IRLF 
 
 ELECTRIC 
 
 PAGET HIGGS. LL.D. 
 
GIFT OF 
 
ELECTRIC TRANSMISSION OF POWER. 
 
ELECTRIC TRANSMISSION OF POWER 
 
 ITS PRESENT POSITION AND 
 ADVANTAGES. 
 
 BY PAGET HIGGS, LL.D., D.Sc., 
 
 TELFOKD PRIZEMAN AND ASSOCIATE OF THE INSTITUTION OF CIVIL 
 
 ENGINEERS ; 
 
 AUTHOR OF ' THE ELECTRIC LIGHT IN ITS PRACTICAL APPLICATIONS,' ' ELECTRIC 
 LIGHTING,' ' ELECTRICAL FORMULA ' (MOLESWORTH), ETC. 
 
 LONDON : 
 
 E. & F. N. SPON, 46, CHAEING CEOSS. 
 
 NEW YOEK: 446, BEOOME STEEET. 
 
 1879. 
 
 J, C. Cebrian, 
 
PEEFACE. 
 
 IT is needless to dwell upon the benefits of economical 
 transmission of power. Where distance is involved, none 
 of the existing systems are so nearly perfect as to leave 
 no room for fresh trials ; on the contrary, all kinds of 
 manufactures and trades are alive to a simple means of 
 transmitting power. 
 
 Extensive experience with dynamo-electric machines 
 and their various uses has shown me that electric trans- 
 mission has before it a very wide field. For this reason, 
 I have collected into the following pages the most re- 
 liable data on this subject, and have added some experi- 
 mental results from my own working. I hope I have 
 furnished to the inquirer that information which will 
 enable him to form his own opinion. It may be well to 
 point out that I do not propose a system of my own nor 
 advocate specially. 
 
 First describing the machines employed, their relative 
 merits and demerits, there is next considered the me- 
 chanical ratio of the efficiency of this method of trans- 
 mission, and its applicability either to short or long 
 
 249962 
 
VI PREFACE. 
 
 distances. Some objections that have been advanced are 
 met, and in conclusion are given some of the most 
 definite advantages of employing electricity. 
 
 I hope that the desire to afford information upon a 
 comparatively novel subject may be taken in palliation of 
 shortcomings in style and arrangement. 
 
 PAGET HIGGS. 
 
CONTENTS. 
 
 CHAPTER I. 
 
 PAGE 
 
 DYNAMO-ELECTRIC MACHINES 1 
 
 CHAPTER II. 
 THE GRAMME MACHINE 
 
 CHAPTER III. 
 THE BRUSH MACHINE 11 
 
 CHAPTER IV. 
 
 THE WALLACE-FARMER AND SIEMENS MACHINES 19 
 
 CHAPTER V. 
 
 EFFICIENCY OP DYNAMO-ELECTRIC MACHINES 24 
 
 CHAPTER VI. 
 
 PRACTICABILITY OF TRANSMISSION OF POWER BY ELECTRICITY . 34 
 
yiii CONTENTS. 
 
 CHAPTER VII. 
 
 PAGE 
 
 EFFICIENCY OF COUPLED MACHINES 47 
 
 CHAPTER VIII. 
 
 COMPARATIVE EFFICIENCY or VARIOUS MACHINES 59 
 
 CHAPTER IX. 
 
 OTHER THEORETICAL CONSIDERATIONS 78 
 
 CHAPTER X. 
 
 CONCLUSIONS 85 
 
ELECTEIC TRANSMISSION OF POWER. 
 
 CHAPTER I. 
 
 DYNAMO-ELECTRIC MACHINES. 
 
 WITHOUT the invention of the dynamo-electric machine, 
 transmission of power by electricity could never have 
 become an accomplished fact. But the growth of elec- 
 trical invention has been so rapid that it may be de- 
 sirable to indicate what is meant by a dynamo-electric 
 machine, and advisable briefly to review this branch of 
 electricity. 
 
 The principles of magneto-electricity were elucidated 
 by Faraday, who found that when a bar of iron is sur- 
 rounded by a coil or helix of wire and a magnet is 
 approached to or drawn from the bar, a current of elec- 
 tricity is induced in the coil. Further, he found that when 
 one pole of the magnet was approached to the bar, the 
 electrical current had a direction opposite to that electrical 
 current produced when the magnet was receded from, the 
 bar : also that the opposite poles of the magnet had 
 opposite actions, or, in other words, produced by the same 
 movement currents of opposite directions. His researches 
 proved that the soft iron and the magnet might change 
 places, and that, generally, electric currents were produced 
 in a coil placed in a magnetic field, either by changes of 
 intensity of this magnetic field, or by the coil being made 
 to cut through magnetic rays of different intensities. 
 
2 ; ELECTRIC TRANSMISSION OF POWER, 
 
 The practical application of this important addition to 
 electrical knowledge soon appeared in the first magneto- 
 electric machine, constructed in 1833, by Pixii. In this 
 machine a horse-shoe magnet was caused to revolve with 
 its poles before those of a double electro-magnet. This 
 machine had the mechanical disadvantage that the heavier 
 part, the permanent magnet, was put in motion. Clarke 
 improved upon this construction in machines of small 
 dimensions, the magnets in which were fixed, and the coil 
 caused to rotate. Machines virtually on the principle 
 of Clarke's machine, but of larger size, were soon con- 
 structed by Holmes, of London, and the Compagnie 
 1'Alliance, of Paris. All these machines may be classed 
 as magneto-electric, that is to say, the current produced 
 depends upon the action of magnets upon an electrical 
 circuit. 
 
 Magneto-electric machines are quite distinct from 
 electro-magnetic machines, in which the electrical current 
 is made to produce movement, being itself generated by 
 a source foreign to the motor. 
 
 Magneto-electric machines are disadvantageous in use, 
 because their effect does not increase with their dimensions, 
 and machines for the production of powerful currents 
 become cumbersome and costly. The rapid rotation, and 
 consequently rapid reversals of magnetism of the iron 
 core, give rise to great heating of the working parts, and 
 to the necessity of cooling these with water. The step 
 from magneto-electric to dynamo-electric machines was 
 due to Mr. S. Alfred Varley, Sir Charles Wheatstone, and 
 Dr. Werner Siemens, who quite independently discovered 
 and worked upon the same principle of accumulation by 
 mutual action, the priority falling to Mr. Varley by his 
 patent. In this construction of machine, induced currents 
 are caused to circulate in the electro-magnet coils that 
 produce them, and are in this way increased. By this 
 mutual action currents are produced, the limit of intensity 
 
DYNAMO-ELECTRIC MACHINES. 6 
 
 of which is co-equal with the maximum limit of magnetic 
 saturation. 
 
 This principle of accumulation by mutual action is now 
 employed in all machines where currents of great intensity 
 are required. 
 
 As all these machines can be made to yield electricity, 
 through rotation imparted to them by the expenditure of 
 mechanical power, so can this power be reclaimed, in part, 
 by causing the current generated by one machine to be 
 passed into the coils of a second machine. This second 
 machine will then rotate in an opposite direction, about 
 50 per cent, of the mechanical power expended upon 
 the pulley of the first machine being obtainable from 
 the pulley of the second. This is the basis of electrical 
 transmission of power. 
 
 B 2 
 
ELECTRIC TRANSMISSION OF FOWEK. 
 
 CHAPTEE II. 
 
 THE GRAMME MACHINE. 
 
 THE machine invented by M. Gramme is essentially the 
 parent of present dynamo-electric machines. To compre- 
 hend the principle of the Gramme machine, let Fig. 1 
 
 FIG. 1. 
 
 represent a magnetised bar, A B, and a conducting helix, 
 capable of moving to and fro on the bar. If the helix is 
 brought towards the bar from its position at X, an 
 induced current is produced at each movement. These 
 currents are in the same direction while the helix passes 
 the middle, M, of the bar, A B, until it leaves the opposite 
 pole, B. Thus, in the entire course of the helix on to and 
 from the magnet, two distinct periods are to be distin- 
 guished : in the first half of the movement the currents 
 are direct, and in the second they are inverted. If, instead 
 of moving from left to right, as we have supposed, the 
 movement is from right to left, everything occurs as 
 before, with the exception that the currents are opposite. 
 Let two magnets, A B, and B' A' (Fig. 2), be placed end 
 to end, in contact by poles of the same name, B B'. The 
 whole forms a single magnet with a consequent point at 
 
THE GRAMME MACHINE. 5 
 
 the centre. If the helix is moved with relation to this 
 system, it is traversed by a positive current during the 
 first movement, between A and B ; by a negative current 
 
 FIG 2. 
 
 FIG. 3. 
 
 in the second, from B to B' ; again by a negative current 
 in the third, from B' to A'; and finally by a positive 
 current, when leaving A'. 
 
 Eeplacing the straight magnets by two semi-circular 
 magnets (Fig. 3), put end to end, the poles of the same 
 name together, there occur 
 the two poles, A A', B B', 
 and the results are the 
 same as in the preceding, 
 MM' being the two neutral 
 points. 
 
 The essential part of the 
 Gramme machine is a soft- 
 iron ring, furnished with 
 an insulated copper helix 
 wound on the whole length 
 of the iron. The extre- 
 mities of this helix are 
 soldered together, so as to 
 form a continuous wire without issuing or re-entrant end. 
 If the wire is denuded exteriorly, the part bared forms 
 a straight band running round the whole of the circum- 
 ference Friction-pieces, M and M', are applied to the 
 bared part of the helix. When the ring is placed before 
 the poles, S and N, of a magnet, the soft iron is magnetised 
 
6 ELECTRIC TRANSMISSION OF POWER. 
 
 by induction, and there occur in the ring two poles, 
 N' and S', opposed to the poles S and N. If the ring 
 revolves between the poles of a permanent magnet, the 
 induced poles developed in the ring always remain in the 
 same relation with regard to the poles N and S, and are 
 subject to displacement in the iron itself with a velocity 
 equal, and of contrary direction, to that of the ring. 
 Whatever may be the rapidity of the movement, the poles 
 N' S' remain fixed, and each part of the copper helix 
 Successively will pass before them. 
 
 An element of this helix will be the locale of a current 
 
 FIG. 4. 
 
 of a certain direction when traversing the path M S M' 
 (Fig 4), and of a current of inverse direction to the first 
 when passing through the path M' N M. And, as all the 
 elements of the helix possess the same property, all parts 
 of the helix above the line M M' will be traversed by cur- 
 rents of the same direction, and all parts beneath the line 
 by a current of inverse direction to the preceding. 
 
 These two currents are evidently equal and opposite, 
 and balance one another. When two voltaic batteries, 
 composed of the same number of elements, are coupled in 
 opposition, it is necessary only to put the extremities of a 
 circuit in communication with the poles common to the 
 
THE GRAMME MACHINE. 7 
 
 two batteries, and the currents become associated in 
 quantity. 
 
 M. Gramme collects the currents developed in the ring 
 of his machine by establishing collectors on the line M M', 
 where the currents in contrary direction encounter each 
 other. 
 
 In practice, Gramme does not denude the wire of the 
 ring. Fig. 5 shows the wire and coils. One or two coils 
 
 B 
 
 (B) are shown in position, and with the iron ring laid 
 bare, and cut. 
 
 Insulated radial pieces, E, are each attached to the 
 issuing end of a coil, and to the entrant end of the follow- 
 ing coil. The currents are collected on the pieces, E, as 
 they would be on the denuded wire. Their bent parts, 
 brought parallel to the axle, are carried through and 
 beyond the interior of the ring, and are brought near 
 one another upon a cylinder of small diameter. The 
 friction-brushes on the pieces are in a plane perpendicular 
 to the polar line S and N that is, at the middle or 
 neutral points M and M'. The intensity of the current 
 
8 
 
 ELECTEIC TRANSMISSION OF POWER. 
 
 increases with, the velocity of rotation ; the electro-motive 
 force is proportional to the velocity. Gramme modifies 
 his machine so as to produce effects of tension or of 
 
 quantity, by winding the ring with fine or coarse wire. 
 With equal velocities of the ring the electric tension will 
 be' proportional to the number of convolutions of the wire. 
 
THE GRAMME MACHINE. 
 
 9 
 
 Figs. 6 and 7 represent a Gramme machine ; it consists 
 of two flanks of cast iron, arranged vertically, and con- 
 nected by four iron bars, serving as cores to electro- 
 magnets. The axle is of steel ; its bearings are relatively 
 very long. The central ring has two wires wound parallel 
 
 FIG. 7. 
 
 on the soft iron, and connected to two collectors to re- 
 ceive the currents. The poles of the electro-magnet are 
 of large size, and embrace seven-eighths of the total cir- 
 cumference of the central ring. Four brushes collect the 
 currents produced. The electro-magnet is placed in the 
 circuit. The total length of the machine, pulley included, 
 
10 ELECTRIC TRANSMISSION OP POWER. 
 
 is 31 J inches, its width. 1 foot 9J inches, and its height 
 23 inches. Its weight is 880 Ibs. 
 
 The double coil is connected to 120 conductors, 60 on 
 each side. Its exterior diameter is 27 inches ; the weight 
 of wire wound on is 31 Ibs. The electro-magnet bars have 
 a diameter of 2J inches, and a length of 15 1 inches. The 
 total weight of wire wound on the four bars is 211 Ibs. 
 The winding of the wires on the ring is effected as if two 
 complete bobbins were put one beside the other, and 
 these two bobbins may be connected in tension or in 
 quantity. 
 
THE BKUSH MACHINE. 
 
 11 
 
 CHAPTER III. 
 
 THE BRUSH MACHINE. 
 
 MR. BRUSH, the inventor of the machine bearing his name, 
 considers that even the best forms of magneto-electric 
 apparatus are unnecessarily bulky, heavy, and expensive, 
 and are more or less wasteful of mechanical power. The 
 armature of the Brush machine (Figs. 8 to 11) is of 
 
 FJG. 8. 
 
 iron, in the form of a ring, and is attached to a hub, 
 which is rigidly attached to the shaft C (Fig. 8). The 
 armature, instead of having a uniform cross section, as in 
 the Gramme machine, is provided with grooves, or depres- 
 sions, in a direction at right angles with its magnetic 
 
12 ELECTRIC TRANSMISSION OF POWER. 
 
 axis or length. These grooves are wound full of insulated 
 copper wire, and are of any suitable number. The advan- 
 tage of winding the wire on the armature depressions is 
 twofold. The projecting portion of the armature between 
 the sections of wire may be made to revolve very close to 
 the poles N N and S S of the magnets, from which the 
 magnetic force is derived, thus utilising the inductive 
 force of the latter to a much greater extent than is possible 
 in the case of annular armatures entirely covered with 
 wire, which therefore cannot be brought very near the 
 magnets. Owing to the exposure of a very considerable 
 portion of the armature to the atmosphere, the heat, which 
 is always developed by the rapidly succeeding magnetisa- 
 tions and demagnetisations of armatures in motion, is 
 rapidly dissipated by radiation and convection. In the 
 case of armatures completely covered with wire, the 
 escape of heat is very slow, so that they must be run at a 
 comparatively low rate of speed, with corresponding effect, 
 in order to prevent injurious heating. Opposite sections 
 on the armature may have their first or their last ends 
 joined together, and their remaining ends connected with 
 two segments of metal of the commutator cylinder E, 
 which is carried by the shaft C, and is of insulating 
 material (Fig. 9). 
 
 The two metal segments 
 are placed opposite each 
 other on the cylinder, 
 and are each of a length 
 less than half the cir- 
 cumference of the latter, 
 thus exposing the in- 
 sulating cylinder in 
 two places diametrically 
 opposite each other and 
 alternating with the 
 metal segments. The two segments, say S 3 and S 7 , cor- 
 
THE BRUSH MACHINE. 13 
 
 responding to sections 3 and 7 of wire, hold a position 
 on the cylinder in advance of those of the preceding 
 sections S 2 and S 6 to the same angular extent that the 
 sections 3 and 7 in question are in advance of sections 
 2 and 6. In this arrangement the number of segments 
 is equal to the number of sections, each segment being 
 connected with but one section. The first and last ends 
 of each section can, however, be attached to two opposite 
 segments, the commutator cylinder, in that case, being 
 constructed with double the number of segments as in 
 the former case, thus making the number of segments 
 double the number of sections. Two metallic plates 
 or brushes, insulated from each other, press lightly upon 
 the cylinder E at opposite points, so selected that while 
 each section of wire on the armature is passing from 
 one neutral point to the other, the corresponding seg- 
 ments on the cylinder will be in contact with them. 
 These plates or brushes collect the currents of electricity 
 generated by the revolution of the armature, one being 
 positive and the other negative. When the section 
 of wire is .passing the neutral points on the arma- 
 ture, the plates are in contact with the insulating 
 material of the cylinder between the corresponding seg- 
 ments, thus cutting the section, which is at the time 
 useless, out of the circuit altogether. The necessity for 
 thus insulating each section from the plates during the 
 time it is inactive becomes obvious when it is considered 
 that, if this were not done, the idle section would afford 
 a passage for the current generated in the active sections. 
 During the time a section or bobbin is passing from one 
 neutral point of the armature to the next one, an electric 
 impulse, constant in direction, but varying in electro- 
 motive force, is induced in it. This electro-motive force, 
 starting from nothing at the neutral point, quickly in- 
 creases to nearly its maximum, and remains almost con- 
 stant until the section is near the next neutral point, 
 
14 ELECTRIC TRANSMISSION OF POWER. 
 
 when it rapidly falls to zero as the neutral point is 
 reached. 
 
 The insulating spaces are made of such a length that a 
 section or bobbin is cut out of the circuit, not only when 
 it is at the neutral points, but also during the time when 
 its electro-motive force is rising and falling at the 
 beginning and end of an impulse. 
 
 If the insulating space is too short, so as to keep or 
 bring a section in the circuit, while its electro-motive 
 force is low, then the current from the other sections, 
 being of superior electro-motive force, will overcome this 
 weak current and discharge through this section. If the 
 insulating spaces are a little longer than necessary, no 
 material inconvenience results. A suitable length for 
 practical purposes is easily determined experimentally. 
 It is found in practice that the neutral points of the 
 armature in motion are considerably in advance of their 
 theoretical position, this circumstance being attributed to 
 the time required to saturate any point of the armature 
 with magnetism, so that the given point is carried beyond 
 the point of greatest magnetic intensity of the field before 
 receiving its maximum charge. M. Gramme however be- 
 lieves it due to the reaction, by induction, of the armature 
 coils upon the cores and coils of the electro-magnet. 
 
 It is necessary to adjust the commutator cylinder on 
 the revolving shaft of the machine with special reference 
 to the neutral points of the armature when in motion, 
 in order that its insulating space may correspond with 
 the neutral points. This adjustment is made experi- 
 mentally as follows : The commutator cylinder having been 
 placed approximately in its proper position, the machine 
 is started, and the presence or absence of sparks at the 
 points of contact between the plates and commutator 
 cylinder is noted. If sparks occur, the commutator 
 cylinder is turned slightly forward or backward on its 
 axis, until the sparks disappear. 
 
THE BRUSH MACHINE. 15 
 
 The presence of sparks when the commutator is even 
 slightly out of its proper position is easily explained. 
 If a break between a pair of segments and the plates oc- 
 curs while the corresponding section of wire on the arma- 
 ture is still active, a spark is produced by the interruption 
 of the current, while if the break occurs too late the 
 section in question will have become neutral, and then 
 commenced to conduct the current from the active sec- 
 tions, and the interruption of this passage causes a spark in 
 this instance. If the commutator is much removed from 
 its proper position in either direction, the sparks are so 
 great as to very rapidly destroy both the commutator 
 and the brushes, while the current from the machine is 
 correspondingly diminished. 
 
 With the arrangement, where the first and last ends of 
 each of two opposite sections are attached to two opposite 
 segments the intensity of the induced electrical current 
 will be that due to the length of wire in a single section 
 only, while the quantity will be directly as the number 
 of sections. By doubling the size of each bobbin, and 
 diminishing their number one half, a current of double 
 the intensity and one half the quantity of the former will 
 be obtained. This effect, however, can be secured in 
 another manner, by connecting the first and last ends of 
 the two opposite sections together, and joining the re- 
 maining ends only to two opposite segments, as illustrated 
 in Fig. 10. This arrange- 
 ment is found most con- FlG * "' 
 venient in practice. 
 
 The arrangement of the 
 
 cylinder E with segments / i / T V-\- \{ZTff ~~7^\ 
 S (Fig. 9) is usually re- (( ( / j/-~fel^ ( ) 
 placed by another, in 
 which the last end of one 
 section and the first end 
 of the succeeding may be connected with a strip of metal 
 
16 ELECTRIC TRANSMISSION OF POWER. 
 
 attached to the cylinder, parallel with its axis, as in the 
 Siemens and Gramme machines. These metallic strips or 
 conductors are equal in number to the sections of wire on the 
 armature, and are insulated from each other. The plates 
 press upon the cylinder, in this case, at points correspond- 
 ing to the neutral points of the armature, thus being at 
 right angles with their position in the first arrangement. 
 This plan, which is the one commonly used with annular 
 armatures, gives fair results, but is subject to a serious 
 disadvantage from which the first is free. The difficulty 
 is, that the sections of wire, when at or near the neutral 
 points of the armature, contribute little or no useful effect, 
 but the current from the other sections must pass through 
 these in order to reach the plates, thus experiencing a 
 considerable and entirely useless resistance ; and, owing to 
 the opposite directions of the currents through the active 
 sections on opposite sides of the neutral points, these cur- 
 rents, by passing through the idle sections, tend strongly 
 to produce "consequent" points in the armature where the 
 neutral points should be, thus interfering seriously with 
 the theoretical distribution of the magnetism of the 
 armature. The electro-magnets H are excited by the 
 whole or a portion of the electric current derived from 
 the revolving armature, as is usual in apparatus of this 
 kind, the novel feature of this part of the machine con- 
 sisting of the manner in which the magnetic poles are 
 presented to the armature ; this arrangement is such that 
 a very large proportion of the entire surface of the arma- 
 ture is constantly presented to the poles of the magnets, 
 thus securing uniformity of magnetisation, as well as 
 maximum amount. The iron segments, constituting the 
 poles of the magnets, are arranged on both sides of the 
 armature. The pieces N N, or S S, may be connected at 
 their outer edges, thus forming one piece, and enclosing 
 the armature still more. In the other dynamo-electric 
 machines no magnetic field is maintained when the ex- 
 
THE BKUSH MACHINE. 
 
 17 
 
 ternal circuit is opened, except that due to residual mag- 
 netism; hence the electro-motive force developed by 
 the machine in this condition is very feeble. It is only 
 when the external circuit is closed through a resistance 
 
 \\ 
 
 not too large that powerful currents are developed, owing 
 to the strong magnetic field produced by the circulation 
 of the currents themselves around the field magnets. 
 By diverting from external work a portion of the 
 
 c 
 
18 ELECTEIC TRANSMISSION OF POWER. 
 
 current of the machine, and using it either alone, or in 
 connection with the rest of the current for working the 
 field magnets, a permanent field may be obtained. 
 
 Mr. Brush winds the cores of the field magnets with a 
 quantity of a comparatively fine wire, having a high 
 resistance in comparison with that of the external circuit, 
 and the rest of the wire in the machine. The ends of 
 this wire are so connected with other parts of the machine 
 that when the latter is running, a current of electricity 
 constantly circulates in the wire, whether the external 
 circuit be closed or not. The high resistance of -this wire 
 prevents the passage through it of more than a small 
 proportion of the whole current capable of being evolved 
 by the machine ; therefore the available external current 
 is not materially lessened. When this device, called a 
 " teaser," is used in connection with field magnets, also 
 wound with coarse wire (Fig. 11), for the purpose of still 
 further increasing the magnetic field by employing the 
 main current for this purpose, then the "teaser" may be 
 so arranged that the current which passes through it will 
 also circulate in the coarse wire, thus increasing efficiency 
 
THE WALLACE-FARMER AND SIEMENS MACHINES. 19 
 
 CHAPTER IV. 
 
 THE WALLACE-FARMER AND SIEMENS MACHINES. 
 
 IN the Wallace-Farmer machine (Fig. 12) the magnetic 
 field is produced by two horse-shoe electro-magnets, but 
 with poles of opposite character facing each other. 
 
 FIG. 12. 
 
 Between the arms of the magnets, and passing through 
 the uprights supporting them, is the shaft, carrying at its 
 centre the rotating armature. This consists of a disc of 
 cast iron, near the periphery of which, and at right angles 
 to either face, are iron cores, wound with insulated wire, 
 thus constituting a double series of coils. The armature 
 
 c2 
 
20 
 
 ELECTRIC TRANSMISSION OF POWER. 
 
 coils (Figs. 13 and 14) being connected end to end, the 
 loops so formed are connected in the same manner, and 
 to a commutator of the same construction as that of the 
 Gramme. As the armature rotates, the cores pass between 
 the opposed north and south poles of the field magnets, 
 and the current generated depends on the change of 
 
 FIG. 13. 
 
 FIG. 14. 
 
 polarity of the cores. It will be seen that this constitutes 
 a double machine, each series of coils, with its commutator, 
 being capable of use independently of the other ; but in 
 practice the electrical connections are so made that the 
 currents generated in the two series of armature coils pass 
 through the field magnet coils, and are joined in one 
 external circuit. 
 
 This form of armature also presents considerable un- 
 covered surface of iron to the cooling effect of the air, but, 
 like that of the Brush, presents considerable resistance to 
 rotation. 
 
 In the Wallace-Farmer machine there is considerable 
 heating of the armature, the temperature being sometimes 
 sufficiently high to melt sealing-wax. 
 
 In the Siemens machine, the conductor of insulated 
 copper wire is coiled in several lengths and convolutions 
 
THE WALLACE-FARMER AND SIEMENS MACHINES. 21 
 
 upon a cylinder shown in transverse (Fig. 15), and in end 
 view by Fig. 16. Each convolution is parallel to the 
 
 FIG. 15. 
 
 longitudinal axis of the cylinder, and the whole surface of 
 the cylinder is covered with wire, laid on in six sections. 
 
 FIG. 16. 
 
 Surrounding the wire cylinder for about two-thirds of its 
 surface are curved iron bars, the space between these 
 
22 ELECTRIC TRANSMISSION OF POWER. 
 
 curved bars and the wire cylinder being as small as is 
 consistent with the free rotation of the cylinder. The 
 curved bars are themselves the prolongations of the cores 
 of large flat electro-magnets; the coils of these electro- 
 magnets and the wire of the cylinder (from brush to 
 brush) forms a continuous electrical circuit. Upon revo- 
 lution of the wire cylinder, which is supported upon a 
 longitudinal axis in proper bearings, the axis carrying a 
 pulley, a current is generated in it, and this current, 
 initially weak, is directed into the coils of the electro- 
 magnets, magnetising the cores, which induce a still 
 stronger current in the wire cylinder. This mutual 
 action continues until the magnetic limit of the iron is 
 attained. At every revolution of the wire cylinder, the 
 maximum magnetic power acting upon each convolution 
 is attained when the convolution passes through the 
 middle of both magnetic fields, and this power falls to 
 zero when the convolution is perpendicular to that 
 position. Each convolution is therefore subject to a 
 neutral position, and by Lenz's law a convolution starting 
 from that position on the one side of the axis towards the 
 north pole of the electro-magnet would be subject to a 
 direct induced current, and that portion of the convolution 
 on the opposite side of the axis will be traversed by a 
 current of opposite direction, as regards a given point, 
 but of the same direction as regards circuit. 
 
 Each of the six sections of wire coiled upon the cylinder 
 consists of two separate coils, the whole having twenty- 
 four ends ; two of these ends are brought to each of the 
 segments of a circular commutator in such a manner 
 that the whole six double sections form a continuous 
 circuit, but not one continuous helix. 
 
 In order that the segments may be properly presented 
 to the collecting brushes, the connections are arranged 
 according to their relative momentary position. The 
 electric currents are collected upon two wire brushes 
 
THE WALL ACE- FARMER AND SIEMENS MACHINES. 23 
 
 tangential to the segments of the commutator, and these 
 brushes form, through the electro-magnets, the two elec- 
 trodes of the machine ; and to the electro-magnet ends are 
 connected the conducting wires leading to the system 
 where the current is to be utilised. 
 
 The dimensions, weights, number of revolutions made 
 by the cylinder, and HP. required for driving, are for 
 three sizes of the machine, as under : 
 
 Dimension in laches. 
 
 Weight 
 in Ibs. 
 
 Revolutions 
 of 
 Cylinder. 
 
 HP. 
 
 Length. 
 
 Width. 
 
 Height. 
 
 25 
 
 21-0 
 
 8-8 
 
 298 
 
 1,100 
 
 U to 2 
 
 29 
 
 26-0 
 
 9-5 
 
 419 
 
 850 
 
 3 3^ 
 
 44 
 
 28-3 
 
 12-6 
 
 1,279 
 
 480 
 
 9 10 
 
24 ELECTKIC TRANSMISSION OF POWER. 
 
 CHAPTER V. 
 
 EFFICIENCY OF DYNAMO-ELECTRIC MACHINES. 
 
 WHEN two machines are coupled in circuit for the trans- 
 mission of the power of a prime mover, we may consider 
 two causes of efficiency : (1) that of the first machine as a 
 current generator, and (2) that of the two machines con- 
 sidered together as a transmitting system. In a paper 
 read before the Institution of Mechanical Engineers, by 
 Dr. Hopkinson, it has been pointed out that it is desirable 
 to know what dynamo-electric machines can do with 
 varied and known resistances in the circuit and with 
 varied speeds of rotation ; and what amount of power is 
 absorbed in each case. 
 
 The mechanical energy communicated by the steam- 
 engine or other motor is not immediately converted into 
 the energy of heat, but is first converted into the energy 
 of an electric current in a conducting circuit. The whole 
 of what is needed to be known may be more easily ascer- 
 tained and expressed if the subject of inquiry is stated as : 
 what current a machine will produce under various con- 
 ditions of circuit ; and at what expenditure of mechanical 
 power. The subject has been treated more or less by 
 Edlund (Pogg. Annal., 1867 and 1868), Houston and 
 Thomson in America, Mascart ('Journal de Physique,' 
 March 1878), Trowbridge ('Philosophical Magazine,' 
 March 1879), Schwendler (' Eeport on Electric Light 
 Experiments '). Dr. Hopkinson limits his inquiry to an 
 account of some experiments on the production of currents 
 by a Siemens medium-sized machine, the machine which 
 
EFFICIENCY OF DYNAMO-ELECTKIC MACHINES. 25 
 
 is said to produce a light of 6000 candles, by an expendi- 
 ture of 3 HP. The intensity of the magnetic field in 
 such machines as the Siemens and ordinary Gramme 
 machines may be regarded as a function of the current 
 passing ; to learn what this function is for the machine in 
 question, we may construct a curve in which the abscissae 
 represent currents passing, and the ordinates the electro- 
 motive force for a given speed of rotation. But the power 
 of a current, that is its energy per second, is the product 
 of the electro-motive force and its intensity ; this is in all 
 cases less than the power required to drive the machine, 
 and the ratio between the two may fairly be called the 
 efliciency of the machine. Consider the case of a pump 
 forcing water through a pipe against friction ; then 
 electric current corresponds to the water passing per 
 second, and electro-motive force to the difference of 
 pressure on the two sides of the pump ; and just as the 
 product of pressure and volume per second is power, so 
 the product of electro-motive force and current is power ; 
 which is directly comparable with the power expended in 
 driving the machine or the pump, as the case may be. 
 The peculiarity of the so-called dynamo-electric machine 
 lies in this, that which corresponds to the difference of 
 pressure (the electro-motive force) depends directly on 
 what corresponds to the volume passed (the current). 
 Each experiment requires the determination of the speed, 
 the driving power, the resistances in oironit, and the 
 current passing. 
 
 In Dr. Hopkinson's measurements, the speed of the 
 steam engine was maintained very constant by means of a 
 governor specially arranged for great sensitiveness. The 
 speed was varied by means of a weight and a spring, 
 attached to a lever on the throttle-valve spindle. The 
 power was transmitted from the engine to a countershaft 
 by means of a strap, and by a second strap from the 
 countershaft to the pulley of the machine. On this second 
 
26 
 
 ELECTEIC TRANSMISSION OF POWER. 
 
 strap was the dynamometer (Fig. 17), arranged as used by 
 the Author, and described in a paper read before the 
 Institution of Civil Engineers, 1877-8. 
 
 The tension difference in the two parts of the strap 
 of the dynamometer and the velocity of rotation of 
 the machine being known, the power received was 
 
EFFICIENCY OF DYNAMO-ELECTRIC MACHINES. 27 
 
 obtained, expressed in gram-centimetres per second. 
 Multiplying by 981, the value of gravity in centimetres 
 and seconds, the power is then expressed in ergs * per 
 second, and is ready for comparison with the results of 
 the electrical experiments. 
 
 The dynamo-electric machine in these trials was a 
 Siemens medium size; the armature coil has fifty-six 
 divisions, and the brushes are single, not divided that 
 is, each brush is in connection with one segment of the 
 commutator at each instant. The leading wire was 100 
 yards of seven copper wires, insulated with tape and india- 
 rubber, and having a diameter of about 9'6 millimetres. 
 The current passing was ascertained by the heating of the 
 calorimeter, or by measuring the difference of potential at 
 the extremities of a resistance, all the resistances of the 
 circuit being known. The resistance coils comprised ten 
 coils of common brass wire, each wound round a couple of 
 wooden uprights driven into a baseboard common to the 
 set; each wire was about 60 metres long, and of No. 17 
 Birmingham wire-gauge, weighing about 14*6 grammes 
 per metre. Each terminal was connected to a cup of 
 mercury excavated in the baseboard, so that the coils 
 could be placed in series or in parallel circuit at pleasure. 
 The resistance of each coil being about 3 ohms, this set 
 could be arranged to give resistances varying from 3 to 
 30 ohms. 
 
 The calorimeter was a double copper vessel ; a resistance 
 coil of uncovered German-silver wire nearly 2 metres long, 
 1-5 millimetres in diameter, and having a resistance of about 
 i ohm, was suspended within it from an ebonite cover, 
 
 * The dyne is the force which will in one second impart to one 
 gramme a velocity of one centimetre per second, and an erg is the work 
 done by a dyne working through a centimetre ; a horse-power may be 
 taken as three-quarters of an ergten per second, an ergten being 
 10 10 ergs. See Keport of Brit. Assoc. 1873, and Everett, 'On the 
 Centimetre-Gramme Second System of Units.' 
 
28 ELECTKIC TRANSMISSION OF POWER. 
 
 which also carried a little brass stirrer ; and the calorimeter 
 was filled with water to the level determined by the mark 
 of a scriber. It was, of course, necessary to know the 
 capacity of the calorimeter for heat. It was filled with 
 warm water up to the mark, and the coil placed in posi- 
 tion; 120 grammes of water were then withdrawn, and 
 the temperature of the calorimeter was observed to be 
 58 8 centigrade ; after the lapse of one minute it was 
 58 3 centigrade ; after a second minute, 57 9 centigrade. 
 120 grammes of cold water, temperature 13* 3 centigrade, 
 were then suddenly introduced through a hole in the 
 ebonite cover, and it was found that two minutes after 
 the reading of 57*9 centigrade, the temperature was 
 50 centigrade ; hence it was inferred that the capacity 
 of the calorimeter is equal to that of 750 grammes of 
 water. The resistance coils were on the binary scale, 
 from -J- ohm to 1024 ohms. The battery was a single 
 element of Daniell's battery, in which the sulphate of 
 zinc solution floats on the sulphate of copper ; its electro- 
 motive force is assumed to be f volt. The resistances 
 added in the battery circuit are pencil lines on glass, 
 such as are described in the ' Philosophical Magazine,' 
 February, 1879. Preliminary to experiments on the cur- 
 rent, determinations of resistances were made. When 
 the ends of the cable were connected, the resistance was 
 found to be 0*129 ohm. The resistances in the machine 
 were found to be as follows, when cold : magnet coils, 
 0-156 and 0-152 respectively; armature coil, 0-324; 
 total, 0*632. Direct examination was made of the whole 
 machine in eight positions of the commutator, giving 
 643 ohm, with a maximum variation from the mean of 
 6 per cent. After running the machine for some time, 
 the resistance was found to be 683, an increase which 
 would be accounted for by a rise of temperature of 12 
 centigrade, or thereabouts. The resistance of the calori- 
 meter is 20, without its leading wire, which may bo 
 
EFFICIENCY OF DYNAMO-ELECTRIC MACHINES. 29 
 
 taken as 01. There were thus three leading resistances 
 which must "be considered: (1), the resistance of the 
 machine and leading wire, assumed throughout as 0'8l, 
 denoted by c^ (2), the resistance of the brass coils, C, 
 calculated from the several determinations, with the addi- 
 tion of the resistance of the leading wire, 0*02, and 
 denoted by c 2 ; (3), when present, the resistance of the 
 calorimeter and leading wire denoted by c 3 . 
 
 Two approximate corrections were employed, and 
 should be detailed. The first is the correction for the 
 considerable heating of the resistance coils c. These 
 were arranged in two sets of five each, five being in 
 parallel circuit, and two sets in series. The current from 
 the machine, being about 7 * 4 webers in each wire, was 
 passed for three or four minutes ; the circuit was then 
 broken, and the resistance c 2 was determined within one 
 second of breaking circuit, when it was found to be about 
 5 per cent, greater than when cold. As the resistance 
 was falling, the following was adopted as a rule of cor- 
 rection : square the current in a single wire, and increase 
 the resistance c 2 by T ^ per cent, for every unit in the 
 square. The second correction is due to the fact that 
 the calorimeter was losing heat all the time it was 
 being used. It was assumed that it loses 0*01 centigrade 
 per minute for every 1 centigrade, by which the tem- 
 perature of the calorimeter exceeds that of the air ; this 
 correction is, of course, based on the experiment already 
 mentioned. 
 
 The method of calculation may now be explained : 
 E is the total resistance of the circuit, equal to 
 
 c i 4- C 2 + C 3 ; 
 
 Q is the current passing in webers ; 
 E the electro-motive force round the circuit in volts ; 
 W x the work per second converted into heat in the 
 
 circuit, as determined by the galvanometer, 
 
 measured in ergtens per second ; 
 
30 ELECTRIC TRANSMISSION OF POWER. 
 
 W 2 is the work per second as determined by the calori- 
 
 meter ; 
 W 3 is the work per second as determined by the dyna- 
 
 mometer, less the power required to drive the 
 
 machine when the circuit is open. 
 II P is the equivalent of W 3 in HP. ; n is the number 
 
 of revolutions per minute of the armature. Then : 
 
 Q = 981 X X i, 
 
 T> 
 
 also W 2 = - multiplied by the mechanical equivalent of 
 
 the heat generated per second in the calorimeter. 
 
 The accompanying tables give the results of the ex- 
 periments. A power of 0-21 ergtens, or 0*28 HP., was 
 required to drive the machine at 720 revolutions on open 
 circuit. An examination of the table shows that the 
 efficiency of the machine is about 90 per cent, exclusive 
 of friction. Comparing experiments 11 and 13, and also 
 the last four experiments, it is seen that the electro-motive 
 force is proportional to the speed of rotation within the 
 errors of observation. Experiments 14, 15, and 16 were 
 intended to ascertain the effect of displacing the commu- 
 tator brushes. 
 
 The principal object of the experiments was to ascertain 
 how the electro-motive force depended on the current. 
 This relation is represented by a curve (Fig. 18) in which 
 the abscissae represent the currents flowing, or the values of 
 Q in the table, and the ordinates the electro-motive forces, 
 or the values of E reduced to a speed of 720 revolutions 
 per minute. The curve may also be taken to represent 
 the intensity of the magnetic field. There will be a point 
 of inflection in the curve near the origin. The experi- 
 ments 1 to 5 indicate that this is the true form of the 
 curve, and it is confirmed in a remarkable manner by a 
 
EFFICIENCY OF DYNAMO-ELECTRIC MACHINES. 31 
 
 special experiment. A resistance intermediate between 
 5J and 4 was used in circuit, and E and Q were deter- 
 mined in two different ways ; first, by starting with an 
 open circuit, which was then closed ; secondly, by starting 
 with a portion of the resistance short circuited, and a very 
 powerful current passing, and then breaking the short 
 circuit. It was found that E and Q were four times as 
 great in the latter case as in the former. The curve 
 (Fig. 18) will also determine what current will flow at 
 any given speed of rotation of the machine, and under 
 any conditions of the circuit, whether of resistance or of 
 opposed electro-motive forces. It will also give very 
 approximate indications of the corresponding curve for 
 other machines of the same configuration, but in which 
 the number of times the wire passes round the electro- 
 magnet or the armature is different. 
 
 It will be well to compare these results with those 
 obtained by others. M. Mascart worked on a Gramme 
 machine with comparatively low currents ; he represents 
 his results approximately by the formula, 
 
 E = (a + 6 Q), 
 
 where a and b are constants. This corresponds to the 
 rapidly-rising part of the above curve. Mr. Trowbridge 
 with a Siemens machine obtained a maximum efficiency 
 of 76 per cent., and states that the machine was running 
 below its normal velocity. Mr. Schwendler's precis states 
 that the loss of power with a Siemens machine in pro- 
 ducing currents of over 20 webers is 12 per cent. Now, 
 taking Dr. Hopkinson's experiments, 4 to 19, the mean 
 value of W x is 3 '027, and of W 3 3-304; adding to the 
 latter 0-21, the power required to drive the machine 
 when no current passes, it appears that 13*8 per cent, of 
 the power applied is wasted. Again, taking experiments 
 4, 6, 8, 10, and 12, the mean value of W 2 is 2-888 and of 
 W 3 , 3*076, indicating a waste of power amounting to 
 
32 
 
 ELECTRIC TRANSMISSION OF POWER. 
 
 12 per cent. Of the loss, 28 HP. is accounted for by fric- 
 tion of the journals and commutator brush ; the remainder 
 
 Electromotor* *6rc 
 
 is expended in local currents, or by loss of kinetic energy 
 of current when sparks occur at the commutator. 
 
EFFICIENCY OF DYNAMO-ELECTRIC MACHINES. 33 
 
 HCDOO-)H<X>(M'*ih-C<lrtHHO(MT-l 
 I-H i-H CM CN CO CO CO rjn SO ^H CO ^ -^1 
 
34 ELECTRIC TRANSMISSION OF POWER. 
 
 CHAPTER VI. 
 
 PRACTICABILITY OF TRANSMISSION OF POWER BY ELECTRICITY. 
 
 To deal with objections first, we may regard the trans- 
 mission of large electric currents as considered by Mr. J. T. 
 Sprague, who examines the suggestions of Mr. Siemens. 
 In a lecture delivered at Glasgow, March 14, 1878, and 
 since published, Mr. Siemens says, " The principal objec- 
 tion that has been raised by electricians to the conveyance 
 of power to the distance of miles, is on account of the ap- 
 parently rapid increase in the size of the conductor required 
 with increase of distance. In order that the magneto- 
 electric machine may work under the most favourable 
 conditions, it should have an internal resistance depending 
 in a great measure upon the nature of the work to be 
 performed, but not exceeding for quantative effects 1 ohm 
 or unit of resistance. If the resistance is greater, a notable 
 proportion of the power expended will be converted into 
 heat in the conductors, causing both loss of effect and 
 great inconvenience. By another law the electrical re- 
 sistance of the circuit exterior to the machine should be 
 somewhat, but not much, larger than the internal resistance, 
 say 1 5 unit. The external resistance is composed of two 
 elements, namely, the conductor, and the resistance of the 
 electric lamp or electro-magnetic engine, which latter may 
 be taken also as amounting to 1 unit, leaving only half a 
 unit available for the conductor. These conditions deter- 
 mine really the size of the conductor for any distance to 
 which the current has to be conveyed. 
 
 " Suppose the distance to be half a mile, a copper wire 
 of * 23-inch diameter will produce the half-unit resistance, 
 
PRACTICABILITY OF ELECTEIC TRANSMISSION. 35 
 
 which is already a wire of considerable dimensions, for 
 the purpose of working a single lamp. If the distance "be 
 doubled wire of the same thickness will give twice the 
 electrical resistance, and in order to reduce it again to 
 half a unit its sectional area must be doubled, so that a 
 conductor of 30 miles' length would require to be 60 2 = 
 3,600 times the weight of the half-mile conductor, and 
 this enormous increase in weight would certainly be re- 
 quired if the object to be accomplished was the working 
 of one electric lamp by a dynamo-electric machine. My 
 critics have, however, fallen into the error of overlooking 
 the fact that half-a-unit resistance is the same for a circuit 
 capable of working one lamp as it is for working 100 or 
 1000 lamps. 
 
 " Electricity is not conducted upon the conditions ap- 
 pertaining to a pipe conveying a ponderable fluid, the 
 resistance of which increases with the square of the velo- 
 city of flow ; it is, on the contrary, a matter of indifference 
 what amount of energy is transmitted through an electric 
 conductor ; the only limit is imposed by the fact that 
 in transmitting electric energy, the conductor itself re- 
 tains a certain amount proportional to that transmitted, 
 which makes its appearance therein in the form of 
 heat." 
 
 This heat, as Mr. Siemens goes on to explain, would 
 increase the resistance of the conductor ; but to simplify 
 the problem that heat and its effects are not taken into 
 account in the following remarks, Mr. Sprague assumes 
 that the heat is radiated away or got rid of, so as to keep 
 the conductor at a uniform temperature. According 
 to Mr. Sprague, there are two ways of regarding " re- 
 sistance " : 
 
 1. In Ohm's formulas it is constant for all currents. 
 So is the diameter of a pipe transmitting water. The same 
 pipe will deliver any variable quantity or current of 
 water corresponding to the pressure; so the same wire 
 
 D 2 
 
36 ELECTRIC TRANSMISSION OF POWER. 
 
 will deliver any variable quantity or current of electricity 
 corresponding to the electro-motive force. This aspect of 
 resistance then is a mathematical one, existing only in 
 calculations. 
 
 2. True, or practical resistance, is measurable by the 
 energy required to overcome it. The energy expended 
 by a current in passing a given conductor (resistance 
 in the mathematical sense being simply the reciprocal of 
 the conducting power under unit condition) varies as the 
 square of the current or velocity of flow. 
 
 Therefore, electricity is really conducted under pre- 
 cisely the " conditions appertaining to a pipe conveying a 
 ponderable fluid." 
 
 The resistances in a circuit are of several orders : 
 
 1. That of the actual conductor itself, which is constant. 
 
 2. Any work effected by the current. This may in some 
 cases be expressed as a counter electro-motive force, in 
 others simply as a resistance, but in either case it can be 
 represented in ohms, or as a reduced length; but the 
 expression of it is variable, because it depends upon the 
 energy expended from moment to moment, and it must be 
 expressed by the square root of that energy involved in 
 Ohm's formulae. 
 
 When all forms of energy expended are thus expressed 
 as resistance in ohms, the ratio of useful work done, to 
 the inevitable expenditure in developing and transmitting 
 the energy to the work, is exactly proportional to the 
 resistance of each part of the circuit. 
 
 There is a difficulty, continues Mr. Sprague, in applying 
 these principles to the illustrations employed by Mr. Sie- 
 mens, in that we do not know what is meant by the 
 resistance of 1 ohm at the point of work done. If by 
 that is meant simply the wire resistance of an electro- 
 motor or of a lamp, these belong to the side of energy lost 
 or expended ; if the work to be done is not included in 
 the 1 ohm, then it would seem that, as it would act as an 
 
PRACTICABILITY OF ELECTRIC TRANSMISSION. 37 
 
 additional resistance, the internal resistance of the generat- 
 ing machine must be increased in order to develop the 
 requisite electro-motive force. 
 
 For the present purpose, then, which is to indicate the 
 nature of the problem and the difficulties to be met, rather 
 than how to overcome them, Mr. Siemens' actual figures may 
 be taken, and the 1 ohm be assumed as the relative useful 
 ratio of the lamp or motor engine. Here we meet at once 
 the problem, what is the work done in, or the mechanical 
 equivalent of an electric light of, say, 1000 candles?* 
 Does any one know ? The problem involves these simul- 
 taneous measures illuminating power, resistance, and 
 current. With batteries of known electro-motive force 
 this can replace the latter data required. We have all 
 sorts of statements, from 5 to 1 ohm for resistance, to the 
 figures given by Messrs. Ayrton and Perry, which come 
 out as follows : 
 
 Grooves in 
 Series 
 E. M. F. 1-8. 
 
 Total 
 E. M. F. 
 
 Volts. 
 
 Resistance. 
 
 Current 
 Webers. 
 
 Energy in 
 Arc, 
 Foot-lbs. 
 
 Battery. 
 
 Arc. 
 
 Total. 
 
 60 
 
 108-0 
 
 12-0 
 
 12-0 
 
 24-0 
 
 5-33 
 
 15,082 
 
 80 
 
 144-0 
 
 16-0 
 
 20-0 
 
 36-0 
 
 4-00 
 
 14,157 
 
 122 
 
 219-6 
 
 24-4 
 
 30-0 
 
 54-4 
 
 4-04 
 
 21,647 
 
 Unfortunately there is no measure of the light produced 
 these three cases. Taking the common statement 
 
 m 
 
 that such a light consumes 1 HP. of an engine (though 
 Mr. Siemens states that his smaller size converts 2 HP., 
 and gives 1250 candles) and take the resistance as 1 ohm 
 in the arc and 1 5 in the machine and conductor ; this 
 
 * As far as regards the conductor, it is immaterial whether the 
 current conveyed is utilised to produce light or motor-power. Hence 
 the words of the argument have been retained. 
 
38 ELECTRIC TRANSMISSION OF POWER. 
 
 gives 33,000 -f- j = 13,200 feet pounds expended in the 
 
 2 ' 5 
 
 arc, a very singular approximation (considering by how 
 different a road it has been reached) to the figures above. 
 The mechanical equivalent of the weber-ohm current per 
 second is "787 foot pound, or 44*24 per minute. 
 
 13,200 
 
 ~ = 289-37, the square root of which, 17-273, 
 
 represents the current developing 13,200 foot pounds per 
 minute in the ohm resistance, a useful effect of 4 of the 
 power expended. 
 
 If, now, 100 such lights were to be applied to the same 
 circuit conditions, it would be necessary to put in circuit 
 ten in series, and ten such series in multiple arc to main- 
 tain their total joint resistance = 1, and the current would 
 have to be 17,273 X 10 - 172-73, developing 100 times as 
 much heat in machine and conductor, and still expending 
 6 of the power in transmission. This also supposes that 
 there is perfect insulation, and no loss on the road, a con- 
 dition of things not likely to be attained in practice. In 
 converting the current again into mechanical power, the 
 * 4 of power sent would be reduced by the effective ratio 
 of the transforming machine. 
 
 In regard to Mr. Siemens' proposal to convey 1000 HP. 
 a distance of 30 miles through a conductor 3 inches in 
 diameter, he says, " The electrical resistance of the con- 
 ductor would be 0-18 unit, and supposing that the total 
 resistance in circuit was made 2-5 units, which, as I 
 before stated, gives a favourable working condition, it 
 
 0*18 
 
 follows that X 1000 = 72 HP. would be expended in 
 2 * 5 
 
 heating the conductor. This would represent about 15 Ibs. 
 of coal per hour, a quantity quite insufficient to raise a 
 mass of 1900 tons of copper, with a surface of 132,000 
 square feet to a sensibly-heated condition." 
 
PRACTICABILITY OF ELECTKIC TEANSMISSION. 39 
 
 It seems from this, the proposal is not to convey 1000 HP. 
 but only so much as is possible out of that original power. 
 Then, giving machine 1 and conductor 0*18 ohm resistance, 
 we have 1 32 left for useful work ; so we divide it : 
 
 1 Dynamo machine 400 HP. 
 0-18 Conductor 72 
 
 1 32 Engine or lights 528 
 
 This latter figure being reduced in actual work to pro- 
 bably 300 at most. 
 
 To obtain the 300 HP., then, we have to provide : 
 
 1. Machines for converting the electricity into 300 HP. 
 
 2. 1900 tons of best copper rod carefully insulated. 
 
 3. Machines capable of converting 1000 HP. into electri- 
 
 city. 
 
 4. Appliances and processes for getting rid of 400 HP. 
 
 worth of heat in this latter machinery. 
 
 Mr. Siemens says he is convinced that the sectional 
 area of the conductor might safely be reduced to 2 inches, 
 giving half the weight of the conductor ; but as the con- 
 verting engines would probably cost as much as gas 
 engines of equal power, the question resolves itself into 
 this, is it better worth while to lay down even 950 tons 
 of copper, and fit up the 1000 H.P. engines, or to pur- 
 chase the fuel needed to work the 300 H.P. engines where 
 they are to be used? That is a question that might 
 receive different answers in the mountains of Chili, and 
 where coal is to be obtained at even the most extreme 
 English prices. 
 
 Mr. Sprague's views are practically answered by the 
 able paper presented to the Franklin Institute by 
 Professors Thomson and Houston ; the statements made 
 as to the size and cost of the cable that would be needed 
 to convey the power of Niagara Falls to a distance of 
 several hundred miles by electricity, having induced with 
 
40 ELECTRIC TRANSMISSION OF POWER. 
 
 the Authors the hope that they may throw light upon this 
 interesting subject. 
 
 As an example of some of the statements alluded to, 
 the following are cited, viz. : That made by a certain 
 electrician, who asserts that the thickness of the cable 
 required to convey the current that could be produced by 
 the power of Niagara, would require more copper than 
 exists in the enormous deposits in the region of Lake 
 Superior. Another statement estimates the cost of the 
 cable at about 12 per lineal foot. 
 
 As a matter of fact, however, the thickness of the cable 
 required to convey such power is of no particular moment, 
 and the Professors state that it is possible, should it be 
 deemed desirable, to convey the total power of Niagara 
 a distance of 500 miles or more by a copper cable not exceeding 
 one-half of an inch in thickness. This, however, is an 
 extreme case, and the exigencies of practical working 
 would not require such restrictions as to size. The follow- 
 ing considerations will elucidate this matter: Suppose 
 two machines connected by a cable of, say, 1 mile in 
 length. One of these machines, for example A, is pro- 
 ducing current by the expenditure of power ; the other 
 machine, B, used as an electrical motor, is producing 
 power by the current transmitted to it from A by the 
 cable C. The other terminals, x and y, are either put to 
 earth or connected by a separate conductor. 
 
 Let us suppose that the electro-motive force of the 
 current which flows is unity, since, by the revolution of 
 B, a counter electro -motive force is produced to that of A, 
 the electro-motive force of the current that flows is mani- 
 festly the difference of the two. Let the resistance of A 
 and B together be equal to unity, and that of the mile of 
 cable and connections between them the 01 of this unit. 
 
 TT 1 
 
 Then the current which flows will be C = = = 
 
 E 1-01 
 If, now, an additional machine A' and an additional motor 
 
PRACTICABILITY OF ELECTRIC TRANSMISSION. 41 
 
 B', and an additional mile of cable be introduced into the 
 above circuit, the electro-motive force will be doubled, 
 and the resistances will be doubled, the current strength 
 
 E 1 + 1 2 
 
 remaining the same as C = g == JTQI + I . OI = ^02* 
 
 Here it will be seen that the introduction of the two 
 additional machines A' B' has permitted the length of the 
 cable, C, to be doubled without increasing the strength of 
 the current which flows, and yet allowing the expenditure 
 of double the power at A A', and a double recovery at 
 B B' of power, or, in other words, a double transmission of 
 power without increase of current. 
 
 Increase now the number of machines at A to, say, one 
 thousand, and one of those at B in like proportion, and 
 the distance between them, or the length of the cable, one 
 thousand times, or in the case we have supposed make it 
 one thousand miles, its diameter remaining the same, then, 
 although the same current will flow, yet, we have a thousand 
 times the expenditure of power at one end of the cable and a 
 thousand-fold recovery at the other end, without increase of 
 current. And the same will be true for any other pro- 
 portion. 
 
 Since the electro-motive force is increased in proportion 
 to the increase of power transmission, the insulation of 
 the cable and machines would require to be proportion- 
 ally increased. 
 
 As an example it may be mentioned that a dynamo- 
 electric machine used for A may have a resistance of, say, 
 40 ohms and produce an electro-motive force of, say, 400 
 volts. Such a machine might require from three to five 
 horse-power when used in connection with a suitable motor 
 B, for recovery of the power transmitted. 
 
 If the resistance of the motor B be, say, 60 ohms, and 
 the cable transmitting the currents a distance of 1 mile 
 
 be 1 ohm, then the current C = ^- = . 
 
42 ELECTRIC TRANSMISSION OF POWER. 
 
 If, now, 1000 machines and 1000 motors and 1000 
 miles of cable, each of the same relative resistances, 
 
 1000 X 400 
 
 be used the current C = -Z-T^TT ;r- which has mani- 
 
 1000 x 101 
 
 festly the same value as before. If the supposition of the 
 power used to drive one machine be correct, then from 
 3000 to 5000 HP. would be expended in driving the 
 machines, and possibly about 50 per cent, of this amount 
 recovered. Then we have from 1500 to 2000 HP. con- 
 veyed a distance of 1000 miles. What diameter of copper 
 cable will be required for such transmission ? Since this 
 cable is supposed to have the resistance of 1 ohm to the 
 mile, calculation would place the requisite thickness at 
 about J inch. If, however, the distance be only 500 miles, 
 then the resistance per mile may be doubled, or the 
 section of the cable be decreased one half, or its diameter 
 will be less than one-fifth of an inch. 
 
 For the consumption of 1,000,000 HP. a cable of about 
 3 inches in diameter would suffice under the same condi- 
 tions. However, by producing a much higher electro- 
 motive force, the section of the cable could be propor- 
 tionally reduced until the theoretical estimates given in 
 the preceding lines might be fulfilled. The enormous 
 electro-motive force required in the above calculation 
 would, however, necessitate such perfect insulation of the 
 cable that the practical limits might soon be reached. The 
 amount of power required to be conveyed in any one 
 direction would, of course, be dependent upon the uses 
 that could be found for it, and it is hardly conceivable 
 that any one locality could advantageously use the 
 enormous supposed power we have referred to. 
 
 Stripped of its theoretical considerations, the important 
 fact still remains, that with a cable of very limited size 
 an enormous quantity of power may be transferred to 
 considerable distances. The burning of coal in the mines, 
 and the consequence of the power generated by the flow 
 
PRACTICABILITY OF ELECTRIC TRANSMISSION. 43 
 
 of rivers, may therefore be regarded as practicable, 
 always, however, remembering that a loss of about 50 per 
 cent, will be almost unavoidable. 
 
 In a subsequent series of experiments, details of which 
 are unpublished, the Professors Thomson and Houston 
 have succeeded in transmitting considerable power through 
 a wire only 004 inch in diameter. Sir William Thomson 
 has made statements that are in general accordance with 
 these views. Mr. Siemens has remarked that the electrical 
 transmission of power, although new and untried, is one 
 of considerable interest, and an amount of from 40 to 
 50 per cent, is recovered at the end of the line. By 
 putting one machine to work with an expenditure of, say, 
 3 HP., a power could be produced and utilised at a dis- 
 tance not exceeding half a mile or a mile, according to the 
 size and length of the conductor, equal to nearly one-half 
 that amount. If at certain stations 100 HP. were so 
 exerted, it would be possible to distribute over a town 
 power which would be exceedingly convenient and free 
 from the dangers and troubles attending caloric motors, 
 and with an expenditure of fuel certainly not greater, 
 because, although perhaps only 40 per. cent, of the power 
 exerted at the central station was actually obtained at the 
 further station, it was nevertheless obtained at a very low 
 rate. A 100-HP. engine, economically constructed, would 
 produce 1 HP. with less than 3 Ibs. of coal, whereas a 
 small motor of 2 or 3 HP. would consume probably 6 to 
 8 Ibs. of coal per hour. Bearing that difference in mind, 
 the magneto-electric machine would be an economical one. 
 How far the principle would be applicable ultimately for 
 the utilisation of such natural forces as water-power from 
 a distance, remains to be seen. The difficulty is in regard 
 to the length of the electrical conductor. Its resistance 
 increased in the ratio of its length ; and as the increased 
 resistance would mean loss of useful effect in the same 
 proportion, it would be necessary to double the area of 
 
44 ELECTRIC TRANSMISSION OF POWER. 
 
 the electric conductor in doubling its length, in order to 
 maintain the same ratio of efficiency ; but, if that were 
 done, the resistance might be increased to many miles, 
 and, he believed, profitably, without further loss of power. 
 
 Professors Houston and Thomson have, however, shown 
 as noted in the preceding lines how this loss is to be 
 avoided. 
 
 In order to get the best effect out of a dynamo-electric 
 machine, there should be an external resistance not ex- 
 ceeding the resistance of the wire in the machine. 
 Hitherto, Mr. Siemens continues, it has been found not 
 economical to increase the resistance in the machine to 
 more than 1 ohm, otherwise there was a loss of current 
 through the heating of the coil. If, therefore, there was 
 a machine with 1 ohm resistance, there ought to be a con- 
 ductor transmitting the power to the electro-magnetic 
 engine not exceeding 1 ohm. If, instead of going 1 mile, 
 it was desired to go 2 miles, it would be necessary first of 
 all to employ a conductor twice the length ; but that con- 
 ductor would give 2 ohms resistance, and would therefore 
 destroy much of the effect. To bring it back to 1 ohm 
 resistance, it would be necessary to put down a second 
 wire, or to double the area of the first, and in that case 
 there would be a wire of twice the length and twice the 
 area, therefore four times the weight and four times the 
 cost. That pointed to an increase in the cost and in the 
 weight of the conductor in the square ratio of the distance. 
 Having twice the area to deal with, a second generator 
 could be put on, and electricity enough to work two 
 machines could be sent through the double area to a 
 double distance. The moment that was done, the con- 
 ductor was increased, for the power was transmitted only 
 in the proportion of the increase of the length ; but that 
 was not enough. The < electric conductor did not resist 
 the motion of electricity in the same manner as a pipe 
 resisted the flow of liquid through it, but an ohm's 
 
PRACTICABILITY OF ELECTRIC TRANSMISSION. 45 
 
 resistance was an ohm's resistance for a larger as well as 
 for a smaller current flowing through it, which resistance 
 was only increased by a rise of temperature in the con- 
 ductor. This rise of temperature was kept down by 
 dissipation of heat from the conductor ; or, considering 
 that the longer and doubled conductor would possess four 
 times the amount of surface for the dissipation than the 
 single and short conductor, it would be capable of trans- 
 mitting four times the amount of electric current. It 
 might, therefore, be said that it was no dearer to transmit 
 electro-motive force to the greater than to the smaller 
 distance, as regarded weight and cost of conductor, a 
 result which seemed startling, but which he nevertheless 
 ventured to put forward with considerable confidence. 
 In uniting the two longer conductors into one, the surface 
 would, however, be increased only in the ratio of ,J 2 : 1 ; 
 therefore the relative transmitting power between the 
 longer and shorter conductor would, strictly speaking, be 
 increased in the ratio of 1:2^2, or 1:2* 83, and the 
 longer conductor would be dearer than the shorter per 
 unit of electro-motive force transmitted in the proportion 
 of 4:2-83. 
 
 Sir William Thomson has remarked that the question 
 of the heat developed in the wire was the fundamental 
 question with reference to the quantity of metal required 
 to communicate the effect to a distance. The most prac- 
 tical way of producing the result would be to put the 
 wire in the shape of a copper tube. Having a copper tube, 
 with a moderate amount of copper in its sectional area, 
 and a current of water flowing through it with occasional 
 places to let it off, and places to allow water to be 
 admitted for the purpose of cooling, there would be, with- 
 out any injury to the insulation, a power of carrying off 
 heat practically unlimited. He believed that with an ex- 
 ceedingly moderate amount of copper, it would be possible 
 to carry the electric energy to a distance of several 
 
46 ELECTRIC TRANSMISSION OF POWER. 
 
 hundred miles. The economical and engineering moral of 
 the theory appeared to be that towns henceforth would be 
 lighted by coals burned at the pit's mouth, where it was 
 cheapest. The carriage expense of electricity was nothing, 
 while that of coal was sometimes the greater part of its 
 cost. The dross at the pit's mouth, which was formerly 
 wasted, could be used for working dynamo-engines of the 
 most economical kind. Nothing could exceed the practical 
 importance of this fact. The power transmissible by these 
 machines was not simply sufficient for working sewing- 
 machines and turning lathes, but by putting together a 
 sufficient number any amount of HP. might be developed. 
 Taking the case of the machines required to develop 1000 
 HP., he believed it would be found comparable with the 
 cost of a 1000 HP. engine; and he need not point out 
 the vast economy to be obtained by the use of such a fall 
 as that of Niagara, or the employment of waste coal at the 
 pit's mouth. 
 
EFFICIENCY OF COUPLED MACHINES. 47 
 
 CHAPTEE VII. 
 
 EFFICIENCY OF COUPLED MACHINES. 
 
 As regards the efficiency of the system comprising two 
 machines, the following quotation from a paper read by 
 the Author before the Institution of Civil Engineers, 
 1878 (for which the Telford Medal was awarded), will 
 fully elucidate this point : 
 
 The means at present employed for the transmission of 
 power to a distance are well known. In adding to the 
 list it may be well to point out that between the use of 
 electricity, when obtained from a voltaic battery, and 
 conveyed to an electro-magnetic motor by conducting 
 wires, and the employment of dynamo-machines, there is 
 just the difference that results in obtaining the electric 
 light by a Grove or a Bunsen battery, and in taking the 
 light from the current produced by the dynamo-machine. 
 In the one case an expensive chemical action is converted 
 into force ; in the other, the force produced by a steam or 
 other economical motor is transmitted. With the electro- 
 magnetic motor the system is generative ; with the 
 dynamo-machine, the current acts merely as a means of 
 transmitting power produced by an independent motor. 
 In point of fact, this independent motor may be a natural 
 source of power, such as the fall of water, the utilisation 
 of the product of oil wells, with prime-movers situated at 
 these wells, etc. 
 
 The limit set by distance to the transmission of power, 
 by means at present adopted, has been comparatively 
 narrow. Hydraulic power has been the most adaptable, 
 with, however, several important disadvantages. Although 
 
48 ELECTRIC TRANSMISSION OF POWER. 
 
 electricity as a means of transmission is also limited by 
 the distance to be traversed, the limit is in this case much 
 more extensible, and under favourable instances practically 
 disappears. The limit is dependent upon the quantity of 
 electricity that can be conveyed by the conductor, since 
 mechanical efficiency depends upon the magnetic energy. 
 
 For the transmission of power, say from a steam or 
 water motor initially, the following system is adopted : 
 First, a strap or belt from the motor is carried to the 
 pulley of the driving dynamo-electric machine which 
 generates the current. By leading wires of the required 
 length, the electrical current generated in the first 
 machine is conveyed to the terminals of a second and 
 precisely similar machine. Thus the first machine 
 generates the current which is utilised in imparting 
 motion to the second machine. It remains to review 
 the probable efficiency of such a system. This subject 
 has been treated in its mathematical relations by M. 
 Mascart in the ' Journal de Physique.' 
 
 It is well known that all magneto-electric machines, 
 when set in motion by a current, induce in themselves, as 
 electrical systems, currents opposing the motive current. 
 For example, when a current from some source is directed 
 into the coils of a dynamo-machine, the coil commences to 
 revolve. Immediately it commences to revolve, it also 
 begins to act as a generator, and sets up a current which 
 is opposite in direction to the motive current, and sub- 
 tractive from the strength of the latter. The current- 
 strength from the source is, therefore, at a maximum when 
 the second machine, or that driven by the current, is at 
 rest. From consideration it is easily obtained that the 
 greatest work is to be yielded by the second machine 
 when the strength of the current given by the first 
 machine, or source, has been reduced to one-half by the 
 induced current from the second machine. With these 
 machines it has been generally found that the current- 
 
EFFICIENCY OF COUPLED MACHINES. 
 
 49 
 
 strength is proportional to the velocity or number of 
 revolutions of the cylinder ; so that, supposing two equal 
 
 FIG. 19. 
 
 nOO Rex* of 
 
 FIG. 20. 
 
 tlOO Rou* of 1*6 Kachinjer 
 
 
 
 
 
 
 
 
 
 
 
 
 /^ 
 
 
 "^ 
 
 \ 
 
 
 
 
 
 / 
 
 
 
 
 \ 
 
 
 
 
 / 
 
 / 
 
 
 
 
 
 
 
 
 00 *00 SOO SOO TOO SCO SOO WOO TOO 12C 
 Rar* of """*' Machine 
 
 machines arranged for the transmission of power, the 
 amount of work reclaimable from the second machine will 
 
 E 
 
50 
 
 ELECTRIC TRANSMISSION OF POWER. 
 
 be 50 per cent, of that employed upon the first, and the 
 number of revolutions of the armature of the second 
 machine corresponding to the maximum of work reclaimed 
 will be half the number made by the first. 
 
 Figs. 19 to 21 show curves drawn through six points 
 from results actually obtained. The revolutions of the 
 cylinder of the second machine are represented as abscissae 
 
 FIG. 21. 
 
 1300 Rjevf of V*> 
 
 
 
 , 
 
 ^ 
 
 . 
 
 L ^-- 
 
 \ 
 
 
 
 
 
 / 
 
 
 
 
 
 ^ 
 
 ^ 
 
 
 
 1 
 
 
 
 
 
 
 X 
 
 *> 400 600 600 TOO SCO 9OO ' 10 
 
 OO rn 
 
 'o ma 
 
 Rev* of 2~ 
 
 and the work reclaimed as ordinates. The numerical 
 values are given in the following table : 
 
 KESULTS OF EXPERIMENTS WITH DYNAMO-MACHINES FOR THE TRANS- 
 MISSION OF POWER BY THE ELECTRIC CURRENT. 
 
 Fig. 19. 
 
 Fig. 20. 
 
 Fig. 21. 
 
 Machine A, at 1100 Revo- 
 
 Machine A, at 11 00 Revo- 
 
 Machine A, at 1400 Revo- 
 
 lutions Driving C. 
 
 lutions Driving B. 
 
 lutions Driving B. 
 
 Revolutions 
 ofC. 
 
 Per cent, of 
 Work Re- 
 claimed. 
 
 Revolutions 
 ofB. 
 
 Per cent, of 
 Work Re- 
 claimed. 
 
 Revolutions 
 ofB. 
 
 Per cent, of 
 Work Re- 
 claimed. 
 
 1,008 
 
 27 
 
 884 
 
 34 
 
 1,199 
 
 39 
 
 730 
 
 36 
 
 808 
 
 43 
 
 1,031 
 
 44 
 
 584 
 
 38 
 
 767 
 
 44 
 
 863 
 
 48 
 
 501 
 
 39 
 
 625 
 
 45 
 
 691 
 
 49 
 
 420 
 
 37 
 
 481 
 
 39 
 
 500 
 
 37 
 
 359 
 
 35 
 
 385 
 
 32 
 
 
 
 
 
EFFICIENCY OF COUPLED MACHINES. 51 
 
 The departures from the theoretical values are somewhat 
 marked, but are within the limits of error that occur with 
 this class of measurements, made with no great attempt 
 at accuracy. 
 
 In order to ascertain the effects of resistance in the 
 circuit connecting the driving and driven engines, two 
 machines were connected by leading wires, having resist- 
 ance of J unit, 1 unit, and 1J unit respectively. The 
 machines were two of the smallest Siemens type, and gave 
 without inserted resistance an efficiency of 44 per cent. ; 
 with % unit resistance added to the circuit the efficiency 
 was reduced to 38 per cent., giving a loss of 6 per cent. ; 
 with 1 unit of added resistance the efficiency fell to 32 per 
 cent., giving a loss of 12 per cent. ; and with Ij unit added 
 resistance the efficiency was 26 per cent., giving a loss 
 of 18 per cent. The experiments clearly proved that the 
 loss of efficiency is proportional to the added resistance. 
 
 With a machine having O'Oo unit resistance, a current 
 of 5 webers through one ohm has been obtained, with an 
 expenditure of 2 HP. This gave a current of which the 
 mechanical value, when the machine was connected to a 
 precisely similar machine, was 56,000 foot-lbs., with the 
 second machine at rest; and a resultant current of 
 29,000 foot-lbs. with the second machine in motion, the 
 HP. expended being maintained constant. The work re- 
 claimed, measured on the dynamometer, was 48 per cent., 
 closely agreeing with the efficiency of one-half. As to 
 the effect of circuit resistance on the transmission of power 
 in the instance quoted, the addition of 1 J unit resistance 
 reduced the efficiency to 26 per cent, with the particular 
 machines employed; but if convolutions of wire were 
 added to the cylinder of the machine the efficiency would 
 again attain its maximum. It should be noted' that the 
 theoretical efficiency of 50 per cent, is referred to the use 
 of two equal and similar machines, one used as the driving, 
 the other as the driven machine. It is quite probable 
 
 E 2 
 
52 ELECTRIC TRANSMISSION OF POWER. 
 
 that a larger percentage of work reclaimed might be 
 attained by some other arrangement of machines. By 
 driving one machine by two others coupled in series, the 
 results of three readings gave : speed of small machines, 
 1060 revolutions; speed of medium machine, 1820 revo- 
 lutions. The medium machine driven by one small 
 machine gave the following results, taken from three 
 readings : speed of small machine, 1060 revolutions ; speed 
 of medium machine, 780 revolutions. It would thus be 
 seen that the speed of the medium machine had been 
 rather more than doubled by driving it from two machines 
 coupled in series. The best conditions for work admitted 
 of direct proof. Two equal machines being employed, and 
 a galvanometer put in circuit between them, the deflec- 
 tions showed that when the second machine was at rest, 
 the current was of twice the intensity that occurred when 
 the second machine was giving out its best work. 
 
 M. Mascart has shown that if the number of revolutions 
 of the first machine were kept constant, the greatest effi- 
 ciency would be attained when the number of the revolu- 
 tions of the second machine were nearly equal to unity. 
 But he has also proved that when the greatest amount of 
 power was given off by the second machine, it would make 
 half the number of revolutions of the first machine, and 
 then the first machine would require half the power to 
 drive it which was required when the second machine was 
 standing, and of that power one half would be transmitted 
 by the second machine. This is a very different thing from 
 the conclusion that the maximum efficiency was one half. 
 
 In some experimental researches on magneto-electric 
 machines, MM. Mascart and Angot, in the 'Journal de 
 Physique,' vol. vii. p. 78, investigate the reaction of the 
 magnets and the electro-magnets. Previous considerations 
 in a former article* by these authors, give only a first ap- 
 
 Vide Minutes of Proceedings Inst. C.E., vol. L., p. 302. 
 
EFFICIENCY OF COUPLED MACHINES. 53 
 
 proximation to the action of machines containing magnets 
 or electro-magnets. It has been supposed that the mag- 
 netism of permanent magnets is invariable, and that that 
 of electro-magnets depends only upon the intensity of 
 the currents by which they are surrounded ; but there 
 exist between the magnets and the currents reactions 
 that may greatly modify the results. Electro-dynamic 
 machines which include neither magnet nor soft iron 
 give rise to no new correction, the time necessary for 
 the manifestation of the electro-dynamic forces being 
 inappreciable. 
 
 In magnetic machines of the second type the effective 
 magnetism of the permanent magnets is changed in a 
 complex manner by the influence of the bobbins. If it 
 be admitted that the variation of the magnetism of the 
 magnets is proportional to the magnetic power of the 
 bobbins, which is in direct ratio to the intensity of the 
 current, it is to be seen that the magnetism of the magnets 
 will be increased when they exercise an attraction between 
 the two systems, and that it will be diminished in the 
 case of repulsion. The diminution of repulsive force will 
 be greater than the increase of attractive force, since the 
 magnets may be supposed to be in a condition bordering 
 upon saturation ; there will result from this fact a slight 
 diminution of work, and this may be represented by a 
 term proportional to the square of the intensity of the 
 current. The equations * then become for the motor 
 machine, 
 
 K = NH = NI(A-BI) 
 
 E = 
 
 * I and i are current intensities ; E primary electro-motive force ; 
 E contrary electro-motive force ; R total resistance ; N and n number of 
 revolutions in the two machines in corresponding cases. K is the me- 
 chanical work in time di. The other relations are explained in the text. 
 
54 ELECTRIC TRANSMISSION OF POWER. 
 
 Whence is deduced, 
 
 instead of E = N A. The electro-motive force of induc- 
 tion, for a given velocity, is as much weaker as that of 
 the battery is stronger. The machine left to itself has 
 still a velocity, the limit of which is given by the condi- 
 tion 1 = 0, which is 
 
 A 
 
 as if the reaction had not been taken into account. The 
 efficiency is diminished, because it has for expression, 
 
 _ E__ NA AB 
 
 E E T N - 
 E 
 
 To calculate the coefficients A and B the limit of velo- 
 city N of the motor machine must be determined, whence 
 is deduced 
 
 A- E 
 N.' 
 
 as measure for the efficiency for a given velocity ; thus 
 the equation 
 
 B 
 
 obtains, whence is deduced 
 
 N 
 
 iv. ~ r 
 B = E 
 
 
EFFICIENCY OF COUPLED MACHINES. 55 
 
 The limit of velocity N is easily obtained by experi- 
 ment, since it is proportional to the electro -motive force 
 of the battery employed, which may be chosen as weak as 
 desired. 
 
 When the machine is employed as electro-motor, the 
 
 condition of production 2 > R is always realised for 
 a very weak current, and equilibrium exists when 
 
 or 
 
 A n A n A 
 
 B B + .B Jt F 
 
 n xt 
 
 The apparatus behaves as a battery, the electro-motive 
 force of which is proportional to the velocity, with the 
 conditions of adding to the actual resistance a fictitious 
 resistance itself proportional to the velocity. The inten- 
 sity will then have a limiting value given by the equation, 
 
 _A. 
 = B' 
 
 In magneto-electric machines, that is to say with fixed 
 and moving electro-magnets, the influence of the wires of 
 a system of bobbins on the opposed electro-magnets gives, 
 as in the preceding, an increase of attractive forces and a 
 greater diminution of repulsive forces, which again intro- 
 duces into the work a negative variation proportional to 
 the magnetism and to the intensity of the current that 
 may be considered comprised in the term C^ M I 2 . On the 
 other hand, the reciprocal influence of the electro-magnets 
 gives also a diminution of work, which is sensibly propor- 
 tional to the square of the magnetisation, and may be 
 comprehended in the term C 2 M 2 I 2 , so that there will be 
 
56 ELECTRIC TRANSMISSION OF POWER. 
 
 nothing to modify the theory. The reaction which is 
 weak in the machines of the second type, plays on the 
 contrary an important part in composite machines consist- 
 ing of magnets and electro-magnets. If it be considered 
 that the magnetism of fixed magnets is modified by a 
 quantity proportional to the magnetisation of the electro- 
 magnets, there results a diminution of work proportional 
 to the square of magnetisation, or to M 2 I 2 . 
 The efficiency is 
 
 T _ 2 
 
 JE _ N (A 4- A! M) A+AiM R 
 " E; ~ ~E7~ A 2 M 2 
 
 ~K~ 
 
 If the current is sufficiently weak, so that the coefficient 
 M has the constant value M , it becomes 
 
 an expression of the same form as for machines of the 
 second type of magneto-electric machines. The greater 
 number of electric motors enter into the category, because 
 they are nearly always formed of two systems of electro- 
 magnets or, what is the same, of a system of fixed electro- 
 magnets, and of movable pieces of soft iron. In these 
 machines work has for expression, 
 
 K = NH = NP (C + d M-f C 2 M 2 ). 
 
 If the intensity is feeble the parenthesis may be repre- 
 sented by a constant A, and 
 
 K = N A I 2 , 
 
 and the electro-motive force of induction is 
 E = N A I. 
 
EFFICIENCY OF COUPLED MACHINES. 57 
 
 For the other part, 
 
 I K = E - E = K I - N A I, 
 
 whence is deduced 
 
 The Gramme machine with electro-magnets enters into 
 the same type in theory, but entirely differs from the 
 preceding in construction. This machine the Authors 
 have studied as an electro-motor only. The resistance of 
 the machine is not constant, because the commutator 
 brush communicates successively with the different bobbins 
 of the ring, but does not vary more than T ^-g- ; the mean 
 is 1*104 ohm. The Authors have added successively 
 exterior resistances to the amount of 200 ohms, and have 
 varied the speed from a quarter of a revolution to nineteen 
 revolutions per second. It should be remarked that this 
 enormous speed can be obtained on very resistant circuits 
 only, because the intensity increases so rapidly that with 
 a shorter circuit all the disposable power of the motor, 
 which equalled 5 HP., could not be utilised. All the 
 quantities are reduced into absolute units (webers), and 
 the resistance expressed in ohms. The phenomena are 
 regular when the resistance does not exceed 10 ohms, nor 
 the speed of the machine ten revolutions per second. 
 Thus, if the quantity is inferior to 0*08 weber, it is 
 proportional to the speed, and in inverse ratio to the total 
 resistance of the circuit. For larger quantities the con- 
 stant has for expression , which depends only upon 
 
 the intensity of the current. This result accords with 
 theory. The electro-motive force is 
 
 n i (C + C x M + C 2 M 2 ), 
 
58 ELECTKIC TRANSMISSION OF POWER, 
 
 which gives 
 
 The values of - increasing nearly proportionally to the 
 
 quantity, calculations can be effected by the following 
 empirical formula, 
 
 = 0-286 + 0-4f, 
 n 
 
 where f is the quantity of current, R the resistance of the 
 whole circuit, and n the number of revolutions of the 
 Gramme-armature. 
 
COMPAKATIVE EFFICIENCY OF VARIOUS MACHINES. 59 
 
 CHAPTEE VIII. 
 
 COMPARATIVE EFFICIENCY OF VARIOUS MACHINES. 
 
 NOTHING can be done in the inter-comparison of any 
 natural force until accurate measurements have been 
 made. For those measurements we are indebted to a great 
 extent to the labours of the committee on dynamo-elec- 
 tric machines formed by the Franklin Institute, and to 
 Professors Houston and Thomson's report as to the 
 ratio of efficiency in the conversion of motive-power into 
 electricity. 
 
 In entering this comparatively new field of research, 
 peculiar difficulties occurred, owing to conditions that do 
 not exist in the various forms of batteries used as sources 
 of electrical power. In many battery circuits a high 
 external resistance may be employed, and the electro- 
 motive force remains comparatively constant, while in 
 dynamo-electric machines, in which the reaction principle 
 is employed, the introduction of a very high external 
 resistance into the circuit must be necessarily attended 
 by decided variations in the electro-motive force due to 
 changes in the intensity of the magnetic field in which 
 the currents have their origin. Moreover, a considerable 
 difficulty is experienced in the great variations in the 
 behaviour of these machines when the resistance of the 
 external work is changed. Changes due to loss of con- 
 ductivity by heating, also take place in the machine 
 itself. These variations are also attended by changes in 
 the power required to drive the machine, and in the speed 
 of running, which again re-act on the current generated. 
 These are certain normal conditions in the running of 
 
60 ELECTRIC TRANSMISSION OF POWER. 
 
 dynamo-electric machines under which all measurements 
 can be made, viz. : 
 
 The circuit must be closed, since, on opening, all elec- 
 trical manifestations cease. 
 
 The speed of the machine must be, as nearly as possible, 
 constant. 
 
 The power required to maintain a given rate of speed 
 must be, as nearly as possible, constant. 
 
 The machines submitted to the Committee for determi- 
 nation were as follows, viz. : 
 
 1. Two machines of different size, and of somewhat 
 different detailed construction, built according to the 
 invention of Mr. C. F. Brush, and styled respectively in 
 the same report as A 1 , the larger of the two machines, and 
 A 2 , the smaller. 
 
 2. Two machines, known as the Wallace-Farmer 
 machines, differing in size and in minor details of con- 
 struction, and designated respectively as B 1 , the larger of 
 the two, and B 2 , the smaller. In the case of the machine 
 B 1 , the experiments were discontinued after the measure- 
 ment of the resistances was made, insufficient power 
 being at disposal to maintain the machine at its proper 
 rate of speed. 
 
 3. A Gramme machine of the ordinary construction. 
 All the above machines are constructed so that the 
 
 whole current traverses the coils of the field magnets, 
 being single current machines, in which the reaction 
 principle is employed. In the case of the machine desig- 
 nated A 2 , the commutators are so arranged as to permit 
 the use of two separate circuits when desired. 
 
 For the purpose of preserving a ready measure of the 
 current produced by each machine, under normal con- 
 ditions, a shunt was constructed by which an inconsider- 
 able but definite proportion of the current was caused to 
 traverse the coils of a galvanometer, thus giving with 
 each machine a convenient deflection, which could at any 
 
COMPARATIVE EFFICIENCY OF VARIOUS MACHINES. 61 
 
 time be reproduced. As the interposition of this shunt in 
 the circuit did not appreciably increase its resistance, the 
 normal conditions of running were preserved. 
 
 As indicating the preservation of normal conditions in 
 any case, the speed of running and the resistances being 
 the same as in any previous run, it was found that when 
 there was an equal expenditure of power, as indicated by 
 the dynamometer, the current produced, as indicated by 
 the galvanometer, was in each case the same. 
 
 Certain of the machines experimented with heated 
 considerably on a prolonged run ; most of the tests, there- 
 fore, were made when the machines were as nearly as 
 possible at about the temperature of the surrounding 
 air. 
 
 It is evident that no other standard could be well 
 adopted, as under a prolonged run the temperature of the 
 different parts of the machine would increase very un- 
 equally ; and, moreover, it would be impossible to make 
 any reliable measurements of the temperatures of many 
 such parts. 
 
 In measuring the resistance of the machines, a Wheat- 
 stone's bridge, with a sliding contact, was used in con- 
 nection with a galvanometer and a suitable voltaic battery. 
 In taking the resistances of the machines, several measure- 
 ments were made with the armatures in different positions, 
 and the mean of these measurements taken as the true 
 resistance. 
 
 To determine the value of the current, two methods 
 were selected, one based on the production of heat in a 
 circuit of known resistance, and the other upon the com- 
 parison of a definite proportion of the current with that 
 of a Daniell's battery. 
 
 In the application of the first method, eight litres of 
 water, at a known temperature, were taken and placed in 
 a suitable non-conducting vessel. In this was immersed 
 a German-silver wire, and a sliding contact adjusted to 
 
62 ELECTRIC TRANSMISSION OF POWER. 
 
 afford a resistance equal to that of the exterior resistance 
 under consideration. 
 
 This was now introduced into the circuit of the machine. 
 All these arrangements having been made, the temperature 
 of the water was accurately obtained by a delicate ther- 
 mometer. The current from the machine running under 
 normal conditions was allowed to pass, for a definite time, 
 through the calorimeter so provided. From the data thus 
 obtained, after making the necessary corrections as to the 
 weight of the water employed, the total heating effect in 
 the exterior circuit, as given in Table II., was deduced. 
 
 Since the heat in various portions of an electrical 
 circuit is directly proportional to the resistance of those 
 portions, the total heat of the circuit was easily calculated, 
 and is given in Table III., in English heat units. 
 
 For ease of reference, the constant has been given for 
 conversion of these units into the now commonly accepted 
 units of heat. 
 
 Having thus obtained the heating effect, the electrical 
 current is 
 
 X 772 
 
 where C = the weber current per ohm ; "W, the weight of 
 water in pounds ; h, the increase of temperature in degrees 
 Fahr. ; 772, Joule's constant ; E, the resistance in ohms ; 
 t, the time in seconds; and c, the constant 0-737335, the 
 equivalent in foot-lbs. of one weber per ohm per second. 
 The currents so deduced for the different machines are 
 given in Table IV. 
 
 The other method employed for measuring the current, 
 viz. the comparison of a definite portion thereof with the 
 current from a Daniell's battery, was as follows : 
 
 A shunt was constructed, of which one division of the 
 circuit was 0-12 ohm and the other 3000 ohms. In this 
 latter division of the circuit was placed a low-resistance 
 
COMPAEATIVE EFFICIENCY OF VAEIOUS MACHINES. 63 
 
 galvanometer, on which convenient deflections were 
 obtained. This shunt being placed in the circuit of the 
 machine, the galvanometer deflections were carefully 
 noted. These substituted resistances were immersed in 
 water, in order to maintain an equable temperature. 
 
 Three Daniell's cells were carefully set up and put in 
 circuit with the same galvanometer, and with a set of 
 standard resistance coils. Eesistances were unplugged 
 sufficient to produce the same deflections as those noted 
 with the shunt above mentioned. 
 
 The shunt ratio, as nearly as could conveniently be 
 obtained, was g^-fonj-. Then the formula 
 
 c = 
 
 sn xl'079 ? 
 
 ir~ 
 
 where C equals the weber current ; s, the reciprocal of the 
 shunt ratio ; n, the number of cells employed ; 1-079, the 
 assumed normal value of the electro- motive force of a 
 Daniell's cell, and JR, the resistances in the circuit with 
 the battery, gives at once the current. In comparison 
 with the total resistances of the circuit, the internal 
 resistance of the battery was so small as to be neglected. 
 The results obtained were as follows : 
 
 Name of Machine. 
 
 Shunt 
 Ratio. 
 
 Number of 
 Daniell's 
 Cells. 
 
 Resistances 
 Unplugged 
 
 Speed 
 of 
 
 Machine. 
 
 
 
 3 
 
 Ohms. 
 2 710 
 
 Revo- 
 lutions. 
 1 340- 
 
 Small Brush 
 
 
 
 3 700 
 
 1 400 
 
 Wallace-Farmer . . . .1 
 Gramme . . . 
 
 j > 
 > 
 
 
 i > 
 
 8,320 
 6,980 
 4 800 
 
 844 
 1,040 
 800 
 
 
 > 
 
 > i 
 
 
 
 The weber currents, as calculated from the above data, 
 are given in Table IV. 
 
64 
 
 ELECTRIC TRANSMISSION OF POWER. 
 
 From the results thus derived, the electro-motive force 
 was deduced by the general formula, 
 
 E = C x R. 
 
 The electro-motive force thus calculated will be found 
 in Table IV. 
 
 TABLE L* SHOWING WEIGHT, POWER ABSORBED, &c., BY DYNAMO- 
 ELECTRIC MACHINES, TESTED BY A COMMITTEE OF THE FRANKLIN 
 INSTITUTE, 1877-78. 
 
 
 A Copper- wire in 
 
 
 
 00 .- 
 
 
 
 Name of 
 Machine. 
 
 c 
 ^ Armature. 
 
 Field Magnets. 
 
 25* 
 
 ts || 
 
 pounds of 
 Power 
 
 HP. 
 
 
 3 
 
 
 
 
 
 
 
 
 
 ila 
 
 
 
 
 Size. 
 
 Weight. 
 
 Size. 
 
 Weight. 
 
 s 
 
 
 
 
 Inch. 
 
 Ibs. 
 
 Inch. 
 
 Ibs. 
 
 
 
 
 Large Brush 
 
 475 0-081 
 
 32 
 
 0-134 
 
 100 
 
 1,340 
 
 107-606 
 
 3-26 
 
 Small 
 
 390 0-063 
 
 24 
 
 0-096 
 
 80 
 
 1,400 
 
 124-248 
 
 3-76 
 
 Large Wal-j 
 
 600 0-042 
 
 50 
 
 0-114 
 
 125 
 
 800 
 
 
 ' 
 
 lace . ./ 
 
 
 
 
 
 
 
 
 Small 
 
 350 0-043 
 
 18f 
 
 0-098 
 
 41 
 
 1,000 
 
 128-544 
 
 3-89 
 
 Gramme . 
 
 366 0-059 
 
 104 
 
 0-108 
 
 104 
 
 800 
 
 60-992 
 
 1-84 
 
 Statements are frequently made, when speaking of 
 certain dynamo-electric machines, that they are equal to 
 a given number of Darnell's or other well-known battery 
 cells. It is evident, however, that no such comparison 
 can properly be made, since the electro-motive force of a 
 dynamo-electric machine, in which the reaction principle 
 is employed, changes considerably with any change in the 
 relative resistances of the circuit of which it forms a part, 
 while that of any good form of battery, disregarding pola- 
 risation, remains approximately constant. The internal 
 
 * These reports have been condensed to show merely the power ex- 
 pended and returnable by dynamo-electric machines. 
 
COMPARATIVE EFFICIENCY OF VARIOUS MACHINES. 65 
 
 resistance of dynamo-electric machines is, as a rule, very 
 much lower than that of any ordinary series of battery 
 cells, as generally constructed, and therefore, to obtain 
 with a battery conditions equivalent to those in a dynamo- 
 electric machine, a sufficient number of cells in series would 
 have to be employed to give the same electro-motive force ; 
 while, at the same time, the size of the cells, or their 
 number in multiple arc, would require to be such that the 
 internal resistance should equal that of the machine. 
 
 Suppose, for example, that it be desired to replace the 
 large Brush machine by a battery whose electro -motive 
 force and internal and external resistances are all equal 
 to that of the machine, and that we adopt as a standard 
 a Daniell's cell, of an internal resistance of, say, one ohm. 
 Eeferring to Table IV., the electro- motive force of this 
 machine is about 39 volts, to produce which about 
 37 cells, in series, would be required ; but, by Table II., 
 the internal resistance of this machine is about 49 ohm. 
 To reduce the resistance of our standard cells to this 
 figure, when 37 cells are employed in series, 76 cells in 
 multiple arc would be required. Therefore, the total 
 number of cells necessary to replace this machine would 
 equal 37 X 76, or 2812 cells, working over the same 
 external resistance. It must be borne in mind, however, 
 that although the machine is equal to 2812 of the cells 
 taken, that no other arrangement of these cells than that 
 mentioned, viz. 76 in multiple arc and 37 in series, could 
 reproduce the same conditions, and, moreover, the external 
 resistances must be the same. The same principles 
 applied to other machines would, when the internal 
 resistance was great, require a large number of cells, but 
 arranged in such a way as to be extremely wasteful, from 
 by far the greater portion of the work being done in over- 
 coming the resistance of the battery itself. 
 
 The true comparative measure of the efficiency of 
 dynamo-electric machines as means for converting motive- 
 
66 ELECTRIC TRANSMISSION OF POWER. 
 
 power into work derived from electrical currents, is found 
 by comparing the units of work consumed with the equi- 
 valent unit of work appearing in the circuit external to the 
 machine. In Table V. the comparative data are given. 
 
 The heat due to local circuits in the conducting masses 
 of metal in the machines, irrespective of the wire, consumes 
 force in what may be conveniently described as the local 
 action of the machine, and is manifestly comparable to the 
 well-known local action of the voltaic battery, since in 
 each case it not only acts to diminish the effective current 
 produced but also adds to the cost. 
 
 No determinations made with an unknown or abnormal 
 external resistance can be of any value, since the propor- 
 tion of work done, in the several portions of an electrical 
 circuit, depends upon and varies with the resistances they 
 offer to its passage. If, therefore, in separate determina- 
 tions with any particular machine, the resistance of that 
 part of a circuit the work of which is measured, be in one 
 instance large in proportion to the remainder of the 
 circuit, and in another small, the two measurements thus 
 made would give widely different results, since in the 
 case where a large resistance was interposed in this part 
 of the circuit, the percentage of the total work appearing 
 there would be greater than if the small resistance had 
 been used. Wherever an attempt has been made to deter- 
 mine the efficiency of a single machine, or of the relative 
 efficiency of a number of machines, by noting the quantity 
 of gas evolved in a voltameter, or by the electrolysis of 
 copper sulphate in a decomposing cell, when the resist- 
 ance of the voltameter or decomposing cell did not 
 represent the normal working resistance, it is manifest 
 that the results cannot properly be taken as a measure of 
 the actual efficiency. 
 
 During any continued run, the heating of the wire of 
 the machine, either directly by the current, or indirectly 
 from conduction from those parts of the machine heated 
 
COMPAEATIVE EFFICIENCY OF VAKIOUS MACHINES. 67 
 
 by local action, as explained in a former part of this 
 report, produces an increased resistance, and a consequent 
 falling off in the effective current. Thus, in Table II., at 
 the temperature of 73-5 Fahr., A 1 , the large Brush 
 machine, had a resistance of 485 ohms, while at 88 Fahr., 
 at the armature coils, it was 0*495 ohm. These differences 
 were still more marked in the case of B 1 . 
 
 In A 2 , the small Brush machine, it will be noticed that 
 two separate values are given for the resistance of the 
 machine. These correspond to different connections, viz. 
 the resistance, 1*239 ohms, being the connection at the 
 commutator for low resistance, the double conducting 
 wires being coupled in multiple arc, while 5*044 ohms 
 represent the resistance when the sections of the double 
 conductor are coupled at the commutator in series. 
 
 Eeferring to Table III., the numbers given in the 
 column headed " Heat in external circuit " are the measure 
 of the total heating power in that portion of the circuit 
 external to the machine. 
 
 In the column headed " Total heat of circuit " are 
 given the quantities of heat developed in the whole 
 circuit, which numbers, compared with those in the pre- 
 ceding column, furnish us with the relative proportions of 
 the work of the circuit, which appear in the external 
 circuit. 
 
 The column headed " Heat per ohm per second " gives 
 the relative work per ohm of resistance in each case, and 
 these numbers, multiplied by the total resistance, give the 
 total energy of the current expressed in heat units per 
 second. 
 
 In Table IV. are given the results of calculation and 
 measurement as to the electrical work of each machine. 
 
 It is evident to those acquainted with the principles of 
 electrical science, that in the weber current and the unit 
 electro-motive force, we have the data for comparing the 
 work of these machines with that of any other machine or 
 
 F 2 
 
68 
 
 ELECTRIC TRANSMISSION OF POWER. 
 
 S < 
 
 % * 
 
 S I i 
 
 s I ^ 
 
 & E | 
 
 S g 
 
 <- <j <j 
 
 3 2 I 
 
 8 3 1 
 
 .8 - i 
 
 -=3 b ^ 
 
 
 . 1 1 
 
 3.3 . 
 
 S^.-a 2o ^ o co co 
 P5*S g Jo cp 05 ; p co 
 
 ~8;3 '" H rH (>l CO t> CO CO CO 
 
 cococococo cocococo 
 
 ooooo -ocpoo 
 
 OOOOO 0000 
 
 iO CO t^" O5 CO GO CO O5 
 
 OOr-i rH (NCOrHrH 
 
 10 tn 10 10 >o 
 
 COO5OCOOCOCOCOCOCO 
 HHrH<MOCOrHC5O5CpCp 
 
 "-* W .,,,.,, 
 
 t>coi>i>t>'-!t>i> 
 
 l- s " 
 
 n w 
 
COMPARATIVE EFFICIENCY OF VARIOUS MACHINES. 69 
 
 M O 
 
 II 
 
 111!; 
 
 r s lli 
 
 I > .s a) S 
 
 1^1 
 
 W h ft ! 
 
 Bs 
 
 i mill 
 
 as 
 
 2o5 
 fio 
 
 
 
 
 
 
 (MOO 
 
 t> t> rH 
 
 O rH (M 
 
 f-t rH rH 
 
 3 $ 
 GO O GO 
 
 i"^ O^l CO rH O5 O1 CO 
 
 CO CO (M O GO O IO 
 
 CO CO -<tl I-H O i-H (M 
 
 O O O O O O O 
 
 8 
 
 s s 
 
 CO rH O 
 
 CO CO rH CO 
 CO CO CO t** 
 
 g 
 
 ? ? 
 
 O H 
 
 CO (M 
 (N CO 
 
 CO (M CO O O 
 
 Oi CO O (M O IO 
 
 O5 CO rH TH O CO 
 
 CO CO CO CO CO CO CO 
 CO CO GO CO CO CO CO 
 
 & o 
 
70 
 
 ELECTEIC TRANSMISSION OF POWER. 
 
 a I 
 
 * 
 
 o o 
 
 w Q 
 
 gq 
 
 o i 
 
 II 
 
 5S 
 
 M CO 
 
 !l 
 
 s g 
 
 1 
 
 < Q 
 
 icj 
 
 .^i 
 
 IffPfi 
 
 pe 
 d. 
 
 . 
 
 ISI2 
 
 ^ * 
 
 o 
 
 o ^ 
 
 5 s 
 
 i I C5 CO 
 
 s 2 
 
COMPARATIVE EFFICIENCY OF VARIOUS MACHINES. 71 
 
 battery, whether used for light, heat, or electrolysis, or 
 any other form of electrical work. 
 
 The values of the weber current, as deduced from the 
 heat developed, and from the comparison with a Daniell's 
 cell, do not exactly agree; nor could this have been 
 expected, when the difficulty of minutely reproducing the 
 conditions as to speed, resistance, etc., is considered. 
 
 By comparison of the electro-motive force of the different 
 machines, it appears that no definite unit seems to have 
 been aimed at by all the makers. 
 
 Table Y. is designed especially to permit a legitimate 
 comparison of the relative efficiency in converting motive- 
 power into current. The actual dynamometer reading is 
 given in the first column. On account of the differences 
 of construction and differences in speed of running, the 
 friction and resistance of the air vary greatly, being least 
 with the Gramme, as might be expected, since the form 
 of the revolving armature and the speed of the machine 
 conduce to this result. This is, of course, a point greatly 
 in favour of the Gramme machine. 
 
 That portion of the power expended available for pro- 
 ducing current is given in the third column, being the 
 remainder, after deducting the friction, as above men- 
 tioned ; but this power is not in any case fully utilised in 
 the normal circuit. This is found to be the case by com- 
 paring calculations of the total work of the circuit in 
 foot-lbs. expended in producing such current as given in 
 the appropriate column. 
 
 For instance, in the case of A 1 , the large Brush machine, 
 the available force for producing current is 89,656 foot-lbs. 
 per minute, of which only 53,646 reappear as heat in the 
 circuit. The balance is most probably expended in the 
 production of local currents in the various conducting 
 masses of metal composing the machine. The amount 
 thus expended in local action is given in the column 
 designated "F. P., unaccounted for in the circuit." A 
 
72 
 
 ELECTRIC TRANSMISSION OF POWER. 
 
 1 1 
 
 g Q 
 
 : 
 
 3 2 
 
 i 5 
 
 
 HI* 
 
 1-8 = 1 
 il|< 
 
 iflll 
 
 i, g <U O 
 
 ;&=3B 
 
 ll 
 
 3 
 
 O ^ 
 O G5 
 
 s 
 
 ss 
 
 CO ^H 
 
 S; 
 
 r> oo co 
 
 ^ ^ S 
 
 (M (M 
 
 co cq 
 
 S ^ 
 
 O CO 
 Ci CO 
 t>~ CQ 
 
 CO O CO 
 
 o ^ 
 t> (M 
 
 s 
 
 H O 
 
 " s 
 
 M -M >i 
 
 M pq O 
 
COMPARATIVE EFFICIENCY OF VARIOUS MACHINES. 73 
 
 comparison of the figures in this column is decidedly in 
 favour of the Gramme machine, it requiring the smallest 
 proportion of power expended to be lost in local action. 
 When, however, we consider that the current produced 
 by the large Brush machine is nearly double that pro- 
 duced by the Gramme, the disproportion in the local 
 action is not so great. 
 
 The determinations made enabled the following opinions 
 to be formed as to the comparative merits of the machines 
 submitted for examination : 
 
 The Gramme machine is the most economical, con- 
 sidered as a means for converting motive-power into 
 electrical current, giving a useful result equal to 38 per 
 cent., or to 41 per cent., after deducting friction and 
 the resistance of the air. In this machine the loss of 
 power in friction and local action is the least, the speed 
 being comparatively low. 
 
 The large Brush machine comes next in order of effi- 
 ciency, giving useful effect equal to 31 per cent, of the 
 total power used, or 37^ per cent, after deducting friction. 
 This machine is, indeed, but little inferior in this respect 
 to the Gramme, having, however, the disadvantage of 
 high speed, and a greater proportionate loss of power in 
 friction, etc. This loss is nearly compensated by the 
 advantage this machine possesses over the others of working 
 with a high external, compared with the internal, resist- 
 ance, this also insuring comparative absence of heating in 
 the machine. This machine gave the most powerful 
 current. 
 
 The small Brush machine stands third in efficiency, 
 giving a useful result equal to 27 per cent., or 31 per 
 cent, after deducting friction. Although somewhat 
 inferior to the Gramme, it is, nevertheless, a machine 
 admirably adapted to the production of intense currents, 
 and has the advantage of being made to furnish currents 
 of widely varying electro-motive force. By suitably 
 
74 ELECTEIC TRANSMISSION OF POWER. 
 
 connecting the machine, as before described, the electro- 
 motive force may be increased to over 120 volts. It 
 possesses, moreover, the advantage of division of the 
 conductor into two circuits, a feature which, however, is 
 also possessed by some forms of other machines. The 
 simplicity and ease of repair of the commutator are also 
 advantages. Again, this machine does not heat greatly. 
 
 The Wallace-Farmer machine does not return to the 
 effective circuit as large a proportion of power as the 
 other machines, although it uses, in electrical work, a 
 large amount of power in a small space. The cause of its 
 small economy is the expenditure of a large proportion of 
 the power in the production of local action. By remedying 
 this defect a very admirable machine would be produced. 
 After careful consideration of all the facts, the Committee 
 unanimously concluded that the small Brush machine, 
 though somewhat less economical than the Gramme ma- 
 chine, or the large Brush machine, was, of the machines 
 experimented with, the best adapted for the various pur- 
 poses of the Institute, chiefly for the following reasons: 
 It is adapted to the production of currents of widely- 
 varying electro-motive force, and from the mechanical 
 details of its construction, especially at the commutators, 
 it possesses great ease of repair to the parts subject to 
 wear. 
 
 During the competitive trials at the Franklin Institute, 
 as to the relative efficiency of the machines, as noted in 
 the preceding pages, Professors Houston and Thomson 
 took the opportunity thus afforded to make a careful 
 study of many interesting circumstances which influence 
 the efficiency of these machines. 
 
 A convenient arrangement of the particular circum- 
 stances to be discussed is : (1) those affecting the internal 
 work of the machines ; (2) those affecting the external 
 work; and (3) the relations between the internal and 
 external work. 
 
COMPARATIVE EFFICIENCY OF VARIOUS MACHINES. 75 
 
 The mechanical energy employed to give motion to a 
 dynamo-electric machine is expended in two ways : (1) 
 in overcoming the friction and the resistance of the air ; 
 and (2) in moving the armature of the machine through 
 the magnetic field, the latter, of course, constituting solely 
 the energy available for producing electrical currents. 
 The greatest amount of power expended in the first way 
 was noticed to be about 17 per cent, of the total power 
 employed. This expenditure was clearly traceable to the 
 high speed required by the machine. The speed, there- 
 fore, required to properly operate a machine is an import- 
 ant factor in ascertaining its efficiency. The above percent- 
 age of loss may not appear great ; but when it is com- 
 pared with the total work done in the external circuit, 
 constituting as it did in this particular instance over 
 50 per cent, of the latter, and about 33 per cent, of the 
 total work of the circuit, its influence is not to be dis- 
 regarded. In another instance the work consumed as 
 friction was equal to about 80 per cent, of that appearing 
 in the external circuit as heat, while in the Gramme 
 machine experimented with this percentage fell to 20, and 
 was only about 7 per cent, of the total power consumed in 
 driving the machine. 
 
 In regard to the second way in which mechanical 
 energy is consumed, in overcoming the resistance neces- 
 sary to move the armature through the magnetic field, or, 
 in other words, to produce electrical currents, it must not 
 be supposed that all this electrical work appears in the 
 circuit of the machine, since a considerable portion is 
 expended in producing local circuits in the conducting 
 masses of metal, other than the wire, composing the 
 machine. 
 
 The following instances of the relation between the 
 actual work of the circuit, and that expended in local 
 action, will show that this latter is in no wise to be 
 neglected. In one instance an amount of power, some- 
 
76 ELECTEIC TRANSMISSION OP POWER. 
 
 what more than double the total work of the circuit, was 
 thus expended. In another instance it constituted less 
 than one-third the total work of the circuit. 
 
 Of course, work expended in local action is simply 
 thrown away, since it adds only to the heating of the 
 machine. And, since the latter increases its electrical 
 resistance, it is doubly injurious. 
 
 The local action of dynamo-electric machines is analo- 
 gous to the local action of a battery, and is equally 
 injurious in its effect upon the available current. 
 
 Again, in regard to the internal work of a machine, 
 since all this is eventually reduced to heat in the machine, 
 the temperature during running must continually rise 
 until the loss by radiation and convection into the sur- 
 rounding air equals the production, and thus the machine 
 will acquire a constant temperature. This temperature, 
 however, will differ in different machines, according to 
 their construction, and to the power expended in pro- 
 ducing the internal work, being, of course, higher when 
 the power expended in producing the internal work is 
 proportionally high. 
 
 If, therefore, a machine during running acquires a high 
 temperature when a proper external resistance is employed, 
 its efficiency will be low. But it should not be supposed 
 that because a machine, when run without external re- 
 sistance that is, on short circuit heats rapidly, that 
 inefficiency is shown thereby. On the contrary, should a 
 machine remain comparatively cool when a proper ex- 
 ternal resistance is employed, and heat greatly when put 
 on short circuit, these conditions should be regarded as a 
 proof of its efficiency. 
 
 In regard to the second division, the external work of 
 the machine, this may be applied in the production of 
 light, heat, electrolysis, magnetism, &c. 
 
 Perhaps the highest estimate that can be given of the 
 efficiency of dynamo-electric machines, as ordinarily used, 
 
COMPAKATIVE EFFICIENCY OF VARIOUS MACHINES. 77 
 
 is not over 50 per cent.; measurements have not given 
 more than 38 per cent. Future improvements may in- 
 crease this proportion. Since the efficiency of an ordinary 
 steam-engine and boiler in utilising the heat of the fuel 
 is probably over-estimated at 20 per cent., the apparent 
 maximum percentage of heat that could be recovered from 
 the current developed in a dynamo-electric machine 
 would be over-estimated at 10 per cent. The economical 
 heating of buildings by means of electricity may, there- 
 fore, be regarded as totally impracticable. 
 
 In respect to the relations that should exist between 
 the external and the internal work of dynamo-electric 
 machines, it will be found that the greatest efficiency will, 
 of course, exist where the external work is much greater 
 than the internal work, and this will be proportionally 
 greater as the external resistance is greater. 
 
78 ELECTRIC TRANSMISSION OF POWER. 
 
 CHAPTER IX. 
 
 OTHER THEORETICAL CONSIDERATIONS. 
 
 MR. DESMOND FITZGERALD lias pointed out that in the case 
 
 pi 
 
 of any electro-motor the equation I = is strictly ap- 
 plicable. 
 
 In the voltaic battery, however, a variation of E does 
 not necessarily affect E which is altogether independent 
 of such variation when this occurs in the external portion 
 
 of the circuit. Thus we have generally I cc , or current 
 
 varies inversely as the resistance in circuit. 
 
 Again, a variation of E does not necessarily affect R ; 
 and, when the external resistance of the circuit bears a 
 high ratio to the battery resistance, a variation of the 
 electro-motive force, from E to E x and addition to, or 
 diminution of, the number of cells in series causes the 
 
 TT 
 current to vary approximately in the ratio =* Accurately, 
 
 the variation in any case is determined by the ratio 
 
 TT T? 
 
 ^ * when p is the resistance of the cell or cells 
 & K -f- jj p 
 
 added or subtracted. Thus, 
 
 E 1 E x R E! 
 
 E X ER-j-Ep ~ R+7 
 
 Thus, in the case of a telegraph circuit, for instance, we 
 have, approximately, I cc E. On the other hand, in the 
 
OTHER THEORETICAL CONSIDERATIONS. 79 
 
 dynamo-electric machine, converting into electrical work 
 
 1 E 2 
 
 a given HP., I cc =., since the ratio being constant, 
 f K -ti 
 
 E 2 cc K, E x /X and cc --~ = --L. Thus, any 
 
 variation of B in this case necessarily affects E. 
 
 Again, any variation of E necessarily affects R ; and the 
 
 product E I being constant, we have I x =, a somewhat 
 
 Jij 
 
 startling result, which to some observers has appeared 
 contradictory to the law of Ohm. With this, however, it 
 is in perfect accord in effect, since E cc J K, R cc E 2 , 
 
 E E 1 
 
 and x = - ; or, when E is varied, the current varies 
 xv xj- 1 jit 
 
 inversely as the electro-motive force, because the resistance 
 varies as the square of this value. 
 
 It will be seen that R cc E 2 - , and that the same 
 
 quantity of work will be done by the current whatever 
 may be the resistance in circuit. 
 
 If hp. be taken to express the total horse-power con- 
 verted into electrical work (in the whole circuit), under 
 the best conditions, with a Gramme machine of the form 
 experimented with at the Franklin Institute, 
 
 HP. = hp. X 1-39, 
 
 and the efficiency of the machine is expressed by 
 hp. 
 
 HP. 
 
 = 0-72 (nearly). 
 
 Or the machine can convert into electrical work 72 per 
 cent, of the energy expended upon it. 
 
 The ratio = is the measure of the efficiency of dynamo- 
 
80 ELECTRIC TRANSMISSION OF POWER. 
 
 electric machines. In the case of the Gramme machine 
 under the best conditions, we have 
 
 HP. = hp. x 1-39. 
 
 Mr. L. Schwendler has observed that the currents pro- 
 duced by dynamo-electric machines, as the insertion of a 
 Bell telephone (used as a shunt) will easily prove, are not 
 steady. The dynamo-electric machine with the greatest 
 number of sections in the induction cylinder gives the 
 steadiest current. Twelve sections are found to be neces- 
 sary and sufficient. That the current produced by any 
 dynamo-electric machine through a given constant total 
 resistance in circuit increases permanently with the speed 
 of the induction cylinder. This increase of current for 
 low speeds is more than proportional to the speed ; after- 
 wards it becomes proportional, and for high speeds the 
 increase of current is less than proportional to the speed. 
 The current has, however, no maximum for any speed, but 
 reaches its greatest value at an infinite speed. This same 
 law, as the total resistance in circuit is supposed to be 
 constant, of course holds good also for the electro-motive 
 force of the dynamo-electric machine. 
 
 Keeping the speed constant, the electro-motive force of 
 any dynamo-electric machine decreases rapidly with in- 
 crease of external resistance. This decrease is more rapid 
 the smaller the internal resistance of the dynamo-electric 
 machine is made. Hence the currents must decrease much 
 more rapidly than proportional to the total resistance in 
 circuit. As in the case of speed, the electro-motive force 
 has no maximum for a certain external resistance, but 
 approaches permanently its greatest value for an external 
 resistance equal nil. It appears that the function which 
 connects electro-motive force and speed is the same as 
 that which connects electro-motive force and external 
 resistance. We have only to substitute for speed the 
 
OTHER THEOKETICAL CONSIDERATIONS. 81 
 
 inverse of resistance, and vice versa. As to the maximum 
 work by a current in a resistance r, the current decreased 
 much more rapidly than the total resistance in circuit 
 increased, and this resistance r should invariably be made 
 smaller than the remaining resistance of the circuit, i.e., 
 smaller than the internal resistance of dynamo-electric 
 machines plus resistance of leading wires. 
 
 With regard to the electro-motive force of a dynamo- 
 electric machine as a function of the resistance and speed, 
 it appears that the formulae are most probably correct for 
 all dynamo-electric machines if the loss of current by 
 transmission is taken into account : 
 
 E being the E M F, ra the internal resistance, and r the ex- 
 ternal resistance, including resistance of leading wire. 
 k and a are independent of m and r, and are the functions 
 of the speed of the induction cylinder, containing also the 
 construction coefficients, e is the basis of the natural 
 logarithm. Further, 
 
 E 1 = K 
 
 E 1 being the E M F, and v the speed of the induction 
 cylinder. k l and a 1 are independent of v and are functions 
 of m and r only. These two functions, E and E 1 , correspond 
 to all the characteristics of the curves found by experi- 
 ment, and they also fulfil the limit conditions. 
 
 In respect to the regularity of the production of currents 
 by dynamo-electric machines at different periods, if the 
 brushes are well set, and if they are placed as nearly as 
 
 G 
 
82 ELECTRIC TRANSMISSION OF POWER. 
 
 possible in the neutral line of the commutator,* the pro- 
 .duction of current is perfectly regular, and measurements 
 taken through the same external resistance at the most 
 distant periods agree most perfectly with each other, sup- 
 posing the correction for variation in speed and internal 
 resistance to be applied. Disregarding the heating of the 
 dynamo-electric machine by the current, the time required 
 to arrive at dynamic equlibrium, i.e., when force trans- 
 mitted, current, and magnetism received are constant, is 
 very short indeed, especially for strong currents. 
 
 As the power which is represented by the measured 
 current working through a given resistance can never 
 exceed the original power transmitted to the machine, we 
 can, from current, resistance, and force measurements, 
 frame a formula which checks the probability of the 
 results. This formula is : 
 
 C< .33^/^^. 
 r-\~m 
 
 W 1 is the total power consumed by any dynamo-electric 
 machine when producing the observed current C in a 
 circuit of resistance r -j- m ; w l is the power consumed by 
 the dynamo-electric machine when producing no current 
 (i.e. driven empty, circuit open, external resistance in- 
 finite) ; r is the external resistance, and m the internal 
 resistance. In the above formula C is in webers, W 1 and 
 w l in meg-ergs per second, and r and m in Siemens' 
 units. Of late, exaggerated statements of the performance 
 of dynamo-electric machines have been made, the absurdity 
 of which would have become evident at once if the above 
 formula had been applied as a check to the results. 
 
 If all the work ( W 1 w l ) were transformed into available 
 
 * M. A. Breguet states that the maximum and steadiest current 
 results from the brushes being placed at an angle with the neutral 
 line, dependent in amount upon v. 
 
OTHER THEORETICAL CONSIDERATIONS. 
 
 83 
 
 W 1 10 
 current in the external circuit, then = unity, where 
 
 W is the total work performed by the observed current in 
 a circuit of known resistance. In practice it will be found, 
 
 . 
 however, that -- > 1 (for many reasons). This ex- 
 
 presson, 
 
 
 , is called the coefficient of transmission, 
 
 and designated by the letter k. k is different for the 
 different dynamo-electric machines which have been tried, 
 and decreases with increase of current. Producing cur- 
 rents above 24 webers, the following average vahies of 
 k have been obtained : 
 
 i Average Current 
 in Webers. 
 
 1 
 
 01 
 
 31 
 
 
 
 1 
 
 12 
 
 31 
 
 1 
 
 1 
 
 28 
 
 27 
 
 9 
 
 W 
 
 , w is the useful work done in the circuit 
 W 1 w 1 
 
 by the current As the resistance of dynamo-electric 
 machines and leading wires cannot be made nil, the 
 coefficient of efficiency must be always smaller than 
 unity. For currents above 24 webers, we have : 
 
 e. ' Average Current. 
 
 0-62 
 
 29-5 
 
 0-53 
 
 31-0 
 
 0-47 
 
 32-6 
 
 0-30 
 
 27-9 
 
84 ELECTRIC TRANSMISSION OF POWER. 
 
 As to the practical mechanical equivalent of the currents 
 
 W 1 ?i 
 
 produced by dynamo-electric machines, it = ~ , where 
 
 O 
 
 is the current in webers. Above 24 webers, different 
 dynamo-electric machines produce the weber at the fol- 
 lowing comsumption of power: 1 weber at 686*5 meg- 
 ergs per second, 1 weber at 736 meg-ergs per second, 
 
 1 weber at 920 meg- ergs per second. 
 
CONCLUSIONS. 85 
 
 CHAPTER X. 
 
 CONCLUSIONS. 
 
 THE feasibility of electric transmission of power having 
 been proved from consideration of mechanical efficiency 
 both as regards current developed from mechanical power 
 and as mechanical power reclaimed from the current thus 
 produced, we have learnt from unimpeachable evidence 
 that the power reclaimed may easily amount to 48 per 
 cent, of that expended in the first instance. This amount 
 of reclaimed power is indubitably superior to that obtained 
 with compressed air, and approaches the practical effi- 
 ciency of hydraulic transmission. Electric transmission 
 has, however, the unparalleled advantage of being superior 
 to the obstacle presented by distance, whilst it is at the 
 same time easily portable, and can be changed in direction, 
 as well as in intensity, at will. No force appears in the 
 connecting portions or conductor, such as appears during 
 mechanical transmission with shafting, or in pipes with 
 compressed air or water. The conductor appears inert, 
 and can be shifted, bent, or in any way moved whilst 
 transmitting many horse-power. Its continuity must not, 
 of course, be interrupted. 
 
 The source of power and the point of reclamation may 
 be relatively situated most awkwardly, but the electric 
 conductor can be brought round the sharpest corner, or 
 carried through the most private room without incon- 
 venience. There is nothing to burst or give way. The 
 same circuit as may be tapped to provide the means of 
 working power-machinery can be as conveniently tapped 
 to work a sewing-machine. 
 
86 ELECTRIC TRANSMISSION OF POWER. 
 
 In mining operations electric transmission will doubt- 
 less become of the highest value, since it involves no 
 danger. Machines for this purpose could be easily con- 
 structed without a commutator, so that sparks could be 
 avoided, with only small loss of power. The ready 
 portability offers great inducements to the mining 
 engineer. For ploughing by power, trials made in France 
 show that electricity can replace steam with advantage 
 and economy. And, in Scotland, power obtained from a 
 waterfall has been transmitted one mile and a half. 
 
 Dredges could be reduced in size, and worked from a 
 central motor, so that smaller channels could be cleansed 
 mechanically than are now subject to this method. In 
 mills and factories inaccessible rooms can be utilised for 
 power- worked machinery. These are but a few advan- 
 tages. A millennium might be anticipated when the water- 
 power of a country shall be available at every door, for 
 electric-power conductors can be laid in the streets more 
 easily than gas or water-pipes. 
 
 But, says the economist, what about cost? Acknow- 
 ledging these great advantages, what is there to pay for 
 them ? And the economist can be satisfactorily answered. 
 Leaving out of count the scheme proposed by Sir William 
 Thomson, in which we might have our water conveyed to 
 us through pipes, the metal of which conducted the 
 electricity for our power, we have to consider what is 
 necessary in transmitting power electrically. 
 
 First, we require to generate our electricity, and water- 
 power is, of course, preferable if available. If not avail- 
 able to generate electricity, it surely will not be available 
 to compress air or force water, because these are only to 
 be carried through comparatively short distances, and the 
 original power question may be cancelled from the equation 
 as being a common element. Keference, it need scarcely 
 be said, is made only to cases where distance is involved. 
 As our efficiency is good, we have only to consider (1) the 
 
CONCLL'SibivS/ 
 
 ' 87 
 
 cost of the motor and moved engines, and (2) the cost of 
 the conducting systems. 
 
 The motor and moved engines being in practice iden- 
 tical, the consideration of one suffices for. both. These 
 machines, as has been shown, are very simple in con- 
 struction, and consist essentially of so much cast-iron and 
 insulated copper wire, the market prices of which are 
 known, so that the cost of any machine for developing so 
 much horse-power may be easily calculated. The labour 
 of construction should form an unimportant item, for none 
 of the skill is involved such as is required in the con- 
 struction of even the most common steam, air, or gas- 
 engine. The quantities of materials required are but 
 little, if more, costly, in the case of electric machines, 
 and this excess of cost is due. to infrequency of de- 
 mand. The construction of machines of size hitherto 
 unattempted is not required, and it has been shown by 
 Prof. Thomson that electric machines of 1000 HP., as 
 proposed by Dr. Siemens, are not necessary, so that there 
 would be no need to attempt to refute the question of cost 
 of so unusually large-sized engine as of that Mr. Sprague has 
 entered into. It has been shown that ten 100- HP. engines 
 would give better results as regards efficiency, whilst at 
 the same time it would be nearly impossible that all the 
 machines could fall out of repair simultaneously. 
 
 The arrangements of machines being thus consonant with 
 the use of a small conductor, as shown in the previous pages, 
 there is the further advantage in laying this conductor, 
 that no air or water-tight joints have to be made. Taking 
 such joints into consideration, it would be easy to show by 
 figures that an efficiently insulated electric conductor to 
 transmit the same power could be laid at less cost than with 
 air or water, and certainly less than with gas pipes. 
 
 The advantages of electric transmission, it is to be 
 hoped, are worthy therefore of the attention of every 
 engineer interested in transmitting power. 
 
LONDON : 
 
 PBINTED BY WILLIAM CLOWES AND SONS, 
 STAMFORD STREET AND CHARING CROSS. 
 
BOOKS RELATING 
 
 TO 
 
 APPLIED SCIENCE, 
 
 PUBLISHED BY 
 
 E, & F, N, SPON, 
 
 LONDON : 46, CHARING CROSS. 
 
 NEW YORK : 446, BROOME STREET. 
 
 The Ornamental Penmaris, Engraver s, Sign Writer 's, 
 
 and Stone Cutter's Pocket-Book of Alphabets ; including Church Text, 
 Egyptian, Egyptian Perspective, French, French Antique, French 
 Renaissance, "German Text, Italic, Italian Shaded, Italian Hair Line, 
 Monograms, Old English, Old Roman, Open Roman, Open Stone, Orna- 
 mental Roman, Latin, Rustic, Tuscan, etc. Fcap. 8vo, sewn, 6d. 
 
 Algebra Self-Taught. By W. P. HIGGS, M.A., 
 
 D.Sc., LL.D., Assoc. Inst. C.E., Author of ' A Handbook of the Differ- 
 ential Calculus,' etc. Crown 8vo, cloth, 2s. 6d. 
 
 CONTENTS : 
 
 Symbols and the Signs of Operation The Equation and the Unknown Quantity- 
 Positive and Negative Quantities Multiplication Involution Exponents Negative Expo- 
 nents Roots, and the Use of Exponents as Logarithms Logarithms Tables of Logaiithms 
 and Proportionate Parts Transformation of System of Logarithms Common Uses of 
 Common Logarithms Compound Multiplication and the Binominal Theorem Division, 
 Fractions and Ratio Continued Proportion The Series and the Summation of the Series 
 Limit of Series Square and Cube Roots Equations List of Formulae, etc. 
 
 Progressive Lessons in Applied Science. By EDWARD 
 
 SANG, F.R.S.E. Crown 8vo, cloth, each Part, 3.$-. 
 
 Part i. Geometry on Papet Part 2. Solidity, Weight, and Pressure Part 3. Trigono- 
 metry, Vision, and Surveying Instruments. 
 
 On Designing Belt Gearing. By E. J. COWLING 
 
 WELCH, Mem. Inst. Mech. Engineers, Author of 'Designing Valve 
 Gearing.' Fcap. 8vo, sewed, 6d. 
 
CATALOGUE OF SCIENTIFIC BOOKS 
 
 Arbitrations : a Text-book for Surveyors in Tabu- 
 lated form. By BANISTER FLETCHER, F.R.I.B.A., Author of 'Model 
 Houses,' etc. Crown 8vo, cloth, 5-r. 
 
 CONTENTS : 
 
 What matters may be submitted to Arbitration Of the Submission Of Revocation 
 Who may Arbitrate Powers of the Arbitrators Of Joint Arbitrators and Umpires Of 
 Evidence Of the Award Of Costs and Charges Advice to Plaintiffs and Defendants 
 Appendix of Forms. 
 
 A Handbook of Formula, Tables, and Memoranda, 
 
 for Architectural Surveyors and others engaged in Building. By J. T. 
 HURST, C.E. Twelfth edition, thoroughly revised and re-written. 
 Royal 3 2mo, roan, $j. CONTAINING : 
 
 Formulae and Tables for the Strength of Materials, Roofs, Water Supply, Drainage, Gas, 
 and other matters useful to Architects and Builders Information connected with Sanitary 
 Engineering Memoranda on the several Trades used in Building, including a Description of 
 Materials and Analyses for Prices of Builders' Work The Practice of Builders' Measure- 
 ment Mensuration and the Division of Land Tables of the Weights of Iron and other 
 Building Materials Constants of Labour Valuation of Property Summary of the Practice 
 in Dilapidations Scale of Professional Charges for Architects and Surveyors Tables of 
 English and French Weights and Measures. 
 
 " It is no disparagement to the many excellent publications we refer to, to say that in our 
 opinion this little pocket-book of Hurst's is the very best of them all, without any exception. 
 It would be useless to attempt a recapitulation of the contents, for it appears to contain almost 
 everything that anyone connected with building could require, and, best of all, made up in a 
 compact form for carrying in the pocket, measuring only 5 in. by 3 in., and about \ in. thick, 
 in a limp cover. We congratulate the author on the success of his laborious and practically 
 compiled little book, which has received unqualified and deserved praise from every profes- 
 sional person to whom we have shown it." Ut Dublin Builder, 
 
 A Treatise on the Use of Belting for the Trans- 
 mission of Power ; with numerous Illustrations of approved and actual 
 methods of arranging Main Driving and Quarter-Twist Belts, and of Belt 
 Fastenings. Examples and Rules in great number for Exhibiting and 
 Calculating the Size and Driving Power of Belts. Plain, Particular, and 
 Practical Directions for the Treatment, Care, and Management of Belts. 
 Descriptions of many varieties of Beltings, together with chapters on the 
 Transmission of Power by Ropes ; by Iron and Wood Frictional Gearing ; 
 on the Strength of Belting Leather ; and on the Experimental Investiga- 
 tions of Morin, Briggs, and others for determining the Friction of Belts 
 under different Tensions, which are presented clearly and fully, with the 
 Text and Tables unabridged. By JOHN H. COOPER, M.E. I vol., demy 
 8vo, cloth, 15^. 
 
 Researches on the Action of the Blast Furnace. By 
 
 CHARLES SCHINZ. Translated from the German by W. H. Maw and 
 Moritz Miiller. Plates, crown 8vo, cloth, 8s. 6d. 
 
 Spans Builders Pocket-Book of Prices and Memo- 
 randa. Edited by W. YOUNG, Architect. Royal 321110, roan, 41. 6d. ; 
 or cloth, red edges, 3-r. 6d. Published annually. Sixth edition now 
 ready. 
 
PUBLISHED BY E. & F. N. SPON. 3 
 
 Long-Span Railway Bridges, comprising Investiga- 
 tions of the Comparative Theoretical and Practical Advantages of the 
 various adopted or proposed Type Systems of Construction, with numerous 
 Formulae and Tables giving the weight of Iron or Steel required in 
 Bridges from 300 feet to the limiting Spans ; to which are added similar 
 Investigations and Tables relating to Short-span Railway Bridges. Second 
 and revised edition. ByB. BAKER, Assoc. Inst. C.E. Plates, crown 8vo, 
 cloth, 5.5-. 
 
 The Builder s Clerk ; a Guide to the Management 
 
 of a Builder's Business. By THOMAS BALES. Fcap. 8vo, cloth, is. 6d. 
 
 The Cabinet Maker ; being a Collection of the most 
 
 approved Designs in the Mediaeval, Louis-Seize, and Old-English styles, 
 for the use of Cabinet Makers, Carvers, etc. By R. CHARLES. 96 plates, 
 folio, half-bound, 2is. 
 
 The Elementary Principles of Carpentry. By 
 
 THOMAS TREDGOLD. Revised from the original edition, and partly 
 re-written, by JOHN THOMAS HURST. Contained in 517 pages of letter- 
 press, and illustrated with 48 plates and 150 -wood engravings. Second 
 edition, crown 8vo, cloth, iSs. 
 
 Section I. On the Equality and Distribution of Forces Section II. Resistance of 
 Timber Section III. Construction of Floors Section IV. Construction of Roofs Sec- 
 tion V. Construction of Domes and Cupolas Section VI. Construction of Partitions 
 Section VII. Scaffolds, Staging, and Gantries Section VIII. Construction of Centres for 
 Bridges Section IX. Coffer-dams, Shoring, and Strutting Section X. Wooden Bridges 
 and Viaducts Section XI. Joints, Straps, and other Fastenings Section XII. Timber. 
 
 "A considerable time having elapsed since the publication of the second edition of this 
 work, which was the last that had been revised by the author, his death occurring soon after, 
 a new edition that would embrace recent improvements and examples was much required. 
 Our stock of knowledge regarding the strength of materials has been largely increased, owing 
 to the labours of Hodgkinson, Kirkaldy, and others. The rapid development of the railway 
 system throughout the world has contributed greatly to the introduction of new methods and 
 to the multiplication of examples in the art of construction. More perfect and scientific 
 appliances in the erection of large works have been substituted for the primitive methods used 
 in the last generation. These have all tended more or less to tax the ability and knowledge 
 of the carpenter. The opening up and development of the resources of new countries have 
 introduced varieties of timber, many of them possessing useful properties, not the least of 
 which is. that of resisting the attack of sea-worms and insects a cause of destruction that has 
 hitherto been a source of much anxiety to the Profession. 
 
 " In order to adapt this work as far as possible to the requirements of the modern 
 carpenter, it has been necessary to re-write the articles on Pillars, Bridges, and Timber ; to 
 add new sections on Coffer-Dams, Scaffolds, etc., and to revise the remainder of the work 
 throughout. And for the more complete illustration of these subjects several new plates and 
 woodcuts have been added. 
 
 "The Editor trusts that this edition will merit the confidence of the Profession as a book of 
 reference, and afford at the same time valuable assistance to the student." 
 
 Engineering Notes. By FRANK ROBERTSON, Fellow 
 
 Roy. Astron. So<x, late first Lieut. R.E., and ' Civil Engineer Public 
 Works Department in India. 8vo, cloth, 12s. 6d. 
 
 The object of this work is to supply an exhaustive digest of all that is known on each 
 subject, so far as is necessary and sufficient for an Engineer in practice, especially in India. 
 
 B 2 
 
CATALOGUE OF SCIENTIFIC BOOKS 
 
 A Practical Treatise on Casting and Founding, 
 
 including descriptions of the modern machinery employed in the art. By 
 N. E. SPRETSON, Engineer. With 82 plates drawn to scale, 412 pp. 
 Demy 8vo, cloth, iSs. 
 
 A Pocket-Book for Chemists, Chemical Manufacturer^ 
 
 Metallurgists, Dyers, Distillers, Brewers, Sugar Refiners, Photographers, 
 Students, etc., etc. By THOMAS BAYLEY, Assoc. R.C. Sc. Ireland, Ana- 
 lytical and Consulting Chemist, Demonstrator of Practical Chemistry, 
 Analysis, and Assaying, in the Mining School, Bristol. Royal 32mo, 
 roan, gilt edges, 5^. 
 
 SYNOPSIS OF CONTENTS : 
 
 Atomic Weights and Factors Useful Data Chemical Calculations Rules for Indirect 
 Analysis Weights and Measures Thermometers "and Barometers Chemical Physics 
 Boiling Points, etc. Solubility of Substances Methods of Obtaining Specific Gravity Con- 
 version of Hydrometers Strength of Solutions by Specific Gravity Analysis Gas Analysis 
 Water Analysis Qualitative Analysis and Reactions Volumetric Analysis Manipulation- 
 Mineralogy Assaying Alcohol Beer Sugar Miscellaneous Technological matter 
 relating to Potash, Soda, Sulphuric Acid, Chlorine, Tar Products, Petroleum, Milk, Tallow, 
 Photography, Prices, Wages, etc., etc. 
 
 A Practical Treatise on Coal Mining. By GEORGE 
 
 G. ANDRE, F.G.S., Assoc. Inst. C.E.., Member of the Society of Engineers, 
 with 82 lithographic plates. 2 vols., royal 410, cloth, 3/. 12s. 
 
 CONTENTS : 
 
 I. Practical Geology II. Coal, its Mode of Occurrence, Composition, and Varieties III. 
 Searching for Coal IV. Shaft-sinking V. Driving of Levels, or Narrow Work VI. Systems 
 of Working VII. Getting the Coal VIII. Haulage IX. Windine X. Drainage XI. 
 Ventilation XII. Incidental Operations XIII. Surface Work XIV. Management and 
 Accounts XV. Characteristics of the Coal Fields of Great Britain and America. 
 
 Spons* Information for Colonial Engineers. Edfted 
 
 by J. T. HURST. Demy 8vo, sewed. 
 
 No. i, Ceylon. By ABRAHAM DEANE, C.E. 2s. 6d. 
 CONTENTS : 
 
 Introductory Remarks Natural Productions Architecture and Engineering Topo- 
 graphy, Trade, and Natural History Principal Stations Weights and Measures, etc., etc. 
 
 No. 2. Southern Africa, including the Cape Colony, Natal, and the 
 Dutch Republics. By HENRY HALL, F.R.G.S., F.R.C.I. With 
 Map. 3J. 6d. CONTENTS : 
 
 General Description of South Africa Physical Geography with reference to Engineering 
 Operations Notes on Labour and Material in Cape Colony Geological Notes on Rock 
 Formation in South Africa Engineering Instruments for Use in South Africa Principal 
 Public Works in Cape Colony: Railways, Mountain Roads and Passes, Harbour Works^ 
 Bridges, Gas Works, Irrigation and Water Supply, Lighthouses, Drainage and Sanitary 
 Engineering, Public Buildings, Mines Table of Woods in South Africa Animals used for 
 Draught Purposes Statistical Notes Table of Distances Rates of Carriage, etc. 
 
 No. 3. India. B^ F. C. DANVERS, Assoc. Inst. C.E. With Map. 4*. 6d~ 
 CONTENTS : 
 
 Physical Geography of India Building Materials Roads Railways Bridges Irriga- 
 tion River Works Harbours Lighthouse Buildings Native Labour The Principal 
 Trees of India Money Weights and Measures Glossary of Indian Terms, etc. 
 
PUBLISHED BY E. & F. N. SPON. 
 
 The Clerk of Works; a Vade Mecum for all engaged 
 
 in the Superintendence of Building Operations. By G. G. HOSKINS, 
 F.R.I.B.A. Fcap. 8vo, cloth, u. 6d. 
 
 Coffee Planting in Southern India and Ceylon. By 
 
 E. C. P. HULL. Crown 8vo, cloth, $s. 
 
 Tropical Agriculture; or, the Culture, Preparation, 
 
 Commerce, and Consumption of the Principal Products of the Vegetable 
 Kingdom, as furnishing Food, Clothing, Medicine, etc., and in their 
 relation to the Arts and Manufactures ; forming a practical treatise and 
 Handbook of Reference for the Colonist, Manufacturer, Merchant, and 
 Consumer, on the Cultivation, Preparation for Shipment, and Commercial 
 Value, etc., of the various Substances obtained from Trees and Plants 
 entering into the Husbandry of Tropical and Sub-Tropical Regions. By 
 P. L. SIMMONDS. Second Edition, revised and improved, in one thick 
 vol. 8vo, cloth, I/, is. 
 
 Compensations; a Text-book for Surveyors, in tabu- 
 lated form. By BANISTER FLETCHER. Crown 8vo, cloth, 5.$-. 
 CONTENTS : 
 
 The Varieties of Damage for which Claims may arise Various Classes of Property 
 Points to be observed in Surveys Notices to Treat Nature of Damage for which Claims 
 can and cannot be sustained What Property can be compulsorily taken When Entry on 
 Property can and cannot be compulsorily madeyOf Goodwill and Stock and of the various 
 Legal Methods of Settlement of Disputed Claims together with Full and Explicit Instruc- 
 tions on the Methods of Valuing and of Making Claims ; with Comments on Cases arising 
 under the Metropolis Local Management and Metropolitan Buildings Acts ; the whole given 
 in a Practical and Comprehensive Form, supplemented by a copious Appendix, containing 
 many Useful Forms and Precedents, and also Tables for the Valuation of Freeholds, Lease- 
 holds, Reversions, and Life- Interests. 
 
 Cotton Cultivation in its various details; the Barrage 
 
 of Great Rivers, and Instructions for Irrigating, Embanking, Draining, 
 and Tilling Land in Tropical and other Countries possessing high thermo- 
 metric temperatures, especially adapted to the improvement of the cultural 
 soils of India. By JOSEPH GIBBS, Member Institute Civil Engineers. 
 With 5 plates. Crown 8vo, cloth, "js. 6d. 
 
 Dilapidations; a Text-book for Architects and Sur- 
 veyors, in Tabulated Form. By BANISTER FLETCHER, Fellow Royal 
 Inst. Brit. Arch. (Author of * Model Houses ' ), showing who are liable for 
 Dilapidations, and the extent of the liability of Lessors, Lessees, Tenants 
 at will, Tenants by elegit, Statute, Merchant, or Staple Tenants in fee 
 simple, Tenants in tail, Tenants for life, Tenants for years without 
 impeachment of Waste, Mortgagor, Mortgagee in possession, Yearly 
 Tenants, Tenants in common, and joint Tenants, Rights of coparceners ; 
 also what are dilapidations and waste, and further fully instructs the 
 surveyor how to take and value them, to which is added the duties of 
 surveyors, with a table of legal cases, embracing the most recent, and 
 illustrated throughout by examples drawn from the author's experience, 
 and latest legal decisions. Crown 8vo, cloth, 5j. 
 
CATALOGUE OF SCIENTIFIC BOOKS 
 
 Spons Dictionary of Engineering, Civil, Mechanical? 
 
 Military, and Naval', with technical terms in French, German, Italian, 
 and Spanish, 3100 pp., and nearly 8000 engravings, in super-royal 8vo r 
 in 8 divisions, 5/. S.T. Complete in 3 vols., cloth, 5/. $s. Bound in a 
 superior manner, half-morocco, top edge gilt, 3 vols., 61. 12s. 
 
 A Treatise on the Origin, Progress, Prevention, and 
 
 Cure of Dry Rot in Timber; with Remarks on the Means of Preserving 
 Wood from Destruction by Sea- Worms, Beetles, Ants, etc. By THOMAS 
 ALLEN BRITTON, late Surveyor to the Metropolitan Board of Works, 
 etc., etc. Plates, crown Svo, cloth, 7^. 6d. 
 
 A General Table for facilitating the Calculation of 
 
 Earthworks for Railways, Canals, etc. ; with a Table of Proportional 
 Parts. By FRANCIS BASHFORTH, M.A., Fellow of St. John's College, 
 Cambridge. In Svo, cloth, with mahogany slide, 4$-. 
 
 " This little volume should become the handbook of every person whose duties require even 
 occasional calculations of this nature : were it only that it is more extensively applicable than 
 any other in existence, we could cordially recommend it to our readers ; but when they learn 
 that the use of it involves only half the labour of all other Tables constituted for the same 
 purposes, we offer the strongest of all recommendations that founded on the value of time." 
 Mechanic's Magazine. 
 
 A General Sheet Table for facilitating the Calculation 
 
 of Earthworks. By F. BASHFORTH, M.A. 6</. 
 
 A Handbook of Electrical Testing. By H. R. 
 
 KEMPE, Assoc. of the Society of Telegraph Engineers. Fcap. 8vo, 
 cloth, 5^. 
 
 Electricity; its Theory, Sources, and Applications. 
 
 By JOHN T. SPRAGUE, Member of the Society of Telegraph Engineers. 
 With 91 woodcuts and 30 valuable Tables. Crown Svo, cloth, 8.r. 
 
 Electricity and the Electric Telegraph. By GEORGE 
 
 B. PRESCOTT. With 564 woodcut illustrations, Svo, cloth, iSs. 
 
 Electro -Telegraphy. By FREDERICK S. BEECHEY, 
 
 Telegraph Engineer, a Book for Beginners. Fcap. Svo, cloth, is. 6d. 
 
 Engineering Papers. By GRAHAM SMITH. Svo, 
 
 cloth, $s. CONTENTS: 
 
 Mortar: "Miller Prize" Paper Practical Ironwork : " Miller Prize " Paper Retaining 
 Walls: Paper read at the Edinburgh and Leith Engineers' Society. With Addenda and 
 Discussions to each. 
 
 Spons Engineers and Contractors Illustrated Book 
 
 of Prices of Machines, Tools, Ironwork, and Contractors' 1 Material. 
 Royal Svo, cloth, 'js. 6d. 
 
 The Gas Consumers Handy Book. By WILLIAM 
 
 RICHARDS, C.E. i8mo, sewed, 6d. 
 
PUBLISHED BY E. & F. N. SPON. 
 
 A Pocket-Book of Use/id Formidce and Memoranda 
 
 for Civil and Mechanical Engineers. By GUILFORD L. MOLESWORTH, 
 Mem. Ins. C. E., Consulting Engineer to the Government of India for 
 State Railways. Nineteenth edition, with a valuable contribution on 
 Telegraphs by R. S. BROUGH and Dr. PAGET HIGGS. 32mo, roan, 6s. 
 Ditto, interleaved with ruled Paper for Office use, gs. Ditto, printed on 
 India paper, 6s. SYNOPSIS OF CONTENTS: 
 
 Surveying, Levelling, etc. Strength and Weight of Materials Earthwork, Brickwork, 
 Masonry, Arches, etc. Struts, Columns, Beams, and Trusses Flooring, Roofing, and Roof 
 Trusses Girders, Bridges, etc. Railways and Roads Hydraulic Formulae Canals, Sewers, 
 Waterworks, Docks Irrigation and Breakwaters Gas, Ventilation, and Warming Heat, 
 Light, Colour, and Sound Gravity : Centres, Forces, and Powers Millwork, Teeth of 
 Wheels, Shafting, etc. Workshop Recipes Sundry Machinery Animal Power Steam and 
 the Steam Engine Water-power, Water-wheels, Turbines, etc. Wind and Windmills 
 Steam Navigation, Ship Building, Tonnage, etc. Gunnery, Projectiles, etc. Weights, 
 Measures, and Money Trigonometry, Conic Sections, and Curves Telegraphy Mensura- 
 tion Tables of Areas and Circumference, and Arcs of Circles Logarithms, Square and 
 Cube Roots, Powers Reciprocals, etc. Useful Numbers Differential and Integral Calcu- 
 lus Algebraic Signs Telegraphic Construction and Formulae. 
 
 " Most of our readers are already acquainted with Molesworth's Pocket-book, and not a 
 few, we imagine, are indebted to it for valuable information, or for refreshers of the memory. 
 The book has been re-arranged, the supplemental formulas and tables added since the first 
 issue having now been incorporated with the body of the book in their proper positions, the 
 whole making a handy size for the pocket. Every care has been taken to ensure correctness, 
 
 both clerically and typographically, and the book is an indispensable vade-mecum for the 
 id the professional man." English Mechanic. 
 
 mechanic anc 
 
 Spons Tables and Memoranda for Engineers; 
 
 selected and arranged by J. T. HURST, C.E., Author of 'Architectural 
 Surveyors' Handbook,' 'Hurst's Tredgold's Carpentry,' etc. 641110, roan, 
 gilt edges, third edition, revised and improved, is. Or in cloth case, 
 is. 6d. 
 
 This work is printed in a pearl type, and is so small, measuring only z in. by if in. by 
 i in. thick, that it may be easily carried in the waistcoat pocket. 
 
 " It is certainly an extremely rare thing for a reviewer to be called upon to notice a volume 
 measuring but 23 in. by if in., yet these dimensions faithfully represent the size of the handy 
 little book before us. The volume which contains 118 printed pages, besides a few blank 
 pages for memoranda is, in fact, a true pocket-book, adapted for being carried in the waist- 
 coat pocket, and containing a far greater amount and variety of information than most people 
 
 would imagime could be compressed into so small a space The little volume has been, 
 
 compiled with considerable care and judgment, and we can cordially recommend it to our 
 readers as a useful little pocket companion." Engineering. 
 
 The French- Polisher s Manual. By a French- 
 
 Polisher; containing Timber Staining, Washing, Matching, Improving, 
 Painting, Imitations, Directions for Staining, Sizing, Embodying, 
 Smoothing, Spirit Varnishing, French-Polishing, Directions for Re- 
 polishing. Third edition, royal 32mo, sewed, 6d. 
 
 Analysis, Technical Valuation, Purification and Use 
 
 of Coal Gas. By the Rev. W. R. BOWDITCH, M. A. With wood engravings, 
 8vo, cloth, 12s. 6d. 
 
 Condensation of Gas Purification of Gas Light Measuring Place of Testing Gas- 
 Test Candles The Standard for Measuring Gas-light Test Burners Testing Gas for 
 Sulphur Testing Gas for Ammonia Condensation by Bromine Gravimetric Method of 
 taking Specific Gravity of Gas Carburetting or Naphthalizing Gas Acetylene Explosions 
 of Gas Gnawing of Gaspipes by Rats Pressure as related to Public Lighting, etc. 
 
CATALOGUE OF SCIENTIFIC BOOKS 
 
 A Practical Treatise on the Manufacture and Distri- 
 bution of Coal Gas. By WILLIAM RICHARDS. Demy 410, with numerous 
 wood engravings and large plates, cloth, 28^. 
 
 SYNOPSIS OF CONTENTS. 
 
 Introduction History of Gas Lighting Chemistry of Gas Manufacture, by Lewis 
 Thompson, Esq., M.R.C.S. Coal, with Analyses, by J. Paterson, Lewis Thompson, and 
 G. R. Hislop, Esqrs. Retorts, Iron and Clay Retort Setting Hydraulic Main Con- 
 densersExhausters Washers and Scrubbers Purifiers Purification History of Gas 
 Holder Tanks, Brick and Stone, Composite, Concrete, Cast-iron, Compound Annular 
 Wrpught-iron Specifications Gas Holders Station Meter Governor Distribution 
 Mains Gas Mathematics, or Formulae for the Distribution of Gas, by Lewis Thompson, Esq. 
 Services Consumers' Meters Regulators Burners Fittings Photometer Carburization 
 of Gas Air Gas and Water Gas Composition of Coal Gas, by Lewis Thompson, Esq. 
 Analyses of Gas Influence of Atmospheric Pressure and Temperature on Gas Residual 
 Products Appendix Description of Retort Settings, Buildings, etc., etc. 
 
 Practical Geometry and Engineering Drawing ; a 
 
 Course of Descriptive Geometry adapted to the Requirements of the 
 Engineering Draughtsman, including the determination of cast shadows 
 and Isometric Projection, each chapter being followed by numerous 
 examples ; to which are added rules for Shading Shade-lining, etc., 
 together with practical instructions as to the Lining, Colouring, Printing, 
 and general treatment of Engineering Drawings, with a chapter on 
 drawing Instruments. By GEORGE S. CLARKE, Lieut. R.E., Instructor 
 in Mechanical Drawing, Royal Indian Engineering College, Cooper's 
 Hill. 20 plates, 410, cloth, 15^. 
 
 The Elements of Graphic Statics. By Professor 
 
 KARL VON OTT, translated from the German by G. S. CLARKE, Lieut. 
 R.E., Instructor in Mechanical Drawing, Royal Indian Engineering 
 College, Cooper's Hill. Crown 8vo, cloth, 5^. 
 
 A Practical Treatise on Heat, as applied to the 
 
 Useful Arts', for the Use of Engineers, Architects, etc. By THOMAS 
 Box. Second edition, revised and enlarged, crown 8vo, cloth, 12s. 6d. 
 
 Hints to Young Engineers. By J. W. WILSON, 
 
 A.I.C.E., Principal of the Crystal Palace School of Engineering. I2mo, 
 sewed, 6</. 
 
 The New Formula for Mean Velocity of Discharge 
 
 of Rivers and Canals. By W. R. KUTTER, translated from articles in 
 the ' Cultur-Ingenieur.' By Lowis D'A. JACKSON, Assoc. Inst. C.E. 
 8vo, cloth, I2s. 6d. 
 
 Office Hydraulic Tables ; for the use of Engineers 
 
 engaged in Waterworks, giving the Discharge and Dimensions of Rivers, 
 Channels, and Pipes. By J. NEVILLE. On a large folio sheet, is. 
 
 Hydraidics of Great Rivers ; being Observations and 
 
 Surveys on the Largest Rivers of the World. By J. J. REVY. Imp. 410, 
 cloth, with eight large plates and charts, 2l. 2s. 
 
PUBLISHED BY E. & F. N. SPON. 
 
 Hops, their Cultivation, Commerce, and Uses in 
 
 various Countries. By P. L. SiMMONDS. Cown 8vo, cloth, 4*. 6d. 
 
 Practical Hydraulics ; a Series of Rules and Tables 
 
 for the use of Engineers, etc., etc. By THOMAS Box. Fourth edition, 
 numerotis plates, post 8vo, cloth, 5-r. 
 
 Tke Indicator Diagram Practically Considered. By 
 
 N. P. BURGH, Engineer. Numerous illustrations, fifth edition. Crown 
 8vo, cloth, 6s. 6d. 
 
 " This volume^ possesses one feature which renders it almost unique ; this feature is the 
 mode in which it is illustrated. It is not difficult to take a diagram if the instrument is once 
 set, and the setting with stationary engines is occasionally easy enough, but circumstances 
 continually arise under which the young engineer is completely at a loss as to how to obtain 
 a diagram. All uncertainty will be removed by referring to the book under consideration : 
 here we have drawings of the arrangements to be adopted under every conceivable circum- 
 stance, drawings, we may add, illustrating the practice of the best engineers of the day." 
 Engineer. 
 
 Link- Motion and Expansion Gear Practically Con- 
 sidered. By N. P. BURGH, Engineer. Illustrated -with 90 plates and 229 
 wood engravings, small 4to, handsomely half-bound in morocco, 2/. 2s. 
 
 The Mechanician and Constructor for Engineers, 
 
 comprising Forging, Planing, Lining, Slotting, Shaping, Turning, Screw 
 Cutting, etc. By CAMERON KNIGHT. Containing ^plates, 1147 illus- 
 trations, and iff] pages of letterpress, 410, half-morocco, 2/. 12s. 6d. 
 
 T/ie Essential Elements of Practical Mechanics; 
 
 based on the Principle of Work, designed for Engineering Students. By 
 OLIVER BYRNE, formerly Professor of Mathematics, College for Civil 
 Engineers. Second edition, illustrated by numerous -wood engravings, 
 post 8vo, cloth, is. 6d. 
 
 CONTENTS : 
 
 Chap. I. How Work is Measured by a Unit, both with and without reference to a Unit 
 of Time Chap. 2. The Work of Living Agents, the Influence of Friction, and introduces 
 one of the most beautiful Laws of Motion Chap. J. The principles expounded in the first and 
 second chapters are applied to the Motion of Bodies Chap. 4. The Transmission of Work by 
 simple Machines Chap. 5. Useful Propositions and Rules. 
 
 The Practical Millwright's and Engineers Ready 
 
 Reckoner; or Tables for finding the diameter and power of cog-wheels, 
 diameter, weight, and power of shafts, diameter and strength of bolts, etc. 
 By THOMAS DIXON. Fourth edition, I2ino, cloth, 3-r. 
 
 CONTENTS: 
 
 Diameter and Power of Wheels Diameter, Weight, and Power of Shafts Multipliers for 
 Steam used Expansively Diameters and Strength of Bolts Size and Weight of Hexagonal 
 Nuts Speed of Governors for Steam Engines Contents of Pumps Working Barrels Cir- 
 cumferences and Areas of Circles Weight of Boiler Plates French and English Weights and 
 Measures, etc. 
 
io CATALOGUE OF SCIENTIFIC BOOKS 
 
 The Principles of Mechanics and their Application to 
 
 Prime Movers, Naval Architecture, Iron Bridges, Water Supply, etc. By 
 W. J. MILLAR, C.E., Secretary to the Institution of Engineers and Ship- 
 builders, Scotland. Crown 8vo, cloth, qs. 6d. 
 
 A Practical Treatise on Mill-gearing, Wheels, Shafts, 
 
 Riggers, etc.', for the use of Engineers. By THOMAS Box. Crown 8vo, 
 cloth, second edition, 7^. 6d. 
 
 Mining Machinery; a Descriptive Treatise on the 
 
 Machinery, Tools, and other Appliances used in Mining. By G. G. 
 ANDRE, F.G.S., Assoc. Inst. C.E., Mem. of the Society of Engineers. 
 Royal 4to, uniform with the Author's Treatise on Coal Mining, con- 
 taining 182 plates, accurately drawn to scale, with descriptive text, ia 
 2 vols., cloth, s/. i2j. CONTENTS: 
 
 Machinery for Prospecting, Excavating, Hauling, and Hoisting Ventilation Pumping 
 Treatment of Mineral Products, including Gold and Silver, Copper, Tin, and Lead, Iron,. 
 Coal, Sulphur, China Clay, Brick Earth, etc. 
 
 The Pattern Makers Assistant ; embracing Lathe 
 
 Work, Branch Work, Core Work, Sweep Work, and Practical Gear 
 Construction, the Preparation and Use of Tools, together with a lanje 
 collection of Useful and Valuable Tables. By JOSHUA ROSE, M.E. 
 With 250 ilhistrations. Crown 8vo, cloth, los. 6d. 
 
 The Science and Art of the Manufactitre of Portland 
 
 Cement, with observations on some of its constructive applications, 'with 
 numerous illustrations. By HENRY REID, C.E., Author of 'A Practical 
 Treatise on Concrete,' etc., etc. 8vo, cloth, iSs. 
 
 The Draughtsman s Handbook of Plan and Map 
 
 Drawing', including instructions for the preparation of Engineering, 
 Architectural, and Mechanical Drawings. With numerous illustrations' 
 in the text, and 33 plates (15 printed in colours']. By G. G. ANDRK, 
 F.G.S., Assoc. Inst. C.E. 4to, cloth, 15^. 
 
 CONTENTS : 
 
 The Drawing Office and its Furnishings Geometrical Problems Lines, Dots, and their 
 Combinations Colours, Shading, Lettering, Bordering, and North Points Scales Plotting 
 Civil Engineers' and Surveyors' Plans Map Drawing Mechanical and Architectural 
 Drawing Copying and Reducing Trigonometrical Formulae, etc., etc. 
 
 The Railway Builder ; a Handbook for Estimating- 
 
 the Probable Cost of American Railway Construction and Equipment. 
 By WILLIAM J. NICOLLS, Civil Engineer. Illustrated, full bound, pocket- 
 book form, *]s. 6d. 
 
 Rock Blasting: a Practical Treatise on the means 
 
 employed in Blasting Rocks for Industrial Purposes. By G. G. ANDRE, 
 F.G.S., Assoc. Inst. C.E. With 56 illustrations and 12 plates, 8vo, cloth, 
 los. 6d. 
 
PUBLISHED BY E. & F. N. SPON. ii 
 
 Surcharged and different Forms of Retaining Walls. 
 
 By J. S. TATE. Cuts, 8vo, sewed, 2s. 
 
 A Treatise on Ropemaking as practised in public and 
 
 private Rope-yards, with a Description of the Manufacture, Rules, Tables 
 of Weights, etc., adapted to the Trade, Shipping, Mining, Railways, 
 Builders, etc. By R. CHAPMAN, formerly foreman to Messrs. Hudclart 
 and Co., Limehouse, and late Master Ropemaker to H.M. Dockyard, 
 Deptford. Second edition, 12 mo, cloth, 3^. 
 
 Sanitary Engineering ; a Series of Lectures given 
 
 before the School of Engineering, Chatham. Division I. Air. Division II. 
 Water. Division III. The Dwelling. Division IV. The Town and 
 Village. Division V. The Disposal of Sewage. Copiously illustrated. 
 By J. BAILEY DENTON, C.E., F.G.S., Honorary Member of the Agri- 
 cultural Societies of Norway, Sweden, and Hanover, and Author of the 
 'Farm Homesteads of England,' 'Village Sanitary Economy,' 'Storage 
 of W T ater,' 'Sewage Farming,' etc. Royal 8vo, cloth, 25^. 
 
 Sanitary Engineering; a Guide to the Construction 
 
 of Works of Sewerage and House Drainage, with Tables for facilitating 
 the calculations of the Engineer. By BALDWIN LATHAM, C.E., M. Inst. 
 C.E., F.G.S., F.M.S., Past-President of the Society of Engineers. Second 
 edition, with, numerous plates and woodcuts, 8vo, cloth, il. los. 
 
 Cleaning and Scouring ; a Manual for Dyers, Laun- 
 dresses, and for Domestic Use. By S. CHRISTOPHER. i8mo, sewed, 6d. 
 
 A Practical Treatise on modern Screw-Propulsion. 
 
 By N. P. BURGH, Engineer. Illustrated with 52 large plates and 103 
 woodcuts, 410, half- morocco, 2/. 2s. 
 
 Screw Cutting Tables for Engineers and Machinists, 
 
 giving the values of the different trains of Wheels required to produce 
 Screws of any pitch, calculated by Lord Lindsay, M.P., F.R.S., F.R.A.S., 
 etc. Royal 8vo, cloth, oblong, 2.5. 
 
 Screw Cutting Tables, for the use of Mechanical 
 
 Engineers, showing the proper arrangement of Wheels for cutting the 
 Threads of Screws of any required pitch, with a Table for making the 
 Universal Gas-pipe Threads and Taps. By W. A. MARTIN, Engineer. 
 Second edition, royal 8vo, oblong, cloth, is. 
 
 Vazeeri Rupi, the Silver Country of the Vazeers, in 
 
 Kulu : its Beauties, Antiquities, and Silver Mines, including a Trip over 
 the lower Himalayah Range and Glaciers. By J. CALVERT, F.G.S., 
 Mem. Inst. C.E. Illustrated ivith a map and coloured plates, 8vo, cloth, 
 i6s. 
 
12 CATALOGUE OF SCIENTIFIC BOOKS 
 
 A Treatise on a Practical Method of Designing Slide 
 
 Valve Gears by Simple Geometrical Construction, based upon the principles 
 enunciated in Euclid's Elements, and comprising the various forms of 
 Plain Slide Valve and Expansion Gearing ; together with Stephenson's, 
 Gooch's, and Allan's Link-Motions, as applied either to reversing or to 
 variable expansion combinations. By EDWARD J. COWLING WELCH, 
 Memb. Inst. Mechanical Engineers. Crown 8vo, cloth. 6s. 
 
 The Slide Valve practically considered. By N. P. 
 
 BURGH, Engineer. Seventh edition, containing 88 illustrations , and 
 12.1 pages of letterpress, crown 8vo, cloth, $s. 
 
 A Pocket-Book for Boiler Makers and Steam Users, 
 
 comprising a variety of useful information for Employer and Workman, 
 Government Inspectors, Board of Trade Surveyors, Engineers in charge 
 of Works and Slips, Foremen of Manufactories, and the general Steam- 
 using Public. By MAURICE JOHN SEXTON. Royal 32mo, roan, gilt 
 edges, 5-r. 
 
 Practical Treatise on Steam Boilers and Boiler 
 
 Making. By N. P. BURGH, Mem. Inst. Mec. Eng. Illustrated by 1163 
 wood engravings and 50 large folding plates of working drawings, royal 4to, 
 half-morocco, 3/. 13^. 6d. 
 
 Modern Compound Engines ; being a Supplement to 
 
 Modern Marine Engineering. By N. P. BURGH, Mem. Inst. Mech. Eng. 
 Numerous large plates of working drawings, 4to, cloth, iSs. 
 
 The following Firms have contributed Working Drawings of their best and most modern 
 examples of Engines fitted in the Royal and Mercantile Navies : Messrs. Maudslay, Rennie , 
 Watt, Dudgeon, Humphreys, Ravenhill, Jackson, Perkins, Napier, Elder, Laird, Day, 
 Allibon. 
 
 A Practical Treatise on the Steam Engine, con- 
 taining Plans and Arrangements of Details for Fixed Steam Engines, 
 with Essays on the Principles involved in Design and Construction. By 
 ARTHUR RIGG, Engineer, Member of the Society of Engineers and of 
 the Royal Institution of Great Britain. Demy 4to, copiously illustrated 
 with woodcuts and 96 plates, in one Volume, half- bound morocco, 2/. 2s. 
 
 This work is not, in any sense, an elementary treatise, or history of the steam engine, but 
 is intended to describe examples of Fixed Steam Engines without entering into the wide 
 domain of locomotive or marine practice. To this end illustrations will be given of the most 
 recent arrangements of Horizontal, Vertical, Beam, Pumping, Winding, Portable, Semi- 
 portable, Corliss, Allen, Compound, and other similar Engines, by the most eminent Firms in 
 Great Britain and America. The laws relating to the action and precautions to be observed 
 in the construction of the various details, such as Cylinders, Pistons, Piston-rods, Connecting- 
 rods, Cross-heads, Motion-blocks, Eccentrics, Simple, Expansion, Balanced, and Equilibrium 
 Slide-valves, and Valve-gearing will be minutely dealt with. In this connection will be found 
 articles upon the Velocity of Reciprocating Parts and the Mode of Applying the Indicator, 
 Heat and Expansion of Steam Governors, and the like. It is the writer's desire to draw 
 illustrations from every possible source, and give only those rules that present practice deems 
 
PUBLISHED BY E. & K N. SPON. 13 
 
 The Steam Engine considered as a Heat Engine : a 
 
 Treatise on the Theory of the Steam Engine, illustrated by Diagrams, 
 Tables, and Examples from Practice. By JAS. H. COTTERILL, M.A., 
 Professor of Applied Mechanics in the Royal Naval College. 8vo, cloth, 
 12s. 6d. 
 
 Modern Marine Engineering applied to Paddle and 
 
 Screw Propulsion ; consisting of 36 plates, 259 wood engravings, and 
 403 pages of descriptive matter, the whole being an exposition of the 
 present practice of the following firms : Messrs. J. Penn and Sons ; 
 Maudslay, Sons, and Field ; James Watt and Co. ; J. and G. Rennie ; 
 R. Napier and Sons ; J. and W. Dudgeon ; Ravenhill and Hodgson ; 
 Humphreys and Tennant ; Mr. J. F. Spencer ; and Messrs. Forester and 
 Co. By N. P. BURGH, Engineer, 4to, cloth, 2/. 5*. 
 
 A Pocket- Book of Practical Rides for the Proportions 
 
 of Modern Engines and Boilers for Land and Marine purposes. By N. P. 
 BURGH. Sixth edition, revised, with Appendix, royal 32mo, roan, 4^. 6d. 
 
 Details of High-Pressure Engine, Beam Engine, Condensing, Marine Screw Engines, 
 Oscillating Engines, Valves, etc., Land and Marine Boilers, Proportions of Engines produced 
 by the Rules. Proportions of Boilers, etc. 
 
 A Practical Treatise on the Science of Land and 
 
 Engineering Surveying, Levelling, Estimating Quantities, etc., with a 
 general description of the several Instruments required for Surveying, 
 Levelling, Plotting, etc. By H. S. MERRETT. 41 fine plates with Illus- 
 trations and Tables, royal 8vo, cloth, Jhird edition, 12s. 6d. 
 
 PRINCIPAL CONTENTS : 
 
 Part i. Introduction and the Principles of Geometry. Part 2. Land Surveying.; com- 
 prising General Observations The Chain Offsets Surveying by the Chain only Surveying 
 Hilly Ground To Survey an Estate or Parish by the Chain only Surveying with the 
 Theodolite Mining and Town.' Surveying Railroad Surveying Mapping Division and 
 Laying out of Land Observations on Enclosures Plane Trigonometry. Part 3. Levelling 
 Simple and Compound Levelling The Level Book Parliamentary Plan and Section- 
 Levelling with a Theodolite Gradients Wooden Curves To Lay out a Railway Curve 
 Setting out Widths. Part 4. Calculating Quantities generally for Estimates Cuttings and 
 Embankments Tunnels Brickwork Ironwork Timber Measuring. Part 5. Description 
 and Use of Instruments in Surveying and Plotting The Improved Dumpy Level Troughton's 
 Level The Prismatic Compass Proportional Compass Box ^Sextant Vernier Panta- 
 graph Merrett's Improved Quadrant Improved Computation Scale The Diagonal Scale 
 Straight Edge and Sector. Part 6. Logarithms of Numbers Logarithmic Sines and 
 Co-Sines, Tangents and Co-Tangents Natural Sines and Co- Sines Tables for Earthwork, 
 for Setting out Curves, and for various Calculations, etc., etc., etc. 
 
 The Chemistry of Sulphuric Acid Mamifacture. By 
 
 HENRY ARTHUR SMITH. Cuts, crown 8vo, cloth, 4^. 6d. 
 
 CONTENTS : 
 
 Ground Plan of Kilns for Burning Sulphur Ores Section of Pyrites Furnace On the 
 Presence of Arsenic Methods for Removal of Arsenic An Experimental Examination of the 
 Circumstances which determine the Action of the Gases in the Lead Chamber On the Dis- 
 tribution of Gases in the Lead Chamber On the Temperature at which Nitnc Acid acts upon 
 Sulphurous Acid On the Distribution of Heat in the Lead Chamber An Inquiry into the 
 Best Form of Leaden Chamber, etc. 
 
14 CATALOGUE OF SCIENTIFIC BOOKS 
 
 The Principles and Practice of Engineering, Trigono- 
 
 metrical, Siibterrancozis, and Marine Surveying. By CHARLES BOURNE, 
 C.E. Third edition, numerous plates and woodcuts, 8vo, cloth, 5-r. 
 
 Table of Logarithms of the Natural Numbers, from 
 
 i to 108,000. By CHARLES BABBAGE, Esq., M.A. Stereotyped edition, 
 royal 8vo, cloth, 7-r. 6d. 
 
 To ensure the correctness of these Tables of Logarithms, they were compared with Callett's, 
 Vega's, Mutton's, Briggs', Gardiner's, and Taylor's Tables of Logarithms, and carefully read 
 by nine different readers ; and further, to remove any possibility of an error remaining, the 
 stereotyped sheets were hung up in the Hall at Cambridge University, and a reward offered 
 to anyone who could find an inaccuracy. So correct are these Tables, that since their first 
 issue in 1827 no error has been discovered. 
 
 BARLOW'S Tables of Squares, Cubes, Square Roots, 
 
 Cube Roots, Reciprocals of all Integer Numbers up to 10,000. Post 8vo, 
 cloth, 6s. 
 
 CAMUS (M,) Treatise on the Teeth of Wheels, demon- 
 
 strating the best forms which can be given to them for the purposes of 
 Machinery, such as Mill-work and Clock-work, and the art of finding 
 their numbers, translated from the French. Third edition, carefully revised 
 ; and enlarged, with details of the present practice of Millwrights, Engine 
 Makers, and other Machinists. By ISAAC HAWKINS. Illustrated by 
 i$ plates, 8vo, cloth, 5*. 
 
 The Practical Sugar Planter; a complete account 
 
 ,of the Cultivation and Manufacture of the Sugar Cane, according to the 
 latest and most approved processes, describing and comparing the different 
 systems pursued in the East and West Indies and the Straits of Malacca, 
 adjid .the relative expenses and advantages attendant upon each, being the 
 result of sixteen years' experience as a Sugar Planter in those Countries. 
 By LEONARD WRAY, Esq. 8vo, cloth, ios. 6d. 
 
 Laying and Repairing Electric Telegraph Cables. By 
 
 Capt. V. HOSKKER, Royal Danish Engineers. Crown 8vo, cloth, 
 
 The Practice of Hand Turning in Wood, Ivory, Shell, 
 
 etc^, with Instructions for Turning such Work in Metal as may be required 
 in .the Practice of Turning in Wood, Ivory, etc., also an Appendix on 
 'Ornamental Turning. By FRANCIS C AMPIN. Second edition, -with wood 
 engravings^ ,crowji .8vo, cloth (a book for beginners), 6s. 
 
 CONTENTS : 
 
 On Lathes~-Turning ToolsTurning Wood Drilling Screw Cutting Miscellaneous 
 Apparatus and ProcessesTurning Particular Forms Staining Polishing Spinning Metals 
 -Materials Ornamental Turning, etc. 
 
PUBLISHED BY E. & F. N. SPON. 15 
 
 Health and Comfort in House Building, or Ventila- 
 tion -with Warm Air by Self-Acting Suction Ptrzver, with Review of the 
 mode of Calculating the Draught in Hot- Air Flues, and with some actual 
 Experiments. By J. DRYSDALE, M.D., and J. \V. HAYWARD, M.D. 
 Second edition, with Supplement, demy 8vo, with plates, cloth, Js. 6</.j 
 the Supplement separate, 6d. 
 
 Treatise on Valve-Gears, with special consideration 
 
 of the* Link-Motions of Locomotive Engines. By Dr. GUSTAV ZEUNER. 
 Third edition, revised and enlarged, translated from the German, with the 
 .special permission of the author, by MORITZ MULLER. Plates, 8vo, 
 '* cloth, I2J. 6d. 
 
 Treatise on Watchwork, Past and Present. By the 
 
 Rev. H. L. NELTHROPP, M.A., F.SA. Numerous illustrations, crown 
 8vo, cloth, 6s. 6d. CONTENTS : 
 
 Definitions of Words and Terms used in Watchwork Tools Time Historical Sum- 
 mary On Calculations of the Numbers for Wheels and Pinions; their Proportional Sizes, 
 Trains, etc. Of Dial Wheels, or Motion Work Length of Time of Going witKbut Winding 
 up The Verge The Horizontal The Duplex The Lever The Chronometer Repeating 
 Watches Keyless Watches The Pendulum, or Spiral Spring Compensation Jewelling of 
 Pivot Holes Clerkenwell Fallacies of the Trade Incapacity of Workmen How to Choose 
 and Use a Watch, etc. 
 
 The Present Practice of Sinking and Boring Wells, 
 
 with Geological Considerations and Examples of Wells. By ERNEST 
 SPON, Member of the Society of Engineers, of the Franklin Institute, of 
 the Iron and Steel Institute, and of the Geologists' Association. Crown 8vo, 
 cloth, illustrated by 276 diagrams and engravings to scale, "js. 6d. 
 
 Workshop Receipts for Manufacturers, Mechanics, 
 
 and Scientific Amateurs. By ERNEST SPON. With numerous illustrations, 
 45 PP-> crown 8vo, cloth, 5-r. 
 
 CONTAINING RECEIPTS FOR 
 
 Bookbinding Bronzes and Bronzing Candles Cement Cleaning Colour-washing 
 Concretes Dipping Acids Drawing Office Details Drying Oils Dyeing Dynamite 
 Electro-Metallurgy (Cleaning, Dipping, Scratch-brushing, Batteries, Baths, and Deposits of 
 
 ounry xures reezng umnates urnure reams, s, oses, acquers, an 
 Pastes Gilding Glass Cutting, Cleaning, Frosting, Drilling, Darkening, Bending. Staining, 
 and Painting Glass Making Glues Gold Graining Gums Gun Cotton Gunpowder- 
 Horn Working Indiarubber Ink (Writing and Printing) Japans, Japanning, and kindred 
 processes Lacquers Lathing Leather Lubricants Marble Working Matches Mortars 
 Nitro-Glycerine Oils Paper Paper Hanging Painting in Oils, in Water Colours, as 
 well as Fresco, House, Transparency, Sign, and Carriage Painting Photography Pig- 
 ments Plastering Polishes Pottery (Clays, Bodies, Glazes, Colours, Oils, Stains, Fluxes, 
 Enamels, and Lustres) Scouring Silvering Soap Solders Tanning Taxidermy Tem- 
 pering Metals Treating Horn, Mother-o'Pearl, and like substances Varnishes, Manufacture 
 and Use of Veneering Washing Waterproofing Welding Whitewashing. Besides 
 Receipts relating to the lesser Technological matters and processes, such as the Manufacture 
 and Use of Stencil Plates, Blacking, Crayons, Paste, Putty, Wax, Size, Alloys, Catgut, Tun- 
 bridge Ware, Picture Frame and Architectural Mouldings, Compos, Cameos, and others too 
 numerous to mention. 
 
1 6 PUBLISHED BY E. & F. N. SPON. 
 
 THE TRANSACTIONS OF THE SOCIETY OF 
 ENGINEERS. 
 
 Published Annually. 8vo, cloth, price 15^. 
 
 THE JOURNAL OF THE IRON AND STEEL 
 INSTITUTE. 
 
 Published Half-yearly. 8vo, sewed, price Js. 6d. 
 
 THE JOURNAL OF THE SOCIETY OF TELEGR^f H 
 ENGINEERS. 
 
 Published Quarterly. 8vo, sewed, price fs. 6d. 
 
 THE PKOOEEDINaS OF THE ASSOCIATION OP SANITARY 
 AND MUNICIPAL ENGINEERS AND SURVEYORS. 
 
 Published Annually. 8vo, cloth, price los. 6</, 
 
 NOW IN COURSE OF PUBLICATION. 
 
 To be completed in about 30 Monthly Parts, each Part containing 64 pp., 
 with mimeroits illustrations^ super-royal 8vo, price 2s. 
 
 SPONS' ENCYCLOPEDIA 
 
 OF THE 
 
 INDUSTRIAL ARTS, MANUFACTURES, AND COMMERCIAL 
 
 PRODUCTS. 
 EDITED BY GEO. G. ANDRE, F.G.S., Assoc. INST. C.E. 
 
 NOW IN COURSE OF PUBLICATION. 
 
 To be completed in about 15 Monthly Parts, each Part containing 64 pp., 
 with numerous illustrations, super-royal 8vo, price 2s. 
 
 A SUPPLEMENT 
 
 TO 
 
 SPONS 1 DICTIONARY OF ENGINEERING, 
 
 CIVIL, MECHANICAL, MILITARY, AND NAVAL. 
 EDITED BY ERNEST SPON, MEMB. Soc. ENGINEERS. 
 
 London: E. & F. N. SPON, 46, Charing Cross. 
 New York : 446, Broome Street. 
 
 r 
 

 
 OE ^ 
 
I OOUO 
 
 249962