessel was to have been 250 feet long, of 40 feet beam, and 28 feet deep. The machinery was designed to furnish 700 indicated horse-power. The plating was proposed to be 4-1/2 inches thick--the same thickness of armor as was adopted 10 years later by the French for their comparatively rude constructions. In 1854, such marked progress had been made in the construction of ordnance that Mr. Stevens was no longer willing to proceed with the original plans, fearing that, were the ship completed, it might prove not invulnerable, and might throw some discredit upon its designer, as well as upon the navy of which it was to form a part. The work, which had, in those years of peace, progressed very slowly and intermittently, was therefore stopped entirely, the vessel given up, and in 1854 the keel of a ship of vastly greater size and power was laid down. The new design was 415 feet long, of 45 feet beam, and of something over 5,000 tons displacement. The thickness of armor proposed was 6-3/4 inches--2-1/4 inches thicker than that of the first French and British iron-clads--and the machinery was designed by Mr. Stevens to be of 8,624 indicated horse-power, driving twin-screws, and propelling the vessel 20 miles or more an hour. As with the preceding design, the progress of construction was intermittent and very slow. Government advanced funds, and then refused to continue the work; successive administrations alternately encouraged and discouraged the engineer; and he finally, cutting loose entirely from all official connections, went on with the work at his own expense. The remarkable genius of the elder Stevens was well reflected in the character of his son, and is in no way better exemplified than by the accuracy with which, in this great ship, those forms and proportions, both of hull and machinery, were adopted which are now, twenty-five years later, recognized as most correct under similar conditions. The lines of the vessel are beautifully fair and fine, and are what J. Scott Russell has called "wave-lines," or trochoidal lines, such as Rankine has shown to be the best possible for easy propulsion. The proportion of length to midship dimensions is such as to secure the speed proposed with a minimum resistance, and to accord closely with the proportions arrived at and adopted by common consent in present transoceanic navigation by the best--not to say radical--builders. The death of Robert L. Stevens occurred in April, 1856, when this larger vessel had advanced so far toward completion that the hull and machinery were practically finished, and it only remained to add the armor-plating, and to decide upon the form of fighting-house and upon the number and size of guns. The construction of the vessel, which had proceeded slowly and intermittently during the years of peace, as successive administrations had considered it necessary to continue the payment of appropriations, or had stopped temporarily in the absence of any apparent immediate necessity for continuance of the work, was again interrupted by his death. The name of Robert L. Stevens will be long remembered as that of one of the greatest of American mechanics, the most intelligent of naval architects, and as the first, and one of the greatest, of those to whom we are indebted for the commencement of the mightiest of revolutions in the methods and implements of modern naval warfare. American mechanical genius and engineering skill have rarely been too promptly recognized, and no excuse will be required for an attempt (which it is hoped may yet be made) to place such splendid work as that of the Messrs. Stevens in a light which shall reveal both its variety and extent and its immense importance. While Fulton was introducing the steamboat upon the waters of New York Bay and the Hudson River, and while the Stevenses, father and sons, were rapidly bringing out a fleet of steamers on the Delaware River and Bay, other mechanics were preparing to contest the field with them as opportunity offered, and as legislative acts authorizing monopoly expired by limitation or were repealed. About 1821, Robert L. Thurston, John Babcock, and Captain Stephen T. Northam, of Newport, R. I., commenced building steamboats, beginning with a small craft intended for use at Slade's Ferry, on an arm of Narragansett Bay, near Fall River. They afterward built vessels to ply on Long Island Sound. One of their earliest boats was the Babcock, built at Newport in 1826. The engine was built by Thurston and Babcock, at Portsmouth, R. I. They were assisted in their work by Richard Sanford, and with funds by Northam. The engine was of 10 or 12 inches diameter of cylinder, and 3 or 4 feet stroke of piston. The boiler was a form of "pipe-boiler," subsequently (1824) patented by Babcock. The water used was injected into the hot boiler as fast as required to furnish steam, no water being retained in the steam-generator. This boat was succeeded, in 1827-'28, by a larger vessel, the Rushlight, for which the engine was built by James P. Allaire, at New York, while the boat was built at Newport. The boilers of both vessels had tubes of cast-iron. The smaller of these boats was of 80 tons burden; it steamed from Newport to Providence, 30 miles, in 3-1/2 hours, and to New York, a distance of 175 miles, in 25 hours, using 1-3/4 cord of wood.[82] Thurston and Babcock subsequently removed to Providence, where the latter soon died. Thurston continued to build steam-engines at this place until nearly a half-century later, dying in 1874.[83] The establishment founded by him, after various changes, became the Providence Steam-Engine Works. [82] _American Journal of Science_, March, 1827; _London Mechanics' Magazine_, June 16, 1827. [83] "New Universal Cyclopædia," vol. iv., 1878. James P. Allaire, of New York, the West Point Iron Foundery, at West Point, on the Hudson River, and Daniel Copeland and his son, Charles W. Copeland, on the Connecticut River, were also early builders of engines for steam-vessels. Daniel Copeland was probably the first (1850) to adopt a slide-valve working with a lap to secure the expansion of steam. His steamboats were then usually stern-wheel vessels, and were built to ply on several routes on the Connecticut River and Long Island Sound. The son, Charles W. Copeland, went to West Point, and while there designed some heavy marine steam-machinery, and subsequently designed several steam vessels-of-war for the United States Navy. He was the earliest designer of iron steamers in the United States, building the Siamese in 1838. This steamer was intended for use on Lake Pontchartrain and the canal to New Orleans. It had two hulls, was 110 feet long, and drew but 22 inches of water, loaded. The two horizontal non-condensing engines turned a single paddle-wheel placed between the two hulls, driving the boat 10 miles an hour. The hull was constructed of plates of iron 10 feet long, formed on blocks after having been heated in a furnace constructed especially for the purpose. The frames were of T-iron, which was probably here used for the first time. The same engineer, associated with Samuel Hart, a well-known naval constructor, built, in 1841, for the United States Navy, the iron steamer Michigan, a war-vessel intended for service on the great northern lakes. This vessel is still in service, and in good order. The hull is 162-1/2 feet in length, 27 feet in breadth, and 12-1/2 feet in depth, measuring 500 tons. The frames were made of T-iron, stiffened by reverse bars of L-iron. The keel-plate was 5/8 inch thick, the bottom plates 3/8, and the sides 3/16 inch. The deck-beams were of iron, and the vessel, as a whole, was a good specimen of iron-ship building. During the period from 1830 to 1840, a considerable number of the now standard details of steam-engine and steamboat construction were devised or introduced by Copeland. He was probably the first to use (on the Fulton, 1840) an independent engine to drive the blowing-fans where an artificial draught was required. He made a practice of fitting his steamers with a "bilge-injection," by means of which the vessel could be freed of water, through the condenser and air-pump, when leaking seriously; the condensing-water is, in such a case, taken from inside the vessel, instead of from the sea. This is probably an American device. It was in use in the United States previously to 1835, as was the use of anthracite coal on steamers, which was continued by Copeland in manufacturing and in air-furnaces, as well as on steamboats. He also modified the form of Stevens's double-poppet valve, giving it such shape that it was comparatively easy to grind it tight and to keep it in order. In 1825, James P. Allaire, of New York, built compound engines for the Henry Eckford, and subsequently constructed similar engines for several other steamers, one of which, the Sun, made the trip from New York to Albany in 12 hours 18 minutes. He used steam at 100 pounds pressure. Erastus W. Smith afterward introduced this form of engine on the Great Lakes, and still later they were introduced into British steamers. The machinery of the steamer Buckeye State was constructed at the Allaire Works, New York, in 1850, from the designs of John Baird and Erastus W. Smith, the latter being the designing and constructing engineer. The steamer was placed on the route between Buffalo, Cleveland, and Detroit, in 1851, and gave most satisfactory results, consuming less than two-thirds the fuel required by a similar vessel of the same line fitted with the single-cylinder engine. The steam-cylinders of this engine were placed one within the other, the low-pressure exterior cylinder being annular. They were 37 and 80 inches in diameter respectively, and the stroke was 11 feet. Both pistons were connected to one cross-head, and the general arrangement of the engine was similar to that of the common form of beam-engine. The steam-pressure was from 70 to 75 pounds--about the maximum pressure adopted a quarter of a century later on transatlantic lines. This steamer was of high speed, as well as economical of fuel. In the year 1830, there were 86 steamers on the Hudson River and in Long Island Sound. During the early part of the nineteenth century, the introduction of the steamboat upon the waters of the great rivers of the interior of the United States was one of the most notable details of its history. Inaugurated by the unsuccessful experiment of Evans, the building of steamboats on those waters, once commenced, never ceased; and a generation after Fitch's burial on the shore of the Ohio, his last wish--that he might lie "where the song of the boatman would enliven the stillness of his resting-place, and the music of the steam-engine soothe his spirit"--was fulfilled day by day unceasingly. Nicholas J. Roosevelt was, as has been already stated, the first to take a steamboat down the great rivers. His boat was built at Pittsburgh in 1811, under an arrangement with Fulton and Livingston, from Fulton's plans. It was called the "New Orleans," was of about 200 tons burden, and was propelled by a stern-wheel, assisted, when the winds were favorable, by sails carried on two masts. The hull was 138 feet long, 30 feet beam, and the cost of the whole, including engines, was about $40,000. The builder, with his family, an engineer, a pilot, and six "deck-hands," left Pittsburgh in October, 1811, reaching Louisville in 70 hours (steaming about 10 miles an hour), and New Orleans in 14 days, steaming from Natchez. The next steamers built on Western waters were probably the Comet and the Vesuvius, both of which were in service some time. The Comet was finally laid aside, and the engine used to drive a mill, and the Vesuvius was destroyed by the explosion of her boilers. As early as 1813 there were two shops at Pittsburgh building steam-engines. Steamboat-building now became an important and lucrative business in the West; and it is stated that as early as 1840 there were a thousand steamers on the Mississippi and its tributaries. In the Washington, built at Wheeling, Va., in 1816, under the direction of Captain Henry M. Shreve, the boilers, which had previously been placed in the hold, were carried on the main-deck, and a "hurricane-deck" was built over them. Shreve substituted two horizontal direct-acting engines for the single upright engine used by Fulton, drove them by high-pressure steam without condensation, and attached them, one on each side the boat, to cranks placed at right angles. He adopted a cam cut-off expanding the steam considerably, and the flue-boiler of Evans. At that time the voyage from New Orleans to Louisville occupied three weeks, and Shreve was made the subject of many witticisms when he predicted that the time would ultimately be shortened to ten days. It is now made in four days. The Washington was seized at New Orleans, in 1817, by order of Livingston, who claimed that his rights included the monopoly of the navigation of the Mississippi and its tributaries. The courts decided adversely on this claim, and the release of the Washington was the act which removed every obstacle to the introduction of steam-navigation throughout the United States. The first steamer on the Great Lakes was the Ontario, built in 1816, at Sackett's Harbor. Fifteen years later, Western steamboats had taken the peculiar form which has since usually distinguished them. The use of the steam-engine for ocean-navigation kept pace with its introduction on inland waters. Begun by Robert L. Stevens in the United States, in the year 1808, and by his contemporaries, Bell and Dodd, in Great Britain, it steadily and rapidly advanced in effectiveness and importance, and has now nearly driven the sailing fleet from the ocean. Transatlantic steam-navigation began with the voyage of the American steamer Savannah from Savannah, Ga., to St. Petersburg, Russia, _via_ Great Britain and the North-European ports, in the year 1819. Fulton, not long before his death, planned a vessel, which it was proposed to place in service in the Baltic Sea; but circumstances compelled a change of plan finally, and the steamer was placed on a line between Newport, R. I., and the city of New York; and the Savannah, several years later, made the voyage then proposed for Fulton's ship. The Savannah measured 350 tons, and was constructed by Crocker & Fickett, at Corlears Hook, N. Y. She was purchased by Mr. Scarborough, of Savannah, who placed Captain Moses Rogers, previously in command of the Clermont and of Stevens's boat, the Ph[oe]nix, in charge. The ship was fitted with steam-machinery and paddle-wheels, and sailed for Savannah April 27, 1819, making the voyage successfully in seven days. From Savannah, the vessel sailed for Liverpool May 26th, and arrived at that port June 20th. During this trip the engines were used 18 days, and the remainder of the voyage was made under sail. From Liverpool the Savannah sailed, July 23d, for the Baltic, touching at Copenhagen, Stockholm, St. Petersburg, and other ports. At St. Petersburg, Lord Lyndock, who had been a passenger, was landed; and, on taking leave of the commander of the steamer, the distinguished guest presented him with a silver tea-kettle, suitably inscribed with a legend referring to the importance of the event which afforded him the opportunity. The Savannah left St. Petersburg in November, passing New York December 9th, and reaching Savannah in 50 days from the date of departure, stopping four days at Copenhagen, Denmark, and an equal length of time at Arundel, Norway. Several severe gales were met in the Atlantic, but no serious injury was done to the ship. The Savannah was a full-rigged ship. The wheels were turned by an inclined direct-acting low-pressure engine, having a steam-cylinder 40 inches in diameter and 6 feet stroke of piston. The paddle-wheels were of wrought-iron, and were so attached that they could be detached and hoisted on board when it was desired. After the return of the ship to the United States, the machinery was removed and was sold to the Allaire Works, of New York. The steam-cylinder was exhibited by the purchasers at the "World's Fair" at New York thirty years later. The vessel was employed, as a sailing-vessel, on a line between New York and Savannah, and was finally lost in the year 1822. Under sail, with a moderate breeze, this ship is said to have sailed about three knots, and to have steamed five knots. Pine-wood was used as the fuel, which fact accounts for the necessity of making the transatlantic voyage partly under sail. Renwick states that another vessel, ship-rigged and fitted with a steam-engine, was built at New York in 1819, to ply between New York and Charleston, and to New Orleans and Havana, and that it proved perfectly successful as a steamer, having good speed, and proving an excellent sea-boat. The enterprise was, however, pecuniarily a failure, and the vessel was sold to the Brazilian Government after the removal of the engine. In 1825 the steamer Enterprise made a voyage to India, sailing and steaming as the weather and the supply of fuel permitted. The voyage occupied 47 days. Notwithstanding these successful passages across the ocean, and the complete success of the steamboat in rivers and harbors, it was asserted, as late as 1838, by many who were regarded as authority, that the passage of the ocean by steamers was quite impracticable, unless possibly they could steam from the coasts of Europe to Newfoundland or to the Azores, and, replenishing their coal-bunkers, resume their voyages to the larger American ports. The voyage was, however, actually accomplished by two steamers in the year just mentioned. These were the Sirius, a ship of 700 tons and of 250 horse-power, and the Great Western, of 1,340 tons and 450 horse-power. The latter was built for this service, and was a large ship for that time, measuring 236 feet in length. Her wheels were 28 feet in diameter, and 10 feet in breadth of face. The Sirius sailed from Cork April 4, 1838, and the Great Western from Bristol April 8th, both arriving at New York on the same day--April 23d--the Sirius in the morning, and the Great Western in the afternoon. The Great Western carried out of Bristol 660 tons of coal. Seven passengers chose to take advantage of the opportunity, and made the voyage in one-half the time usually occupied by the sailing-packets of that day. Throughout the voyage the wind and sea were nearly ahead, and the two vessels pursued the same course, under very similar conditions. Arriving at New York, they were received with the greatest possible enthusiasm. They were saluted by the forts and the men-of-war in the harbor; the merchant-vessels dipped their flags, and the citizens assembled on the Battery, and, coming to meet them in boats of all kinds and sizes, cheered heartily. The newspapers of the time were filled with the story of the voyage and with descriptions of the steamers themselves and of their machinery. A few days later the two steamers started on their return to Great Britain, the Sirius reaching Falmouth safely in 18 days, and the Great Western making the voyage to Bristol in 15 days, the latter meeting with head-winds and working, during a part of the time, against a heavy gale and in a high sea, at the rate of but two knots an hour. The Sirius was thought too small for this long and boisterous route, and was withdrawn and replaced on the line between London and Cork, where the ship had previously been employed. The Great Western continued several years in the transatlantic trade. Thus these two voyages inaugurated a transoceanic steam-service, which has steadily grown in extent and in importance. The use of steam-power for this work of extended ocean-transportation has never since been interrupted. During the succeeding six years the Great Western made 70 passages across the Atlantic, occupying on the voyages to the westward an average of 15-1/2 days, and eastward 13-1/2. The quickest passage to New York was made in May, 1843, in 12 days and 18 hours, and the fastest steaming was logged 12 months earlier, when the voyage from New York was made in 12 days and 7 hours. Meantime, several other steamers were built and placed in the transatlantic trade. Among these were the Royal William, the British Queen, the President, the Liverpool, and the Great Britain. The latter, the finest of the fleet, was launched in 1843. This steamer was 300 feet long, 50 feet beam, and of 1,000 horse-power. The hull was of iron, and the whole ship was an example of the very best work of that time. After several voyages, this vessel went ashore on the coast of Ireland, and there remained several weeks, but was finally got off, without having suffered serious injury--a remarkable illustration of the stanchness of an iron hull when well built and of good material. The vessel was repaired, and many years afterward was still afloat, and engaged in the transportation of passengers and merchandise to Australia. The "Cunard Line" of transatlantic steamers was established in the year 1840. The first of the line--the Britannia--sailed from Liverpool for New York, July 4th of that year, and was followed, on regular sailing-days, by the other three of the four ships with which the company commenced business. These four vessels had an aggregate tonnage of 4,600 tons, and their speed was less than eight knots. To-day, the tonnage of a single vessel of the fleet exceeds that of the four; the total tonnage has risen to many times that above given. There are 50 steamers in the line, aggregating nearly 50,000 horse-power. The speed of the steamships of the present time is double that of the vessels of that date, and passages are not infrequently made in eight days. The form of steam-engine in most general use at this time, on transatlantic steamers, was that known as the "side-lever engine." It was first given the standard form by Messrs. Maudsley & Co., of London, about 1835, and was built by them for steamers supplied to the British Government for general mail service. The steam-vessels of the time are well represented in the accompanying engraving (Fig. 91) of the steamship Atlantic--a vessel which was shortly afterward (1851) built as the pioneer steamer of the American "Collins Line." This steamship was one of several which formed the earliest of American steamship-lines, and is one of the finest examples of the type of paddle-steamers which was finally superseded by the later screw-fleets. The "Collins Line" existed but a very few years, and its failure was probably determined as much by the evident and inevitable success of screw-propulsion as by the difficulty of securing ample capital, complete organization, and efficient general management. This steamer was built at New York--the hull by William Brown, and the machinery by the Novelty Iron-Works. The length of the hull was 276 feet, its breadth 45 feet, and the depth of hold 31-1/2 feet. The width over the paddle-boxes was 75 feet. The ship measured 2,860 tons. The form of the hull was then peculiar in the fineness of its lines; the bow was sharp, and the stern fine and smooth, and the general outline such as best adapted the ship for high speed. The main saloon was about 70 feet long, and the dining-room was 60 feet in length and 20 feet wide. The state-rooms were arranged on each side the dining "saloon," and accommodated 150 passengers. These vessels were beautifully fitted up, and with them was inaugurated that wonderful system of passenger-transportation which has since always been distinguished by those comforts and conveniences which the American traveler has learned to consider his by right. [Illustration: FIG. 91.--The Atlantic, 1851.] The machinery of these ships was, for that time, remarkably powerful and efficient. The engines were of the side-lever type, as illustrated in Fig. 92, which represents the engine of the Pacific, designed by Mr. Charles W. Copeland, and built by the Allaire Works. [Illustration: FIG. 92.--The Side-Lever Engine, 1849.] In this type of engine, as is seen, the piston-rod was attached to a cross-head working vertically, from which, at each side, links, _B C_, connected with the "side-lever," _D E F_. The latter vibrated about a "main centre" at _E_, like the overhead beam of the more common form of engine; from its other end, a "connecting-rod," _H_, led to the "cross-tail," _W_, which was, in turn, connected to the crank-pin, _I_. The condenser, _M_, and air-pump, _Q_, were constructed in the same manner as those of other engines, their only peculiarities being such as were incident to their location between the cylinder, _A_, and the crank, _I J_. The paddle-wheels were of the common "radial" form, covered in by paddle-boxes so strongly built that they were rarely injured by the heaviest seas. These vessels surpassed, for a time, all other sea-going steamers in speed and comfort, and made their passages with great regularity. The minimum length of voyage of the Baltic and Pacific, of this line, was 9 days 19 hours. During the latter part of the period the history of which has been here given, the marine steam-engine became subject to very marked changes in type and in details, and a complete revolution was effected in the method of propulsion. This change has finally resulted in the universal adoption of a new propelling instrument, and in driving the whole fleet of paddle-steamers from the ocean. The Great Britain was a screw-steamer. The screw-propeller, which, as has been stated, was probably first proposed by Dr. Hooke in 1681, and by Dr. Bernouilli, of Groningen, at about the middle of the eighteenth century, and by Watt in 1784, was, at the end of the century, tried experimentally in the United States by David Bushnell, an ingenious American, who was then conducting the experiments with torpedoes which were the cause of the incident which originated that celebrated song by Francis Hopkinson, the "Battle of the Kegs," using the screw to propel one of his submarine boats, and by John Fitch, and by Dallery in France. Joseph Bramah, of Great Britain, May 9, 1785, patented a screw-propeller identical in general arrangement with those used to-day. His sketch exhibits a screw, apparently of very fair shape, carried on an horizontal shaft, which passes out of the vessel through a stuffing-box, the screw being wholly submerged. Bramah does not seem to have put his plan in practice. It was patented again in England, also, by Littleton in 1794, and by Shorter in 1800. John Stevens, however, first gave the screw a practically useful form, and used it successfully, in 1804 and 1805, on the single and the twin screw boats which he built at that time. This propelling instrument was also tried by Trevithick, who planned a vessel to be propelled by a steam-engine driving a screw, at about this time, and his scheme was laid before the Navy Board in the year 1812. His plans included an iron hull. Francis Pettit Smith tried the screw also in the year 1808, and subsequently. Joseph Ressel, a Bohemian, proposed to use a screw in the propulsion of balloons, about 1812, and in the year 1826 proposed its use for marine propulsion. He is said to have built a screw-boat in the year 1829, at Trieste, which he named the Civetta. The little craft met with an accident on the trial-trip, and nothing more was done. The screw was finally brought into general use through the exertions of John Ericsson, a skillful Swedish engineer, who was residing in England in the year 1836, and of Mr. F. P. Smith, an English farmer. Ericsson patented a peculiar form of screw-propeller, and designed a steamer 40 feet in length, of 8 feet beam, and drawing 3 feet of water. The screw was double, two shafts being placed the one within the other, revolving in opposite directions, and carrying the one a right-hand and the other a left-hand screw. These screws were 5-1/4 feet in diameter. On her trial-trip this little steamer attained a speed of 10 miles an hour. Its power as a "tug" was found to be very satisfactory; it towed a schooner of 140 tons burden at the rate of 7 miles, and the large American packet-ship Toronto was towed on the Thames at a speed of 5 miles an hour. Ericsson endeavored to interest the British Admiralty in his improvements, and succeeded only so far as to induce the Lords of the Admiralty to make an excursion with him on the river. No interest was awakened in the new system, and nothing was done by the naval authorities. A note to the inventor from Captain Beaufort--one of the party--was received shortly afterward, in which it was stated that the excursionists had not found the performance of the little vessel to equal their hopes and expectations. All the interests of the then existing engine-building establishments were opposed to the innovation, and the proverbial conservatism of naval men and naval administrations aided in procuring the rejection of Ericsson's plans. Fortunately for the United States, it happened, at that time, that we had in Great Britain both civil and naval representatives of greater intelligence, or of greater boldness and enterprise. The consul at Liverpool was Mr. Francis B. Ogden, of New Jersey, a gentleman who was somewhat familiar with the steam-engine and with steam-navigation. He had seen Ericsson's plans at an earlier period, and had at once seen their probable value. He was sufficiently confident of success to place capital at the disposal of the inventor. The little screw-boat just described was built with funds of which he furnished a part, and was named, in his honor, the Francis B. Ogden. Captain Robert F. Stockton, an officer of the United States Navy, and also a resident of New Jersey, was in London at the time, and made an excursion with Ericsson on the Ogden. He was also at once convinced of the value of the new method of application of steam-power to ship-propulsion, and gave the engineer an order to build two iron screw-steamboats for use in the United States. Ericsson was induced, by Messrs. Ogden and Stockton, to take up his residence in the United States.[84] The Stockton was sent over to the United States in April, 1839, under sail, and was sold to the Delaware & Raritan Canal Company. Her name was changed, and, as the New Jersey, she remained in service many years. [84] This distinguished inventor is still a resident of New York (1878). The success of the boat built by Ericsson was so evident that, although the naval authorities remained inactive, a private company was formed, in 1839, to work the patents of F. P. Smith, and this "Ship-Propeller Company" built an experimental craft called the Archimedes, and its trial-trip was made October 14th of the same year. The speed attained was 9.64 miles an hour. The result was in every respect satisfactory, and the vessel, subsequently, made many voyages from port to port, and finally circumnavigated the island of Great Britain. The proprietors of the ship were not pecuniarily successful in their venture, however, and the sale of the vessel left the company a heavy loser. The Archimedes was 125 feet long, of 21 feet 10 inches beam, and 10 feet draught, registering 232 tons. The engines were rated at 80 horse-power. Smith's earlier experiments (1837) were made with a little craft of 6 tons burden, driven by an engine having a steam-cylinder 6 inches in diameter and 15 inches stroke of piston. The funds needed were furnished by a London banker--Mr. Wright. Bennett Woodcroft had also used the screw experimentally as early as 1832, on the Irwell, near Manchester, England, in a boat of 55 tons burden. Twin-screws were used, right and left handed respectively; they were each two feet in diameter, and were given an expanding pitch. The boat attained a speed of four miles an hour. Experiments made subsequently (1843) with this form of screw, and in competition with the "true" screw of Smith, brought out very distinctly the superiority of the former, and gave some knowledge of the proper proportions for maximum efficiency. In later examples of the Woodcroft screw, the blades were made detachable and adjustable--a plan which is still a usual one, and which has proved to be, in some respects, very convenient. When Ericsson reached the United States, he was almost immediately given an opportunity to build the Princeton--a large screw-steamer--and at about the same time the English and French Governments also had screw-steamers built from his plans, or from those of his agent in England, the Count de Rosen. In these latter ships--the Amphion and the Pomona--the first horizontal direct-acting engines ever built were used, and they were fitted with double-acting air-pumps, having canvas valves and other novel features. The great advantages exhibited by these vessels over the paddle-steamers of the time did for screw-propulsion what Stephenson's locomotive--the Rocket--did for railroad locomotion ten years earlier. Congress, in 1839, had authorized the construction of three war-vessels, and the Secretary of the Navy ordered that two be at once built in the succeeding year. Of these, one was the Princeton, the screw-steamer of which the machinery was designed by Ericsson. The length of this vessel was 164 feet, beam 30-1/2 feet, and depth 21-1/2 feet. The ship drew from 16-1/2 to 18 feet of water, displacing at those draughts 950 and 1,050 tons. The hull had a broad, flat floor, with sharp entrance and fine run, and the lines were considered at that time remarkably fine. The screw was of gun-bronze, six-bladed, and was 14 feet in diameter and of 35 feet pitch; i. e., were there no slip, the screw working as if in a solid nut, the ship would have been driven forward 35 feet at each revolution. The engines were two in number, and very peculiar in form; the cylinder was, in fact, a _semi_-cylinder, and the place of the piston-rod, as usually built, was taken by a vibrating shaft, or "rock-shaft," which carried a piston of rectangular form, and which vibrated like a door on its hinges as the steam was alternately let into and exhausted from each side of it. The great rock-shaft carried, at the outer end, an arm from which a connecting-rod led to the crank, thus forming a "direct-acting engine." The draught in the boilers was urged by blowers. Ericsson had adopted this method of securing an artificial draught ten years before, in one of his earlier vessels, the Corsair. The Princeton carried a XII-inch wrought-iron gun. This gun exploded after a few trials, with terribly disastrous results, causing the death of several distinguished men, including members of the President's cabinet. The Princeton proved very successful as a screw-steamer, attaining a speed of 13 knots, and was then considered very remarkably fast. Captain Stockton, who commanded the vessel, was most enthusiastic in praise of her. Immediately there began a revolution in both civil and naval ship-building, which progressed with great rapidity. The Princeton was the first of the screw-propelled navy which has now entirely displaced the older type of steam-vessel. The introduction of the screw now took place with great rapidity. Six steamers were fitted with Ericsson's screw in 1841, 9 in 1842, and nearly 30 in the year 1843. In Great Britain, France, Germany, and other European countries, the revolution was also finally effected, and was equally complete. Nearly all sea-going vessels built toward the close of the period here considered were screw-steamers, fitted with direct-acting, quick-working engines. It was, however, many years before the experience of engineers in the designing and in the construction and management of this new machinery enabled them to properly proportion it for the various kinds of service to which they were called upon to adapt it. Among other modifications of earlier practice introduced by Ericsson was the surface-condenser with a circulating pump driven by a small independent engine. The screw was found to possess many advantages over the paddle-wheel as an instrument for ship-propulsion. The cost of machinery was greatly reduced by its use; the expense of maintenance in working order was, however, somewhat increased. The latter disadvantage was, nevertheless, much more than compensated by an immense increase in the economy of ship-propulsion, which marked the substitution of the new instrument and its impelling machinery. When a ship is propelled by paddles, the motion of the vessel creates, in consequence of the friction of the fluid against the sides and bottom, a current of water which flows in the direction in which the ship is moving, and forms a current following the ship for a time, and finally losing all motion by contact with the surrounding mass of water. All the power expended in the production of this great stream is, in the case of the paddle-steamer, entirely lost. In screw-steamers, however, the propelling instrument works in this following current, and the tendency of its action is to bring the agitated fluid to rest, taking up and thus restoring, usefully, a large part of that energy which would otherwise have been lost. The screw is also completely covered by the water, and acts with comparative efficiency in consequence of its submersion. The rotation of the screw is comparatively rapid and smooth, also, and this permits the use of small, light, fast-running engines. The latter condition leads to economy of weight and space, and consequently saves not only the cost of transportation of the excess of weight of the larger kind of engine, but, leaving so much more room for paying cargo, the gain is found to be a double one. Still further, the quick-running engine is, other things being equal, the most economical of steam; and thus some expense is saved not only in the purchase of fuel, but in its transportation, and some still additional gain is derived from the increased amount of paying cargo which the vessel is thus enabled to carry. The change here described was thus found to be productive of enormous direct gain. Indirectly, also, some advantage was derived from the greater convenience of a deck clear from machinery and the great paddle-shaft, in the better storage of the lading, the greater facility with which the masts and sails could be fitted and used; and directly, again, in clear sides unencumbered by great paddle-boxes which impeded the vessel by catching both sea and wind. The screw was, for some years, generally regarded as simply auxiliary in large vessels, assisting the sails. Ultimately the screw became the essential feature, and vessels were lightly sparred and were given smaller areas of sail, the latter becoming the auxiliary power. In November of the year 1843, the screw-steamer Midas, Captain Poor, a small schooner-rigged craft, left New York for China, on probably the first voyage of such length ever undertaken by a steamer; and in the following January the Edith, Captain Lewis, a bark-rigged screw-vessel, sailed from the same port for India and China. The Massachusetts, Captain Forbes, a screw-steamship of about 800 tons, sailed for Liverpool September 15, 1845, the first voyage of an American transatlantic passenger-steamer since the Savannah's pioneer adventure a quarter of a century before. Two years later, American enterprise had placed both screw and paddle steamers on the rivers of China--principally through the exertions of Captain R. B. Forbes--and steam-navigation was fairly established throughout the world. On comparing the screw-steamer of the present time with the best examples of steamers propelled by paddle-wheels, the superiority of the former is so marked that it may cause some surprise that the revolution just described should have progressed no more rapidly. The reason of this slow progress, however, was probably that the introduction of the rapidly-revolving screw, in place of the slow-moving paddle-wheel, necessitated a complete revolution in the design of their steam-engines; and the unavoidable change from the heavy, long-stroked, low-speed engines previously in use, to the light engines, with small cylinders and high piston-speed, called for by the new system of propulsion, was one that necessarily occurred slowly, and was accompanied by its share of those engineering blunders and accidents that invariably take place during such periods of transition. Engineers had first to learn to design such engines as should be reliable under the then novel conditions of screw-propulsion, and their experience could only be gained through the occurrence of many mishaps and costly failures. The best proportions of engines and screws, for a given ship, were determined only by long experience, although great assistance was derived from the extensive series of experiments made with the French steamer Pelican. It also became necessary to train up a body of engine-drivers who should be capable of managing these new engines; for they required the exercise of a then unprecedented amount of care and skill. Finally, with the accomplishment of these two requisites to success must simultaneously occur the enlightenment of the public, professional as well as non-professional, in regard to their advantages. Thus it happens that it is only after a considerable time that the screw attained its proper place as an instrument of propulsion, and finally drove the paddle-wheel quite out of use, except in shoal water. Now our large screw-steamers are of higher speed than any paddle-steamers on the ocean, and develop their power at far less cost. This increased economy is due not only to the use of a more efficient propelling instrument, and to changes already described, but also, in a great degree, to the economy which has followed as a consequence of other changes in the steam-engine driving it. The earliest days of screw-propulsion witnessed the use of steam of from 5 to 15 pounds pressure, in a geared engine using jet-condensation, and giving a horse-power at an expense of perhaps 7 to 10, or even more, pounds of coal per hour. A little later came direct-acting engines with jet-condensation and steam at 20 pounds pressure, costing about 5 or 6 pounds per horse-power per hour. The steam-pressure rose a little higher with the use of greater expansion, and the economy of fuel was further improved. The introduction of the surface-condenser, which began to be generally adopted some ten years ago, brought down the cost of power to from 3 to 4 pounds in the better class of engines. At about the same time, this change to surface-condensation helping greatly to overcome those troubles arising from boiler-incrustation which had prevented the rise of steam-pressure above about 25 pounds per square inch, and as, at the same time, it was learned by engineers that the deposit of lime-scale in the marine boiler was determined by temperature rather than by the degree of concentration, and that all the lime entering the boiler was deposited at the pressure just mentioned, a sudden advance took place. Careful design, good workmanship, and skillful management, made the surface-condenser an efficient apparatus; and, the dangers of incrustation being thus lessened, the movement toward higher pressures recommenced, and progressed so rapidly that now 75 pounds per square inch is very usual, and more than 125 pounds has since been attained. The close of this period was marked by the construction of the most successful types of paddle-steamers, the complete success of transoceanic steam-transportation, the introduction of the screw-propeller and the peculiar engine appropriate to it, and, finally, a general improvement, which had finally become marked both in direction and in rapidity of movement, leading toward the use of higher steam-pressure, greater expansion, lighter and more rapidly-working machinery, and decidedly better design and construction, and the use of better material. The result of these changes was seen in economy of first cost and maintenance, and the ability to attain greater speed, and to assure greater safety to passengers and less risk to cargo. The introduction of the changes just noted finally led to the last great change in the form of the marine steam-engine, and a revolution was inaugurated, which, however, only became complete in the succeeding period. The non-success of Hornblower and of Wolff, and others who had attempted to introduce the "compound" or double-cylinder engine on land, had not convinced all engineers that it might not yet be made a successful rival of the then standard type; and the three or four steamers which were built for the Hudson River at the end of the first quarter of the nineteenth century are said to have been very successful vessels. Carrying 75 to 100 pounds of steam in their boilers, the Swiftsure and her contemporaries were by that circumstance well fitted to make that form of engine economically a success. This form of engine was built occasionally during the succeeding quarter of a century, but only became a recognized standard type after the close of the epoch to the history of which this chapter is devoted. That latest and greatest advance in the direction of increased efficiency in the marine steam-engine was, however, commenced very soon after Watt's death, and its completion was the work of nearly a half-century. [Illustration] CHAPTER VI. _THE STEAM-ENGINE OF TO-DAY._ ... "And, last of all, with inimitable power, and 'with whirlwind sound,' comes the potent agency of steam. In comparison with the past, what centuries of improvement has this single agent comprised in the short compass of fifty years! Everywhere practicable, everywhere efficient, it has an arm a thousand times stronger than that of Hercules, and to which human ingenuity is capable of fitting a thousand times as many hands as belonged to Briareus. Steam is found in triumphant operation on the seas; and, under the influence of its strong propulsion, the gallant ship-- 'Against the wind, against the tide, Still steadies with an upright keel.' It is on the rivers, and the boatman may repose on his oars; it is on highways, and exerts itself along the courses of land-conveyance; it is at the bottom of mines, a thousand feet below the earth's surface; it is in the mills, and in the workshops of the trades. It rows, it pumps, it excavates, it carries, it draws, it lifts, it hammers, it spins, it weaves, it prints. It seems to say to men, at least to the class of artisans: 'Leave off your manual labor; give over your bodily toil; bestow but your skill and reason to the directing of my power, and I will bear the toil, with no muscle to grow weary, no nerve to relax, no breast to feel faintness!' What further improvement may still be made in the use of this astonishing power it is impossible to know, and it were vain to conjecture. What we do know is, that it has most essentially altered the face of affairs, and that no visible limit yet appears beyond which its progress is seen to be impossible."--DANIEL WEBSTER. THE PERIOD OF REFINEMENT--1850 TO DATE. By the middle of the present century, as we have now seen, the steam-engine had been applied, and successfully, to every great purpose for which it was fitted. Its first application was to the elevation of water; it next was applied to the driving of mills and machinery; and it finally became the great propelling power in transportation by land and by sea. At the beginning of the period to which we are now come, these applications of steam-power had become familiar both to the engineer and to the public. The forms of engine adapted to each purpose had been determined, and had become usually standard. Every type of the modern steam-engine had assumed, more or less closely, the form and proportions which are now familiar; and the most intelligent designers and builders had been taught--by experience rather than by theory, for the theory of the steam-engine had then been but little investigated, and the principles and laws of thermo-dynamics had not been traced in their application to this engine--the principles of construction essential to successful practice, and were gradually learning the relative standing of the many forms of steam-engine, from among which have been preserved a few specially fitted for certain specific methods of utilization of power. During the years succeeding the date 1850, therefore, the growth of the steam-engine had been, not a change of standard type, or the addition of new parts, but a gradual improvement in forms, proportions, and arrangements of details; and this period has been marked by the dying out of the forms of engine least fitted to succeed in competition with others, and the retention of the latter has been an example of "the survival of the fittest." This has therefore been a Period of Refinement. During this period invention has been confined to details; it has produced new forms of parts, new arrangements of details; it has devised an immense variety of valves, valve-motions, regulating apparatus, and a still greater variety of steam-boilers and of attachments, essential and non-essential, to both engines and boilers. The great majority of these peculiar devices have been of no value, and very many of the best of them have been found to have about equal value. All the well-known and successful forms of engine, when equally well designed and constructed and equally well managed, are of very nearly equal efficiency; all of the best-known types of steam-boiler, where given equal proportions of grate to heating-surface and equally well designed, with a view to securing a good draught and a good circulation of water, have been found to give very nearly equally good results; and it has become evident that a good knowledge of principles and of practice, on the part of the designer, the constructor, and the manager of the boiler, is essential in the endeavor to achieve economical success; that good engineering is demanded, rather than great ingenuity. The inventor has been superseded here by the engineer. The knowledge acquired in the time of Watt, of the essential principles of steam-engine construction, has since become generally familiar to the better class of engineers. It has led to the selection of simple, strong, and durable forms of engine and boiler, to the introduction of various kinds of valves and of valve-gearing, capable of adjustment to any desired range of expansive working, and to the attachment of efficient forms of governor to regulate the speed of the engine, by determining automatically the point of cut-off which will, at any instant, best adjust the energy exerted by the expanding steam to the demand made by the work to be done. The value of high pressures and considerable expansion was recognized as long ago as in the early part of the present century, and Watt, by combining skillfully the several principal parts of the steam-engine, gave it very nearly the shape which it has to-day. The compound engine, even, as has been seen, was invented by contemporaries of Watt, and the only important modifications since his time have occurred in details. The introduction of the "drop cut-off," the attachment of the governor to the expansion-apparatus in such a manner as to determine the degree of expansion, the improvement of proportions, the introduction of higher steam and greater expansion, the improvement of the marine engine by the adoption of surface-condensation, in addition to these other changes, and the introduction of the double-cylinder engine, after the elevation of steam-pressure and increase of expansion had gone so far as to justify its use, are the changes, therefore, which have taken place during this last quarter-century. It began then to be generally understood that expansion of steam produced economy, and mechanics and inventors vied with each other in the effort to obtain a form of valve-gear which should secure the immense saving which an abstract consideration of the expansion of gases according to Marriotte's law would seem to promise. The counteracting phenomena of internal condensation and reëvaporation, of the losses of heat externally and internally, and of the effect of defective vacuum, defective distribution of steam, and of back-pressure, were either unobserved or were entirely overlooked. It was many years, therefore, before engine-builders became convinced that no improvement upon existing forms of expansion-gear could secure even an approximation to theoretical efficiency. The fact thus learned, that the benefit of expansive working has a limit which is very soon reached in ordinary practice, was not then, and has only recently become, generally known among our steam-engine builders, and for several years, during the period upon which we now enter, there continued the keenest competition between makers of rival forms of expansion-gear, and inventors were continually endeavoring to produce something which should far excel any previously-existing device. In Europe, as in the United States, efforts to "improve" standard designs have usually resulted in injuring their efficiency, and in simply adding to the first cost and running expense of the engines, without securing a marked increase in economy in the consumption of steam. SECTION I.--STATIONARY ENGINES. "STATIONARY ENGINES" had been applied to the operation of mill-machinery, as has been seen, by Watt and by Murdoch, his assistant and pupil; and Watt's competitors, in Great Britain and abroad, had made considerable progress before the death of the great engineer, in its adaptation to its work. In the United States, Oliver Evans had introduced the non-condensing high-pressure stationary engine, which was the progenitor of the standard engine of that type which is now used far more generally than any other form. These engines were at first rude in design, badly proportioned, rough and inaccurate as to workmanship, and uneconomical in their consumption of fuel. Gradually, however, when made by reputable builders, they assumed neat and strong shapes, good proportions, and were well made and of excellent materials, doing their work with comparatively little waste of heat or of fuel. One of the neatest and best modern designs of stationary engine for small powers is seen in Fig. 93, which represents a "vertical direct-acting engine," with base-plate--a form which is a favorite with many engineers. The engine shown in the engraving consists of two principal parts, the cylinder and the frame, which is a tapering column having openings in the sides, to allow free access to all the working parts within. The slides and pillow-blocks are cast with the column, so that they cannot become loose or out of line; the rubbing surfaces are large and easily lubricated. Owing to the vertical position, there is no tendency to side wear of cylinder or piston. The packing-rings are self-adjusting, and work free but tight. The crank is counterbalanced; the crank-pin, cross-head pin, piston-rod, valve-stem, etc., are made of steel; all the bearing surfaces are made extra large, and are accurately fitted; and the best quality of Babbitt-metal only used for the journal-bearings. [Illustration: FIG. 93.--Vertical Stationary Steam-Engine.] The smaller sizes of these engines, from 2 to 10 horse-power, have both pillow-blocks cast in the frame, giving a bearing each side of the double cranks. They are built by some constructors in quantities, and parts duplicated by special machinery (as in fire-arms and sewing-machines), which secures great accuracy and uniformity of workmanship, and allows of any part being quickly and cheaply replaced, when worn or broken by accident. The next figure is a vertical section through the same engine. [Illustration: FIG. 94.--Vertical Stationary Steam-Engine. Section.] Engines fitted with the ordinary rigid bearings require to be erected on a firm foundation, and to be kept in perfect line. If, by the settling of the foundation, or from any other cause, they get out of line, heating, cutting, and thumping result. To obviate this, modern engines are often fitted with self-adjusting bearings throughout; this gives the engine great flexibility and freedom from friction. The accompanying cuts show clearly how this is accomplished. The pillow-block has a spherical shell turned and fitted into the spherically-bored pillow-block, thus allowing a slight angular motion in any direction. The connecting-rod is forged in a single piece, without straps, gibs, or key, and is mortised through at each end for the reception of the brass boxes, which are curved on their backs, and fit the cheek-pieces, between which they can turn to adjust themselves to the pins, in the plane of the axis of the rod. The adjustment for wear is made by wedge-blocks and set screws, as shown, and they are so constructed that the parts cannot get loose and cause a break-down. The cross-head has adjustable gibs on each side, turned to fit the slides, which are cast solidly in the frame, and bored out exactly in the line with the cylinder. This permits it freely to turn on its axis, and, in connection with the adjustable boxes in the connecting-rod, allows a perfect self-adjustment to the line of the crank-pin. The out-board bearing may be moved an inch or more out of position in any direction, without detriment to the running of the engine, all bearings accommodating themselves perfectly to whatever position the shaft may assume. The ports and valve-passages are proportioned as in locomotive practice. The valve-seat is adapted to the ordinary plain slide or D-valve, should it be preferred, but the balanced piston slide-valve works with equal ease whether the steam-pressure is 10 or 100 pounds, and at the same time gives double steam and exhaust openings, which greatly facilitates the entrance of the steam to, and its escape from, the cylinder, thus securing a nearer approach to boiler-pressure and a less back-pressure, saving the power required to work an ordinary valve, and reducing the wear of valve-gear. This is a type of engine frequently seen in the United States, but more rarely in Europe. It is an excellent form of engine. The vertical direct-acting engine is sometimes, though rarely, built of very considerable size, and these large engines are more frequently seen in rolling-mills than elsewhere. Where much power is required, the stationary engine is usually an horizontal direct-acting engine, having a more or less effective cut-off valve-gear, according to the size of engine and the cost of fuel. A good example of the simpler form of this kind of engine is the small horizontal slide-valve engine, with independent cut-off valve riding on the back of the main valve--a combination generally known among engineers as the Meyer system of valve-gear. This form of steam-engine is a very effective machine, and does excellent work when properly proportioned to yield the required amount of power. It is well adapted to an expansion of from four to five times. Its disadvantages are the difficulty which it presents in the attachment of the regulator, to determine the point of cut-off by the heavy work which it throws upon the governor when attached, and the rather inflexible character of the device as an expansive valve-gear. The best examples of this class of engine have neat heavy bed-plates, well-designed cylinders and details, smooth-working valve-gear, the expansion-valve adjusted by a right and left hand screw, and regulation secured by the attachment of the governor to the throttle-valve. The engine shown in the accompanying illustration (Fig. 95) is an example of an excellent British stationary steam-engine. It is simple, strong, and efficient. The frame, front cylinder-head, cross-head guides, and crank-shaft "plumber-block," are cast in one piece, as has so generally been done in the United States for a long time by some of our manufacturers. The cylinder is secured against the end of the bed-plate, as was first done by Corliss. The crank-pin is set in a counterbalanced disk. The valve-gear is simple, and the governor effective, and provided with a safety-device to prevent injury by the breaking of the governor-belt. An engine of this kind of 10 inches diameter of cylinder, 20 inches stroke of piston, is rated by the builders at about 25 horse-power; a similar engine 30 inches in diameter of cylinder would yield from 225 to 250 horse-power. In this example, all parts are made to exact size by gauges standardized to Whitworth's sizes. [Illustration: FIG. 95.--Horizontal Stationary Steam-Engine.] [Illustration: FIG. 96.--Horizontal Stationary Steam-Engine.] In American engines (as is seen in Fig. 96), usually, two supports are placed--the one under the latter bearing, and the other under the cylinder--to take the weight of the engine; and through them it is secured to the foundation. As in the vertical engine already described, a valve is sometimes used, consisting of two pistons connected by a rod, and worked by an ordinary eccentric. By a simple arrangement these pistons have always the same pressure inside as out, which prevents any leakage or blowing through; and they are said always to work equally as well and free from friction under 150 pounds pressure as under 10 pounds per square inch, and to require no adjustment. It is more usual, however, to adopt the three-ported valve used on locomotives, with (frequently) a cut-off valve on the back of this main valve, which cut-off valve is adjusted either by hand or by the governor. Engines of the class just described are especially well fitted, by their simplicity, compactness, and solidity, to work at the high piston-speeds which are gradually becoming generally adopted in the effort to attain increased economy of fuel by the reduction of the immense losses of heat which occur in the expansion of steam in the metallic cylinders through which we are now compelled to work it. One of the best known of recent engines is the Allen engine, a steam-engine having the same general arrangement of parts seen in the above illustration, but fitted with a peculiar valve-gear, and having proportions of parts which are especially calculated to secure smoothness of motion and uniformity of pressure on crank-pin and journals, at speeds so high that the inertia of the reciprocating parts becomes a seriously-important element in the calculation of the distribution of stresses and their effect on the dynamics of the machine. In the Allen engine,[85] the cylinder and frame are connected as in the engine seen above, and the crank-disk, shaft-bearings, and other principal details, are not essentially different. The valve-gear[86] differs in having four valves, one at each end on the steam as well as on the exhaust side, all of which are balanced and work with very little resistance. These valves are not detachable, but are driven by a link attached to and moved by an eccentric on the main shaft, the position of the valve-rod attachment to which link is determined by the governor, and the degree of expansion is thus adjusted to the work of the engine. The engine has usually a short stroke, not exceeding twice the diameter of cylinder, and is driven at very high speed, generally averaging from 600 to 800 feet per minute.[87] This high piston-speed and short stroke give very great velocity of rotation. The effect is, therefore, to produce an exceptional smoothness of motion, while permitting the use of small fly-wheels. Its short stroke enables entire solidity to be attained in a bed of rigid form, making it a very completely self-contained engine, adapted to the heaviest work, and requiring only a small foundation. [85] The invention of Messrs. Charles T. Porter and John F. Allen. [86] Invented by Mr. John F. Allen. [87] Or not far from 600 times the cube root of the length of stroke, measured in feet. The journals of the shaft, and all cylindrical wearing surfaces, are finished by grinding in a manner that leaves them perfectly round. The crank-pin and cross-head pin are hardened before being ground. The joints of the valve-gear consist of pins turning in solid ferrules in the rod-ends, both hardened and ground. After years of constant use thus, no wear occasioning lost time in the valve-movements has been detected. High speed and short strokes are essential elements of economy. It is now well understood that all the surfaces with which the steam comes in contact condense it. Obviously, one way to diminish this loss is to reduce the extent of surface to which the steam is exposed. In engines of high speed and short stroke, the surfaces with which the steam comes in contact, while doing a given amount of work, present less area than in ordinary engines running at low speed. Where great steadiness of motion is desired, the expense of coupled engines is often incurred. Quick-running engines do not require to be coupled; a single engine may give greater uniformity of motion than is usually obtained with coupled engines at ordinary speeds. The ports and valve-movements, the weight of the reciprocating parts, and the size and weight of the fly-wheels, should be calculated expressly for the speeds chosen. The economy of the engine here described is unexcelled by the best of the more familiar "drop cut-off" engines. An engine reported upon by a committee of the American Institute, of which Dr. Barnard was chairman, was non-condensing, 16 inches in diameter of cylinder, 30 inches stroke, making 125 revolutions per minute, and developed over 125 horse-power with 75 pounds of steam in the boiler, using 25-3/4 pounds of steam per indicated horse-power, and 2.87 pounds of coal--an extraordinarily good performance for an engine of such small power. The governor used on this engine is known as the Porter governor. It is given great power and delicacy by weighting it down, and thus obtaining a high velocity of rotation, and by suspending the balls from forked arms, which are given each two bearing-pins separated laterally so far as to permit considerable force to be exerted in changing speeds without cramping those bearings sufficiently to seriously impair the sensitiveness of the governor. This engine as a whole may be regarded as a good representative of the high-speed engine of to-day. Since this change in the direction of high speeds has already gone so far that the "drop cut-off" is sometimes inapplicable, in consequence of the fact that the piston would, were such a valve-gear adopted, reach the end of its stroke before the detached valve could reach its seat; and since this progress is only limited by our attainments in mechanical skill and accuracy, it seems probable that the "positive-motion expansion-gear" type of engine will ultimately supersede the now standard "drop cut-off engine." The best known and most generally used class of stationary engines at the present time is, however, that which has the so-called "drop cut-off," or "detachable valve-gear." The oldest well-known form of valve-motion of this description now in use is that known as the Sickels cut-off, patented by Frederick E. Sickels, an American mechanic, about the year 1841, and also built by Hogg, of New York, who placed it upon the engine of the steamer South America. The invention is claimed for both Hogg and Sickels. It was introduced by the inventor in a form which especially adapted it to use with the beam-engine used on the Eastern waters of the United States, and was adapted to stationary engines by Messrs. Thurston, Greene & Co., of Providence, R. I., who made use of it for some years before any other form of "drop cut-off" came into general use. The Sickels cut-off consisted of a set of steam-valves, usually independent of the exhaust-valves, and each raised by a catch, which could be thrown out, at the proper moment, by a wedge with which it came in contact as it rose with the opening valve. This wedge, or other equivalent device, was so adjusted that the valve should be detached and fall to its seat when the piston reached that point in its movement, after taking steam, at which expansion was to commence. From this point, no steam entering the cylinder, the piston was impelled by the expanding vapor. The valve was usually the double-poppet. Sickels subsequently invented what was called the "beam-motion," to detach the valve at any point in the stroke. As at first arranged, the valve could only be detached during the earlier half-stroke, since at mid-stroke the direction of motion of the eccentric rod was reversed and the valve began to descend. By introducing a "wiper" having a motion transverse to that of the valve and its catch, and by giving this wiper a motion coincident with that of the piston by connecting it with the beam or other part of the engine moving with the piston, he obtained a kinematic combination which permitted the valve to be detached at any point in the stroke, adding a very simple contrivance which enabled the attendant to set the wiper so that it should strike the catch at any time during the forward movement of the "beam-motion." On stationary engines, the point of cut-off was afterward determined by the governor, which was made to operate the detaching mechanism, the combination forming what is sometimes called an "automatic" cut-off. The attachment of the governor so as to determine the degree of expansion had been proposed before Sickels's time. One of the earliest of these contrivances was that of Zachariah Allen, in 1834, using a cut-off valve independent of the steam-valve. The first to so attach the governor to a _drop cut-off_ valve-motion was George H. Corliss, who made it a feature of the Corliss valve-gear in 1849. In the year 1855, N. T. Greene introduced a form of expansion-gear, in which he combined the range of the Sickels beam-motion device with the expansion-adjustment gained by the attachment of the governor, and with the advantages of flat slide-valves at all ports--both steam and exhaust. Many other ingenious forms of expansion valve-gear have been invented, and several have been introduced, which, properly designed and proportioned to well-planned engines, and with good construction and management, should give economical results little if at all inferior to those just named. Among the most ingenious of these later devices is that of Babcock & Wilcox, in which a very small auxiliary steam-cylinder and piston is employed to throw the cut-off valve over its port at the instant at which the steam is to be cut off. A very beautiful form of isochronous governor is used on this engine, to regulate the speed of the engine by determining the point of cut-off. In Wright's engine, the expansion is adjusted by the movement, by the regulator, of cams which operate the steam-valves so that they shall hold the valve open a longer or shorter time, as required. Since compactness and lightness are not as essential as in portable, locomotive, and marine engines, the parts are arranged, in stationary engines, with a view simply to securing efficiency, and the design is determined by circumstances. It was formerly usual to adopt the condensing engine in mills, and wherever a stationary engine was required. In Europe generally, and to some extent in the United States, where a supply of condensing water is obtainable, condensing engines and moderate steam-pressures are still employed. But this type of engine is gradually becoming superseded by the high-pressure condensing engine, with considerable expansion, and with an expansion-gear in which the point of cut-off is determined by the governor. [Illustration: FIG. 97.--Corliss Engine.] [Illustration: FIG. 98--Corliss Engine Valve-Motion.] The best-known engine of this class is the Corliss engine, which is very extensively used in the United States, and which has been copied very generally by European builders. Fig. 97 represents the Corliss engine. The horizontal steam-cylinder is bolted firmly to the end of the frame, which is so formed as to transmit the strain to the main journal with the greatest directness. The frame carries the guides for the cross-head, which are both in the same vertical plane. The valves are four in number, a steam and an exhaust valve being placed at each end of the steam-cylinder. Short steam-passages are thus secured, and this diminution of clearance is a source of some economy. Both sets of valves are driven by an eccentric operating a disk or wrist-plate, _E_ (Fig. 98), which vibrates on a pin projecting from the cylinder. Short links reaching from this wrist-plate to the several valves, _D D_, _F F_, move them with a peculiarly varying motion, opening and closing them rapidly, and moving them quite slowly when the port is either nearly open or almost closed. This effect is ingeniously secured by so placing the pins on the wrist-plate that their line of motion becomes nearly transverse to the direction of the valve-links when the limit of movement is approached. The links connecting the wrist-plate with the arms moving the steam-valves have catches at their extremities, which are disengaged by coming in contact, as the arm swings around with the valve-stem, with a cam adjusted by the governor. This adjustment permits the steam to follow the piston farther when the engine is caused to "slow down," and thus tends to restore the proper speed. It disengages the steam-valve earlier, and expands the steam to a greater extent, when the engine begins to run above the proper speed. When the catch is thrown out, the valve is closed by a weight or a strong spring. To prevent jar when the motion of the valve is checked, a "dash-pot" is used, invented originally by F. E. Sickels. This is a vessel having a nicely-fitted piston, which is received by a "cushion" of water or air when the piston suddenly enters the cylinder at the end of the valve-movement. In the original water dash-pot of Sickels, the cylinder is vertical, and the plunger or piston descends upon a small body of water confined in the base of the dash-pot. Corliss's air dash-pot is now often set horizontally. [Illustration: FIG. 99.--Greene Engine.] In the Greene steam-engine (Fig. 99), the valves are four in number, as in the Corliss. The cut-off gear consists of a bar, _A_, moved by the steam-eccentric in a direction parallel with the centre-line of the cylinder and nearly coincident as to time with the piston. On this bar are tappets, _C C_, supported by springs and adjustable in height by the governor, _G_. These tappets engage the arms _B B_, on the ends of rock-shafts, _E E_, which move the steam-valves and remain in contact with them a longer or shorter time, and holding the valve open during a greater or less part of the piston-stroke, as the governor permits the tappets to rise with diminishing engine-speed, or forces them down as speed increases. The exhaust-valves are moved by an independent eccentric rod, which is itself moved by an eccentric set, as is usual with the Corliss and with other engines generally, at right angles with the crank. This engine, in consequence of the independence of the steam-eccentric, and of the contemporary movement of steam valve-motion and steam-piston, is capable of cutting off at any point from beginning to nearly the end of the stroke. The usual arrangement, by which steam and exhaust valves are moved by the same eccentric, only permits expansion with the range from the beginning to half-stroke. In the Corliss engine the latter construction is retained, with the object, in part, of securing a means of closing the valve by a "positive motion," should, by any accident, the closing not be effected by the weight or spring usually relied upon. [Illustration: FIG. 100.--Thurston's Greene-Engine Valve-Gear.] The steam-valve of the Greene engine, as designed by the author, is seen in Fig. 100, where the valve, _G H_, covering the port, _D_, in the steam-cylinder, _A B_, is moved by the rod, _J J_, connected to the rock-shaft, _M_, by the arm, _L K_. The line, _K I_, should, when carried out, intersect the valve-face at its middle point, under _G_. The characteristics of the American stationary engine, therefore, are high steam-pressure without condensation, an expansion valve-gear with drop cut-off adjustable by the governor, high piston-speed, and lightness combined with strength of construction. The pressure most commonly adopted in the boilers which furnish steam to this type of engine is from 75 to 80 pounds per square inch; but a pressure of 100 pounds is not infrequently carried, and the latter pressure may be regarded as a "mean maximum," corresponding to a pressure of 60 pounds at about the commencement of the period here considered--1850. Very much greater pressures have, however, been adopted by some makers, and immensely "higher steam" has been experimented with by several engineers. As early as 1823, Jacob Perkins[88] commenced experimenting with steam of very great tension. As has already been stated, the usual pressure at the time of Watt was but a few pounds--5 or 7--in excess of that of the atmosphere. Evans, Trevithick, and Stevens, had previously worked steam at pressures of from 50 to 75 pounds per square inch, and pressures on the Western rivers and elsewhere in the United States had already been raised to 100 or 150 pounds, and explosions were becoming alarmingly frequent. [88] Perkins was a native of Newburyport, Mass. He was born July 9, 1766, and died in London, July 30, 1849. He went to England when fifty-two years of age, to introduce his inventions. Perkins's experimental apparatus consisted of a copper boiler, of a capacity of about one cubic foot, having sides 3 inches in thickness. It was closed at the bottom and top, and had five small pipes leading from the upper head. This was placed in a furnace kept at a high temperature by a forced combustion. Safety-valves loaded respectively to 425 and 550 pounds per square inch were placed on each of two of the steam-pipes. Perkins used the steam generated under these great pressures in a little engine having a piston 2 inches in diameter and a stroke of 1 foot. It was rated at 10 horse-power.[89] [89] It was when writing of this engine that Stuart wrote, in 1824: "Judging from the rapid strides the steam-engine has made _during the last forty years_ to become a universal first-mover, and from the experience that has arisen from that extension, we feel convinced that every invention which diminishes its size without impairing its power brings it a step nearer to the assistance of the 'world's great laborers,' the husbandman and the peasant, for whom, as yet, it performs but little. At present, it is made occasionally to tread out the corn. What honors await not that man who may yet direct its mighty power to plough, to sow, to harrow, and to reap!" The progress of the steam-engine during those forty years does not to-day appear so astounding. The sentiment here expressed has lost none of its truth, nevertheless. In the year 1827, Perkins had attained working pressures, in a single-acting, single-cylinder engine, of upward of 800 pounds per square inch. At pressures exceeding 200 pounds, he had much trouble in securing effective lubrication, as all oils charred and decomposed at the high temperatures then unavoidably encountered, and he finally succeeded in evading this seemingly insurmountable obstacle by using for rubbing parts a peculiar alloy which required no lubrication, and which became so beautifully polished, after some wear, that the friction was less than where lubricants were used. At these high pressures Perkins seems to have met with no other serious difficulty. He condensed the exhaust-steam and returned it to the boiler, but did not attempt to create a vacuum in his condenser, and therefore needed no air-pump. Steam was cut off at one-eighth stroke. In the same year, Perkins made a compound engine on the Woolf plan, and adopted a pressure of 1,400 pounds, expanding eight times. In still another engine, intended for a steam-vessel, Perkins adopted, or proposed to adopt, 2,000 pounds pressure, cutting off the admission at one-sixteenth, in single-acting engines of 6 inches diameter of cylinder and 20 inches stroke of piston. The steam did not retain boiler-pressure at the cylinder, and this engine was only rated at 30 horse-power.[90] [90] Galloway and Hebert, on the Steam-Engine. London, 1836. Stuart follows a description of Perkins's work in the improvement of the steam-engine and the introduction of steam-artillery by the remark: " ... No other mechanic of the day has done more to illustrate an obscure branch of philosophy by a series of difficult, dangerous, and expensive experiments; no one's labors have been more deserving of cheering encouragement, and no one has received less. Even in their present state, his experiments are opening new fields for philosophical research, and his mechanism bids fair to introduce a new style into the proportions, construction, and form, of steam-machinery." Perkins's experience was no exception to the general rule, which denies to nearly all inventors a fair return for the benefits which they confer upon mankind. Another engineer, a few years later, was also successful in controlling and working steam under much higher pressures than are even now in use. This was Dr. Ernst Alban, a distinguished German engine-builder, of Plau, Mecklenburg, and an admirer of Oliver Evans, in whose path he, a generation later, advanced far beyond that great pioneer. Writing in 1843, he describes a system of engine and boiler construction, with which he used steam under pressures about equal to those experimentally worked by Jacob Perkins, Evans's American successor. Alban's treatise was translated and printed in Great Britain,[91] four years later. [91] "The High-Pressure Steam-Engine," etc. By Dr. Ernst Alban. Translated by William Pole, F. R. A. S. London, 1847. Alban, on one occasion, used steam of 1,000 pounds pressure. His boilers were similar in general form to the boiler patented by Stevens in 1805, but the tubes were horizontal instead of vertical. He evaporated from 8 to 10 pounds of water into steam of 600 to 800 pounds pressure with each pound of coal. He states that the difficulty met by Perkins--the decomposition of lubricants in the steam-cylinder--did not present itself in his experiments, even when working steam at a pressure of 600 pounds on the square inch, and he found that less lubrication was needed at such high pressures than in ordinary practice. Alban expanded his steam about as much as Evans, in his usual practice, carrying a pressure of 150 pounds, and cutting off at one-third; he adopted greatly increased piston-speed, attaining 300 feet per minute, at a time when common practice had only reached 200 feet. He usually built an oscillating engine, and rarely attached a condenser. The valve was the locomotive-slide.[92] The stroke was made short to secure strength, compactness, cheapness, and high speed of rotation; but Alban does not seem to have understood the principles controlling the form and proportions of the expansive engine, or the necessity of adopting considerable expansion in order to secure economy in working steam of great tension, and therefore was, apparently, not aware of the advantages of a long stroke in reducing losses by "dead-space," in reducing risk of annoyance by hot journals, or in enabling high piston-speeds to be adopted. He seems never to have attained a sufficiently high speed of piston to become aware that the oscillating cylinder cannot be used at speeds perfectly practicable with the fixed cylinder. [92] Invented by Joseph Maudsley, of London, 1827. Alban states that one of his smallest engines, having a cylinder 4-1/2 inches in diameter and 1 foot stroke of piston, with a piston-speed of but 140 to 160 feet per minute, developed 4 horse-power, with a consumption of 5.3 pounds of coal per hour. This is a good result for so small an amount of work, and for an engine working at so low a speed of piston. An engine of 30 horse-power, also working very slowly, required but 4.1 pounds of coal per hour per horse-power. The work of Perkins and of Alban, like that of their predecessors, Evans, Stevens, and Trevithick, was, however, the work of engineers who were far ahead of their time. The general practice, up to the time which marked the beginning of the modern "period of refinement," had been but gradually approximating that just described. Higher pressures were slowly approached; higher piston-speeds came slowly into use; greater expansion was gradually adopted; the causes of losses of heat were finally discovered, and steam-jacketing and external non-conducting coverings were more and more generally applied as builders became more familiar with their work. The "compound engine" was now and then adopted; and each experiment, made with higher steam and greater expansion, was more nearly successful than the last. Finally, all these methods of securing economy became recognized, and the reasons for their adoption became known. It then remained, as the final step in this progression, to combine all these requisites of economical working in a double-cylinder engine, steam-jacketed, well protected by non-conducting coverings, working steam of high pressure, and with considerable expansion at high piston-speed. This is now done by the best builders. One of the best examples of this type of engine is that constructed by the sons of Jacob Perkins, who continued the work of their father after his death. Their engines are single-acting, and the small or high-pressure cylinder is placed on the top of the larger or low-pressure cylinder. The valves are worked by rotating stems, and the loss of heat and burning of packing incident to the use of the common method are thus avoided. The stuffing-boxes are placed at the end of long sleeves, closely surrounding the vertical valve-stems also, and the water of condensation which collects in these sleeves is an additional and thorough protection against excessively high temperature at the packing. The piston-rings are made of the alloy which has been found to require no lubrication. Steam is usually worked at from 250 to 450 pounds, and is generated in boilers composed of small tubes three inches in diameter and three-eighths of an inch thick, which are tested under a pressure of 2,500 pounds per square inch. The safety-valve is usually loaded to 400 pounds. The boiler is fed with distilled water, obtained principally by condensation of the exhaust-steam, any deficiency being made up by the addition of water from a distilling apparatus. Under these conditions, but 1-1/4 pound of coal is consumed per hour and per horse-power. THE PUMPING-ENGINE in use at the present time has passed through a series of changes not differing much from that which has been traced with the stationary mill-engine. The Cornish engine is still used to some extent for supplying water to towns, and is retained at deep mines. The modern Cornish engine differs very little from that of the time of Watt, except in the proportions of parts and the form of its details. Steam-pressures are carried which were never reached during the preceding period, and, by careful adjustment of well-set and well-proportioned valves and gearing, the engine has been made to work rather more rapidly, and to do considerably more work. It still remains, however, a large, costly, and awkward contrivance, requiring expensive foundations, and demanding exceptional care, skill, and experience in management. It is gradually going out of use. This engine, as now constructed by good builders, is shown in section in Fig. 101. A comparison with the Watt engine of a century earlier will at once enable any one to appreciate the extent to which changes may be made in perfecting a machine, even after it has become complete, so far as supplying it with all essential parts can complete it. [Illustration: FIG. 101.--Cornish Pumping-Engine, 1880.] In the figure, _A_ is the cylinder, taking steam from the boiler through the steam-passage, _M_. The steam is first admitted above the piston, _B_, driving it rapidly downward and raising the pump-rod, _E_. At an early period in the stroke the admission of steam is checked by the sudden closing of the induction-valve at _M_, and the stroke is completed under the action of expanding steam assisted by the inertia of the heavy parts already in motion. The necessary weight and inertia is afforded, in many cases, where the engine is applied to the pumping of deep mines, by the immensely long and heavy pump-rods. Where this weight is too great, it is counterbalanced, and where too small, weights are added. When the stroke is completed, the "equilibrium valve" is opened, and the steam passes from above to the space below the piston, and an equilibrium of pressure being thus produced, the pump-rods descend, forcing the water from the pumps and raising the steam-piston. The absence of the crank, or other device which might determine absolutely the length of stroke, compels a very careful adjustment of steam-admission to the amount of load. Should the stroke be allowed to exceed the proper length, and should danger thus arise of the piston striking the cylinder-head, _N_, the movement is checked by buffer-beams. The valve-motion is actuated by a plug-rod, _J K_, as in Watt's engine. The regulation is effected by a "cataract," a kind of hydraulic governor, consisting of a plunger-pump, with a reservoir attached. The plunger is raised by the engine, and then automatically detached. It falls with greater or less rapidity, its velocity being determined by the size of the eduction-orifice, which is adjustable by hand. When the plunger reaches the bottom of the pump-barrel, it disengages a catch, a weight is allowed to act upon the steam-valve, opening it, and the engine is caused to make a stroke. When the outlet of the cataract is nearly closed, the engine stands still a considerable time while the plunger is descending, and the strokes succeed each other at long intervals. When the opening is greater, the cataract acts more rapidly, and the engine works faster. This has been regarded until recently as the most economical of pumping-engines, and it is still generally used in freeing mines of water, and in situations where existing heavy pump-rods may be utilized in counterbalancing the steam-pressure, and, by their inertia, in continuing the motion after the steam, by its expansion, has become greatly reduced in pressure. In this engine a gracefully-shaped and strong beam, _D_, has taken the place of the ruder beam of the earlier period, and is carried on a well-built wall of masonry, _R_. _F_ is the exhaust-valve, by which the steam passes to the condenser, _G_, beside which is the air-pump, _H_, and the hot-well, _I_. The cylinder is steam-jacketed, _P_, and protected against losses of heat by radiation by a brick wall, _O_, the whole resting on a heavy foundation, _Q_. The Bull Cornish engine is also still not infrequently seen in use. The Cornish engine of Great Britain averages a duty of about 45,000,000 pounds raised one foot high per 100 pounds of coal. More than double this economy has sometimes been attained. [Illustration: FIG. 102.--Steam-Pump.] A vastly simpler form of pumping-engine without fly-wheel is the now common "direct-acting steam-pump." This engine is generally made use of in feeding steam-boilers, as a forcing and fire pump, and wherever the amount of water to be moved is not large, and where the pressure is comparatively great. The steam-cylinder, _A R_, and feed-pump, _B Q_ (Fig. 102), are in line, and the two pistons have usually one rod, _D_, in common. The two cylinders are connected by a strong frame, _N_, and two standards fitted with lugs carry the whole, and serve as a means of bolting the pump to the floor or to its foundation. The method of working the steam-valve of the modern steam-pump is ingenious and peculiar. As shown, the pistons are moving toward the left; when they reach the end of their stroke, the face of the piston strikes a pin or other contrivance, and thus moves a small auxiliary valve, _I_, which opens a port, _E_, and causes steam to be admitted behind a piston, or permits steam to be exhausted, as in the figure, from before the auxiliary piston, _F_, and the pressure within the main steam-chest then forces that piston over, moving the main steam-valve, _G_, to which it is attached, admitting steam to the left-hand side of the main piston, and exhausting on the right-hand side, _A_. Thus the motion of the engine operates its own valves in such a manner that it is never liable to stop working at the end of the stroke, notwithstanding the absence of the crank and fly-wheel, or of independent mechanism, like the cataract of the Cornish engine. There is a very considerable variety of pumps of this class, all differing in detail, but all presenting the distinguishing feature of auxiliary valve and piston, and a connection by which it and the main engine each works the valve of the other combination. [Illustration: FIG. 103.--The Worthington Pumping-Engine, 1876. Section.] [Illustration: FIG. 104.--The Worthington Pumping-Engine.] In some cases these pumps are made of considerable size, and are applied to the elevation of water in situations to which the Cornish engine was formerly considered exclusively applicable. The accompanying figure illustrates such a pumping-engine, as built for supplying cities with water. This is a "compound" direct-acting pumping-engine. The cylinders, _A B_, are placed in line, working one pump, _F_, and operating their own air-pumps, _D D_, by a bell-crank lever, _L H_, connected to the pump-buckets by links, _I K_. Steam exhausted from the small cylinder, _A_, is further expanded in the large cylinder, _B_, and thence goes to the condenser, _C_. The valves, _N M_, are moved by the valve-gear, _L_, which is actuated by the piston-rod of a similar pair of cylinders placed by the side of the first. These valves are balanced, and the balance-plates, _R Q_, are suspended from the rods, _O P_, which allow them to move with the valves. By connecting the valves of each engine with the piston-rod of the other, it is seen that the two engines must work alternately, the one making a stroke while the other is still, and then itself stopping a moment while the latter makes its stroke. Water enters the pump through the induction-pipe, _E_, passes into the pump-barrel through the valves, _V V_, and issues through the eduction-valves, _T T_, and goes on to the "mains" by the pipe, _G_, above which is seen an air-chamber, which assists to preserve a uniform pressure on that side the pump. This engine works very smoothly and quietly, is cheap and durable, and has done excellent duty. Beam pumping-engines are now almost invariably built with crank and fly-wheel, and very frequently are compound engines. The accompanying illustration represents an engine of the latter form. [Illustration: FIG. 105.--Double-Cylinder Pumping-Engine, 1878.] [Illustration: FIG. 106.--The Lawrence Water-Works Engine.] _A_ and _B_ are the two steam-cylinders, connected by links and parallel motion, _C D_, to the great cast-iron beam, _E F_. At the opposite end of the beam, the connecting-rod, _G_, turns a crank, _H_, and fly-wheel, _L M_, which regulates the motion of the engine and controls the length of stroke, averting all danger of accident occurring in consequence of the piston striking either cylinder-head. The beam is carried on handsomely-shaped iron columns, which, with cylinders, pump, and fly-wheel, are supported by a substantial stone foundation. The pump-rod, _I_, works a double-acting pump, _J_, and the resistance to the issuing water is rendered uniform by an air-chamber, _K_, within which the water rises and falls when pressures tend to vary greatly. A revolving shaft, _N_, driven from the fly-wheel shaft, carries cams, _O P_, which move the lifting-rods seen directly over them and the valves which they actuate. Between the steam-cylinders and the columns which carry the beams is a well, in which are placed the condenser and air-pump. Steam is carried at 60 or 80 pounds pressure, and expanded from 6 to 10 times. [Illustration: FIG. 107.--The Leavitt Pumping-Engine.] A later form of double-cylinder beam pumping-engine is that invented and designed by E. D. Leavitt, Jr., for the Lawrence Water-Works, and shown in Figs. 106 and 107. The two cylinders are placed one on each side the centre of the beam, and are so inclined that they may be coupled to opposite ends of it, while their lower ends are placed close together. At their upper ends a valve is placed at each end of the connecting steam-pipe. At their lower ends a single valve serves as exhaust-valve to the high-pressure and as steam-valve to the low-pressure cylinder. The pistons move in opposite directions, and steam is exhausted from the high-pressure cylinder directly into the nearer end of the low-pressure cylinder. The pump, of the "Thames-Ditton" or "bucket-and-plunger" variety, takes a full supply of water on the down-stroke, and discharges half when rising and half when descending again. The duty of this engine is reported by a board of engineers as 103,923,215 foot-pounds for every 100 pounds of coal burned. The duty of a moderately good engine is usually considered to be from 60 to 70 millions. This engine has steam-cylinders of 17-1/2 and 36 inches diameter respectively, with a stroke of 7 feet. The pump had a capacity of about 195 gallons, and delivered 96 per cent. Steam was carried at a pressure of 75 pounds above the atmosphere, and was expanded about 10 times. Plain horizontal tubular boilers were used, evaporating 8.58 pounds of water from 98° Fahr. per pound of coal. STEAM-BOILERS.--The steam supplied to the forms of stationary engine which have been described is generated in steam-boilers of exceedingly varied forms. The type used is determined by the extent to which their cost is increased in the endeavor to economize fuel by the pressure of steam carried, by the greater or less necessity of providing against risk of explosion, by the character of the feed-water to be used, by the facilities which may exist for keeping in good repair, and even by the character of the men in whose hands the apparatus is likely to be placed. As has been seen, the changes which have marked the growth and development of the steam-engine have been accompanied by equally marked changes in the forms of the steam-boiler. At first, the same vessel served the distinct purposes of steam-generator and steam-engine. Later, it became separated from the engine, and was then specially fitted to perform its own peculiar functions; and its form went through a series of modifications under the action of the causes already stated. When steam began to be usefully applied, and considerable pressures became necessary, the forms given to boilers were approximately spherical, ellipsoidal, or cylindrical. Thus the boilers of De Caus (1615) and of the Marquis of Worcester (1663) were spherical and cylindrical; those of Savery (1698) were ellipsoidal and cylindrical. After the invention of the steam-engine of Newcomen, the pressures adopted were again very low, and steam-boilers were given irregular forms until, at the beginning of the present century, they were again of necessity given stronger shapes. The material was at first frequently copper; it is now usually wrought-iron, and sometimes steel. The present forms of steam-boilers may be classified as plain, flue, and tubular boilers. The plain cylindrical or common cylinder boiler is the only representative of the first class in common use. It is perfectly cylindrical, with heads either flat or hemispherical. There is usually attached to the boiler a "steam-drum" (a small cylindrical vessel), from which the steam is taken by the steam-pipe. This enlargement of the steam-space permits the mist, held in suspension by the steam when it first rises from the surface of the water, to separate more or less completely before the steam is taken from the boiler. [Illustration: FIG. 108.--Babcock & Wilcox's Vertical Boiler.] Flue-boilers are frequently cylindrical, and contain one or more cylindrical flues, which pass through from end to end, beneath the water-line, conducting the furnace-gases, and affording a greater area of heating-surface than can be obtained in the plain boiler. They are usually from 30 to 48 inches in diameter, and one foot or less in length for each inch of diameter. Some are, however, made 100 feet and more in length. The boiler is made of iron 1/4 to 3/8 of an inch in thickness, with hemispherical or carefully stayed flat heads, and without flues. The whole is placed in a brickwork setting. These boilers are used where fuel is inexpensive, where the cost of repairing would be great, or where the feed-water is impure. A cylindrical boiler, having one flue traversing it longitudinally, is called a Cornish boiler, as it is generally supposed to have been first used in Cornwall. It was probably first invented by Oliver Evans in the United States, previous to 1786, at which time he had it in use. The flue has usually a diameter 0.5 or 0.6 the diameter of the boiler. A boiler containing two longitudinal flues is called the Lancashire boiler. This form was also introduced by Oliver Evans. The flues have one-third the diameter of the boiler. Several flues of smaller diameter are often used, and when a still greater proportional area of heating-surface is required, tubes of from 1-1/4 inch to 4 or 5 inches in diameter are substituted for flues. The flues are usually constructed by riveting sheets together, as in making the shell or outer portion. They are sometimes welded by British manufacturers, but rarely if ever in the United States. Tubes are always "lap-welded" in the process of rolling them. Small tubes were first used in the United States, about 1785. In portable, locomotive, and marine steam-boilers, the fire must be built within the boiler itself, instead of (as in the above described stationary boilers) in a furnace of brickwork exterior to the boiler. The flame and gases from the furnace or fire-box in these kinds of boiler are never led through brick passages en route to the chimney, as often in the preceding case, but are invariably conducted through flues or tubes, or both, to the smoke-stack. These boilers are also sometimes used as stationary boilers. Fig. 108 represents such a steam-boiler in section, as it is usually exhibited in working drawings. Provision is made to secure a good circulation of water in these boilers by means of the "baffle-plates," seen in the sketch, which compel the water to flow as indicated by the arrows. The tubes are frequently made of brass or of copper, to secure rapid transmission of heat to the water, and thus to permit the use of a smaller area of heating-surface and a smaller boiler. The steam-space is made as large as possible, to secure immunity from "priming" or the "entrainment" of water with the steam. This type of steam-boiler, invented by Nathan Read, of Salem, Mass., in 1791, and patented in April of that year, was the earliest of the tubular boilers. In the locomotive boiler (Fig. 109), as in the preceding, the characteristics are a fire-box at one end of the shell and a set of tubes through which the gases pass directly to the smoke-stack. Strength, compactness, great steaming capacity, fair economy, moderate cost, and convenience of combination with the running parts, are secured by the adoption of this form. It is frequently used also for portable and stationary engines. It was invented in France by M. Seguin, and in England by Booth, and used by George Stephenson at about the same time--1828 or 1829. [Illustration: FIG. 109.--Stationary "Locomotive" Boiler.] Since the efficiency of a steam-boiler depends upon the extent of effective heating-surface per unit of weight of fuel burned in any given time--or, ordinarily, upon the ratio of the areas of heating and grate surface--peculiar expedients are sometimes adopted, having for their object the increase of heating-surface, without change of form of boiler and without proportionate increase of cost. One of these methods is that of the use of Galloway conical tubes (Fig. 110). These are very largely used in Great Britain, but are seldom if ever seen in the United States. The Cornish boiler, to which they are usually applied, consists of a large cylindrical shell, 6 feet or more in diameter, containing one tube of about one-half as great dimensions, or sometimes two of one-third the diameter of the shell each. Such boilers have a very small ratio of heating to grate surface, and their large tubes are peculiarly liable to collapse. To remove these objections, the Messrs. Galloway introduced stay-tubes into the flues, which tubes are conical in form, and are set in either a vertical or an inclined position, the larger end uppermost. The area of heating-surface is thus greatly increased, and, at the same time, the liability to collapse is reduced. The same results are obtained by another device of Galloway, which is sometimes combined with that just described in the same boiler. Several sheets in the flue have "pockets" worked into them, which pockets project into the flue-passage. [Illustration: FIG. 110.] Another device is that of an American engineer, Miller, who surrounds the furnace of cylindrical and other boilers with water-tubes. The "fuel-economizers" of Greene and others consist of similar collections of tubes set in the flues, between the boiler and the chimney. "_Sectional_" boilers are gradually coming into use with high pressures, on account of their greater safety against disastrous explosions. The earliest practicable example of a boiler of this class was probably that of Colonel John Stevens, of Hoboken, N. J. Dr. Alban, who, forty years later, attempted to bring this type into general use, and constructed a number of such boilers, did not succeed. Their introduction, like that of all radical changes in engineering, has been but slow, and it has been only recently that their manufacture has become an important branch of industry. A committee of the American Institute, of which the author was chairman, in 1871, examined several boilers of this and the ordinary type, and tested them very carefully. They reported that they felt "confident that the introduction of this class of steam-boilers will do much toward the removal of the cause of that universal feeling of distrust which renders the presence of a steam-boiler so objectionable in every locality. The difficulties in thoroughly inspecting these boilers, in regulating their action, and other faults of the class, are gradually being overcome, and the committee look forward with confidence to the time when their use will become general, to the exclusion of older and more dangerous forms of steam-boilers." The economical performance of these boilers with a similar ratio of heating to grate surface is equal to that of other kinds. In fact, they are usually given a somewhat higher ratio, and their economy of fuel frequently exceeds that of the other types. Their principal defect is their small capacity for steam and water, which makes it extremely difficult to obtain steady steam-pressure. Where they are employed, the feed and draught should be, if possible, controlled by automatic attachments, and the feed-water heated to the highest attainable temperature. Their satisfactory working depends, more than in other cases, on the ability of the fireman, and can only be secured by the exercise of both care and skill. Many forms of these boilers have been devised. Walter Hancock constructed boilers for his steam-carriage of flat plates connected by stay-bolts, several such sections composing the boiler; and about the same time (1828) Sir Goldsworthy Gurney constructed for a similar purpose boilers consisting of a steam and a water reservoir, placed one above the other, and connected by triangularly-bent water-tubes exposed to the heat of the furnace-gases. Jacob Perkins made many experiments looking to the employment of very high steam-pressures, and in 1831 patented a boiler of this class, in which the heating-surfaces nearest the fire were composed of iron tubes, which tubes also served as grate-bars. The steam and water space was principally comprised within a comparatively large chamber, of which the walls were secured by closely distributed stay-bolts. For extremely high pressures, boilers composed only of tubes were used. Dr. Ernst Alban described the boiler already referred to, and its construction and operation, and stated that he had experimented with pressures as high as 1,000 pounds to the square inch. The Harrison steam-boiler, which has been many years in use in the United States, consists of several sections, each of which is made up of hollow globes of cast-iron, communicating with each other by necks cast upon the spheres, and fitted together with faced joints. Long bolts, extending from end to end of each row, bind the spheres together. (_See_ Fig. 111.) [Illustration: FIG. 111.--Harrison's Sectional Boiler.] An example of another modern type in extensive use is given in Fig. 112, a semi-sectional boiler, which consists of a series of inclined wrought-iron tubes, connected by T-heads, which form the vertical water-channels, at each end. The joints are faced by milling them, and then ground so perfectly tight that a pressure of 500 pounds to the square inch is insufficient to produce leakage. No packing is used. The fire is made under the front and higher end of the tubes, and the products of combustion pass up between the tubes into a combustion-chamber under the steam and water drum; hence they pass down between the tubes, then once more up through the space between the tubes, and off to the chimney. The steam is taken out at the top of the steam-drum near the back end of the boiler. The rapid circulation prevents to some extent the formation of deposits or incrustations upon the heating-surfaces, sweeping them away and depositing them in the mud-drum, whence they are blown out. Rapid circulation of water, as has been shown by Prof. Trowbridge, also assists in the extraction of the heat from the gases, by the presentation of fresh water continually, as well as by the prevention of incrustation. [Illustration: FIG. 112.--Babcock and Wilcox's Sectional Boiler.] Attempts have been made to adapt sectional boilers to marine engines; but very little progress has yet been made in their introduction. The Root sectional boiler (Fig. 113), an American design, which is in extensive use in the United States and Europe, has also been experimentally placed in service on shipboard. Its heating-surface consists wholly of tubes, which are connected by a peculiarly formed series of caps; the joints are made tight with rubber "grummets." [Illustration: FIG. 113.--Root Sectional Boiler.] SECTION II.--PORTABLE AND LOCOMOTIVE ENGINES. Engines and boilers, when of small size, are now often combined in one structure which may be readily transported. Where they have a common base-plate simply, as in Fig. 114, they are called, usually, "semi-portable engines." These little engines have some decided advantages. Being attached to one base, the combined engine and boiler is easily transported, occupies little space, and may very readily be mounted upon wheels, rendering it peculiarly well adapted for agricultural purposes. [Illustration: FIG. 114.--Semi-Portable Engine, 1878.] The example here shown differs in its design from those usually seen in the market. The engine is not fastened to or upon the boiler, and is therefore not affected by expansion, nor are the bearings overheated by conduction or by ascending heat from the boiler. The fly-wheel is at the base, which arrangement secures steadiness at the high speed which is a requisite for economy of fuel. The boilers are of the upright tubular style, with internal fire-box, and are intended to be worked at 150 pounds pressure per inch. They are fitted with a baffle-plate and circulating-pipe, to prevent priming, and also with a fusible plug, which will melt and prevent the crown-sheet of the boiler burning, if the water gets low. [Illustration: FIG. 115.--Semi-Portable Engine, 1878.] Another illustration of this form of engine, as built in small sizes, is seen below. The peculiarity of this engine is, that the cylinder is placed in the top of the boiler, which is upright. By this arrangement the engine is constantly drawing from the boiler the hottest and driest steam, and there is thus no liability of serious loss by condensation, which is rapid, even in a short pipe, when the engine is separate from the boiler. The engine illustrated is rated at 10 horse-power, and makers are always expected to guarantee their machines to work up to the rated power. The cylinder is 7 by 7 inches, and the main shaft is directly over it. On this shaft are three eccentrics, one working the pump, one moving the valves, and the third one operating the cut-off. The driving-pulley is 20 inches in diameter, and the balance-wheel 30 inches. The boiler has 15 1-1/4-inch flues. It is furnished with a heater in its lower portion. The boiler of this engine is tested up to 200 pounds, and is calculated to carry 100 pounds working pressure, though that is not necessary to develop the full power of the engine. The compactness of the whole machine is exceptional. It can be set up in a space 5 feet square and 8 feet high. The weight of the 10 horse-power engine is 1,540 pounds, and of the whole machine 4,890 pounds, boxed for shipment. Every part of the mechanism usually fits and works with the exactness of a gun-lock, as each piece is carefully made to gauge. Portable engines are those which are especially intended to be moved conveniently from place to place. The engine is usually attached to the boiler, and the feed-pump is generally attached to the engine. The whole machine is carried on wheels, and is moved from one place to another, usually by horses, but sometimes by its own engine, which is coupled by an engaging and disengaging apparatus to the rear-wheels. English builders have usually excelled in the construction of this class of steam-engine, although it is probable that the best American engines are fully equal to them in design, material, and construction. The later work of the best-known English builders has given economical results that have surprised engineers. The annual "shows" of the Royal Agricultural Society have elicited good evidence of skill in management as well as of excellence of design and construction. Some little portable engines have exhibited an economical efficiency superior to that of the largest marine engines of any but the compound type, and even closely competing with that form. The causes of this remarkable economy are readily learned by an inspection of these engines, and by observation of the method of managing them at the test-trial. The engines are usually very carefully designed. The cylinders are nicely proportioned to their work, and their pistons travel at high speed. Their valve-gear consists usually of a plain slide-valve, supplemented by a separate expansion-slide, driven by an independent eccentric, and capable of considerable variation in the point of cut-off. This form of expansion-gear is very effective--almost as much so as a drop cut-off--at the usual grade of expansion, which is not far from four times. The governor is usually attached to a throttle-valve in the steam-pipe, an arrangement which is not the best possible under variable loads, but which produces no serious loss of efficiency when the engine is driven, as at competitive trials, under the very uniform load of a Prony strap-brake and at very nearly the maximum capacity of the machine. The most successful engines have had steam-jacketed cylinders--always an essential to maximum economy--with high steam and a considerable expansion. The boilers are strongly made, and are, as are also all other heated surfaces, carefully clothed with non-conducting material, and well lagged over all. The details are carefully proportioned, the rods and frames are strong and well secured together, and the bearings have large rubbing-surfaces. The connecting-rods are long and easy-working, and every part is capable of doing its work without straining and with the least friction. In handling the engines at the competitive trial, most experienced and skillful drivers are selected. The difference between the performances of the same engine in different hands has been found to amount to from 10 to 15 per cent., even where the competitors were both considered exceptionally skillful men. In manipulating the engine, the fires are attended to with the utmost care; coal is thrown upon them at regular and frequent intervals, and a uniform depth of fuel and a perfectly clean fire are secured. The sides and corners of the fire are looked after with especial care. The fire-doors are kept open the least possible time; not a square inch of grate-surface is left unutilized, and every pound of coal gives out its maximum of calorific power, and in precisely the place where it is needed. Feed-water is supplied as nearly as possible continuously, and with the utmost regularity. In some cases the engine-driver stands by his engine constantly, feeding the fire with coal in handfuls, and supplying the water to the heater by hand by means of a cup. Heaters are invariably used in such cases. The exhaust is contracted no more than is absolutely necessary for draught. The brake is watched carefully, lest irregularity of lubrication should cause oscillation of speed with the changing resistance. The load is made the maximum which the engine is designed to drive with economy. Thus all conditions are made as favorable as possible to economy, and they are preserved as invariable as the utmost care on the part of the attendant can make them. These trials are usually of only three or five hours' duration, and thus terminate before it becomes necessary to clean fires. The following are results obtained at the trial of engines which took place in July, 1870, at the Oxford Agricultural Fair: KEY: A: Number. B: Diameter. C: Stroke. D: Nominal. E: Dynamometric. F: Point of cut off. G: Revolutions per minute. H: Pounds coal per horse-power per hour. ---------------+-------------+-----+--------------+------+------+---- MAKERS' NAME | CYLINDERS. | | HORSE-POWER. | | | AND +-----+-------+ +-------+------+ | | RESIDENCE. | A | B | C | D | E | F | G | H ---------------+-----+-------+-----+-------+------+------+------+---- | |Inches.| In. | | | | | Clayton, | | | | | | | | Shuttleworth | 1 | 7 | 12 | 4 | 4.42 | ... |121.65|3.73 & Co., Lincoln | | | | | | | | | | | | | | | | Brown & May, | | | | | | | | Devizes | 1 | 7-3/16| 12 | 4 | 4.19 | 11.48|125.65|4.44 | | | | | | | | Reading Iron- | | | | | | | | Works Company, | 1 | 5-3/4 | 14 | 4 | 4.16 | ... |145.7 |4.65 Reading | | | | | | | | ---------------+-----+-------+-----+-------+------+------+------+---- These were horizontal engines, attached to locomotive boilers. At a similar exhibition held at Bury, in 1867, considerably better results even than these were reported, as below, from engines of similar size and styles: KEY: A: Number. B: Diameter. C: Stroke. D: Nominal. E: Dynamometric. F: Point of cut off. G: Revolutions per minute. H: Pounds coal per horse-power per hour. ---------------+-------------+-----+--------------+------+------+---- MAKERS' NAME | CYLINDERS. | | HORSE-POWER. | | | AND +-----+-------+ +-------+------+ | | RESIDENCE. | A | B | C | D | E | F | G | H ---------------+-----+-------+-----+-------+------+------+------+---- | |Inches.| In. | | | | | Clayton, | | | | | | | | Shuttleworth | 1 |10 | 20 | 10 | 11.00| 3.10 | 71.5 | 4.13 & Co., Lincoln | | | | | | | | | | | | | | | | Reading Iron- | | | | | | | | Works Company, | 1 | 8-5/8 | 20 | 10 | 10.43| 1.4 |109.4 | 4.22 Reading | | | | | | | | ---------------+-----+-------+-----+-------+------+------+------+---- With all these engines steam-jackets were used; the feed-water was highly and uniformly heated by exhaust-steam; the coal was selected, finely broken, and thrown on the fire with the greatest care; the velocity of the engines, the steam-pressure, and the amount of feed-water, were very carefully regulated, and all bearings were run quite loose; the engine-drivers were usually expert "jockeys." The next illustration represents the portable steam-engine as built by one of the oldest and most experienced manufacturers of such engines in the United States. In the boilers of these engines the heating-surface is given less extent than in the stationary engine-boiler, but much greater than in the locomotive, and varies from 10 to 20 square feet per horse-power. The boilers are made very strong, to enable them to withstand the strains due to the attached engine, which are estimated as equivalent to from one-tenth to one-fifth that due to the steam-pressure. The boiler is sometimes given even double the strength usual with stationary boilers of similar capacity. The engine is mounted, in this example, directly over the boiler, and all parts are in sight and readily accessible to the engineer. [Illustration: FIG. 116.--The Portable Steam-Engine, 1878.] One of these engines, of 20 horse-power, has a steam-cylinder 10 inches in diameter and 18 inches stroke of piston, making 125 revolutions per minute, and has 9 square feet of grate-surface and 288 feet of heating-surface. It weighs about 4-1/2 tons. Steam is carried at 125 pounds. In the class of engines just described, the draught is obtained by the blast of the exhaust-steam which is led into the chimney. Such engines are now sold at from $120 to $150 per horse-power, according to size and quality, the smaller engines costing most. The usual consumption of fuel is from 4 to 6 pounds per hour and per horse-power, burning from 15 to 20 pounds on each square foot of grate, and each pound evaporating about 8 pounds of water. A usual weight is, for the larger sizes, 500 pounds per horse-power. [Illustration: FIG. 117.--The Thrashers' Road-Engine, 1878.] These engines are sometimes arranged to propel themselves, as in the Mills "Thrashers'" road-engine or locomotive, of which the accompanying engraving is a good representation. This engine is proportioned for hauling a tank containing 10 barrels, or more, of water and a grain-separator over all ordinary roads, and to drive a thrashing-machine or saw-mill, developing 20 or 25 horse-power. This example of the road-engine has a boiler built to work at 250 pounds of steam; the engine is designed for a maximum power of 30 horses. This engine has a balanced valve and automatic cut-off, and is fitted with a reversing-gear for use on the road. The driving-wheels are of wrought-iron, 56 inches diameter and 8 inches wide, with cast-iron driving-arms. Both wheels are drivers on curves as well as on straight lines. The engine is guided and fired by one man, and the total weight is so small that it will pass safely over any good country bridge. A brake is attached, to insure safety when going down-hill. Although designed to move at a speed of about three miles per hour, the velocity of the piston may be increased so that four miles per hour may be accomplished when necessary. [Illustration: FIG. 118.--Fisher's Steam-Carriage.] This is an excellent example of this kind of engine as constructed at the present time. The strongly-built boiler, with its heater, the jacketed cylinder, and light, strong frame of the engine, the steel running-gear, the carefully-covered surfaces of cylinder and boiler, and excellent proportions of details, are illustrations of good modern engineering, and are in curious contrast with the first of the class, built a century earlier by Smeaton. Steam-carriages for passengers are now rarely built. Fig. 118 represents that designed by Fisher about 1870 or earlier. It was only worked experimentally. [Illustration: FIG. 119.--Road and Farm Locomotive.] The above is an engraving of a road and farm locomotive as built by one of the most successful among several British firms engaged in this work. The capacity of these engines has been determined by experiment by the author in the United States, and abroad by several distinguished engineers. The author made a trial of one of these engines at South Orange, N. J., to determine its power, speed, and convenience of working and man[oe]uvring. The following were the principal dimensions: Weight of engine, complete, 5 tons 4 cwt. 11,648 pounds. Steam-cylinder--diameter 7-3/4 inches. Stroke of piston 10 inches. Revolution of crank to one of driving-wheels 17 Driving-wheels--diameter 60 inches. " breadth of tire 10 inches. " weight, each 450 pounds. Boiler--length over all 8 feet. " diameter of shell 30 feet. " thickness of shell 7/16 inch. " fire-box sheets, outside, thickness 1/2 inch. Load on driving-wheels, 4 tons 10 cwt. 10,080 pounds. The boiler was of the ordinary locomotive type, and the engine was mounted upon it, as is usual with portable engines. The steam-cylinder was steam-jacketed, in accordance with the most advanced practice here and abroad. The crank-shaft and other wrought-iron parts subjected to heavy strains were strong and plainly finished. The gearing was of malleableized cast-iron, and all bearings, from crank-shaft to driving-wheel, on each side, were carried by a single sheet of half-inch plate, which also formed the sides of the fire-box exterior. The following is a summary of the conclusions deduced by the author from the trial, and published in the _Journal of the Franklin Institute_: A traction-engine may be so constructed as to be easily and rapidly man[oe]uvred on the common road; and an engine weighing over 5 tons may be turned continuously without difficulty on a circle of 18 feet radius, or even on a road but little wider than the length of the engine. A locomotive of 5 tons 4 hundredweight has been constructed, capable of drawing on a good road 23,000 pounds up a grade of 533 feet to the mile, at the rate of four miles an hour; and one might be constructed to draw more than 63,000 pounds up a grade of 225 feet to the mile, at the rate of two miles an hour. It was further shown that the coefficient of traction with heavily-laden wagons on a good macadamized road is not far from .04; the traction-power of this engine is equal to that of 20 horses; the weight, exclusive of the weight of the engine, that could be drawn on a level road, was 163,452 pounds; and the amount of fuel required is estimated at 500 pounds a day. The advantages claimed for the traction-engine over horse-power are: no necessity for a limitation of working-hours; a difference in first cost in favor of steam; and in heavy work on a common road the expense by steam is less than 25 per cent. of the average cost of horse-power, a traction-engine capable of doing the work of 25 horses being worked at as little expense as 6 or 8 horses. The cost of hauling heavy loads has been estimated at 7 cents per ton per mile. Such engines are gradually becoming useful in steam-ploughing. Two systems are adopted. In the one the engine is stationary, and hauls a "gang" of ploughs by means of a windlass and wire rope; in the other the engine traverses a field, drawing behind it a plough or a gang of ploughs. The latter method has been proposed for breaking up prairie-land. Thus, thirty years after the defeat of the intelligent, courageous, and persistent Hancock and his coworkers in the scheme of applying the steam-engine usefully on the common road, we find strong indications that, in a new form, the problem has been again attacked, and at least partially solved. One of the most important of the prerequisites to ultimate success in the substitution of steam for animal power on the highway is that our roads shall be well made. As the greatest care and judgment are exercised, and an immense outlay of capital is considered justifiable, in securing easy grades and a smooth track on our railroad routes, we may readily believe that similar precaution and outlay will be found advisable in adapting the common road to the road-locomotive. It would seem to the engineer that the natural obstacles generally supposed to stand in the way have, after all, no real existence. The principal inconvenience that may be anticipated will probably arise from the carelessness or avarice of proprietors, which may sometimes cause them to appoint ignorant and inefficient engine-drivers, giving them charge of what are always excellent servants, but terrible masters. Nevertheless, as the transportation of passengers on railroads is found to be attended with less liability to loss of life or injury of person than their carriage by stage-coach, it will be found, very probably, that the general use of steam in transporting freight on common roads may be attended with less risk to life or property than to-day attends the use of horse-power. The STEAM FIRE-ENGINE is still another form of portable engine. It is also one of the latest of all applications of steam-power. The steam fire-engine is peculiarly an American production. Although previously attempted, their permanently successful introduction has only occurred within the last fifteen years. [Illustration: FIG. 120.--The Latta Steam Fire-Engine.] As early as 1830, Braithwaite and Ericsson, of London, England, built an engine with steam and pump cylinders of 7 and 6-1/2 inches diameter, respectively, with 16 inches stroke of piston. This machine weighed 2-1/2 tons, and is said to have thrown 150 gallons of water per minute to a height of between 80 and 100 feet. It was ready for work in about 20 minutes after lighting the fire. Braithwaite afterward supplied a more powerful engine to the King of Prussia, in 1832. The first attempt made in the United States to construct a steam fire-engine was probably that of Hodge, who built one in New York in 1841. It was a strong and very effective machine, but was far too heavy for rapid transportation. The late J. K. Fisher, who throughout his life persistently urged the use of steam-carriages and traction-engines, designing and building several, also planned a steam fire-engine. Two were built from his design by the Novelty Works, New York, about 1860, for Messrs. Lee & Larned. They were "self-propellers," and one of them, built for the city of Philadelphia, was sent to that city over the highway, driven by its own engines. The other was built for and used by the New York Fire Department, and did good service for several years. These engines were heavy, but very powerful, and were found to move at good speed under steam and to man[oe]uvre well. The Messrs. Latta, of Cincinnati, soon after succeeded in constructing comparatively light and very effective engines, and the fire department of that city was the first to adopt steam fire-engines definitely as their principal reliance. This change has now become general. The steam fire-engine has now entirely displaced the old hand-engine in all large cities. It does its work at a fraction of the cost of the latter. It can force its water to a height of 225 feet, and to a distance of more than 300 feet horizontally, while the hand-engine can seldom throw it one-third these distances; and the "steamer" may be relied upon to work at full power many hours if necessary, while the men at the hand-engine soon become fatigued, and require frequent relief. The city of New York has 40 steam fire-engines. One engine to every 10,000 inhabitants is a proper proportion. In the standard steam fire-engine (Fig. 120) reciprocating engines and pumps are adopted, as seen in section in Fig. 121, in which _A_ is the furnace, and _B_ the set of closely-set vertical fire-tubes in the boiler. _C_ is the combustion-chamber, _D_ the smoke-pipe, and _R_ the steam-space. _E_ is the steam-cylinder, and _F_ the pump, which is seen to be double-acting. There are two pairs of engines and pumps, working on cranks, set at right angles, and turning a balance-wheel seen behind them. _G_ is the feed-pump which supplies water to the boiler, _H_ the air-chamber which equalizes the water-pressure, which reaches it through the pipe, _I J_. _K_ is the feed-water tank, under the driver's seat, _L_, which, with the engines and boiler, are carried on the frame, _M M_. The fireman stands on the platform, _N_. When it is necessary to move the machine, an endless chain connects the crank-shaft with the rear-wheels, and the engine, with pumps shut off, is thus made to drive the wheels at any desired speed. [Illustration: FIG. 121.--The Amoskeag Engine. Section.] [Illustration: FIG. 122.--The Silsby Rotary Steam Fire-Engine.] A self-propelling engine by the Amoskeag Company had the following dimensions and performance: Weight, 4 tons; speed, 8 miles per hour; steam-pressure, 75 pounds per square inch; height of stream from 1-1/4-inch nozzle, 225 feet; 1-3/4-inch nozzle, 150 feet; distance horizontally, 1-1/4-inch nozzle, 300 feet; 1-3/4-inch, 250 feet--a performance which contrasts wonderfully with that of the hand-worked fire-engine which these engines have now superseded. It has recently become common to construct the steam fire-engine with rotary engine and pump (Fig. 122). The superiority of a rotary motion for a steam-engine is apparently so evident that many attempts have been made to overcome the practical difficulties to which it is subject. One of these difficulties, and the principal one, has been the packing of the part which performs the office of the piston in the straight cylinder. Robert Stephenson once expressed the opinion that a rotary engine would never be made to work successfully, on account of this difficulty of packing. The most palpable of the advantages of the rotary engine are the reduction in the size of the engine, claimed to result from the great velocity of the piston; the avoidance of great accidental strains, especially noticed in propelling ships; and a great saving of the power which is asserted to be expended in the reciprocating engine in overcoming the inertia while changing the direction of the motions. These advantages adapt the rotary engine, in an especial manner, to the driving of a locomotive or steam fire-engine. [Illustration: FIG. 123.--Rotary Steam-Engine.] [Illustration: FIG. 124.--Rotary Pump.] In the Holly rotary engine, seen in Fig. 123, eccentrics and sliding-cams, which are frequently used in rotary engines, and which are objectionable on account of their great friction, are avoided. Corrugated pistons, or irregular cams, _C D_, are adopted, forming chambers within the cases. In the engine the steam enters at _A_, at the bottom of the case, and presses the cams apart. The only packing used is in the ends of the long metal cogs, which are ground to fit the case and are kept out by the momentum of the cams, assisted by a slight spring back of the packing-pieces. The friction on the pump (Fig. 124) is said to be less than in the engine. This is the reason given in support of the claim that the rotary engine forces water to a given distance with from one-fourth to one-third the steam-pressure necessary to drive all reciprocating engines. The smaller amount of power necessary to do the work, the less strain and consequent wear and tear upon the whole machine, are said to make it more durable and reliable. The pump being chambered, its liability to injury by the use of dirty or gritty water is lessened, and it is stated that it will last for years, pumping gritty water that would soon cut out a piston-pump. The pump used with this engine is, as shown in the above illustration, somewhat similar to the rotary engine driving it. Each of the revolving pistons has three long teeth bearing against the cylinder, and packed, to prevent leakage, like the engine-cams. They are carried on steel shafts coupled to the engine-shafts. The water enters at _E_ and is discharged at _F_, and the passages are purposely made large in order that sand, chips, and dirt, which may enter with the water, may pass through. The rotary engine is gradually coming into use for various special purposes, where small power is called for, and where economy of fuel is not important; but it has never yet competed, and may perhaps never in the future compete, with the reciprocating-piston engine where large engines are required, or where even moderate economy of fuel is essential. This form of engine has assumed so little importance, in fact, in the application of the steam-engine, that comparatively little is known of its history. Watt invented a rotary engine, and Yule many years afterward (1836) constructed such engines at Glasgow. Lamb patented another in 1842, Behrens still another in 1847. Napier, Hall, Massey, Holly, La France, and others, have built engines of this class in later times. Nearly all consist either of cams rotating in gear, as in those above sketched, or of a piston set radially in a cylinder of small diameter, which turns on its axis within a much larger cylinder set eccentrically, the piston, as the former turns, sliding in and out of the smaller cylinder as its outer edge slides in contact with the inner surface of the larger. In some forms of rotary engine, a piston revolves on a central shaft, and a sliding abutment in the external cylinder serves to separate the steam from the exhaust side and to confine the steam expanding while doing work. Nearly all of these combinations are also used as pumps. Fire-engines, made by the best-known American builders of engines, with reciprocating engines and pumps, such as are in general use in the United States, have become standard in general plan and arrangement of details. These are probably the best illustrations of extreme lightness, combined with strength of parts and working power, which have ever been produced in any branch of mechanical engineering. By using a small boiler crowded with heating-surface, very carefully proportioned and arranged, and with small water-spaces; by adopting steel for running-gear and working parts wherever possible; by working at high piston-speed and with high steam-pressure; by selecting fuel with extreme care--by all these expedients, the steam fire-engine has been brought, in this country, to a state of efficiency far superior to anything seen elsewhere. Steam is raised with wonderful promptness, even from cold water, and water is thrown from the nozzle at the end of long lines of hose to great distances. But this combination of lightness with power is only attained at the expense of a certain regularity of action which can only be secured by greater water and steam capacity in the boiler. The small quantity of water contained within the boiler makes it necessary to give constant attention to the feed, and the tendency, almost invariably observed, to serious foaming and priming not only compels unintermitted care while running, but even introduces an element of danger which is not to be despised, even though the machine be in charge of the most experienced and skillful attendants. Even the greatest care, directed by the utmost skill, would not avail to prevent frequent explosions, were it not for the fact that it rarely, if ever, happens that accidents to such boilers occur from low water, unless the boiler is actually completely emptied of water. In driving them at fires, they frequently foam so violently that it is utterly impossible to obtain any clew to the amount of water present, and the attendant usually keeps his feed-pump on and allows the foaming to go on. As long as water is passing into the boiler it is very unlikely that any portion will become overheated and that accident will occur. Such management appears very reckless, and yet accident from such a cause is exceedingly rare. The changes which have been made in LOCOMOTIVE-CONSTRUCTION during the past few years have also been in the direction of the refinement of the earlier designs, and have been accompanied by corresponding changes in all branches of railroad-work. The adjustment of parts to each other and proportioning them to their work, the modification of the minor details to suit changes of general dimensions, the improvement of workmanship, and the use of better material, have signalized this latest period. Special forms of engine have been devised for special kinds of work. Small, light tank-engines (Fig. 125), carrying their own fuel and water without "tenders," are used for moving cars about terminal stations and for making up trains; powerful, heavy, slow-moving engines, of large boiler-capacity and with small wheels, are used on steep gradients and for hauling long trains laden with coal and heavy merchandise; and hardly less powerful but quite differently proportioned "express"-engines are used for passenger and mail service. [Illustration: FIG. 125.--Tank-Engine, New York Elevated Railroad.] [Illustration: FIG. 126.--Forney's Tank-Locomotive.] A peculiar form of engine (Fig. 126) has been designed by Forney, in which the whole weight of engine, tender, coal, and water, is carried by one frame and on one set of wheels, the permanent weight falling on the driving-wheels and the variable load on the truck. These engines have also a comparatively short wheel-base and high pulling-power. The lightest tank-engines of the first class mentioned weigh 8 or 10 tons; but engines much lighter than these, even, are built for mines, where they are sent into the galleries to bring out the coal-laden wagons. The heaviest engines of this class attain weights of 20 or 30 tons. The heaviest engine yet constructed in the United States is said to be one in use on the Philadelphia & Reading Railroad, having a weight of about 100,000 pounds, which is carried on 12 driving-wheels. [Illustration: FIG. 127.--British Express Engine.] [Illustration: FIG. 128.--The Baldwin Locomotive. Section.] [Illustration: FIG. 129.--The American Type of Express-Engine, 1878.] A locomotive has two steam-cylinders, either side by side within the frame, and immediately beneath the forward end of the boiler, or on each side and exterior to the frame. The engines are non-condensing, and of the simplest possible construction. The whole machine is carried upon strong but flexible steel springs. The steam-pressure is usually more than 100 pounds. The pulling-power is generally about one-fifth the weight under most favorable conditions, and becomes as low as one-tenth on wet rails. The fuel employed is wood in new countries, coke in bituminous coal districts, and anthracite coal in the eastern part of the United States. The general arrangement and the proportions of locomotives differ somewhat in different localities. In Fig. 127, a British express-engine, _O_ is the boiler, _N_ the fire-box, _X_ the grate, _G_ the smoke-box, and _P_ the chimney. _S_ is a spring and _R_ a lever safety-valve, _T_ is the whistle, _L_ the throttle or regulator valve, _E_ the steam-cylinder, and _W_ the driving-wheel. The force-pump, _B C_, is driven from the cross-head, _D_. The frame is the base of the whole system, and all other parts are firmly secured to it. The boiler is made fast at one end, and provision is made for its expansion when heated. Adhesion is secured by throwing a proper proportion of the weight upon the driving-wheel, _W_. This is from about 6,000 pounds on standard freight-engines, having several pairs of drivers, to 10,000 pounds on passenger-engines, per axle. The peculiarities of the American type (Fig. 128) are the truck, _I J_, or bogie, supporting the forward part of the engine, the system of equalizers, or beams which distribute the weight of the machine equally over the several axles, and minor differences of detail. The cab or house, _r_, protecting the engine-driver and fireman, is an American device, which is gradually coming into use abroad also. The American locomotive is distinguished by its flexibility and ease of action upon even roughly-laid roads. In the sketch, which shows a standard American engine in section, _A B_ is the boiler, _C_ one of the steam-cylinders, _D_ the piston, _E_ the cross-head, connected to the crank-shaft, _F_, by the connecting-rod, _G H_ the driving-wheels, _I J_ the truck-wheels, carrying the truck, _K L_; _N N_ is the fire-box, _O O_ the tubes, of which but four are shown. The steam-pipe, _R S_, leads the steam to the valve-chest, _T_, in which is seen the valve, moved by the valve-gear, _U V_, and the link, _W_. The link is raised or depressed by a lever, _X_, moved from the cab. The safety-valve is seen at the top of the dome, at _Y_, and the spring-balance by which the load is adjusted is shown at _Z_. At _a_ is the cone-shaped exhaust-pipe, by which a good draught is secured. The attachments _b_, _c_, _d_, _e_, _f_, _g_--whistle, steam-gauge, sand-box, bell, head-light, and "cow-catcher"--are nearly all peculiar, either in construction or location, to the American locomotive. The cost of passenger-locomotives of ordinary size is about $12,000; heavier engines sometimes cost $20,000. The locomotive is usually furnished with a tender, which carries its fuel and water. The standard passenger-engine on the Pennsylvania Railroad has four driving-wheels, 5-1/2 feet diameter; steam-cylinders, 17 inches diameter and 2 feet stroke; grate-surface 15-1/2 square feet, and heating-surface 1,058 square feet. It weighs 63,100 pounds, of which 39,000 pounds are on the drivers and 24,100 on the truck. The freight-engine has six driving-wheels, 54-5/8 inches in diameter. The steam-cylinders are 18 inches in diameter, stroke 22 inches, grate-surface 14.8 square feet, heating-surface 1,096 feet. It weighs 68,500 pounds, of which 48,000 are on the drivers and 20,500 on the truck. The former takes a train of five cars up an average grade of 90 feet to the mile. The latter is attached to a train of 11 cars. On a grade of 50 feet to the mile, the former takes 7 and the latter 17 cars. Tank-engines for very heavy work, such as on grades of 320 feet to the mile, which are found on some of the mountain lines of road, are made with five pairs of driving-wheels, and with no truck. The steam-cylinders are 20-1/8 inches in diameter, 2 feet stroke; grate-area, 15-3/4 feet; heating-surface, 1,380 feet; weight with tank full, and full supply of wood, 112,000 pounds; average weight, 108,000 pounds. Such an engine has hauled 110 tons up this grade at the speed of 5 miles an hour, the steam-pressure being 145 pounds. The adhesion was about 23 per cent. of the weight. In checking a train in motion, the inertia of the engine itself absorbs a seriously large portion of the work of the brakes. This is sometimes reduced by reversing the engine and allowing the steam-pressure to act in aid of the brakes. To avoid injury by abrasion of the surfaces of piston, cylinder, and the valves and valve-seats, M. Le Chatelier introduces a jet of steam into the exhaust-passages when reversing, and thus prevents the ingress of dust-laden air and the drying of the rubbing surfaces. This method of checking a train is rarely resorted to, however, except in case of danger. The introduction of the "continuous" or "air" brake, which can be thrown into action in an instant on every car of the train by the engine-driver, is so efficient that it is now almost universally adopted. It is one of the most important safeguards which American ingenuity has yet devised. In drawing a train weighing 150 tons at the rate of 60 miles an hour, about 800 effective horse-power is required. A speed of 80 miles an hour has been often attained, and 100 miles has probably been reached. The American locomotive-engine has a maximum life which may be stated at about 30 years. The annual cost of repairs is from 10 to 15 per cent. of its first cost. On moderately level roads, the engine requires a pint of oil to each 25 miles, and a ton of coal to each 40 or 50 miles run. One of the best-managed railroads in the United States reports expenses as follows for one month: Number "train-miles" run per ton of coal burned 53.95 " " " " quart of oil used 34.44 Passenger-cars hauled 1 mile per ton of coal 275.7 Other " " " " " 634.8 Cost repairs per mile run $2 43 " fuel " " 3 64 " oil and waste per mile run 62 " wages of engine-men per mile run 6 22 All other expenses per mile 1 91 Total cost per "train-mile" run 14 82 Although the above sketch and description represent the construction and performance of the standard locomotive of the present time, there are indications that the compound arrangement of engines will ultimately be adopted. This will involve a considerable change of proportions, greatly increasing the volume and weight of steam-cylinders, but enabling the designer to more than proportionally decrease the weight of boiler and the quantity of fuel carried. There is no serious objection to their use, however, and no insuperable difficulty in the construction of the "double-cylinder" type of engine for the locomotive. A few such engines have already been put in service. In these engines the high-pressure cylinder is placed on one side and the larger low-pressure cylinder on the other side of the locomotive, thus having but two cylinders, as in the older plan. The valve-gear is the Stephenson link, as in the ordinary engine. At starting, the steam is allowed to act on both pistons; but after a few revolutions the course of the steam is changed, and the exhaust from the smaller cylinder, instead of passing into the chimney, is sent to the larger cylinder, which is at the same time cut off from the main steam-pipe. When the engine is ascending a steep gradient the steam may, if necessary, be taken from the boiler into both cylinders, as when starting. Compound engines of this kind have been used on the French line of railroad from Bayonne to Biarritz. They were designed by Mallet and built at Le Creuzot. The steam-cylinders are of 9-1/2 and 15-3/4 inches diameter, and of 17-3/4 inches stroke of piston. The four driving-wheels are 4 feet in diameter, and the total weight of engine is 20 tons. The boiler has 484-1/2 square feet of heating-surface, and is built to carry 10 atmospheres pressure. When hauling trains of 50 tons at 25 miles an hour, these engines require about 15 pounds of good coal per mile. The total length of the railways in operation in the United States on the 1st day of January, 1877, was 76,640 miles,[93] being an average of one mile of railway for every 600 inhabitants. The railways are as follows: [93] January, 1884, over 120,000 miles. Miles. Alabama 1,722 Alaska 0 Arizona 0 Arkansas 787 California 1,854 Colorado 950 Connecticut 925 Dakota 290 Delaware 285 Florida 484 Georgia 2,308 Idaho 0 Illinois 6,980 Indiana 4,072 Indian Territory 281 Iowa 3,937 Kansas 3,226 Kentucky 1,464 Louisiana 539 Maine 987 Maryland 1,092 Massachusetts 1,825 Michigan 3,437 Minnesota 2,024 Mississippi 1,028 Missouri 3,016 Montana 0 Nebraska 1,181 Nevada 714 New Hampshire 942 New Jersey 1,594 New Mexico 0 New York 5,520 North Carolina 1,371 Ohio 4,680 Oregon 251 Pennsylvania 5,896 Rhode Island 182 South Carolina 1,352 Tennessee 1,638 Texas 2,072 Utah 486 Vermont 810 Virginia 1,648 Washington 110 West Virginia 576 Wisconsin 2,575 Wyoming 459 ------ Total 76,640 In 1873 came the great financial crisis, with its terrible results of interrupted production, poverty, and starvation, and an almost total cessation of the work of building new railroads. The largest number of miles ever built in any one year were constructed in 1872. The greatest mileage is in Illinois, reaching 6,589; the smallest in Rhode Island, 136, and in Washington Territory, 110. The State of Massachusetts has one mile of railroad to 4.86 miles of territory, this ratio being the greatest in the country. The longest road in operation is the Chicago & Northwestern, extending 1,500 miles; the shortest, the Little Saw-Mill Run Road in Pennsylvania, which is but three miles in length. The total capital of railways in the country is $6,000,000,000, or an average of $100,000 per mile. The earnings for the year 1872 amounted to $454,969,000, or $7,500 per mile. The largest net earnings recorded as made on any road were gained by the New York Central & Hudson River, $8,260,827; the smallest on several roads which not only earned nothing, but incurred a loss. The catastrophe of 1873-'74 revealed the fact that the latter condition of railroad finances was vastly more common than had been suspected; and it is still doubtful whether the existing immense network of railroads which covers the United States can be made, as a whole, to pay even a moderate return on the money invested in their construction. At the period of maximum rate of extension of railroads in the United States--1873--the reported lengths of the railroads of Europe and America were as follows:[94] [94] _Railroad Gazette._ RAILROADS IN EUROPE AND AMERICA IN 1873. ----------------------------+------------+-------------+------------ COUNTRIES. | Railroads, | Population. | Area, | Miles. | | Sq. Miles. ----------------------------+------------+-------------+------------ United States | 71,565 | 40,232,000 | 2,492,316 Germany | 12,207 | 40,111,265 | 212,091 Austria | 5,865 | 35,943,592 | 227,234 France | 10,333 | 36,469,875 | 201,900 Russia in Europe | 7,044 | 71,207,794 | 1,992,574 Great Britain, 1872 | 15,814 | 31,817,108 | 120,769 Belgium | 1,301 | 4,839,094 | 11,412 Netherlands | 886 | 3,858,055 | 13,464 Switzerland | 820 | 2,669,095 | 15,233 Italy | 3,667 | 26,273,776 | 107,961 Denmark | 420 | 1,784,741 | 14,453 Spain | 3,401 | 16,301,850 | 182,758 Portugal | 453 | 3,987,867 | 36,510 Sweden and Norway | 1,049 | 5,860,122 | 188,771 Greece | 100 | 1,332,508 | 19,941 ----------------------------+------------+-------------+------------ The railroads in Great Britain comprise over 15,000 miles of track now being worked in the United Kingdom, on which have been expended $2,800,000,000. This sum is equal to five times the amount of the annual value of all the real property in Great Britain, and two-thirds of the national debt. After deducting all the working expenses, the gross net annual revenue of all the roads exceeds by $110,000,000 the total revenue from all sources of Belgium, Holland, Portugal, Denmark, Sweden and Norway. An army of 100,000 officers and servants is in the employ of the companies, and the value of the rolling-stock exceeds $150,000,000. SECTION III.--MARINE ENGINES. The changes which have now become completed in the marine steam-engine have been effected at a later date than those which produced the modern locomotive. On the American rivers the modification of the beam-engine since the time of Robert L. Stevens has been very slight. The same general arrangement is retained, and the details are little, if at all, altered. The pressure of steam is sometimes as high as 60 pounds per square inch. [Illustration: FIG. 130.--Beam-Engine.] The valves are of the disk or poppet variety, rising and falling vertically. They are four in number, two steam and two exhaust valves being placed at each end of the steam-cylinder. The beam-engine is a peculiarly American type, seldom if ever seen abroad. Fig. 130 is an outline sketch of this engine as built for a steamer plying on the Hudson River. This class of engine is usually adopted in vessels of great length, light draught, and high speed. But one steam-cylinder is commonly used. The cross-head is coupled to one end of the beam by means of a pair of links, and the motion of the opposite end of the beam is transmitted to the crank by a connecting-rod of moderate length. The beam has a cast-iron centre surrounded by a wrought-iron strap of lozenge shape, in which are forged the bosses for the end-centres, or for the pins to which the connecting-rod and the links are attached. The main centre of the beam is supported by a "gallows-frame" of timbers so arranged as to receive all stresses longitudinally. The crank and shaft are of wrought-iron. The valve-gear is usually of the form already mentioned as the Stevens valve-gear, the invention of Robert L. and Francis B. Stevens. The condenser is placed immediately beneath the steam-cylinder. The air-pump is placed close beside it, and worked by a rod attached to the beam. Steam-vessels on the Hudson River have been driven by such engines at the rate of 20 miles an hour. This form of engine is remarkable for its smoothness of operation, its economy and durability, its compactness, and the latitude which it permits in the change of shape of the long, flexible vessels in which it is generally used, without injury by "getting out of line." [Illustration: FIG. 131.--Oscillating Engine and Feathering Paddle-Wheel.] For paddle-engines of large vessels, the favorite type, which has been the side-lever engine, is now rarely built. For smaller vessels, the oscillating engine with feathering paddle-wheels is still largely employed in Europe. This style of engine is shown in Fig. 131. It is very compact, light, and moderately economical, and excels in simplicity. The usual arrangement is such that the feathering-wheel has the same action upon the water as a radial wheel of double diameter. This reduction of the diameter of the wheel, while retaining maximum effectiveness, permits a high speed of engine, and therefore less weight, volume, and cost. The smaller wheel-boxes, by offering less resistance to the wind, retard the progress of the vessel less than those of radial wheels. Inclined engines are sometimes used for driving paddle-wheels. In these the steam-cylinder lies in an inclined position, and its connecting-rod directly connects the crank with the cross-head. The condenser and air-pump usually lie beneath the cross-head guides, and are worked by a bell-crank driven by links on each side the connecting-rod, attached to the cross-head. Such engines are used to some extent in Europe, and they have been adopted in the United States navy for side-wheel gunboats. They are also used on the ferry-boats plying between New York and Brooklyn. [Illustration: FIG. 132.--The Two Rhode Islands, 1836-1876.] Among the finest illustrations of recent practice in the construction of side-wheel steamers are those built for the several routes between New York and the cities of New England which traverse Long Island Sound. Our illustration exhibits the form of these vessels, and also shows well the modifications in structure and size which have been made during this generation. The later vessel is 325 feet long, 45 feet beam, 80 feet wide over the "guards," and 16 feet deep, drawing 10 feet of water. The "frames" upon which the planking of the hull is fastened are of white-oak, and the lighter and "top" timbers of cedar and locust. The engine has a steam-cylinder 90 inches in diameter and 12 feet stroke of piston.[95] On each side the great saloons which extend from end to end of the upper deck are state-rooms, containing each two berths and elegantly furnished. The engine of this vessel is capable of developing about 2,500 horse-power. The great wheels, of which the paddle-boxes are seen rising nearly to the height of the hurricane-deck, are 37-1/2 feet in diameter and 12 in breadth. The hull of this vessel, including all wood-work, weighs over 1,200 tons. The weight of the machinery is about 625 tons. The steamer makes 16 knots an hour when the engine is at its best speed--about 17 revolutions per minute--and its average speed is about 14 knots on its route of 160 miles. The coal required to supply the furnaces of such a vessel and with such machinery would be about 3 tons per hour. or a little over 2-1/2 pounds per horse-power. The construction of such a vessel occupies, usually, about a year, and costs a quarter of a million dollars. [95] The steam-cylinders of the engines of steamers Bristol and Providence are 110 inches in diameter and of 12 feet stroke. [Illustration: FIG. 133.--A Mississippi Steamboat.] The non-condensing direct-acting engine is used principally on the Western rivers, driven by steam of from 100 to 150 pounds pressure, and exhausts its steam into the atmosphere. It is the simplest possible form of direct-acting engine. The valves are usually of the "poppet" variety, and are operated by cams which act at the ends of long levers having their fulcra on the opposite side of the valve, the stem of which latter is attached at an intermediate point. The engine is horizontal, and the connecting-rod directly attached to cross-head and crank-pin without intermediate mechanism. The paddle-wheel is used, sometimes as a stern-wheel, as in the plan of Jonathan Hulls of one and a half century ago, sometimes as a side-wheel, as is most usual elsewhere. One of the most noted of these steamers, plying on the Mississippi, is shown in the preceding sketch. One of the largest of these steamers was the Grand Republic,[96] a vessel 340 feet long, 56 feet beam, and 10-1/4 feet depth. The draught of water of this great craft was 3-1/2 feet forward and 4-1/2 aft. The two sets of compound engines, 28 and 56 inches diameter and of 10 feet stroke, drive wheels 38-1/2 feet in diameter and 18 feet wide. The boilers were steel. A steamer built still later on the Ohio has the following dimensions: Length, 225 feet; breadth, 35-1/2 feet; depth, 5 feet; cylinders, 17-3/8 inches in diameter, 6 feet stroke; three boilers. The hull and cabin were built at Jeffersonville, Ind. She has 40 large state-rooms. The cost of the steamer was $40,000. [96] Burned in 1877. These vessels have now opened to commerce the whole extent of the great Mississippi basin, transporting a large share of the products of a section of country measuring a million and a half square miles--an area equal to many times that of New York State, and twelve times that of the island of Great Britain--an area exceeding that of the whole of Europe, exclusive of Russia and Turkey, and capable, if as thoroughly cultivated as the Netherlands, of supporting a population of between three and four hundred millions of people. The steam-engine and propelling apparatus of the modern ocean-steamer have now become almost exclusively the compound or double-cylinder engine, driving the screw. The form and the location of the machinery in the vessel vary with the size and character of the ship which it drives. Very small boats are fitted with machinery of quite a different kind from that built for large steamers, and war-vessels have usually been supplied with engines of a design radically different from that adopted for merchant-steamers. [Illustration: FIG. 134.--Steam-Launch, New York Steam-Power Company.] The introduction of _Steam-Launches_ and small pleasure-boats driven by steam-power is of comparatively recent date, but their use is rapidly increasing. Those first built were heavy, slow, and complicated; but, profiting by experience, light and graceful boats are now built, of remarkable swiftness, and having such improved and simplified machinery that they require little fuel and can be easily managed. Such boats have strong, carefully-modeled hulls, light and strong boilers, capable of making a large amount of dry steam with little fuel, and a light, quick-running engine, working without shake or jar, and using steam economically. [Illustration: FIG. 135.--Launch-Engine.] The above sketch represents the engine built by a New York firm for such little craft. This is the smallest size made for the market. It has a steam-cylinder 3 inches in diameter and a stroke of piston of 5 inches, driving a screw 26 inches in diameter and of 3 feet pitch. The maximum power of the engine is four or five times the nominal power. The boiler is of the form shown in the illustrations of semi-portable engines, and has a heating-surface, in this case, of 75 square feet. The boat itself is like that seen on page 386, and is 25 feet long, of 5 feet 8 inches beam, and draws 2-1/4 feet of water. These little machines weigh about 150 pounds per nominal horse-power, and the boilers about 300. Some of these little vessels have attained wonderful speed. A British steam-yacht, the Miranda, 45-1/2 feet in length, 5-3/4 feet wide, and drawing 2-1/2 feet of water, with a total weight of 3-3/4 tons, has steamed nearly 18-1/2 miles an hour for short runs. The boat was driven by an engine of 6 inches diameter of cylinder and 8 inches stroke of piston, making 600 revolutions per minute, driving a two-bladed screw 2-1/2 feet in diameter and of 3-1/3 feet pitch. Its machinery had a total weight of two tons. Another English yacht, the Firefly, is said to have made 18.94 miles an hour. A little French yacht, the Hirondelle, has attained a speed of 16 knots, equal to about 18-1/2 miles, an hour. This was, however, a much larger vessel than the preceding. One of the most remarkable of these little steamers is a torpedo-boat built for the United States navy. This vessel is 60 feet long, 6 feet wide, and 5 feet deep; its screw is 38 inches in diameter and of 5 feet pitch, two-bladed, and is driven, by a very light engine and boiler, 400 revolutions per minute, the boat attaining a speed of 19 to 20 miles an hour. Another little vessel, the Vision, made nearly as great speed, developing 20 horse-power with engine and boiler weighing but about 400 pounds. Yachts of high speed require such weight and bulk of engine that but little space is left for cabins, and they are usually exceedingly uncomfortable vessels. In the Miranda the weight of machinery is more than one-half the total weight of the whole. An illustration of the more comfortable and more generally liked pleasure-yacht is the Day Dream. The length is 105 feet, and the boat draws 5-1/2 feet of water. There are two engines, having steam-cylinders 14 inches in diameter and of the same length of stroke, direct-acting, condensing, and driving a screw, of 7 feet diameter and of 10-1/2 feet pitch, 135 revolutions a minute, giving the yacht a speed of 13-1/2 knots an hour. [Illustration: FIG. 136.--Horizontal, Direct-acting Naval Screw-Engine.] In larger vessels, as in yachts, in nearly all cases, the ordinary screw-engine is direct-acting. Two engines are placed side by side, with cranks on the shaft at an angle of 90° with each other. In merchant-steamers the steam-cylinders are usually vertical and directly over the crank-pins, to which the cross-heads are coupled. The condenser is placed behind the engine-frame, or, where a jet-condenser is used, the frame itself is sometimes made hollow, and serves as a condenser. The air-pump is worked by a beam connected by links with the cross-head. The general arrangement is like that shown in Figs. 137 and 138. For naval purposes such a form is objectionable, since its height is so great that it would be exposed to injury by shot. In naval engineering the cylinder is placed horizontally, as in Fig. 136, which is a sectional view, representing an horizontal, direct-acting naval screw-engine, with jet-condenser and double-acting air and circulating pumps. _A_ is the steam-cylinder, _B_ the piston, which is connected to the crank-pin by the piston-rod, _D_, and connecting-rod, _E_. _F_ is the cross-head guide. The eccentrics, _G_, operate the valve, which is of the "three-ported variety," by a Stephenson link. Reversing is effected by the hand-wheel, _C_, which, by means of a gear, _m_, and a rack, _k_, elevates and depresses the link, and thus reverses the valve. [Illustration: FIG. 137.--Compound Marine Engine. Side Elevation.] The trunk-engine, in which the connecting-rod is attached directly to the piston and vibrates within a trunk or cylinder secured to the piston, moving with it, and extending outside the cylinder, like an immense hollow piston-rod, is frequently used in the British navy. It has rarely been adopted in the United States. [Illustration: FIG. 138.--Compound Marine Engine. Front Elevation and Section.] In nearly all steam-vessels which have been built for the merchant service recently, and in some naval vessels, the compound engine has been adopted. Figs. 137 and 138 represent the usual form of this engine. Here _A A_, _B B_ are the small and the large, or the high-pressure and the low-pressure cylinders respectively. _C C_ are the valve-chests. _G G_ is the condenser, which is invariably a surface-condenser. The condensing water is sometimes directed around the tubes contained within the casing, _G G_, while the steam is exhausted around them and among them, and sometimes the steam is condensed within the tubes, while the injection-water which is sent into the condenser to produce condensation passes around the exterior of the tubes. In either case, the tubes are usually of small diameter, varying from five-eighths to half an inch, and in length from four to seven feet. The extent of heating-surface is usually from one-half to three-fourths that of the heating-surface of the boilers. The air and circulating pumps are placed on the lower part of the condenser-casting, and are operated by a crank on the main shaft at _N_; or they are sometimes placed as in the style of engine last described, and driven by a beam worked by the cross-head. The piston-rods, _T S_, are guided by the cross-heads, _V V_, working in slipper-guides, and to these cross-heads are attached the connecting-rods, _X X_, driving the cranks, _M M_. The cranks are now usually set at right angles; in some engines this angle is increased to 120°, or even 180°. Where it is arranged as here shown, an intermediate reservoir, _P O_, is placed between the two cylinders to prevent the excessive variations of pressure that would otherwise accompany the varying relative motions of the pistons, as the steam passes from the high-pressure to the low-pressure cylinder. Steam from the boilers enters the high-pressure steam-chest, _X_, and is admitted by the steam-valve alternately above and below the piston as usual. The exhaust steam is conducted through the exhaust passage around into the reservoir, _P_, whence it it is taken by the low-pressure cylinder, precisely as the smaller cylinder drew its steam from the boiler. From the large or low-pressure cylinder the steam is exhausted into the condenser. The valve-gear is usually a Stephenson link, _g e_, the position of which is determined, and the reversal of which is accomplished, by a hand-wheel, _o_, and screw, _m n p_, which, by the bell-crank, _k i_, are attached to the link, _g e_. The "box-framing" forms also the hot-well. The surface-condenser is cleared by a single-acting air-pump, inside the frame, at _T_. The feed-pump and the bilge-pumps are driven from the cross-head of the air-pump. [Illustration: John Elder.] The successful introduction of the double-cylinder engine was finally accomplished by the exertions of a few engineers, who were at once intelligent enough to understand its advantages, and energetic and enterprising enough to push it forward in spite of active opposition, and powerful enough, pecuniarily and in influence, to succeed. The most active and earnest of these eminent men was John Elder, of the firm of Randolph, Elder & Co., subsequently John Elder & Co., of Glasgow.[97] [97] _Vide_ "Memoir of John Elder," W. J. M. Rankine, Glasgow, 1871. Elder was of Scotch descent. His ancestors had, for generations, shown great skill and talent in construction, and had always been known as successful millwrights. John Elder was born at Glasgow, March 8, 1824, and died in London, September 17, 1869. He was educated at the Glasgow High-School and in the College of Engineering at the University of Glasgow, where, however, his attendance was but for a short time. He learned the trade under his father in the workshops of the Messrs. Napier, and became an unusually expert draughtsman. After spending three years in charge of the drawing-office at the engine-building works of Robert Napier, where his father had been manager, Elder became a partner in the firm which had previously been known as Randolph, Elliott & Co., in the year 1852. The firm commenced building iron vessels in 1860. In the mean time, the experiments of Hornblower and Wolff, of Allaire and Smith, and of McNaught, Craddock, and Nicholson, together with the theoretical investigations of Thompson, Rankine, Clausius, and others, had shown plainly in what direction to look for improvement upon then standard engines, and what direction practice was taking with all types. The practical deductions which were becoming evident were recognized very early by Elder, and he promptly began to put in practice the principles which his knowledge of thermo-dynamics and of mechanics enabled him to appreciate. He adopted the compound engine, and coupled his cranks at angles of 180°, in order to avoid losses due to the friction of the crank-shaft in its bearings, by effecting a partial counterbalancing of pressures on the journals. Elder was one of the first to point out the fact that the compound engine had proved itself more efficient than the single-cylinder engine, only when the pressure of steam carried and the extent to which expansion was adopted exceeded the customary practice of his time. His own practice was, from the first, successful, and from 1853 to 1867 he and his partners were continually engaged in the construction of steamers and fitting them with compound engines. The engines of their first vessel, the Brandon, required but 3-1/4 pounds of coal per hour and per horse-power, in 1854, when the usual consumption was a third more. Five years later, they had built engines which consumed a third less than those of the Brandon; and thenceforward, for many years, their engines, when of large size, exhibited what was then thought remarkable economy, running on a consumption of from 2-1/4 to 2-1/2 pounds. In the year 1865 the British Government ordered a competitive trial of three naval vessels, which only differed in the form of their engines. The Arethusa was fitted with trunk-engines of the ordinary kind; the Octavia had three steam-cylinders, coupled to three cranks placed at angles of 120° with each other; and the Constance was fitted with compound engines, two sets of three cylinders each, and each taking steam from the boiler into one cylinder, passing it through the other two with continuous expansion, and finally exhausting from the third into the condenser. These vessels, during one week's steaming at sea, averaged, respectively, 3.64, 3.17, and 2.51 pounds of coal per hour and per horse-power, and the Constance showed a marked superiority in the efficiency of the mechanism of her engines, when the losses by friction were compared. The change from the side-lever single-cylinder engine, with jet-condenser and paddle-wheels, to the direct-acting compound engine, with surface-condenser and screw-propellers, has occurred within the memory and under the observation of even young engineers, and it may be considered that the revolution has not been completely effected. This change in the design of engine is not as great as it at first seemed likely to become. Builders have but slowly learned the principles stated above in reference to expansion in one or more cylinders, and the earlier engines were made with a high and low pressure cylinder working on the same connecting-rod, and each machine consisted of four steam-cylinders. It was at last discovered that a high-pressure single-cylinder engine exhausting into a separate larger low-pressure engine might give good results, and the compound engine became as simple as the type of engine which it displaced. This independence of high and low pressure engines is not in itself novel, for the plan of using the exhaust of a high-pressure engine to drive a low-pressure condensing engine was one of the earliest of known combinations. The advantage of introducing double engines at sea is considerably greater than on land. The coal carried by a steam-vessel is not only an item of great importance in consequence of its first cost, but, displacing its weight or bulk of freight which might otherwise be carried, it represents so much non-paying cargo, and is to be charged with the full cost of transportation in addition to first cost. The best of steam-coal is therefore usually chosen for steamers making long voyages, and the necessity of obtaining the most economical engines is at once seen, and is fully appreciated by steamship proprietors. Again, an economy of one-fourth of a pound per horse-power per hour gives, on a large transatlantic steamer, a saving of about 100 tons of coal for a single voyage. To this saving of cost is to be added the gain in wages and sustenance of the labor required to handle that coal, and the gain by 100 tons of freight carried in place of the coal. For many years the change which has here been outlined, in the forms of engine and the working of steam expansively, was retarded by the inefficiency of methods and tools used in construction. With gradual improvement in tools and in methods of doing work, it became possible to control higher steam and to work it successfully; and the change in this direction has been steadily going on up to the present time with all types of steam-engine. At sea this rise of pressure was for a considerable time retarded by the serious difficulty encountered in the tendency of the sulphate of lime to deposit in the boiler. When steam-pressure had risen to 25 pounds per square inch, it was found that no amount of "blowing out" would prevent the deposition of seriously large quantities of this salt, while at the lower pressures at first carried at sea no troublesome precipitation occurred, and the only precaution necessary was to blow out sufficient brine to prevent the precipitation of common salt from a supersaturated solution. The introduction of surface-condensation was promptly attempted as the remedy for this evil, but for many years it was extremely doubtful whether its disadvantages were not greater than its advantages. It was found very difficult to keep the condensers tight, and boilers were injured by some singular process of corrosion, evidently due to the presence of the surface-condenser. The simple expedient of permitting a very thin scale to form in the boiler was, after a time, hit upon as a means of overcoming this difficulty, and thenceforward the greatest obstacle to the general introduction was the conservative disposition found among those who had charge of marine machinery, which conservatism regarded with suspicion every innovation. Another trouble arose from the difficulty of finding men neither too indolent nor too ignorant to take charge of the new condenser, which, more complicated and more readily disarranged than the old, demanded a higher class of attendants. Once introduced, however, the surface-condenser removed the obstacle to further elevation of steam-pressure, and the rise from 20 to 60 pounds pressure soon occurred. Elder and his competitors on the Clyde were the first to take advantage of the fact when these higher pressures became practicable. The lightness of engine and the smaller weight of boiler secured when the simpler type of "compound" engine is used are great advantages, and, when coupled with the fact that by no other satisfactory device can great expansion and consequent economy of fuel be obtained at sea, the advantages are such as to make the adoption of this style of engine imperative for ship-propulsion. This extreme lightness in machinery has been largely, also, the result of very careful and skillful designing, of intelligent construction, and of care in the selection and use of material. British builders had, until after the introduction of these later types of vessels-of-war, been distinguished rather by the weight of their machinery than for nice calculation and proportioning of parts. Now the engines of the heavy iron-clads are models of good proportions, excellence in materials, and of workmanship, which are well worthy of study. The weight per indicated horse-power has been reduced from 400 or 500 pounds to less than half that amount within the last ten years. This has been accomplished by forcing the boilers--although thus, to some extent, losing economy--by higher steam-pressure, a very much higher piston-speed, reduction of friction of parts, reduction of capacity for coal-stowage, and exceedingly careful proportioning. The reduction of coal-bunker capacity is largely compensated by the increase of economy secured by superheating, by increased expansion, elevation of piston-speed, and the introduction of surface-condensation. A good marine steam-engine of the form which was considered standard 15 or 20 years ago, having low-pressure boilers carrying steam at 20 or 25 pounds pressure as a maximum, expanding twice or three times, and having a jet-condenser, would require about 30 or 35 pounds of feed-water per horse-power per hour; substituting surface-condensation for that produced by the jet brought down the weight of steam used to from 25 to 30 pounds; increasing steam-pressure to 60 pounds, expanding from five to eight times, and combining the special advantages of the superheater and the compound engine with surface-condensation, has reduced the consumption of steam to 20, or even, in some cases, 15 pounds of steam per horse-power per hour. Messrs. Perkins, of London, guarantee, as has already been stated, to furnish engines capable of giving a horse-power with a consumption of but 1-1/4 pound of coal. Mr. C. E. Emery reports the United States revenue-steamer Hassler, designed by him, to have given an ordinary sea-going performance which is probably fully equal to anything yet accomplished. The Hassler is a small steamer, of but 151 feet in length, 24-1/2 feet beam, and 10 feet draught. The engines have steam-cylinders 18.1 and 28 inches diameter, respectively, and of 28 inches stroke of piston, indicating 125 horse-power; with steam at 75 pounds pressure, and at a speed of but 7 knots, the coal consumed was but 1.87 pound per horse-power per hour. The committee of the British Admiralty on designs of ships-of-war have reported recently: "The carrying-power of ships may certainly be to some extent increased by the adoption of compound engines in her Majesty's service. Its use has recently become very general in the mercantile marine, and the weight of evidence in favor of the large economy of fuel thereby gained is, to our minds, overwhelming and conclusive. We therefore beg earnestly to recommend that the use of compound engines may be generally adopted in ships-of-war hereafter to be constructed, and applied, whenever it can be done with due regard to economy and to the convenience of the service, to those already built." The forms of screws now employed are exceedingly diverse, but those in common use are not numerous. In naval vessels it is common to apply screws of two blades, that they may be hoisted above water into a "well" when the vessel is under sail, or set with the two blades directly behind the stern-post, when their resistance to the forward motion of the vessel will be comparatively small. In other vessels, and in the greater number of full-power naval vessels, screws of three or four blades are used. The usual form of screw (Fig. 139) has blades of nearly equal breadth from the hub to the periphery, or slightly widening toward their extremities, as is seen in an exaggerated degree in Fig. 140, representing the form adopted for tug-boats, where large surface near the extremity is more generally used than in vessels of high speed running free. In the Griffith screw, which has been much used, the hub is globular and very large. The blades are secured to the hub by flanges, and are bolted on in such a manner that their position may be changed slightly if desired. The blades are shaped like the section of a pear, the wider part being nearest the hub, and the blades tapering rapidly toward their extremities. A usual form is intermediate between the last, and is like that shown in Fig. 141, the hub being sufficiently enlarged to permit the blades to be attached as in the Griffith screw, but more nearly cylindrical, and the blades having nearly uniform width from end to end. [Illustration: FIG. 139.--Screw-Propeller.] [Illustration: FIG. 140.--Tug-boat Screw.] [Illustration: FIG. 141.--Hirsch Screw.] The pitch of a screw is the distance which would be traversed by the screw in one revolution were it to move through the water without slip; i. e., it is double the distance _C D_, Fig. 140. _C D´_ represents the helical path of the extremity of the blade _B_, and _O E F H K_ is that of the blade _A_. The proportion of diameter to the pitch of the screw is determined by the speed of the vessel. For low speed the pitch may be as small as 1-1/4 the diameter. For vessels of high speed the pitch is frequently double the diameter. The diameter of the screw is made as great as possible, since the slip decreases with the increase of the area of screw-disk. Its length is usually about one-sixth of the diameter. A greater length produces loss by increase of surface causing too great friction, while a shorter screw does not fully utilize the resisting power of the cylinder of water within which it works, and increased slip causes waste of power. An empirical value for the probable slip in vessels of good shape, which is closely approximate usually, is _S_ = 4(_M_/_A_), in which _S_ is the slip per cent., and _M_ and _A_ are the areas of the midship section and of the screw-disk in square feet. The most effective screws have slightly greater pitch at the periphery than at the hub, and an increasing pitch from the forward to the rear part of the screw. The latter method of increasing pitch is more generally adopted alone. The thrust of the screw is the pressure which it exerts in driving the vessel forward. In well-formed vessels, with good screws, about two-thirds of the power applied to the screw is utilized in propulsion, the remainder being wasted in slip and other useless work. Its efficiency is in such a case, therefore, 66 per cent. Twin screws, one on each side of the stern-post, are sometimes used in vessels of light draught and considerable breadth, whereby decreased slip is secured. As has already been stated, the introduction of the compound engine has been attempted, but with less success than in Europe, by several American engineers. The most radical change in the methods of ship-propulsion which has been successfully introduced in some localities has been the adoption of a system of "wire-rope towage." It is only well adapted for cases in which the steamer traverses the same line constantly, moving backward and forward between certain points, and is never compelled to deviate to any considerable extent from the path selected. A similar system is in use in Canada, but it has not yet come into use in the United States, notwithstanding the fact that, wherever its adoption is practicable, it has a marked superiority in economy over the usual methods of propulsion. With chain or rope traction there is no loss by slip or oblique action, as in both screw and paddle-wheel propulsion. In the latter methods these losses amount to an important fraction of the total power; they rarely, if ever, fall below a total of 25 per cent., and probably in towage exceed 50 per cent. The objection to the adoption of chain-propulsion, as it is also often called, is the necessity of following closely the line along which the chain or the rope is laid. There is, however, much less difficulty than would be anticipated in following a sinuous route or in avoiding obstacles in the channel or passing other vessels. The system is particularly well adapted for use on canals. The steam-boilers in use in the later and best marine engineering practice are of various forms, but the standard types are few in number. That used on river-steamers in the United States has already been described. [Illustration: FIG. 142.--Marine Fire-tubular Boiler. Section.] Fig. 142 is a type of marine tubular boiler which is in most extensive use in sea-going steamers for moderate pressure, and particularly for naval vessels. Here the gases pass directly into the back connection from the fire, and thence forward again, through horizontal tubes, to the front connection and up the chimney. In naval vessels the steam-chimney is omitted, as it is there necessary to keep all parts of the boiler as far below the water-line as possible. Steam is taken from the boiler by pipes which are carried from end to end of the steam-space, near the top of the boiler, the steam entering these pipes through small holes drilled on the other side. Steam is thus taken from the boiler "wet," but no large quantity of water can usually be "entrained" by the steam. A marine boiler has been quite extensively introduced into the United States navy, in which the gases are led from the back connection through a tube-box around and among a set of upright water-tubes, which are filled with water, circulation taking place freely from the water-space immediately above the crown-sheet of the furnace up through these tubes into the water-space above them. These "water-tubular" boilers have a slight advantage over the "fire-tubular" boilers already described in compactness, in steaming capacity, and in economical efficiency. They have a very marked advantage in the facility with which the tubes may be scraped or freed from the deposit when a scale of sulphate of lime or other salt has formed within them by precipitation from the water. The fire-tubular boiler excels in convenience of access for plugging up leaking tubes, and is much less costly than the water-tubular. The water-tube class of boilers still remain in extensive use in the United States naval steamers. They have never been much used in the merchant service, although introduced by James Montgomery in the United States and by Lord Dundonald in Great Britain twenty years earlier. Opinion still remains divided among engineers in regard to their relative value. They are gradually reassuming prominence by their introduction in the modified form of sectional boilers. [Illustration: FIG. 143.--Marine High-Pressure Boiler. Section.] Marine boilers are now usually given the form shown in section in Fig. 143. This form of boiler is adopted where steam-pressures of 60 pounds and upward are carried, as in steam-vessels supplied with compound engines, cylindrical forms being considered the best with high pressures. The large cylindrical flues, therefore, form the furnaces as shown in the transverse sectional view. The gases rise, as shown in the longitudinal section, through the connection, and pass back to the end of the boiler through the tubes, and thence, instead of entering a steam-chimney, they are conducted by a smoke-connection, not shown in the sketch, to the smoke funnel or stack. In merchant-steamers, a steam-drum is often mounted horizontally above the boiler. In other cases a separator is attached to the steam-pipe between boilers and engines. This usually consists of an iron tank, divided by a vertical partition extending from the top nearly to the bottom. The steam, entering the top at one side of this partition, passes underneath it, and up to the top on the opposite side, where it issues into a steam-pipe leading directly to the engine. The sudden reversal of its course at the bottom causes it to leave the suspended water in the bottom of the separator, whence it is drained off by pipes. The most interesting illustrations of recent practice in marine engineering and naval architecture are found in the steamers which are now seen on transoceanic routes for the merchant service, and, in the naval service, in the enormous iron-clads which have been built in Great Britain. The City of Peking is one of the finest examples of American practice. This vessel was constructed for the Pacific Mail Company. The hull is 423 feet long, of 48 feet beam, and 38-1/2 feet deep. Accommodations are furnished for 150 cabin and 1,800 steerage passengers, and the coal-bunkers "stow" 1,500 tons of coal. The iron plates of which the sides and bottom are made are from 11/16 to one inch in thickness. The weight of iron used in construction was about 5,500,000 pounds. The machinery weighed nearly 2,000,000 pounds, with spare gear and accessory apparatus. The engines are compound, with two steam-cylinders of 51 inches and two of 88 inches diameter, and a stroke of piston of 4-1/2 feet. The condensing water is sent through the surface-condensers by circulating-pumps driven by their own engines. Ten boilers furnish steam to these engines, each having a diameter of 13 feet, a length of 13-1/2 feet, and a thickness of "shell" of 13/16 inch. Each has three furnaces, and contains 204 tubes of an outside diameter of 3-1/4 inches. All together, they have 520 square feet of grate-surface and 17,000 square feet of heating-surface. The area of cooling-surface in the condensers is 10,000 square feet. The City of Rome, a ship of later design, is 590 feet long, "over all," 52 feet beam, 52 feet deep, and measures 8,300 tons. The engines, of 8,500 horse-power, will drive the vessel 18 knots (21 miles) an hour; they have six steam-cylinders (three high and three low pressure), and are supplied with steam by 8 boilers heated by 48 furnaces. The hull is of steel, the bottom double, and the whole divided into ten compartments by transverse bulkheads. Two longitudinal bulkheads in the engine and boiler compartments add greatly to the safety of the vessel. The most successful steam-vessels in general use are these screw-steamers of transoceanic lines. Those of the transatlantic lines are now built from 350 to 550 feet long, generally propelled from 12 to 18 knots (14 to 21 miles) an hour, by engines of from 3,000 to 8,000 horse-power, consuming from 70 to 250 tons of coal a day, and crossing the Atlantic in from eight to ten days. These vessels are now invariably fitted with the compound engine and surface-condensers. One of these vessels, the Germanic, has been reported at Sandy Hook, the entrance to New York Harbor, in 7 days 11 hours 37 minutes from Queenstown--a distance, as measured by the log and by observation, of 2,830 miles. Another steamer, the Britannic, has crossed the Atlantic in 7 days 10 hours and 53 minutes. These vessels are of 5,000 tons burden, of 750 "nominal" horse-power (probably 5,000 actual). [Illustration: FIG. 144.--The Modern Steamship.] The modern steamship is as wonderful an illustration of ingenuity and skill in all interior arrangements as in size, power, and speed. The size of sea-going steamers has become so great that it is unsafe to intrust the raising of the anchor or the steering of the vessel to manual power and skill; and these operations, as well as the loading and unloading of the vessel, are now the work of the same great motor--steam. The now common form of auxiliary engine for controlling the helm is one of the inventions of the American engineer F. E. Sickels, who devised the "Sickels cut-off," and was first invented about 1850. It was exhibited at London at the International Exhibition of 1851. It consists[98] principally of two cylinders working at right angles upon a shaft geared into a large wheel fastened by a friction-plate lined with wood, and set by a screw to any desired pressure on the steering-apparatus. The wheel turned by the steersman is connected with the valve-gear of the cylinders, so that the steam, or other motor, will move the rudder precisely as the helmsman moves the wheel adjusting the steam-valves. This wheel thus becomes the steering-wheel. The apparatus is usually so arranged that it may be connected or disconnected in an instant, and hand-steering adopted if the smoothness of the sea and the low speed of the vessel make it desirable or convenient. This method was first adopted in the United States on the steamship Augusta. [98] "Official Catalogue," 1862, vol. iv., Class viii., p. 123. The same inventor and others have contrived "steam-windlasses," some of which are in general use on large vessels. The machinery of these vessels is also often fitted with a steam "reversing-gear," by means of which the engines are as easily man[oe]uvred as are those of the smallest vessels, to which hand-gear is always fitted. In one of these little auxiliary engines, as devised by the author, a small handle being adjusted to a marked position, as to the point marked "stop" on an index-plate, the auxiliary engine at once starts, throws the valve-gear into the proper position--as, if a link-motion, into "middle-gear"--thus stopping the large engines, and then it itself stops. Setting the handle so that its pointer shall point to "ahead," the little engine starts again, sets the link in position to go ahead, thus starting the large engines, and again stops itself. If set at "back," the same series of operations occurs, leaving the main engines backing and the little "reversing engine" stopped. A number of forms of reversing engine are in use, each adapted to some one type of engine. The hull of the transatlantic steamer is now always of iron, and is divided into a number of "compartments," each of which is water-tight and separated from the adjacent compartments by iron "bulkheads," in which are fitted doors which, when closed, are also water-tight. In some cases these doors close automatically when the water rises in the vessel, thus confining it to the leaking portion. Thus we have already seen a change in transoceanic lines from steamers like the Great Western (1837), 212 feet in length, of 35-1/2 feet beam, and 23 feet depth, driven by engines of 450 horse-power, and requiring 15 days to cross the Atlantic, to steamships over 550 feet long, 55 feet beam, and 55 feet deep, with engines of 10,000 horse-power, crossing the Atlantic in 7 days; iron substituted for wood in construction, the cost of fuel reduced one-half, and the speed raised from 8 to 18 knots and over. In the earlier days of steamships they were given a proportion of length to breadth of from 5 to 6 to 1; in forty years the proportion increased until 11 to 1 was reached. The whole naval establishment of every country has been greatly modified by the recent changes in methods of attack and defense; but the several classes of ships which still form the naval marine are all as dependent upon their steam-machinery as ever. [Illustration: H. B. M. Iron-Clad Captain. H. B. M. Iron-Clad Thunderer. U. S. Iron-Clad Dictator. U. S. Iron-Clad Monitor. H. B. M. Iron-Clad Giatton. French Iron-Clad Dunderberg. FIG. 145.--Modern Iron-Clads.] It is only recently that the attempt seems to have been made to determine a classification of war-vessels and to plan a naval establishment which shall be likely to meet fully the requirements of the immediate future. It has hitherto been customary simply to make each ship a little stronger, faster, or more powerful to resist or to make attack than was the last. The fact that the direction of progress in naval science and architecture is plainly perceivable, and that upon its study may be based a fair estimate of the character and relative distribution of several classes of vessels, seems to have been appreciated by very few. In the year 1870 the writer proposed[99] a classification of vessels other than torpedo-vessels, which has since been also proposed in a somewhat modified form by Mr. J. Scott Russell.[100] The author then remarked that the increase so rapidly occurring in weight of ordnance and of armor, and in speed of war-vessels, would probably soon compel a division of the vessels of every navy into three classes of ships, exclusive of torpedo-vessels, one for general service in time of peace, the others for use only in time of war. [99] _Journal Franklin Institute_, 1870. H. B. M. S. Monarch. [100] London _Engineering_, 1875. "The first class may consist of unarmored vessels of moderate size, fair speed under steam, armed with a few tolerably heavy guns, and carrying full sail-power. "The second class may be vessels of great speed under steam, unarmored, carrying light batteries and as great spread of canvas as can readily be given them; very much such vessels as the Wampanoag class of our own navy were intended to be--calculated expressly to destroy the commerce of an enemy. "The third class may consist of ships carrying the heaviest possible armor and armament, with strongly-built bows, the most powerful machinery that can be given them, of large coal-carrying capacity, and unencumbered by sails, everything being made secondary to the one object of obtaining victory in contending with the most powerful of possible opponents. Such vessels could never go to sea singly, but would cruise in couples or in squadrons. It seems hardly doubtful that attempts to combine the qualities of all classes in a single vessel, as has hitherto been done, will be necessarily given up, although the classification indicated will certainly tend largely to restrict naval operations." The introduction of the stationary, the floating, and the automatic classes of torpedoes, and of torpedo-vessels, has now become accomplished, and this element, which it was predicted by Bushnell and by Fulton three-quarters of a century ago would at some future time become important in warfare, is now well recognized by all nations. How far it may modify future naval establishments cannot be yet confidently stated, but it seems sufficiently evident that the attack, by any navy, of stationary defenses protected by torpedoes is now quite a thing of the past. It may be perhaps looked upon as exceedingly probable that torpedo-ships of very high speed will yet drive all heavily-armored vessels from the ocean, thus completing the historic parallel between the man-in-armor of the middle ages and the armored man-of-war of our own time.[101] [101] _Vide_ "Report on Machinery and Manufactures, etc., at Vienna," by the author, Washington, 1875. Of these classes, the third is of most interest, as exhibiting most perfectly the importance and variety of the work which the steam-engine is made to perform. On the later of these vessels, the anchor is raised by a steam anchor-hoisting apparatus; the heavier spars and sails are handled by the aid of a steam-windlass; the helm is controlled by a steering-engine, and the helmsman, with his little finger, sets in motion a steam-engine, which adjusts the rudder with a power which is unimpeded by wind or sea, and with an exactness that could not be exceeded by the hand-steering gear of a yacht; the guns are loaded by steam, are elevated or depressed, and are given lateral training, by the same power; the turrets in which the guns are incased are turned, and the guns are whirled toward every point of the compass, in less time than is required to sponge and reload them; and the ship itself is driven through the water by the power of ten thousand horses, at a speed which is only excelled on land by that of the railroad-train. The British Minotaur was one of the earlier iron-clads. The great length and consequent difficulty of man[oe]uvring, the defect of speed, and the weakness of armor of these vessels have led to the substitution of far more effective designs in later constructions. The Minotaur is a four-masted screw iron-clad, 400 feet long, of 59 feet beam and 26-1/2 feet draught of water. Her speed at sea is about 12-1/2 knots, and her engines develop, as a maximum, nearly 6,000 indicated horse-power. Her heaviest armor-plates are but 6 inches in thickness. Her extreme length and her unbalanced rudder make it difficult to turn rapidly. With _eighteen men at the steering-wheel_ and sixty others on the tackle, the ship, on one occasion, was 7-1/2 minutes in turning completely around. These long iron-clads were succeeded by the shorter vessels designed by Mr. E. J. Reed, of which the first, the Bellerophon, was of 4,246 tons burden, 300 feet long by 56 feet beam, and 24-1/2 feet draught, of the 14-knot speed, with 4,600 horse-power; and having the "balanced rudder" used many years earlier in the United States by Robert L. Stevens,[102] it can turn in four minutes with eight men at the wheel. The cost of construction was some $600,000 less than that of the Minotaur. A still later vessel, the Monarch, was constructed on a system quite similar to that known in the United States as the Monitor type, or as a turreted iron-clad. This vessel is 330 feet long, 57-1/2 feet wide, and 36 feet deep, drawing 24-1/2 feet of water. The total weight of ship and contents is over 8,000 tons, and the engines are of over 8,500 horse-power. The armor is 6 and 7 inches thick on the hull, and 8 inches on the two turrets, over a heavy teak backing. The turrets contain each two 12-inch rifled guns, weighing 25 tons each, and, with a charge of 70 pounds of powder, throwing a shot of 600 pounds weight with a velocity of 1,200 feet per second, and giving it a _vis viva_ equivalent to the raising of over 6,100 tons one foot high, and equal to the work of penetrating an iron plate 13-1/2 inches thick. This immense vessel is driven by a pair of "single-cylinder" engines having steam-cylinders _ten feet_ in diameter and of 4-1/2 feet stroke of piston, driving a two-bladed Griffith screw of 23-1/2 feet diameter and 26-1/2 feet pitch, 65 revolutions, at the maximum speed of 14.9 knots, or about 17-1/2 miles, an hour. To drive these powerful engines, boilers having an aggregate of about 25,000 square feet (or more than a half-acre) of heating-surface are required, with 900 square feet of grate-surface. The refrigerating surface in the condensers has an area of 16,500 square feet--over one-third of an acre. The cost of these engines and boilers was £66,500. [102] Still in use on the Hoboken ferry-boats. Were all this vast steam-power developed, giving the vessel a speed of 15 knots, the ship, if used as a "ram," would strike an enemy at rest with the tremendous "energy" of 48,000 foot-tons--equal to the shock of the projectiles of eight or nine such guns as are carried by the iron-clad itself, simultaneously discharged upon one spot. But even this great vessel is less formidable than later vessels. One of the latter, the Inflexible, is a shorter but wider and deeper ship than the Monarch, measuring 320 feet long, 75 feet beam, and 25 draught, displacing over 10,000 tons. The great rifles carried by this vessel weigh 81 tons each, throwing shot weighing a half-ton from behind iron-plating two feet in thickness. The steam-engines are of about the same power as those of the Monarch, and give this enormous hull a speed of 14 knots an hour. The navy of the United States does not to-day possess iron-clads of power even approximating that of either of several classes of British and other foreign naval vessels. The largest vessel of any class yet constructed is the Great Eastern (Fig. 146), begun in 1854 and completed in 1859, by J. Scott Russell, on the Thames, England. This ship is 680 feet long, 83 feet wide, 58 feet deep, 28 feet draught, and of 24,000 tons measurement. There are four paddle and four screw engines, the former having steam-cylinders 74 inches in diameter, with 14 feet stroke, the latter 84 inches in diameter and 4 feet stroke. They are collectively of 10,000 actual horse-power. The paddle-wheels are 56 feet in diameter, the screw 24 feet. The steam-boilers supplying the paddle-engines have 44,000 square feet (more than an acre) of heating-surface. The boilers supplying the screw-engines are still larger. At 30 feet draught, this great vessel displaces 27,000 tons. The engines were designed to develop 10,000 horse-power, driving the ship at the rate of 16-1/2 statute miles an hour. [Illustration: FIG. 146.--The Great Eastern.] The figures quoted in the descriptions of these great steamships do not enable the non-professional reader to form a conception of the wonderful power which is concentrated within so small a space as is occupied by their steam-machinery. The "horse-power" of the engines is that determined by James Watt as the maximum obtainable for eight hours a day from the strongest London draught-horses. The ordinary average draught-horse would hardly be able to exert two-thirds as much during the eight hours' steady work of a working-day. The working-day of the steam-engine, on the other hand, is twenty-four hours in length. [Illustration: FIG. 147.--The Great Eastern at Sea.] The work of the 10,000 horse-power engines of the Great Eastern could be barely equaled by the efforts of 15,000 horses; but to continue their work uninterruptedly, day in and day out, for weeks together, as when done by steam, would require at least three relays, or 45,000 horses. Such a stud would weigh 25,000 tons, and if harnessed "tandem" would extend thirty miles. It is only by such a comparison that the mind can begin to comprehend the utter impossibility of accomplishing by means of animal power the work now done for the world by steam. The cost of the greater power is but about one-tenth that of horse-power, and by its means tasks are accomplished with ease which are absolutely impossible of accomplishment by animal power. It is estimated that the total steam-power of the world is about 15,000,000 horse-power, and that, were horses actually employed to do the work which these engines would be capable of doing were they kept constantly in operation, the number required would exceed 60,000,000. Thus, from the small beginnings of the Comte d'Auxiron and the Marquis de Jouffroy in France, of Symmington in Great Britain, and of Henry, Rumsey, and Fitch, and of Fulton and Stevens, in the United States, steam-navigation has grown into a great and inestimable aid and blessing to mankind. We to-day cross the ocean with less risk, and transport ourselves and our goods at as little cost in either time or money as, at the beginning of the century, our parents experienced in traveling one-tenth the distance. It is largely in consequence of this ingenious application of a power that reminds one of the fabled genii of Eastern romance, that the mechanic and the laborer of to-day enjoy comforts and luxuries that were denied to wealth, and to royalty itself, a century ago. The magnitude of our modern steamships excites the wonder and admiration of even the people of our own time; and there is certainly no creation of art that can be grander in appearance than a transatlantic steamer a hundred and fifty yards in length, and weighing, with her stores, five or six thousand tons, as she starts on her voyage, moved by engines equal in power to the united strength of thousands of horses; none can more fully awaken a feeling of awe than an immense structure like the great modern iron-clads (Fig. 145), vessels having a total weight of 8,000 to 10,000 tons, and propelled by steam-engines of as many horse-power, carrying guns whose shot penetrate solid iron 20 inches thick, and having a power of impact, when steaming at moderate speed, sufficient to raise 35,000 tons a foot high. Far more huge than the Monarch among the iron-clads even is that prematurely-built monster, the Great Eastern (Fig. 147), already described, an eighth of a mile long, and with steam doing the work of a stud of 45,000 horses. Thus we are to-day witnessing the literal fulfillment of the predictions of Oliver Evans and of John Stevens, and almost that contained in the couplets written by the poet Darwin, who, more than a century ago, before even the earliest of Watt's improvements had become generally known, sang: "Soon shall thy arm, unconquered Steam, afar Drag the slow barge, or drive the rapid car; Or, on wide-waving wings expanded, bear The flying chariot through the fields of air." [Illustration] CHAPTER VII. _THE PHILOSOPHY OF THE STEAM-ENGINE._ THE HISTORY OF ITS GROWTH; ENERGETICS AND THERMO-DYNAMICS. "Of all the features which characterize this progressive economical movement of civilized nations, that which first excites attention, through its intimate connection with the phenomena of production, is the perpetual and, so far as human foresight can extend, the unlimited growth of man's power over Nature. Our knowledge of the properties and laws of physical objects shows no sign of approaching its ultimate boundaries; it is advancing more rapidly, and in a greater number of directions at once, than in any previous age or generation, and affording such frequent glimpses of unexplored fields beyond as to justify the belief that our acquaintance with Nature is still almost in its infancy."--MILL. The growth of the philosophy of the steam-engine presents as interesting a study as that of the successive changes which have occurred in its mechanism. In the operation of the steam-engine we find illustrated many of the most important principles and facts which constitute the physical sciences. The steam-engine is an exceedingly ingenious, but, unfortunately, still very imperfect, machine for transforming the heat-energy obtained by the chemical combination of a combustible with the supporter of combustion into mechanical energy. But the original source of all this energy is found far back of its first appearance in the steam-boiler. It had its origin at the beginning, when all Nature came into existence. After the solar system had been formed from the nebulous chaos of creation, the glowing mass which is now called the sun was the depository of a vast store of heat-energy, which was thence radiated into space and showered upon the attendant worlds in inconceivable quantity and with unmeasured intensity. During the past life of the globe, the heat-energy received from the sun upon the earth's surface was partly expended in the production of great forests, and the storage, in the trunks, branches, and leaves of the trees of which they were composed, of an immense quantity of carbon, which had previously existed in the atmosphere, combined with oxygen, as carbonic acid. The great geological changes which buried these forests under superincumbent strata of rock and earth resulted in the formation of coal-beds, and the storage, during many succeeding ages, of a vast amount of carbon, of which the affinity for oxygen remained unsatisfied until finally uncovered by the hand of man. Thus we owe to the heat and light of the sun, as was pointed out by George Stephenson, the incalculable store of potential energy upon which the human race is so dependent for life and all its necessaries, comforts, and luxuries. This coal, thrown upon the grate in the steam-boiler, takes fire, and, uniting again with the oxygen, sets free heat in precisely the same quantity that it was received from the sun and appropriated during the growth of the tree. The actual energy thus rendered available is transferred, by conduction and radiation, to the water in the steam-boiler, converts it into steam, and its mechanical effect is seen in the expansion of the liquid into vapor against the superincumbent pressure. Transferred from the boiler to the engine, the steam is there permitted to expand, doing work, and the heat-energy with which it is charged becomes partly converted into mechanical energy, and is applied to useful work in the mill or to driving the locomotive or the steamboat. Thus we may trace the store of energy received from the sun and contained in our coal through its several changes until it is finally set at work; and we might go still further and observe how, in each case, it is again usually re-transformed and again set free as heat-energy. The transformation which takes place in the furnace is a chemical change; the transfer of heat to the water and the subsequent phenomena accompanying its passage through the engine are physical changes, some of which require for their investigation abstruse mathematical operations. A thorough comprehension of the principles governing the operation of the steam-engine, therefore, can only be attained after studying the phenomena of physical science with sufficient minuteness and accuracy to be able to express with precision the laws of which those sciences are constituted. The study of the philosophy of the steam-engine involves the study of chemistry and physics, and of the new science of energetics, of which the now well-grown science of thermo-dynamics is a branch. This sketch of the growth of the steam-engine may, therefore, be very properly concluded by an outline of the growth of the several sciences which together make up its philosophy, and especially of the science of thermo-dynamics, which is peculiarly the science of the steam-engine and of the other heat-engines. These sciences, like the steam-engine itself, have an origin which antedates the commencement of the Christian era; but they grew with an almost imperceptible growth for many centuries, and finally, only a century ago, started onward suddenly and rapidly, and their progress has never since been checked. They are now fully-developed and well-established systems of natural philosophy. Yet, like that of the steam-engine and of its companion heat-engines, their growth has by no means ceased; and, while the student of science cannot do more than indicate the direction of their progress, he can readily believe that the beginning of the end is not yet reached in their movement toward completeness, either in the determination of facts or in the codification of their laws. When Hero lived at Alexandria, the great "Museum" was a most important centre, about which gathered the teachers of all then known philosophies and of all the then recognized but unformed sciences, as well as of all those technical branches of study which had already been so far developed as to be capable of being systematically taught. Astronomical observations had been made regularly and uninterruptedly by the Chaldean astrologers for two thousand years, and records extending back many centuries had been secured at Babylon by Calisthenes and given to Aristotle, the father of our modern scientific method. Ptolemy had found ready to his hand the records of Chaldean observers of eclipses extending back nearly 650 years, and marvelously accurate.[103] [103] Their estimate of the length of the Saros, or cycle of eclipses--over 19 years--was "within 19-1/2 minutes of the truth."--DRAPER. A rude method of printing with an engraved roller on plastic clay, afterward baked, thus making up ceramic libraries, was practised long previous to this time; and in the alcoves in which Hero worked were many of these books of clay. This great Library and Museum of Alexandria was founded three centuries before the birth of Christ, by Ptolemy Soter, who established as his capital that great Egyptian city when the death of his brother, the youthful but famous conqueror whose name he gave it, placed him upon the throne of the colossal successor of the then fallen Persian Empire. The city itself, embellished with every ornament and provided with every luxury that the wealth of a conquered world or the skill, taste, and ingenuity of the Greek painters, sculptors, architects, and engineers could provide, was full of wonders; it was a wonder in itself. This rich, populous, and magnificent city was the metropolis of the then civilized world. Trade, commerce, manufactures, and the fine arts were all represented in this splendid exchange, and learning found its most acceptable home and noblest field within the walls of Ptolemy's Museum; its disciples found themselves welcomed and protected by its founder and his successors, Philadelphus and the later Ptolemies. The Alexandrian Museum was founded with the declared object of collecting all written works of authority, of promoting the study of literature and art, and of stimulating and assisting experimental and mathematical scientific investigation and research. The founders of modern libraries, colleges, and technical schools have their prototype in intelligence, public spirit, and liberality, in the first of the Ptolemies, who not only spent an immense sum in establishing this great institution, but spared no expense in sustaining it. Agents were sent out into all parts of the world, purchasing books. A large staff of scribes was maintained at the museum, whose duty it was to multiply copies of valuable works, and to copy for the library such works as could not be purchased. The faculty of the museum was as carefully organized as was the plan of its administration. The four principal faculties of astronomy, literature, mathematics, and medicine were subdivided into sections devoted to the several branches of each department. The collections of the museum were as complete as the teachers of the undeveloped sciences of the time could make them. Lectures were given in all branches of study, and the number of students was sometimes as great as twelve or thirteen thousand. The number of books which were collected here, when the barbarian leaders of the Roman troops under Cæsar burned the greater part of it, was stated to be 700,000. Of these, 400,000 were within the museum itself, and were all destroyed; the rest were in the temple of Serapis, and, for the time, escaped destruction. The greatest of all the great men who lived at Alexandria at the time of the establishment of the museum was Aristotle, the teacher of Alexander and the friend of Ptolemy. It is to Aristotle that we owe the systematization of the philosophical ideas of Plato and the creation of the inductive method, in which has originated all modern science. It is to the learned men of Alexandria that we are indebted for so effective an application of the Aristotelian philosophy that all the then known sciences were given form, and were so thoroughly established that the work of modern science has been purely one of development. The inductive method, which built up all the older sciences, and which has created all those of recent development, consists, first, in the discovery and quantitative determination of facts; secondly, when a sufficient number of facts have been thus observed and defined, in the grouping of those facts, and the detection, by a study of their mutual relations, of the natural laws which give rise to or regulate them. This simple method is that--and the only--method by which science advances. By this method, and by it only, do we acquire connected and systematic knowledge of all the phenomena of Nature of which the physical sciences are cognizant. It is only by the application of this Aristotelian method and philosophy that we can hope to acquire exact scientific knowledge of existing phenomena, or to become able to anticipate the phenomena which are to distinguish the future. The Aristotelian method of observing facts, and of inductive reasoning with those facts as a basis, has taught the chemist the properties of the known elementary substances and their characteristic behavior under ascertained conditions, and has taught him the laws of combination and the effects of their union, enabling him to predict the changes and the phenomena, chemical and physical, which inevitably follow their contact under any specified set of conditions. It is this process which has enabled the physicist to ascertain the methods of molecular motion which give us light, heat, or electricity, and the range of action and the laws which govern the transfer of energy from one of these modes of motion to another. It was this method of study which enabled James Watt to detect and to remedy the defects of the Newcomen engine, and it is by the Aristotelian philosophy that the engineer of to-day is taught to construct the modern steamship, and to predict, before the keel is laid or a blow struck in the workshop or the ship-yard, what will be the weight of the vessel, its cargo-carrying capacity, the necessary size and power of its engines, the quantity of coal which they will require per day while crossing the ocean, the depth at which the great hull will float in the water, and the exact speed that the vessel will attain when the engines are exerting their thousand or their ten thousand horse-power. It was at Alexandria that this mighty philosophy was first given a field in which to work effectively. Here Ptolemy studied astronomy and "natural philosophy;" Archimedes applied himself to the studies which attract the mathematician and engineer; Euclid taught his royal pupil those elements of geometry which have remained standard twenty-two centuries; Eratosthenes and Hipparchus studied and taught astronomy, and inaugurated the existing system of quantitative investigation, proving the spherical form of the earth; and Ctesibius and Hero studied pneumatics and experimented with the germs of the steam-engine and of less important machines. When, seven centuries later, the destruction of this splendid institution was signalized by the death of that brilliant scholar and heathen teacher of philosophy, Hypatia, at the hands of the more heathenish fanatics who tore her in pieces at the foot of the cross, and by the dispersion of the library left by Cæsar's soldiers in the Serapeum, a true philosophy had been created, and the inductive method was destined to live and to overcome every obstacle in the path of enlightenment and civilization. The fall of the Alexandrian Museum, sad as was the event, could not destroy the new philosophical method. Its fruits ripened slowly but surely, and we are to-day gathering a plentiful harvest. Science, literature, and the arts, all remained dormant for several centuries after the catastrophe which deprived them of the light in which they had flourished so many centuries. The armies of the caliphs made complete the shameful work of destruction begun by the armies of Cæsar, and the Alexandrian Library, partly destroyed by the Romans, was completely dispersed by the Patriarchs and their ignorant and fanatical followers; and finally all the scattered remnants were burned by the Saracens. But when the thirst for conquest had become satiated or appeased, the followers of the caliphs turned their attention to intellectual pursuits, and the ninth century of the Christian era saw once more such a collection of philosophical writings, collected at Bagdad, as could only be gathered by the power and wealth of the later conquerors of the world. Philosophy once again resumed its empire, and another race commenced the study of the mathematics of India and of Greece, the astronomy of Chaldea, and of all the sciences which originated in Greece and in Egypt. By the conquest of Spain by the Saracens, the new civilization was imported into Western Europe and libraries were gathered together under the Moorish rulers, one of which numbered more than a half-million volumes. Wherever Saracen armies had extended Mohammedan rule, schools and colleges, libraries and collections of philosophical apparatus, were scattered in strange profusion; and students, teachers, philosophers, of all--the speculative as well as the Aristotelian--schools, gathered together at these intellectual ganglia, as enthusiastic in their work as were their Alexandrian predecessors. The endowment of colleges, that truest gauge of the intelligence of the wealthy classes of any community, became as common--perhaps more so--as at the present time, and provision was made for the education of rich and poor alike. The mathematical sciences, and the wonderful and beautiful phenomena which--but a thousand years later--were afterward grouped into a science and called chemistry, were especially attractive to the Arabian scholars, and technical applications of discovered facts and laws assisted in a wonderfully rapid development of arts and manufactures. When, a thousand years after Christ, the centre of intellectual activity and of material civilization had drifted westward into Andalusia, the foundation of every modern physical science except that now just taking shape--the all-grasping science of energetics--had been laid with experimentally derived facts; and in mathematics there had been erected a symmetrical and elegant superstructure. Even that underlying principle of all the sciences, the principle of the persistence of energy, had been, perhaps unwittingly, enunciated. Distinguished historians have shown how the progress of civilization in Europe resulted in the creation, during the middle ages, of the now great middle class, which, holding the control of political power, governs every civilized nation, and has come into power so gradually that it was only after centuries that its influence was seen and felt. This, which Buckle[104] calls the intellectual class, first became active, independently of the military and of the clergy, in the fourteenth century. In the two succeeding centuries this class gained power and influence; and in the seventeenth century we find a magnificent advance in all branches of science, literature, and art, marking the complete emancipation of the intellect from the artificial conditions which had so long repressed its every effort at advancement. [104] "History of Civilization in England," vol. i., p. 208. London, 1868. Another great social revolution thus occurred, following another period of centuries of intellectual stagnation. The Saracen invaders were driven from Europe; the Crusaders invaded Palestine, in the vain effort to recover from the hands of the infidels the Holy Sepulchre and the Holy Land; and intestine broils and inter-state conflicts, as well as these greater social movements, withdrew the minds of men once more from the arts of peace and the pursuits of scholars. It is not, then, until the beginning of the seventeenth century--the time of Galileo and of Newton--that we find the nations of Europe sufficiently quiet and secure to permit general attention to intellectual vocations, although it was a half-century earlier (1543) that Copernicus left to the world that legacy which revolutionized the theories of the astronomers and established as correct the hypothesis which made the sun the centre of the solar system. Galileo now began to overturn the speculations of the deductive philosophers, and to proclaim the still disputed principle that the book of Nature is a trustworthy commentary in the study of theological and revealed truths, so far as they affect or are affected by science; he suffered martyrdom when he proclaimed the fact that God's laws, as they now stand, had been instituted without deference to the preconceived notions of the most ignorant of men. Bruno had a few years earlier (1600) been burned at the stake for a similar offense. Galileo was perhaps the first, too, to combine invariably in application the idea of Plato, the philosophy of Aristotle, and the methods of modern experimentation, to form the now universal scientific method of experimental philosophy. He showed plainly how the grouping of ascertained facts, in natural sequence, leads to the revelation of the law of that sequence, and indicated the existence of a principle which is now known as the law of continuity--the law that in all the operations of Nature there is to be seen an unbroken chain of effect leading from the present back into a known or an unknown past, toward a cause which may or may not be determinable by science or known to history. Galileo, the Italian, was worthily matched by Newton, the prince of English philosophers. The science of theoretical mechanics was hardly beginning to assume the position which it was afterward given among the sciences; and the grand work of collating facts already ascertained, and of definitely stating principles which had previously been vaguely recognized, was splendidly done by Newton. The needs of physical astronomy urged this work upon him. Da Vinci had, in the latter half of the fifteenth century, summarized as much of the statics of mechanical philosophy as had, up to his time, been given shape; he also rewrote and added very much to what was known on the subject of friction, and enunciated its laws. He had evidently a good idea of the principle of "virtual velocities," that simple case of equivalence of work, in a connected system, which has done such excellent service since; and with his mechanical philosophy this versatile engineer and artist curiously mingled much of physical science. Then Stevinus, the "brave engineer of Bruges," a hundred years later (1586), alternating office and field work, somewhat after the manner of the engineer of to-day, wrote a treatise on mechanics, which showed the value of practical experience and judgment in even scientific work. And thus the path had been cleared for Newton. Meantime, also, Kepler had hit upon the true relations of the distances of the planets and their periodic times, after spending half a generation in blindly groping for them, thus furnishing those great landmarks of fact in the mechanics of astronomy; and Galileo had enunciated the laws of motion. Thus the foundation of the science of dynamics, as distinguished from statics, was laid, and the beginning was made of that later science of energetics, of which the philosophy of the steam-engine is so largely constituted. Hooke, Huyghens, and others, had already seen some of the principal consequences of these laws; but it remained for Newton to enunciate them with the precision of a true mathematician, and to base upon them a system of dynamical laws, which, complemented by his announcement of the existence of the force of gravitation, and his statement of its laws, gave a firm basis for all that the astronomer has since done in those quantitative determinations of size, weight, and distance, and of the movements of the heavenly bodies, which compel the wonder and admiration of mankind. The Arabians and Greeks had noticed that the direction taken by a body falling under the action of gravitation was directly toward the centre of the earth, wherever its fall might occur; Galileo had shown, by his experiments at Pisa, that the velocity of fall, second after second, varied as the numbers 1, 3, 5, 7, 9, etc., and that the distances varied as the squares of the total periods of time during which the body was falling, and that it was, in British feet, very nearly sixteen times the square of that time in seconds. Kepler had proved that the movements of the heavenly bodies were just such as would occur under the action of central attractive forces and of centrifugal force. Putting all these things together, Newton was led to believe that there existed a "force of gravity," due to the attraction, by the great mass of the earth, of its own particles and of neighboring bodies, like the moon, of which force the influence extended as far, at least, as the latter. He calculated the motion of the earth's satellite, on the assumption that his theory and the then accepted measurements of the earth's dimensions were correct, and obtained a roughly approximate result. Later, in 1679, he revised his calculations, using Picard's more accurate determination of the dimensions of the earth, and obtained a result which precisely tallied with careful measurements, made by the astronomers, of the moon's motion. The science of mechanics had now, with the publication of Newton's "Principia," become thoroughly consistent and logically complete, so far as was possible without a knowledge of the principles of energetics; and Newton's enunciations of the laws of motion, concise and absolutely perfect as they still seem, were the basis of the whole science of dynamics, as applied to bodies moving freely under the action of applied forces, either constant or variable. They are as perfect a basis for that science as are the primary principles of geometry for the whole beautiful structure which is built up on them. The three perfect qualitative expressions of dynamical law are: 1. Every free body continues in the state in which it may be, whether of rest or of rectilinear uniform motion, until compelled to deviate from that state by impressed forces. 2. Change of motion is proportional to the force impressed, and in the direction of the right line in which that force acts. 3. Action is always opposed by reaction; action and reaction are equal, and in directly contrary directions. We may add to these principles a definition of a force, which is equally and absolutely complete: _Force_ is that which produces, or tends to produce, motion, or change of motion, in bodies. It is measured statically by the weight that will counterpoise it, or by the pressure which it will produce, and dynamically by the velocity which it will produce, acting in the unit of time on the unit of mass. The quantitative determinations of dynamic effects of forces are always readily made when it is remembered that the effect of a force equal to its own weight, when the body is free to move, is to produce in one second a velocity of 32.2 feet per second, which quantity is the unit of dynamic measurement. _Work_ is the product of the resistance met in any instance of the exertion of a force, into the distance through which that force overcomes the resistance. _Energy_ is the work which a body is capable of doing, by its weight or inertia, under given conditions. The energy of a falling body, or of a flying shot, is about 1/64 its weight multiplied by the square of its velocity, or, which is the same thing, the product of its weight into the height of fall or height due its velocity. These principles and definitions, with the long-settled definitions of the primary ideas of space and time, were all that were needed to lead the way to that grandest of all physical generalizations, the doctrine of the persistence or conservation of all energy, and to its corollary declaring the equivalence of all forms of energy, and also to the experimental demonstration of the transformability of energy from one mode of existence to another, and its universal existence in the various modes of motion of bodies and of their molecules. Experimental physical science had hardly become acknowledged as the only and the proper method of acquiring knowledge of natural phenomena at the time of Newton; but it soon became a generally accepted principle. In physics, Gilbert had made valuable investigations before Newton, and Galileo's experiments at Pisa had been examples of similarly useful research. In chemistry, it was only when, a century later, Lavoisier showed by his splendid example what could be done by the skillful and intelligent use of quantitative measurements, and made the balance the chemist's most important tool, that a science was formed comprehending all the facts and laws of chemical change and molecular combination. We have already seen how astronomy and mathematics together led philosophers to the creation and the study of what finally became the science of mechanics, when experiment and observation were finally brought to their aid. We can now see how, in all these physical sciences, four primitive ideas are comprehended: matter, force, motion, and space--which latter two terms include all relations of position. Based on these notions, the science of mechanics comprehends four sections, which are of general application in the study of all physical phenomena. These are: _Statics_, which treats of the action and effect of forces. _Kinematics_, which treats of relations of motion simply. _Dynamics_, or kinetics, which treats of simple motion as an effect of the action of forces. _Energetics_, which treats of modifications of energy under the action of forces, and of its transformation from one mode of manifestation to another, and from one body to another. Under the latter of these four divisions of mechanical philosophy is comprehended that latest of the minor sciences, of which the heat-engines, and especially the steam-engine, illustrate the most important applications--_Thermo-dynamics_. This science is simply a wider generalization of principles which, as we have seen, have been established one at a time, and by philosophers widely separated both geographically and historically, by both space and time, and which have been slowly aggregated to form one after another of the sciences, and out of which, as we now are beginning to see, we are slowly evolving wider generalizations, and thus tending toward a condition of scientific knowledge which renders more and more probable the truth of Cicero's declaration: "One eternal and immutable law embraces all things and all times." At the basis of the whole science of energetics lies a principle which was enunciated before Science had a birthplace or a name: _All that exists, whether matter or force, and in whatever form, is indestructible, except by the Infinite Power which has created it._ That matter is indestructible by finite power became admitted as soon as the chemists, led by their great teacher Lavoisier, began to apply the balance, and were thus able to show that in all chemical change there occurs only a modification of form or of combination of elements, and no loss of matter ever takes place. The "persistence" of energy was a later discovery, consequent largely upon the experimental determination of the convertibility of heat-energy into other forms and into mechanical work, for which we are indebted to Rumford and Davy, and to the determination of the quantivalence anticipated by Newton, shown and calculated approximately by Colding and Mayer, and measured with great probable accuracy by Joule. [Illustration: Benjamin Thompson, Count Rumford.] The great fact of the conservation of energy was loosely stated by Newton, who asserted that the work of friction and the _vis viva_ of the system or body arrested by friction were equivalent. In 1798, Benjamin Thompson, Count Rumford, an American who was then in the Bavarian service, presented a paper[105] to the Royal Society of Great Britain, in which he stated the results of an experiment which he had recently made, proving the immateriality of heat and the transformation of mechanical into heat energy. This paper is of very great historical interest, as the now accepted doctrine of the persistence of energy is a generalization which arose out of a series of investigations, the most important of which are those which resulted in the determination of the existence of a definite quantivalent relation between these two forms of energy and a measurement of its value, now known as the "mechanical equivalent of heat." His experiment consisted in the determination of the quantity of heat produced by the boring of a cannon at the arsenal at Munich. [105] "Philosophical Transactions," 1798. Rumford, after showing that this heat could not have been derived from any of the surrounding objects, or by compression of the materials employed or acted upon, says: "It appears to me extremely difficult, if not impossible, to form any distinct idea of anything capable of being excited and communicated in the manner that heat was excited and communicated in these experiments, except it be motion."[106] He then goes on to urge a zealous and persistent investigation of the laws which govern this motion. He estimates the heat produced by a power which he states could easily be exerted by one horse, and makes it equal to the "combustion of nine wax candles, each three-quarters of an inch in diameter," and equivalent to the elevation of "25.68 pounds of ice-cold water" to the boiling-point, or 4,784.4 heat-units.[107] The time was stated at "150 minutes." Taking the actual power of Rumford's Bavarian "one horse" as the most probable figure, 25,000 pounds raised one foot high per minute,[108] this gives the "mechanical equivalent" of the foot-pound as 783.8 heat-units, differing but 1.5 per cent. from the now accepted value. [106] This idea was not by any means original with Rumford. Bacon seems to have had the same idea; and Locke says, explicitly enough: "Heat is a very brisk agitation of the insensible parts of the object ... so that what in our sensation is heat, in the object is nothing but motion." [107] The British heat-unit is the quantity of heat required to heat one pound of water 1° Fahr. from the temperature of maximum density. [108] Rankine gives 25,920 foot-pounds per minute--or 432 per second--for the average draught-horse in Great Britain, which is probably too high for Bavaria. The engineer's "horse-power"--33,000 foot-pounds per minute--is far in excess of the average power of even a good draught-horse, which latter is sometimes taken as two-thirds the former. Had Rumford been able to eliminate all losses of heat by evaporation, radiation, and conduction, to which losses he refers, and to measure the power exerted with accuracy, the approximation would have been still closer. Rumford thus made the experimental discovery of the real nature of heat, proving it to be a form of energy, and, publishing the fact a half-century before the now standard determinations were made, gave us a very close approximation to the value of the heat-equivalent. Rumford also observed that the heat generated was "exactly proportional to the force with which the two surfaces are pressed together, and to the rapidity of the friction," which is a simple statement of equivalence between the quantity of work done, or energy expended, and the quantity of heat produced. This was the first great step toward the formation of a Science of Thermo-dynamics. Rumford's work was the corner-stone of the science. Sir Humphry Davy, a little later (1799), published the details of an experiment which conclusively confirmed these deductions from Rumford's work. He rubbed two pieces of ice together, and found that they were melted by the friction so produced. He thereupon concluded: "It is evident that ice by friction is converted into water.... Friction, consequently, does not diminish the capacity of bodies for heat." Bacon and Newton, and Hooke and Boyle, seem to have anticipated--long before Rumford's time--all later philosophers, in admitting the probable correctness of that modern dynamical, or vibratory, theory of heat which considers it a mode of motion; but Davy, in 1812, for the first time, stated plainly and precisely the real nature of heat, saying: "The immediate cause of the phenomenon of heat, then, is motion, and the laws of its communication are precisely the same as the laws of the communication of motion." The basis of this opinion was the same that had previously been noted by Rumford. So much having been determined, it became at once evident that the determination of the exact value of the mechanical equivalent of heat was simply a matter of experiment; and during the succeeding generation this determination was made, with greater or less exactness, by several distinguished men. It was also equally evident that the laws governing the new science of thermo-dynamics could be mathematically expressed. Fourier had, before the date last given, applied mathematical analysis in the solution of problems relating to the transfer of heat without transformation, and his "Théorie de la Chaleur" contained an exceedingly beautiful treatment of the subject. Sadi Carnot, twelve years later (1824), published his "Réflexions sur la Puissance Motrice du Feu," in which he made a first attempt to express the principles involved in the application of heat to the production of mechanical effect. Starting with the axiom that a body which, having passed through a series of conditions modifying its temperature, is returned to "its primitive physical state as to density, temperature, and molecular constitution," must contain the same quantity of heat which it had contained originally, he shows that the efficiency of heat-engines is to be determined by carrying the working fluid through a complete cycle, beginning and ending with the same set of conditions. Carnot had not then accepted the vibratory theory of heat, and consequently was led into some errors; but, as will be seen hereafter, the idea just expressed is one of the most important details of a theory of the steam-engine. Seguin, who has already been mentioned as one of the first to use the fire-tubular boiler for locomotive engines, published in 1839 a work, "Sur l'Influence des Chemins de Fer," in which he gave the requisite data for a rough determination of the value of the mechanical equivalent of heat, although he does not himself deduce that value. Dr. Julius R. Mayer, three years later (1842), published the results of a very ingenious and quite closely approximate calculation of the heat-equivalent, basing his estimate upon the work necessary to compress air, and on the specific heats of the gas, the idea being that the work of compression is the equivalent of the heat generated. Seguin had taken the converse operation, taking the loss of heat of expanding steam as the equivalent of the work done by the steam while expanding. The latter also was the first to point out the fact, afterward experimentally proved by Hirn, that the fluid exhausted from an engine should heat the water of condensation less than would the same fluid when originally taken into the engine. A Danish engineer, Colding, at about the same time (1843), published the results of experiments made to determine the same quantity; but the best and most extended work, and that which is now almost universally accepted as standard, was done by a British investigator. James Prescott Joule commenced the experimental investigations which have made him famous at some time previous to 1843, at which date he published, in the _Philosophical Magazine_, his earliest method. His first determination gave 770 foot-pounds. During the succeeding five or six years Joule repeated his work, adopting a considerable variety of methods, and obtaining very variable results. One method was to determine the heat produced by forcing air through tubes; another, and his usual plan, was to turn a paddle-wheel by a definite power in a known weight of water. He finally, in 1849, concluded these researches. [Illustration: James Prescott Joule.] The method of calculating the mechanical equivalent of heat which was adopted by Dr. Mayer, of Heilbronn, is as beautiful as it is ingenious: Conceive two equal portions of atmospheric air to be inclosed, at the same temperature--as at the freezing-point--in vessels each capable of containing one cubic foot; communicate heat to both, retaining the one portion at the original volume, and permitting the other to expand under a constant pressure equal to that of the atmosphere. In each vessel there will be inclosed 0.08073 pound, or 1.29 ounce, of air. When, at the same temperature, the one has doubled its pressure and the other has doubled its volume, each will be at a temperature of 525.2° Fahr., or 274° C, and each will have double the original temperature, as measured on the absolute scale from the zero of heat-motion. But the one will have absorbed but 6-3/4 British thermal units, while the other will have absorbed 9-1/2. In the first case, all of this heat will have been employed in simply increasing the temperature of the air; in the second case, the temperature of the air will have been equally increased, and, besides, a certain amount of work--2,116.3 foot-pounds--must have been done in overcoming the resistance of the air; it is to this latter action that we must debit the additional heat which has disappeared. Now, 2,116.3/(2-3/4) = 770 foot-pounds per heat-unit--almost precisely the value derived from Joule's experiments. Had Mayer's measurement been absolutely accurate, the result of his calculation would have been an exact determination of the heat-equivalent, provided no heat is, in this case, lost by internal work. Joule's most probably accurate measure was obtained by the use of a paddle-wheel revolving in water or other fluid. A copper vessel contained a carefully weighed portion of the fluid, and at the bottom was a step, on which stood a vertical spindle carrying the paddle-wheel. This wheel was turned by cords passing over nicely-balanced grooved wheels, the axles of which were carried on friction-rollers. Weights hung at the ends of these cords were the moving forces. Falling to the ground, they exerted an easily and accurately determinable amount of work, _W_ × _H_, which turned the paddle-wheel a definite number of revolutions, warming the water by the production of an amount of heat exactly equivalent to the amount of work done. After the weight had been raised and this operation repeated a sufficient number of times, the quantity of heat communicated to the water was carefully determined and compared with the amount of work expended in its development. Joule also used a pair of disks of iron rubbing against each other in a vessel of mercury, and measured the heat thus developed by friction, comparing it with the work done. The average of forty experiments with water gave the equivalent 772.692 foot-pounds; fifty with mercury gave 774.083; twenty with cast-iron gave 774.987--the temperature of the apparatus being from 55° to 60° Fahr. Joule also determined, by experiment, the fact that the expansion of air or other gas without doing work produces no change of temperature, which fact is predicable from the now known principles of thermo-dynamics. He stated the results of his researches relating to the mechanical equivalent of heat as follows: 1. The heat produced by the friction of bodies, whether solid or liquid, is always proportional to the quantity of work expended. 2. The quantity required to increase the temperature of a pound of water (weighed _in vacuo_ at 55° to 60° Fahr.) by one degree requires for its production the expenditure of a force measured by the fall of 772 pounds from a height of one foot. This quantity is now generally called "Joule's equivalent." During this series of experiments, Joule also deduced the position of the "absolute zero," the point at which heat-motion ceases, and stated it to be about 480° Fahr. below the freezing-point of water, which is not very far from the probably true value,-493.2° Fahr. (-273° C.), as deduced afterward from more precise data. The result of these, and of the later experiments of Hirn and others, has been the admission of the following principle: Heat-energy and mechanical energy are mutually convertible and have a definite equivalence, the British thermal unit being equivalent to 772 foot-pounds of work, and the metric _calorie_ to 423.55, or, as usually taken, 424 kilogrammetres. The exact measure is not fully determined, however. It has now become generally admitted that all forms of energy due to physical forces are mutually convertible with a definite quantivalence; and it is not yet determined that even vital and mental energy do not fall within the same great generalization. This quantivalence is the sole basis of the science of Energetics. The study of this science has been, up to the present time, principally confined to that portion which comprehends the relations of heat and mechanical energy. In the study of this department of the science, thermo-dynamics, Rankine, Clausius, Thompson, Hirn, and others have acquired great distinction. In the investigations which have been made by these authorities, the methods of transfer of heat and of modification of physical state in gases and vapors, when a change occurs in the form of the energy considered, have been the subjects of especial study. According to the law of Boyle and Marriotte, the expansion of such fluids follows a law expressed graphically by the hyperbola, and algebraically by the expression PV^{_x_} = A, in which, with unchanging temperature, _x_ is equal to 1. One of the first and most evident deductions from the principles of the equivalence of the several forms of energy is that the value of x must increase as the energy expended in expansion increases. This change is very marked with a vapor like steam--which, expanded without doing work, has an exponent less than unity, and which, when doing work by expanding behind a piston, partially condenses, the value of _x_ increases to, in the case of steam, 1.111 according to Rankine, or, probably more correctly, to 1.135 or more, according to Zeuner and Grashof. This fact has an important bearing upon the theory of the steam-engine, and we are indebted to Rankine for the first complete treatise on that theory as thus modified. Prof. Rankine began his investigations as early as 1849, at which time he proposed his theory of the molecular constitution of matter, now well known as the theory of molecular vortices. He supposes a system of whirling rings or vortices of heat-motion, and bases his philosophy upon that hypothesis, supposing sensible heat to be employed in changing the velocity of the particles, latent heat to be the work of altering the dimensions of the orbits, and considering the effort of each vortex to enlarge its boundaries to be due to centrifugal force. He distinguished between real and apparent specific heat, and showed that the two methods of absorption of heat, in the case of the heating of a fluid, that due to simple increase of temperature and that due to increase of volume, should be distinguished; he proposed, for the latter quantity, the term heat-potential, and for the sum of the two, the name of thermo-dynamic function. [Illustration: Prof. W. J. M. Rankine.] Carnot had stated, a quarter of a century earlier, that the efficiency of a heat-engine is a function of the two limits of temperature between which the machine is worked, and not of the nature of the working substance--an assertion which is quite true where the material does not change its physical state while working. Rankine now deduced that "general equation of thermo-dynamics" which expresses algebraically the relations between heat and mechanical energy, when energy is changing from the one state to the other, in which equation is given, for any assumed change of the fluids, the quantity of heat transformed. He showed that steam in the engine must be partially liquefied by the process of expanding against a resistance, and proved that the total heat of a perfect gas must increase with rise of temperature at a rate proportional to its specific heat under constant pressure. Rankine, in 1850, showed the inaccuracy of the then accepted value, 0.2669, of the specific heat of air under constant pressure, and calculated its value as 0.24. Three years later, the experiments of Regnault gave the value 0.2379, and Rankine, recalculating it, made it 0.2377. In 1851, Rankine continued his discussion of the subject, and, by his own theory, corroborated Thompson's law giving the efficiency of a perfect heat-engine as the quotient of the range of working temperature to the temperature of the upper limit, measured from the absolute zero. During this period, Clausius, the German physicist, was working on the same subject, taking quite a different method, studying the mechanical effects of heat in gases, and deducing, almost simultaneously with Rankine (1850), the general equation which lies at the beginning of the theory of the equivalence of heat and mechanical energy. He found that the probable zero of heat-motion is at such a point that the Carnot function must be approximately the reciprocal of the "absolute" temperature, as measured with the air thermometer, or, stated exactly, that quantity as determined by a perfect gas thermometer. He confirmed Rankine's conclusion relative to the liquefaction of saturated vapors when expanding against resistance, and, in 1854, adapted Carnot's principle to the new theory, and showed that his idea of the reversible engine and of the performance of a cycle in testing the changes produced still held good, notwithstanding Carnot's ignorance of the true nature of heat. Clausius also gave us the extremely important principle: It is impossible for a self-acting machine, unaided, to transfer heat from one body at a low temperature to another having a higher temperature. Simultaneously with Rankine and Clausius, Prof. William Thomson was engaged in researches in thermo-dynamics (1850). He was the first to express the principle of Carnot as adapted to the modern theory by Clausius in the now generally quoted propositions:[109] [109] _Vide_ Tait's admirable "Sketch of Thermodynamics," second edition, Edinburgh, 1877. 1. When equal mechanical effects are produced by purely thermal action, equal quantities of heat are produced or disappear by transformation of energy. 2. If, in any engine, a reversal effects complete inversion of all the physical and mechanical details of its operation, it is a perfect engine, and produces maximum effect with any given quantity of heat and with any fixed limits of range of temperature. William Thomson and James Thompson showed, among the earliest of their deductions from these principles, the fact, afterward confirmed by experiment, that the melting-point of ice should be lowered by pressure 0.0135° Fahr, for each atmosphere, and that a body which contracts while being heated will always have its temperature decreased by sudden compression. Thomson applied the principles of energetics in extended investigations in the department of electricity, while Helmholtz carried some of the same methods into his favorite study of acoustics. The application of now well-settled principles to the physics of gases led to many interesting and important deductions: Clausius explained the relations between the volume, density, temperature, and pressure of gases, and their modifications; Maxwell reëstablished the experimentally determined law of Dalton and Charles, known also as that of Gay-Lussac (1801), which asserts that all masses of equal pressure, volume, and temperature, contain equal numbers of molecules. On the Continent of Europe, also, Hirn, Zeuner, Grashof, Tresca, Laboulaye, and others have, during the same period and since, continued and greatly extended these theoretical researches. During all this time, a vast amount of experimental work has also been done, resulting in the determination of important data without which all the preceding labor would have been fruitless. Of those who have engaged in such work, Cagniard de la Tour, Andrews, Regnault, Hirn, Fairbairn and Tate, Laboulaye, Tresca, and a few others have directed their researches in this most important direction with the special object of aiding in the advancement of the new-born sciences. By the middle of the present century, the time which we are now studying, this set of data was tolerably complete. Boyle had, two hundred years before, discovered and published the law, which is now known by his name[110] and by that of Marriotte,[111] that the pressure of a gas varies inversely as its volume and directly as its density; Dr. Black and James Watt discovered, a hundred years later (1760), the latent heat of vapors, and Watt determined the method of expansion of steam; Dalton, in England, and Gay-Lussac, in France, showed, at the beginning of the nineteenth century, that all gaseous fluids are expanded by equal fractions of their volume by equal increments of temperature; Watt and Robison had given tables of the elastic force of steam, and Gren had shown that, at the temperature of boiling water, the pressure of steam was equal to that of the atmosphere; Dalton, Ure, and others proved (1800-1818) that the law connecting temperatures and pressures of steam was expressed by a geometrical ratio; and Biot had already given an approximate formula, when Southern introduced another, which is still in use. [110] "New Experiments, Physico-Mechanical, etc., touching the Spring of Air," 1662. [111] "De la Nature de l'Air," 1676. The French Government established a commission in 1823 to experiment with a view to the institution of legislation regulating the working of steam-engines and boilers; and this commission, MM. de Prony, Arago, Girard, and Dulong, determined quite accurately the temperatures of steam under pressures running up to twenty-four atmospheres, giving a formula for the calculation of the one quantity, the other being known. Ten years later, the Government of the United States instituted similar experiments under the direction of the Franklin Institute. The marked distinction between gases, like oxygen and hydrogen, and condensible vapors, like steam and carbonic acid, had been, at this time, shown by Cagniard de la Tour, who, in 1822, studied their behavior at high temperatures and under very great pressures. He found that, when a vapor was confined in a glass tube in presence of the same substance in the liquid state, as where steam and water were confined together, if the temperature was increased to a certain definite point, the whole mass suddenly became of uniform character, and the previously existing line of demarkation vanished, the whole mass of fluid becoming, as he inferred, gaseous. It was at about this time that Faraday made known his then novel experiments, in which gases which had been before supposed permanent were liquefied, simply by subjecting them to enormous pressures. He then also first stated that, above certain temperatures, liquefaction of vapors was impossible, however great the pressure. Faraday's conclusion was justified by the researches of Dr. Andrews, who has since most successfully extended the investigation commenced by Cagniard de la Tour, and who has shown that, at a certain point, which he calls the "critical point," the properties of the two states of the fluid fade into each other, and that, at that point, the two become continuous. With carbonic acid, this occurs at 75 atmospheres, about 1,125 pounds per square inch, a pressure which would counterbalance a column of mercury 60 yards, or nearly as many metres, high. The temperature at this point is about 90° Fahr., or 31° Cent. For ether, the temperature is 370° Fahr., and the pressure 38 atmospheres; for alcohol, they are 498° Fahr., and 120 atmospheres; and for bisulphide of carbon, 505° Fahr., and 67 atmospheres. For water, the pressure is too high to be determined; but the temperature is about 775° Fahr., or 413° Cent. Donny and Dufour have shown that these normal properties of vapors and liquids are subject to modification by certain conditions, as previously (1818) noted by Gay-Lussac, and have pointed out the bearing of this fact upon the safety of steam-boilers. It was discovered that the boiling-point of water could be elevated far above its ordinary temperature of ebullition by expedients which deprive the liquid of the air usually condensed within its mass, and which prevent contact with rough or metallic surfaces. By suspension in a mixture of oils which is of nearly the same density, Dufour raised drops of water under atmospheric pressure to a temperature of 356° Fahr.--180° Cent.--the temperature of steam of about 150 pounds per square inch. Prof. James Thompson has, on theoretical grounds, indicated that a somewhat similar action may enable vapor, under some conditions, to be cooled below the normal temperature of condensation, without liquefaction. Fairbairn and Tate repeated the attempt to determine the volume and temperature of water at pressures extending beyond those in use in the steam-engine, and incomplete determinations have also been made by others. Regnault is the standard authority on these data. His experiments (1847) were made at the expense of the French Government, and under the direction of the French Academy. They were wonderfully accurate, and extended through a very wide range of temperatures and pressures. The results remain standard after the lapse of a quarter of a century, and are regarded as models of precise physical work.[112] [112] _See_ Porter on the Steam-Engine Indicator for the best set of Regnault's tables generally accessible. Regnault found that the total heat of steam is not constant, but that the latent heat varies, and that the sum of the latent and sensible heats, or the total heat, increases 0.305 of a degree for each degree of increase in the sensible heat, making 0.305 the specific heat of saturated steam. He found the specific heat of superheated steam to be 0.4805. Regnault promptly detected the fact that steam was not subject to Boyle's law, and showed that the difference is very marked. In expressing his results, he not only tabulated them but also laid them down graphically; he further determined exact constants for Biot's algebraic expression, log. _p_ = _a_ - _b_A^{_x_} - _c_B^{_x_}; making _x_ = 20 + _t_° Cent.; _a_ = 6.264035; log. _b_ = 0.1397743; log. _c_ = 0.6924351; log. A = [=1].9940493, and log. B = [=1].9983439; _p_ is the pressure in atmospheres. Regnault, in the expression for the total heat, H = A + _bt_, determined on the centigrade scale [theta] = 606.5 + 0.305 _t_ Cent. For the Fahrenheit scale, we have the following equivalent expressions: H = 1,113.44° + 0.305 _t_° Fahr., if measured from 0° Fahr. = 1,091.9° + 0.305 (_t_° - 32) Fahr.,; } if measured from = 1,081.94° + 0.305 _t_° Fahr., } the freezing-point. For latent heat, we have: L = 606.5° - 0.695 _t_° Cent. = 1,091.7°- 0.695 (_t_° - 32) Fahr. = 1,113.94°- 0.695 _t_° Fahr. Since Regnault's time, nothing of importance has been done in this direction. There still remains much work to be done in the extension of the research to higher pressures, and under conditions which obtain in the operation of the steam-engine. The volumes and densities of steam require further study, and the behavior of steam in the engine is still but little known, otherwise than theoretically. Even the true value of Joule's equivalent is not undisputed. Some of the most recent experimental work bearing directly upon the philosophy of the steam-engine is that of Hirn, whose determination of the value of the mechanical equivalent was less than two per cent. below that of Joule. Hirn tested by experiment, in 1853, and repeatedly up to 1876, the analytical work of Rankine, which led to the conclusion that steam doing work by expansion must become gradually liquefied. Constructing a glass steam-engine cylinder, he was enabled to see plainly the clouds of mist which were produced by the expansion of steam behind the piston, where Regnault's experiments prove that the steam should become drier and superheated, were no heat transformed into mechanical energy. As will be seen hereafter, this great discovery of Rankine is more important in its bearing upon the theory of the steam-engine than any made during the century. Hirn's confirmation stands, in value, beside the original discovery. In 1858 Hirn confirmed the work of Mayer and Joule by determining the work done and the carbonic acid produced, as well as the increased temperature due to their presence, where men were set at work in a treadmill; he found the elevation of temperature to be much greater in proportion to gas produced when the men were resting than when they were at work. He thus proved conclusively the conversion of heat-energy into mechanical work. It was from these experiments that Helmholtz deduced the "modulus of efficiency" of the human machine at one-fifth, and concluded that the heart works with eight times the efficiency of a locomotive-engine, thus confirming a statement of Rumford, who asserted the higher efficiency of the animal. Hirn's most important experiments in this department were made upon steam-engines of considerable size, including simple and compound engines, and using steam sometimes saturated and sometimes superheated to temperatures as high, on some occasions, as 340° Cent. He determined the work done, the quantity of heat entering, and the amount rejected from, the steam-cylinder, and thus obtained a coarse approximation to the value of the heat-equivalent. His figure varied from 296 to 337 kilogrammetres. But, in all cases, the loss of heat due to work done was marked, and, while these researches could not, in the nature of the case, give accurate quantitative results, they are of great value as qualitatively confirming Mayer and Joule, and proving the transformation of energy. Thus, as we have seen, experimental investigation and analytical research have together created a new science, and the philosophy of the steam-engine has at last been given a complete and well-defined form, enabling the intelligent engineer to comprehend the operation of the machine, to perceive the conditions of efficiency, and to look forward in a well-settled direction for further advances in its improvement and in the increase of its efficiency. A very concise _résumé_ of the principal facts and laws bearing upon the philosophy of the steam-engine will form a fitting conclusion to this historical sketch. The term "energy" was first used by Dr. Young as the equivalent of the work of a moving body, in his hardly yet obsolete "Lectures on Natural Philosophy." Energy is the capacity of a moving body to overcome resistance offered to its motion; it is measured either by the product of the mean resistance into the space through which it is overcome, or by the half-product of the mass of the body into the square of its velocity. Kinetic energy is the actual energy of a moving body; potential energy is the measure of the work which a body is capable of doing under certain conditions which, without expending energy, may be made to affect it, as by the breaking of a cord by which a weight is suspended, or by firing a mass of explosive material. The British measure of energy is the foot-pound; the metric measure is the kilogrammetre. Energy, whether kinetic or potential, may be observable and due to mass-motion; or it may be invisible and due to molecular movements. The energy of a heavenly body or of a cannon-shot, and that of heat or of electrical action, are illustrations of the two classes. In Nature we find utilizable potential energy in fuel, in food, in any available head of water, and in available chemical affinities. We find kinetic energy in the motion of the winds and the flow of running water, in the heat-motion of the sun's rays, in heat-currents on the earth, and in many intermittent movements of bodies acted on by applied forces, natural or artificial. The potential energy of fuel and of food has already been seen to have been derived, at an earlier period, from the kinetic energy of the sun's rays, the fuel or the food being thus made a storehouse or reservoir of energy. It is also seen that the animal system is simply a "mechanism of transmission" for energy, and does not create but simply diverts it to any desired direction of application. All the available forms of energy can be readily traced back to a common origin in the potential energy of a universe of nebulous substance (chaos), consisting of infinitely diffused matter of immeasurably slight density, whose "energy of position" had been, since the creation, gradually going through a process of transformation into the several forms of kinetic and potential energy above specified, through intermediate methods of action which are usually still in operation, such as the potential energy of chemical affinity, and the kinetic forms of energy seen in solar radiation, the rotation of the earth, and the heat of its interior. The _measure_ of any given quantity of energy, whatever may be its form, is the product of the resistance which it is capable of overcoming into the space through which it can move against that resistance, i. e., by the product RS. Or it is measured by the equivalent expressions (MV^{2})/2, or WV^{2}/2_g_, in which W is the weight, M is the "mass" of matter in motion, V the velocity, and _g_ the dynamic measure of the force of gravity, 32-1/6 feet, or 9.8 metres, per second. There are three great laws of energetics: 1. The sum total of the energy of the universe is invariable. 2. The several forms of energy are interconvertible, and possess an exact quantitative equivalence. 3. The tendency of all forms of kinetic energy is continually toward reduction to forms of molecular motion, and to their final dissipation uniformly throughout space. The history of the first two of these laws has already been traced. The latter was first enunciated by Prof. Sir William Thomson in 1853. Undissipated energy is called "Entrophy." The science of thermo-dynamics is, as has been stated, a branch of the science of energetics, and is the only branch of that science in the domain of the physicist which has been very much studied. This branch of science, which is restricted to the consideration of the relations of heat-energy to mechanical energy, is based upon the great fact determined by Rumford and Joule, and considers the behavior of those fluids which are used in heat-engines as the media through which energy is transferred from the one form to the other. As now accepted, it assumes the correctness of the hypothesis of the dynamic theory of fluids, which supposes their expansive force to be due to the motion of their molecules. This idea is as old as Lucretius, and was distinctly expressed by Bernouilli, Le Sage and Prévost, and Herapath. Joule recalled attention to this idea, in 1848, as explaining the pressure of gases by the impact of their molecules upon the sides of the containing vessels. Helmholtz, ten years later, beautifully developed the mathematics of media composed of moving, frictionless particles, and Clausius has carried on the work still further. The general conception of a gas, as held to-day, including the vortex-atom theory of Thomson and Rankine, supposes all bodies to consist of small particles called molecules, each of which is a chemical aggregation of its ultimate parts or atoms. These molecules are in a state of continual agitation, which is known as heat-motion. The higher the temperature, the more violent this agitation; the total quantity of motion is measured as _vis viva_ by the half-product of the mass into the square of the velocity of molecular movement, or in heat-units by the same product divided by Joule's equivalent. In solids, the range of motion is circumscribed, and change of form cannot take place. In fluids, the motion of the molecules has become sufficiently violent to enable them to break out of this range, and their motion is then no longer definitely restricted. The laws of thermo-dynamics are, according to Rankine: 1. Heat-energy and mechanical energy are mutually convertible, one British thermal unit being the equivalent in heat-energy of 772 foot-pounds of mechanical energy, and one metric _calorie_ equal to 423.55 kilogrammetres of work. 2. The energy due to the heat of each of the several equal parts into which a uniformly hot substance may be divided is the same; and the total heat-energy of the mass is equal to the sum of the energies of its parts.[113] [113] This uniformity is not seen where a substance is changing its physical state while developing its heat-energy, as occurs with steam doing work while expanding. It follows that the work performed by the transformation of the energy of heat, during any indefinitely small variation of the state of a substance as respects temperature, is measured by the product of the absolute temperature into the variation of a "function," which function is the rate of variation of the work so done with temperature. This function is the quantity called by Rankine the "heat-potential" of the substance for the given kind of work. A similar function, which comprehends the total heat-variation, including both heat transformed and heat needed to effect accompanying physical changes, is called the "thermo-dynamic function." Rankine's expression for the general equation of thermo-dynamics includes the latter, and is given by him as follows: J_dh_ = _d_H = _kd_[tau] + [tau]_d_F = [tau]_d_[phi], in which J is Joule's equivalent, _dh_ the variation of total heat in the substance, _kd_[tau] the product of the "dynamic specific heat" into the variation of temperature, or the total heat demanded to produce other changes than a transformation of energy, and [tau]_d_F is the work done by the transformation of heat-energy, or the product of the absolute temperature, [tau], into the differential of the heat-potential. [phi] is the thermo-dynamic function, and [tau]_d_[phi] measures the whole heat needed to produce, simultaneously, a certain amount of work or of mechanical energy, and, at the same time, to change the temperature of the working substance. Studying the behavior of gases and vapors, it is found that the work done when they are used, like steam, in heat-engines, consists of three parts: (_a._) The change effected in the total actual heat-motion of the fluid. (_b._) That heat which is expended in the production of internal work. (_c._) That heat which is expended in doing the external work of expansion. In any case in which the total heat expended exceeds that due the production of work on external bodies, the excess so supplied is so much added to the intrinsic energy of the substance absorbing it. The application of these laws to the working of steam in the engine is a comparatively recent step in the philosophy of the steam-engine, and we are indebted to Rankine for the first, and as yet only, extended and in any respect complete treatise embodying these now accepted principles. It was fifteen years after the publication of the first logical theory of the steam-engine, by Pambour,[114] before Rankine, in 1859, issued the most valuable of all his works, "The Steam-Engine and other Prime Movers." The work is far too abstruse for the general reader, and is even difficult reading for many accomplished engineers. It is excellent beyond praise, however, as a treatise on the thermo-dynamics of heat-engines. It will be for his successors the work of years to extend the application of the laws which he has worked out, and to place the results of his labors before students in a readily comprehended form. [114] "Théorie de la Machine à Vapeur," par le Chevalier F. M. G. de Pambour, Paris, 1844. William J. Macquorn Rankine, the Scotch engineer and philosopher, will always be remembered as the author of the modern philosophy of the steam-engine, and as the greatest among the founders of the science of thermo-dynamics. His death, while still occupying the chair of engineering at the University of Glasgow, December 24, 1872, at the early age of fifty-two, was one of the greatest losses to science and to the profession which have occurred during the century. CHAPTER VIII. _THE PHILOSOPHY OF THE STEAM-ENGINE._ ITS APPLICATION; ITS TEACHINGS RESPECTING THE CONSTRUCTION OF THE ENGINE AND ITS IMPROVEMENT. "Oftentimes an Uncertaintie hindered our going on so merrily, but by persevering the Difficultie was mastered, and the new Triumph gave stronger Heart unto us."--RALEIGH. "If everything which we cannot comprehend is to be called an impossibility, how many are daily presented to our eyes! and in contemning as false that which we consider to be impossible, may we not be depreciating a giant's effort to give an importance to our own weakness?"--MONTAIGNE. "They who aim vigorously at perfection will come nearer to it than those whose laziness or despondency makes them give up its pursuit from the feeling of its being unattainable."--CHESTERFIELD. As has been already stated, the steam-engine is a machine which is especially designed to transform energy, originally dormant or potential, into active and usefully available kinetic energy. When, millions of years ago, in that early period which the geologists call the carboniferous, the kinetic energy of the sun's rays, and of the glowing interior of the earth, was expended in the decomposition of the vast volumes of carbonic acid with which air was then charged, and in the production of a life-sustaining atmosphere and of the immense forests which then covered the earth with their almost inconceivably luxuriant vegetation, there was stored up for the benefit of the human race, then uncreated, an inconceivably great treasure of potential energy, which we are now just beginning to utilize. This potential energy becomes kinetic and available wherever and whenever the powerful chemical affinity of oxygen for carbon is permitted to come into play; and the fossil fuel stored in our coal-beds or the wood of existing forests is, by the familiar process of combustion, permitted to return to the state of combination with oxygen in which it existed in the earliest geological periods. The philosophy of the steam-engine, therefore, traces the changes which occur from this first step, by which, in the furnace of the steam-boiler, this potential energy which exists in the tendency of carbon and oxygen to combine to form carbonic acid is taken advantage of, and the utilizable kinetic energy of heat is produced in equivalent amount, to the final application of resulting mechanical energy to machinery of transmission, through which it is usefully applied to the elevation of water, to the driving of mills and machinery of all kinds, or to the hauling of "lightning" trains on our railways, or to the propulsion of the Great Eastern. The kinetic heat-energy developed in the furnace of the steam-boiler is partly transmitted through the metallic walls which inclose the steam and water within the boiler, there to evaporate water, and to assume that form of energy which exists in steam confined under pressure, and is partly carried away into the atmosphere in the discharged gaseous products of combustion, serving, however, a useful purpose, _en route_, by producing the draught needed to keep up combustion. The steam, with its store of heat-energy, passes through tortuous pipes and passages to the steam-cylinder of the engine, losing more or less heat on the way, and there expands, driving the piston before it, and losing heat by the transformation of that form of energy while doing mechanical work of equivalent amount. But this steam-cylinder is made of metal, a material which is one of the best conductors of heat, and therefore one of the very worst possible substances with which to inclose anything as subtile and difficult of control as the heat pervading a condensible vapor like steam. The process of internal condensation and reëvaporation, which is the great enemy of economical working, thus has full play, and is only partly checked by the heat from the steam-jacket, which, penetrating the cylinder, assists by keeping up the temperature of the internal surface and checking the first step, condensation, which is an essential preliminary to the final waste by reëvaporation. The piston, too, is of metal, and affords a most excellent way of exit for the heat escaping to the exhaust side. Finally, all unutilized heat rejected from the steam-cylinder is carried away from the machine, either by the water of condensation, or, in the non-condensing engine, by the atmosphere into which it is discharged. Having traced the method of operation of the steam-engine, it is easy to discover what principles are comprehended in its philosophy, to learn what are known facts bearing upon its operation, and to determine what are the directions in which improvement must take place, what are the limits beyond which improvement cannot possibly be carried, and, in some directions, to determine what is the proper course to pursue in effecting improvements. The general direction of change in the past, as well as at present, is easily seen, and it may usually be assumed that there will be no immediate change of direction in a course which has long been preserved, and which is well defined. We may, therefore, form an idea of the probable direction in which to look for improvement in the near future. Reviewing the operations which go on in this machine during the process of transformation of energy which has been outlined, and studying it more in detail, we may deduce the principles which govern its design and construction, guide us in its management, and determine its efficiency. In the furnace of the boiler, the quantity of heat developed in available form is proportional to the amount of fuel burned. It is available in proportion to the temperature attained by the products of combustion; were this temperature no higher than that of the boiler, the heat would all pass off unutilized. But the temperature produced by a given quantity of heat, measured in heat-units, is greater as the volume of gas heated is less. It follows that, at this point, therefore, the fuel should be perfectly consumed with the least possible air-supply, and the least possible abstraction of heat before combustion is complete. High temperature of furnace, also, favors complete combustion. We hence conclude that, in the steam-boiler furnace, fuel should be burned completely in a chamber having non-conducting walls, and with the smallest air-supply compatible with thorough combustion; and, further, that the air should be free from moisture, that greatest of all absorbents of heat, and that the products of combustion should be removed from the furnace before beginning to drain their heat into the boiler. A fire-brick furnace, a large combustion-chamber with thorough intermixture of gases within it, good fuel, and a restricted and carefully-distributed supply of air, seem to be the conditions which meet these requisites best. The heat generated by combustion traverses the walls which separate the gases of the furnace from the steam and water confined within the boiler, and is then taken up by those fluids, raising their temperature from that of the entering "feed-water" to that due the steam-pressure, and expanding the liquid into steam occupying a greatly-increased volume, thus doing a certain amount of work, besides increasing temperature. The extent to which heat may thus be usefully withdrawn from the furnace-gases depends upon the conductivity of the metallic wall, the rate at which the water will take heat from the metal, and the difference of temperature on the two sides of the metal. Extended "heating-surface," therefore, a metal of high conducting power, and a maximum difference of temperature on the two sides of the separating wall of metal, are the essential conditions of economy here. The heating-surface is sometimes made of so great an area that the temperature of the escaping gases is too low to give good chimney-draught, and a "mechanical draught" is resorted to, revolving "fan-blowers" being ordinarily used for its production. It is most economical to adopt this method. The steam-boiler is generally constructed of iron--sometimes, but rarely, of cast-iron, although "steel," where not hard enough to harden or temper, is better in consequence of its greater strength and homogeneousness of structure, and its better conductivity. The maximum conductivity of flow of heat for any given material is secured by so designing the boiler as to secure rapid, steady, and complete circulation of the water within it. The maximum rapidity of transfer throughout the whole area of heating-surface is secured, usually, by taking the feed-water into the boiler as nearly as possible at the point where the gases are discharged into the chimney-flue, withdrawing the steam nearer the point of maximum temperature of flues, and securing opposite directions of flow for the gases on the one side and the water on the other. Losses of heat from the boiler, by conduction and radiation to surrounding bodies, are checked as far as possible by non-conducting coverings. The mechanical equivalent of the heat generated in the boiler is easily calculated when the conditions of working are known. A pound of pure carbon has been found to be capable of liberating by its perfect combustion, resulting in the formation of carbonic acid, 14,500 British thermal units, equivalent to 14,500 × 772 = 11,194,000 foot-pounds of work, and, if burned in one hour, to 11194000/1980000 = 5.6 horse-power. In other words, with perfect utilization, but 10/56 = 0.177, or about one-sixth, of a pound of carbon would be needed per hour for each horse-power of work done. But even good coal is not nearly all carbon, and has but about nine-tenths this heat-producing power, and it is usually rated as yielding about 10,000,000 foot-pounds of work per pound. The evaporative power of pure carbon being rated at 15 pounds of water, that of good coal may be stated at 13-1/2. In metric measures, one gramme of good coal should evaporate about 13-1/2 grammes of water from the boiling-point, producing the equivalent of about 3,000,000 kilogrammetres of work from the 7,272 _calories_ of heat thus generated. A gramme of pure carbon generates in its combustion 8,080 _calories_ of heat. Per hour and per horse-power, 0.08, or less than one-twelfth, of a kilogram of carbon burned per hour evolves heat-energy equal to one horse-power. Of the coal burned in a steam-boiler, it rarely happens that more than three-fourths is utilized in making steam; 7,500,000 foot-pounds (1,036,898 kilogrammetres) is, therefore, as much energy as is usually sent to the engine per pound of good coal burned in the steam-boiler. The "efficiency" of a good steam-boiler is therefore usually not far from 0.75 as a maximum. Rankine estimates this quantity for ordinary boilers of good design and with chimney-draught at 0.92 E = ------------; 1 + 0.5(F/S) in which F/S is the ratio of weight of fuel burned per square foot of grate to the ratio of heating to grate surface; this is a formula of fairly close approximation for general practice. The steam in the engine first drives the piston some distance before the induction or steam valve is closed, and it then expands, doing work, and condensing in proportion to work done as the expansion proceeds, until it is finally released by the opening of the exhaust or eduction valve. Saturated steam is modified in its action by a process which has already been described, condensing at the beginning and reëvaporating at the end of the stroke, thus carrying into the condenser considerable quantities of heat which should have been utilized in the development of power. Whether this operation takes place in one cylinder or in several is only of importance in so far as it modifies the losses due to conduction and radiation of heat, to condensation and reëvaporation of steam, and to the friction of the machine. It has already been seen how these losses are modified by the substitution of the compound for the single-cylinder engine. The laws of thermo-dynamics teach, as has been stated, that the proportion of the heat-energy contained in the steam or other working fluid which may be transformed into mechanical energy is a fraction (H_{1} - H_{2})/H_{1}, of the total, in which H_{1} and H_{2} are the quantities of heat contained in the steam at the beginning and at the end of its operation, measuring from the absolute zero of heat-motion. In perfect gases, H_{1} - H_{2} [tau]_{1} - [tau]_{2} T_{1} - T_{2} ------------- = --------------------- = -------------------- H_{1} [tau]_{1} T_{1} + 461.2° Fahr. but in imperfect gases, and especially in vapors which, like steam, condense, or otherwise change their physical state, this equality may still exist, (H_{1} - H_{2})/H_{1} = ([tau]_{1} - [tau]_{2})/[tau]_{1}; and the fluid is equally efficient with the perfect gas as a working substance in a heat-engine. In any case it is seen that the efficiency is greatest when the whole of the heat is received at the maximum and rejected at the minimum attainable temperatures. Assuming this expression strictly accurate, a hot-air engine working from 413.6° Fahr, or 874.8° absolute temperature, down to 122° Fahr, or 583.2° absolute, should have an efficiency of 0.263, transforming that proportion of available heat into mechanical work. The engines of the steamer Ericsson closely approached this figure, and gave a horse-power for each 1.87 pound of coal burned per hour. Steam expands in the steam-cylinder quite differently under different circumstances. If no heat is either communicated to it or abstracted from it, however, it expands in an hyperbolic curve, losing its tension much more rapidly than when expanded without doing work, in consequence both of its change of volume and its condensation. The algebraic expression for this method of expansion is, according to Rankine, PV^{1.111} = C, a constant, or, according to other authorities, from PV^{1.135} = C to PV^{1.140} = C. The greater the value of the exponent of V, the greater the efficiency of the fluid between any two temperatures. The maximum value has been found to be given where the steam is saturated, but perfectly dry, at the commencement of its expansion. The loss due to condensation on the cooled interior surface of the cylinder at the commencement of the stroke and the subsequent reëvaporation as expansion progresses is least when the cylinder is kept hot by its steam-jacket and when least time is given during the stroke for this transfer of heat between the metal and the vapor. It may be said that, all things considered, therefore, losses of heat in the steam-cylinder are least when the steam enters dry, or moderately superheated, where the interior surfaces are kept hottest by the steam-jacket or by the hot-air jacket sometimes used, and where piston-speed and velocity of rotation are highest.[115] The best of compound engines, using steam of seventy-five pounds pressure and condensing, usually require about two pounds of coal per hour--20,000,000 foot-pounds of energy at the furnace--to develop a horse-power, i. e., about ten times the heat-equivalent of the mechanical work which they accomplish. Were the steam to expand like the permanent gases, they would have a theoretical efficiency of about one-quarter; actually, the efficiency is only one-tenth. The steam-engine, therefore, utilizes about two-fifths the heat-energy theoretically available with the best type of engine in general use. By far the greater part, nearly all, in fact, of the nine-tenths wasted is rejected in the exhaust steam, and can only be saved by some such method as is hereafter to be suggested of retaining that heat and returning it to the boiler. [115] In some cases, as in the Allen engine, the speed of piston has become very high, approaching 800((stroke)^{1/3}). The mechanical power which has now been communicated to the mechanism of the engine by the transfer of the kinetic energy of the hot steam to the piston is finally usefully applied to whatever "mechanism of transmission" forms the connection with the machinery driven by the engine. In this transfer, there is some loss in the engine itself, by friction. This is an extremely variable amount, and it can be made very small by skillful design and good workmanship and management. It may be taken at one-half pound per square inch of piston for good engines of 100 horse-power and upward, but is often several pounds in very small engines. It is least when the rubbing surfaces are of different materials, but both of smooth, hard, close-grained metal, well lubricated, and where advantage is taken of any arrangement of parts which permits the equilibration of pressure, as on the shaft-bearings of double and triple engines. The friction of a steam-engine of large size and good design is usually between five and seven per cent. of its total power. It increases rapidly as the size of engine decreases. Having now traced somewhat minutely the growth of the steam-engine from the beginning of the Christian era to the present time, having rapidly outlined the equally gradual, though intermittent, growth of its philosophy, and having shown how the principles of science find application in the operation of this wonderful machine, we are now prepared to study the conditions which control the intelligent designer, and to endeavor to learn what are the lessons taught us by science and by experience in regard to the essential requisites of efficient working of steam and economy in the consumption of fuel. We may even venture to point out definitely the direction in which improvement is now progressing as indicated by a study of these requisites, and may be able to perceive the natural limits to such progress, and possibly to conjecture what must be the character of that change of type which only can take the engineer beyond the limit set to his advance so long as he is confined to the construction of the present type of engine. First, we must consider the question: _What is the problem, stated precisely and in its most general form, that engineers have been here attempting to solve?_ After stating the problem, we will examine the record with a view to determine what direction the path of improvement has taken hitherto, to learn what are the conditions of efficiency which should govern the construction of the modern steam-engine, and, so far as we may judge the future by the past, by inference, to ascertain what appears to be the proper course for the present and for the immediate future. Still further, we will inquire, what are the conditions, physical and intellectual, which best aid our progress in perfecting the steam-engine. This most important problem may be stated in its most general, yet definite, form as follows: _To construct a machine which shall, in the most perfect manner possible, convert the kinetic energy of heat into mechanical power, the heat being derived from the combustion of fuel, and steam being the receiver and the conveyer of that heat._ The problem, as we have already seen, embodies two distinct and equally important inquiries: The first: What are the scientific principles involved in the problem as stated? The second: How shall a machine be constructed that shall most efficiently embody, and accord with, not only those scientific principles, but also all of those principles of engineering practice that so vitally affect the economical value of every machine? The one question is addressed to the man of science, the other to the engineer. They can be satisfactorily answered, even so far as our knowledge at present permits, after studying with care the scientific principles involved in the theory of the steam-engine under the best light that science can afford us, and by a careful study of the various steps of improvement that have taken place and of accompanying variations of structure, analyzing the effect of each change, and tracing the reasons for them. The theory of the steam-engine is too important and too extensive a subject to be satisfactorily treated here in even the most concise possible manner. I can only attempt a plain statement of the course which seems to be pointed out by science as the proper one to pursue in the endeavor to increase the economical efficiency of steam-engines. The teachings of science indicate that _success in economically deriving mechanical power from the energy of heat-motion will, in all cases, be the greater as we work between more widely separated limits of temperature, and as we more perfectly provide against losses by dissipation of heat in directions in which it is unavailable for the production of power_. Scientific research, as we have seen, has proved that, in all known varieties of heat-engine, a large loss of effect is unavoidable from the fact that we cannot, in the ordinary steam-engine, reduce the lower limit of temperature, in working, below a point which is far above the absolute zero of temperature--far above that point at which bodies have no heat-motion. The point corresponding to the mean temperature of the surface of the earth is above the ordinary lower limit. The higher the temperature of the steam when it enters the steam cylinder, and the lower that which it reaches before the exhaust occurs, the greater, science tells us, will be our success, provided we at the same time avoid waste of heat and power. Now, looking back over the history of the steam-engine, we may briefly note the prominent improvements and the most striking changes of form, and may thus endeavor to obtain some idea of the general direction in which we are to look for further advance. Beginning with the machine of Porta, at which point we may first take up an unbroken thread, it will be remembered that we there found a single vessel performing the functions of all the parts of a modern pumping-engine; it was, at once, boiler, steam-cylinder, and condenser, as well as both a lifting and a forcing pump. The Marquis of Worcester divided the engine into two parts, using a separate boiler. Savery duplicated that part of the engine of Worcester which performed the several parts of pump, steam-cylinder, and condenser, and added the use of water to effect rapid condensation, perfecting, so far as it was ever perfected, the steam-engine as a simple machine. Newcomen and Calley next separated the pump from the steam-engine proper, producing the modern steam-engine--the engine as a train of mechanism; and in their engine, as in Savery's, we noticed the use of surface condensation first, and subsequently that of the jet thrown into the midst of the steam to be condensed. Watt finally effected the crowning improvements, and completed the movement o£ "differentiation" by separating the condenser from the steam-cylinder. Here this process of change ceased, the several important operations of the steam-engine now being conducted each in a separate vessel. The boiler furnished the steam, the cylinder derived from it mechanical power, and it was finally condensed in a separate vessel, while the power which had been obtained from it in the steam-cylinder was transmitted through still other parts, to the pumps, or wherever work was to be done. Watt, also, took the initiative in another direction. He continually increased the efficiency of the machine by improving the proportions of its parts and the character of its workmanship, thus making it possible to render available many of those improvements in detail upon which effectiveness is so greatly dependent and which are only useful when made by a skillful workman. Watt and his contemporaries also commenced that movement toward higher pressures of steam and greater expansion which has been the most striking feature noticed in the progress of steam-engineering since his time. Newcomen used steam of barely more than atmospheric pressure and raised 105,000 pounds of water one foot high with a pound of coal consumed. Smeaton raised the pressure somewhat and increased the duty considerably. Watt started with a duty double that of Newcomen and raised it to 320,000 foot-pounds per pound of coal, with steam at 10 pounds pressure. To-day, Cornish engines of the same general plan as those of Watt, but worked with 40 to 60 pounds of steam and expanding three or four times, do a duty probably averaging, with the better class of engines, 600,000 foot-pounds per pound of coal. The compound pumping-engine runs the figure up to above 1,000,000. The increase in steam-pressure and in expansion since Watt's time has been accompanied by a very great improvement in workmanship--a consequence, very largely, of the rapid increase in perfection, and in the wide range of adaptation of machine-tools--by higher skill and intelligence in designing engines and boilers, by increased piston-speed, greater care in obtaining dry steam, and in keeping it dry until thrown out of the cylinder, either by steam-jacketing or by superheating, or both combined; it has further been accompanied by a greater attention to the important matter of providing carefully against losses by radiation and conduction of heat. We use, finally, the compound or double-cylinder engine for the purpose of saving some of the heat usually lost in internal condensation and reëvaporation, and precipitation of condensed vapor from great expansion. It is evident that, although there is a limit, tolerably well defined, in the scale of temperature, below which we cannot expect to pass, a degree gained in approaching this lower limit is more remunerative than a degree gained in the range of temperature available by increasing temperatures.[116] [116] The fact here referred to is easily seen if it is supposed that an engine is supplied with steam at a temperature of 400° above absolute zero and works it, without waste, down to a temperature of 200°. Suppose one inventor to adapt the engine to the use of steam of a range from 500° down to 200°, while another works his engine, with equally effective provision against losses, between the limits of 400° and 100°, an equal range with a lower mean. The first case gives an efficiency of one-half, the second three-fifths, and the third three-fourths, the last giving the highest effect. Hence the attempt made by the French inventor, Du Trembly, about the year 1850, and by other inventors since, to utilize a larger proportion of heat by approaching more closely the lower limit, was in accordance with known scientific principles. We may summarize the result of our examination of the growth of the steam-engine thus: _First._ The process of improvement has been one, primarily, of "differentiation;"[117] the number of parts has been continually increased; while the work of each part has been simplified, a separate organ being appropriated to each process in the cycle of operations. [117] This term, though perhaps not familiar to engineers, expresses the idea perfectly. _Secondly._ A kind of secondary process of differentiation has, to some extent, followed the completion of the primary one, in which secondary process one operation is conducted partly in one and partly in another portion of the machine. This is illustrated by the two cylinders of the compound engine and by the duplication noticed in the binary engine. _Thirdly._ The direction of improvement has been marked by a continual increase of steam-pressure, greater expansion, provision for obtaining dry steam, high piston-speed, careful protection against loss of heat by conduction or radiation, and, in marine engines, by surface condensation. The direction which improvement seems now to be taking, and the proper direction, as indicated by an examination of the principles of science, as well as by our review of the steps already taken, would seem to be: working between the widest attainable limits of temperature. Steam must enter the machine at the highest possible temperature, must be protected from waste, and must retain, at the moment before exhaust, the least possible amount of heat. He whose inventive genius, or mechanical skill, contributes to effect either the use of higher steam with safety and without waste, or the reduction of the temperature of discharge, confers a boon upon mankind. In detail: In the engine, the tendency is, and may probably be expected to continue, in the near future at least, toward higher steam-pressure, greater expansion in more than one cylinder, steam-jacketing, superheating, a careful use of non-conducting protectors against waste, and the adoption of still higher piston-speeds. In the boiler: more complete combustion without excess of air passing through the furnace, and more thorough absorption of heat from the furnace-gases. The latter will probably be ultimately effected by the use of a mechanically produced draught, in place of the far more wasteful method of obtaining it by the expenditure of heat in the chimney. In construction we may anticipate the use of better materials, and more careful workmanship, especially in the boiler, and much improvement in forms and proportions of details. In management, there is a wide field for improvement, which improvement we may feel assured will rapidly take place, as it has now become well understood that great care, skill, and intelligence are important essentials to the economical management of the steam-engine, and that they repay, liberally, all of the expense in time and money that is requisite to secure them. In attempting improvements in the directions indicated, it would be the height of folly to assume that we have reached a limit in any one of them, or even that we have approached a limit. If further progress seems checked by inadequate returns for efforts made, in any case, to advance beyond present practice, it becomes the duty of the engineer to detect the cause of such hinderance, and, having found it, to remove it. A few years ago, the movement toward the expansive working of high steam was checked by experiments seeming to prove positive disadvantage to follow advance beyond a certain point. A careful revision of results, however, showed that this was true only with engines built, as was then common, in utter disregard of all the principles involved in such a use of steam, and of the precautions necessary to be taken to insure the gain which science taught us should follow. The hinderances are mechanical, and it is for the engineer to remove them. The last remark is especially applicable to the work of the engineer who is attempting to advance in the direction in which, as already intimated, an unmistakable revolution is now progressing, the modification of the modern steam-engine to adapt it safely and successfully to run at the high piston-speed, and great velocity of rotation which have been already attained and which must undoubtedly be greatly exceeded in the future. As there is no known and definite limit to the economical increase of speed, and as the limit set by practical conditions is continually being set farther back as the builder acquires greater skill and attains greater accuracy of workmanship and the power to insure greater rigidity of parts and durability of wearing surfaces, we must anticipate a continued and indefinite progress in this direction--a progress which must evidently be of advantage, whatever may be the direction that other changes may take. It is evident that this adaptation of the steam-engine to great speed of piston is the work now to be done by the engineer. The requisites to success are obvious, and may be concisely stated as follows: 1. Extreme accuracy in proportions. 2. Perfect accuracy in fitting parts to each other. 3. Absolute symmetry of journals. 4. Ample area and maximum durability of rubbing surfaces. 5. Perfect certainty of an ample and continuous lubrication. 6. A nicely calculated and adjusted balance of reciprocating parts. 7. Security against injury by shock, whether due to the presence of water in the cylinder or to looseness of running parts. 8. A "positive-motion" cut-off gear. 9. A powerful but sensitive and accurately-working governor determining the degree of expansion.[118] [118] The author is not absolutely confident on the latter point. It may be found more economical and satisfactory, ultimately, to determine the point of cut-off by an automatic apparatus adjusting the expansion-gear _by reference to the steam-pressure_, regulating the speed by attaching the governor elsewhere. The author has devised several forms of apparatus of the kind referred to. 10. Well-balanced valves and an easy-working valve-gear. 11. Small volume of "dead-space," or "clearance," and properly adjusted "compression." It would seem sufficiently evident that the engine with detachable ("drop") cut-off valve-gear must, sooner or later, become an obsolete type, although the substitution of springs or of steam-pressure for gravity in the closing of the detached valve may defer greatly this apparently inevitable change. The "engine of the future" will not probably be a "drop cut-off engine." As regards the construction of the engine as a piece of mechanism, the principles and practice of good engineering are precisely the same, whether applied in the designing of the compound or of the ordinary type of steam-engine. The proportioning of the two machines to each other in such manner as to form an effective whole, by procuring approximately equal amounts of work from both, is the only essential peculiarity of compound-engine design which calls for especial care, and the method of securing success in practice may be stated to be, for both forms of engines, as follows: 1. A good design, by which is meant-- _a._ Correct proportions, both in general dimensions and in arrangement of parts, and proper forms and sizes of details to withstand safely the forces which may be expected to come upon them. _b._ A general plan which embodies the recognized practice of good engineering. _c._ Adaptation to the specific work which it is intended to perform, in size and in efficiency. It sometimes happens that good practice dictates the use of a comparatively uneconomical design. 2. Good construction, by which is meant-- _a._ The use of good material. _b._ Accurate workmanship. _c._ Skillful fitting and a proper "assemblage" of parts. 3. Proper connection with its work, that it may do that work under the conditions assumed in its design. 4. Skillful management by those in whose hands it is placed. _In general_, it may be stated that, to secure maximum economical efficiency, steam should be worked at as high a pressure as possible, and the expansion should be fixed as nearly as possible at the point of maximum economy for that pressure. In general, the number of times which the volume of steam may be expanded in the standard single-cylinder, high-pressure engine with maximum economy, is not far from 1/2 sqrt(P), where P is the pressure in pounds per square inch; it rarely exceeds 0.75 sqrt(P). This may be exceeded in double-cylinder engines. It is even more disadvantageous to cut off too short than to "'follow' too far." With considerable expansion, steam-jacketing and moderate superheating should be adopted, to prevent excessive losses by internal condensation and reëvaporation; and expansion should take place in double cylinders, to avoid excessive weight of parts, irregularity of motion, and great loss by friction. To secure this vitally important economy, it is advisable to seek some practicable method of lining the cylinder with a non-conducting material. This plan, as has been seen, was adopted by Smeaton, in constructing Newcomen engines a century ago. Smeaton used wood on his pistons, and Watt tried wood as a material for steam-cylinder linings. That material is too perishable at temperatures now common, and no metal has yet been substituted, or even discovered, which answers the same purpose. The loss will also be reduced by increasing the speed of rotation and velocity of piston. Where no effectual means can be found of preventing contact of the steam with a good absorbent and conductor of heat, it will be found best to sacrifice some of the efficiency due to the change of state of the vapor, by superheating it and sending it into the cylinder at a temperature considerably exceeding that of saturation. With low steam and slowly-moving pistons, it is better to pursue the latter course than to attempt to increase the efficiency of the engine by greater expansion. External surfaces should be carefully covered by non-conductors and non-radiators, to prevent losses by conduction and radiation of heat. It is especially necessary to reduce back-pressure and to obtain the most perfect vacuum possible without overloading the air-pump, if it is desired to obtain the maximum efficiency by expansion, and it then becomes also very necessary to reduce losses by "dead-spaces" and by badly-adjusted valves. The piston-speed should be as great as can be sustained with safety. Good engines should not require more than W = (200/sqrt(P)) where W = the weight of steam per hour and per horse-power; the best practice gives about W = (180/sqrt(P)) in large engines with dry steam, high piston-speed, and good design, construction, and management. The expansion-valve gear should be simple. The point of cut-off is perhaps best determined by the governor. The valve should close rapidly, but without shock, and should be balanced, or some other device should be adopted to make it easy to move and free from liability to cutting or rapid wear. The governor should act promptly and powerfully, and should be free from liability to oscillate, and to thus introduce irregularities which are sometimes not less serious than those which the instrument is intended to prevent. Friction should be reduced as much as possible, and careful provision should be made to economize lubricants as well as fuel. The Principles of Steam-Boiler Construction are exceedingly simple; and although attempts are almost daily made to obtain improved results by varying the design and arrangement of heating-surface, the best boilers of nearly all makers of acknowledged standing are practically equal in merit, although of very diverse forms. In making boilers, the effort of the engineer should evidently be: 1. To secure complete combustion of the fuel without permitting dilution of the products of combustion by excess of air. 2. To secure as high temperature of furnace as possible. 3. To so arrange heating-surfaces that, without checking draught, the available heat shall be most completely taken up and utilized. 4. To make the form of boiler such that it shall be constructed without mechanical difficulty or excessive expense. 5. To give it such form that it shall be durable, under the action of the hot gases and of the corroding elements of the atmosphere. 6. To make every part accessible for cleaning and repairs. 7. To make every part as nearly as possible uniform in strength, and in liability to loss of strength by wear and tear, so that the boiler when old shall not be rendered useless by local defects. 8. To adopt a reasonably high "factor of safety" in proportioning parts. 9. To provide efficient safety-valves, steam-gauges, and other appurtenances. 10. To secure intelligent and very careful management. In securing complete combustion, the first of these desiderata, an ample supply of air and its thorough intermixture with the combustible elements of the fuel are essential; for the second--high temperature of furnace--it is necessary that the air-supply shall not be in excess of that absolutely needed to give complete combustion. The efficiency of a furnace in making heat available is measured by T - T´ E = -------; T - _t_ in which E represents the ratio of heat utilized to the whole calorific value of the fuel, T is the furnace-temperature, T´ the temperature of the chimney, and _t_ that of the external air. The higher the furnace-temperature and the lower that of the chimney, the greater the proportion of heat available. It is further evident that, however perfect the combustion, no heat can be utilized if either the temperature of the chimney approximates to that of the furnace, or if the temperature of the furnace is reduced by dilution approximately to that of the boiler. Concentration of heat in the furnace is secured, in some cases, by special expedients, as by heating the entering air, or as in the Siemens gas-furnace, heating both the combustible gases and the supporter of combustion. Detached fire-brick furnaces have an advantage over the "fire-boxes" of steam-boilers in their higher temperature; surrounding the fire with non-conducting and highly heated surfaces is an effective method of securing high furnace-temperature. In arranging heating-surface, the effort should be to impede the draught as little as possible, and so to place them that the circulation of water within the boiler should be free and rapid at every part reached by the hot gases. The directions of circulation of water on the one side and of gas on the other side of the sheet should, whenever possible, be opposite. The cold water should enter where the cooled gases leave, and the steam should be taken off farthest from that point. The temperature of chimney-gases has thus been reduced in practice to less than 300° Fahr., and an efficiency equal to 0.75 to 0.80 the theoretical has been attained. The extent of heating-surface simply, in all of the best forms of boiler, determines the efficiency, and in them the disposition of that surface seldom affects it to any great extent. The area of heating-surface may also be varied within very wide limits without very greatly modifying efficiency. A ratio of 25 to 1 in flue and 30 to 1 in tubular boilers represents the relative area of heating and grate surfaces as chosen in the practice of the best-known builders. The material of the boiler should be tough and ductile iron, or, better, a soft steel containing only sufficient carbon to insure melting in the crucible or on the hearth of the melting-furnace, and so little that no danger may exist of hardening and cracking under the action of sudden and great changes of temperature. Where iron is used, it is necessary to select a somewhat hard, but homogeneous and tough, quality for the fire-box sheets or any part exposed to flames. The factor of safety is invariably too low in this country, and is never too high in Europe. Foreign builders are more careful in this matter than our makers in the United States. The boiler should be built strong enough to bear a pressure at least six times the proposed working-pressure; as the boiler grows weak with age, it should be occasionally tested to a pressure far above the working-pressure, which latter should be reduced gradually to keep within the bounds of safety. In the United States, the factor of safety is seldom more than four in the new boilers, frequently much less, and even this is reduced practically to one and a third by the operation of our inspection-laws. The principles just enunciated are those generally, perhaps universally, accepted principles which are stated in all text-books of science and of steam-engineering, and are accepted by both engineers and men of science. These principles are correct, and the deductions which have been here formulated are rigidly exact, as applied to all types of heat-engine in use; and they lead us to the determination, in all cases, of the "modulus" of efficiency of the engine, i. e., to the calculation of the ratio of its actual efficiency to that efficiency which it would have, were it absolutely free from loss of heat by conduction or radiation, or other method of loss of heat or waste of power, by friction of parts or by shock. The best modern marine compound engines sometimes, as we have seen, consume as little as two pounds of coal per horse-power and per hour; but this is but about one-tenth the power derivable from the fuel, were all its heat thoroughly utilized. This loss may be divided thus: 70 per cent. rejected in exhausted steam; 20 per cent. lost by conduction and radiation and by faults of mechanism and design; and only the 10 per cent. remaining is utilized. Thirty per cent. of the heat generated in the furnace is usually lost in the chimney, and of the remainder, which enters the engine, 20 per cent. at most is all which we can hope to save any portion of by improvements effected in our best existing type of steam-engine. It has already been shown how the engineer can best proceed in attempting this economy. The direction in which further improvement must take place in the standard type of engine is plainly that which shall most efficiently check losses by internal condensation and reëvaporation by the transfer of heat to and from the metal of the steam-cylinder. The condensation of steam doing work is evidently not a disadvantage, but, on the contrary, a decided advantage. A new type of engine can, if at all, probably only supersede the common form when engineers can employ steam of very high pressure, and adopt much greater range of expansion than is now usual. Great velocity of piston and high speed of rotation are also essential in the attempt to make any revolution in steam-engine construction a success. When a new form of steam-engine is likely to be introduced, if at all, can be scarcely even conjectured. It seems evident that its success is to be secured, if a revolution is ever to occur, by the adoption of high steam-pressures, of great piston speeds, by care and skill in design, by the use of exceptionally excellent materials of construction, by great perfection of workmanship, and by intelligence in its management. Experiment and experience will probably lead gradually to the general and safe employment of much higher steam-pressures and very greatly increased piston-speeds, and may ultimately reveal and remove all those difficulties which must invariably be expected to be met here, as in all other attempts to effect radical changes, however important they may be. [Illustration] * * * * * _Scientific Publications._ =THE HUMAN SPECIES.= By A. DE QUATREFAGES, Professor of Anthropology in the Museum of Natural History, Paris. 12mo, cloth, $2.00. The work treats of the unity, origin, antiquity, and original localization of the human species, peopling of the globe, acclimatization, primitive man, formation of the human races, fossil human races, present human races, and the physical and psychological characters of mankind. =STUDENTS' TEXT-BOOK OF COLOR; or, MODERN CHROMATICS.= With Applications to Art and Industry. With 130 Original Illustrations, and Frontispiece in Colors. By OGDEN N. ROOD, Professor of Physics in Columbia College. 12mo, cloth, $2.00. "In this interesting book Professor Rood, who, as a distinguished Professor of Physics in Columbia College, United States, must be accepted as a competent authority on the branch of science of which he treats, deals briefly and succinctly with what may be termed the scientific _rationale_ of his subject. But the chief value of his work is to be attributed to the fact that he is himself an accomplished artist as well as an authoritative expounder of science."--_Edinburgh Review, October, 1879, in an article on "The Philosophy of Color._" =EDUCATION AS A SCIENCE.= By ALEXANDER BAIN, LL. D. 12mo, cloth, $1.75. "This work must be pronounced the most remarkable discussion of educational problems which has been published in our day. We do not hesitate to bespeak for it the widest circulation and the most earnest attention. It should be in the hands of every school-teacher and friend of education throughout the land."--_New York Sun._ =A HISTORY OF THE GROWTH OF THE STEAM-ENGINE.= By ROBERT H. THURSTON, A. M., C. E., Professor of Mechanical Engineering in the Stevens Institute of Technology, Hoboken, N. J., etc. With 163 Illustrations, including 15 Portraits. 12mo, cloth, $2.50. "Professor Thurston almost exhausts his subject; details of mechanism are followed by interesting biographies of the more important inventors. If, as is contended, the steam-engine is the most important physical agent in civilizing the world, its history is a desideratum, and the readers of the present work will agree that it could have a no more amusing and intelligent historian than our author."--_Boston Gazette._ =STUDIES IN SPECTRUM ANALYSIS.= By J. NORMAN LOCKYER, F. R. S., Correspondent of the Institute of France, etc. With 60 Illustrations. 12mo, cloth, $2.50. "The study of spectrum analysis is one fraught with a peculiar fascination, and some of the author's experiments are exceedingly picturesque in their results. They are so lucidly described, too, that the reader keeps on, from page to page, never flagging in interest in the matter before him, nor putting down the book until the last page is reached."--_New York Evening Express._ =GENERAL PHYSIOLOGY OF MUSCLES AND NERVES.= By Dr. I. ROSENTHAL, Professor of Physiology at the University of Erlangen. With seventy-five Woodcuts. ("International Scientific Series.") 12mo, cloth, $1.50. "The attempt at a connected account of the general physiology of muscles and nerves is, as far as I know, the first of its kind. The general data for this branch of science have been gained only within the past thirty years."--_Extract from Preface._ =SIGHT=: An Exposition of the Principles of Monocular and Binocular Vision By JOSEPH LE CONTE, LL. D., author of "Elements of Geology"; "Religion and Science"; and Professor of Geology and Natural History in the University of California. With numerous Illustrations. 12mo, cloth, $1.50. "It is pleasant to find an American book which can rank with the very best of foreign works on this subject. Professor Le Conte has long been known as an original investigator in this department; all that he gives us is treated with a master-hand."--_The Nation._ =ANIMAL LIFE=, as affected by the Natural Conditions of Existence. By KARL SEMPER, Professor of the University of Würzburg. With 2 Maps and 106 Woodcuts, and Index. 12mo, cloth, $2.00. "This is in many respects one of the most interesting contributions to zoölogical literature which has appeared for some time."--_Nature._ =THE ATOMIC THEORY.= By AD. WURTZ, Membre de l'Institut; Doyen Honoraire de la Faculté de Médecine; Professeur à la Faculté des Sciences de Paris. Translated by E. CLEMINSHAW, M. A., F. C. S., F. I. C., Assistant Master at Sherborne School. 12mo, cloth, $1.50. "There was need for a book like this, which discusses the atomic theory both in its historic evolution and in its present form. And perhaps no man of this age could have been selected so able to perform the task in a masterly way as the illustrious French chemist, Adolph Wurtz. It is impossible to convey to the reader, in a notice like this, any adequate idea of the scope, lucid instructiveness, and scientific interest of Professor Wurtz's book. The modern problems of chemistry, which are commonly so obscure from imperfect exposition, are here made wonderfully clear and attractive."--_The Popular Science Monthly._ =THE CRAYFISH.= An Introduction to the Study of Zoölogy. By Professor T. H. HUXLEY, F. R. S. With 82 Illustrations. 12mo, cloth, $1.75. "Whoever will follow these pages, crayfish in hand, and will try to verify for himself the statements which they contain, will find himself brought face to face, with all the great zoölogical questions which excite so lively an interest at the present day." "The reader of this valuable monograph will lay it down with a feeling of wonder at the amount and variety of matter which has been got out of so seemingly slight and unpretending a subject."--_Saturday Review._ =SUICIDE=: An Essay In Comparative Moral Statistics. By HENRY MORSELLI, Professor of Psychological Medicine in Royal University, Turin. 12mo, Cloth, $1.75. "Suicide" is a scientific inquiry, on the basis of the statistical method, into the laws of suicidal phenomena. Dealing with the subject as a branch of social science, it considers the increase of suicide in different countries, and the comparison of nations, races, and periods in its manifestation. The influences of age, sex, constitution, climate, season, occupation, religion, prevailing ideas, the elements of character, and the tendencies of civilization, are comprehensively analyzed in their bearing upon the propensity to self-destruction. Professor Morselli is an eminent European authority on this subject. It is accompanied by colored maps illustrating pictorially the results of statistical inquiries. =VOLCANOES: What they Are and what they Teach.= By J. W. JUDD, Professor of Geology in the Royal School of Mines (London). With Ninety-six Illustrations. 12mo. Cloth, $2.00. "In no field has modern research been more fruitful than in that of which Professor Judd gives a popular account in the present volume. The great lines of dynamical, geological, and meteorological inquiry converge upon the grand problem of the interior constitution of the earth, and the vast influence of subterranean agencies.... His book is very far from being a mere dry description of volcanoes and their eruptions; it is rather a presentation of the terrestrial facts and laws with which volcanic phenomena are associated."--_Popular Science Monthly._ "The volume before us is one of the pleasantest science manuals we have read for some time."--_Athenæum._ "Mr. Judd's summary is so full and so concise that it is almost impossible to give a fair idea in a short review."--_Pall Mall Gazette._ =THE SUN.= By C. A. YOUNG, Ph. D., LL. D., Professor of Astronomy in the College of New Jersey. With numerous Illustrations. 12mo. Cloth, $2.00. "Professor Young is an authority on 'The Sun,' and writes from intimate knowledge. He has studied that great luminary all his life, invented and improved instruments for observing it, gone to all quarters of the world in search of the best places and opportunities to watch it, and has contributed important discoveries that have extended our knowledge of it. "It would take a cyclopædia to represent all that has been done toward clearing up the solar mysteries. Professor Young has summarized the information, and presented it in a form completely available for general readers. There is no rhetoric in his book; he trusts the grandeur of his theme to kindle interest and impress the feelings. His statements are plain, direct, clear, and condensed, though ample enough for his purpose, and the substance of what is generally wanted will be found accurately given in his pages."--_Popular Science Monthly._ =ILLUSIONS: A Psychological Study.= By JAMES SULLY, author of "Sensation and Intuition," etc. 12mo. Cloth. $1.50. This volume takes a wide survey of the field of error, embracing in its view not only the illusions commonly regarded as of the nature of mental aberrations or hallucinations, but also other illusions arising from that capacity for error which belongs essentially to rational human nature. The author has endeavored to keep to a strictly scientific treatment--that is to say, the description and classification of acknowledged errors, and the exposition of them by a reference to their psychical and physical conditions. "This is not a technical work, but one of wide popular interest, in the principles and results of which every one is concerned. The illusions of perception of the senses and of dreams are first considered, and then the author passes to the illusions of introspection, errors of insight, illusions of memory, and illusions of belief. The work is a noteworthy contribution to the original progress of thought, and may be relied upon as representing the present state of knowledge on the important subject to which it is devoted."--_Popular Science Monthly._ =THE BRAIN AND ITS FUNCTIONS.= By J. LUYS, Physician to the Hospice de la Salpêtrière. With Illustrations. 12mo. Cloth, $1.50. "No living physiologist is better entitled to speak with authority upon the structure and functions of the brain than Dr. Luys. His studies on the anatomy of the nervous system are acknowledged to be the fullest and most systematic ever undertaken. Dr. Luys supports his conclusions not only by his own anatomical researches, but also by many functional observations of various other physiologists, including of course Professor Ferrier's now classical experiments."--_St. James's Gazette._ "Dr. Luys, at the head of the great French Insane Asylum, is one of the most eminent and successful investigators of cerebral science now living; and he has given unquestionably the clearest and most interesting brief account yet made of the structure and operations of the brain. We have been fascinated by this volume more than by any other treatise we have yet seen on the machinery of sensibility and thought; and we have been instructed not only by much that is new, but by many sagacious practical hints such as it is well for everybody to understand."--_The Popular Science Monthly._ =THE CONCEPTS AND THEORIES OF MODERN PHYSICS.= By J. B. STALLO. 12mo. Cloth, $1.75. "Judge Stallo's work is an inquiry into the validity of those mechanical conceptions of the universe which are now held as fundamental in physical science. He takes up the leading modern doctrines which are based upon this mechanical conception, such as the atomic constitution of matter, the kinetic theory of gases, the conservation of energy, the nebular hypothesis, and other views, to find how much stands upon solid empirical ground, and how much rests upon metaphysical speculation. Since the appearance of Dr. Draper's 'Religion and Science,' no book has been published in the country calculated to make so deep an impression on thoughtful and educated readers as this volume.... The range and minuteness of the author's learning, the acuteness of his reasoning, and the singular precision and clearness of his style, are qualities which very seldom have been jointly exhibited in a scientific treatise."--_New York Sun._ =THE FORMATION OF VEGETABLE MOULD, THROUGH THE ACTION OF WORMS, WITH OBSERVATIONS ON THEIR HABITS.= By CHARLES DARWIN, LL. D., F. R. S., author of "On the Origin of Species," etc., etc. With Illustrations. 12mo, cloth. Price, $1.50. "Mr. Darwin's little volume on the habits and instincts of earth-worms is no less marked than the earlier or more elaborate efforts of his genius by freshness of observation, unfailing power of interpreting and correlating facts, and logical vigor in generalizing upon them. The main purpose of the work is to point out the share which worms have taken in the formation of the layer of vegetable mould which covers the whole surface of the land in every moderately humid country. All lovers of nature will unite in thanking Mr. Darwin for the new and interesting light he has thrown upon a subject so long overlooked, yet so full of interest and instruction, as the structure and the labors of the earth-worm."--_Saturday Review._ "Respecting worms as among the most useful portions of animate nature, Dr. Darwin relates, in this remarkable book, their structure and habits, the part they have played in the burial of ancient buildings and the denudation of the land, in the disintegration of rocks, the preparation of soil for the growth of plants, and in the natural history of the world."--_Boston Advertiser._ =ANTS, BEES, AND WASPS.= A Record of Observations on the Habits of the Social Hymenoptera. By Sir JOHN LUBBOCK, Bart., M. P., F. R. S., etc., author of "Origin of Civilization, and the Primitive Condition of Man," etc., etc. With Colored Plates. 12mo, cloth, $2.00. "This volume contains the record of various experiments made with ants, bees, and wasps during the last ten years, with a view to test their mental condition and powers of sense. The principal point in which Sir John's mode of experiment differs from those of Huber, Forel, McCook, and others, is that he has carefully watched and marked particular insects, and has had their nests under observation for long periods--one of his ants' nests having been under constant inspection ever since 1874. His observations are made principally upon ants because they show more power and flexibility of mind; and the value of his studies is that they belong to the department of original research." "We have no hesitation in saying that the author has presented us with the most valuable series of observations on a special subject that has ever been produced, charmingly written, full of logical deductions, and, when we consider his multitudinous engagements, a remarkable illustration of economy of time. As a contribution to insect psychology, it will be long before this book finds a parallel."--_London Athenæum._ =DISEASES OF MEMORY=: An Essay in the Positive Psychology. By TH. RIBOT, author of "Heredity," etc. Translated from the French by William Huntington Smith. 12mo, cloth, $1.50. "M. Ribot reduces diseases of memory to law, and his treatise is of extraordinary interest."--_Philadelphia Press._ "Not merely to scientific, but to all thinking men, this volume will prove intensely interesting."--_New York Observer._ "M. Ribot has bestowed the most painstaking attention upon his theme, and numerous examples of the conditions considered greatly increase the value and interest of the volume."--_Philadelphia North American._ "To the general reader the work is made entertaining by many illustrations connected with such names as Linnæus, Newton, Sir Walter Scott, Horace Vernet, Gustave Doré, and many others."--_Harrisburg Telegraph._ "The whole subject is presented with a Frenchman's vivacity of style."--_Providence Journal._ "It is not too much to say that in no single work have so many curious cases been brought together and interpreted in a scientific manner."--_Boston Evening Traveller._ =MYTH AND SCIENCE.= By TITO VIGNOLI. 12mo, cloth, price, $1.50. "His book is ingenious; ... his theory of how science gradually differentiated from and conquered myth is extremely well wrought out, and is probably in essentials correct."--_Saturday Review._ "The book is a strong one, and far more interesting to the general reader than its title would indicate. The learning, the acuteness, the strong reasoning power, and the scientific spirit of the author, command admiration."--_New York Christian Advocate._ "An attempt made, with much ability and no small measure of success, to trace the origin and development of the myth. The author has pursued his inquiry with much patience and ingenuity, and has produced a very readable and luminous treatise."--_Philadelphia North American._ "It is a curious if not startling contribution both to psychology and to the early history of man's development."--_New York World._ =MAN BEFORE METALS.= By N. JOLY, Professor at the Science Faculty of Toulouse; Correspondent of the Institute. With 148 Illustrations, 12mo. Cloth, $1.75. "The discussion of man's origin and early history, by Professor De Quatrefages, formed one of the most useful volumes in the 'International Scientific Series,' and the same collection is now further enriched by a popular treatise on paleontology, by M. N. Joly, Professor in the University of Toulouse. The title of the book, 'Man before Metals,' indicates the limitations of the writer's theme. His object is to bring together the numerous proofs, collected by modern research, of the great age of the human race, and to show us what man was, in respect of customs, industries, and moral or religious ideas, before the use of metals was known to him."--_New York Sun._ "An interesting, not to say fascinating volume."--_New York Churchman._ =ANIMAL INTELLIGENCE.= By GEORGE J. ROMANES, F. R. S., Zoölogical Secretary of the Linnæan Society, etc. 12mo. Cloth, $1.75. "My object in the work as a whole is twofold: First, I have thought it desirable that there should be something resembling a text-book of the facts of Comparative Psychology, to which men of science, and also metaphysicians, may turn whenever they have occasion to acquaint themselves with the particular level of intelligence to which this or that species of animal attains. My second and much more important object is that of considering the facts of animal intelligence in their relation to the theory of descent."--_From the Preface._ "Unless we are greatly mistaken, Mr. Romanes's work will take its place as one of the most attractive volumes of the 'International Scientific Series.' Some persons may, indeed, be disposed to say that it is too attractive, that it feeds the popular taste for the curious and marvelous without supplying any commensurate discipline in exact scientific reflection; but the author has, we think, fully justified himself in his modest preface. The result is the appearance of a collection of facts which will be a real boon to the student of Comparative Psychology for this is the first attempt to present systematically well-assured observations on the mental life of animals."--_Saturday Review._ "The author believes himself, not without ample cause, to have completely bridged the supposed gap between instinct and reason by the authentic proofs here marshaled of remarkable intelligence in some of the higher animals. It is the seemingly conclusive evidence of reasoning; powers furnished by the adaptation of means to ends in cases which can not be explained on the theory of inherited aptitude or habit."--_New York Sun._ =THE SCIENCE OF POLITICS.= By SHELDON AMOS, M. A., author of "The Science of Law," etc. 12mo. Cloth, $1.75. "To the political student and the practical statesman it ought to be of great value."--_New York Herald._ "The author traces the subject from Plato and Aristotle in Greece, and Cicero in Rome, to the modern schools in the English field, not slighting the teachings of the American Revolution or the lessons of the French Revolution of 1793. Forms of government, political terms, the relation of law, written and unwritten, to the subject, a codification from Justinian to Napoleon in France and Field in America, are treated as parts of the subject in hand. Necessarily the subjects of executive and legislative authority, police, liquor, and land laws are considered, and the question ever growing in importance in all countries, the relations of corporations to the state."--_New York Observer._ =THE FUNDAMENTAL CONCEPTS OF MODERN PHILOSOPHIC THOUGHT, CRITICALLY AND HISTORICALLY CONSIDERED.= By RUDOLPH EUCKEN, Ph. D., Professor in Jena. With an Introduction by NOAH PORTER, President of Yale College. One vol., 12mo, 304 pages. Cloth. Price, $1.75. President Porter declares of this work that "there are few books within his knowledge which are better fitted to aid the student who wishes to acquaint himself with the course of modern speculation and scientific thinking, and to form an intelligent estimate of most of the current theories." =MIND IN THE LOWER ANIMALS IN HEALTH AND DISEASE.= By W. LAUDER LINDSAY, M. D., F. R. S. E., etc. 2 vols., 8vo. Cloth, $4.00. "The author of this work, which, regarded merely as an accumulation of verified and classified facts, is a unique and precious contribution to the data of comparative psychology, claims that he entered on his inquiry without any theory to defend, support, or illustrate. We are bound to say that, while his general conclusions are boldly and continually avowed, his claim of fairness and caution is justified by his method of examining particular phenomena; that he seems willing at all times to renounce any impression or belief which is shown to be scientifically untenable."--_New York Sun._ "In this work--two volumes of over 500 pages--Dr. Lindsay marshals a proportionately large number of facts against those philosophers who maintain that the intelligence of man differs in kind and not simply in degree from that of the lower animals. It is one purpose of his book to show that the main differences between man and the lower animals exist rather in their physical than in their mental structure. In this way of thinking, all animals possess not the semblance of, but the true substance of mind and will."--_New York World._ "So far as we are aware there has been no treatise upon the subject of animal intelligence so broad in its foundations, so well considered, or so scientific in its methods of inquiry, as that which has been prepared by Dr. W. Lauder Lindsay in two large volumes, the first being devoted to a study of animal mind in health, and the second to animal mind in disease. We may safely say that his work is, in some respects, the most important essay of the kind that has yet been undertaken. His observations have been supplemented by a thorough mastery of the history and literature of the subject, and hence his conclusions rest upon the broadest possible foundation of safe induction. There is a good analytical index to the book, as there ought to be to every work of the kind."--_New York Evening Post._ =THE ELEMENTARY PRINCIPLES OF SCIENTIFIC AGRICULTURE.= By N. T. LUPTON, LL. D., Professor of Chemistry in Vanderbilt University, Nashville, Tenn. 18mo. Cloth. Price, 45 cents. =A GLOSSARY OF BIOLOGICAL, ANATOMICAL, AND PHYSIOLOGICAL TERMS.= By THOMAS DUNMAN. Small 8vo. Cloth. 161 pages. Price, $1.00. "It has been the author's task to furnish here a small and convenient but very complete glossary of those terms; and he has done this so well, both in his choice of terms for definition and in his clear exposition of their etymological and technical meaning, as to leave nothing to be desired in this direction."--_New York Evening Post._ _For sale by all booksellers, or any work sent by mail, post-paid, on receipt of price._ D. APPLETON & CO., Publishers, 1, 3, & 5 Bond Street, New York. SCIENTIFIC LECTURES AND ESSAYS. =Popular Lectures on Scientific Subjects.= By H. HELMHOLTZ, Professor of Physics in the University of Berlin. First Series. Translated by E. ATKINSON, Ph. D., F. C. S. With an Introduction by Professor TYNDALL. With 51 Illustrations. 12mo. Cloth, $2.00. _CONTENTS._--On the Relation of Natural Science to Science in General.--On Goethe's Scientific Researches.--On the Physiological Causes of Harmony in Music--Ice and Glaciers.--Interaction of the Natural Forces.--The Recent Progress of the Theory of Vision.--The Conservation of Force.--Aim and Progress of Physical Science. =Popular Lectures on Scientific Subjects.= By H. HELMHOLTZ. Second Series. 12mo. Cloth, $1.50. _CONTENTS._--Gustav Magnus.--In Memoriam.--The Origin and Significance of Geometrical Axioms.--Relation of Optics to Painting.--Origin of the Planetary System.--On Thought in Medicine.--Academic Freedom in German Universities. "Professor Helmholtz's second series of 'Popular Lectures on Scientific Subjects' forms a volume of singular interest and value. He who anticipates a dry record of facts or a sequence of immature generalization will find himself happily mistaken. In style and method these discourses are models of excellence, and, since they come from a man whose learning and authority are beyond dispute, they may be accepted as presenting the conclusions of the best thought of the times in scientific fields."--_Boston Traveler._ =Science and Culture, and other Essays.= By Professor T. H. HUXLEY, F. R. S. 12mo. Cloth, $1.50. "Of the essays that have been collected by Professor Huxley in this volume, the first four deal with some aspect of education. Most of the remainder are expositions of the results of biological research, and, at the same time, illustrations of the history of scientific ideas. Some of these are among the most interesting of Professor Huxley's contributions to the literature of science."--_London Academy._ "It is refreshing to be brought into converse with one of the most vigorous and acute thinkers of our time, who has the power of putting his thoughts into language so clear and forcible."--_London Spectator._ =Scientific Culture, and other Essays.= By JOSIAH PARSONS COOKE, Professor of Chemistry and Mineralogy in Harvard College. 12mo. Cloth, $1.00. These essays are an outcome of a somewhat large experience in teaching physical science to college students. Cambridge, Massachusetts, early set the example of making the student's own observations in the laboratory or cabinet the basis of all teaching, either in experimental or natural history science; and this example has been generally followed. "But in most centers of education," writes Professor Cooke, "the old traditions so far survive that the great end of scientific culture is lost in attempting to conform even laboratory instruction to the old academic methods of recitations and examinations. To point out this error, and to claim for science-teaching its appropriate methods, was one object of writing these essays." _For sale by all booksellers; or sent by mail, post-paid, on receipt of price._ New York: D. APPLETON & CO., 1, 3, & 5 Bond Street.