FIRST BOOK o0 SC IE N C E, DESIGNED FOR PUBLIC AND PRIVATE, SCHOOLS. BY W-A;.'NORTON & J. A. PORTER, PROFESSORS IN YALE COLLEGE. PART I. NATURAL PHILOSOPHY AND ASTRONOMY. PART II. CHEMISTRY AND ALLIED SCIENCES. PUBLISHED BY A. S. BARNES & CO., 51 AND 58 JOHN STREET. 1858. Entered according to Act of Congress, in the year 1858, by JoiN A. PORTER and WM. A. NORTON, In the Clerk's Office of the District Court of the United States for the Southern District of New York. GEO. W. WOOD, PRINTER, No. 2 Dutch-st., N. Y. C O N T E N T S. PART I.-NATURAL PHILOSOPHY. PAAG CHAPTER I.-Mechanical Properties of Bodies...................... 11 II. —Mechanics of Solids................................. 16 III.-Mechanics of Fluids................................. 59 IV.-Sound........................................ 77 V.- Light.............................................. 90 VI.-Electricity......................................... 116 VII.-Magnetism.................................... 138 VIII.-Theoretical Astronomy.............................. 153 IX.-Descriptive Astronomy.............................. 175 PART II.-CHEMISTRY. PAGE CHAPTER I.-Atoms and Attraction............................... 15 II.-Light........................................... 20 III.-Heat............................................... 23 IV.-Meteorology........................................ 43 V.-Steam............................................. 52 VI.-Electricity.................................... 61 VII.-Metalloids.......................................... 71 VIII.-Metals............................................. 109 IX.-Oxides and Sulphurets............................. 124 X.-Salts............................................... 128 XI.-The Daguerreotype................................... 137 XII.-Chemical Analysis................................... 138 XIII.-Vegetable Chemistry................................ 139 XIV. —Agricultural Chemistry.......................... 162 XV. —Physiology and Physiological Chemistry............... 168 XVI.-Circulation of Matter................................ 181 XVII.-Geology........................................... 183 PREFACE. THE present little volume treats of the elements of Natural Science, and is designed to meet the wants of young persons, who do not intend to pursue a complete course of academical study. The catechetical form has been adopted, as better adapted to class recitation, in the case of young pupils, than the ordinary didactic form, and as admitting of greater condensation. It has, also, the important advantage of permitting a more rigid adherence to a logical method in the treatment of topics, and thus securing greater distinctness of conception, and consecutiveness of thought, on the part of the pupil. The mental culture to be derived from the exercise of framing answers to the questions put by the teacher, can be truly realized only by the more advanced student. The young beginner is seldom capable of making his answers sufficiently precise, nor will he readily acquire by practice alone the habit of accurate statement. As in a book intended for the young no opportunity should be neglected of addressing the mind through the Vi PREFACE. eye, the principles stated are copiously illustrated by pictorial representations. Especial pains are taken that clear conceptions should be obtained of the fundamental principles of the different branches of Natural Science. With the view of accomplishing this object more effectually, the method is pursued of ascending from particulars to generals. Practical applications of principles are added wherever they could be introduced to advantage. INTRODUCTION. As a fitting introduction to the pleasant task that is before us, we will take a general survey of' the ground to be passed over. On glancing hastily over it we might conjecture that the order of things in the realm of inanimate Nature was fixed and invariable; but on a nearer view we perceive that all things, inanimate as well as animate, are subject to change. We soon discover, too, that change follows change in a certain established succession, and that a beautiful order and harmony everywhere prevail. We recognize the operation of natural causes as invariably producing certain effects, and so rise from the conception of that which is changeable and transient to that which is unalterable and everlasting. Looking farther, we discern the secret workings of the primary cause of this universal activity of change. We call it Force, and seem to see in it the subtile chain by which the universe is bound to the throne of the Creator. Our first great object, then, will be to inspect the characteristic forms which this primary principle of change assumes, or the so-called forces of nature, and examine into the effects they produce. While engaged in this interesting study we shall learn how these natural agents are made serviceable to man, and brought to labor obediently to his requirements. After taking this comprehensive survey, we will descend to a lower point of view, and inquire into the various means by which external Nature produces impressions on our senses. When " the Spirit of God moved upon the face of the waters," and Force began to execute its divine commission, to evoke order out of chaos, Light burst into existence, the first of all created things, proclaiming the ultimate design of creation. The Divine Power which created the universe has sustained it and will sustain it through all Viii INTRODUCTION. time, and the all-bounteous light, fulfilling its destiny, now gladdens the earth and its teeming world of life as with the smile of His beneficence. It will be a pleasant task to follow the flashing light in its movements, study its deportment under different circumstances, and divine, if possible, by what subtile handicraft a beauteous drapery of many-colored light is daily fashioned and spread over the earth. It will be interesting, too, to scan the wonderful contrivances which the ingenuity of mall has devised to increase his power of vision-the microscope, which discloses to view a new world of thronging life existing unheeded everywhere around us, and the telescope, which reveals the existence of innumerable shining worlds peopling the depths of immensity. In the same connection the philosophy of sound will occupy our attention. We shall seek to understand its nature, the manner in which it is produced and conveyed to the ear, and the various ways in which it is modified in its character and affected in its propagation. The magical charm that dwells in the " concord of sweet sounds" will yield up its secret to our scrutiny. Changing again our point of view, and seeking for the physical actions which bodies may have on each other, a new avenue opens out before us, conducting into a region not yet fully explored, but which has already rewarded research with many wonderful curiosities and valuable treasures. It is found that, besides light, and its ordinary attendant, Heat, other active principles, called Electricity and Magnetism, are intimately, associated with the particles of bodies. In these ethereal principles, ever mysteriously at work in the most hidden recesses of nature, and coming forth at the call of science, are recognized but new forms of force, clothed with almost spiritual bodies. Thus far our contemplations are mostly confined to the face of.the earth. Looking away from the earth we see bending over us the blue dome of the sky, and admire its wondrous fretwork of stars. Observing attentively, it is perceived that the vaulted sky, with its luminous tracery, is not motionless and firmly established upon the broad pavement of the earth, but is in reality an ever-shifting panorama of celestial lights, gliding noiselessly over us. If we were to believe with the sages of the olden time, we might suppose a succession of crystalline spheres, freighted with.stars, to be rolling around, and almost hear the music of their ceaseless revolution. But this may not be in the present day; a Copernicus has lived in a previous age, at the wave of whose hand all the INTRODUCTION. ix complicated celestial apparatus of man's creation has passed away "like the baseless fabric of a vision." We now look through the filmy blue veil of the atmosphere into the immeasurable depths of space, and wonder unceasingly at the glories which fill immensity. The imaginary foundations of the earth are broken up, and it comes forth arrayed in a garment of light, to take its place among the rolling stars that circle around the sun. The system of the world has expanded into proportions that transcend our highest powers of conception; but its strange complexity has dissolved into a divine simplicity. In its:unrestrained flight through the fields of space, the mind seems almost to grasp the infinite, in extent and duration. Time past and time future swell into proportions before inconceivable. The vast cycles of change going on in the heavens seem, as it has been sublimely said, like the recurring beats of the pendulum of eternity. And so, too, by sounding the depths of space, from star to star, with the ethereal light for a sounding line, we almost measure off the infinity of distance. How greatly it tends also to enlarge our ideas of the past duration of the universe, to know that the light which comes from yon star, struggling into view in the field of the telescope, is wearied with the flight of tens of thousands of years. If it should be imagined that the earth, if a shining star, bears about it no indications of a past existence, immeasurable by the flight of years, the geologist will tell us that the records of such an existence are found inscribed by the hand of time, or rather the finger of God, upon tables of stone buried beneath its surface. -Passing over-their upturned edges, he unfolds these tablets one after another, and reads the history of the earth as there traced in unfading characters. There is found, too, in the very structure and constitution of the rocky framework of the earth undoubted traces of a primeval age, when the mountains, and even the whole earth, were melted with fervent heat, and the flames played with their forked tongues over the wide regions that are now glowing with beauty and teeming with a bounteous life. This fiery conflict was in fact the process by which the materials for the things of life that were to spring up from the earth were prepared. Countless ages passed away, the flickering flames died out, and the earth lost its.vesture of fire. Another succession of ages rolled by, and the uplifted mountains began to show their tops above a waste of waters, and dot its wide expanse with islands. These rose and sank, and one wave of revolution after another swept over the face of the 1* X INTRODUCTION. earth, until at last the continents stood firm, and the sea was shut up within its bounds. Successive worlds of animal and vegetable life came and passed away, keeping pace with the changes that occurred in the material world, until man appeared as the " lord of creation" and the consummation of the Divine plan. These teachings of the book of Nature in regard to the great antiquity of the earth and the material universe, are now well understood to be in harmony with the Mosaic account of creation. The volume of Creation and the Bible, two books of revelation from the same Divine Author, can not but confirm and illustrate each other when rightly understood, Should it be supposed by the reader that such studies, however interesting or ennobling they may be, can have but little practical utility, we would remind him of the time-honored maxim, that "Science is the handmaid of Art." In fact, Science has responded to the demands of Art, and attended upon its progress in all the past. As new discoveries in science have been made, new industrial arts have sprung up. The most insignificant scientific truths have thus proved to be treasures of incalculable value to mankind. Nor have those truths which seemed to be too exalted ever to wear the homely garb of working-day life, failed to do good service in be. half of the material interests of mankind. The shining orbs that move so far above us, are lights in the firmament " for signs and for seasons, and for days and for years;" and white-winged commerce bears its treasures across the sea under the guidance of the remote stars. Science has given to the iron-horse his breath of fire and sinews of strength-disarmed the lightning of its terrors, and compelled it to wait upon man as his swift-winged messenger. Science has taught the sun-beam to daguerreotype the " human face divine." Science invents machinery, contrives articles of convenience and luxury, and in a thousand ways cheers and adorns the pathway of our daily life. FIRST BOOK OF NATURAL PHILOSOPHY AND ASTRONOMY. CHAPTER I.;MECHANICAL PROPERTIES OF BODIES. 1. Is a piece of wood, or a pebble, or an iron bar, all solid matter? It is part matter and part empty space. 2. Is there as much matter in a piece of wood as in an iron bar of the same size? There is less matter and more empty space in the wood than in the iron. 3. How is this fact generally expressed? It is said that iron is denser, or more compact, than wood. 4. What are the empty spaces in the interior of bodies called? Pores. The pores are visible in many substances; for example, in sponge, cork, and some kinds of wood. 12 NATURAL PHILOSOPHY. 5. Are the pores in the interior of bodies entirely devoid of matter of any kind? The larger visible pores contain air; and the more minute pores, in even the densest substances, contain a very subtile ether, which also fills all space. 6. Can a body of matter be divided into smaller and smaller parts without any apparent limit? It can. 7. What are the two ways in whieh matter can be divided and subdivided? Xiechanically, that is, by pounding, grinding, etc.; and by solution. 8. Give an example of the minute subdivision of matter by solution. A grain of blue vitriol, smaller than the smallest pea, will give a blue tinge to half a gallon of water containing 20 drops of spirits of hartshorn. In this half gallon there are 250,000 drops. 9. Are there any last particles that can not be divided any further? Chemistry informs us that there are 10. What are these indivisible particles called? Atoms. Every body of matter is made up of indivisible atoms. 11. Are these atoms so close together as to be in actual contact? They are not, they always stand apart from each other. 12. What holds them together? Each particle pulls the others toward it, or attracts them, just as a magnet attracts a piece of iron that is brought near it. MECHANICAL PROPERTIES OF BODIES. 13 13. What is this attraction between atoms called? The attraction of cohesion, or simply cohesion. 14. Why do not the atoms rush together, and all bodies become perfectly solid? Because the heat collected between or around the atoms exerts a repulsion, and keeps them a certain distance apart. 15. How do we know that heat has this effect? If the heat be increased the particles are forced farther apart, and if it be diminished they draw nearer together. 16. What have you to say of the forces of attraction and repulsion exerted between the atoms of bodies? That their energy is enormously great. 17. Illustrate the astonishing energy of the attraction between atoms. The strongest iron wire, of one quarter of an inch in thickness, could not be broken by the united strength of five horses. 18. Illustrate the repulsion exerted between atoms from the effect of heat. The explosive force of gunpowder projects heavy cannon balls to great distances, and rends the hardest rocks into fragments. 19. Have substances different mechanical properties? They have; for example, iron is hard, and chalk is soft; glass is brittle, and gold is malleable. 20. Are there any other metals that can be hammered out into leaves, or rolled into sheets, besides gold? Silver, lead, aluminum, tin, copper, zinc, platinum, and iron are all malleable. 14 NATURAL PHILOSOPHY. 21. What is meant when it is said that a certain metal, or other substance, is DUCTILE? That it can be drawn out into a wire or thread. *22. What metals are ductile? Platinum, silver, iron, copper, and gold. Zinc, tin, and lead are also ductile in an inferior degree. 23. What may be said of melted glass? That it is very ductile. It can be drawn out, or spun into fine threads. 24. Why does a piece of India rubber when stretched fly back if left to itself? Because the particles, when displaced, tend to recover their original positions. 25. Do we observe the same tendency under other circumstances? We do; for example, when we squeeze an India rubber ball in our hand, or bend a piece of whalebone. 26. What is said of such a substance? That it is elastic. 27. Mention other highly elastic substances. Glass, ivory, steel, air, and all gases. 28. In how many different states does matter exist? In three states-solid, liquid, and gaseous. A stone is solid, water is liquid, and air is gaseous. 29. How may a substance be made to pass from one of these states into another? By increasing or diminishing the amount of heat which it contains. Water is converted into vapor by heat, and into ice by cold. MECHANICAL PROPERTIES OF BODIES. 15 30. Suppose two polished plates of glass or metal are laid one on the other, and slightly pressed? It will be found if we undertake to separate them, that they stick together. 31. What is the force that holds the plates together called? Attraction of adhesion, or simply adhesion. 32. What is the reason that if two panes of common window glass are placed on each other they do not adhere? Because they are not even and smooth enough to come into close contact. 33. Mention one or two familiar facts that are to be explained by adhesion. The marks made in writing with chalk or a lead pencil; the sticking of dust to the walls and furniture of rooms. 34. Does adhesion manifest itself between liquids and solids, as well as between solids? Tt does; if I dip my finger into water it becomes wet, because a film of water adheres to it. 35. Mention other illustrations of adhesion between liquids and solids. Writing with ink, painting, varnishing, smearing rubbing surfaces in machinery with oil. 36. Does attraction manifest itself between bodies at a distance, as well as between those which are in close contact? It does; the earth attracts all bodies, and causes them, if unsupported, to fall toward its surface. 16 NATURAL PHILOSOPHY. CHAPTER II. MECHANICS OF SOLIDS. INERTIA OF MATTER-PRODUCTION OF MOTION. 37. Do we ever see a chair in a room or a stone on level ground set, itself in motion of its own accord? We do not. 38. To start such a body, what must be done? It must be pushed, or pulled, or struck, with a certain force. 39. If a stone or a ball be rolled on the ground, it goes only a certain distance and then stops —does it stop itself of its own accord? It does not; it encounters a resisting force which gradually checks its motion and finally stops it. 40. What is this resisting force called? Friction; it arises from the roughness of the ground. 41. Can you mention any facts which go to show that there is such a force in operation in the case supposed? If a boy undertakes to draw a hand sled on the bare ground, he must pull quite hard, but on the smooth snow he can draw it very easily. 42. Suppose a round stone be rolled on smooth ice? It would go much farther than on the rough ground; the smoother the ice is the farther it wTill go. MECHANICS OF SOLIDS. 17 43. We sometimes see a moving body, as a rolling ball, suddenly move off in a new direction-does it change the direction of its motion by its own inherent power? It does not; it is made to take a new direction by striking against some obstacle, or by receiving a blow from one side. 44. In view of what has now been stated, what may we conclude? That matter is perfectly passive or inert. 45. By what are all the motions and changes of motion that we observe produced? By the action of external forces upon bodies. 46. How is the VELOCITY, or rate of motion, of a moving body measured? By the space which the body passes over in a second, or any other interval of time. 47. If there were no friction, or other resistance in operation, would the continued exertion of a force be necessary to keep up the motion? It would not; a body once set in motion would move on forever with the same velocity, and in the same direction. 48. Can we realize this supposition of a motion free from all re, Distances? We can not; in every case of motion on the earth there is, of necessity, some resistance in play. 49. To keep up the motion of a body unchanged, what, then, is necessary? That a force should be continually exerted just sufficient to overcome the resistance. 2 18 NATURAL PHILOSOPHY. 50. Illustrate. When a horse draws a loaded wagon at a uniform pace, of some three miles an hour, his muscular effort continually overcomes the friction. 51. Give another illustration of the same principle. When a train of cars proceeds at an unvarying speed, of say 25 miles per hour, the power of the locomotive neutralizes all the resistances, and so keeps up the velocity acquired at the outset. 52. Is any particular amount of force required to overcome the inertia of a body and set the body in motion? The smallest force would produce some motion, no matter how large the body might be, if it were not opposed by a resistance. 53. How has this truth been strikingly illustrated? It has been said that the kick of a fly moves the earth. 54. Give another illustration. If there were no friction to be counteracted, a small boy could set a train of cars in motion. 55. Is there any exception to the general truth that bodies of matter do not move of their own accord? There is; a man, or any animal, can move or stop moving at pleasure. 56. Do external forces take effect upon men and animals, as well as upon ordinary bodies of inert matter? They do; if the support upon which we stand gives way we fall to the ground, just as a body of inert matter would. MECHANICS OF SOLIDS. 19 57. Every one knows that if a horse, when going fast, suddenly stops, his rider is thrown forward-what is the reason of this? It is owing to the inertia' of matter; the rider merely retains the motion he had in common with the horse. 58. How do you explain the fact that, when a man jumps from a carriage in rapid motion, he falls forward as soon as his feet strike the ground? In the same way; he is going forward just as fast when he reaches the ground as when he left the carriage. 59. When a circus rider, Fig. 1. standing on a galloping horse, wishes to leap over a rope, what does he do? He merely jumps up, and allows the motion -_ which he has to carry him past it.. EFFECTS OF FORCES UNDER DIFFERENT CIRCUMSTANCES. 60. When a force acts by PULLING, as when a horse draws a wagon, what is it called? A force of tractiors. 61. When a force aqs by PUSHING from behind or from above, what is it termed? A force of pressure. 62. Will the same blow from a club communicate as great a velocity to a large ball as to a small one? It will not; if the large ball contains twice as much 20 NATURAL PHILOSOPHY. matter as the small one, it will go only one half as fast. 63. The velocity imparted to any body perfectly free to move, by a given amount of force, depends, then, upon what? Upon the quantity of matter in the body. If the mass be great, the velocity is proportionally small. 64. That the same velocity may be imparted to a large mass as a small one, what is necessary? The force applied inust be greater in the same proportion that the mass is larger. 65. How can the effect of a force on a body be counteracted, so that no motion will ensue? By applying a force of equal intensity in the opposite direction. 66. Illustrate by an example. If two men of equal strength pull at opposite ends of the same rope, it will not move. 67. Suppose two blows of equal force are given to the same ball, at the same moment, in opposite directions? The ball will remain at rest, just as if it had not been struck at all. 68. When a body moves forward constantly at the same rate, as when a horse trots for two hours with the same speed, what kind of motion is it said to have? A tintformn motion. 69. When a body goes faster and faster every instant; as a falling stone does, what is its motion called? Accelerated motion. MECHANICS OF SOLIDS. 21 70. When a stone is thrown upward, it moves slower and slower every instant-what motion is it said to have? Retarded motion. GRAVITY, AND OTHER FORCES. 71. When either end of a magnet is brought near a small nail lying on a table, what happens? Fig. 2. The nail is drawn into contact with the magnet, and is there held by a considerable force. 72. What is this force called? The attraction of the magnet. 73. What is the reason that if a stone or other body be raised from the ground, and then left to itself, it falls with an accelerated motion? Because the earth continually attracts it, just as a magnet attracts a nail. 74. What is this force of attraction called? Gravity, or the Attraction qf Gravitation. 75. What is the entire force which draws the body down called? The weight of the body. 76. What is meant when it is said that a body is HEAVY? That it has weight. 77. How may a heavy body be prevented from falling? By placing it on some solid support, or suspending it from some fixed point above. 78. Illustrate by an example. A bbok put on a table is supported and can not fall. 22 NATURAL PHILOSOPHY. A lamp suspended by a rod or chain from the ceiling of a church, is thereby prevented from falling. 79. With what force does the book press upon the table, and the lamp pull downward upon the chain? With its own weight. 80. Are all bodies equally heavy? They are not; their weight is in proportion to the quantity of matter they contain. 81. Have two different substances the same weight when of the same bulk? They have not. A piece of iron is denser, or contains more matter, than a piece of wood of the same size, and it is also heavier. 82. How is the fact that one substance is, from its essential nature, heavier than another often expressed? It is said that its specific gravity is greater. 83. What amount of force must we exert upward to lift a heavy body from the ground? A force a little greater that the weight of the body. 84. When a grocer puts a quantity of sugar in his scales, and says that it weighs one pound, what is meant? That the weight, or downward pressure of the sugar, is the same as that of the pound weight which balances it in the other scale. 85. Is the quantity of matter also the same in each scale? It is. IECHANICS OF SOLIDS. 23 86. Give an example of the operation of another force similar to gravity. The elastic force of a steel spring gradually uncoiling drives the wheels of a watch. 87. Are all forces of the same essential nature with gravity? Some forces act by a sudden impulse, and produce their whole effect in an instant, or in a very short interval of time. 88. Give an instance of motion produced by such an impulsive force. The explosive force of gunpowder impels a ball with great velocity out of a gun. 89. Why should a heavy iron ball shot from a cannon strike with such destructive force against any solid obstacle that it meets? All the force that was expended in projecting it from the cannon is suddenly exerted against the immovable obstacle. 90. What is the force which a moving body exerts, or is capable of exerting, against an immovable obstacle called? The momentum of the body. MOMENTUM OF A MOVING BODY. 91. What does the momentum of a moving body depend upon? Its mass and its velocity. 92. Which has the greatest momentum, a cannon ball or a musket ball fired with the same velocity? A cannon ball; it will strike a wall with greater force because its mass is greater. 24 NATIURAL PHILOSOPHY. 93. Why are very heavy cannon bhlls used to batter down the walls of a besieged fortress? Because of the great momentiyv with which they strike. 94. Light comes to us from the sun with tel, astonishing velocity of 191,000 miles per second: if we suppose it to ~csist of particles a thousand times smaller than the smallest shot, with what force would a particle of light strike? With a fbrce equal to the momentum of a half ounce ball fired with the velocity of 2,000 feet per second. 95. What is this an instance of? A very great momentum, resulting from the enormous velocity of a very small particle of matter. 96. What is the reason that when two trains of railroad cars, on the same track, meet under full speed, the effects of the collision rce so destructive? The masses in motion are very great, and they also rwu," together with great velocity. 97. Give one or two familiar examples of important effects prn duced by momentum. A nail is easily driven by a hammer. Red hot iron is wrought into any shape by a blacksmith with his sledge. hammer. 98. What is a PILE? A long stick of timber, sharpened at one end, that it may more easily be driven into the ground. 99. How are piles driven far into the ground? By the momentum of a heavy mass of iron let fall upon the top. MECHANICS OF SOLIDS. 25 100. Are the useful applications of momentum confined to solid bodies in motion? They are not. The force of running water is used to drive mill-wheels. The wind impels ships across the sea; and on land turns the wind-mill. ACTION AND RELECTION. 101. Suppose the two bodies, A and B, Fig. 8. represented in Fig. 3, are both moving in the direction indicated by the arrow, and that A overtakes B and comes into collis- -. ion with it, what will be the result? A A will lose a portion of its mo-: mentum, and B will gain an equal amount. 102. How is this generally expressed? It is said that A acts on B, and B reacts on A; and that the action and reaction are equal and directly opposed to each other. 103. Is it universally true that whatever force one body exerts upon another, the second body exerts on the first in the opposite direction? It is; action and reaction are always equal and directly opposed. 104. Illustrate this important principle by a simple example. A book lying on a table presses on it by its weight, and is supported by the equal reaction of the table. 105. Mention another familiar illustration. If we clap our hands, each hand receives the same blow. 2 26 NATURAL PHILOSOPHY. 106. Suppose a man pulls at one end of a rope that is attached to a post? The post pulls at the other end just as hard as he does. 107. A magnet attracts a piece of iron that is brought near itaccording to the principle of action and reaction, what is also true? That the iron attracts the magnet with an equal force. 108. Does the same principle hold good in the case of the attraction which the earth exerts upon bodies at its surface? It does; all bodies react upon the earth with a force equal to the earth's attraction. 109. Does the earth, then, move to meet a falling stone? It does; but, owing to its enormous mass, its motion is exceedingly slow in comparison with that of the stone. 110. Has the principle of the equality of action and reaction any thing to do with the voluntary motions of men and animals? It has; the immediate cause of all such motions is the reaction of something against which the muscular force of the animal is exerted. 111. Illustrate. When we walk, it is the reaction of the earth to the force we exert that enables us to move. 112. How does a bird fly? It strikes the air with its wings, and the reaction of the air bears it forward. 113. How does a fish swim? By the reaction of the water to the pressure which it exerts against it with its fins and tail. MECHANICS OF SOLIDS. 27 114. Is the principle the same in every other case of motion in which the original source of power is within the moving'body? It is; for example, a steamboat is propelled by the reaction of the water to the pressure of the revolving paddles. 115. If a large ship comes into collision with a small vessel at sea, do they receive the same or a different shock? The same. EFFECTS OF COLLISION ON THE MOTION OF BODIES. 116. When two balls, moving on the same line, as in Fig. 37 page 25, come into collision, what are the circumstances of their motion after the collision? If they are inelastic they keep on together; but if they are elastic, like India rubber or ivory, they separate, and take different velocities. 117. Why do elastic balls separate after collision? B3ecause they are both compressed by the shock, and then recover their form with a certain force, which urges them asunder. 118. How may this effect be illustrated? Fig. 4. The result is the same as if there i were a steel spring. between the two 4 bodies, that was compressed by the A shock, and then recovered itself. 119. If an elastic ivory ball should come against another of the same size at rest, what would be the effect of the collision? The moving ball would stop, and its motion would be taken up by the other. 28 NATURAL PHILOSOPHY. 120. Does a blow from a club, given to an India rubber ball, send it off any faster because the ball is elastic? It does; nearly twice as fast. 121. If an elastic ball be thrown ob- Fig.5. liquely against an immovable wall, as shown in Fig. 5, in what direction will it glance off? If it be thrown in a direction A B, it will bound off in another direction, B C, equally oblique to the wall. 122. If an India rubber ball were perfectly elastic, how high would it rebound if dropped on the floor? To the height from which it fell. RELATIVE MIOTION. 123. What is relative motion? The motion of one body with respect to another which is also in motion. 124. Give an example. A man walking on the deck of a ship that is under sail is in motion relative to the bow or stern of the ship, and the whole ship at the same time moves forward and carries him along. 125. Suppose he were to run toward the stern at the same rate that the ship goes forward? He would keep continually over the same point on the surface of the water. While he would be in motion rela MECHANICS OF SOLIDS. 29 tively to the ship, he would be at rest in relation to the water. 126. If, as a steamboat was leaving her wharf, a person standing at the stern should throw an apple directly backward with the same velocity that the boat is going forward, how would the apple appear to move to a person on shore? It would be seen to drop directly down into the water. 127. If two trains of cars, on the same railroad, were proceeding in opposite directions, at the respective rates of 20 miles and 30 miles per hour, with what velocity would they approach? Fifty miles per hour. 128. If they were proceeding in the same direction, what would their relative velocity be? Ten miles per hour. They would approach at this rate if the faster of the two trains were behind the other. COMPOUND MOTION. 129. Can the same body have two different motions at the same time? It can; some examples have just been given. 130. What is the actual motion of a body that has at the same time two or more different motions called? Compound motion. 131. Give an example of compound motion. The case of a boat rowed across a river at the same time that it is carried down stream by the current. 30 NATURAL PHILOSOPHY. 132. If the boat should be rowed steadily Fig. 6. across the river, in the direction A B. and D should be carried down by a uniform current __ a distance B D, what line would it actually follow? The straight line A D. 133. Suppose two persons were to kick the same foot ball at the same instant, the one Fig.. toward B and the other toward C, what diree- / tion would it take? A direction A D, intermediate between the directions in which the two blows A c were given. 134. Would either impulse change the velocity in the direction of the other? It would not. 135. If'one impulse would have sent it to B in a second, and the other to C, where would it be from the joint action of the two at the end of a second? It would be at D. 136. If a boy, while in the act of running along Fig. 8. the line E F, should throw a ball from A toward B, would the ball go directly to B? It would not; it would continue to go for- \ /p ward as fast as the boy does; and so, having two motions, would pursue an interme-, diate line of direction, as A D. 137. Where must another boy, who wishes to catch the ball, stand? Somewhere on the line A D; and thus in advance of the line of direction in which it was thrown from A. MECHANICS OF SOLIDS. 31 138. Suppose a man, riding in a wagon, tosses an apple directly upward, will it come down into his hands again? It will; because it moves along horizontally as fast as the man does. MOTION IN A CURVED LINE. 139. Does a ball fired from a Fig. 9. gun pursue a straight line through the air? It follows a curved line, as shown in Fig. 9. 140. Why does it not proceed in the direction in which it was fired? Because its weight continually draws it downward into a new direction. 141. How far could a cannon ball be fired if it were not retarded by the resistance of the air? More than 30 miles. 142. What is the greatest distance that a cannon ball has actually been projected? Only about three and a half miles; so great is the effect of the resistance of the air. 143. If a bullet pursues a curved line through the air, how. is it that a marksman, in firing a rifle, aims at the mark he wishes to hit? The line of fire is somewhat inclined to the line of aim, and intersects it. 32 NATURAL PHILOSOPHY. 144. Illustrate by Fig. 10. Fig. 10. - _ —-----------— ______. a,'bL a b is the line of aim, and c d is the line in which the bullet leaves the gun. The bullet follows the curved line, and is on the line of aim at the distant point mn, or n. 145. To what height could a cannon ball be fired vertically upward, if it were not for the resistance of the air? Sixteen miles. 146. With what velocity and force would it return to the earth? With the same that it leaves the gun. 147. With what velocity should a cannon ball Fig. 11. be projected horizontally from the top of a mountain, to go entirely around the earth, supposing that it did not encounter the resistance of the air? About five miles per second. 148. Mention other instances of motion in a curved line. The drops of water in a fountain rise and fall in beautiful curves. Brooks and rivers often flow through verdant valleys in graceful serpentine lines. 149. What kind of motion has the moon in space? Fig. 12. The moon moves in a vast circle around the earth. 150. What force is it that continually draws the moon out of its direction of motion into a circle? The attraction of the earth. MECHANICS OF SOLIDS. 33 151. How much less is this force at the distance of the moon than at the earth's surface? About 3,600 times less. CENTRIFUGAL FORCE. Fig. 13. 152. When a stone is whirled round in a sling held in the hand, it is perceived that it pulls outward upon the hand; what is this force, that acts along the string fromn the centre outward, called? The Centrifugal Force. 153. What name is given to the force which draws the stone inward and keeps it in the circle? Centripetal Force. Fig. 14. 154. How are these two forces related to each other? They are of equal intensity, and pull in opposite directions,4V it /at the two ends of the string. 155.'Explain more particularly. The centripetal force pulls inward at the inner end, and the centrifugal force pulls outward at the outer end. 156. What keeps the cord stretched? These two forces pulling at its two ends; just as a rope is stretched by two men pulling at the ends. 2* 34: NATURAL PHILOSOPHY. 157. Suppose the stone should be whirled more rapidly, what would be the cojsequence? The opposing centripetal and centrifugal forces would be increased, and the string might break. 158. If the string should be sud- Fig. 15. denly released from the hand, or should break, what would be the resuit? The stone would fly off in a tangent, as Fig. 15 shows. 159. How does that appear? As soon as the string gives way, there is no longer any force operating to change its direction, and it continues on, by virtue of its inertia, in the direction in which it is moving at that instant. 160. Does the centrifugal force have any effect after the string gives way? It does not; it instantly ceases to act. 161. Are the same two forces in operation in other cases of circular motion, as in the revolution of the moon around the earth, and of the earth around the sun? They are; the centripetal force in these cases is the attraction of the central body around which the revolution is performed. 162. Suppose a round body turns about an Fig. 16. axis, like a top? All its parts will be animated by a centrifugal force pulling directly outward from the axis, as represented in Fig. 16. MEGHANICS OF SOLIDS. 35 163. What parts of the rotating body will be urged outward by the greatest force? Those which are most remote from the axis. This is indicated in the figure by the comparative size of the arrows. 164. How may the ac- Fig. 17. tion of the centrifugal force, in the case of a rotating body, be illustrated experimentally? By the apparatus represented in Fig. 17. 165. Of what does it consist? It consists of two circular iron or brass hoops, so thin as to be flexible, and an arrangement for setting them in rapid rotation around the upright rod to which they are attached. 166. If they are made to turn rapidly, what will be the result? They will be flattened at the top and bottom, and bulge out at the middle, as represented in the figure. 167. If a ball of moist clay, or other yielding material, should be set whirling about an axis, what would happen? It would be more or less flattened, in a similar manner. 168. Might it be brought Fig. 18. to the form of a flat disc, as shown at d, Fig. 18? It might, if the ma- d terial should be sufficiently tenacious, by making it turn rapidly. 36 NATURAL PHILOSOPHY. 169. How does the potter make use of the centrifugal force to aid him in his useful handicraft? A piece of clay is placed on a rapidly moving flat wheel, and the clay flattens out in endeavoring to move from the centre; with the aid of his fingers and a little tool he, with great dexterity, turns cup after cup, and saucer after saucer. 170. How is our common window glass manufactured into sheets? A mass of molten glass, on an iron rod, is made to turn rapidly round; it spreads out on the table into a thin round plate, from which afterwards are cut different sized panes. 171. It has been ascertained that the earth is somewhat flattened at its poles-what is the explanation of this curious fact? The earth rotates about an axis, and it took that form under the influence of the centrifugal force, ages ago, when its entire mass was in a fluid.state. 172. It is well known that large grindstones, turned rapidly by machinery, are occasionally broken into fragments that fly in every direction-what force is it that produces these violent effects? The centrifugal force. This pulls outward with such energy as to overcome the cohesion between the particles of the stone, and the fragments fly off in a tangent. 173. Why can we not turn a sharp corner when running fast? Because the effort we make is opposed by an energetic centrifugal force. 174. What is the reason that a train of cars, in passing rapidly around a curve on a railroad, is liable to be thrown off the track? The centrifugal force in operation causes the flanges on the outside wheels to press against the outer rails. MIECHIANICS OF SOLIDS. 37 175 Why do the circus rider and his horse lean toward the centre of the ring? To counteract the effect of the centrifugal force. A skater, for the same reason, leans to the inside, when he is describing a curve on the ice. CENTRE OF GRAVITY. 176. If a rod or cane be placed Fig. 19. on the edge of a stationary body, by - _ sliding it along we may find a point about which the weights of the two parts will balance each other; what is this point called? The centtre of'ravity of the rod. Every body has its centre of gravity, or point about which, if supported, the body will balance itself in any position. 177. Why has the name centre of gravity been given to Fig. 20. this point? Because the entire weight of the body may be considered as collected and taking effect there. 9 178. Illustrate. The body is drawn down by its weight, just as if a man were pulling downward with a certain force upon a cord attached to its centre of gravity. 179. In bodies of a regular form, as shown in Fig. 21, where is the centre of gravity situated? Fig. 21. At C, tile centre of' figile. 38 NATURAL PIILOSOPHY. STABILITY OF HEAVY BODIES. 180. When is a heavy body said to be STABLE, or to have STABILITY? When it is so supported that if disturbed from its position it will fall back again. 181. Give an example. Fig. 22. Fig. 23. The pend'ulum of a clock, represented in Fig. 22; or a _plumbline, shown in Fig. 23. 182. How is it with a body of any form suspended from a point directly over.... its centre of gravity (Fig. 24), or with bodies standing on their bases (Fig. 25)? Fig.24. They are all stable. 183. When is a body said to be UNSTABLE? When it is poised on a point or edge directly under its centre of gravity; so that if disturbed!i from its position it will upset. This is illustrated in Fig. 26. Fig. 95. Fig. 26. 184. Give another example. A pole standing on one end; if it be displaced, in the least, from that position, it will upset. MECHANICS OF SOLIDS.' 89 185. How may an upright pole be balanced on the finger, and kept from falling for some time? By shifting the position of the finger from one side to the other, so as to counteract the tendency to fall. 186. What is the general rule with regard to the movements of a heavy body disturbed from its position of rest? Its centre of gravity tends to the lowest possible position, and finally settles there. 187. Mention one or two illustrations of this tendency. The oscillations, to and fro, of the pendulum of a clock. Or the similar movements of a swing. 188. In order that a body standing on the level ground may have stability, what is necessary? That the centre of gravity Fig. 27. Fig. 28. should be directly over some point of the base of contact, as in Fig. 25 or Fig. 2 7. -x - --, 189. Suppose the centre of gravity overhangs the base, as shown in Fig. 28? The body will upset. 190. Does the stability of a body depend on the breadth of its base? It does; the broader the base the greater the stability. 191. Mention a familiar case in which this principle is applied. The legs of chairs are commonly spread out below the seat to give them greater firmness and security. 192. Mention other instances of the application of the same prin. cip]e. Candlesticks, table lamps, goblets, wine-glasses, and many 40 NATURAL PHILOSOPHY. other articles of household furniture, have stability given to them by a broad foundation. 193. Is the stability of a body Fig. 29. standing on a level surface the greater for the centre of gravity being low? It is. It will require a greater displacement to overturn it, as shown in Fig. 29. It will also be less liable to upset if placed on a sloping surface. 194. Where is this shown? Fig. 30. In Fig. 30; the body B is on the A/ point of overturning, but the body A, with a lower centre of gravity, stands firm. 195. Illustrate by a familiar fact. A wagon loaded with stone is less liable to upset than one loaded with hay. Fig.81. 196. By what are ATTITUDES controlled? By the necessity of preserving the centre of gravity. 197. Illustrate by an example. If a man carries a load on his back, he stoops forward to keep the centre of gravity over his feet. 198. Suppose he bears a load in one hand or on one shoulder? He leans to the other side, and if he carries it in his arms he leans backward, for the same purpose. MECHANICS OF FLUIDS. 65 351. Give an example of the operation of this principle. Water is conveyed into cities by large iron pipes, and rises in small pipes in the houses to the level, or nearly so, of the water in the distant reservoir. BUOYANT ACTION OF LIQUIDS ON IMMERSED SOLIDS. 352. What is the reason that when a stone, or any other body, held in the hand, is entirely immersed in water, it tends downward with less force than before, as if it had lost part of its weight? The upward pressure of the water on the under part of the stone is greater than the downward pressure on the upper part. 353. The excess of pressure underneath will then tend to support the weight of the body-what is this called? The buoyant efort of the liquid. 354. What is its amount? It is equal to the weight of the liquid which the body displaces. 355. What will happen, then, if the liquid is denser and heavier than the body? The body will rise to the surface, and float with a certain part above the surface. 356. Illustrate by an example. A cork, if put under water, will rise and float with three quarters of its bulk out of water. 357. A cannon ball, which sinks so readily in water, will float on quicksilver-what is the explanation of this curious fact? Quicksilver is more than 13 times heavier than water, and is heavier than iron. 4 66 NATURAL PHIILOSOPTHY. 358. Would a cannon ball have any less tendency to sink at the depth of a mile in the ocean than just below the surface? It would not, unless the water is denser at that great depth. In point of fact its density is only about Tmoth greater at that depth. 359. What weight will a floating body, as an empty cask, or a boat, bear up without sinking? The excess of the weight of water that it can displace above its own weight. 360. Suppose a ship is loaded with a cargo weighing 800 tons, how much more water does she displace than when unloaded? An amount weighing 800 tons. When unloaded, the quantity of water displaced will be equal in weight to the entire weight of the ship. 361. What is the explanation of the fact that iron boats are constructed which draw less water than similar boats built of wood? The entire weight of the iron boat is less than that of the boat constructed of wood. 362. If an iceberg, of a regular form is seen at sea floating with 50 feet out of water, what is its depth below the surface of the sea? 270 feet. WATER WHEELS. 363. By what is the machinery of mills and factories often driven? By water wheels; the most common forms are represented in Figs. 68, 69, and'TO. MECIANICS OF FLUIDS. 67 364. What is the wheel represented in Fig. 68 Fig. Gs. called?. An Overshot TWheel. The water shoots over the top into the buckets that are set -n on the rim. 365. What is it that moves the wheel? The weight of the water in the buckets. The buckets are full on one side of the wheel Fig. 69. and empty on the other. 366. What is the wheel shown in Fig. 69 called? An Undershot Wheel. The water shoots under the wheel, and strikes — riii1 - l!-: H1i 11 i icy: against the floats at the bottom. 367. Explain Fig. 70. Fig. 70. It represents a wheel intermediate between the other two, called the Breast Wheel. 368. Where does the water come on to the wheel? Somewhere between the top and bottom, frequently about midway. 369. Which is the most efficient of these three wheels? The overshot wheel. 370. Are there any other forms of water wheel in use? There are also wheels that whirl around horizontally, called Turbines. 68 NATURAL PHILOSOPHY. 371. What may be said of these? That they are the most efficient form of water wheels, and have lately come into extensive use. PRESSURE OF THE AIR. 372. The body of air confined within a vessel, or room, presses outward against the walls of its inclosure-what is this outward pressure called? The Elastic Force, or Pressure of the Air. 373. What have you to say of the condition of any limited portion of the external air? It presses outward in the same manner. 374. What sustains and counteracts this outward pressure? The equal inward pressure of the surrounding air. 375. If we apply the mouth to the upper Fig. 71. end of a small glass tube, which has the lower end under water, and withdraw the air from it by suction, what will take place? The water will rise in the tube and enter the mouth. 376. What causes it to rise after the air has been removed from the tube? The pressure of the air upon the surface of the water outside of the tube. 377. What do the arrow, in the figure, and the dotted line leading from it, show? The pressure of the air on the surface of the water, at MECHANICS OF FLUIDS. 69 a certain point, and how it is transmitted and forces the water up the tube. 378. It is often said, in such cases, that we draw the water up by suction-what do we really do? We simply remove the air from the tube, and then the pressure of the outer air crowds the water into the empty space, or vacuuwzt, formed within the tube. 379. Why does not the same pressure force the water up the tube before the air is withdrawn? Because the elastic pressure of the air within the tube is equal to this transmitted pressure, and neutralizes it. 380. If I were to take a glass tube, 33 inches long, fill Fig. 72. it with quicksilver, and close the open end with the finger, then invert the tube, dip the lower end in a vessel of quicksilver, and remoa-e the finger, what would be the result? The quicksilver would fall in the tube, until it stood about 30 inches above the level in the vessel. 381. What supports the column of quicksilver 30 inches high? The pressure of the air on the surface of the quicksilver outside of the tube. 382. If the open end of the tube were of the size of a square inch, what would be the weight of the column of quicksilver supported by the atmospheric pressure? Nearly 15 pounds. 383. What, then, is the pressure of the air in pounds on every square inch? About 15 pounds; and 2,125 pounds, or nearly a ton on every square foot. 70 NATURAL PHILOSOPHY. 384. What is a BAROMETER? It is simply the contrivance represented in Fig. 72, pro.vided with a scale for reading off the height of the mercury in the tube. 385. What does it make known? The amount of the pressure of the air at any time. 386. Does this pressure vary? Somewhat from day to day, with variations of temperature, and changes in the weather. 387. If a barometer be taken to the top of a mountain, or carried up in a balloon, does the mercury continue to stand at the same height in the tube? It does not; it falls more and more the higher the barometer is carried. 388. What does this show? That the pressure of the atmosphere gradually decreases from the earth's surface upward. 389. What may we infer from this fact? That the pressure of the air at any point is the weight of the entire column of air that rests on that point. 390. Caln the height of a mountain be determined by observing how much the mercury in the barometer falls, when the barometer is carried from the bottom to the top of the mountain? It can; near the level of the sea an ascent of 93 feet is attended with a fall of -j-th of an inch in the height of the barometer. 391. How high will the atmospheric pressure cause water to rise in a very long tube from which the air has been removed? Thirty-four feet. MECHANICS OF FLUIDS. 71 392. How may the pressure of the air on solids be readily Fig. 73. shown experimentally? By taking a tube, open at one end, into which a solid piston has been fitted air tight. 393. If a small orifice be made at the bottom of the tube, and the piston be pressed down to the bottom-on closing this orifice and undertaking to raise the piston, what will be observed? The piston will be held down with considerable I force; as it rises, a vacuum will be formed below it, and so the pressure of the air on its upper side has to be overcome. AIR PUMP. 394. What is an AIR PUMP? It is a contrivance by means Fig. 24. of which the air confined within f a vessel can be removed from it, and a vacuum obtained. 395. Its essential parts are represented in Fig. 74 —what are they? _M__ c1 An upright cylinder, C, into which a piston, P, is fitted air tight. 396. Is this piston solid? It has an opening at its centre, covered by a valve that opens upward. There is another valve opening upward, fitted to an orifice at E, in the bottom of the pump. 72 NATURAL PHILOSOPHY. 397. Where does this orifice in the bottom of the pump lead? It leads, by means of a small pipe, to the vessel A, from which the air is to be removed. This vessel is called the Receiver. 398. Suppose the piston is pressed down to the bottom of the pump, what happens when it is drawn up? The pressure of the air in the pipe opens the lower valve, and air flows through the opening from the receiver, and fills the empty space which the piston leaves behind it. 399. What happens when the piston is forced down again? All the air that is below it passes through the open valve in the piston, and mixes with the external air. 400. When the piston is raised again, what takes place? More air flows out of the receiver; and, in this way, by repeatedly raising and depressing the piston, the air may be nearly all withdrawn from the receiver. 401. Whenever the piston is raised, the pressure of the air upon it has to be overcome-how is the power requisite for this obtained? In some pumps by means of a long lever; but the more common expedient is to combine two pumps in such a manner that the pressures on the two pistons will balance each other. 402. What is Fig. 76 designed to rep- Fig. 75. resent? A celebrated experiment performed by Otto Von Guerike, the inventor of the air pump. 403. Describe it briefly. Two hollow hemispheres of copper were nicely fitted to MECHANICS OF FLUIDS. 73 each other, and the space within them exhausted of air, through a cock by means of an air pump. These hemispheres are represented in Fig. 75. 404. What was then done? It was then found that the hemispheres were held together so firmly by the pressure of the external air that several horses could not exert sufficient force to separate them. Fig. T6. PUMPS FOR RAISING WATER. 405. What does Fig. 77 represent? The common sucking pump. 406. Describe it. It consists of two tubes of unequal size, one on top of the other, and an air tight piston, P, that can be moved up and down in the upper tube, by applying a power to the piston rod. There are also two valves opening upward, one at E, and the other in the piston. 407. What is the use of the valves? They allow the air or water to pass up through the opening over which they are placed, but prevent it from going down again. 4 74 NATURAL PHILOSOPHY. 408. When the piston is worked up and down, what is the effect? The air is first pump- Fig. 77. ed out; as it is re- Fig. 7S. moved, the water rises in the lower pipe, then into the body of the pump, and finally gets A above the piston and is delivered at the spout. 409. What causes the water to rise in the pump in proportion as the air in it is removed? The pressure of the air outside of the pump, on the surface z - of the water in the well. 410. Explain Fig. 78. It represents another form of pump called the Forcing Ptump. The piston is solid, and the upper valve is at F. 411. How does it operate? The air is pumped out, and the water rises to the piston, just as in the sucking pump. 412. What takes place after that? Whenever the piston is forced down, the water below it is driven up the pipe G, and through the valve F. MECHANICS OF FLUIDS. 75 413. The water is represented as passing from this pipe into a closed vessel, A-what is this vessel called? An air vessel. 414. For what purpose is it used? The water that is forced into it crowds the air in it to the upper part, and this condensed air pressing on the surface of the water impels it up the ascending pipe, H, in a constant stream. 415. What kind of pump is used in the Fig. 79. FIRE ENGINE? The forcing pump; the long handles -_ which the firemen move up and down work two force pumps. 416. Into what do these two pumps force the water? Into an air tight box, A. From this it is driven out through the pipe and hose in a constant stream. THE SIPHON. 417. What is a SIPHON? Fig. 80. It is a bent tube, having its two branches of unequal length. 418. To what general purpose is it applied? To draw water and other liquids from vessels. 419. How does it operate? The shorter leg is plunged into the vessel of 76 NATURAL PHI-IILOSOPHY. water, the mouth is then applied to the lower end, and the siphon filled with water by suction. 420. Will the water continue to run after the mouth is taken away? It will. 421. The pressure of the air on the water in the vessel should fill the siphon with water as soon as the air is sucked out of it-but why should the water afterward flow steadily out at the lower end? Because there is a pressure in all parts of the tube to keep it flowing in that direction. 422. Show that this is the case at the top of the siphon. The pressure of the air acts upward at both ends of the siphon; and the pressure at each end is loaded with the weight of water in that leg. 423. What follows from that? The pressure at the end of the short leg has the smallest load upon it, therefore the pressure transmitted from that end to the top of the siphon will be the greatest. SOUND. 77 CHAPTER IV. SOUND. NATURE AND PRODUCTION OF SOUND. 424. WHAT kind of motion has a stretched cord when it is drawn to one side, and suddenly let go? Fig. 81. It vibrates to and fro, like a pendulum. This is represented in Fig. 81. The dotted lines show the extent of the vibrations.! 425. How may the tension of the cord be increased? By screwing up the upper hook. 426. What happens during each vibration of the cord? The cord acts against the air with a certain force. 427. When the cord is tightly stretched and forced to one side, it vibrates with great rapidity-what is the result of this rapid vibra. tion? Sound is produced. 428. How is sound produced by a vibrating cord, or ally other vibrating body? The vibrations of the sounding body are communicated to the surrounding air; and spreading in all directions through the air, reach the ear. 429. What is the impression they make on the nerves within the ear called? The Sensation of Sound. 7T8 NATURAL PHILOSOPHY. 430. What does the vibratory or tremnbling motion imparted to the air, and spreading out in all directions from the body, form? A spherical Wave of Sound. 431. Do the particles rise and fall in a wave of sound, as in a wave of water? They do not; they move forward and backward through a very short distance-that is, directly from and toward the sounding body. 432. Does a sounding body send out a regular succession of waves, corresponding to the successive vibrations? It does. 433. What does each wave convey to the ear? The slight impulse with which the body acts against the air, and originates the wave. 434. If we consider only the trembling movement that is conveyed, or PROPAGATED, by a single line of particles reaching from the body to the ear-what have we? Fig. 82. W hat is sometimes called a....................................................... Ray of Sound. 435. Does a sounding body, for example, Fig. 83. the tuning fork represented in Fig. 83, send out rays of sound in all directions? It does; and they all proceed with the same velocity. 436. Do sounds differ in their character, or QUALITY? They do. We distinguish between the crack of a whip, the report of a pistol, and the blow of a hammer; the sounds produced by the filing of a saw SOUND. 79 are harsh and grating to the ear, while the notes from a flute are soft and pleasing. 437. How is it that the ear thus distinguishes between sounds? The vibrations of sounding bodies are all faithfully repeated in the ear, and all their peculiarities are impressed on the delicate nerves of the ear. 438. Mention a fact or two in illustration of the great delicacy of the human ear. A practiced ear can distinguish between two sounds, the one having 80 vibrations in a second, and the other 81. It can also distinguish the different instruments of a band, when playing together the same note. 439. When a harp string is struck, or an empty glass tumbler tapped with the finger nail, why do we hear a MUSICAL SOUND? Because the vibrations of the string, or glass, are repeated with perfect regularity. 440. When the impulses on the ear succeed each other at exactly equal intervals, the sound is then a pleasing one-does the ear take notice of the rapidity of the vibrations? It does, with the greatest nicety. If one musical string vibrates more rapidly than another, it produces a sound of a higher Pitch. 441. If one string of a violin vibrates twice as fast as another, what is said of the two sounds produced? That one is an Octave higher in pitch than the other. 442. What is the range of sensibility of the human ear to musical sounds? The lowest, or most grave, musical note of which the ear is sensible, is produced by 8 vibrations in a second; 80 NATURAL PHILOSOPHY. and the highest, or most acute, note, by 24,000 vibrations in a second. 443. Compare the highest and lowest notes of an ordinary piano forte. The lowest is produced by 27- vibrations in a second, and the highest by 3,520. 444. If a glass tumbler be made to ring with a musical sound, by tapping it with the finger nail, what is the reason that the sound ceases if the finger be placed on the rim? The pressure of the finger stops the vibrations. 445. If water be poured into the tumbler, and it then be tapped, why does it give a note of a lower pitch? Because it vibrates less rapidly than before. The pitch of a musical sound depends on the rapidity of vibration. 446. What does the loudness of a sound depend upon? The force with which the sounding body, acts against the air, and so upon the ear also, in each vibration. 447. Illustrate by an example, If a violin player wishes to produce a loud note he draws his bow violently across the string; the string is thus made to vibrate through a greater distance, and act upon the air with more force. 448. Give another illustration. A large bell gives out a louder sound than a small one; for two reasons-because the extent of the vibrations is greater, and the mass in vibration is larger. SOUND. 81 PROPAGATION OF SOUND IN THE AIR. 449. Mention some facts which go to show that sound is not con-,eyed, instantaneously, from the sounding body to the ear. We do not hear the blows of a hammer, at a distance, at the same instant that we see them struck. The report of a gun is always heard later than the flash is seen. A flash of lightning from a distant thunder cloud is seen several seconds before the thunder clap arrives. 450. What is the velocity of sound through the air? 1124 feet per second. 451. Why does the loudness of a sound diminish as it is propagated through the air, from the sounding body? Because the original impulse communicated to the air is spread over a greater space. 452. Does the intensity of sound also vary with the state of the weather? It does. Sounds are louder when they come with the wind, and in a cold than in a warm day; also in a humid than a dry state of the air, but they are obstructed by falling rain or snow. 453. Mention one or two striking facts in illustration of the great distance at which sounds may be heard over water and ice. It is related in the account of the Third Polar Expedition of Captain Parry that a conversation was once held across the harbor of Port Bowen, a mile and a quarter wide. What is still more remarkable, the human voice has been heard across the Straits of Gibraltar, a distance of ten miles. 4* 82 NATURAL PHILOSOPHY. 454. What is the greatest distance at which any sound has been heard? The cannonade of a sea-fight between the English and Dutch, in 1672, was heard across England in Wales, a distance of over 200 miles. The explosions of volcanoes among the Andes, in South America, are said to have been heard at a much greater distance than this. 455. How can we ascertain the distance of an approaching thunder cloud? By noting the number of seconds in the interval between a flash of lightning and the thunder clap that follows it, and allowing 1,124 feet for every second. 456. Hotels and large dwelling houses are frequently provided with SPEAKING TUBESI leading from one story to another. What is the reason that the lowest whisper at one end of the tube is distinctly heard at the other end? The sound is confined to the tube, and does not spread and become weakened, as in the open air. 457. How far has a low whisper been heard through a pipe? More than half a mile; through a continuous line of empty water pipes laid in the streets of Paris. 458. Why can we hear more distinctly along the outside wall of a house than at a distance from it? Because the sound is prevented from spreading on the side on which the wall is. 459. Why do we hear better at night than in the day time? Because the air is generally stiller and of more uniform density, and in the quiet of the night our ears are more sensitive to the impressions of sound. 80UND. 83 ECIHOS. 460. What happens when a sound strikes against an obstacle, as the side of a house, or the wall of a room, or a rocky cliff'? It rebounds, or glances off, like an elastic ball, and is heard at a certain distance, in the direction in which it proceeds, as an Echo. 461. Illustrate by an example. A person looking into a very deep well hears every word that he speaks repeated to him from the water at the bottom of the well. 462. Mention another illustration. If I should stand at some distance from the wall of a house and clap my hands, I would hear the same sound again as an echo from the house. 463. How far must you be from the wall in a perpendicular direction to hear a distinct echo? More than 62 feet. 464. If you were to stand at A, Fig. 84, and Fig. 84. clap your hands, another person standing at B g may hear an echo-how is the sound reflected to him??D As the figure shows; it strikes obliquely against the wall, and glances off with the same obliquity. 465. Does it ever happen that a loud sound is followed by more than one echo? In particular localities echos are returned in succession 84 NATURAL PHILOSOPHY. from a number of surrounding objects. For example, at West Point, on the IIudson, the report of the morning and of the evening gun is prolonged by repeated echos from the surrounding highlands. 466. Mention another example. There is a locality near the foot of Mount Washington, on the west side, where to the blast of a single horn a full band seems to reply from the adjacent heights. 467. Give another example. On the %Wengern Alp, in Switzerland, the prolonged note of the Alpine horn is caught up by the mountain heights and dies away into the softest melody in the upper sky. 468. What may be said of spacious rooms with vaulted ceilings, or surmounted by lofty domes? They return every sound in a multiplicity of echos. 469. Illustrate by an example. In the Rotunda of the Capitol at Washington, the hearing of conversation is much confused by the innumerable echos of every sound, received from the walls and the dome overhead. 470. What curious fact is observed in such spacious inclosures with curved walls or ceilings? The sound produced at one point is often concentrated at another distant point, so that the faintest whisper can be heard from one to the other, although inaudible between the two. Such a room is called a Whispering Gallary. SOUND. 85 471. Illustrate by Fig. 85, which rep- Fig. 85. resents a room of an oval shape. All the rays of sound proceed- / ing from a certain point, S, after _ ___ striking against the curved wall -- are collected into a focus at F. 472. Give an example of a WHISPERING GALLERY. At the base of the dome in St. Paul's Church, London, the feeblest sound is conveyed from one side to the other of the dome, a distance of more than 130 feet, but is not heard at any intermediate point. 473. When we speak in a room, why do we not always hear distinct echos from the walls and ceiling? Because, unless the room is large, the interval of time between the sound of the voice and the return of the echo is too short; the two are heard as one sound. 474. Why do we hear so much better in a room than in the open air? Because the sound is strengthened by the reverberation from the walls, ceiling, and floor. 475. What is the effect of curtains, carpets, and furniture in a public room? They make it less easy to speak in, by deadening the echo and dispersing the sound. We may see this, by observing how much louder the voice sounds Fig. 86. in an empty than in a furnished room. 476. How are deaf people enabled to hear? By putting an Ear Trumpet to their ear. 86 NATURAL PHILOSOPHY. 477. How does this act to strengthen the sound? It concentrates at the ear all the rays of sound that enter the large open mouth of the trumpet. 478. When a fireman wishes to throw his voice to a distance, what instrument does he use? A Speaking Trumpet. 479. How does a speak- Fig. 87. ing trumpet act to strengathen the sound? - __-> Fig. 87 shows that the rays of sound are reflected from the interior of the trumpet, and all proceed on in the same direction. 480. How far may a strong man's voice, sent through a trumpet 24 feet in length, be heard? At a distance of three miles. PROPAGATION OF SOUND IN LIQUIDS AND SOLIDS. 481. Is sound conveyed through liquids and solids, as well as through the air? It is, and with greater velocity. 482. What is the velocity of sound in water? 4,708 feet per second, or about 41 times the velocity of sound in the air. 483. Can sounds be heard farther under water than in the air? They can. Franklin, plunging his head under water, SOUND. 87 heard distinctly the blows of two stones struck together at the distance of half a mile. 484. How far has the sound of a bell, struck under water, been heard? A distance of nine miles. 485. What is the velocity with which sound is transmitted by cast iron? 11,090 feet, or a little over two miles per second. 486. What is its velocity of propagation through solid substances in gl. -,-al? From 7 to 17 times greater than through the air. 487. What general truth may be stated with regard to the conduction of sound by solids? Sounds are conducted with greater distinctness by solids than by the air, or even by liquids. 488. Mention one or two facts that strikingly illustrate the facility with which sounds are conveyed by solids. The scratching of a pin at one end of a long beam can be distinctly heard, if the ear be applied at the other end. The ticking of a watch can be heard as well by placing it between the teeth as by putting it at the ear. 489. Is the ground a good conductor of sound? It is; by putting the ear to the ground we may ascertain the fact of the approach of a horse, wagon, or train of cars, before the sound reaches us through the air. 490. Do sounds pass from the air into a solid, the wall of a building, for instance, and then into the air again on the other side? They do; but in doing so they experience a great dim 88 NATURAL PHILOSOPHIY. inution of intensity. We can hear in a perfectly tight room sounds from without, but they are much weakened. MUSICAL INSTRUMENTS. 491. What are STRINGED INSTRUMENTS? Musical instruments, in which the sounds result from the vibrations of stretched cords or wires. For example, the violin, guitar, piano, and AEolian harp are all stringed instruments. 492. What are the stretched cords employed in these instruments called?.Musical Strings. They are of different lengths and sizes, as in the piano; or of the same length but of different sizes, as in the violin. 493. Which strings give the notes of highest pitch? The shorter and smaller strings; because they vibrate most rapidly. Every note has its particular length or size of string, and particular number of vibrations. 494. Has the force by which a musical string is stretched any thing to do with the pitch of the note that it gives? If the tension of the string be increased, it will vibrate more rapidly, and give out a note of higher pitch. 495. What are WIND INSTRUMENTS? Musical instruments in which the notes are produced by the vibrations of columns of air within the instrnment; for example, the flute, the trumpet, and the organ. 496. From what do the deep base notes of the organ proceed? From the long and large pipes; and the high notes from the short pipes. SOUND. 89 THE VOICE. 497. How are the sounds of the voice produced? The organs of voice form a wind instrument; the air contained in the mouth, throat, and upper part of the windpipe is set in vibration. 498. By what? By a stream of air forced from the lungs through a narrow opening in the upper part of the windpipe. 499. How is this narrow orifice formed? By the partial closing of a kind of membranous valve in the windpipe. THE EAR. 500. What is the process of hearing? The vibrations conveyed from the sounding body are collected by tile outer visible ear, pass. through the contracted opening into the ear-tube, and strike, at the bottom of the tube, on a stretched membrane, called the Drum, or Tymlpanun, of the ear. 501. Explain farther. The vibrations imparted to the drum are propagated through another tube to a second membrane, and from this directly to the fluid of the internal ear, and to the delicate fibres of the nerves of hearing, spread out in the fluid. The nerves convey the impressions to the mind. 5 90 NATURAL PHILOSOPHY. CHAPTER V. LIGHT. NATURE AND TRANSIISSION OF LIGHT. 502. WHAT is a LUMINOUS BODY? A body that gives off light; the sun, for example, is said to be luminous. 503. How do we see a luminous body? The light thrown off from it passes into our eyes and produces the sensation of sight. 504. What did the great English philosopher, Sir Isaac Newton, suppose light to be, in its essential nature? He conceived that light consists of exceedingly minute particles given off from the sun and other luminous bodies. He supposed that the minute particles of light passing into the eye produce the sensation of sight, as the particles of fiagrant matter passing from flowers to the nose, produce the sensation of smell. 505. What is the view now entertained by philosophers of the nature of light? That it is analogous to sound; that there is a subtile ether filling all space, which is the medium of light, as ~air is the medium of sound. 506. Of what is light conceived to consist? Of vibrations of this elastic ether, excited by the lumin LIGHT. 91 ous body, and propagated in all directions through the ether; as sound consists of vibrations of the air, excited by the sounding body, and propagated through the air. 507. According to this view, how is the sensation of sight produced? Luminous bodies send off waves of light, as sounding bodies send off waves of sound. These waves, striking upon the nerves of our eyes, produce the sensation of sight. 508. By what names are these two views concerning the nature of light distinguished? The latter is called the Wave iTheory of Light, the other, the Newtonian Theory. 509. Does light proceed in straight lines? It does. We can not see through a Fig. SB. small bent tube, such as is represented in Fig. 88. 510. Do all bodies give off light at all times? They do not; some bodies, like the sun, are, in their nature, self-luminous, and others, like a house or a tree, are non-luminous. 511. How do non-luminous bodies become temporarily luminous? By receiving light from the sun, or some other self-luminous body. For example, a candle brought into a dark room renders the walls and furniture temporarily luminous, and therefore visible. 512. What is a ray of light? It is a single line of light proceeding from a luminous point. 92 NATURAL PHILOSOPHY. 513. What does Fig. 89 represent? Fig. 89. The line of minute particles in a ray of light. 514. Do the particles in a ray of light move swiftly through space? It was so supposed by Newton, but it is now known that they are stationary particles of ether, along which vibrations or trembling movements are conveyed in rapid succession. 515. Do rays of light proceed from every point of the sun, or other luminous object-? They do; and in every direction. 516. How is this truth generally expressed? It is said that light radiates in every direction front every point of a luminous body. 517. Fig. 90 shows that individual rays of light Fig. 90. emitted from a luminous point separate more widely the farther they proceed-how is this fact usually stated?......... Such rays are said to diverge, and they < 71 \ are called Diverging R]ays. 518. What consequence follows from the divergence of light? That light decreases in intensity as it recedes from its source. 519. Illustrate by an example. We receive less light from a candle the farther we are from it; because the same amount of light is spread over a greater space. LIGHT. 93 520. What does Fig. 91 represent? Fig. 91. A small pencil of diverging rays v_ proceeding from a point in the flame of a candle to the eye. Every point in the flame sends to the eye such a pencil of rays. 521. What is the velocity of light? 191,000 miles per second. 522. At that rate, in how short a time would light pass entirely around the earth? In one eighth of a second. 523. What is a TRANSPARENT substance or MEDIUM? One through which light passes freely; glass, for example, is transparent. 524. What is an OPAQUE substance? One that does not admit light to pass through it; a stone, for example, is opaque. 525. If a book is held before a candle in the evening, it intercepts the light that falls upon it, and its shadow is thrown upon the wall-why is the shadow on the wall larger than the book? Because the rays of light that pass by its edges diverge from each other. 526. How far does the shadow cast by the book extend? From the book to the wall, where it is intercepted. 527. What is the form of the shadow cast by a round body, the moon, for example, illuminated by Fig. 92. the sun? It tapers to a point, as shown in Fig. 92. 94 NATURAL PHILOSOPHY. 528. What becomes of the light that falls on an opaque substance? A part is reflected back, the rest enters the substance, and is stopped, or absorbed by it. ABSORPTION OF LIGHT. 529. Do glass, water, and other transparent media absorb any portion of the light that enters them? Every transparent medium absorbs more or less light, according to its thickness. 530. How far does the light of the sun penetrate into the depths of the sea? About 700 feet. At the bottom of the deep ocean there is utter darkness. 531. Does the atmosphere extinguish any portion of the light that comes from the sun and stars? It does; even in its purest state it absorbs a large quantity of light, especially toward the horizon. 532. How do we know that the atmosphere has this effect? It causes the stars to shine more dimly.toward the horizon, and strips the sun of so much of his brightness at' sunset that our eyes can bear the full light of his disc. 533. How much farther is it through the atmosphere in the direction of the horizon than perpendicularly upward? It is 13 times farther. 534. What appearance have the stars seen through the thin air above the top of a lofty mountain? They shine with a much brighter lustre than when viewed through the whole depth of the atmosphere. LIGHT. 95 REFLECTION OF LIGHT. 535. How are surrounding objects made visible to us by day? Light falls upon them from the sun and sky, and is reflected to our eyes. 536. Is this light reflected in any particular direction? It is reflected in all directions; it radiates from every point of the surface, as if that point were shining with its own light. 537. Suppose a ray of light falls upon the polished surface Fig. 93. of a mirror, in what direction is it reflected? Fig. 93 shows that it glances off, just as an India rubber ball does when thrown against a wall. 538. If the light falls perpendicularly on the -surface of the mirror, in what direction does it leave it? It returns in the same line, as a ball bounds back when thrown directly against a wall. 539. How is it that in looking into a common mirror or lookingglass, we see the images of objects that are in front of the mirror? An object always appears to be in the direction in which the rays from it enter the eye, and the rays from the object which, after reflection, enter the eye, come from the mirror. 540. What does Fig. 94 show? Fig. 94. How rays radiating from'' any point of a luminous ob-!::; ject, as an arrow, may fall "i upon a mirror, be reflected off / 96 NATURAL PHILOSOPHY. to the eye, and enter it as if they came from a point behind the mirror. 541. What is seen, then, behind the mirror? An image of the arrow; that is, what appears to be the arrow, but is not. 542. Where does the reflection take place in the case of the common looking-glass? Chiefly at the smooth surface of the quicksilver that is spread over the back part of the glass. 543. Does not the front surface of the glass reflect light also? It does; in the evening the windows in our houses become so many mirrors, in which the objects within the room are reflected. 544. Why is this reflection not perceptible by day? Because the impression of the reflected light on the eye is effaced by that of the strong light that comes from without. 545. What does Fig. 95. Fig. 95 represent? An amusing a' Ec.. toy, called the, 1 Magic Perspec- e tive. A coin or any thing else held at k, can be seen by the eye at the other end, though a book be held between them at b. 546. How can that be? The light from the coin follows the course shown by the arrows. It is reflected from mirrors at mn, o, n, and i. LIGHT. 97 547. What does Fig. 96 represent? Fig. 96. The reflection from a Concave Miirror, of a beam of rays, sup- - - posed to come from a point of the sun's disc. 548. What is the course of the reflected rays? They all converge to the focus, F. 549. What is such a collection of rays converging to a focus called? A pencil of Converging Rays. 550. Suppose a white screen, of paper or cloth, were placed there to receive them, what would be seen at F? A bright point. This point can be seen also without a screen, by placing the eye in the position shown in the figure. 551. Suppose light were to fall on the concave mirror from all points of the sun's disc, what would be seen at F? A small bright circle, which would be an image of the sun.,52. Explain Fig. 97. Fig. 97. The concave mirror, M, forms in the air, at I, an inverted image of the arrow, A. The course of the rays proceeding from a single point of the arrow, before and after reflection, is shown in the figure. 553. If the object were at I, near the mirror, where would its image be? At A, and it would be larger than the object. 5 98 NATURAL PHILOSOPHY., 554. Is the image of an object that is in front of a concave mirror ever seen behind the mirror, as in a common looking-glass? It has that position when the object is quite near the mirror, and it appears to be much larger than the object. 555. Of what material are concave mirrors usually made? Of a metallic alloy of tin and copper, called Speculum fetal, that admits of a high polish, and does not tarnish readily. They are sometimes made of copper, steel, or silver; or of glass quicksilvered on the back. 556. When formed of speculum metal, what are they ordinarily called? Specutla. 557. Concave reflectors are used with great effect in light-housesin what manner are they set up? A number of mirrors are fastened on the outside of an iron circular rim, and a lamp is placed in the focus of each mirror. Fig. 98. 558. Fig. 98 represents one of the mirrors thus arranged-for what purpose is it employed? To throw the light of the lamp far out to sea. It does this by reflecting all the rays that fall upon it in nearly the same direction. REFRACTION OF LIGHT. 559. What occurs when a ray of light passes from the air into a denser medium, as air or water? It is bent, or refracted, so as to pursue a direction more nearly perpendicular to the surface. LIGHT. 99 560. Where is this effect represented to the eye? Fig. 99. In Fig. 99, where a ray of light is represented as entering and passing through a thick piece of glass. 561. Is it refracted again in passing out of the glass into the air? It is, but in the opposite direction, as the figure shows. 562. Does it recover its original direction on leaving the glass? It does, if the thickness of the glass is everywhere the same, as in the case of common window glass. 563. What is the reason that, in looking through a pane of window glass, we sometimes see objects displaced Fig. 100. from their true position? A. Because the outer and inner sur. /-i faces of the glass, in such instances, are not even and truly parallel. Fig. 100 represents such a case, and shows the course pursued by a ray of light coming from an object at A. 564. What is the result? The object appears to be in the direction in which the light enters the eye, and is thus displaced toward the right. 565. What illusion is produced by the refraction of light in pass. ing from water into air? It causes objects immersed in water to appear to be higher than they really are. 100 NATURAL PHILOSOPHY. 566. What does Fig. 101 show? Fig. 101. That a stick partially immersed in water ~ appears, from this cause, to be bent or broken at the surface. 567. Every one knows that a shallow stream never _ appears to be as deep as it really is-what is the reason? The bottom is elevated by refraction. 568. An interesting illustration of the refraction Fig. 102. of light is represented in Fig. 102-what is it? A coin, placed in a tea cup so as to be concealed from the eye, will rise into full view, if the cup be filled with water. 569. What is Fig. 103 designed to show? Fig. 103. That a ray of light falling perpendicularly on a refracting surface, passes on without experiencing any change of direction; also that light is bent most out of - its course when it enters the surface very - obliquely. 570. Do all transparent substances effect the same change in the course of the light? They do not; the refracting power of glass is greater than that of water, and the refracting Fig. 104. power of the diamond is much great- W.. er than that of glass. 571. What does Fig. 104 represent? A A glass prism; the prism has three faces, and its ends are triangular. LIGHT. 101 572. What else is shown in the figure? The direction in which a ray of light coming from a candle is bent on entering and leaving the prism. 573. What effect has the prism, in the position shown in the figure, on the apparent direction of the object? The object appears to be in the direction a c, and above its true position. 574. What is a common LENS, or BURNING Fig. 105. GLASS? It is a circular piece of glass, rounded on both sides, so as to be thicker at the middle than at the edges. 575. What is the ordinary effect of Fig. 106. a lens upon the rays of light that pass through it? It concentrates them at a fo- l cus, as shown in Fig. 106. 576. On what line is this focus situated? On the line passing from the luminous point through the centre of the lens. 577. When the rays are parallel, or come from a distant point, what is the point of concentration called? The Focus of the lens; and the distance from the lens to the focus is called the Focal -Distance or Focal length of the lens. Fig. 107. 578. What does Fig. 107 show? In what manner images of objects are formed by a lens. 102 IATURAL PHILOSOPHY. 579. Explain how the image of the arrow is formed. A pencil of rays proceeding from each point of the arrow falls on the lens, is concentrated into a focus, and thus forms an image of the point. 580. When the arrow is at A, remote from the lens, where is its image formed? At I, a little outside of the focus of the lens; it is smaller than the arrow, and inverted. 581. If the arrow is at I, a little outside the focus, where is its image? At A, remote from the lens; it is now much larger than the arrow. MICROSCOPES. 582. What is a pocket microscope? It is a small lens, with which minute objects may be magnified. 583. Suppose we wish to magnify the letters of a book, in what position must the microscope be held? Between the eye and the open page of the book, and so near the page that the letters shall be ini the focus of the lens. 584. How does a pocket microscope magnify objects? It enables us to see them distinctly at a shorter distance than we can with the naked eye. 585. How can the letters of a book, or any small object, be magnified without the use of a lens? By looking closely at them through a small hole pricked in a card with a needle. LIGHT. 103 586. When the magnified image of an object is formed in Lhe air, as represented in Fig. 107; and the image is received on a white screen, what is the consequence? The light from the object is spread over a larger space, and the image appears indistinct. 587. How can it be rendered distinct? By throwing a strong light upon the object, and darkening the room. 588. What two Fig. 108. ways are there of accomplishing this? One is by concentrating the light of the sun upon the object; when this is done, the magnifying lens becomes a Solar M2icroscope. 589. Where is the microscope placed? In a tube, and one end of the tube is screwed into a hole in a window-shutter of a darkened room. 590. How ls the light of the sun thrown upon the animalcule that is to be magnified? A mirror on the outside of the window throws it upon a a large lens within the tube, and this concentrates it upon the object. 591. How is the magnified object seen? It is received on a screen in the dark room, placed at the distance of 20 or 30 feet from the microscope, and is visible from all parts of the room. 104 NATURAL PHILOSOP-IY. 592.. How much does a good solar microscope magnify? About 10 million times; that is, it would take 10 million animalcules to fill up the spot on the screen that is occupied by the image of one of them. 593. Mention some of the astonishing results that have been obtained with the solar microscope. The most diminutive insects are magnified into creatures of large size. A drop of vinegar is seen thronged with eels, and a film of stagnant water becomes a large pool, in which a host of strange animals are darting about and preying on one another. 594. Mention other remarkable results. The delicate and intricate structure of plants and flowers is distinctly seen, and the wonderful processes of crystallization, from the beginning to the close, go on before the eye. 595. What is the Fig. 109. second method of illuminating objects that are to be magnified? E By concentra- M ting on them tile light of a lamp — - this is the arrangement in the Xagic Lantern. 596. What objects are put near the focus of the magnifying lens? Small pictures, painted in transparent colors on glass LIGHT. 105 597. Why is the apparatus represented in Fig. 109 called a magic lantern? Because of the astonishing effects and wonderful illusions that may be produced by it. 598. What is the best and most convenient form of microscope for the careful examination of minute objects? The Compound Aficroscope. The object is seen through two lenses placed at the ends of a tube about seven inches long. 599. What is the magnifying power of COMPOUND microscopes? They have been made to magnify 3,000 times, and to show lines marked on glass so close together that 80,000 of them would occupy only an inch. TELESCOPES. 600. What is the construction of the common telescope for viewing the heavenly bodies? Fig. 110. It consists of two lenses placed at the opposite ends of a long tube. 601. What are these called? The smaller one, into which the eye looks, is called the eye-glass, and the other the object-glass. 602. What is the diameter of the object-glass called? The aperture of the telescope; the quantity of light 5* 106 NATURAL PHILOSOPHY. coming from the object, that enters the telescope and passes on to the eye, depends upon the size of this lens. 603. How does a telescope enable us to see distant objects more distinctly? The object-glass forms an image of the object at its focus within the tube, and the eye-glass magnifies that image, just as a pocket microscope magnifies the letters of a book. 604. How does the telescope enable the astronomer to see remote objects in the heavens, which are not visible to the naked eye? The object-glass is much larger than the pupil of the eye, and condenses into a small space near the eye a much larger quantity of light than the naked eye would receive. This may be seen on referring to Fig. 110. 605. What is the power of a telescope to reveal remote invisible objects called? Its space-penetrating power. 606. How is the magnifying power of a telescope ascertained? By dividing the focal length of the object-glass by the focal length of the eye-glass. For example, if the former were 20 feet and the latter 1 inch (or J-.th of a foot), the magnifying porer would be 12 times 20, or 240. 607. Long telescopes must then be more powerful than short ones -does not the real effectiveness and value of a telescope depend also upon the size of the object-glass? It does; a telescope of large aperture furnishes more light, and thus admits of the use of a more powerful eyeglass. We have already seen that it is more effective for the discovery of remote invisible objects. LIGHT.!O7 608. Is the same eye-glass used in the examination of all objects? It is not; telescopes are furnished with several eyeglasses, to be used in looking at different bodies and in different states of the atmosphere. 609. Where is the largest and best refracting telescope in the world to be found? At. the Cambridge Observatory, near Boston; its objectglass is 15 inches across, and its focal length 22- feet. 610. What is its highest magnifying power? 2,000; its lowest magnifying power is 180. 611. Does a common SPY-GLASS differ in any respect from a telescope for viewing the stars? It has additional glasses inside of the tube to make objects, seen through it, appear erect. 612. How does a REFLECTING TELESCOPE differ from that which has just been described? A large concave mirror takes the place of the objectglass; this mirror is at the bottom of a long hollow tube which rests on the ground. 613. Where does the observer stand? tIe stands with his back toward the object, at the elevated mouth of the tube; and looks through the eye-glass at the image thrown just before it by the concave mirror. 614. The largest reflecting telescope that has ever been made, was constructed by Lord Rosse, an Irish nobleman, and is of enormous size- ive its dimensions. The mirror is 6 feet across; the tube is 7 feet in diameter, and 52 feet long. The highest magnifying power of this monster telescope is about 9,000. 108 NATURAL PHILOSOPHY. THE EYE. 615. The essen- Fig. 111. tial parts of the eye L, are represented in ll J Fi-. 111-describe it. I, The eye is a hollow ball corn- posed of several membranes, and filled with a transparent liquid; within this is suspended a semi-liquid mass, of the shape of a lens, and called the Crystalline Lens. This is seen at e. 616. What is the action of Fig. 112. the eye on a pencil of rays pro- d ceeding to it from any point of a luminous object? The rays are all made to converge to a point on the back part of the eye, as shown in Fig. 112. 617. What is formed on the back part of the eye? An inverted image or picture of the object. 618. What is spread over the back part of the eye to receive it? The Retina. This is a fine net-work of fibres proceeding from the optic nerve that communicates with the brain; it is represented in Fig. 111. 619. What lies immediately in front of the crystalline lens? An opaque screen with a hole in its centre, through which the light passes. LIGHT. 109 620. What is this screen called? The Iris; the round opening at its centre is called the Pupil of the eye. The pupil is the aperture or window of the eye. 621. Is the pupil always of the same size? It contracts when the light becomes strong, and dilates when it grows feeble; so as always to allow the proper quantity of light to pass into the eye. 622. What produces this change? The stimulus of the light upon the nerves of the iris either directly or by transmission from the retina. 623. Why do we see more distinctly, in the evening, after we have been out in the dark a little while, than we did at first? Because the pupil dilates gradually. On the other hand, if we come from the dark into the presence of a strong light we are dazzled at first by it, because the pupil does not contract instantly. DECOMPOSITION OF LIGHT. 624. What does a ray of white light, from the sun or other source of light, consist of? Several rays of Fig. 118. different colors. [ 625. How may this be shown? By admitting a ray of solar light through a very i1t0 NATURAL PHILOSOPHY. small hole in a window shutter into a dark room, and allowing it to pass through a prism, as represented in Fig. 113. 626. What is observed on the white screen? A beautiful display of brilliant colors, like a piece of a rainbow, called the Solar Spectrum. 627. How does the prism separate these colors and throw them on different parts of the screen? It refracts some more than others. 628. Mention the seven colors of the spectrum, beginning with the color that is least refracted. Red, orange, yellow, green, blue, indigo, and violet. 629. By whom was the decomposition of light with a prism first accomplished? By Sir Isaac Newton. 630. Is it now believed that white light really consists of seven pure colors? The present belief is that it is composed of but three simple colors, red, yellow, and blue. 631. Who has established this? Sir David Brewster, of Scotland. 632. What has he shown to be true with regard to the other colors of the spectrum, viz., orange, green, indigo, and violet? That they are but different combinations of the three simple colors; orange, for example, is chiefly a mixture of red and yellow, and green of yellow and blue. 633. How was the orange colored light of the spectrum separated into its elementary colors by Sir David Brewster? By passing it through a piece of blue glass of a certain LIGHT. 111 thickness. This extinguished the red light, and allowed the yellow to pass on to the eye. 634. It would seen, then, that all the red light does not go to one part of the spectrum, all the yellow to another part, and all the blue to another, as Newton supposed? Some portion of each of these colors is found in all parts of the spectrum. 635. Why does one ray of light affect the eye with the sensation of red, another with the sensation of yellow, and a third with' the sensation of blue? The particles of ether vibrate more rapidly in a ray of yellow than in one of red light, and more rapidly in one of blue than in one of yellow light. These different rates of vibration produce different impressions on the retina. 636. To show the wonderful' sensibility of the eye, mention the number of vibrations, per second, of each of the three simple colors? In red light there are 458 trillions of vibrations in a second, in yellow light there are 535 trillions, and in blue light 622 trillions. The retina of the eye distinguishes between these numbers, so enormously great. 637. To what do the different colored rays correspond, among sounds? To musical sounds of different pitch; thus blue may be said to be light of a higher pitch than yellow, and yellow to be light of a higher pitch than red. 638. Does the eye take the same delight in the variety and harmony of colors that the ear does in the variety and concord of musical sounds? It does. 112 NATURAL PHILOSOPHY. 639. What colors, of the spectrum, harmonize ~with each other, or make an agreeable impression when seen together? Red harmonizes with bluish green, orange with blue, yellow with indigo, green with reddish violet, and violet with yellowish green. 640. What is the explanation of the flashing brilliancy of the diamond? The diamond has a very high refracting power; as a consequence a strong light is reflected from the back part of the stone, and the light that enters one of the faces and passes out at another is widely dispersed into its elementary colors. For this purpose faces are cut on the original stone. THE RAINBOW. 641. What is Fig. 114 Fig. 114. designed to show? The manner in which is the rainbow is formed by the reflection of sun light from falling drops of rain. 642. Trace the course of the light. It enters a drop, is reflected from the back part of it, comes out again at the front part, and passes on to the eye. 643. What is the cause of the colors of the rainbow? The separation of the colored rays of which the sun's LIGHT. 113 light is composed, as the light enters and leaves the drop. 644. What is the order of the colors in the rainbow? The red is uppermost and the violet undermost. 645. We often see a second and fainter bow higher than the first -how is this formed? By rays that enter the drops at the lower part, experience two reflections at the back part of the drops, pass out at the upper part, and proceed on to the eye, as represented in Fig. 114. 646. Why is this bow fainter than the other? Because the light suffers two reflections, instead of one, and considerable light is lost in the act of reflection. 647. Do two different persons see the same rainbow? They do not; they see the same colors, but these proceed from different drops. 648. When is the rainbow usually seen? In the afternoon, when the sun shines at the same time that it is raining to the east of us. It is also sometimes seen in the west, on a showery morning. 649. Is it ever seen under any other circumstances? We often see cataracts that send up clouds of spray spanned by its beautiful arch; and, in a bright day, its brilliant colors lend a new beauty and grace to fountains sparkling in the light of the sun. 6 114 NATURAL PHILOSOPHY. COLORS OF BODIES. 650. Why is one object, as a wafer, red; another, as a lemon, yellow; another, green, etc.? Because each reflects to the eye the light of its own color. 651. The color is not, then, any quality necessarily belonging to the substance? It is not; for the colors of flowers, trees, and other ob jects, are only seen when light from the sun, or some other source, falls on them. Besides, the same substance has not always the same color. 652. Explain by an example. Phosphorus, for example, is of a pale yellow color, but, if melted and cooled suddenly, it becomes perfectly black. 653. Give another example. Charcoal is black and opaque, but the sparkling diamond, which is the same substance in another form, is ae clear and transparent as glass. 654. What, then, is all the beautiful variety of colors in nature owing to? To different arrangements of the particles of bodies. It is by this simple expedient that the beneficent Creator has so clothed the earth with beauty, and made it a delight to the eye. 655. Transparent gems, different varieties of glass, and many liquids are variously colored-to what do they owe their color? Principally to colored light transmitted through them. LIGHT. 115 They extinguish certain colors, and allow others to pass through to the eye. 656. Is the red light that comes from a red object, or the yellow light that comes from a yellow object, a pure unmixed color? It is a mixture of that color with more or less of each of the other colors. 657. What simple proof have we of this? It is observed that a colored object always appears of the color, whatever it may be, of the light that is thrown upon it. 658. We say that charcoal is black-is black a positive color? Perfect blackness is the absence of all color and all light. An object is said to be black when it reflects a feeble light to us. Black is no more a color than silence is sound. 659. Why do certain objects, paper for instance, appear white? Because they reflect the different colors in about the proportion in which they are combined in white light. 116 NATURAL PHILOSOPHY. CHAPTER VI. ELECTRICITY. EXCITATION AND CHARACTERISTIC EFFECTS OF ELECTRICITY. 660. IF a thick glass tube be taken in the hand, Fig. 115. rubbed briskly with a dry woolen cloth, or a silk hand-, kerchief, and then brought near to light substances,, _ _ as small pieces of paper, small balls of elder pith, etc., lying on a table, what will be observed? The little pieces of paper, or pith balls, will fly into contact with the glass tube, and then dart off again. They will continue to fly up and down for some time. 661. How does the glass tube produce these effects? It at first attracts these light bodies into contact with it, and then repels them away from it. 662. Will any other substance, besides glass, when held in the hand and rubbed, attract light bodies? Sealing wax, and many other substances, when rubbed, will act on light bodies just as glass does. 663. What is this peculiar state into which the surface of the glass is brought, by rubbing, called? The state of Electrical Excitement; the glass is said to be electrically excited, or electrified. 664. What is supposed to be the nature of this excitement? The friction, from rubbing, is supposed to disengage on ELECTRICITY. 117 the surface an exceedingly thin and subtile fluid, which is called electricity. 665. Is friction the only mode of developing electricity? The electric fluid may be disengaged by the simple pressure of one surface against another, also by heat, and chemical action. Every cause that produces any agitation among the particles of bodies, disturbs the electrical equilibrium, and sets free some of the electricity that is intimately associated with these particles. 666. Suppose'an excited glass tube, or stick of sealing wax, were to be drawn through the hand, closed tightly upon it, what would be the result? Its electrical excitement would be destroyed. 667. How is this explained? The electric fluid passes off into the arm, and descends through the body into the floor; from thence it flows off into the ground. 668. Under this idea, what is the human body said to be? A good conductor of electricity. 669. If the excited glass tube, or sealing wax, be touched, at one point only, with the knuckle, will the electric fluid be drawn off from all points of the surface? It will not; only from the spot that is touched. 670. What may we infer from this? That the electric fluid does not flow freely from one particle of glass, or sealing wax, to another. 671. What are such substances that obstruct the passage of electricity called? Non-conductors of electricity. Some substances are bet 118 NATURAL PHILOSOPHY. ter non-conductors, that is, offer more resistance to the flow of electricity than others. 672. Can a brass or iron rod be excited by holding it in the hand and rubbing it, as a glass tube can be? It can not; but a metallic rod can be feebly excited, if it. is provided with a non-conducting handle of glass by which it is held. 673. How are these facts explained? The rod is a good conductor of electricity; if the hand touches it, the electricity flows off into the'ground as fast as it is disengaged; when a glass handle is used, a nonconductor is interposed between the rod and the hand. 674. When, as in the case of a metallic rod held by a glass handle, an electrified conductor is supported by means of a non-conductor, so that the electricity can not flow off into the ground-in what state is it said to be? It is said to be insulated. 675. What does Fig. 116 represent? Fig. 116. A piece of electrical apparatus, called the Electric Pendulum. 674. Of what does it consist? Of a small pith ball, suspended by a silk thread, which serves to insulate it. 677. If an excited glass tube be brought near the pith ball, what will happen? The ball will be attracted by the tube, will touch the glass, and after having touched it will immediately be repelled. ELECTRICITY. 119 678. Suppose the attempt is made to bring the tube nearer to it? If that be done, it will move farther off, showing that it is now repelled by the glass. 679. When the pith ball is in contact with the tube, being a good conductor, it becomes charged with electricity-what may we infer from the fact of the repulsion of the ball by the tube? That an electrified body repels any other body that is in the same state of electrical excitement with itself. 680. How may we show that each Fig. 117. of the two electrified bodies repels the other? By taking two insulated pith balls, hanging side by side, and charging them both by bringing them into contact with an excited glass tube. 2) 681. If this be done, what will be observed? The balls will be seen to stand apart from each other, as the figure shows, and to be both of them repelled by the glass tube. 682. Suppose that I were to touch the two balls, and thereby draw off their electricity, what would be observed? They would fall together, and now, being in their natural state, would be attracted by the glass. THE TWO ELECTRICAL STATES. 683. We have just seen that a pith ball, charged with electricity from a glass tube, is repelled by the tube-if I were to bring near 120 NATURAL PHILOSOPHY. the ball thus charged a stick of sealing wax, excited by rubbing it with woolen cloth, would it repel the ball, just as the glass does? On the contrary, it would attract it. 684. What must we infer from this? That there are two different states of electrical excitement; the one is produced by rubbing glass with woolen cloth, the other by rubbing sealing wax with the same. 685. How are they explained? There are supposed to be two electric fluids in all bodies, instead of one, called respectively Vitreous Electricity and Resinous Electricity, or Positive and l~egative electricities. 686. What is supposed to be the ordinary condition of these two fluids? They are so combined in the natural state of bodies, that they have no sensible action on surrounding bodies. 687. What is the effect of friction? It separates the positive and negative fluids, and causes one to collect on the body rubbed, and the other on the rubber. 688. Is the rubber, then, always in the opposite electrical state from the surface rubbed? It is; if one gives signs of positive electricity, the other, if properly insulated, will give signs of negative electricity. 689. What other explanation of the two electrical states has been devised? Franklin supposed that there is but one electric fluid in bodies, and that the positive excitement is an excess of fluid above the natural share, and the negative a deficiency. ELECTRICITY. 121 690. What are the supposed relations of the two fluids to one another? They mutually attract each other; but each exerts a repulsive action on another portion of the same fluid. 691. Can the two fluids be separated in any other way than by rubbing the surfaces of two bodies together? They can also be separated in any body by bringing another electrified body near to it. 692. In Fig. 118 we have a large brass Fig. 118. ball on a glass support, near a brass cylinder, insulated in the same manner-if the ball were charged with positive, or vitreous:i| electricity, what effect would it have on the cylinder? It would separate the two electricities in the cylinder, attract the negative to the nearer, and repel the positive to the farther end. 693. If the cylinder, when in this state, were to be touched by the hand, what would be the effect? The positive electricity would flow off into the ground, but the negative would remain. 694. Why does not the negative electricity flow off like the other? It is held fast by the attraction of the positive electricity on the ball. In this condition it is said to be disguised. 695. Suppose the ball were to be brought nearer and nearer to the cylinder, what would take place before they came into contact? A vivid spark of light, attended with a snapping noise, would pass from the one to the other. This is called the Electric Spark. 6 122 NATURAL PHILOSOPHY. 696. Under what circumstances is it seen and heard? Whenever a good conductor is brought very near to an electrified body; for example, if I were to touch an electrified body with my knuckle, I would receive a spark. 697. How is the electric spark supposed to be produced? By the rushing of the two electric fluids together through the intervening air. 698. When do we see the electric spark exhibited on an enormous scale? When a flash of lightning passes from a cloud to the earth. The slight snap of the ordinary spark is now the loud thunder. CONDUCTORS AND NON-CONDUCTORS. 699. What substances are good conductors of electricity? The metals, charcoal, the ground, water and most liquids, trees and animals, vapor, flame and smoke, and many other substances, are good conductors. 700. Do they all conduct electricity equally well? They do not; the metals are much better conductors than water, or trees, or animals. 701. Are there any absolutely perfect conductors? There are no perfect conductors, and no perfect nonconductors; and the same body, a glass rod for example, may conduct a large charge of electricity, and completely obstruct the flow of a small charge. ELECTRICITY. 123 702. What substances belona to the class of non-conductors? Gum-lac, gutta-percha, resin, wax, glass, hair, wool, dry paper, baked wood, India rubber, oils, etc. 703. Is the air a conductor or a non-conductor of electricity? Dry air is a non-conductor, but moist air is a good conductor. 704. What important consequence follows from this? That electrical experiments do not succeed well when the air is humid; the disengaged electricity is rapidly conducted off by the moist air. DISTRIBUTION OF ELECTRICITY OVER THE SURFACE OF INSULATED CONDUCTORS. 705. When an insulated conductor: like the large brass ball in Fig. 118, is electrified, does the electricity pervade the whole mass of the body? It does not; it is confined entirely to the surface. 706. How may it be shown Fig. 119. that electricity in such cases collects on the outer surface? By covering an electrified ball with two covers provided with insulating handles, as represented in Fig. 119. 707. If this be done, what will be the result? The electricity will flow from the ball into the covers; on removing these carefully, they will be found to be charged, but not a trace of electricity will be found remaining on the ball. 124 NATURAL PHILOSOPHY. 708. Does the electric fluid diffuse itself equally over the surface of insulated conductors? It does, when the conductor is a round ball. On the surfaces of long bodies it accumulates at the ends. It is also more intense at the corners and edges of bodies than at other parts of their surface. 709. What is the state of the case when the surface tapers to a point? The electricity collects in such large quantities at the point that it escapes and flows off quietly through the air to some other body, or diffuses itself in the atmosphere. 710. If a p inted metallic rod, or a needle, held in the hand, be brought within a few feet of a charged conductor, what will be the effect? The electricity will be rapidly but silently drawn off; no spark will be seen. 711. Who first studied the effect of metallic points in discharging electrified bodies? Franklin. 712. Did he make an important application of it? He did, in the construction of the LIGHTNING ROD. He made the rod pointed at the top, that it might in a thunder-storm draw off silently the electricity from the charged clouds over-head. 713. For any other purpose? To direct any inevitable discharge to the rod, and thus convey it to the ground without injury to the house. ELECTRICITY. 125 ELECTRICAL MACHINE. 714. What is an electrical Fig. 120. machine? A machine employed for developing electricity in large quantities. Fig. 120 _ represents one form of electrical machine. 715. Of what does it consist? A circular plate of thick glass turned by a winch, two pairs of rubbers, an insulated conductor, called the PRIME CONDUCTOR, and a framed support. 716. What are the rubbers? Each of the rubbers is a small cushion covered with leather, over which is spread a layer of an amalgam of zinc and quicksilver; this greatly augments the exciting effect of the rubber. 717. Where may the two pairs of rubbers be seen in the figure? At the top and bottom of the plate; the rubbers in each pair are so arranged as to press against both surfaces of the' plate. 718. Where is the prime conductor shown? At f, f, and g; it is insulated by the glass supports, h. 126 NATURAL PHILOSOPHY. 719. How is the electricity that is excited by the friction of the amalgam on the surface of the glass plate, drawn off on to the prime conductor? By means of metallic points that extend out toward tho glass, on both sides; these are at i and i. 720. How may a body be charged with electricity from the prime conductor? By extending a metallic rod, or chain, from it to the prime conductor. 721. Give some account of the most remarkable electrical machine ever made. The largest and most famous electrical machine ever constructed, was made for the Teylerian Museum at Haarlem. When in full action, a zigzag flash would dart from the prime conductor, a distance of ten feet, to a neighboring conductor, and by bringing a metallic ball near to it, 300 sparks, forked like lightning, and two feet in length, could be obtained from it in a minute. Its attractive influence on light bodies extended to a distance of 40 feet. LEYDEN JAR. 722. When there is occasion to accumulate a much larger quantity of electricity than can be obtained at once from the prime conductor of an electrical machine, what piece of electrical apparatus is employed? The Leyden Jar. 723. What is its construction? Fig. 121 represents a Leyden jar; it is a large glass ELECTRICITY. 127 jar, coated, both on the inside and outside, to Fig. 121. within a few inches of the top, with tin foil. The month is closed with a stopper of baked wood, and a brass rod, terminating in a knob, K and connected with the inside coating, passes through the stopper. 724. Can electricity pass from the inside to the outside coating? It can not. 725. How is the jar charged? The outside is connected with the ground by touching it with the hand or in some other way, and a metallic rod or chain is extended from the knob to the prime conductor of an electrical machine. 726. What does Fig. 122 Fig. 122. represent? A jar in the act of being charged. 727. On turning the electrical machine, what will take place? The positive electricity will flow in a continuous stream from the prime conductor into the jar, until it becomes fully charged. Positive electricity will, at the same time, flow steadily from the outside coating into the ground. 128 NATURAL PHILOSOPHY. 728. Why should the electricity continue to flow into the jar for some time? Because it is attracted by the negative electricity that is retained on the outside of the jar. The reaction of this negative electricity renders insensible a large quantity of positive electricity on the inside. 729. How is the jar discharged? By bringing the outside and inside into conducting connection with each other; the two electricities rush together along this connection. 730. What is a common method of discharging the jar? By means of the Discharging Rod represented in Fig. 122. It consists of two curved brass rods terminating in knobs, and having a common joint at the end of an insulating glass handle. 731. How is it used? One of the knobs is first brought into contact with the outside coating, and then the other is made to touch the knob of the jar. 732. What takes place just as the two knobs are brought to gether? The jar is discharged, with a loud report, and a vivid flash of light. 733. Suppose a person were to touch the outside of the jar with one hand, and the knob with the other? The discharge would take place through his arms and chest, and he would experience a sudden convulsive shock, called the Electric Shock. ELECTRICITY. 129 734. Can several persons receive the electric shock at the same time? They can, by taking hold of hands, and the person at one end of the line touching the outside of the jar, and the one at the other end touching the knob. 735. Explain Fig. 123. Fig. 128. It represents a combination of Leyden jars, called an Electric Battery. ~. 736. What have you to say of the electric battery? A much larger quantity of electricity can be accumulated with it, and much greater effects produced, than can be obtained with a single jar. 737. Illustrate by a remarkable example. An electric battery of enormous size was constructed, to be used with the great IHaarlem electrical machine; it consisted of 100 jars, each 13 inches in diameter, and 2 feet high. The discharge of this battery would rend the hardest wood to pieces, and would kill a dog instantly if passed through the head and spine. VARIOUS EFFECTS OF ELECTRICITY. Attraction and Repulsion. 738. How may electrical attraction and repulsion be illustrated in an interesting manner? By the apparatus called the Electric Bells, shown in Fig 124. 6* 130 NATURAL PHILOSOPHY. 739. Describe it. Fig. 124. Three small bells are suspended from a brass rod, the two outer ones by brass chains, and the middle one by a silk I thread; between the bells are hung, by K silk threads, two metallic clappers. i 740. How are the bells made to ring? The middle bell is connected with the floor by a brass chain, and the rod from which they are all suspended is brought into connection with the prime conductor of the electrical machine. 741. What follows on turning the machine? The electricity flows into the two outer bells; these attract the little clappers, which become charged as soon as they strike against them, and are then repelled off, strike against the middle bell. and become discharged. 742. What happens then? Fig. 125. The clappers are attracted again by - the outer bells. In this way a constant ringing is kept up while the machine is turned. In a similar way little puppets, made of elder pith, may be made to dance by placing them between two metallic plates. 743. How must the plates be arranged? The lower plate must communicate with the ground, and the other with the prime conductor of an electrical machine in action. ELECTRICITY. 131 744. What will be the action of the plates on the puppets placed between them? The figures will be attracted by the upper plate, then repelled from it, then discharged by the lower plate, then attracted by the upper plate again, etc. 745. What is Fig. 126? Fig. 126. The Electrica See-saw moved in a126. similar manner by electrical attraction and repulsion. The chains shown in the figure effect the necessary connections. 746. Explain Fig. 127. Fig. 127. It represents an amusing illustration of electrical repulsion. It is an artificial head covered with long hair; the stem is placed in the hole at the top of the prime conductor, and when the machine is turned, the hairs - stand aloof in the ludicrous manner shown by the figure. 7*47. Can a person be silently and insensibly filled with electricity? He can, by standing on an Insulating Stool with glass legs, and taking hold of a brass rod that rests on the prime conductor. In this condition his clothing will attract particles of dust, pieces of paper, and other light bodies; his hair will stand out, and sparks may be taken 132 NATURAL PHILOSOPHY. from his hands, his ears, his nose, or from any part of him. 748. Mention two or three instances of violent effects produced by the mutual repulsion of particles of bodies highly charged with electricity. The charge of a large Leyden jar passed through water confined in a small glass tube and between two wires that nearly meet at the center, shatters the tube and scatters it into fragments. A quire of paper, placed between two metallic balls, may be perforated with the charge from a battery. 749. Mention other instances of similar effects produced by repulsion. In a similar manner, brittle bodies, as pieces of loaf sugar, sealing wax, hard wood, stones, etc., may be broken and scattered into fragments. 750. How are all the violent effects of lightning, such as the shattering of trees, and stripping them of their bark, the destruction of articles of furniture in houses, etc., produced? By the strong repulsion existing between the highly charged particles of the bodies that lie in the path of the lightning. This effect of repulsion may sometimes be greatly increased by the sudden conversion of the moisture in these bodies into steam. Heating Effects of the Electric Discharge. 751. Can combustibles be set on fire by electricity in motion? Ether and spirits of wine can be inflamed by the electric spark received from the prime conductor of an elec trical machine. ELECTRICITY. 133 752. Can solid combustibles be inflamed by the electric discharge? Gunpowder will explode, and tow dipped in powdered resin will burst into flame, if the spark from a good-sized Leyden jar be passed through them. 753. Can metals be heated by the electric discharge, passed through them? They may be melted, and even burned up, if they are used in the state of a fine wire to conduct the charge of a powerful battery. 754. In order that heat may be produced by electricity, what is necessary? That a considerable quantity of electricity should be in motion, and meet with resistance at the point where the heat is to be produced? 755. What is the reason that lightning often sets fire to a building that it strikes? Because of the resistance that the flash meets with from the combustibles through which it passes. 756. Will an ordinary lightning rod convey a flash of lightning to the ground without being materially heated? It will; but the points of lightning rods have sometimes been melted, when struck by lightning. Electric lig;ht. 75t. Under what circumstances is light produced by the electric discharge? Whenever the electric current passes through any space that is occupied by air; at every such point light is produced. 134 NATURAL PHILOSOPHY. 758. What does Fig. 129 represent? Fig. 129. A glass plate, with narrow strips of tin foil pasted on it, which have been cut across, here and there, with a E - -_ — knife, so as to form letters. 759. If the ring at the top be brought into communication with the electrical machine, and the chain on the right with the floor, on working the machine in a dark room, what will be observed? The letters will flash out in the darkness as letters of light. Fig. 130. 760. Is any luminous appearance connected with the flow of electricity from a pointed rod? y,~ When positive electricity flows off friom a pointed rod connected with a prime conductor, a brush of light is seen at the Fig. 181. point, as represented in Fig. 130. 761. What is observed when negative electricity escapes from a metallic point, or the point is held in the hand and presented to the prime conductor? It is seen to be illuminated by a minute but brilliant star. 762. Explain Fig. 131. It represents a glass tube several feet long, having a pointed wire at the top and a brass ball at the bottom. If this tube be exhausted of air, by means of an air pump, a stream of electricity may be made to pass through it from one end to the other. ELECTRICITY. 135 763. How may this be accomplished? By connecting the lower end with the floor and the upper end with the prime conductor of an electrical machine. 764. What is the appearance of the light given out? It plays in soft and flickering streams of varying colors, fromn one end of the tube to the other, and offers a strong resemblance to the fitful gleamings of the Aurora Borealis. 765. Is the light faint in proportion as there is less air left in the tube? It is; when the vacuum is made as perfect as possible, there is still some air left in the tube; but for this there would be no light at all. 766. Is electric light given out only when the electric stream flows through the air. It is also produced when the electric current flows through any gas or vapor, as the vapor of ether, and is of various colors. ATMOSPHERIC ELECTRICITY. 767. How did Franklin establish that lightning and electricity are identically the same? He drew the lightning down from the clouds, by means of a kite, and showed that it would produce the same effects as electricity. 768. Where did Franklin perform this remarkable experiment? At Philadelphia, in the summer of 1752. 136 NATURAL PHILOSOPHY. 769. Was the experiment repeated elsewhere? During the following summer Al. de Romas, of France, raised a kite to the height of 550 feet, into the midst of a thunder-cloud, and obtained at the end of the wire coiled around the string, sheets of fire ten feet in length and an inch in thickness, accompanied with explosions louder than the report of a pistol. 770. What is the usual mode of collecting electricity from the atmosphere for the sake of observation and experiment? By means of an insulated metallic rod terminating in a point directed upward. It is also sometimes collected by means of long insulated wires stretched on the tops of lofty poles. 771. What is the ordinary electric state of the atmosphere? It is charged with more or less of positive electricity; the quantity increases from the surface of the earth upward. 772. What is the electric condition of thunder-eclouds? Sometimes positive and sometimes negative; and the same is true of the air in stormy weather. 773. Do thunder-clonds always discharge to the earth? They do not, but generally from one to another. 774. When lightning strikes near to us, what is the character of the thunder? It is a peculiar rattling, crackling noise, that continues for a short time. 775. Why is the sound prolonged? Because it does not reach the ear from all points of the lightning's path at the same instant. ELECTRICITY. 137 776. What is the original cause of thunder? The sudden violent movement imparted to the air by the lightning in its passage. 777. What is the immediate cause of this movement? The mutual repulsion of the particles electrified by the lightning. 778. What is the explanation of the heavy roll of thunder that often follows the first explosion after a short interval? It is probably occasioned by reverberations of the original sound from the clouds. 779. What are some of the circumstances by which the sound that reaches the ear may be modified? The zigzag or other form of the lightning's path, the number of simultaneous flashes, and the direction pursued by the flash. 7 138 NATrURAL PHILOSOPHY. CHAPTER VII. MAGNETISM. PROPERTIES OF MAGNETS. 780. WHAT is a loadstone? Fig. 182. A piece of iron ore found in the earth, which has the property of attracting iron. 781. Does the loadstone attract a piece of iron with the same force at whatever part of its surface the iron is presented? The attraction is the strongest at two opposite points, called Poles. These are at N. and S. in Fig. 132. 782. In passing from the poles to the middle of the loadstone, how does the attraction vary? It decreases rapidly, and near the middle vanishes altogether. 783. What is supposed to be the cause of this attraction? A subtile fluid within the mass of the loadstone that has in some way been excited into action. 784. What is this fluid, or principle, whatever it may be, called? J/fagnetism; and the loadstone is said to be a Mfagnet. MAGNETISM. 139 785. What is the general opinion of the philosophers of the present day as to the nature of the principle of magnetism? It is believed that magnetism is electricity in a peculiar state of motion. This belief is founded upon the fact that the effects produced by magnetism may be obtained from currents of electricity circulating in wires. 786. What effect has a loadstone or magnet upon a piece Fig. 183. of malleable iron brought into contact with one of its poles, as shown in Fig. 133? It converts it at once into a magnet, as may be shown by applying a key to the other end. 787. Suppose, instead of malleable iron, a piece of hard steel be applied to either pole of a magnet? The steel will also become a magnet, but the full effect will not be produced at once, and will be much less than on the iron. 788. How is it with cast iron? Cast iron resists the magnetizing action of the magnet with about the same force that cast steel does. 789. What will happen if the piece of soft iron be withdrawn from the mnagnet? It will return at once to its former condition. 790. Will the same be true of the piece of steel? It will not, the steel will have become a permanent magnet, like the loadstone. 791. What is such a magnet called? An Artificial M}[agnet. The loadstone is called a Natural.Magnet. 140 NATURAL PHILOSOPHY. 792. Fig. 134 represents an artificial steel magnet-where are Fig. the two poles? 134 At the ends of the magnet. 793. To magnetize a small steel bar completely, what must be done? The bar must be rubbed several times, in the same direction, from end to end, against one of the poles of a strong magnet. 794. If a magnet be suspended at its middle, what position will it take? S It will point north and south. If it should be drawn out of this position, it would immediately return to it again. 795. What name is given to the pole at the north end? It is called the North pole of the magnet, and the other the South pole. 796. How may the unequal distribution of magnetism Fig. 135. over the bar be shown?... By rolling the bar in iron filings; the filings q will adhere in the largest clusters at the ends and along the edges. X 797. Does the attractive power exerted by the pole of a magnet take effect through paper, wood, stone, etc.? It does, but diminishes rapidly as the distance from the pole increases. 798. Illustrate this by stating the result of a simple:, " experiment. If a sheet of paper be inserted between the: pole of a magnet and a piece of iron, the at MAGNETISM. 141 traction is much less than when there is an actual contact. 799. Is the power of a magnet weakened by use? On the contrary, additions may be made from day to day to the weight that it first supports. 800. What inference may be drawn from the fact that the magnet does not lose its virtue? That the piece of iron in contact with the pole does not draw its magnetism from the magnet, but contains the principle of magnetism within itself. 801. What may be inferred from the fact that the magnet is strengthened by use? That the magnetism developed in the contiguous iron reacts on the magnet, and brings into action a new portion of its magnetism. 802. What is the sustaining power of good bar-magnets? Bar-magnets are seldom found capable of supporting more than their own weight of iron. 803. Have small magnets greater proportional power than large ones? They have; a small magnet set in a ring and worn by Sir Isaac Newton, is said to have lifted 250 times its own weight. 804. If a steel wire that has been mag- Fig. 186. ietized is cut into small pieces, what is true IL Si S] snl- sil s of each piece? Each piece is found to have a north pole at one end, 142 NATURAL PHILOSOPHY. and a south pole at the other end; as shown by the letters n and s in Fig. 136. 805. What is inferred from this? That a magnet is made up of lines of particles all of which are little magnets, with the same poles turned the same way. 806. How is this explained? There are supposed to be two magnetic fluids, as there are two electric fluids, and these are combined in each particle. 807. What may be said of this explanation? It is the simplest conception by which the facts can be represented, but is not believed to be a reality. 808. What are the two supposed fluids called? Austral and Boreal. 809. What is supposed to take lFig. 187. place when a bar of iron or steel is NI-M - -(-co- S magnetized? These fluids are separated in each of its particles by the action of the magnet; the austral fluid is made to occupy one half of each particle, and the boreal fluid the other half: 810. We have seen that each pole of a magnet attracts iron or steel-what is the nature of the action of two magnets on each other? The north pole of each magnet attracts the south pole of the other, but repels the north pole; and the south pole of each magnet attracts the north and repels the south pole of the other. MArGNETISM1. 143 811. We have seen that if either pole of a magnet be ap- Fig.138 plied to the end of a small bar of iron, the bar will become a N magnet-which pole will be developed on the end of the bar touched by the magnet? The pole of the opposite name; and if the bar is not too long, the pole of the same name will be developed at the other end; this is illustrated S in Fig. 138. 812. What may be said then of the attraction between a magnet and a piece of iron brought into contact with it? It is really an attraction between the opposite poles of two magnets. 813. What is a Horse Shoe-Magnet? Fig. 139. It is an artificial steel magnet bent into a shape resembling a horse shoe; the poles are at the two ends and are therefore by the side of each other. A piece of soft iron extends across from one pole to the other, and from this weights may be suspended by means of A a hook. 814. What is this piece of iron called? A keeper, or armature. It is so called because by means of it the full power of the magnet may be preserved for any length of time. 815. What may be said of the power of the horse shoe-magnet to support weights? Its sustaining power is much more than double the natural attraction of either pole for a piece of iron. 144 NATURAL PHILOSOPHY. 816. Can a piece of iron or steel be Fig. 140. magnetized in any other way than by - touching it, or rubbing it with a magnet? It can be more effectually magnetized by placing it within a coil of copper wire through which an electric current is made to pass; as shown in Fig. 140. 817. What is an Electro-Magnet? Fig. 141. Fig. 141 represents an electro-magnet; it is a piece of soft iron, generally in the shape of a horse shoe, with a coil i i of copper wire wound around its ends. The iron is temporarily magnetized, by passing through the coil an electric current, from a galvanic battery. 818. How does the power of an electro-magnet compare with that of a permanent horse shoemaanet? It is vastly greater; the largest horse shoe steel magnets support from 50 to 100 lbs.; but large electromagnets may be made to sustain more than a ton. An electro-magnet has in fact been constructed capable of supporting 5,000 pounds weight. TERRESTRIAL MAGNETISM. 819. What is a Magnetic, or Compass Needle? It is a thin magnetized bar of steel, poised on a pivot a iout which it turns freely. MAGNETISM. 145 820. What important fact does it make known, by Fig. 142. 4he position which it takes up and obstinately rerains? It points out, as if by instinct, in what direction North lies. E 821. What is the most important application of the magnetic needle? The Xiiariner's Compass; as a guide to the mariner in steering his course across the trackless ocean. By night and by day, in storms and in calms, the compass needle is ever true to the pole. 822. When was this directive property, as it is called, of the magnetic needle first discovered? It was known to the Chinese a thousand years and more before the commencement of the Christian era. 823. When was the Mariner's Compass first used? The Chinese appear to have steered vessels by the compass early in the Christian era, but it was not known in Europe until about the twelfth century. 824. Who was the first European navigator that is known to have sailed by the compass? Vasco de Gainma, in his first expedition into India. 825. Does the compass needle point due north at all parts of the earth? It deviates, or declines, more or less from the true north at almost every place. 826. In which direction, to the east or to the west of north? At some places to the east and at other places to the west of north. 7 146 NATURAL PHILOSOPHY. 827. On which side of north does the magnetic needle point in the United States? In New England, New York, New Jersey, Pennsylvania, Maryland, Delaware, and the eastern part of Virginia, it points West of north. 828. In all other parts of the United States, even to the Pacific coast, how does it point? To the East of north. 829. Suppose an imaginary line to be traced through a series of places at which the needle points due north, what is such a line called? A Line of no Variation. A line of no variation is represented in Fig. 144, p. 148, proceeding from the magnetic pole and traversing the Western Continent. 830. As a ship sails across the Atlantic, from New York to Liverpool, how does the direction in which the needle points vary? At setting sail it deviates about 7 degrees to the west of north, and afterward continually farther and farther, until, when the ship arrives at the port of Liverpool, it declines no less than 24 degrees to the west of due north. 831. How then does the mariner, when he is out to sea, know where the true north lies? He has the means of ascertaining how far the needle declines from the due north, by making an astronomical observation. 832. In any other way? Also, by consulting a chart on which are recorded the results of previous observations on the direction of the needle. MaGNETISM. 147 833. In what direction does the compass needle point in high northern latitudes? At most localities very much to the west or east of north. 834. In what direction at Barrow's Straits and Melville Island? What we call the north pole of the needle points toward the south. 835. Are the same differences in the position taken up by the compass needle, observed in the Southern as in the Northern Hemisphere? They are, and it is the same pole of the needle that points south in the two hemispheres. 836. If a magnetic needle be freely Fig. 143. suspended by its centre of gravity, so that either end can move up or down, in what position will it settle? In a position such as is represented in Fig. 143, in which the north end dips very much below a horizontal line. 837. What is the amount of the depression or dip of the north end of the needle in these latitudes? About 73 degrees, or nearly three fourths of a right angle. 838. How is the ordinary compass needle brought into a horizontal position? By making the south end heavier than the other. 839. In traveling north does the dip increase or decrease? It increases; and in going south it decreases. 148 NATURAL PHILOSOPHY. 840. Is the dipping needle hor- Fig. 144. izontal in any part of the earth? S _ It is horizontal in the vicin- ity of the equator; all along / a certain line running round - the earth, and lying partly to.the north and partly to the ~ south of the equator. 841. What is this line called? The JAlanetic Equator. 842. Are there any localities on the earth where the dipping needle points directly down? There are four such points; two in the Northern and two in the Southern Hemisphere. 843. What are these points called? The Mfagnetic Poles of the earth. 844. Where are they situated? The strongest of the two north magnetic poles is on the continent of North America, and the other to the north of Siberia. The strongest south magnetic pole is on the Antarctic Continent, to the south of Australia. 845. In what latitude and longitude is the North American pole? It is in longitude 97 degrees, and latitude 70 degrees. 846. Have the magnetic poles actually been reached by any of the Arctic and Antarctic voyagers? The North American pole was reached by Commander Ross, of the English navy, on the 1st of June, 1831. MAGNETISM. 149 847. Is the intensity of the earth's magnetic force everywhere the same? In the northern parts of this continent it is nearly twice as great as in the vicinity of the equator. 848. In what direction does this force act on the magnetic needle? In the direction indicated by the dipping needle; that is, in these latitudes, very much inclined to the horizontal line. 849. How does the earth, as a whole, act on the magnetic needle? As if it contained, within its mass, a great magnet, or rather two great magnets. 850. Where are the poles of these imaginary magnets situated? At a great depth in the earth, and directly below the magnetic poles at the surface. 851. Is it believed that there are actually such magnets embedded in the earth? It is not. 852. Is the real cause of the earth's magnetic action known with certainty? It is not, but it is supposed to be due to the perpetual circulation of electric currents around the earth. 853. Is the magnetic action of the earth on the needle exerted from year to year, in exactly the same direction, and with the same intensity? It is not; the compass-needle turns slowly either toward the west or toward the east, from one year to another. 854. In what direction is the north end of the needle slowly turning in New England and the Middle States? Toward the west; it has been moving in that direction 150 NATURAL PHILOSOPHY. since about the year 1815. During the eighteenth century its motion was eastward. 855. What is the direction of the annual movement of the needle in Western Europe? Toward the east; the slow movement in that direction began about the year 1815. 856. In London the compass-needle now points 22 degrees west of north —did it ever point due north there? It did, about the year 1660. 857. Is this steady movement of the magnetic needle from year to year the only motion that it has? It is not; it oscillates to and fro, very slightly, during each year, and also every day. 858. What other movements has it? Irregular movements that occur at any hour, and can not, like the others, be foreseen. 859. What especial arrangements have been adopted for observing these movements? fagnetic Observatories have been erected in all parts of the earth, and fitted up with long magnetic bars, delicately suspended, and all the appliances required for the nicest observations. 860. What are some of the remarkable results that have been obtained from the observations made in these observatories, upon the disturbances of the magnetic needle? Most of the large irregular disturbances occur at about the same instant over the extent of a whole continent. 861. Illustrate by examples. The needle begins to move at the same instant at MAGNETISM. 151 Philadelphia as at Toronto in Upper Canada; at the same instant at Paris as at St. Petersburg. 862. What other important result has been obtained? It has been discovered that there are occasional periods of many hours' duration, in which remarkable disturbances occur. These are called iMagnetic Storms. 863. To what are the regular and irregular movements of the magnetic needle for the most part traceable? To some influence of the sun. 864. What remarkable evidence of the sun's disturbing action has recently been obtained? It is found that the disturbances of the needle are uniformly the greatest and most frequent in those years in which the spots are largest and most numerous on the sun's surface. 865. What does this curious fact show? That a magnetic needle, on the earth, trembles in sympathy with the commotions that occur on the sun's surface. 866. It is observed that the shooting beams, or Streamers, of the Aurora Borealis have a position corresponding to that of the dipping needle; does the needle appear to have any magnetic sympathy with the fitful changes and beautiful coruscations of an aurora? An auroral display is generally attended with capricious movements of the magnetic needle. Sometimes the same aurora seems to affect all the magnetic needles both of the Western and Eastern continents. 152 NATURAL PHILOSOPHY. DIA-MAGNETISM. 867. Are there any other substances, besides iron, that are attracted by a magnet? There are-the two metals nickel and cobalt are quite strongly attracted; and many other substances are feebly attracted by a powerful magnet. 868. What remarkable discovery, in reference to the magnetic condition of substances, has recently been made by the celebrated English philosopher, Dr. Faraday? He has discovered a large class of substances that are repelled by both poles of a powerful electro-magnet. These he calls _Dia-llagnetic substances. 869. Mention some of them. The metals bismuth, antimony, zinc, and tin, flint glass, India rubber, alcohol, water, and most vegetables are dia-magnetic. If brought near a powerful magnet they would be repelled from it. 870. What is the magnetic condition of our bodies? The substance of our bodies is dia-magnetic; and Faraday observes that if a man were suspended over the poles of a sufficiently powerful electro-magnet, he would be repelled and lie crosswise to the line of the poles 871. In view of the recent magnetic discoveries made by Faraday and others, what important general conclusion do we arrive at? That the principle of magnetism is not confined to a few substances; but is associated, in one or the other of its two forms, with all matter. THEORETICAL ASTRONOMY. 153 CHAPTER VIII. THEORETICAL ASTRONO M Y. FIGURE OF THE EARTH. 872. WHAT is the form of the earth? The earth is round, or globular, in its form, and isolated in space. 873. What evidence have we that the earth is rund? Navigators have sailed around it and returned to the port from which they set out. 874. Mention a familiar fact that proves the earth to be round. If from a point on the coast we watch a ship that is putting out to sea, we first lose sight of the hull, then of the lower parts of the sails, and finally of the topsail. 875. How is Fig. 145. this a proof of the roundness of the - earth? A person at A, in the figure, could not see any thing that is below the line C C, and as the ship sails on, the hull would first pass below this line, then the lower parts of the sails, and lastly the topsail. 7* 154 ASTRONOMY. 876. This proves that the sea is round-is it known that the land is not much elevated above the general level of the sea? It is; the highest mountains are five miles high, but they are very small in comparison with the vast size of the earth. They are like grains of sand on the surface of an ordinary terrestrial globe. 877. What is meant by the general level of the sea? The surface of the sea supposed to be continued on under the land, so as to form a continuous round surface. 878. What is the size of the earth? It is 4,000 miles from the surface of the earth to the center, and 8,000 miles through to the opposite side. 879. How long would it take a man to walk round the earth, if it vxwas land all the way, and he walked 10 hours every day, at the rate of 3 miles per hour? Two years, three months, and eight days. 880. In a level country, or at sea, we seem to be at the centre of a large circle that surrounds us, and beyond which we can not see — what is this circle that limits our vision called? The visible Aorizon. What we see of the earth's surface lies within this circle. 881. Why does the visible part of the earth appear to be flat? Because the earth is so large and we see so small a portion of it at a time. 882. As we travel over the earth, does the visible horizon change? It does; it travels along with us. THEORETICAL ASTRONOMY. 155 883. What is the point directly overhead called? The zenith. 884. Does this move with us also? It does. 885. Where is the zenith of a person Fig. 146. standing at A (Fig. 146)? z At Z. 886. Where, of the station B? At X. 887. Where, of the stations C and D? At N and Y. 888. What is the relative situation of the zeniths of people living on opposite sides of the earth, and said to be antipodes to each other? Their zeniths lie in opposite directions from the centre of the earth. 889. What is uyp and what is down? At any station up is from the centre of the earth, and down is toward it. 890. Is down the same direction at two stations on opposite sides of the earth —A and C, for example? It is not; the same direction that is down at A is up at C. 891. When bodies fall at the two opposite stations A and C, do they move in the same direction? They move toward the centre of the earth at both places, and thus in opposite directions. 156 ASTRONOMY. 892. Why do bodies everywhere fall toward the earth's centre? Because they are attracted by the earth. 893. What did the ancients, in their ignorance of these facts, imagine? That the earth must be supported in some way from below, otherwise it would fall into the bottomless abyss. THE SKY. 894. As we look away from the earth in clear weather, what do we see? The Sky. 895. What appearance does the sky present? It appears like a blue canopy spread over our heads, and resting on the earth at the horizon. 896. What is it in fact? Fig. 147. The earth's atmosphere, which is of a blue color when seen in the mass. 897. What evidence have we that the color of the air, when seen in large masses; is blue? Distant mountains, seen through a large body of air, have a blue tint. 898. How is the appearance of solidity which the skl presents, to be explained? It is an illusion. We actually look through the atmosphere into the depths of space, as through a filmy lJue veil spread over the earth. THEORETICAL ASTRONOMY. 157 899. To what height does the atmosphere extend? To the height of about 50 miles. THE HEAVENS AND THE HEAVENLY BODIES. 900. What is the space outside of the earth and its atmosphere, and extending to an indefinite distance, called? The Heaven, or Heavens. 901. What have you to say of it? That there is a host of shining bodies dispersed through it, which are called -Heavenly Bodies. 902. How are the heavenly bodies classified? They are divided into the Sun, the loon, and the Stars. 903. When the sun is above the horizon we say it is day, and when he is below the horizon we say it is night-what is the explanation of the constant succession of day and night? The sun appears to move in a circle around the earth, and goes all the way round in a day and a night. 904. How does it move during the day? It rises in the east, moves across the sky, and sets in the west. 905. Is the sun really in motion, as it appears to be? It is not; it is stationary in space. 906. What, then, is the true explanation of the succession of night and day? The earth turns about an axis, like a spinning top, and completes a rotation in a day and a night. During 158 ASTRONOMY. the day, the side of the earth on which we are is turned toward the sun, and during the night it is turned away from him. 907. Explain Fig. 148. Fig. 148. N S is the earth's axis, N the north pole, S the south pole, and eq the equator. The arrow shows the direction of the earth's rotation. N N 908. In Fig. 149, in what direction is the ob- F server on the earth supposed to be looking? Toward the south, with the east Fig. 149. on his left and the west on his ~F right. 909. How may the explanation of the succession of day and night be illustrated experimentally? By taking an apple to represent /\ the earth, sticking a bit of paper or wafer on it, to show our position, and turning the apple round by the stem, while it is held before a candle. 910. Does the earth's rotation carry us along in the same direction that the sun appears to move? It does not, but in the opposite direction, or toward the east. 911. What have you to say of the apparent daily revolution of the sun around the earth? It is a mere illusion, produced by the earth's rotation. THEORETICAL ASTRONOMY. 159 912. Show, by Fig. 150, that the ro- Fig. 15. tation of the earth from west to east, q would produce an apparent daily revolution of the sun in the opposite direction. /1 Eion. ~ SunriseA E A W represents the hori- zon at A; E is east and W is west. As the earth turns round, from west to east, the horizon is carried along with it, and goes down at E and rises at WV. 913. What would happen, then, if the sun were at E? The horizon would pass below it, and as we would be unconscious of the earth's motion, the sun would seem to us to come above the apparently stationary horizon, or rise. 914. How would it appear to move after that? It would continue on toward the east, and arrive at Q at the hour of noon. 915. In twelve hours from sunrise how far will the earth's rotation have carried us? Around to B, and the sun will be setting at W., on the left of the figure. We conceive the earth to have been stationary all the while, and the sun appears to us to have passed over, in the sky, from E to W, on the right. 916. If the earth turns round, what is the reason that we are unconscious of the fact? Because we partake of its motion, and can neither see nor feel it move. 160 ASTRONOMY. 917. When is the moon seen? It shines distinctly only at night, but it may sometimes be seen in the sky during the day. 918. Does it appear to rise in the east, move across the sky, and set in the west like the sun? It does, and for the same reason. 919. When are the stars seen? At night only. The stars are not seen by day because the air above us is illuminated by the sun, and the strong light reflected from it effaces the light of the stars. 920. Why do not the stars shine out at once as Fig. 151. soon as the sun has set, instead of coming out one by one? Because the sun still continues to shine upon the upper air; just as his rays linger on the top of a lofty mountain for some time after Nish he has set to the level country below. 921. Where is this Fig. 152. fact made apparent to.. the eye? InFig. 152. The. sun is below the western horizon. The portion of the atmosphere above the horizon, E W, that is not shaded, is still illuminated by the sun, and forms a veil of brightness through which the stars can not be seen. 922. What is the light called, that we thus continue to receive, by reflection from the atmosphere, for an hour or more after sunset? Twilight. THEORETICAL ASTRONOMY. 161 923. What is the reason that it fades by slow degrees in the sky, until finally the stars shine out over the western horizon, and all traces of it have disappeared? Because as the sun descends farther and farther below the horizon, the portion of the atmosphere that continues to receive light from him gradually becomes less and less. 924. Is there a gradual transition from night to day, before sunrise; or a morning as well as an evening twilight? There is, and for a similar reason. 925. How are the stars affected by it? They fade gradually, as the light increases in the sky, and disappear one after another according to their brightness. 926. Have the stars ever been seen during the day? The brighter stars have been seen at the time of a total eclipse of the sun, when the sky has thus become dark during the day. They can also be seen, on any clear day, through a telescope. 927. Do the stars rise and set, and apparently move around the earth, like the sun and moon? They do; the rotation of the earth makes all the heavenly bodies appear to move in this manner. 928. Illustrate by Fig. 150 (p. 159). When the rotation of the earth bears us around beyond the position B, shown in the figure, the horizon will have a position such as is shown by the dotted line, and its continued motion will make the stars appear to rise at e, and set at w. 8 162 ASTRONOMY. 929. Do all the stars appear to rise and set every twenty-four hours? The stars that are far to the north, remain constantly above the horizon, and do not rise and set. 930. How do they appear to move? In circles around a fixed point in the northern heavens, called the Xorth Pole of the heavens. 931. In what direction do they revolve around the pole? In a direction contrary to the motion of the hands of a watch. 932. Explain Fig. 153. Fig. 153. It represents some of the stars of the Crown northern heavens. P is A the pole, and the stars 7 4 ea X move around this point / in the direction shown W a9.,o~er (m \p.-t' },onsead by the arrows. IW N crella /e E is the circle of the \ horizon. \ f in 933. Is the place of the w \ /* E stationary pole in the heavens occupied by a star? There is a bright star near the pole, and for this reason called the Pole Star. 934. MWhat is the situation of the elevated pole in the heavens with respect to the north pole of, the earth? It is directly over it, as shown in Fig. 154, where nl is THEORETICAL ASTRONOMY. 163 the north pole of the earth, Fig. 154. and P the pole of the Z heavens. 935. On what line, then, is the elevated pole of the heav- ens situated? / It lies on the earth's a axis prolonged upward. 936. What general apparent movement of the sphere of the heavens is produced by the rotation of the earth? In consequence of the earth's rotation about an axis, the whole heavens appear to rotate about the same line in the contrary direction. 937. How many degrees are there in the distance from the elevated pole down to the northern horizon; that is, from P to N, in Fig. 154? The same number of degrees that there are in the latitude of the place. 938. What is the imaginary circle that passes through the pole and the zenith called? The 3Meridiamr of the place. It is represented by N P Z Q, in Fig. 154. 939. Where does the equator in the heavens cross the meridian? To the south of the zenith, a distance equal to the latitude of the place. 940. Illustrate by Fig. 154. The equator crosses the meridian at Q, in the figure; and there are as many degrees from Z to Q as from A to q on the earth. 164 ASTRONOMY. 941. How are the stars classified? There are two classes of stars, called, respectively, Fixed Stars and Planets. 942. What are fixed stars? The greater number of stars preserve constantly the same positions in space, and are called fixed stars. 943. How have they been arranged by ancient and modern astronomers? Into groups called Constellations. 944. What stars are represented in Fig. 153? The principal stars of several of the northern constellations. 945. Mention the names of the constellations shown in the figure. Great Bear, Little Bear, Cassiopeia, Swan, Lyra, Dragon's HIead, Northern Crown, Wagoner. 946. What name is given to the two stars of the Great Bear farthest from the tail? They are often called Pointers, because the line of these stars points to the pole star. 947. What are planets? Stars which are not stationary in the heavens, but wander from one constellation to another. 948. How many planets are there? There are seven principal planets, andforty-seven smaller and less noticeable ones, called Asteroids. 949. Mention the names of the principal planets. Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune THEORETICAL ASTRONOMY. 165 950. Are they all visible to the naked eye? All, with the exception of Uranus and INeptune. 951 Which are the brightest and most conspicuous? Venus and Jupiter. These two planets are generally more brilliant than any of the fixed stars. 952. Describe Mars and Saturn. AMars is a bright planet of a reddish color. Saturn shines with a pale dull light. 953. Do the planets wander on from one constellation to another, until they have made the circuit of the heavens? They do; but they are occasionally seen stealing backward. 954. Do they actually revolve around the earth in space? They do not; they all wheel in circles around the s-In. 955. What heavenly body performs its circuit around the earth? The moon. It passes entirely around the earth in 27days. 956. In what direction does the moon move among the stars in the heavens? From west to east. 957. Is the sun apparently stationary in the heavens? It is not; it appears to revolve around the earth in the same direction that the moon does. 958. Does the sun actually revolve around the earth? On the contrary, it is the earth that revolves around the sun. 166 ASTRONOMY. 959. What makes the sun appear Fig. 155. to go around the earth? The revolution of the earth u around the sun. 960. Explain by means of Fig. 15 5.l I) If the earth moves forward A X from A to B, the sun will appear to move from s to u in the heavens. "C 961. What effect has the sun's apparent motion upon the hours of rising and setting of the stars? It causes them to rise and set earlier every day than on the preceding day. 962. Will the same constellations, then, be seen in the same quarter of the heavens, every evening in the year? They will not. At opposite seasons of the year, the same constellations will have opposite positions; so that, with the exception of the northern constellations, which never set, the constellations visible at the same hour in the evening will generally be different. 963. What is the Zodiac? It is a narrow belt of the starry heavens within which the sun and moon and most of the planets pursue their apparent circuits around the earth. 964. What does Fig. 156 represent? The celestial girdle of the zodiac jeweled with stars. 965. How is it divided? Into twelve equal portions, called the Signs of the Zodiac. TIHEORETICAL ASTRONOMY. 167 966. Mention the names of Fig. 156. these signs. Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricornus, / m Aquarius, Pisces. (!| 967. On what day of the year l;\ ( does the sun enter the sign Aries? On the 21st of MSarch, the ~ day of the vernal equinox. 968. What names have been given to the constellations that lie within the limits of the zodiac? The same that have been given to the signs of the zodiac. 969. Do the constellations of the zodiac occupy the same place with the signs of the same names? They did in very ancient times; but the signs have since moved backward in the heavens so far, that the sign Aries now nearly corresponds with the constellation Pisces. THE SOLAR SYSTEM. 970. When we are traveling on a railroad, we notice that trees and other objects near by are constantly shifting their appareat relative positions. In the same way, as the earth proceeds on its course around the sun, our point of view in reference to the heavenly bodies is constantly changingll do the fixed stars appear to change their relative positions on* this account? They do not; the constellations constantly present the 168 ASTRONOMY. same appearance, from whatever position of the earth in its orbit they are viewed. 971. What may we infer from this remarkable fact? That the whole extent of the earth's orbit is but a mere point in comparison to the vast expanse of space that separates it from the stars. 972. Of what heavenly bodies does the Solar System consist? The solar system consists of the sun and the bodies that revolve around the sun. 973. What bodies revolve around the sun? The earth, with the moon circulating around it, and the planets. 974. Are any of the planets attended by revolving bodies, as the earth is by the moon? Jupiter, Saturn, Uranus, and Neptune have such attendants, or Satellites, as they are called. 975. Are there any other bodies belonging to the solar system? There is another class of bodies that move around the sun, called Comets, or hairy stars, from their peculiar appearance. These are only seen occasionally. 976. Mention the principal planets (Including the Earth) in the order of their distance from the sun. Mercury, Venus, the Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. 977. Between what two planets do the forty-seven asteroids revolve? Between MIars and Jupiter. 978. What does Fig. 157 show? The circular paths or orbits of the principal planets, and also the revolution of the moon and the other satellites. THEORETICAL ASTRONOMY. 169 Fig. 157. 979. In what direction do the planets and satellites revolve? In a direction contrary to the motion of the hands of a watch, as the arrows show. 980. Is there any exception to this general rule? The satellites of Uranus furnish one exception. These all revolve in the same direction that the hands of a watch turn. 981. In what direction do the earth and planets turn about their axes? In the same direction that they revolve around the sun. 170 ASTRONOMY. 982. Who first advocated the doctrine that the earth revolves around the sun in company with all the planets, and that the earth turns about an axis? The celebrated astronomer Copernicus, who lived 300 years ago. 983. What force is it that constrains the earth and the planets to follow a circular path around the sun? The attractive force of the sun. 984. How does this force operate? It draws the planet incessantly out of the straight course it would otherwise pursue, into a circle. 985. What force maintains the moon in its orbit around the earth? The attraction of the earth for the moon. 986. Who first discovered the existence of this force operating throughout the solar system, and binding all its parts together? Sir Isaac Newton made this wonderful discovery in the year 1683. 987. What is this force called? Universal Gravitation. 988. Where do the fixed stars lie in space? They are dispersed in every direction around the solar system, but at such enormous distances from it, that the whole solar system dwindles into insignificance in comparison. 989. What is an astronomical observatory? It is a building of a peculiar construction, fitted up with telescopes for observing the heavenly bodies, and with various instruments for ascertaining their directions, and following them in their motions. THEORETICAL ASTRONOMY. 171 990. To what other purposes are astronomical instruments applied? The astronomer, also, from his observatory, sounds the depths of the starry heavens, measures the distance and size of the sun and of the planetary worlds that circle around him, and weighs them, as it were, in a celestial balance. DIMENSIONS OF THE SOLA.R SYSTEM. 991. Are the sun, moon, and planets all round bodies, like the earth? They are, but of various sizes. 992. Are the moon and planets self-luminous bodies? The moon and all the planets are opake, non-luminous bodies, and shine by reflecting the light they receive from the sun. 993. If a globe two feet in diameter be taken to represent the sun, how large a ball would represent the earth, on the same scale? A ball the size of a pea, or less than one quarter of an inch in diameter. 994. How many feet would represent the distance of the earth from the sun? Two hundred and fourteen feet? 995. How many inches the distance of the moon from the earth? Six and a half inches. 996. What would be the distance of Mercury and Venus from the sun, on the same scale? Mercury would be 82 feet distant, and Venus 155 feet. 172 ASTRONOMY. 997. How would the distances of Mars, Fig. 158. NELPTIN[ Jupiter, Saturn, Uranus, and Neptune be rep- N [ resented? The distance of Mars by 327 feet; of Jupiter by less than a quarter of a mile; of Saturn by less than half a mile; of Uranus by three-quarters of a mile; of Neptune by a mile and a quarter. 998. What does Fig. 158 represent? The comparative distances of the URMuS planets from the sun. 999. Mention the periods of revolution of the principal planets. Mercury completes a revolution around the sun in 3 months; Venus in 7- months; the Earth in 3635 days, or one year; Mars in a little less than two years; Jupiter in about 12 years; SATURN Saturn in 29k years; Uranus in 84 _ _. years; and Neptune in 164} years. 1000. How many generations of men succeed each other on the earth while Neptune is ac- JUelTR complishing his annual circuit around the sun? Five. 1001. Mention the planets in the order of their magnitude, beginning with the largest. l Jupiter, Saturn, Uranus,;Neptune, the Earth, Venus, Mars, Mercury. THEORETICAL ASTRONOMY. 173 1002. If the sun be represented by a globe two' feet in diameter, what familiar object would serve to show the comparative size of Jupiter? A moderate-sized orange. 1003.'How might the other planets be represented in their comparative magnitudes? Saturn by a small orange; Uranus and Neptune by good-sized cherries; the Earth and Venus by peas; Mars by a rather large pin's head; and Mercury by a grain of mustard seed. 1004. Do the planets turn upon axes, like the earth? The planets rotate, like the earth, in the same direction that they revolve around the sun. 1005. What is the direction of their motion of rotation, as seen by. an observer looking down upon the north pole of the planet? Contrary to the direction in which the hands of a watch turn. 1006. In what periods of time do they complete a rotation? Mercury, Venus, and Mars, in about 24 hours. Jupiter and Saturn, in about 10 hours. 1007. How much less light and heat does Neptune receive from the sun than the Earth does? Nine hundred times less. 1008. How does the sun's light on the surface of this remote planet compare with the light we receive from the full moon? The sun gives as much light to Neptune as 330 full moons would shed upon the Earth. 1009. How much light and heat is bestowed upon Mercury? Six and a half times as much as the Earth receives. 174 ASTRONOMY. 1010. Have we good reason to suppose that the planets are habitable globes like the earth, and are in fact inhabited by rational beings? We have; they would seem to be fitted to be the abodes of living and rational beings by the same beneficent provisions by which life is maintained and gladdened on the earth. 1011. What are some of these provisions? The sun shines for the planets, as for the earth; day and night succeed each other on their surfaces; and each revolving year the seasons come and go with all their genial variety, as upon the earth. Most if not all of the planets are provided with atmospheres, and many of them are attended by circling moons to give light to them by night. DESCRIPTIVE ASTRONOMY. 175 CHAPTER IX. DESCRIPTIVE ASTRONOMY. TIHE SUN. 1012. WHAT is the part performed by the sun in the solar system? The sun maintains the planets in their orbits by his powerful attraction, and dispenses to all of them the genial influences of light and heat. 1013. What is the size of the sun? It is nearly a million and a half times larger than the earth. The diameter of the sun is 112 times greater than the diameter of the earth, or 888,000 miles. 1014. If the centre of the sun were placed at the centre of the earth, how far would its enormous bulk extend? To nearly twice the distance of the moon. 1015. What do astronomers, on viewing the sun through a telescope, often discern on his disc? Dark spots of various sizes and forms. 1016. What appearance do these spots generally present? A black spot is seen surrounded by a dark border; sometimes the same border incloses a number of black spots. 1T6 ASTRONOMY. 1017. Are Fig. 159. they seen usually as single detached spots % They generally appear in clusters, composed of various numbers, from two to a hundred. 1018. Are spots seen on the sun's disc every year? In some years they are very numerous; in others few, if any, are seen. 1019. What general rule may be stated about their appearance? They occur in greater numbers, and of a larger size, at regular intervals of ten or eleven years. 1020. What is the actual size of the largest spots that have been observed? Spots have been seen that were two or three times as large as the entire surface of the earth. 1021. What is the size of the smallest spot that can be discerned on the surface of the sun with a good telescope? An area about 450 miles in length and breadth, or somewhat larger than the State of New York. 1022. Is the sun a world on fire? It is not; it is a dark, solid body, like the earth, surrounded by a luminous atmosphere. 1023. From what are the light and heat of the sun supposed to proceed? From self-luminous clouds in the sun's atmosphere, several thousand miles above the solid body of the sun. DESCRIPTIVE ASTRONOMY. 177 1024. Do we ever see self-luminous clouds in the earth's atmosphere? The auroral clouds that now and then, in the evening, light up our northern sky, are self-luminous, like the supposed solar clouds. 1025. What is the explanatiou of the sun's spots? They are supposed to be the dark body of the sun, seen through rents made in its luminous envelope. 1026. Has the sun a motion of rotation about an axis, like the earth? It has, and completes a rotation in 251 days. 1027. How does the mass of the sun compare with the united mass of the planets? The huge globe of the sun contains more than 700 times as much matter as all the planets united. THE EARTH. 1028. What is the velocity of the earth in its annual circuit around the sun? Nineteen miles per second. 1029. How much faster does the earth speed on its course than a cannon ball flies through the air? Fifty times faster. 1030. What is the rate of rotation of a point on the earth's equator? 1,520 feet per second, or a little over 1,000 miles per hour. 8* 178 ASTRONOMY. 1031. What is the rate at which points on the earth's surface are carried toward the east, by the earth's rotation, at the latitude of 400? Not quite 800 miles per hour, and it is still less farther to the north. 1032. We have seen that light would pass round the earth eight times in a second-in what length of time does a ray of light come from the sun to the earth? In 8 minutes and 18 seconds. In this interval of time it passes over 95,000,000 of miles. 1033. What is the reason that the days are longer in the summer than in the winter, and that the nights are shorter? Because in the summer the north pole of the earth is turned toward the sun, and in the winter is turned away from him. This is illustrated in Fig. 160. Fig. 160., a rch j 21. Janne 2st o K lecn. Sept. 25ra S 1034. What does the figure show? That in June the sun shines beyond the north pole, and upon more than half of the northern hemisphere; and that DESCRIPTIVE ASTRONTOMY. 179 in December the light of the sun does not reach the north pole, and falls upon less than half of the northern hemisphere. 1035. How does the annual change in the length of the days result from these facts? The figure shows that as the earth turns round, we remain, in the summer, longer in the light than in the dark; and that in the winter it is the reverse of this. 1036. When are the days the longest and the nights the shortest? About the 21st of June. 1037. When are the days the shortest and the nights the longest? About the 22d of December. 1038. Is the longest day of the same length all over the earth? It increases in length from the equator to the pole. 1039. Are the days of unequal length at the equator'? At the equator the day is always 12 hours long, and the night is of the same length. 1040. What is the length of the longest day, as well as the longest night, at the polar circle? Twenty-four hours. 1041. What is its length in latitude 74 degrees? Three months. 1042. How many days and nights are there in the year, at the pole? The year is there divided into one day and one night; each of six months' duration. 180 ASTRONOMY. 1043. How long does the twilight that precedes and follows the polar day of six months last? About a month and a half. 1044. Do the rernaining three months of the polar night form a period of complete darkness? They do not; the moon is above the horizon during one half of this interval, and darkness is often dispelled from the polar sky by the Northern Lights. 1045. What is the apparent motion of the sun in the course of 24 hours, as seen from the pole? His round orb skirts along the circle of the horizon, and accomplishes its entire circuit every 24 hours. 1046. At what periods in the year are the days and nights of equal length, at all parts of the earth? About the 21st of March and 23d of September. 1047. What are these periods called? The Equinoxes. 1048. What is the position of the sun with respect to the poles of the earth on these days? The sun shines directly down upon the equator, and illuminates both poles alike. The positions of the earth at the two equinoxes are shown in Fig. 160. 1049. What is the explanation of the annual change of seasons? The change of seasons is another consequence of the varying position of the poles. 1050. How does that appear? When the north pole of the earth is turned, in the summer months, toward. the sun, not only are the days DESCRIPTIVE ASTRONOMY. 181 longer, but the sun shines down more directly upon the northern hemisphere. 1051. What is Fig. 161 designed to Fig. 161. show' That, at noon, a smaller number of solar rays fall upon any given space on the earth's surface in winter than in summer. 1052. What consequence follows from the two facts just mentioned? The northern hemisphere receives, from these two causes combined, more heat from the sun in the summer than in the winter months. 1053. What is the simple provision by which the beneficent Creator has secured to us the pleasing succession of seasons) and the varying length of days and nights? By inclining the earth's axis, so that it should not be perpendicular to the plane in which the earth moves around the sun. 1054. It has been said that the earth has a globular form —is the the figure of the earth that of an exact sphere? The earth is not a perfect sphere; it is really somewhat flattened at its poles. 1055. To what extent is it flattened? So that the poles are 13 miles nearer the centre of the earth than the equator is. 1056. Is the earth's orbit an exact circle? Strictly speaking, it is slightly oval in its form. 182 ASTRONOMY. 1057. What consequence follows from this? That the earth is a little nearer to the sun in our winter than in the summer. 1058. How much nearer is it on the 1st of January than on the 1st of July? About -3 nearer. 1059. Do the orbits of the planets and the orbit of the moon deviate in their form from true circles? They have the same slightly oval form as the orbit of the earth. 1060. Who first discovered the elliptical form of the planetary orbits? Kepler, a German astronomer, immortalized his name by this and other kindred discoveries, made early in the seventeenth century. 1061. What is the phenomenon known by the name of the Tides? A rise and fall of the surface of the ocean twice in the course of a lunar day, or about 25 hours. 1062. What is the rise of the water called?'lood Tide; and the fall is called Ebb Tide. 1063. What is the interval between one high tide and the next? The average interval is 12- hours. 1064. What is the interval between high tide and low tide? About six hours. 1065. How much later does high tide occur each day than on the preceding day? About 50 minutes later, on the average. DESCRIPTIVE ASTRONOMY. 183 1066. What is the cause of the tides? The tides are produced by the attractive action of the sun and moon upon the waters of the ocean; chiefly by the attraction of the moon. 1067. What fact indicates that the attraction of the moon is the efficient cause by which the tides are produced? It is observed that the time of high water depends upon the position of the moon, and at any given place is always about the same length of time after the moon's passage over the meridian. 1068. Does the moon draw up the waters of the sea by the direct exertion of its whole attractive force? It does not; but by acting unequally on different portions of the sea. 1069. What is the direct result of this unequal action? The waters under the moon are made lighter and those in the distance are made heavier. 1070. What happens in consequence? The surface of the ocean falls where the waters are made heavier, and rises where they are made lighter. 1071. What fact shows that the sun has some effect in producing the tides? The fact that the tides are highest about the times of new and full moon, and lowest at the first and last quarters. 1072. Why should this be the case if the sun acts in connection with the moon to raise the tides? Because at new and full moon the two bodies would 184 ASTRONOMY. tend to produce the same effect, and at the first and last quarters would be opposed to each other. 1073. What are the tides that occur about new and full -moon called? Spriqg Tides; and those which occur at the first and last quarters of the moon are called Neap Tides. 1074. How much higher are the spring tides than the neap tides at New York? Two feet. 1075. Why are there no tides on the large Western lakes? Because those bodies of water are not so large that the moon acts unequally upon their different parts. 1076. How do the actual tides of the Atlantic and Pacific oceans compare with the tides that would be produced if the earth were covered entirely with water? They are very different; the tides are very much modified by the continents. 1077. At what locality on the Atlantic coast of this continent do the highest tides occur? At the head of the Bay of Fundy. 1078. How high does the spring tide rise in the Bay of Fundy? To the height of 60 or 70 feet. 1079. What is the average height of the tides at Boston harbor? Tell feet. 1080. What is it in the harbor of New York? Four feet and one third. 1081. Do the day and night tides rise to the same height? They do very nearly on the Atlantic coast of the DESCRIPTIVE ASTRONOMY. 185 United States, but on the Pacific coast, as a general rule, there is one large and one small tide each day. 1082. What remarkable peculiarity do the tides in the Gulf of Mexico present? On the northern shore of the Gulf of Mexico, from Florida to Texas, there is but one high and one low tide each day. 1083. What is the height of this single-day tide? About one foot. 1084. In what direction does the great tidal wave of the Atlantic Ocean approach the eastern coast of the United States? Nearly at right angles to the general direction of the coast. In like manner the tidal wave of the Pacific Ocean, as it approaches the western coast, is nearly parallel to its general direction. THE MOON. 1085. How does the earth compare with the moon in size? It would take 50 moons to make a world as large as the earth. 1086. How much smaller is the surface of the moon than the surface of the earth? Thirteen times smaller. 1087. Does the moon turn upon an axis, like the earth? It does; and at the same rate that it revolves around the earth. 9 186 ASTRONOMY. 1088. What is the consequence? The same half of the moon is turned all the while toward the earth, and therefore we never see the other half. 1089. How can this be illustrated? By taking an apple in the hand, and walking in a circle around a candle, and at the same time turning the apple, so as to keep the same side always toward the candle. 1090. How long is the solar day on the surface of the moon? A day, on the moon's surface, contains 29- of our days. 1091. Has the moon an atmosphere? It has not; at least it is known that its surface is as free from air as any vacuum we can obtain with an air pump. 1092. Are there any seas or other bodies of water on the moon's surface? There are none on this side of the moon, and it is highly probable that there are none on the other side. 1093. From what may we draw this inference? From the fact that the face of the moon is never covered with mists or clouds. 1094. Does the surface of the moon resemble the surface of the earth? It is diversified by mountains, valleys, and plains, like the earth's surface, but is more rugged and mountainous. DESCRIPTIVE ASTRONOMY. 187 1095. What are the large, dark spots that we see on the moon's disc? The more level parts of the surface. 1096. What were these spots formerly supposed to be? It was once supposed that the dark spots were seas, and they were named accordingly; but it is now known that they are covered with hills, and empty hollows; and therefore can not be bodies of water. 1097. What are the brighter portions of the moon's face? The mountainous regions; these shine in the light of the sun with a silvery lustre. 1098. Do the mountains form distinct ranges on the moon, as on the earth? There are long ranges of lunar mountains; but this is not the prevailing feature. 1099. What is the prevailing feature? Cir'cular rnountainformations; that is, walls, or ranges of mountains, encircling a plain. 1100. Is the inclosed plain on a level with the general surface of the moon? It is generally sunk much below it, forming vast caverns or craters. 1101. What is the depth of these sunken plains? In some instances they are three and a half miles deep. 1102. How have these remarkable facts with regard to the moon been ascertained? Astronomers have made these discoveries by the aid of large telescopes, and other instruments. 188 ASTRONOMY. 1103. What Fig. 162. does Fig. 162 repThe appear- _ 1,, lll: ( ance of the., —-,, "_._.., crescent moon. I,,....L m oon II~8. ~:~FiI,_ as seen through /'> -.... a telescope. _ —. 1104. What _' makes the lower edge so irregular? The sun is just rising along this edge, and the moon's surface is very much broken up into mountains and depressions. 1105. What are the bright spots and lines on the dark part of the moon's face, near this edge? They are the tops of mountains and mountain ranges, illuminated by the rising sun, while the valleys and plains below are still in darkness. 1106. What are the dark spots on the bright face? The shadows of mountains, and deep. craters into which the light of the sun does not penetrate. 1107.. What is the greatest height of the lunar mountains'? Nearly five miles. 1108. Mention a curious fact with regard to certain mountains in the polar regions of the moon's surface. At the poles of the moon there are mountains upon whose lofty summits the sun never sets. It may be truly said that eternal sunshine rests upon their heads. DESCRIPTIVE ASTRONOIMY. 189 1109. We sometimes see the moon as a crescent, sometimes as a half circle, and sometimes as a full circle-what are these different* appearances which the moon presents called? The moon's Phases. 1110. In what length of time does the moon pass through all its phases? Its disc increases from a slender crescent to a full circle in about a fortnight, and then wanes to a small crescent again in another fortnight. 1111. What is the reason of these changes? That half of the moon which is turned toward the sun is illuminated by the sun, while the other half is in the dark, and invisible. 1112. Explain further. We see more of the luminous half in some positions than in others. When the moon is directly between us and the suln, we do not see any of it; when she is a little beyond that position, a small portion of the luminous face comes into view, and has the appearance of a narrow crescent. 1113. She now begins to fill her horns with light. As she revolves beyond this position, what happens? We see more and more of the luminous face, and the disc gradually enlarges to a half circle, and afterward to a full circle. 1114. What does Fig. 163 show? Various positions of the moon in the orbit she describes around the earth, and the corresponding phases. The sun is supposed to be on the left. 190 ASTRONOMY. Fig. 163. 1115. When the moon is just between the earth and sun, what do we 0 say??( That it is.New.M-oon. 1116. When the moon is one quarter of the way round from this first 0 position, and appears as a half circle, what do we say'? That it is the First Quarter. 0 1117. How is it when the moon is half way round, and its shinind disc is a full circle? We then say it is Full iJfoon. 1118. When it has performed three quarters of a revolution, and the disc has decreased to a half circle, what do we say? We say it is the last Quarter. 1119. What is a Lunar Month? The interval of time in which the moon passes from New Moon around to New Mloon again. 1120. How long is this interval? Twenty-nine and a half days. 1121. Does it ever happen that the full moon is deprived for a time of the light of the sun? This phenomenon is occasionally observed. The moon is then said to be eclipsed. 1122. How doos the moon become eclipsed? By passing into the shadow of the earth, as we see represented in Fig. 164. DESCRIPTIVE ASTRONOMY. 191 Fig. 164. 1123. Is the moon entirely invisible while it is passing thr6ugh the earth's shadow? It is not; its disc is still seen shining with a dull reddish light. 1124. What is the explanation of this curious fact? The earth's atmosphere is supposed to act like a lens, and refract a certain portion of light into the interior of the shadow. 1125. Does the moon in circling around the earth, ever come directly between us and the sun, so as to conceal more or less of his disc? This sometimes happens, and we then say, the sun is eclipsed. 1126. What can Fig. 165. you say of Fig. 165? That it shows the moon in such a position, casting its shadow on the earth. Where this shadow falls, the sun is eclipsed. 1127. What is the form of the moon's shadow? It tapers toward a point. 1128. By what is it surrounded? By a space that receives light from only a portion of the sun's disc; this is called the Penumbra. 192 ASTRONOMY. 1129. Is a part of the sun's disc, then, invisible at all places on the earth on which the penumbra falls? It is, and the eclipse is said to be Partial. Where the shadow falls, the whole disc is obscured, or the eclipse is Total. 1130. What is the size of the moon's shadow as thrown on the earth? It is never more than 130 miles broad. 1131. What is the breadth of the penumbral shadow? It can not exceed 5,000 miles. The shadow is usually of an oval form, and its length may be greater than this. 1132. In what direction does this shadow move across the earth? It moves, like the shadow of a flying cloud, over the face of the earth toward the east. 1133. How does it happen that an eclipse of the sun does not occur every new moon? Because the moon generally passes the sun either on the north or south side of him. 1134. Why is not the moon eclipsed every full moon? Because it usually passes to the north or to the south of the earth's shadow. 1135. Does not the moon move around the earth in the same level plane in which the earth moves around the sun? Very nearly, but not exactly. 1136. When the moon comes between the sun and earth, is its shadow always long enough to reach as far as the earth? It often falls short of the earth. In such instances there can not be a total eclipse, but there may be an DESCRIPTIVE ASTRONOMY. 193 Annular eclipse; that is, the visible portion of the sun's disc may have the form of a ring. 1137. How long may an annular eclipse of the sun last at any one place? Twelve and a half minutes. 1138. How long may a total eclipse of the sun last at one place? Eight minutes. 1139. Is there any appearance of light in the sky at the place occupied by the sun, during a total eclipse? There is. The dark body of the moon appears to be surrounded with a halo, or corona of light; and is fringed at certain parts with beautiful rose-colored flames. 1140. What inference. may we draw from this fact? We may infer that the bright surface of the sun is surrounded by a body of luminous matter that extends far into space, and is perhaps continually flowing away from the sun. 1141. When will the next total eclipse of the sun, visible in the United States, occur? On August 7th, 1869. It will be total in North Carolina and Virginia. 1142. How many eclipses of the sun occur each year, visible from some part of the earth? There are never less than two eclipses of the sun in any one year, and there may be as many as five. 1143. Are eclipses of the moon as frequently seen as eclipses of the sun? They are not, when we take the whole earth into ace count; but from any one locality, lunar eclipses are to be seen much oftener than solar eclipses. 9 194 ASTRONOMY. MERCURY. 1144. How large is the planet Mercury? Sixteen times smaller than the earth. 1145. Why is it so seldom visible to the naked eye? Because it is so near to the sun in the heavens. 1146. What has been ascertained in relation to its physical pecu. liarities? That it is a solid body, surrounded by a dense cloudy atmosphere. 1147. Do we ordinarily see the body of the planet? It is supposed not; thick clouds glowing in the light of the sun usually screen it from view. VENUS. 1148. How does Venus compare with the earth in bulk? It is a very little smaller than the earth. 1149. What have you to say of its appearance? That it is the brightest and most beautiful of all the planets. It is, in certain positions, so luminous as to cast shadows at night, and to be seen in broad daylight. 1150. What remarkable appearances does it present, when viewed at different times through a telescope? The same variety of phases that the moon does. 1151. In what position is Venus when she appears as a crescent in the blue field of the telescope? Between the sun and the earth; but to one side of the DESCRIPTIVE ASTRONOMY. 195 sun, as seen in Fig. 166. the sky. Two S such positions are shown near V, in Fig. 166. The tu corresponding apparent positions in the heavens are b and c; the sun appearing to be at S. 1152. What prediction was made by Copernicus, before the invention of the telescope, in reference to this planet? It was boldly predicted by Copernicus that "should men ever see Venus better, they would discern her phases." 1153. By whom was this prediction verified? By Galileo; directing the first telescope that had ever been pointed to the heavens, upon Venus, her spurious disc was gone, and a beautiful crescent hung trembling in its field of view. 1154. What other planet exhibits similar phases in the telescope? Mercury; but the phases of this planet are less distinctly seen. 1155. Why is Venus called the morning and evening star? Because it is either seen in tile castern sky in the 196 ASTRONOMY. early morning, or in the western sky early in the evening. 1156. What may we learn from Fig. 166? lThat Venus may be seen, at different times, on either side of the sun in the heavens. 1157. How long does Venus continue to be an evening star? She is an evening star for 9- months, and a morning star for the same length of time. 1158. In what part of the orbit does she appear as an evening star? In that half of it which lies on the left or east side of the sun; and as a morning star in the other half. 1159. Is Venus, or Mercury, ever seen in the opposite quarter of the heavens from the sun? It is apparent from Fig. 166 that these planets can never be on the opposite side of the earth from the sun. 1160. Is the same true of the other planets? All the other planets revolve on the outside of the earth's orbit, and may be seen, at different times, at all angular distances from the sun in the heavens. 1161. Illustrate by the figure. When the earth is at E, Mars might be at M, or in opposition to the sun, and would rise in the east about the time the sun was setting in the west. 1162. What is known of the physical peculiarities of Venus? Venus is surrounded by a dense and cloudy atmosphere, like Mercury, and has lofty mountains on its surface. DESCRIPTIVE ASTRONOMY. 197 MARS. 1163. What is the size of Mars? Mars is seven times smaller than the earth. Fig. 167. -m', —----------- With the aid of telescopes, astronomers have frequently discerned spots of different shades on Mars, and have supposed they could see the outlines of continents and Seas. 1165. Have the supposed continents and seas the same color? The color of the continents is a dull red, and of the seas greenish. 1166. What is it that gives a red tint to the light of Mars? The ru ddy light reflected from the ha ve frequentlyd. 1167. Are the outlines of continents and seas discernible on any of the other planets and seas discer? They are not. 198 ASTRONOMY. JUPITER. 1168. It has been stated that Jupiter is the largest of the planets -how much larger is it than our earth? It is more than 1,200 times the size of the earth. 1169. What is its diameter? It is 11 times the diameter of the earth, or 87,000 miles. 1170. When Jupiter is ex- Fig. 168. amined with a good telescope, what are always observed on - its disc? Several dark streaks running parallel to his equator, called the Belts of ~Jupiter. -,_ 1171. Do the number, breadth, and situation of these ___ ___-_- _ belts remain always the same? -- On the contrary, they are quite different at different times. 1172. What are these dark belts supposed to be? The dark be dy of the planet seen through tracts of clear sky in a cloudy atmosphere. 1173. What is supposed to give them their common direction? Prevailing winds, similar to the trade-winds on the earth, blowing nearly parallel to the equator. DESCRIPTIVE ASTRONOMY. 199 1174. How many satellites has Jupiter? Four; all of which can be seen in telescopes of the lowest power, and even in a common spy-glass. 1175. Do these satellites ever pass into Jupiter's shadow and become eclipsed? The three satellites nearest to Jupiter are eclipsed every revolution. They are suddenly extinguished as they enter the shadow of the planet, and after a certain interval of time emerge from the shadow, and flash out again in a different place. SATURN. 1176. How large is Saturn? Saturn is nearly 1,000 times larger than the earth. 1177. Is its disc, like that of Jupiter, crossed by dark bands or belts? Belts are sometimes observed on the surface of Saturn, but they are much less distinct than those of Jupiter. 1178. What is the great Fig. 169. peculiarity of this planet? -~l It is surrounded by a luminous ring, en- tirely detached from - --- the body of the planet. - - 1179. What is the size of this ring? The diameter of its _ outer edge is 176,000 miles. The entire dis 200 ASTRONOMY. tance around this edge is no less than 553,000 miles, or 22 times the circumference of the earth. 1180. How far is the inner edge of the ring from the body of the planet? 19,000 miles. 1181. What are the breadth, and thickness of the ring? Its breadth is 29,000 miles; its thickness is not more than 250 miles. 1182. Is the ring single or double? It is double. The space between them, as it appears in telescopes of high power, is shown in Fig. 169. 1183. How many satellites attend upon Saturn? Eight. URANUS AND NEPTUNE. 1184. How much larger is the planet Uranus than the Earth? It is about 80 times larger. 1185. Has any knowledge been obtained of the peculiarities of its surface? Not as yet; no spots have ever been seen on his disc. 1186. How many satellites has Uranus? Their number is not known with certainty; there are certainly four, and probably eight. 1187. How far is Uranus from the sun? 1,824,000 miles, or 19 times the Earth's distance. 1188. How far is Neptune from the sun? Thirty times farther than the Earth. DESCRIPTIvE ASTRONO3IY. 201 1189. How does Neptune compare with Uranus in size? It is a little smaller; its diameter is about 31,000 miles, or 4,000 miles less than the diameter of Uranus. 1190. Have any satellites been discerned attending upon Neptune? One has been seen. Prof. Bond, of the Cambridge Observatory, supposes that he has detected a second satellite, with his large telescope. CO3METS. 1191. What does Fig. 170 Fig. 170. represent? _ The usual appearance of - a comet. 1192. What is the bright J_ point on the left called? The Nucleus; this and.-" - -.. the luminous matter surrounding it, form the Head of the comet. 1193. What appears to proceed from the head in a direction opposite to the sun? A stream or train of similar luminous matter. 1194. What is this called? The Tail of the comet. 1195. Is it uniformly bright throughout its whole extent? It decreases in brightness toward the end, and is less bright along the middle than at the borders. 9* 202 ASTRONOMY. 1196. What may we infer from the last mentioned fact? That the tail is really hollow. 1197. Is the tail of a comet really curved, as shown in Fig. 170 It is usually bent backward, as if it met with a resistance in passing through the ether of space. For example, the tail of the comet of 1744 was bent into nearly a quarter of a circle. 1198. Over how much of the sky does the tail of a comet extend? The apparent length is very different for different comets; in some instances it has been enormously great. 1199. Two bright comets were seen in the years 1618 and 1769how long were the tails of these cornets? They reached as far as the distance from the horizon to the zenith. 1200. Are all comets provided with the luminous appendage called a tail? They are not; for example, the bright comet of 1682 had no tail. 1201. Do comets move round the sun ill circles? Their paths through the fields of space differ very much from circles. 1202. What does Fig. 171 represent? Fig. 171. A portion of the orbit of a comet; the entire orbit is a long oval. 1203. What consequence follows from this fornl of a comet's orbit? It follows that the comet alternately itr/. approaches and recedes from the sun. DESCRIPTIVE ASTRONOMIY. 203 In Fig. 171 the comet approaches the sun until it arrives at its periheliol, P, and then recedes from him. 1204. Do most comets, in moving away from the sun, withdraw to a very great distance from him? The greater number of them pass far beyond the outernost limits of the solar system; and do not return until after the lapse of centuries. 1205. How near did the great comet of 1843 come to the sun? Within 90,000 miles of his surface. This comet is now moving darkly away to its more distant goal, many thousand millions of miles from the sun. 1206. Are comets visible throughout an entire revolution? They are visible during only a small part of their revolution, while they are in the vicinity of the sun. 1207. When will the comet of 1843 return to its perihelion, or nearest point to the sun, and display itself in our firmament again? Some astronomers have predicted its return in 1865; others that it will not make its appearance until the year 2018. 1208. What was the velocity of this comet at the time of its nearest approach to the sun? About 360 miles per second. It passed half way round the sun in about two hours. 1209. What have you to say in respect to the actual size of comets? The nucleus is never more than a few thousand miles in diameter; but the cometic matter is disseminated, in the head and tail, over hundreds of thousands and even millions of miles. 204: ASTRONOMY-. 1210. What was the greatest lenath of the tail of the great comet of 1843? 108,000,000 of miles. 1211. What is the nature and condition of the substance of comets? We only know that it is far more rare and subtile than the thinnest film of vapor that ever makes its appearance in our sky. 1212. Is the tail of a comet permanently connected with the head? Probably not. It is apparently made up of particles of nebulous matter flowing away very rapidly from the head. 1213. What force expels these particles and urges them to such enormous distances from the head of the comet? A repulsive action exerted by the sun. 1214. How many of these remarkable bodies are there, connected with the solar system? Their number is not known, but it is undoubtedly very large. There can not be less than several thousand comets revolving around the sun. 1215. Are the periods of revolution of all the comets that have been observed known and their times of return predicted? The number of comets whose periods and times of return are known with certainty is comparatively small. FIXED STARS. 1216. In a clear night the blue vault of the sky is studded with stars-how many of these stars can be seen at any one time at a given place? Not more than 2,000. DESCRIPTIVE ASTRONOMY. 205 1217. Ho(w many stars can be seen with the naked eye, in the whole heavens? Not more than 7,000. 1218. Are the same constellations visible from all parts of the earth? The constellations that lie around the south pole of the heavens never come above our horizon. At corresponding latitudes in the southern hemisphere of the earth, the same constellations never set. 1219. Which is the most conspicuous of these southern constellations? The Southern Cross. 1220. How many stars are visible with the aid of telescopes? Many millions. 1221. How much farther can a person see into space with the best telescope ever constructed than with the naked eye? About 420 times farther. 1222. How are the fixed stars classified? They are divided into stars of the first mnaynitude, stars of the second mnagnitude, etc., according to their apparent brightness. 1223. How many stars are assigned to the first magnitude? From 20 to 24 only. 1224. Mention the names of some of the stars of the first magnitude which come above our horizon. Sirius (or the dog-star), Arcturus, Regulus, Vega, Capella, Aldebaran. 206 ASTRON-OMY. 1225. Which is the brightest star in the whole heavens? Sirius. Vega is the brightest star in the northern heavens. 1226. How- many stars are there of the second magnitude? Fromn 50 to 60. 1227. How many of the third magnitude? 200. 1228. How is it as we pass to the lower magnitudes? The number increases rapidly. 1229. Is the difference in the brightness of the stars probably owing to a difference of size or a difference of distance? Chiefly, no doubt, to a difference of distance. 1230. Are the stars of our Fig. 172. firmament dispersed in about. equal numbers in every direc-''"';":s,;... tion through space?,. They are mostly disposed in a vast bed, of moderate thickness in comparison with its great extent. 1231. What is the position of the sun in this bed of stars? The position of the sun is shown by the letter s. 1232. What consequence follows from the fact that the sun, with his attendant planets, is located in this thick bed of stars? That the whole heavens appears to us to be encircled by a girdle of stars, so closely compacted together as to be separately invisible to the naked eye. 1233. What is this starry belt called? The Xilky Way. DESCRIPTIVE ASTRONOMY. 207 1234. What is the estimated number of stars in the Milky Way? Eight millions. 1235. How far from us is the nearest fixed star? So inconceivably remote, that its light employs more than three years in journeying to us; although it darts from the sun to the earth in a little over eight minutes. 1236. How much farther removed are the most distant stars that faintly glimmer in the field of a telescope of medium power? About 360 times farther. The light by which we now see them, started on its journey a thousand years ago. 1237. What is the nature and office of the stars? They are doubtless the suns of other planetary systems, upon which they bestow the genial influences of their light and heat. 1238. What is our sun in the firmament of the inhabitants of those celestial worlds? A fixed star. 1239. How would the sun, if seen from the distance of the nearest fixed star, appear? No brighter than a star of the first magnitude does to us; it would not be so bright as Sirius. 1240. Do all the stars preserve their brightness unchanged from night to night and from year to year? Some of them undergo regular variations of brightness; these are called variable stars. 1241. Do any of these stars continue to wane in lustre until they finally disappear, and then reappear again? A few do; there is a variable star in the constellation 208 ASTRONOMY. of the Whale that dies out every 332 days, and remains in darkness for five months. 1242. Have new stars ever made their appearance in the heavens? There are a few instances on record of stars that burst forth suddenly in great splendor, and after a time gradually died out again. 1243. What are double stars, triple stars, etc.? Stars that appear single to the naked eye, but in telescopes seem to consist of two or more stars, very near together. 1244. Are there many such stars? There are several thousand. 1245. Do the two individual stars that make up a double star retain the same relative position from year to year? In numerous instances they are found to be revolving around each other. 1246. In what periods of time do they complete their vast circuits? In periods varying from 30 to 600 years. 1247. Are all the fixed stars, so called, perfectly stationary in the heavens, from year to year? They are not; great numbers of them are observed to be moving rapidly through space. 1248. Give an example of a star that is moving through space. There is a star in the constellation of the Swan, called 61 Cygni, which is moving steadily forward in one direc-.tion, at the rate of 43 miles per second. DESCRIPTIVE ASTRONOMY. 209 1249. Does this rapid movement produce any considerable change in the place of the star in the heavens, in the course of a year? The change is so slight that it is only by very nice telescopic observation that it can be detected at all. 1250. How is this remarkable fact to be explained? By considering the enormous distance of the stars. At the distance of the nearest star the whole solar system would occupy but a mere point on the face of the heavens. 1251. Is the sun stationary in space? The sun, with his attendant system of planets, is moving through space at the rate of nearly five miles per second. 1252. Clusters of stars are seen in various parts of the heavensmention one of the most conspicuous clusters. The Pleiades. 1253. Are there Fig any clusters which can be seen in telescopes only? A large number. For example, there is a beautiful cluster to be seen, with a good telescope, in the constellation Hercules. 1-0 210 ASTRONOMY. 1254. Are there not clusters visible as cloudy specks, in ordinary telescopes, that do not distinctly reveal their individual stars even in the largest telescopes? There are many hundreds of such clusters scattered through space. In the field of view of the monster telescopes of the present day, these are but specks of star-dust. 1255. Are there not other clusters that are just discernible in the laraest telescopes, as mere specks of light? There are; the distance of some of these clusters is estimated to be no less than ten thousand times that of the nearest fixed star. 1256. When did the light that reveals their existence to us start on its journey? More than 30,000 years ago. 1257. Are clusters of stars, or nebulae, all of one and the same form? On the contrary, they occur of almost every variety of form. ILLUSTRATIONS. Fig. 10. a -b c Fig. 32. A F iB p Fig. 33 Fig. 34. _Q A Fig. 48. Fig. 60. 212 N ATURAL PHILOSOPHY. Fig. 51. Fig. 55. Fig. 62. |R (II Fig 65. Fig. 68. Fig. 69. 77~~~~~~~~~~~~~~~~~~~~ III I lt~PIIIII'I~IttI~I PWIN 1311~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ IIII~kIUIILUIILI P PhPPLPPIIP NATURAL PHILOSOPHY. 213 Fig. 74. Fig. 70.,I I l III M Fig. 77.'.Fig. 78. t. Fig. 94. Fig. 91. Lf~ wIl,,. 214 NATURAL PHILOSOPHY. Fig. 95. Fig. 96. Fig. 97. Fig. 101. Fig. 103. Fig. 104. F_g___ 1- Fig. 107. NATURAL PHILOSOPHY. 215 Fig. 120 Fig. 122. i i Fig. 126. Fig. 131. Fig. 145. F /'ig.rFig. 146. ig. 148. d'~t~~~i~DCI~~9~ 3kI 216 ASTRONOMY. Fig 153. Fig. 150. SWugqgoner~ll, \p/,.!Jragonsf * sy Yole.S" ta4;$$ Fig. 155. Fig. 151 Fig. 165. ASTRONOMY. 217 Fig. 163. 0 0 Fig. 166. S Fig. 171., 10 r- sH-; 03 OF AND ALLIED SCIENCES, INCLUDING AN OUTLINE OF AGRICULTURAL CHEMISTRY. BY JOHN A. PORTER, M.A., M.D., PROFESSOR OF ORGANIC CHEMISTRY IN YALE COLLEGE) AUTHOR OF "iPRINCIPLES OF CHEMISTRY." PUBLISHED BY A. S. BARNES & CO., 61 AND 53 JOHN STREET. 1858. PREFACE. THE design of the present little volume is to teach the elements of science to beginners. The subjects presented require little abstraction, and are readily comprehended by the young. Inquiries about natural phenomena arise at a very early period in the minds of children. Then is the time to satisfy them, in order that further inquiry may be elicited. It is also important that such inquiries should be answered in their proper order. More is therefore undertaken in the present work than to give answers to isolated questions concerning natural phenomena. A careful logical sequence is observed in the arrangement of the questions, in order that each may prepare the mind for the next, and the whole subject be thus systematically developed. Avoiding by this means the necessity of frequent repetitions, it has been practicable to realize a great economy of space. It is believed that this method has also an important incidental advantage, as an influence upon the mental habits of the student. 1* X PREFACE. The work is confined to facts of universal interest, and to the illustration of leading principles. It has thus been possible to condense within a small space information which will be of practical value to the pupil who is unable to pursue his studies further. This remark is sufficiently illustrated in the chapter on Agricultural Chemistry. To pupils of another class, such an outline is no less important, as serving to map out the field which they are afterward more thoroughly to explore. INTRODUCTION. BEFORE commencing a journey, it is always agreeable and profitable to trace out upon a map the route which is to be pursued, and to obtain definite impressions of the relative distances and directions of the countries to be visited. For an excursion through the realm of knowledge, such a preliminary survey is no less important and interesting to the student. It is therefore given in the present introduction. Light was the first of all created things. The sun warms the seed in the earth, and his genial rays weave the foliage upon the full grown tree. His light and heat are thus in an important sense X11 INTRODUCTION. the source and beginning of the world's life. It is not inappropriate, then, that we should make these subjects the fountains of the stream of science which we are to follow in its course. The heat of the sun lifts the air into winds, and wings the vapors that rise from the sea. The subject of heat will, therefore, naturally introduce us to that of vapor, and the latter to meteorology, or the consideration of winds, storms, and other atmospheric phenomena. The more intense heat which we are capable of producing by artificial means converts water into steam. The laws of steam and its application in the steam engine, by which it becomes so important an agent in human affairs, follow, therefore, naturally upon the subject of meteorology. Electricity, which is intimately associated with heat and vapor, as their frequent consequence in nature, will next receive our attention. We shall see how this subtile agent, once only known as it flashed through the heavens in the lightning, has been made the willing slave of man, to do his bid INTRODUCTION. Xlll ding in the most widely different spheres. Now chained to the dull business of silvering his spoons and tea pots in the trough of the electro-plater, anon it becomes his Ariel, and wings its way along the telegraphic wire to deliver his messages with the speed and precision of thought itself. Having concluded the consideration of the great forces of nature which act upon the earth, we come next to the science of chemistry, or the consideration of the varied material of which the earth is composed. This latter science teaches us of the nature of the air we breathe, the water we drink, and the soil on which we tread. It informs us how metals are produced from ores, wines from fruit, and liquors from grain, and explains the changes which take place in the formation of all these substances. Instructing us also in relation to the production of plants and the conditions of their growth, it includes the subject of agricultural chleminstry. Informing us also of their office to prepare food for the animal world out of the dead material of the Xiv INTRODUCTION. earth and air, it introduces us to the subject of physiology. After a survey of the most interesting points connected with this branch of science, we return again to the earth itself, to consider it especially with reference to its history and its structure. Its central fires, its imbedded fossils, its rocky strata, and its volcanic vents are treated of in their turn, and with this brief survey of geolo7y, our excursion in the realm of Science is brought to a close. FIRST BOOK OF CHEMISTRY AND ALLIED SCIENCES. CHAPTER I. ATOMS AND ATTRACTION. 1. OF what is matter supposed to be composed? Of small spherical particles, called atoms, which attract each other like so many minute magnets. 2. What proves their minuteness? A single grain of musk will fill a room with its fragrant particles for years without any considerable loss of weight. The particles must be extremely small, or the waste would be more rapid. 3. How many elements or different kinds of matter are there? About sixty. 4. Give. some examples of elements. Iron and carbon are elements. Iron rust, on the other hand, is a compound. 16 ATOMS AND ATrRACTION. 5. What is that force called which binds together atoms of the same kind? It is called the attraction of cohesion, or simply cohesion. 6. Give an illustration of this force. The strength of a horse is insufficient to break an iron wire one eighth of an inch in thickness. 7. Why is this? It is because in every section of the wire the atoms attract each other with a force superior to the strength of the horse. 8. How does the ATTRACTION OF GRAVITATION differ from that of COHESION? It acts at all distances, as, for example, between the sun and the earth, while cohesion acts only at infinitely small distances. 9. What is CHEMICAL ATTRACTION or AFFINITY? It is the force which unites unlike atoms into compounds possessing new properties. 10. Give some examples of chemical attraction. Particles of iron and oxygen unite by chemical attraction to form iron rust, a substance different from either. The gas chlorine and the metal sodium unite by chemical attraction to form common salt. 11. Does chemical attraction act at great distances? It does not. Iron and oxygen, for example, unite to form iron rust only when brought into contact. 12. Illustrate the three kinds of attraction by a single example. The action of the three is illustrated in a falling drop CRYSTALLIZATION. 17 of water. Affinity holds together the atoms of oxygen and hydrogen which make up each particle of water; cohesion unites the particles of water thus formed, and gravitation causes the coherent drop to fall. 13. What are the three states or conditions of matter? The solid, liquid, and gaseous. 14. Give an example of the same substance in these three different states. Solid sulphur, melted sulphur, and vapor of sulphur. 15. What is the difference of these three states with respect to cohesion? In solids, cohesion is strongest, and the atoms are more nearly and firmly bound together. In liquids, cohesion is weaker, and the atoms are farther separated. In gases, the separation is still greater. 16. How are solids made to assume the liquid form by other means than melting? By dissolving them in liquids, as when salt is dissolved in water. 17. What effect does the liquid have? It overcomes the cohesion of the particles and draws them apart, so as to form a solution. 18. When the liquid is dried away, what occurs? Attraction of cohesion brings together the particles of the substance which was dissolved, and makes it solid again. 19. What more does it do than this? It brings them together in beautiful.. forms called crystals. 18 ATOM]S AND ATTRACTION. 20. How may this be shown? By slowly drying a solution of salt on a stove, crystals of the form shown in the figure on the last page will be produced. 21. Of what are these crystals made up? Of smaller crystals called cubes, like the form in the margin. 22. What is said of the variety of crystals? Crystals are, as it were, the flowers of the mineral world, and of almost unlimited variety. Some of the more beautiful forms are given in the following figure. 23. Does any one substance have all this variety of crystals? It does not. As every flower has its own form of leaves and petals, so every substance has its own form or sets of forms, from which it never varies. 24. Illustrate this subject. It is easy to tell different minerals and other substances from one another by the shape of their crystals. Crystalline grains of salt and sugar, for example, may easily be distinguished by this means. 25. While crystals of the same substance may differ throughout or in part in the size of their corresponding surfaces, in what are they always alike? The corresponding angles of different crystals of the same substance are always alike. In this kind of archi CRYSTALLIZATION. 19 tecture, nature seems to pay exclusive attention to the corners and angles. 26. How does the accompanying figure illustrate this statement? It represents crystals of quartz in which the surfaces differ, but the angles are the same. 27. When different substances have nearly the same crystalline form, in what respect do the similar forms generally differ? In the size of their corresponding angles 28. Is it only when dissolved substances become solid that crystals are formed? Crystals are also formed when melted substances or vapors take the solid form. The figure represents crystals of snow. 29. How may these forms of snow crystals be seen? By catching snow flakes on a hat or other dark object in cold weather, and inspecting them in the open air. 30. Are crystals always visible when they exist? By no means. They are sometimes too small to be seen with the naked eye, and in other cases too closely pressed together, as in a bar of cast iron or zinc, to be well distinguished. OTHER CRYSTALLINE FORMS. 11 20{) LIGHT. CHAPTER II. LIGHT. 31. How is light known to be IMPONDERABLE) or without weight? By the fact that an illumined body weighs no more than one unillumined. 32. What is Newton's theory of light? That it is a fluid, thinner or more subtile than air or any gas, and is constantly given off from the sun and all luminous objects. 33. How is the sensation of sight produced according to this theory? By the entrance of particles of this thin fluid into the eye, as particles of fragrant matter passing off from flowers produce the sensation of smell. 34. What is a RAY of light? A line of particles of light. 35. What is a MEDIUM? Any space or substance through which light passed. 36. Mention some of the more important laws of light. 1. Zight proceeds.fron every point of lurni-.,\ notes objects in every direction. Rays of light, "-. for example, proceed from every point of the-,'j:. sun's surface. /'' LIGHT. 21 2. They proceed in straight lines. Light, for example, comes to us in straight lines from the sun. 3. They diverge as they proceed. This is illustrated in the figure. 37. What does the next figure represent? It represents the light of a candle passing through a window and illumining a larger space on the opposite wall. 38. When the wall is twice as far from the candle as the window is, how much sur- A face does the light cover? A surface four times as large as the I window. 39. If the distance of the wall were three times that of the window; what would be the effect? The light would cover a surface nine times as large as the window. 40. State their results more concisely. Distance 2, surface 4; Distance 3, surface 9; Distance 4, surface 16; Distance 5, surface 25. 41. How do these figures of the two columns compare? Those of the second column are the squares of those of the first column. 42. How may the above results be now more briefly stated? The space illumined is as the squares of the distances. 43. What is said of the intensity of light in similar cases? It is diminished in the same proportion as the space it 22 LIGHT. covers is increased. At double the distance it is only one fourth as great, at three times the distance only one ninth, and so on. 44. How is light reflected? It glances off from a mirror with the same degree of obliqueness with which it falls on it. 45. Illustrate this subject. If the sun is in the direction in which the upper K line in the figure points, the mirror will throw its image on the floor in the direction in which the lower line points. 46. What effect would a number of small mirrors, arranged as shown in the figure, have upon the sun's light? Each would reflect it just as obliquely as it fell, and consequently send it to the same point, and make any object held at that point intensely bright. 47. What effect would a concave mirror have? Precisely the same effect, as it may be supposed to be made up of a number of plane 4' mirrors arranged as in the figure. 48. What is the point called to which the rays converge? The focus. 48*. How is the action of lenses explained? The rays of light are always bent out of their original direction in passing from one medium to another. This subject is further explained in works on Natural Philosophy. HEAT. 23 CHAPTER III. HEAT. 49. IF one end of a bar of iron is heated, what happens to the other end? The heat passes along through the bar and makes the other end hot also. 50. What is HEAT? It is regarded as a subtile fluid, thinner than air or any gas. 51. Has it any weight? Like light, it is imponderable, or without weight. 52. How is this known? From the fact that the heated body which contains it weighs no more than a cold onie. 53. What is COLD? Cold is a negative term, signifying the comparative absence of heat. 54. Is any thing absolutely cold, or, in other words, absolutely destitute of heat? Nothing is absolutely destitute of heat. Ice, for example, contains heat, and may be made colder by its withdrawal. 55. What are the principal sources of heat? The sun, the fixed stars, chemical action, electricity, and friction. 24 HEAT. 56. Is it certain that there are distinct sources of heat? It is not; for the heat of the sun may be due to chemical action, and electricity is, as we know, excited both by chemical action and by friction. 57. How much heat does the sun send to the earth? Enough every year to melt a shell of ice enveloping the earth a hundred feet thick. 58. How much does it send in all directions? So much that, if it all came to the earth, it would melt in a year a crust of ice nearly 4,000 miles thick, or 37 feet every minute. 59. How much would the highest heat of a blast furnace melt? Five feet per minute. 60. How much hotter is the sun's surface, then, than the fire of a blast furnace? Seven times as hot. 61. What is said of the heat of the fixed stars in this connection? They are suns of other systems, and altogether give us nearly as much heat as the sun. 62. What would happen if their heat were withdrawn? The earth would not be sufficiently warmed by the sun for the existence of animal or vegetable life. 63. Give an example of heat from CHEMICAL ACTION. The heat of our fires is heat of chemical action between the fuel and the oxygen of the air. 64. Give some examples of heat from FRICTION. The heat produced by slight rubbing is sufficient to set on fire a phosphorus match. Count Rumford is said to HEAT. 25 have caused water to boil by the friction produced in boring a cannon under water. 65. Howv is heat communicated? By conductiorz, convection, and?radiation. 66. What is CONDUCTION? The passage of heat through a body from particle to particle. 67. Give an illustration. When one end of an iron bar is heated, the other end grows hot. 68. How is conduction illustrated to the eye? U Marbles fastened to such a bar with wax, would drop off' in succession as the heat progressed. 69. When does conduction cease? When the heat is equally distributed. 70. What substances are the best conductors? The metals. 71. What substances are comparatively poor conductors? Earth, wood, wool, cotton, fur, and feathers. 72. How is this difference illustrated? Heat will travel along a nail and ignite a match at its end sooner than along a pipe stem of equal length. 73. How are we protected from the central fires of the earth? By the non-conducting power of the rocks and soil which form its crust. 29 26 HEAT. 74. Why is water sooner heated in an iron vessel than in one of porcelain? The metal conducts the heat through from the fire more rapidly. 75. Why is water sooner cooled in an iron vessel than in one of porcelain? The metal conducts the heat outward more rapidly. 76. What is the object of clothing as respects heat? Not to impart heat, but to prevent its escape. 77. What materials are best adapted to this purpose? Wool, cotton, furs, and other fibrous material. 78. Mention an instance of adaptation to climate in the covering of animals. The elephant has but a few straggling hairs, while the polar bear has a thick and fine fur. 79. How does snow keep the earth warmer than it would otherwise be in winter? Snow is a poor conductor, and does not allow the heat of the earth to escape rapidly. 80. What would happen if this were not so? The cold of a single winter would be sufficient to kill whole races of plants. 81. As respects heat, which is the best building material for walls of houses, brick or iron? Brick or wood are better than iron, because they more effectually keep out the heat of the sun in summer, and keep in the heat of fires in winter. HEAT. 27 82. To what is the advantage of double doors and windows to be attributed? To the non-conducting wall of air between them. 83. How is the heat excluded from "refri gerators'?I The space between the double walls is filled with pulverized charcoal. 84. What non-conducting material is used for packing in the casu of fire-proof safes? Gypsum is commonly employed. 85. Why does cold metal feel colder than wood of the same temrn. perature? Because it is a better conductor, and carries off the heat of the hand more rapidly. 86. Why does hot metal feel hotter than wood of the same temperature? Because it is a better conductor and brings heat to its own surface, and thus to the hand, more rapidly. 87. How is it shown that liquids are nonconductors? Water may be boiled in a tube containing ice at the bottom. 88. Mention another proof. Ether may be inflamed on water without heating it below the surface in any considerable degree. 28 HEAT. 89. How, then, is the mass of a liquid heated? On applying the heat below, the portions first heated rise and give place to another portion. 90. Why? Because they expand and become lighter. 91. How long does this process continue? The circulation continues until the liquid has reached its boiling point. 92. How may the circulation be made visible? By adding "flowers of sulphur" to the water and watching the motion of the particles. 93. What is this process of heating called? Convection. 94. How is a room heated by a stove? In part by a similar circulation in the air, and in part by radiation. 95. How is the upward current above the stove shown? By the ascent of a feather or other light object in the current. 96. How is heat distributed through the atmosphere? By a similar circulation. 97. Explain this further. The hot air at the equator rises, and cold air, from north and south, flows in to be heated in turn. HEAT. 29 RADIATION. 98. From what bodies does heat RADIATE or flow out? From all bodies, even the coldest, without exception. 99. Illustrate this subject in the case of a cold body. A bar of mercury, which can only be frozen by extreme cold, would melt if hung in a cavity in a block of ice, by the radiation of heat from the warmer ice. 100. What class of bodies allow heat to pass through them most readily? Transparent bodies, as a general rule. 101. Do they allow heat and light to pass equally well? By no means. Most transparent substances, which allow light to pass quite perfectly, detain a large part of the heat. 102. Give a simple illustration of this difference. A plate of glass held between the face and the fire lets the light through so that we see the fire, but intercepts a large part of the heat. So water allows light to pass, but detains heat. 103. What substance allows heat and light to pass equally well? Transparent rock-salt. 104. Mention some substances which stop the light, but allow the heat to pass. Black glass and smoked quartz crystal. 105. What kind of heat passes very perfectly through all trans. parent substances? The direct heat of the sun passes with its light through all transparent substances. 30 HEAT. 106. Illustrate the difference in this respect between the heat of the sun and that of a fire. The heat of the sun will burn the face through a window, while the same glass would protect from the heat of a fire. 107. Give another illustration. A glass lens or burning-glass which will transmit and concentrate the rays of the sun, stops that of the fire. 108. What effect have highly polished surfaces upon heat which falls upon them? They reflect much of it, and thus retard its entrance. 109. What effect have polished surfaces upon the passage of heat outward from a body'? They retard its passage in this direction also. 110. Illustrate both of the above statements. Liquids take longer to boil, and keep hot longest, in polished vessels. 111. If it were desired to heat a liquid as rapidly and keep it hot as long as possible in the same vessel, how would the object be best accomplished? By admitting the heat through a sooty surface, and then polishing the vessel to confine the heat. 112. Why are polished surfaces supposed to have this effect on retarding the passage of heat? Because of their density or compactness. 113. What surfaces allow of the most ready entrance or absorption of heat? Rough, uncompact surfaces, like cloth and lampblack. HEAT. 31 114. What effect is produced by covering a polished surface with cloth or lampblack? Contrary to what we would suppose, it becomes as good a radiator and absorber as if there were no polished surface beneath it. 115. What follows from this fact? That radiation and absorption depend solely on the nature of the surface, and not on the character of the material beneath it. 116. Does it follow that all substances will give out heat with equal rapidity if their surfaces are the same? It does not. Conducting power, or the rapidity with which the interior supply of heat moves to the surface, is also to be taken into the account. 117. Supposing a mass of metal and one of glass be covered with lampblack, which would cool most rapidly? The metal, owing to its superior conducting power. 118. What effect has color on absorption of the sun's heat? Dark colors absorb most heat, as they absorb most light. 119. How was this proved by Dr. Franklin? By the observation, that when different colored cloths are spread on snow, it melts most rapidly under those which are darkest. 120. What practical inference may be made from this, as to clothing? During exposure to the sun's rays, in the sun, dark clothing is warmer than light. 32 HEAT. 121. Is the superior absorbing power of dark colors confined to the direct heat of the sun? It is. When heat is not associated with intense light, color makes no difference as to absorption. 122. If, as before stated, all bodies are constantly giving out heat, why do they not grow cool? Because they are as constantly receiving that given out by other bodies. 123. What happens if bodies are unequally heated, and then left to cool? The hottest gives out most heat, until all are brought to the same temperature. 124. Why does the earth grow continually colder at night, till toward sunrise? Because its heat is gradually wasting away by radiation into space. 125. Does the air become equally cold? Except where it is in direct contact with the earth, it does not. Solids and liquids being better radiators of heat than gases, the earth often becomes much colder than the air. 126. What advantage is taken of this fact in tropical climates? Water, placed in pans and set in trenches to protect it from currents of air, is frozen when the atmosphere is considerably above the freezing point. 127. What is a CONVEX LENS or BURNTNG-GLASS? It is a piece of glass with two convex surfaces, represented in the next figure. nEAT. 33 128. What effect has it on rays of light and heat? It bends them from their course, and brings rays, before parallel, to a point on i. its opposite side. 129. By what other name is this bending of the rays called? It is called refraction, and is explained in Part II. of this work. 130. What may be substituted for a glass lens? A lens made of two watch-glasses and filled with water may be substituted for one of solid glass. Lenses capable of igniting gunpowder have also been made of ice. CHANGES EFFECTED BY HEAT. 131. Mention some changes which may be effected by heat. Expansion, melting, and vaporization. 132. Mention some changes produced by its withdrawal. Contraction, freezing, and condensation of vapor. 133. Which will grow warmest by equal exposure to the same heat, mercury or water? The same bulk of water requires twice the heating to made it equally hot. 134. How may this fact be expressed in a different way? By saying, that the capacity of water for heat is twice that of mercury. The capacity of other substances for heat differs greatly. 135. What substance has the greatest capacity for heat? Water. 2* 34 HEAT. 136. What influence has this fact on climate? The ocean absorbs much heat in summer and gives it out again in winter, thus moderating the temperature. 137. What is the fire syringe?? It is an instrument designed to produce fire by compression of air. 138. Why is the tinder in the cylinder ignited on forcing down the piston? Compressed air has less capacity for heat than air uncompressed; when compression takes place, the surplus ignites the tinder. EXPANSION. 139. What bodies expand by heat? All bodies, without exception. 140. Give some examples. An iron wire lengthens by heat; the mercury in a thermometer expands and rises by heating; a bladder filled with air will burst by the expansion of the air within it if held near the fire. 141. How is heat supposed to operate in producing expansion? It develops a repulsive force between the particles of matter which overcomes cohesion. 142. How does the expansion of solids by heat compare with that of. liquids and gases? It is much less. HEAT. 35 143. Among solids, which expand the most? The metals. 144. How much does an iron wire expand in length on being heated from zero to 2120? 10 o 145. How may the expansion of metals by heat be illustrated? By arranging a brick, a knitting-needle, and a shin- K gle, as in the figure, and then heating the needle. 146. What will be the effect? The needle will lengthen, and overturn the shingle, if the latter is carefully poised. 147. What application of expansion by heat, and subsequent contraction, is made in the arts? The tires of carriage wheels are put on hot, that they may bind the wheel more firmly by their shrinking or contraction on cooling. 148. Mention another case. Walls that have fallen slightly apart, are sometimes lifted into place by the contraction of heated rods. 149. How is this object effected? An iron rod is run across, through holes in the two walls, then heated by a series of lamps, and, while hot, fastened firmly in each wall. As the rod afterward cools and contracts, it brings the walls with it. 36 HEAT. 150. Why will hot water crack glass? By causing a sudden expansion of the portions with which it comes into contact, and not of the rest. 151. How does this produce fracture? The unexpanded portions beneath have to separate to keep up with the expansion of the rest. 152. How may glass be cut by a hot iron? On the same principle; a crack once commenced, will follow a heated rod or pipe stem drawn over its surface. 153. How is it shown that liquids expand by heat? By simply heating a test tube full of water. The water will heap itself into a convex surface over the mouth of the tube, long before boiling commences. 154. Mention a common case of this expansion. The overflow of water from kettles in the kitchen, before boiling commences. 155. Mention an important exception to the general law of expansion of liquids by heat, and contraction by cold. Very cold water (390 F.) expands by further cold before freezing. 156. What follows from this expansion? That it grows lighter and will float on warmer water, instead of growing heavier and sinking, as it would do if there were no exceptions to the rule. 157. What results from this in nature? As the water of lakes and rivers grows very cold in the IIEAT. 37 early winter it floats, aiid protects the water below from cold. 158. What would happen if this were not the case? The water would keep sinking as it approached the freezing point; warmer water from below would take its place, and this circulation wsould go on until the- whole body of water would be just ready to freeze. 159. What would be the next consequence? The cold of a night or two would be sufficient to convert the whole body of water, from the bottom to the surface, into a mass of ice. 160. What would result from this to fishes and other animals inhabiting the water? They would be destroyed. 161. What would be the effect on climate? The heat of the summer would be insufficient to melt such masses of ice, and temperate climates would be rendered extremely cold. 162. What would be the result to plants and animals? Many species would be destroyed by the increased cold. 163. What would happen to man? If the temperate regions of the earth remained still habitable, he would be reduced to the condition of the Greenlander. 164. How are all these effects prevented? By the arrangement of nature that the very cold which contracts every thing, according to the general law, and 38 ImETr. contracts water down to a certain point, shall expand it just before it freezes. 165. What may be said further of this fact? That it is of the nature of a standing miracle, showing God's power over what are called the laws of nature. 166. Do all liquids expand equally by heat? They do not. Alcohol expands one ninth between the freezing and the boiling point, while water expands but about -23 167. How does this affect the interests of the dealer in spirits? It is much to his advantage to buy in winter and sell in summer. Twenty gallons bought in January will have become, by expansion, twenty-one in July. 168. How much do gases expand by heat? They expand one third by the same heating that expands water -. 169. What is the law of expansion? Starting at the freezing point, all vapors and gases expand 4 for every degree of increased temperature. 170. What is the THERMOMETER? It is an instrument in which expansion is made use of to show changes of temperature. 171. Why would not a straight iron wire answer the purpose? It does not expand sufficiently. 172. What is commonly employed instead? The liquid metal mercury, inclosed in a tube and bulb from which the air has been expelled. HEAT. 39 173. How does it show the temperature? By expanding and rising in the tube with increased heat, and contracting and sinking by cold. 174. How does the manufacturer of a thermometer know where to mark the BOILING POINT? By placing his thermometer in boiling water, and scratching the point to which the mercury rises in the glass. 175. How does he fix the FREEZING POINT? By immersing the instrument in freezing water, or, what is the same thing, in melting snow or ice. 176. What remains to make the instrument complete? To mark it off into degrees, by which the changes of temperature may be expressed. 177. From what point does the graduation begin, or, in other words, what is called 0 or ZERO? The inventor of the Fahrenheit thermometer thought that he could produce absolute cold, or entire absence of heat, by mixing snow and salt; he therefore marked the point to which the mercury falls in such a mixture zero. 178. Why did he choose to call the boiling point 2120. He had to choose some number, and thought this as convenient as any. This being chosen, the freezing point necessarily came at 320. 179. What was the first form of thermometer ever used? A column of air confined in a glass tube over colored water. 40 HEAT. 180. Explain the figure. The figure illustrates the principle of the - air thermometer. The column of air in the test tube lengthens by heat, and contracts again upon cooling. LIQUEFACTION. 181. How are solids converted into LIQUIDS? On being heated up to a certain point, solids are nelted, or converted into liquids. 182. Give an example. At all temperatures below 320, water is solid ice, but the moment the ice is warmed up to 320, by change of weather or other means, it begins to melt. 183. What is the temperature at which this change occurs, called? The melting point. 184. What are the melting points of ice, sulphur, and lead? That of ice is 320; that of sulphur 226~; and that of lead 612~. 185. What remarkable circumstance attends melting or fusion? The disappearance of the heat which has effected the change. 186. Explain this further. A vessel containing ice being set on the fire, neither the ice nor the water formed from it grows any warmer during the whole process of melting. HEAT. 41 187. What becomes of all the heat that must have gone into the ice? It is consumed in converting the ice into water. 188. Can solids become liquids without thus consuming heat? They can not. 189. Mention another case of similar consumption of heat. When ice and salt are mixed, they have the property of becoming liquid. In so doing, they use up or consume the heat of any material near them. 190. What practical application is made of this fact? Cream is frozen and converted into ice cream, by setting a vessel containing it in a mixture of pounded ice and salt. 191. What effect hast the melting of large bodies of snow on the air? Much of the heat of the air is consumed by it, and the advance of spring is thus retarded. 191*. How much heat is consumed in the conversion of ice into water? A quantity sufficient to have raised the temperature of the same weight of water 1420. 191t. Do all bodies, in passing from the solid to the liquid state, consume the same amount of heat? The quantity rendered latent by different substances is very different. 192. Is the heat spoken of as consumed in these cases actually destroyed? It is not; it is only hidden or rendered latent. 42 HEAT. 193. How may it be made to appear again without loss? By re-converting the liquid into a solid. Thus, when water becomes ice, it gives out its latent or combined heat. 194. What application of this fact is sometimes made? In extremely cold weather, tubs of water are sometimes placed in cellars to freeze, and thus, in some degree, moderate the cold. 195. What fact in nature is accounted for on the same principle? The milder climate in the vicinity of lakes and rivers, which freeze in winter, is accounted for on the same principle. 195*. Are all substances fusible? All substances which do not undergo decomposition at high temperatures are fusible. But for the fusion of many the intense heat of the oxy-hydrogen blow-pipe (728), or the galvanic battery (346), is required. 195t. Mention some of the more refractory substances. Carbon, silica, alumina, and magnesia. 195t. Mention a case where decomposition interferes with fusion? Marble decomposes under ordinary circumstances if highly heated. It may, however, be fused by confining it in a gun barrel. METEOROLOGY. 43 CHAPTE-R IV. METEOROLO G Y. 196. WVHAT is WIND? Wind is air in motion. 197. What is the cause of winds? Unequal heating of the earth's atmosphere in different places. 198. How does this produce winds? Air, when heated, grows lighter, and the cooler air flows in to take its place. 199. What causes produce unequal heating of the earth's atmosphere in different places? The principal causes are as follows: (1.) The heat of the sun is greater at the equator than at the poles. (2.) Evaporation keeps the sea comparatively cool in summer, while the land grows hot. Moist places are, for the same reason, cooler than the dry. (3.) Highlands cool the air, while that of valleys remains warm. 200. What results from the greater equatorial heat'? The heated air at the equator rises, and cooler air from the north and south flows in to take its place. 201. What are the limits of this motion of surface winds toward the equator? About 30~ north and 30~ south latitude. 12 44 METEOROLOGY. 202. How is the air returned again north and south? By upper currents, having a contrary direction to those on the surface. 203. How may these motions of the air be figuratively represented? The equatorial regions of the earth may be regarded as a perpetual aerial fountain, fed by surface winds, and returning this air to the earth again beyond the tropics. 204. Are the surface winds thus produced, strictly speaking, north and south winds? They are not. The motion of the earth is so much more rapid at the equator than at the point from which they start, that they strike points to the west of their original aim. That from the north thus becomes a northeast wind, and that from the south a southeast wind. 205. What are these northeast and southeast winds which prevail in the tropics called? They are called trade winds. 206. Are they uniform in their direction at all points within the tropics? In mid ocean they are so, but in the vicinity of continents they are modified by causes already mentioned (199). 207. What tendency have the winds north and south of 300? The surface winds tend toward the poles, where they rise without known cause, and return the air by upper currents to lat. 300. 208. Are these surface winds north and south winds? They are not. Retaining the easterly velocity acquired METEOROLOGY. 45 from the earth at a distance from the poles, as well as the northerly tendency before mentioned, they become southwest winds in the northern and northwest winds in the southern hemisphere. 209. What fact illustrates the general prevalence of westerly winds in the temperate regions? The shorter time required for the outward passage of a sailing vessel to Europe than for its return passage. 210. What would happen but for the circulation and exchange of air which the winds accomplish? The torrid zone would become uninhabitable fiom extreme heat, and the northern regions of the earth from extreme cold. 211. What is the cause of the SEA BREEZE which sets in from the ocean during summer afternoons? The earth heats up more rapidly than the ocean during the day-the air above it rises, and the sea air flows in to take its place. 212. What is the cause of the LAND BREEZE in the night and early morning? The earth cools more rapidly during the night, as it heats more rapidly during the day. The air above it flows seaward to take the place of the warmer air which rises from the sea. 213. Why does the earth become hotter than the sea, when both are exposed to the same sun? Because of the greater capacity of water for heat (134), and also because much of the heat that falls upon the sea is consumed in evaporation. 40 METEOROLOGY. 214. Is there any fixed temperature for VAPORIZATION, as for melting? There is not. Liquids pass off in vapor at all temperatures. 215. Mention a leading property of vapors. They are perfectly transparent. 216. Is the vapor produced at all temperatures the same? It is not; it is thicker or denser in proportion as the temperature is increased. 217. Why is it that the air of a room becomes cooler on sprinkling the floor with water? The water swallows up and renders latent much heat, as it becomes vapor. 218. What liquids produce most cold in their evaporation? Those which, like ether, evaporate most rapidly. 219. What practical application is made of this fact? Ice is artificially produced by the evaporation of ether. 220. How may this be illustrated? By covering a test tube containing a little water with a rag dipped in ether, and then twirling it in the air, to hasten evaporation. 221. What effect is thus produced? A, The ether takes from the tube the heat which it requires to become vapor, and thereby converts the water into ice. 222. What does the atmosphere contain besides simple air? The driest and clearest air always contains more or less aqueous vapor. METEOROLOGY. 47 223. When the air is sufficiently cooled, what becomes of the vapor? It takes the form of visible moisture. 224. Illustrate this subject by a familiar example. Air, near a block of ice, is so cooled that its transparent vapor takes the form of mist in the air, and makes the ice seem to smoke. 225. Mention a second example. The air is so cooled by a pitcher of ice water in summer as to deposit moisture on the pitcher. 226. What phenomenon in nature is accounted for on this principle? Dew. The earth cools by radiation during the night, and then cools the air to such a degree that it yields a portion of its moisture in the form of dew. 227. What other natural phenomena has a similar cause? The mist that forms in summer nights over moist places. 228. How much of its water does the air give up in the abovementioned cases? This depends on how much it contains, and to what extent it is cooled. 229. How much is it capable of containing at 1000 F.? About two cubic inches in every cubic yard. 230. How much at higher temperatures? More than this quantity. 231. How much at 750 F.? About one cubic inch. 48 METEOROLOGY. 232. How much at 500 F.? About half a cubic inch. 233. How much at lower temperatures? Less than half a cubic inch. 234. How much does air yield on being cooled down to 750 F.? It gives up all that it contains above one cubic inch to the cubic yard. 235. How much does it yield on being cooled down to 500 F.? All that it contains above half a cubic inch. 236. When the air contains all the moisture it is capable of containing, how is this fact expressed in a single word? It is said to be saturated. 237. How much water, in the form of vapor, do two cubic yards of saturated air, the one at 1000 and the other at 500, contain? They contain together about two and a half cubic inches. 238. Would they contain this quantity if mixed? They would not; for the temperature of both would become'50, and two cubic yards at 75P can contain only two cubic inches. 239. What would become of the remaining half cubic inch? It would take the form of visible moisture. 240. What phenomena in nature are accounted for on the principle just explained? Fogs and clouds, and the rain which follows them. 241. Whence is air of different temperatures derived to produce fogs? As a general rule, sea air is cooler in summer and METEOROLOGY. 49 warmer in winter than that of the land. They mingle and produce fogs along the coast. 242. How are MORNING FOGS on rivers produced? The land air cooled during the night flows in upon the warmer air of the river, and the surplus vapor of the mixture takes the form of fog. 243. Why does the land air become cooler during the night? Because earth is a better radiator of heat than water. 244. How are CLOUDS produced? Precisely as fogs are, by the mixing of bodies of air at different temperatures by the winds. The mixture has less capacity for moisture than the separate portions taken together, and the surplus assumes the form of a cloud. 245. What very different effects of winds may be here mentioned? A moist wind will produce clouds if it flows over a cold region; while a dry wind will swallow them up as invisible vapor. 246. How are the fogs on the Banks of Newfoundland accounted for? By the mixture of cold winds with the warm air of the Gulf Stream, which passes along that part of the ocean. 247. How is the general presence of clouds in the vicinity of mountain peaks explained? By the admixture of warm air from the valleys with the colder air of the mountains. 248. Why is moist air lighter than dry air? Because the presence of vapor in a measure expands the air. 3 50 METEOROLOGY. 249. How is the milder climate of the vicinity of lakes and rivers which freeze in winter accounted for? By the evolution of the latent heat of water during the process of freezing. IC'___ ent:__I__' __ El A OCEANIC CURRENTS. METEOROLOGY. 51 250. Why does the melting of large bodies of snow have the effect of chilling the air? Because, as before explained, much of the heat of the air is consumed in melting the ice. 251. Is there any thing analogous to the motion of the winds in the waters of the ocean? The waters of the ocean are, like the winds, in constant motion. 252. Describe the course of the currents in the Atlantic Ocean. (The pupil will find the course of these currents represented on the map on the preceding page.) 253. What is the breadth of the Gulf Stream? In the narrows, off the coast of Florida, its breadth is about 32 miles; off Cape Hatteras it is increased to 75 miles. 253*. What is the velocity of the Gulf Stream? Four knots per hour in the " narrows" above mentioned, and three knots in the latitude of Cape Hatteras. 253t. What remarkable peculiarities have the waters of the Gulf Stream? They are warmer by 20~ to 30~ than the waters of the ocean through which they pass, and are of a deep blue color. 253t. To what is their deeper color owing? Probably to their greater saltness, which is a consequence of the more rapid evaporation in the tropical regions from'which the Gulf Stream is supplied. 52 STEAM. CHAPTER V. STEAM. 254. How is it proved that the air has weight? By the fact that a bottle full of air weighs more than one from which the air has been pumped out. 255. How much weight has the air? The air above every square inch of the earth's surface, or of objects near it, weighs about fifteen pounds. 256. How does the air at the surface of the earth differ from that in the upper regions of the atmosphere? It is much more compact and dense, on account of the great weight of the air above it. 257. To what may every cubic inch of such air be likened in this respect? To a cubic inch of compressed India rubber, which constantly strives to regain its original dimensions. 258. Why does not this great pressure, exerted from all sides, crush our bodies? Because our lungs and all the cavities of the body are full of compressed air, which presses outward with just as much force. 259. How is it that our limbs ar6 free to move against such pressure? Because the pressure helps us as much in one direction as it retards us in another. PRESSURE OF THE ATMOSPHERE. 53 260. What is the consequence? That we are not even aware of its existence except by reflection on the subject. 261. To what is the case parallel? To that of a fish, which is not embarrassed by the pressure of the water, because it presses equally in all directions. 262. If a tumbler is filled with water, and E — then lifted to the surface, as represented in the figure, why does not the water run out?' __ The pressure of the atmosphere on the \ surface of the water outside, keeps the water forced up within the tumbler. 263. How much water would the pressure of the air keep sustained in a long tube? A column 34 feet in height. 264. How much mercury? A column of 30 inches. 265. What is the reason of this great difference? It is because the mercury is much heavier than water. 266. What is BOILING? The production of vapor with ebullition, or the formation of bubbles below the surface of a liquid. 267. At what temperature does it occur? At a fixed temperature for every liquid. Water boils at 212~ F., alcohol at 1730, and ether at 960. 268. How much steam does a cubic inch of water produce? 1,696 cubic inches. 54 STEAM. 269. How much will a drop of water, one tenth of an inch in diameter, pro- S E duce? Enough to fill a hollow sphere of the diameter of one and a fifth 0t0 inches. 270. Is steam produced under ordinary circumstances hotter than boiling water? It is not. 271. What has then become of all the heat consumed in convertina boilina water into steam? It has become latent in the steam. 272. How much has thus become latent? Enough to heat the water (if it could be kept water) 1,000 degrees higher, or to make it red hot. 273. How is this fact commonly expressed? This fact is commonly expressed by saying that steam contains 1,000 degrees of latent heat. 274. What change, already mentioned, must happen to water in order that a bubble of steam may form? A small quantity of water must expand into a comparatively large quantity of steam to form it. 275. What resists this expansion? The atmosphere presses upon the surface of the water, and acts through the water to prevent the expansion. 276. To what may water striving to burst into steam be likened? To a piece of India rubber under a mass of iron, which BOILING. 55 can not expand owing to the weight of the mass above it. 277. What change may we imagine in the India rubber which would enable it to expand and lift the iron? An increase of its elasticity. 278. What change is requisite in the water striving to become steam before the bubble of steam can form? Its elasticity must be increased. 279. What has this effect? Heat increases the elasticity or tendency of the particles to separate themselves from each other, and become steam. 280. What happens when this tendency is sufficiently increased by heat? The particles fly apart in spite of the pressure, and successive bubbles are formed. 281. What pressure must steam have before it can overcome the pressure of the air? A pressure slightly superior to that of the air. 282. Why will water boil with less heat on mountains? Because, at great altitudes, there is less pressure of the atmosphere to prevent the expansion of water into steam. 283. What elevation above the level of the sea is required to make a difference of one degree? Every 550 feet makes a difference of one degree. 284. If water boils at 200 degrees on a mountain summit, how high may the mountain be inferred to be?* 12 times 550, or 6,600 feet. * Let the teacher ask other similar questions. 56 STEA. 285. What simple apparatus is then required to take the height of a mountain? A tea kettle and a thermometer. Very delicate apparatus is required to give exact results. 286. Why is greater heat required to boil water in deep caverns? Because at great depths there is greater pressure of the atmosphere to prevent the expansion of steam into water. 287. What depth below the level of the sea is required to make a difference of one degree? Every 550 feet, as before, makes a difference of one degree. 288. If water boils at 214 degrees at the bottom of a cavern, how deep may the cavern be inferred to be? Twice 550, or 1,100 feet. 289. How may the boiling point of water be artificially changed? By conducting the boiling in a closed vessel, having first pumped out the air, and thus diminished the pressure. 290. What practical application is made of this fact in the arts? Sugar syrup is boiled down in this way to avoid the discoloration produced by the greater heat of ordinary boiling. 291. How may water be made to boil by the application of cold? If a tube or flask is corked while boiling is going on, cold water poured on it will renew the boiling. 292. Why? Because cold water condenses the steam, and there is then no pressure of either air or steam to prevent boiling. STEAM BOILERS. 57 293. What causes the`"singing of the tea kettle" before it boils? It is owing to the vibration caused by the collapse of the first steam bubbles as they come into the cold water above. 294. What does the figure represent? An ordinary steam boiler, such as is usually connected with a steam engine. 295. What kind of steam is commonly employed to move steam engines? Steam of great density and pressure. 296. How is such steam formed? By keeping the boiler closed, so that new steam must crowd into that which was formed before. 297. What happens if the steam acquires too great density and pressure? It bursts the boiler. 298. How is this guarded against? By making a hole in the upper part of the boiler, and providing it with a loaded valve, which the steam will open when it acquires too great pressure. 299. How may a boiler be arranged so that it can be told by the eye if the pressure is too great? By connecting a bent tube filled with mercury with the upper part of the boiler, as in the figure. As the pressure increases, the mercury rises higher and higher in the outer arm of the tube. 3* 58 STEAM. 300. What does the figure represent? The cylinder of a steam engine, with a close fitting piston, and pipes leading into the cylinder above and below. 301. What is the office of the PISTON? It is moved up and down by the steam, and itself moves the rest of the machinery. 302. How does the steam move the piston? When the lower pipe from the boiler is opened, the dense steaih suddenly expands into the cylinder and lifts the piston. When the upper pipe is opened, it crowds the piston down again. 303. When new steam comes in one side of the piston, what becomes of the old steam on the other side? In one kind of engine a valve opens at the right time and lets it off into the air. 304. What is the objection to this'method? The old steam has to be crowded out against the pressure of the air, and considerable force is consumed in getting rid of it. 305. Why is such an engine called a HIGH PRESSURE ENGINE? Because steam of higher density and pressure has to be employed, in order to have force enough to spare to crowd out the old steam. 306. What other method is employed to get rid of the old steam? In the low pressure engine a valve opening at the right time lets it off into a side vessel, called the condenser. STEAM ENGINES. 59 307. What happens to it in the condenser? The cold water of the condenser swallows it up very rapidly, and thus produces a sudden vacuum, or empty space, in the cylinder. 308. How are all the valves of the boiler, cylinder, and condenser opened and closed just at the right time? The motion of the piston is communicated to rods, which accomplish this object. 309. Give examples of high and low pressure engines. The engines used on locomotives are high pressurethose used on ocean and river steamers are, for the most part, low pressure engines. 310. What advantage has the high pressure engine for certain uses? 1No condenser being required, it is more compact, and occupies less room. 311. How are houses heated by steam? Iron pipes are made to convey steam through the various apartments. The steam gives out its latent heat, through iron pipes, to the air. Being thus converted into w7ater, it runs back to the boiler, to be re-heated and start again on its journey. 312. What is DISTILLATION? Distillation consists in converting a liquid into vapor, and re-condensing the vapor. 313. How is it illustrated in the figure? Water is supposed to be boiled in the test tube, and 60 STEAM. the steam again condensed in the cooler phial. 314. What is the object of distil- ~ lation? It is to separate the liquid distilled from other substances with which it may be mixed. Thus alcohol, which is made from potatoes or grain by fermentation, is distilled off from the refuse of these materials. ELECTRICITY. 61 CHAPTER VI. ELECTRICITY. 315. WHAT is the NATURAL MAGNET or LOADSTONE? A mineral (oxide of iron) which has the property of attracting metallic iron. 316. What other remarkable property has it? If suspended, the same part of it will always turn north, and the opposite part south. 317. What is the MAGNETIC NEEDLE? A slender steel bar converted into a mnagnet, and balanced on a pivot. 318. What is its important property? When balanced, it turns till one end points north and the other south. 319. What action have different magnets on each other? The north and south poles of different magnets attract each other, while poles of the same name repel. 320. What is said of the earth as respects magnetism? The earth itself may be regarded as an enormous magnet. 321. Why? Because it influences the magnetic needle precisely as a large magnet would do. 62 ELECTRICITY. 322. How is a piece of iron affected when approached to a mag. net? It is itself converted into a magnet. 323. What polarity does the end approached to the south pole of the magnet acquire? North polarity; while the other end at the same time acquires south polarity. i 324. What results in consequence? Attraction between the magnet and the iron. 325. How may this force of attraction be illustrated? A key may in this manner be suspended from a magnet. 326. What bodies besides iron are attracted by magnets? The metal nickel, oxygen gas, and some other bodies, in a less degree. 327. What bodies are repelled? All bodies which are not attracted are in a slight degree repelled. 328. If glass be rubbed with silk, what property does it acquire? It will attract filaments of the silk, as a magnet attracts iron, and will yield a spark to the knuckle. 329. What name is given to these phenomena? They are called electrical. 330. Mention a theory of electricity designed to explain this and similar phenomena. According to one view, both materials contain two electrical fluids in a state of combination, which are so sepa ELECTRICITY. 63 rated by friction that the positive fluid of both accumulates in the glass, and the negative in the silk. 331. What relation do the two bodies possessing different electricities now sustain to each other? That of the opposite poles of two magnets. 332. What happens in consequence? They attract each other. 333. What occurs when two bodies, similarly electrified, are brought near to each other? They repel. 334. How may the human body be readily electrified? - By rapid gliding over a carpet in dry, cold weather. 335. How is it shown to be electrified? By the fact that a gas jet may be lighted by a spark from the knuckle. 336. How is electricity CONDUCTED? It is conducted, like heat, by metals, and other substances in a less degree. Glass and many other materials are non-conductors. 337. By what other means than friction may electricity be excited? By the unequal action of an acid on two metals connected out of the acid, either directly or by a metallic wire. 338. What is such an apparatus called? It is the simplest form of the galvanic battery. 339. What metals and acid are commonly employed in the battery? Zinc, copper, and sulphuric acid. 64 ELECTRICITY. 340. What other metals may be employed? Any two metals, if one of them has the property of being acted on by the acid. 341. How is the current of electricity supposed to flow? From the zinc to the copper within the acid, and in the opposite direction above. 342. When is the circuit said to BE COMPLETED? When the metals are connected as above described, and the acid in contact with the other separated ends. Removal of the acid, or disconnection of the metals above, breaks the circuit, and the current ceases to flow. 343. What are the ELECTRODES? Metallic wires terminating the metallic strips, and sometimes enlarged at the end. 344. How are the two electrodes distinguished? That connected with the copper is the positive, and the one attached to the zinc the negative electrode. 345. How is the galvanic battery made to produce heat? By simply connecting the electrodes while the battery is in action. 346. How intense a heat is thus produced? A heat sufficient to melt platinum, and convert gold and charcoal into vapor. 347. How is the electric light produced? By slightly separating the electrodes, having previously terminated them with charcoal points. 348. Is the light owing to the combustion of the charcoal? It is not; it is analogous to the electric spark pro ELECTRICITY. 65 duced when the knuckle is brought near an excited glass rod. 349. What occurs when the electrodes are dipped into water? If the electrodes are placed near each other in water, while the battery is in c A 1 action, the water is separated into its constituent gases, oxygen and hydrogen. 7 350. Where does the oxygen. collect? The oxygen collects at the positive elec- i trode, and then rises in bubbles. 351. Why at the positive electrode? Because it is itself negative; oxygen and most non-metallic substances are negative. 352. Where does the hydrogen collect? At the negative pole. 353. Why? Because it is itself positive; hydrogen, the metals, and the oxides are all positive. 354. How may the oxygen and hydrogen produced in the above experiment be collected? By bending up the electrodes under a small glass tube. I 355. How may they be SEPARATELY collected? By introducing the electrodes into separate tubes in a similar manner. 356. How are the gases known to be oxygen and hydrogen? By tests which are given in the section on these gases. 66 ELECTRICITY. 357. What happens if the electrodes are dipped into a solution of silver? The silver, being itself positive, collects on the negative electrode 358. What has thus been accomplished? The electrode has been silvered. If a copper spoon or other object is attached to the negative electrode before immersion, this object also becomes itself silvered. 359. What occurs if a solution of gold is substituted for one of silver in the above experiment? The object attached to the negative electrode is then gilded, instead of being silvered. A coating of other metals may be deposited by the same means. 360. What use is made of the process in the arts? Gold and silver plated ware, equal in appearance to solid gold and silver, is thus prepared. 361. How is a coin or other object copied by galvanic means? An impression of it is first taken in wax or some other plastic material, and copper is then deposited in the mold, as in the process for electro-plating. 362. What preparation of the mold is essential? It must be covered with black lead, to make it a conductor of electricity from the wire, or the metal will not deposit. 363. What other means are sometimes employed for producing the mold? The mold itself may be made directly upon the coin, by~ the process for electro-plating. ELECTRICITY. 67 364. What uses are made of this process in the arts? It is used for obtaining copies of pages of type, woodcuts, coins, and engraved copper plates. 365. How perfect are the copper plates thus obtained? So perfect that they can not be distinguished from the original. 366. What is the advantage of the process? It saves the great labor of engraving other plates. 367. What is the advantage of the process in the case of type? A copy being once obtained of the whole page, the printer can use his individual types to set up other matter. 368. How is this end accomplished in another way? By taking what is called a stereotype copy. This consists in making a mold of plaster (361), and then taking a cast from it in ordinary type metal. 369. What is the most common form of the galvanic battery? Smees' battery, represented in the figure, is the most common. It consists of two connected zinc plates, with a silver plate between them. Wires to serve as Hit l electrodes are screwed fast to the plates. 370. Can all the effects before mentioned be produced& byr a single set of plates? They can not; several sets are brought to bear upon the same electrodes. 371. Mention another interesting property of the galvanic current. A coil of wire, uniting the electrodes, through which 13 68 ELECTRICITY. the current is passing, possesses magnetic properties as long as the battery is in action. 372. Mention some other properties. Like a magnet, the coil attracts iron and other magnets. 373. What happens if a bar of soft iron is brought into such a coil? It remains suspended without contact or visible support as long as the battery is kept in action. 374. What fable is thus realized by modern science? The fable of Mohammed's coffin, which is said to have been miraculously suspended in the air. 375. What properties does the suspended bar possess while it remains in the coil? The properties of a magnet. 376. What is such a magnet called? An electro-magnet. 377. How are electro-magnets commonly made? By winding a bar of soft iron, of the shape of a horse shoe, with wire, covered with silk or cotton, and then connecting the ends of the wire with the battery. 378. How is their force as magnets shown? By bringing a mass of iron in the vicinity of the poles. 379. How large a mass of iron has thus been lifted? A mass weighing a ton, or even more. 380. What occurs if the acid is removed from the battery, or the connection with the battery is broken? The mass immediately falls. ELECTRICITY. 69 381. How may electrical currents be the cause of the magnetism of the earth? The circulation of electrical currents around it are supposed to convert the earth into a s,- s great magnet, as the circulation of the current through a coil i-n- >s parts magnetic properties to soft l_ _ iron. 382. Do such currents exist? Such currents are supposed to be excited and kept in motion by the sun heating in turn successive portions of the earth's surface. 383. What are the essential parts of a magnetic telegraph? A galvanic battery connected by wires with an electroilagnet in a distant place. 384. When the operator connects the wire with the battery, what happens in the distant place? The soft iron of the distant electro-magnet becomes magnetic, and lifts up the armature. 385. What happens when the operator disconnects the wire from the battery? The distant electro-magnet lets fall its armature. 386. How may these motions be used to spell out words? One lift may indicate the letter A, two lifts the letter B, and so on. Or the armature may be made to move a lever, and prick each time it rises a strip of paper above it. These pin holes on the paper, some near and some 70 ELECTRICITY. far apart, are interpreted according to a previous agreement. 387. What other use is made of the telegraph, besides that of transmitting intelligence to distant places? It is employed in cities to communicate alarms of fire, and to set in motion apparatus for ringing the alarm bells. 388. What use is made of it in France? In Marseilles a single clock, with wires proceeding from it, is made to indicate the time on numerous dials in the street lamps of the city. 389. What effect has the galvanic current on.the animal body? An inconstant current, produced by alternately breaking and completing the circuit, produces convulsive action of the muscles. 390. How was galvanism discovered? An Italian, named Galvani, after skinning some frogs to make broth for his sick wife, hung them by copper hooks from the iron balcony of his window. The legs of the dead frogs began to twitch, and this was the beginning of the science of galvanism. 391. What was the occasion of their twitching? The copper hook, the iron railing, and the moist muscle by accident formed a galvanic battery; the wind blowing the. legs about alternately broke and completed the circuit, and the convulsive action of the muscles was thus produced. METALLOIDS. 71 CHIAPTER VII. METALLOIDS. OXYGEN. 392. WHAT is OXYGEN? Oxygen is a transparent and colorless gas, a little heavier than the atmosphere. 393. How abundant is it? It is much the most abundant substance in nature. Olie fourth of the air, one ninth of the ocean, and probably half of the solid earth is oxygen. 394. How is it prepared? By heating the rusts or oxides of certain metals. 395. Explain the figure. The figure represents oxide of mercury heated in a tube t expel its oxygen. 396. What remarkable property has the oxygen thus obtained? - Metals will burn in it. 397. How is the experiment made? By lighting a bit of match attached to iron wire, and then placing it in the phial. 72 CHEMISTRY. 398. What happens to the iron? It takes fire and burns with brilliant scintillations. 399. What becomes of the oxygen? It combines with the iron, forming an oxide of iron, and falls in molten globules to the bottom of the phial. 400. What happens to a newly extinguished taper, held in a phial of oxygen? If a little spark remains on the wick, it is re-lighted. 401. What happens to ignited phosphorus under the same circumstances? It burns with a light so brilliant that the eye can scarcely bear it. 402. What becomes of the phosphorus and oxygen? They unite to form white fumes of phosphoric acid, which remain in the phial. 403. What happens to ignited charcoal in oxygen? It burns with extreme brilliancy. 404. What becomes of the charcoal and oxygen in this experiment? They unite to form gaseous carbonic acid. 405. What happens to charcoal when it burns in ordinary air? The same thing as if it were burned in pure oxygen. 406. Why is the combustion less brilliant? Because but one fifth of the air is oxygen. CHLORINE. 73 407. What happens to hard coal, wood, and all combustible substances, when they burn in the air? All combine with its oxygen, and pass off as invisible gases and vapors. 408. What happens to wood and leaves when they decay and disappear? Precisely the same thing. 409. What may such decay be therefore called? A slow combustion. 410. What similar change occurs in the blood? Part of it undergoes a similar slow combustion. 411. What supports this combustion? The oxygen taken into the lungs. 412. What becomes of the invisible gases and vapors which are formed in the combustion? They are breathed out from the lungs. 413. What happens finally to the invisible gases and vapors which are produced in combustion and respiration? They are converted by living plants into new wood, leaves, flowers, and fruit. 414. What office has the oxygen of the air thus served? That of a carrier of oxygen. CHLORINE. 415. What is CHLORINE? Chlorine is a yellowish green gas of peculiar odor, about two and a half times as heavy as the air. 4 74' CHEMISTRY. 416. What common substance contains it? Common salt. 417. Where does chlorine, then, exist in great abundance? In salt mines and the ocean. 418. How is it most readily made? By pouring sulphuric acid on "bleaching powder." 419. What is BLEACHING POWDER? Lime which has been made to absorb chlorine. 420. What is the use of the acid in making chlorine? It combines with the lime, and sets the chlorine at liberty. 421. Mention some properties of chlorine. It combines eagerly with metals, and bleaches vegetable colors. 422. Illustrate its combination with metals. Powdered antimony sprinkled into this gas takes fire immediately. 423. What becomes of the antimor-, and chlorine? They unite to form chloride of antimony. 424. What occurs if the metal sodium is placed in chlorine? The two combine to form common sait. 425. What happens when a rag moistened with camphene is immersed in a phial of chlorine? It is immediately inflamed, with the production of dense black smoke. 426. Why? Camphor is composed of hydrogen and carbon; the CHLORINE. 75 former unites with the chlorine and produces the flame, while the latter separates as smoke. 427. How may cloth be bleached by chlorine? By wetting it and hanging it in the gas. 428. Why is it necessary to wet it? Water contains oxygen, which is required in the process. 429. Why is oxygen required? It is required to burn up the coloring matter of the cloth. 430. How can the oxygen act thus while imprisoned as part of the water? It can not; the chlorine sets it at liberty. 431. How does it do this? By combining with the hydrogen, which is the other constituent of the water. 432. What does the oxygen do when set at liberty? It gradually burns up the coloring matter of the cloth. 433. Why is chlorine used as a disinfectant? It destroys noxious vapors in the air. 434. To what may its particles be likened in this case? To birds of prey, that fly forth to seize the impurities of the atmosphere. 435. In what form is it used for this purpose? As chloride of lime, which allows the chlorine to escape gradually into the air. 436. How may its escape be hastened? By the addition of an acid. 76 CHEMISTRY. IODINE) BROMINE) AND FLUORINE. 437. What is IODINE? Iodine is a bluish black solid, made from the ashes of sea weeds. 438. To what is it analogous? It is quite analogous in its properties to chlorine. 439. What beautiful experiment may be made with it? A single grain of iodine heated in a phial, will fill its interior with beautiful violet vapors. 440. What are its uses? It is used as a medicine, and in the preparation of daguerreotype plates. 441. What is BROMINE? Bromine is a dense reddish brown fluid, made from the waters of certain mineral springs. 442. To what is it analogous? To chlorine and iodine. 443. What is FLUORINE? Fluorine is a yellowish brown gas, of odor somewhat similar to that of chlorine. 444. From what is it made? From the beautiful mineral called "fluor spar." 445. To what is it analogous? Fluorine, also, is analogous to chlorine. 446. What may the above group of four elements be called? The chlorine family. SULPIHUR.. SULPHUR. 447. Where is SULPHUR found? Principally in volcanic regions. In Sicily it is found in beautiful crystals. 448. What minerals contain it? Sulp/urets and sulphates. 449. Mention one of the sulphurets. Sulphuret of iron, or "fool's gold." 450. Mention a SULPHATE. Gypsum, or "plaster of Paris." 451. How may sulphur be made to burn with great brilliancy? By kindling it in oxygen. 452. How may sulphur be made soft and waxy? By high heating and sudden cooling in water. As it falls into the water it takes the form of elastic threads, which may afterward be molded together. 453. For what is such sulphur used? For taking impressions of seals and medallions. It gradually resumes its original hardness. 454. What colors may be bleached by sulphur? Vapors of burning sulphur bleach many vegetable colors. 455. What are these vapors? They are sulphurous acid. 456. What is the principal application made of this property? To bleach straw. 78 CHEMISTRY. 457. May the colors thus bleached be restored? They may be restored by driving out the sulphurous acid. 458. How may this be done? By dipping in dilute oil of vitriol. 459. Can a color bleached by chlorine be thus restored? It can not. 460. For what reason? The coloring matter is destroyed and removed by chlorine, while it is only changed by sulphurous acid. SULPHURIC ACID. 461. What is SULPHURIC ACID? Sulphuric acid is a colorless oily fluid, of intensely acid taste, known in commerce as oil of vitriol. 462. Of what is it composed? Of sulphur, oxygen, and water. 463. How is it prepared? From fumes of burning sulphur, which consist of sulphurous acid. 464. How? By giving the latter more oxygen. 465. What is used for this purpose? Vapor of nitric acid. SfiULPHUR. 79 466. Where are the materials brought together? In large leaden - chainbers. 467. Why is steam inE= admitted into the chambers? Because a certain portion of water is essential in the process. 468. Why are leaden chambers employed? Because most other metals would be corroded by the acids. 469. How is the acid of the chambers concentrated? By boiling it down in vessels of platinum. 470. Why is platinum employed? Because lead and all other metals, excepting gold, would be dissolved by the strong acid. 471. Is sulphuric acid an important product? Millions of pounds are annually employed in the arts. 472. How does sulphuric acid compare in strength with the other acids? It is the strongest of all acids. 473. How is this proved? By the fact that it will drive out other acids from their compounds, as vinegar drives out carbonic acid from chalk. 474. Are not other acids superior in some cases? TJley are. 80 CHESTRuY. 475. Give an example. Nitric acid will dissolve silver and copper, while cold sulphuric acid will not. 476. How does dilute sulphuric acid act on metals? It dissolves most metals. 477. Does it, strictly speaking, dissolve the metals, or their oxides? Their oxides. 478. How are the metals converted into oxides before they dissolve? By seizing oxygen from the water which is present. 479. What is the occasion of the effervescence which accompanies the solution? It is due to the hydrogen of the water escaping after it has been robbed of its oxygen. 480. Mention an important use of sulphuric acid. One important use is to set nitric acid free from the prison in which nature has confined it. 481. In what material is it imprisoned? In ordinary nitre or saltpetre, and some other salts. 482. Mention other important uses of sulphuric acid. It is essential in the preparation of muriatic acid, soda, soap, certain kinds of candles, and certain colors for dyers. These uses are hereafter explained. SULPHUROUS ACID. 483. What is SULPHUROUS ACID? It is a colorless gas, having the smell of a burning match. NrrROGEN. 81 484. Of what is it composed? Of sulphur. The proportion of oxygen is smaller than in sulphuric acid. 485. How is sulphurous acid made? By burning sulphur in air. 486. Give another method. By heating strong sulphuric acid with metals. 487. What effect has the metal? It removes part of the oxygen from the sulphuric acid and. converts it into sulphurous acid. 488. Explain the figure. The figure represents the above X i, process. The gaseous sulphurous acid, as fast as formed, passes through the pipe stems into the phial.. " NITROGEN. 489. What is NITROGEN? Nitrogen is a transparent gas, without taste or odor. 490. Where is it found? About four fifths of the air we breathe is nitrogen. 491. How is it made? By removing the oxygen from ordinary air. 492. How is this best accomplished? By burning phosphorus under an inverted phial. 4* 82 CHEMISTRY. 493. Explain the figure. The figure illustrates the above processes. Water is supplied to take the place of the oxygen as fast as it is removed. 494. In what sense is the oxygen removed? It is removed from the atmosphere of. the phial, and converted, with the phosphorous, into solid phosphoric acid. This dissolves in the water, while the nitrogen remains as a gas. 495. What effect has nitrogen on flame? It extinguishes it. 496. Why is the flame extinguished in this case? For want of oxygen. 497. What are the principal constituents of the atmosphere? Nitrogen and oxygen. 498. In what proportion do they exist in the air? About one fifth oxygen and four fifths nitrogen. 499. What is the principal office of the nitrogen? To dilute the oxygen. 500. What would be the effect if the air were pure oxygen? The slow combustion of certain constituents of the blood would be changed into a rapid one. Fever and death would be the consequence. 501. What other substances exist in the air besides oxygen and nitrogen? Carbonic acid and ammonia. NITROGEN. 83 502. In what proportion? About -'ooth of carbonic acid and uoo-!o0oooth of ammonia. 503. How are such small quantities ascertained? By drawing a large and known i quantity of air through a tube containing materials to absorb the ammonia and carbonic acid, and to retain them while they are weighed. 504. How are the results then calculated? By comparing the weight of the ammonia and carbonic acid obtained with that of the air from which they were extracted. NITRIC ACID. 505. What is NITRIC ACID? Nitric acid is a thin, colorless, and intensely acid fluid. 506. Of what is it composed? Of nitrogen and oxygen. A certain portion of water is also essential to its action.. 507. Describe the figure. i The figure represents the pro- X cess of preparing nitric acid, by heating nitre with sulphuric acid. 84 CHEMISTRY. 508. What is the action of the latter? It takes possession of the potassa in the nitre, and drives out its nitric acid. 509. How does nitric acid act on metals? It attacks them with energy, giving off red fumes during the process. 510. How does it change them? It gives them part of its own oxygen, and converts them into oxides. 511. What are the red fumes evolved in the process? The remnant of the nitric acid, which has been deprived of part of its oxygen. 512. How does the acid act on the oxides which it produces? A new portion of acid dissolves them as fast as they are formed. 513, Are there no exceptions to this rule? There are. Tin and antimony are converted into oxides, but not dissolved. 514. Mention other experiments with nitric acid. f"" Phosphorus or spirits of turpentine thrown on the strong acid is inflamed. PHOSPHOSPHORUS. 515. What is PHOSPORUHS? Phosphorus is a wax-like and nearly colorless solid. 516. What is its most striking property? It is very readily ignited by heat or friction. PHOSPHORUS. 85 517. From what is it made? From bones. 518. What is the chemical composition of bones? They are principally phosphate of lime and gelatine. 519. How is the gelatine removed in preparing phosphorus? It is burned out by fire. 520. How are the lime and phosphoric acid separated? By sulphuric acid and water. 521. What is their action? The acid sets the phosphoric acid at liberty, and the water dissolves it. 522. How is phosphorus made from the phos- __ phoric acid thus obtained? By heating it in an earthen retort with carbon. 523. What is the action of the carbon? It combines with the oxygen of the acid, and passes off as a gas. 524. What becomes of the phosphorus? It also passes off as vapor. 525. How is it made solid? By passing the vapors into water. 526. How may a harmless fire be produced? By covering any object with a solution of phosphorus in ether. 527. What is the cause of the luminous appearance? A very slow combustion of the phosphorus. 86 CHEMISTRY. 528. What does it resemble? The phosphorescence which is observed when a friction match is rubbed faintly in a dark room. 529. How may combustion under water be effected? By pouring oil of vitriol through a tube on phosphorus and chlorate of potash, contained in a, wine glass. 530. What is the agency of the oil of vitriol? To set the chloric acid at liberty. 531. What effect has the free chloric acid? It readily supplies oxygen to burn the phosphorus. 532. What are the uses of phosphorus? Its principal use is in the preparation of friction matches. ARSENIC. 533. What is ARSENIC? It is a gray substance of metallic lustre. 534. Is it a metal? It is commonly ranked as a metal, but in its compounds more nearly resembles non-metallic substances. 535. How is it made? It is made from arsenious acid, by heating with carbon. 536. Explain the figure. The figure illustrates the process. The mixture being heated, the arsenic rises in vapor, and forms a crust on the cool part of the tube. ARSENIC. 87 537. What is ARSENIOUS ACID? It is a white, insoluble substance, commonly known as " ratsbane." 538. Of what is it composed? Of arsenic and oxygen. 539. How is it made? By heating arsenic, or minerals containing it, in the air. 540. What is its most important property? It is extremely poisonous. 541. How is it detected in cases of poisoning? It can be extracted from the contents of the stomach after death. 542. How is the solution thus made known to contain arsenic? Hydrogen is evolved from the solution (610). This gas carries the metal off with it. On holding a white saucer in the flame of tile compound gas, the metal leaves a stain of a steel gray color. 543. How delicate is this test? The three hundredth part of a grain of arsenic may thus be readily detected in a mixture of various substances. 544. What is employed as an antidote to arsenic? Precipitated peroxide of iron (871). ]Milk, sugar, and white of eggs are also given with advantage. 545. What singular practice may be mentioned in connection with this subject? The peasantry of a certain part of Austria are said to eat arsenic in small quantities. 88 CIIEMISTRY. 546. What is its effect? It is said to give increased capacity to endure fatigue. If taken in very minute quantities, its poisonous effects are long delayed. CARBON. 547. Mention different forms of carbon. Charcoal, anthracite coal, plumbago, and the diamond are all forms of carbon. 548. What is PLUMBAGO? It is a gray substance, of metallic lustre, commonly known as "black lead." 549. What does the last figure represent? The common crystalline form of the diamond. 550. How are all the above-named substances known to be carbon? By the fact that they all _produce carbonic acid when they are burned. 551. What further evidence may be given? The carbonic acid produced from any one of l |' i them can be made to yield black carbon. 552. How is CHARCOAL made? By burning heaps of wood covered with earth and sod. 553. What is the object of covering the heap? To prevent complete combustion. cARBON. 89 554. What change takes place in the wood? A large part of its carbon remains, while the other constituents are burned or expelled. 555. How may the production of charcoal be illustrated? By heating a bit of wood in a test tube. 556. Why is this an analogous experiment? Because the access of fresh air during the process is prevented. 557. What is LAMPBLACK? Carbon in fine particles deposited from the smoke of burning rosin. 558. How is BONE-BLACK prepared? By heating bones in closed vessels. 559. Of what does it consist? Of the earth of the bones, and of charcoal produced from their gelatine. 560. What is said of the purifying properties of charcoal? Tainted meat and musty grain mixed with it become sweet. 561. Illustrate its preservative properties. Meats and vegetables keep best if packed in charcoal. Water keeps best in charred vessels. Charred posts are most durable. 562. Illustrate its decolorizing effects. The decolorizing effects of charcoal may be illustrated by pouring water colored with ink through a paper filter 90 CHEMISTRY. filled with animal charcoal. The water comes colorless through the filter. Sugar syrups are whitened by this means. 563. What effect has carbon on ores? o It deprives most ores of their oxygen and con- 0 verts them into metals. CARBONIC ACID. 564. What is CARBONIC ACID? Carbonic acid is a colorless gas, without much taste or smell, and about one and a half times as heavy as the air. 565. Where is it found? It is produced by breathing and combustion, and is found in many mineral waters. 566. How is it made? By burning charcoal in oxygen or air. 567. Mention a second method. By holding a lighted candle as long as it will burn in a bottle of ordinary air. 568. Mention a third method. By pouring vinegar on to chalk in a phial. The carbonic acid drives out the air and fills the vessel. 569. What effect has carbonic acid on a lighted candle? It extinguishes it. CARBON. 91 570. Why? For lack of the free oxygen which is essential to combustion. 571. How may this experiment be varied? The gas may be poured into a second phial containing the candle. 572. To what is this experiment analogous? To pouring water on a lighted candle. 573. Is any thing seen to flow in this experiment? Nothing. The gas is invisible, like the air. 574. What effect has carbonic acid on animals? It is harmless in the stomach, but poisonous in the lungs. 575. Mention two ways in which it acts in the lungs. Negatively, to exclude the air, and positively, as a poison. 576. Are very small quantities injurious in the lungs? They are not. The air always contains small quantities. 577. What is said of the Grotto del Cane? It is a grotto in Italy, the lower portions of which are filled with carbonic acid. A man is safe in it, but a dog, whose head is nearer the ground, is immediately suffocated. 578. What is said of carbonic acid in wells? It often issues from fissures in the earth and collects in wells. 14 92 CHEMISTRY. 579. What danger does it occasion? Danger of suffocation to workmen engaged in cleaning them. 580. How may its presence be detected? If present, it extinguishes a candle lowered into the well. 581. How may it be removed? By repeatedly introducing palls of newly heated charcoal into the well, the gas may be absorbed and removed. 582. What is said of fires unconnected with chimneys? They poison the air with carbonic acid and carbonic oxide. 583. How is carbonic acid solidified? By subjecting the gas to great pressure and cold in a strong vessel it is converted into a solid resembling snow. CARBONIC OXIDE. 584. What is CARBONIC OXIDE? It is a colorless gas, burning with a blue flame. 585. Where is carbonic oxide often produced? In ordinary grates where coal is burned. 586. What is produced in the lower part of the grate? Below, where air is abundant, the coal burns and produces carbonic acid. SILICON AND BORON. 93 587. How is it converted into carbonic oxide? The ignited coal above robs it of part of its oxygen. 588. Why? Because carbon has an affinity for oxygen, and in this part of the grate it finds no free oxygen with which to combine. 589. What happens to the carbonic oxide thus produced? At the top of the fire, where air is plenty, it burns with a blue flame and is re-converted again into carbonic acid. 590. What effect has carbonic oxide on ores? It takes the oxygen from many ores and converts them into metals, 591. What change does the carbonic oxide itself experience? It is at the same time itself converted into carbonic acid. SILICON AND BORON. 592. What is SILICON? It is a dark gray substance of metallic lustre. It is one of the principal constituents of quartz. 593. What is SILICIC ACID? It is a compound of silicon with oxygen. 594. Mention some forms of silicon. Quartz or rock crystal, sea sand, opal, jasper, agate, cornelian, and chalcedony. 94 CHEBMISTRY. 595. What are petrifactions? Copies of vegetable matter in stone. 596. How are they formed? As the vegetable matter decays, particles of silicon or other'mineral matter take one by one the place of the departing atoms. 597. How perfect are these copies? So perfect that the rings of the wood and the structure of the bark are perfectly distinct. 598. What is BORON? Boron is a brown powder, never seen except in the chemist's laboratory. 599. What is BORACIC ACID? Boracic acid is a compound of boron with oxygen. 600. What is its principal compound? Borax or borate of soda. 601. Where is boracic acid found? It forms part of the volcanic vapors which issue from the earth in Tuscany. HYDROGEN. 602. What is HYDROGEN? Hydrogen is a colorless gas, about one fifteenth as heavy as the air. 603. Where is it found? One ninth part of the ocean and of all water in existence is hydrogen. HYDROGEN. 95 604. How is it prepared? From water. 605. By what means? By using a metal to combine with the oxygen of the water and set its hydrogen at liberty. 606. What metal may be used for this purpose? Sodium or potassium. 607. How is the experiment performed? By slipping a piece of the metal under the mouth of an inverted tube or phial, previously filled with water. 608. What then happens? The light metal rises like a cork to the top of the tube and sets the hydrogen at liberty. The gas collects and crowds the water down. 609. What becomes of the metal itself? It combines with the oxygen of the water, forming oxide of sodium or oxide of potassium. 610. What other metals may be used for producing hydrogen from water? Iron or zinc, if an acid is at the same time present. 611. What effect has the acid? It dissolves off the coating of oxide from the metal, and keeps it free to act. 612. Why is no acid necessary in the case of the metal sodium? Water itself will dissolve the oxide of sodium, and thus keep the metal clean. 96 CHEMISTRY. 613. Explain the figure. The materials for making hydrogen are placed in the lower phial, and the. gas collects in the inverted one. 614. How may hydrogen be kindled?? By simply applying a taper at the mouth of the tube from which it is evolved. 615. What is the appearance of its flame? It burns with a faint and scarcely visible flame. 616. What becomes of it when it burns? It unites with the oxygen of the air and forms water. 617. How may this be shown? On holding a cold tumbler over the burning jet, the water condenses and runs down in drops. 618. What property has a mixture of hydrogen and oxy- I / gen? It explodes on being ignited. 619. On what does the explosion depend? On combustion of the hydrogen at the same instant throughout the whole mixture. 620. How is this made possible? By the presence of oxygen at every point. 621. Why does not a phial of hydrogen explode when a jet of it is kindled, as in ~ 618. Because oxygen is present to produce combustion only on the surface of the jet. WATER. 97 622. Mention another form of these experiments for producing an explosion. A tin tube, called the hydrogen gun, is charged with the mixture, stopped with a cork, and then fired as if it were a cannon. 623. What may be substituted for the oxygen in the explosive mixture? Ordinary air. 624. Why is the explosion less violent in this case? Because the air is diluted oxygen. WATER. 625. Of what is water composed? Of oxygen and hydrogen. 626. How is this proved? By separating water into oxygen and hydrogen (349), and also by producing water by the combination of these gases (616). 627. What are the proportions of the two gases in water? Eight parts of oxygen by weight to one of hydrogen. 628. How much are they condensed in uniting? Two thousand cubic inches of the mixed gases make but one cubic inch of water. HYDROCHLORIC ACID. 629. What is HYDROCHLORIC acid? It is a colorless acid, fuming by contact with the air. 5 98 CHEMISTRY. 630. Of what is it composed? Of hydrogen and chlorine. 631. What remarkable property has a mixture of chlorine and hydrogen? The light of the sun will cause it to explode. 632. What is produced in the explosion? The two gases unite to form hydrochloric acid. 633. How is hydrochloric acid commonly made? From common salt, which is a chloride of sodium. 634. How? By putting hydrogen in the place of its sodium. 635. How is this accomplished? By heating with oil of vitriol. 636. What effect has the oil of vitriol? It gives up hydrogen and takes sodium in its place. 637. Into what substance is the oil of vitriol thus changed? Into sulphate of soda. 638. What becomes of the hydrochloric acid? It passes off as vapor. 639. Explain the figure. The figure represents the above process. The acid vapor passes over I into the water, where it is retained. 640. What is thus produced? A solution of muriatic or hydrochloric' acid. 641. What effect has this acid on metals? It dissolves them. HYDROFLUORIC ACID. 99 642. How? The metal takes chlorine from the acid, and then dissolves in the water which is always present. 643. What becomes of the hydrogen? It passes off with effervescence. 644. How is this experiment performed? By simply pouring muriatic acid on zinc or iron. 645. What is AQUA REGIA? A mixture of nitric and muriatic acids. 646. For what is it used? For dissolving gold and platinum, and certain substances which will not dissolve in simple acids. HYDROFLUORIC AND HYDROSULPHIURIC ACIDS. 647. What is HYDROFLUORIC ACID? It is an acid composed of hydrogen and fluorine. 648. How is it made? From fluor spar, just as hydrochloric acid is made from common salt. 649. What remarkable property has this acid?, It dissolves glass. 650. For what is this acid sometimes employed? For etching on glass. 651. How is the glass prepared for the process? It is first covered with wax, and the wax then engraved down to the glass. 100 CHEMISTRY. 652. For what is the acid then used? To corrode the exposed surface in the en- graved lines. 653. What is HYDROSULPHURIC ACID? It is a colorless gas of putrid odor, also known as sulphuretted hydrogen. 654. How is it made? From sulphuret of iron, as hydrochloric acid is made from common salt, and hydrofluoric acid from fluor spar. 655. How is it often produced in nature? In the decay of animal matter, part of its sulphur and hydrogen unite to form this gas. 656. Give an example of such decay. The putrefaction of eggs. 657. What effect has this gas on silver and certain other metals? It blackens them. 658. Why does it blacken silver? Its sulphur unites with the silver and produces black sulphide of silver. 659. What effect has it on paints? It blackens all paints which contain lead. 660. How is the darkening of paints often to be accounted for? By the presence of sulphuretted hydrogen in the air. 661. Why does this gas blacken lead paints? By forming with the lead black sulphide of lead. 662. Are zinc paints discolored by sulphuretted hydrogen? They are not. AMIONIA. 101 663. Why? Because the sulphide of zinc is white. 664. What effect has sulphuretted hydrogen when inhaled? It acts as a poison. 665. How is it often produced in the air? It escapes fiom newly kindled coal fires. AMMONIA. 666. What is AMMONIA? Ammonia is a colorless gas, of pungent smell and alkaline properties (853). 667. Of what is it composed? Of nitrogen and hydrogen. 668. What is its chemical character? It is a base, forming salts with acids. 669. From what is it prepared? From sal ammoniac or muriate of ammonia, in which it exists ready formed. 670. How is it made from this material? By heating it with lime, which combines with the muriatic acid and liberates the ammonia. 671. What other base may be used instead of lime? Any strong base will expel ammonia from its salts. 672. Explain the figure. The figure represents the production of ammonia as above described. The ammonia collects in the upper 102 CHEMISTRY. phial. Gaseous ammonia may also be produced for experiments by heating agua ammonica or hartshorn. 673. Explain the figure. It represents water rising in a jet into a phial of ammonia. 674. To what is this due? Water absorbs ammonia so rapidly as to produce a vacuum. 675. How is AQUA AMMONIi, or "hartshorn," made? By leading ammonia into water. 676. What effect has ammonia on vegetable colors? It restores vegetable blues which have been reddened by acids. 677. What effect has ammonia on acid vapors? It combines with them, producing white fumes. 678. What are the fumes thus produced? Particles of an ammonia salt, formed by the union of the ammonia and acid. 679. Why is this effect produced on waving a bit of paper moistened with mariatic acid in the atmosphere of a stable? Because ammonia is always present in large quantity in such an atmosphere. 680. How is it produced in this case? By the decomposition of animal matter. Part of the nitrogen and hydrogen of the animal matter passes off in decay as ammonia. PHOSPHURETTED HYDROGEN. 103 PIHOSPHURETTED HYDROGEN. 681. What is PHOSPHIUR:ETTED HYDROGEN? Phosphuretted hydrogen is a colorless gas, of a putrid fishy odor. 682. Of what is it composed? Of phosphorus and hydrogen. 683. How is it made? From phosphorus and water. 684. What is the chemical action? Part of the phosphorus combines with hydrogen to form phosphuretted hydrogen, and part with oxygen to form phosphoric acid. 685. What other substance must be present? Potassa, soda, or lime must be present, or the above action does not take place. 686. What remarkable property has this gas? It takes fire as fast as it comes to the air. 687. Explain the figure. The figure represents the preparation and combustion of phosphuretted hydrogen. 688. How are the rings in the figure produced? Every bubble of the gas, as it - burns, bursts into a beautiful ring of white smoke. 689. Of what does this smoke consist? Of particles of phosphoric acid. 104 CHEMISTRY. 690. How is this formed? By the combination of the phosphorus of the gas with the oxygen of the air, during combustion. 691. Does phosphuretted hydrogen occur in nature? It is produced in the decomposition of vegetable and animal matter. 692. What is the "Jack o' Lantern" or "Will o' the Wisp"? It is a wandering light sometimes seen in swamps and graveyards, and is supposed to be caused by the spontaneous combustion of phosphuretted hydrogen. 693. What is LIGHT CARBURETTED HYDROGEN? It is a colorless and inodorous gas, about half as heavy. as the air. 694. Of what is it composed? Two proportions of hydrogen to four of carbon. 695. How is it produced? By the decomposition of vegetable matter under water. 696. Where is it found? In mines, and in the mud of ponds and marshes. 697. What is it thence called? Marsh gas. 698. How may it be artificially produced? An impure material may be produced by heating wood in a close vessel. 699. What property has a mixture of this gas and air? Like mixed hydrogen and air, it is explosive. OLEFIANT GAS. 105 700. What accident results from this property? Fearful explosions in mines. 701. How did Sir Humphrey Davy secure against these? By covering the miners' lamp with wire gauze. 702. What security does this afford? [ Flame will not pass through the interstices of the gauze to ignite the explosive atmosphere of the mine. 703. What is HEAVY CARBURETTED HYDROGEN. A colorless gas of peculiar sweetish odor, also known as olefiant gas. 704. How does it compare in composition with light carburetted hydrogen? It contains twice as much carbon. 705. How is it made? It can be made from alcohol, by the action of oil of vitriol. 706. What effect has the oil of vitriol? It retains part of the elements of the alcohol, and allows the rest to escape as olefiant gas. 707. What is illuminating gas? It is, in great part, a mixture of the light and heavy carburetted hydrogen. 708. How is it made? By heating bituminous coal. 709. What are the principal impurities of coal gas? Ammonia and sulphuretted hydrogen. 5* 106 CHEMISTRY. 710. Explain the figure. The figure illustrates the preparation and purification of illuminating gas. Coal is heated in the lower. f part of the tube. The lower paper wad contains water to retain the ammonia; the second, sugar of lead to retain. the sulphuretted hydrogen. The gas thus purified passes on to the gasometer. 711. What is said of the arrangements ill gas works? They are essentially the same as above described. The coal is heated in iron retorts. Ammonia is washed out of the gas by a jet of water; and sulphuretted hydrogen is retained by lime, instead of lead. 712. How is the gas collected in gasometers? It is allowed to flow upward from the apparatus in which it is produced, and to displace water with which the gasometer is previously filled. The method of filling a gasometer with gas would be illustratedby blowing air through a pipe stem into a full tumbler, lifted above the surface of water, as represented in the figure. 713. How is gas distributed? The gasometer is made to settle down, and the gas is thus crowded out through a pipe fitted into the top. This pipe leads to the "mains," by which it is distributed. FLAME. 107 FLAME. 714. Of what three parts does a flame consist? Of a dark centre, a luminous body, and a faint blue envelop. 715. What is the dark centre? It is unburned gas. 716. Of what does the body consist? Of particles of carbon, heated white hot by the combustion of the hydrogen of the gas. 717. What is said of the blue envelop? The carbon particles are there consumed as they are crowded outward by the flow of new gas. 718. Where is the gas of the flame produced? In the case of a lamp or candle, it is produced in the wick. 719. Out of what material is it produced? Out of the tallow of the candle or the oil of the lamp. 720. How may it be proved that there is no combustion in the interior of the flame? A little phosphorus left on the end of a match may be held in it without ignition. It must be suddenly introduced. 721. Give another proof. A match held through the flame is burned at the sides, but not in the middle. 722. Why is there no combustion in the centre? For want of oxygen. 108 CHEMISTRY. 723. What effect has flame on metals? The outer portion oxidizes or rusts them, the inner portion deoxidizes or re-converts the oxide into metal. 724. Why does the inner portion deoxidize? Because it contains abundant carbon and hydrogen to take oxygen from the metal, and pass off with it as carbonic acid and water. 725. Why does the outer portion oxidize? Because there is an abundant supply of heated air to impart oxygen, or, in other words, to oxidize. 726. How may these effects be illustrated? By moving a penny to and fro through a flame, continuing the experiment till it is highly heated. 727. What phenomenon attends these changes? A beautiful play of colors, like those on soap-bubbles. 728. What is the OXY-HYDROGEN BLOW-PIPE? An apparatus for producing and burning a mixed jet of oxygen and hydrogen. 729. Illustrate the figure. \,/ The figure represents a >:> - simple form of the oxy-hy- h. drogen blow-pipe, and iron a- / wire burning in the flame:.. of the mixed gases. 730. What is the important Ji' property of such a flame?..i/ Its intense heat. I 731. Illustrate its intensity. Platinum, which is infusible in a blast furnace, melts readily in this flame. MErALs. 109 CHAPTER VIII. METALS. 732. WHAT metal exists in common wood ashes? A bluish white metal called potassiurnm, which will float on water, and may be molded like wax. 733. What is its most remarkable property? It is ignited if thrown on water. The same metal exists also in many rocks. 734. What metal exists in common salt? A white metal called sodium, very similar in its properties to potassium. 735. In what other materials is this metal found? In common " soda" and in many rocks. 736. What metal exists in ordinary lime and marble? A white metal called calcium, like the metals above mentioned, of no use in the arts. 737. What metal exists in the magnesia used in medicine? A white metal very nearly resembling calcium. Like calcium, it also exists in many rocks. 738. What metal exists in common clay? A bluish white metal called aluminium. This metal is brilliant and tenacious, and promises to be of use in the arts. It has the advantage over most metals of being as light as glass. 110 CHEMISTRY. IRON. 739. Mention some properties of pure IRON. It is nearly white, quite soft, and can be rolled into thin leaves. 740. Is pure iron often seen? It is only known to the chemist. Commercial iron contains small portions of other substances, which modify its properties. 741. How is iron made? It is made from the ores of iron, which are commonly earthy oxides of iron, by heating with lime and coal. 742. What effect have the lime and coal? The lime removes the earthy portion of the ore as slag, the coal _: carries off the oxygen as carbonic acid gas, and the melted iron sinks __I_____ Il i" - down through the melted slag.l 743. What is this action of the coal called? -Reduction. Other metals are also reduced from their ores by the action of carbon. 744. What is CAST or PIG IRON? Impure iron, as it comes from the furnace. 745. What is its principal impurity? It contains a portion of carbon from the coal. IRON. 111 746. How does this affect iron? It makes it brittle, and at the same time easy to melt. 747. What is wrought iron? Cast iron from which the carbon has been burned out by an oxidizing flame (723). 748. In what kind of a furnace is this process carried on? In what is called a reverberatory furnace, represented in the figure. The flame, mingled with Lo much air, is made to bend over from the grate and play on the surface of the molten iron. 749. What peculiar property has iron at a high temperature? It becomes soft at a high temperature without melting. 750. What use is made of this property? Two pieces thus softened can be welded together, or, in other words, united into one piece. 751. Can not other metals be welded like iron? With the exception of platinum they can not, as they do not grow soft before they melt. 752. What is STEEL? It is iron combined with a small portion of carbon. 753. How is it prepared? By burying wrought iron in charcoal and heating it for a long time. 754. How does steel differ from cast iron? It contains less carbon. 112 CHErMISTRY. 755. Why may not steel be made directly from cast iron, by burn. ing out part of its carbon? It may; and this process has recently been employed to some extent. 756. How is steel softened, to make it workable? By highly heating and then slowly cooling it. This process is called annealing. 757. How are instruments made of soft steel hardened? By re-heating and sudden cooling. 758. How is any portion of the original softness of the steel restored? By heating just in proportion to the softness desired, and subsequent slow cooling. This last process is called temzpering. 759. What is CHROMIUM? A gray and extremely hard metal contained in the mineral called chrome iron. Many of its compounds are used as paints. 760. What is COBALT? Another gray metal, found in the mineral known as arsenical cobalt, and in some other minerals. Its oxide is employed to stain glass blue. 761. What is NICKEL? Nickel is still another gray metal, found in the mineral called copper nickel. It is used in the preparation of the alloy called "German silver." zINc. 113 ZINC. 762. What is ZINC? A bluish white metal, easily tarnished in the air. 763. Mention some of its properties. At common temperatures it is brittle, but if heated it can be rolled into thin sheets. 764. How may zinc be burned? On melting it, and then heating it still more highly, it takes fire and burns, forming white flakes in the air, called "philosopher's wool." 765. What are the uses of zinc? Rolled into sheets, zinc is employed for roofing and similar purposes. 766. What is GALVANIZED IRON? Iron that has been coated with zinc by plunging it into the melted metal. TIN. 767. Describe the metal TIN. Tin is a brilliant white metal, very soft, and not easily tarnished. 768. What happens when a bar of tin is bent? It produces a peculiar sound, called the cry of tin. 769. Why should acid food never be allowed to stand for a long time in tin vessels? Because the acid dissolves a small portion of tin, forming a somewhat poisonous solution. 114 CHEMISTRY. 770. How are common brass pins coated with tin? By boiling them with cream of tartar and tin foil. By an action similar to that of the galvanic battery, the metal is gradually transferred to the pins. 771. How is common tin ware made? By dipping well cleaned sheet iron into melted tin. 772. How may the beautiful crystalline structure of tin be observed? By heating a tin plate highly, and then washing the cooled surface with aqua regia. ANTIMONY. 773. What is ANTIMONY? A bluish white crystalline metal. 774. Mention a peculiar property of antimony. It is so brittle that it may be readily reduced to powder. 775. What happens when antimony is highly heated in the air? It burns with a beautiful white flame. 776. What happens if a red hot globule falls upon the floor? It immediately divides itself into hundreds of little fire balls. 777. What becomes of them? \ \ i / They radiate in all directions, as shown in.-.,, — the figure, leaving a white track behind them. "":';'":". 778. How does chlorine act upon powdered antimony? Sprinkled into this gas antimony at once takes fire. COPPER. 115 779. What are the principal uses of antimony? For the preparation of type metal and other alloys. BISMUTH. 780. Describe the metal BISMUTH. It is of a reddish white color, brittle and crystalline, like antimony. 781. What occurs when it is highly heated in the air? It melts and then burns, forming a white smoke. 782. For what purposes is bismuth used? It is used in making certain alloys. 783. Mention a remarkable property of one of its alloys. An alloy, called "Newton's fusible metal," composed of eight parts of bismuth, five of lead, and three of tin, rnelts in boiling water. COPPER. 784. Describe the metal COPPER. It is of a red color, and can be rolled into very thin leaves. 785. Where is it found? It is found in the metallic condition in great abundance on the shore of Lake Superior. 786. From what is copper commonly obtained? From a mineral called copper pzyrites. 15. 116 CHCEMISTRY. 787. What takes place when copper is heated in the air? A beautiful play of colors, as described in the section on Flamne. 788. Why is copper used for many purposes in preference to iron? Because it rusts less easily. 789. What are the most common alloys containing copper? Gold and silver coins. 790. Of what is the new cent composed? It is an alloy of nickel and copper. LEAD. 791. Describe the metal LEAD. Lead is of a bluish gray color, and one of the heaviest of the metals. 792. What is the principal source of lead? Galena, a mineral composed of lead and sulphur. 793. What happens when lead is heated? It unites with oxygen and forms a yellow compound, called litharge. 794. What is said of the action of pure water on lead pipes? The water dissolves the lead, and becomes more or less poisonous. 795. Has spring water the same effect? The mineral matter which spring water contains, lessens its action on lead, MERCURY. 117 796. How is the action also diminished by use? After a time the interior of the pipes becomes coated with an insoluble compound of lead, which protects them. 797. How can these facts be proved by experiment? By placing bright strips of lead in two tumblers, one containing rain water and the other spring water. 798. What effect will be produced? The former will become turbid, while the latter remains unaffected. 799. How are shot made? By pouring lead through iron sieves, at such a height that the drops will have cooled before they reach the water which receives them below. 800. Mention other uses of lead. It is used in the manufacture of sheet lead, lead pipe, and certain alloys. MIERCURY. 801. Describe the metal MERCURY. It is a white fluid metal, of high lustre and beauty. 802. In what condition is'mercury found-? Sometimes in the metallic form, but more frequently combined with sulphur. 803. How is the metal obtained from this compound? By simply heating it in a current of air. 804. What effect has heat upon mercury? By a sufficient heat, mercury, like water, may be boiled away and converted into vapor. 118 CHEMISTRY. 805. What is an AMALGAI? A compound of mercury with another metal. 806. What metals dissolve in mercury forming alloys? Gold, silver, lead, and several other metals. 807. How may a copper coin be apparently silvered? By rubbing it with metallic mercury. 808. What are the uses of mercury? Mercury is used in making thermometers and barometers; its compounds are extensively employed in medicine. SILVER. 809. Describe the metal SILVER. It is of a white color, and has a brilliant lustre. 810. Why does it lose its color on exposure? It is blackened by the sulphuretted hydrogen always present in the air. 811. In what form is silver found? The sulphuret is its most common ore. It is also found as native or pure silver. Most ores of lead contain silver. 812. Of what is the silver coin of the United States composed? Of ninety parts of silver to ten of copper. 813. What is the process called by which the amount of any metal in an ALLOY or mixture is ascertained? It is called assaying. GOLD. 119 814. Describe the silver assay, or, in other words, state how the proportion of silver in an alloy is ascertained. It is ascertained by adding salt to a solution of the coin, as long as a white curd (chloride of = silver) continues to precipitate. Every particle of salt converts into the white curd a certain def- inite proportion of silver. From the amount of salt used the amount of silver may therefore be calculated. 815. For what else than coin and plate is silver employed? For preparing daguerreotype plates and making the lunar caustic used by surgeons. GOLD. 816. Mention some of the properties of GOLD. It is a yellow metal of brilliant and permanent lustre. 817. Into how thin a leaf may it be hammered? Into a leaf but little more than -yT{1b0th of an inch in thickness. 818. How may this fact be otherwise stated? That a cube of gold, five inches on a side, could be made to cover an acre of ground. 819. How is gold found? Always in the metallic state, either in quartz rock or in the sands of rivers. 820. Is native gold pure? It is not, but commonly contains from 5 to 15 per cent. of silver. 120 CHEMISTRY. 821. How is gold REFINED or freed from this silver? Nitric acid dissolves out the silver and leaves the gold. To make its action thorough, more silver must first be fused into the gold. In removing the added silver, the acid thoroughly removes the original silver with it. 822. How is the gold assay conducted? In the same manner as the refining process. The gold left after the action of the acid is weighed, and the proportion in the coin thus ascertained. 823. How pure is the gold coin of the United States? It contains nine tenths pure gold; the remaining tenth is an alloy of copper and silver. 824. How is the purity of gold expressed? In carats; a carat signifying one twenty-fourth of the whole. 825. What, then, is meant by gold sixteen carats fine? It is meant that sixteen twenty-fourths or two thirds of it is pure gold. 826. How is the process of GILDING on metals usually effected? An amalgam of gold is applied, and the mercury being expelled by heat, the gold remains. 827. What other process is extensively employed? The galvanic method, described on page 66. 828. How is a coating of pure gold produced on articles of jewelry made of impure gold? By the action of heat and nitric acid the impurities are removed from the surface, and pure gold remains. PLATINUM. 121 829. Is there any acid that will dissolve gold? It resists the action of any single acid, but may be dissolved in aquacc regica. PLATINUM. 830. Describe the metal PLATINUM? It resembles steel in color, and is the heaviest of the metals. 831. What is its SPECIFIC GRAVITY? 21; in other words, it weighs 21 times as much as an equal bulk of water. 832. How and where is it found? In small flattened grains, in the sands of certain rivers. 833. Mention some of its properties. Like iron, it may be welded at a high temperature; like gold, it is not acted on by any single acid. 834. Mention another of its properties. It can not be melted by the most intense heat of a blast furnace. 835. What action has platinum upon certain gases? It condenses them upon its surface, thereby increasing their affinities. 836. How is this proved? A platinum sponge will condense and intensify oxygen gas to such a degree in its pores, that a jet of hydrogen blown through it immediately combines with the oxygen and bursts into flame. 6 122 CHEMISTRY. 837. What are the uses of platinum? It is used in the arts for the manufacture of chemical apparatus. 838. Why is it very valuable for this purpose? On account of its extreme infusibility and resistance to acids. ALLOYS. 839. What are ALLOYS? Compounds of metals with metals. 840. Name the more important alloys? Brass, German silver, bronze, pewter, type metal, and solders. 841. What is BRASS? Copper lightened in color by the addition of zinc. 842. What is GERMAN SILVER? Brass still further whitened by nickel. 843. Of what is BRONZE composed? Of copper and tin. 844. What is PEWTER? An alloy of tin, with variable proportions of antimony and lead. 845. What is the composition of TYPE METAL? One part antimony to three parts tin. 846. Of what are SOFT SOLDERS composed? Of variable proportions of tin and lead; the greater the proportion of tin the more easily a solder melts. ALLOYS. 123 847. What are the uses of soft solder? It is used for soldering pewter and tin ware. 848. What is HARD SOLDER or SPELTER? An alloy of equal parts of zinc and copper. 849. What are the uses of hard solder? It is employed for soldering brass, copper, and iron.!TILTO OEU DISTILLATION OF MERCURY. 1^24 OXIDES AND SULPHURETS. CHAPTER IX. OXIDES AND SULPHURETS. OXIDES. 850. WHEN oxygen unites with metals, what compounds are formed? Oxides or rusts. Iron rust is an example. 851. What property is possessed in common by most metallic oxides? They combine with acids, and form compounds called salts. 852. Which of the oxides are termed ALKALIES? The oxides of sodium and potassium. 853. In what respect do the alkalies differ from other oxides? They dissolve readily in water; other oxides are insoluble. ALKALIES AND ALKALINE EARTHS. 854. What is POTASSA, or CAUSTIC POTASH, as it is sometimes called? The oxide of potassium combined with water. 855. In what form is it met with in commerce? In the form of slender sticks, of a white or gray color. 856. From what is it made? From wood ashes, by the use of lime. ALKALIES. 125 856*. Describe the process. Lime being added to a solution of wood ashes, combines with their carbonic acid and settles with it to the bottom of the vessel. 857. Why are soiled' rags cleansed by boiling in a solution of potassa? Because the potassa unites with the grease, and the compound thus formed dissolves in water. 858. How does a solution of potassa act on animal matter? It readily dissolves it; it dissolves the skin, for example, if rubbed between the fingers. 859. How does potassa affect the blue coloring matter of vegetables? It turns them green. A leaf of purple cabbage, for example, is turned green by potassa. 860. Mention another remarkable property of potassa. It has an intense affinity for water. If exposed in a moist atmosphere, it will dissolve in the moisture which it collects from the air. 861. What is SODA? The oxide of sodium. 862. What are the properties of soda? They are very similar to those of potassa. 863. What is LIME? The oxide of calcium. 864. How is it obtained? By heating chalk, marble, or limestone, and thus expelling its carbonic, acid. 126 CHEMISTRY. 865. What happens when cold water is poured upon lime? The lime combines with the water and gives out heat The process is called slaking. 866. Why is heat produced by slaking lime? In accordance with the general law that, whenever a liquid takes the solid form (as water does when combining with lime), its latent heat is given out. 866*. iow are BARYTA and STRONTIA prepared? From their carbonates, by mixing with charcoal and exposing them to a high temperature. ALUMINA AND OTHER OXIDES. 867. What is ALUMINA? The oxide of aluminium? 868. Where is it principally found? In common clay. 869. What precious stones are pure alumina? The sapphire and the ruby. 870. What is said of the remaining metallic oxides? They are powders; some of them colored, others white. 871. What are magnesia and the peroxide of iron. used in medicine? The former is the white oxide of magnesium, the latter a kind of iron rust. 872. What oxides are employed as paints? The red oxide of lead and the white oxide of zinc. 873. Mention the colors imparted to glass by certain of the oxides. Cobalt, blue; manganese, violet; copper, green; silver, yellow. SULPHURETS. 127 874. To what is the green color of common bottle glass owing? To an oxide of iron which it contains. SULPi-URETS. 875. What name is given to the compounds of sulphur and the metals? They are called su7pAides or sulphdurets. 876. Where are they found? Many sulphurets occur as natural minerals; others are produced only by artificial means. 876*. Give an example of the artificial formation of a sulphuret. When a piece of roll sulphur is held against white hot iron, the two substances combine and form sulphuret of iron. 877. Why is the mineral sulphuret of iron called FOOLS' GOLD? Because it strongly resembles gold, and is often foolishly taken for it. This sulphuret is also called iron pyrites. 878. What is GALENA, from which nearly all the lead of commerce is obtained? It is a sulphuret of lead, similar in color to the metal itself. 879. What other sulphuret resembles iron pyrites? Copper pyrites resembles iron pyrites, but may be readily distinguished from it by its greater softness. The former mineral may be cut with a knife. 128 SALTS. CHAPTER X. SALTS. CHLORIDES. 880. WHAT compounds are formed when chlorine unites with metals? Chlorides. 881. Mention some of the more common chlorides. Common salt or chloride of sodium, and calomel or c&'loride of mercury. 882. What is the form of most chlorides? They are either powders or crystals of various colors. 883. Which is the most abundant and important of all chlorides? Common salt. 884. From what source is it procured? It is dug out of salt mines, or obtained by evaporation from sea water. 885. How much common salt does every pound of sea water contain? Nearly half an ounce. 886. What is said of the water of the Dead Sea? It is so dense that a man floats in it breast high. 887. To what is this owing? To the very large proportion of salt it contains. SALTS. 129 888. Describe a crystal of common salt. It is a hollow pyramid, built up of innumerable small cubes. Such crystals are --.. easily made by evaporating a saucer full of salt water slowly on a stove. 889. Why does common salt preserve the flesh of animals from decay? Its effect is in part owing to the fact that it extracts water from the flesh, and thus partially dries it. 890. How may beautiful colored flames be produced. By burning alcohol which contains certain chlorides in solution. 891. Mention some of the colors thus obtained. The chloride of sodium imparts a yellow, that of potassium a violet, and that of copper a blue color. 892. How are the colors of fireworks produced? By adding the above chlorides and certain other substances to the powder of which they are made. 893. What is:'chloride of lime,:; or "bleaching powder?" It is a compound produced by causing lime to absorb chlorine gas. On adding a little acid to it, the chlorine escapes and bleaches any thing in contact -with it. 894. What are the compounds of Iodine, Bromine, and Fluorine with the metals called? These compounds are called respectively Iodides, Bromides, and Fluorides. They resemble in many respects the Chlorides. 6* 130 CHEMISTRY. SULPHATES. 895. What is a SULPHATE? A compound of sulphuric acid with an oxide or base. 896. Mention some of the more common sulphates. Sulphate of magnesia or "Epsom salts," and sulphate of lime or "plaster of Paris." 897. Mention a peculiar property of plaster of Paris. When made into a cream or paste with water, it gradually combines with it and "sets," or becomes hard. 898. For what uses does this property adapt it? For covering walls, and for making ornamental casts. 899. How may the making of casts be illustrated? By shaking a little cream of plaster in a paper box and allowing it to stand for a few minutes. A cast or copy of the box is thus produced. 900. What happens when alum is heated on a shovel or.:, in a pipe bowl? The alum is puffed up by the escape of the water, and " burnt alum" remains. 901. What common name have several of the sulphates received? The name of vitriols8; sulphate of copper is called blue vitriol, sulphate of iron green vitriol, and sulphate of zinc white vitriol. NITRATES. 902. What are compounds of nitric acid and the oxides called? Nitrates. NITRATES. 131 903. Mention some of the more common nitrates. Nitrate of potassa or saltpetre, nitrate of silver or lunar ctaustic, and nitrate of ammonia. 904. For what purpose is saltpetre extensively used? For making gunpowder. 905. What are the other constituents of gunpowder? Powdered sulphur and charcoal. 906. To what is the explosive force of gunpowder owing? To the sudden production of a large volume of gas. 907. What is the principal gas produced in the explosion? Carbonic acid gas. 908. How is this produced? By the combination of the carbon or charcoal of the powder with the oxygen of the saltpetre, which is also a constituent of the mixture. 909. For what purpose is nitrate of silver or "lunar caustic" employed? It is employed in surgical operations to burn or deaden the flesh. 910. What effect is produced by heating nitrate of ammonia? The nitrogen of the compound passes off in combination with part of the oxygen as laughing gas. 911. Why is this gas so called? Because when breathed it has a highly exhilarating effect on the human system. 132 CHEMISTRY. CARBONATES. 912. When carbonic acid unites with oxides, what compounds are formed? Carbonates. 913. Mention some carbonates. Saleratus, soda, sal volatile, and chalk are all carbonates. 914. What is the action of carbonate of potassa or SALERATUS in'raisin-g' bread and cake? The tartaric acid employed with it takes possession of the potassa and sets at liberty the carbonic acid. The latter in its escape puffs up the "sponge." 915. Mention some uses of carbonate of soda, or C soda?' as it is comimonly called. It is used in various manufacturing processes, and also to make seidlitz and soda powders, as well as for raising bread. 916. What peculiar property has carbonate of ammonia or "lsal volatile?;' It is highly volatile, and gradually wastes away with a strong and pungent odor into the air. It is used as " smelling salts," and sometimes also to lighten bread and cake. 917. How can it be proved that it wastes away in the air? If a roll of paper moistened with strong muriatic acid is held near it, dense white clouds are at once produced (677). SILICATES. 133 SILICATES. 918. What are SILICATES? The compounds of silicic acid with oxides are called silicates. 919. Give some examples of silicates. Ordinary mica, sometimes used in the doors of stoves, is a silicate of alumina. Soapstone is a silicate of magnesia. Clay and clay slate are silicates of alumina, containing various impurities. The silicates form a large class of rocks. Feldspar is a double silicate of alumina and potassa. Granite is made up of crystals of quartz, feldspar, and mica. 920. Mention an artificial silicate. Glass is an artificial silicate, or rather a compound of various silicates. 921. What is the composition of common window glass? It is a silicate of lime and soda. 922. How is it made? By melting together chalk, soda, sand, and old glass. 923. How is it made into thin sheets? The fused glass is blown from an iron tube, as soap bubbles are blown from a clay pipe, and the glass bubbles are then opened into sheets. 924. How are hollow vessels of different shapes made? By blowing the bubbles into molds of the required shape. 134 CUEAL ISTRY. 925. What remarkable property has silicate of potassa when made with an excess of potassa? It has the appearance of common glass, but is soluble in water. 926. What use is made of such a solution? It is sometimes employed as a sort of varnish to render wood fire proof. 927. What is the basis of all EARTHENWARE? Clay is the basis of all earthenware, from the finest porcelain to the coarsest brick. 928. How are articles of PORCELAIN made? An extremely fine grained and pure clay, being first fashioned by molds and other means into the required shape, is then dried, baked, and subsequently glazed. 929. What is the object of the glazing? In the case of ordinary earthenware, the object of the glazing is to render the porous material impervious to water. In the case of porcelain, which is baked into a denser mass, the object is to increase HA 4i> its beauty. 930. How is glazing effected? By covering the baked ware with a paste of materials for making a fusi- / ble glass. The ware is then highly heated, and a thin glass or glaze is thus formed on its surface. 931. How is porcelain painted? The metallic oxides, already nice1 BORATES. 135 tioned (873), are used in painting porcelain, being applied before the final glazing. The colors are indestructible, as they are fused into the porcelain itself. 932. How are the patterns on ordinary earthenware produced? They are first printed on paper, and then transferred by moisture and pressure to the unglazed ware. BORATES. 933. What are compounds of boracic acid and oxides called? Borates. 934. Name the most important of these compounds. Borax; this salt is a borate of soda. 935. Where is it found? It is found in the beds of certain lakes in India, when they dry up in summer. 935*. How is it artificially produced? By combining boracic acid with soda. 936. Why does the blacksmith sprinkle borax on the heated iron in WELDING? In order to cleanse t/he surfaces to be united from rust or oxide, so that they will unite more perfectly. 937. How does the borax have this effect?'The fused borax dissolves the oxide and forms with it a glass. This fused glass immediately flies out when the two pieces of metal are struck together. 136 CHEMISTRY. PHOSPHATES. 938. What are PHOSPHATES? Compounds of phosphoric acid with oxides are called phosphates. 939. Give an example of a phosphate. The earthy part of bones is principally phospliate of lime. There is also a mineral called apatite, which is nearly pure phosphate of lime. 939*. How are phosphates artificially produced? Phosphates are artificially produced by combining phosphoric acid with different oxides or bases. 940. What is the material commonly known as "superphosphate of lime,' and extensively used as a fertilizer? It is a mixture of phosphate of lime (bones) and sulphuric acid. 941. What is the object of the sulphuric acid in the mixture? To render the bones soluble, so that their constituents may be absorbed by plants. 942. What other material is commonly added to the "superphosphate?" Guano, or some other material containing ammonia. 942*. What reason exists for the application of phosphate of lime to the soil? This substance, though an essential constitulent of the food of plants, exists in most soils in small proportions, and is therefore peculiarly liable to become exhausted. THE DAGUERREOTYPE. 187 CHAPTER XI. THE DAGUERREOTYPE. 943. WHAT picture in nature is analogous to a daguerreotype in its formation? The image formed on the retina of the eye. 944. What is accomplished in the daguerreotype process? An image thrown by a lens on a silver plate is rendered permanent. 945. How is this accomplished? The plate is made very sensitive by a chemical preparation. The image which falls on it then acts chemically on its surface, just in proportion to the brightness of the different parts of the image. 946. What is the next step in the process? The next step is to expose the plate to vapors of mercury. These adhere and stain the plate white in proportion to the change of surface before produced by the image. The right position and proportion of light and shade is thus produced, and the picture is complete. 946*. What are the agents in the first and most remarkable part of the process? Certain rays, called chemical or actinic rays, which always accompany light. 138 CHEMICAL ANALYSIS. CHAPTER XII. CHEMICAL ANALYSIS. 947. How is chemical analysis effected? By using materials which dissolve, precipitate, or volatilize certain substances and not others. 948. Give an example of analysis by SOLUTION. The process for assaying and refining gold is such an example. The chemist having ascertained that nitric acid dissolves silver, but not gold, uses nitric acid to dissolve out the silver and leave the gold. This is a simple case of chemical analysis. 949. Give an example of analysis by PRECIPITATION. Lime and potash may be separated from one another by simply blowing air from the lungs into the solution of the two through a pipe stem. The lime precipitates as carbonate of lime, while the potash remains in solution. This is a case of analysis by precipitation. 950. Give an example of analysis by DISTILLATION. Sea water may be boiled away, leaving its salt behind. Alcohol is separated from water in the same manner by a gentler heat. VEGETABLE CIHEMISTRY. 139 CHAPTER XIII. VEGETABLE CHEMISTRY. 951. WHAT is ORGANIC CHEMISTRY? It is that division of the science which treats of substances of animal or vegetable origin. 952. How may it be divided _ Into vegetable chemistry and animnal chemistry. 953. What is said of the variety of organic matter? Its variety is almost without limit. 954. Give some idea of this variety. Each of the innumerable flavors of herbs and fruits is owing to the presence of a distinct organic substance. The variety of gums, resins, and coloring matters is scarcely less. Sugar, starch, and wood, blood, milk, and flesh, are a few more among the great number of organic substances. 955. What is especially remarkable in connection with this great variety? The very slight variety of the raw material out of which all these substances are formed. 956. What are the raw materials? Carbonic acid, water, ammonia, and a small proportion of mineral matter. 16 140 CHEMIASTRY. 957. Apart from the mineral matter, what are the four elements which this raw material contains? Carbon, hydrogen, oxygen, and nitrogen. 958. What is still more remarkable than the fact that so many kinds of organic matter are made from the same materials? The fact that some widely different substances contain the different elements in the same proportion. 959. Give some examples of this. Wood, gunm, and starch, although differing in their properties, contain precisely the same proportion of the same elements-carbon, hydrogen, and nitrogen. The oils of turpentine, lemnon, and pepper, so different in their taste, have also precisely the same composition. 960. How. then, are we to account for these differences? We are forced to suppose that they arise from some different way in which the particles are arranged or put together in the different substances. 961. What happens after a seed has been planted a few days? It lets down roots into the soil, and lifts up a leaf or two into the air. 962. From what have these leaves and roots been produced? From the substance of the seed itself. 963. What is this first step in the life of a plant called? Germination. 964. When does the true process of vegetation commence? When the plant begins to live on the materials of the earth and air. GROWTH OF PLANTS. 141 965. What is the office of the leaf'? The office of the leaf is to absorb that portion of the food of the plant which is contained in the air. 966. WIh-at is the office of the root? To draw up mineral matter from the soil, and distribute it by means of the ascending sap. 967. What happens in the leaf? The leaf is the laboratory where these materials are converted into vegetable matter. 968. How is the product distributed through the plant? By means of the descending sap. 969. What change does it afterward experience? It is aft;erward changed into wood, flowers, fruit, etc., in different parts of the plant. 970. What is the refuse of the manufacture of vegetable matter which takes place in the leaf? Oxygen gas is constantly thrown off during the process into the air. 971. Why is so much oxygen rejected? Because the water, which is one of the raw materials (956), contains as large a proportion as can be used. That which comes in with the carbonic acid is therefore rejected. 972. Which are among the more important of vegetable substances? Wood, starch, gluten, sugar, and gum. 973. Where are the first three of these found? Wood forms the mass of the plant; starch and gluten collect in the seed. 142 CHEMISTRY. 974. Where do the sugar and gum principally exist? In the sap and fruit; they also exude from the bark. WOOD. 975. What is the composition of woody fibre? It is composed of carbon, hydrogen, and oxygen. 976. Where is it found? It constitutes the mass of all vegetable organs. 977. In what forms does it occur? It is either hard as in the fibre of oak, soft as in the pulp of fruits, or fibrous like cotton and flax. 978. What purposes, then, does woody fibre serve us in one or the other of its forms? It serves us for shelter, clothing, and food. 979. What happens if wood is heated in a covered pipe-bowl? A quantity of smoke passes out of the stem, and charcoal remains behind in the bowl. 980. What is the process called? Dry distillation. 981. Of what does the smoke consist which is given off in the dry distillation of wood? Of tar, acetic acid, kreosote, carbonic acid gas, and other gases. 982. How are these substances produced? Under the influence of heat the atoms of the wood reoarrange themselves, to form new substances. COAL. 143 983. In what does such distillation differ from ordinary combustion? The former is effected without the help of the oxygen of the air. 984. What similar process goes on in nature? Peat, which may be regarded as a sort of half formed charcoal, is similarly formed by the decay of vegetable matter under water, while various gases are evolved. 985. Whence is the vegetable matter derived from which peat is formed? It has its origin in the green slime, composed of minute plants, which forms in the summer upon stagnant pools, and sinks each season to the bottom. 986. What becomes of the carbonic acid produced in the formation of peat? It often finds its way to the surface in the form of a mineral spring. 987. How is BITUMINOUS COAL formed? By a similar change of vegetable matter buried for ages in the earth. 988. How is ANTHRACITE coal formed,? From bituminous coal which has been subjected to great heat. 989. How may the natural tendency of vegetable matter to decay be checked? By impregnating it with certain metallic salts. 990. What is this process of preserving wood called? The process is called kyanizing. 991. What salts are used in the process? Corrosive sublimate and chloride of zinc have been chiefly used. 14 4 CHEMISTRY. 992. What is said of the KREOSOTE produced during dry distillation? It smells like smoke, and has the same effect in preventing the putrefaction of animal substances. It is sometimes employed instead of the process of "smoking," for curing meats. 993. What is GUN COTTON? Cotton made explosive by treating it with strong nitric acid. 994. Why is gun cotton not likely to supersede gunpowder, for use in firearms? It explodes so suddenly and violently as to injure the piece from which it is fired; it is, besides, too expensive. 995. How is the COLLODION made, which is used instead of court plaster for covering wounds? By dissolving gun cotton in ether. 996. How may wood be converted into sugar? By digesting saw dust with oil of vitriol, and then boiling it with the addition of water, wood is converted into sugar. The acid is afterward separated and the sugar crystallized. The sugar thus produced is of the same sort as that which forms on raisins and dried fruit, and is called grape sugar. 997. What chemical change occurs in this transformation? Wood differs from grape sugar in containing a little less hydrogen and oxygen. Oil of vitriol contains these elements, and yields them to the wood to effect the change. The wood will not take them from simple water. STARCH. 145 998. What other substances may be similarly changed? Cotton and linen rags, which are like wood in their composition. STARCII. 999. What is the composition of STARCH? It is identical in composition with wood and gum. 1000. Where is it found? In most grains and other seeds; in the potato and in many fruits. 1001. From what poisonous nut can starch be obtained for use as food? From the horse-chestnut, which has been used in Europe for the production of flour. 1002. What is the first step in making starch from potatoes? The potatoes are rasped, washed with water, and the milky liquid thus produced is then run through a sieve. 1003. What is done with this milky liquid? The fine starch grains which it contains are allowed to settle, and are then collected and dried. 1004. How is starch manufactured from wheat flour? The flour is mixed with water and allowed to stand until it undergoes putrefaction. During the process the gluten (1081) is destroyed, while the undecomposed starch settles at the bottom of the vessel. 1005. How may starch be converted into sugar? Like woody fibre, it is converted into sugar by boiling with dilute sulphuric acid. 146 CHEMISTRY. 1006. If the sulphuric acid is kept near to the boiling point, without actually boiling, what substance is produced? A gum called dextrine, which is used for making a kind of confectionery called "fig paste," and for various other purposes. SUGAR. 1007. Mention three principal varieties of SUGAR. Cane sugar, obtained from the sugar cane, the beet, and the maple tree; fruit sugar, which exists in acid fruits, and grape sugar or g7tucose, already mentioned (222). 1008. How do these sugars differ from starch in composition? Cane sugar contains an additional atom of oxygen and hydrogen, fruit sugar two of each, and grape sugar four of each. 1009. WVhy is the sugar produced from starch and similar substances called grape sugar? Because it is the same as that found on the surface of raisins or dried grapes. 1010. Is the sugar of the juice of the grape the same? It is not. The sugar of the juice is fruit sugar, which gradually changes itself into grape sugar or glucose, and appears on the surface of the dried fruit. 1011. In what respect do cane and grape sugars differ from each other? Cane sugar contains proportionally more carbon, and, besides, is nearly three times as sweet as grape sugar. S3UJGA. 147 1012. Is any process known by which cane sugar can be produced front starch, wood, etc.? No such process is known; grape sugar can be thus made, but not cane sugar. 1013. Give briefly the process of manufacturing sugar from the cane. The juice is pressed out, then clarified with lime, and finally boiled down until it will crystallize on cooling. The drainings from the crystals form molasses. 1014. How is the raw sugar purified? By dissolving it, and then filtering the solution through bone black. 1015. What change occurs when brewers' yeast is added to a solution of fruit sugar, and the mixture is set aside in a warm place? The sugar is entirely converted into carbonic acid, which passes off, and alcohol, which remains. 1016. What is this process called? Fermentation. 1017. What is the figure designed to show? o o The figure is designed to show that o o a molecule or single particle of fruit, sugar contains just enough atoms of carbon, hydrogen, and oxygen to form two mlolecules of alcohol and four of car- o bonic acid. The whole figure represents a molecule of fruit sugar. The four corner groups represent molecules of carbonic acid, and the two centre groups molecules of alcohol. 148 CHEMISTRY. 1018. Does the figure show the actual shape of the molecules? It does not; this can not be positively known. It only shows their composition. 1019. Does the yeast which is used in this process furnish any oi the material for producing the alcohol and carbonic acid? It does not; it simply acts by its presence, in a manner not perfectly understood, to cause the sugar to change into alcohol and carbonic acid. 1020. Is the result of the process of fermentation different if ordinary sugar, or grape sugar, or molasses, are substituted in the process for fruit sugar? It is not; these materials are first converted into grape sugar during the process, and the grape sugar then into carbonic acid and alcohol. 1021. Is the alcohol obtained in this process ABSOLUTE or PURE ALCOHOL? It is not; it remains mixed with the water which was originally mixed with the sugar. 1022. What is produced when this liquid is distilled? An alcoholic liquor, which, if made from molasses, is called rum. 1023.' How is the process of distillation conducted? The liquid is heated in a large copper vessel, and the alcohol thus expelled in the form of vapor. This vapor is led through a long spiral tube called the worm, and thus condensed to liquid alcohol. 1024. How is alcohol obtained from rum, whisky, and other spirituous liquors? By distilling them with lime, which holds on to the ALCOHOL. 149 remaining water and permits the pure alcohol to pass off. 1025. When alcohol is made from potatoes and grain, what pro. cess must precede that of fermentation? Their starch must be converted into grape sugar. 1026. How is this object effected? By adding bruised malt to the mashed potatoes or grain; malt, like sulphuric acid, converts starch into grape sugar. 1027. To what process is the "wort" thus obtained afterward subjected? As in the case of molasses, yeast is added; the wort ferments, and by distillation yields whisky. 1028. What are wines? Wines are comparatively weak alcoholic liquors, produced by the fermentation of the juice of the grape. 1029. Is it necessary to add yeast to make the juices of fruits ferment? It is not. The juice always contains a material which, by exposure of the juice to the air, forms a ferment within itself. 1030. What are MALT LIQUORS? Liquors which are produced by the fermentation of the extract of malted barley. 1031. How is the malt produced? Barley is moistened and allowed to germinate. The germination is then checked by heat, and the barley has become malt. 150 CHEMISTRY. 1032. Mention some of the uses of alcohol. It is used in medicine for making extracts of roots and herbs, and also as a solvent of oils and resins. 1033. How much alcohol is contained in different spirituous liquors? 1Malt liquors contain from five to ten per cent., wines from five to twenty-five, and rum, brandy, and whisky over fifty per cent. 1034. How is ether made from alcohol? Ether is produced by heating alcohol with oil of vitriol. The oil of vitriol retains part of the hydrogen and oxygen of the alcohol, so that the vapors which pass off and are afterward condensed form a new substance called ether. 1035. What change does dilute alcohol experience if mixed with a little yeast and exposed to the air? It is converted into vinegar. 1036. How is the process conducted? The alcohol is made to trickle through shavings packed in casks, through which the air has free circulation. A few passages through the cask suffice to convert the alcohol into vinegar. 1037. What chemical change does the alcohol undergo in its conversion into vinegar? The oxygen of the air combines with or burns up a portion of its hydrogen, and thus converts it into vinegar. 1038. How is vinegar commonly prepared? By the simple exposure of wine, cider, or other liquids containing alcohol, to the air. The chemical change in this case is the same as above ~described. ACIDS. 151 TANNIC ACID. 1039. What is TANNIN, or tannic acid? It is the substance existing in nut galls and in the bark of many trees, which imparts to them their astringent taste. 1040. When separated from the other substances with which it is combined in nature, what is its appearance? It is a yellowish, gummy mass. 1041. Mention a very valuable property of tannic acid. Dissolved in water, as in tan liquor, it has the property of converting hides into leather. 1042. How is writing ink prepared? By mixing a decoction of nut galls with a solution of green vitriol. 1043. What substances are afterward added to ink? Gum and cloves; the former to keep the ink from settling, the latter to prevent its molding. 1044. What is the dark portion which.gives color to the ink? It is a black precipitate formed by the combination of the tannic acid of the nut galls with the oxide of iron of the green vitriol and oxygen which it gradually absorbs from the air. 1045. Why does the best ink, which is bluish black when first used, change to deep black on the paper? Because it absorbs more oxygen from the air and produces more of the compound above mentioned. 152 CHEMISTRY. TARTARIC ACID. 1046. What is TARTARIC ACID? An organic acid found in the grape. 1047. From what is it prepared? From the cream of tartar or tartrate of potassa, which gradually deposits from wine. 1048. What are the uses of tartaric acid? It is used in calico printing, and in making seidlitz powders and yeast powders. OXALIC ACID. 1049. What is OXALIC ACID? An acid found in the common wood sorrel. 1049*. Describe its appearance and properties. It is a white crystalline solid, and a very dangerous poison. 1050. How is it prepared artificially? Wood, starch, and gum are all converted into oxalic acid by the action of nitric acid. 1051. What chemical change takes place in the process? The nitric acid burns out the hydrogen of these compounds with its oxygen, and at the same time adds to them oxygen. They are thus changed to oxalic acid. 1052. Mention one of the uses of oxalic acid. Combined with potassa, it forms the so-called salt of lemons, employed to remove ink stains. ESSENTIAL 01,S. 153 ESSENTIAL OILS. 1053. What are the ESSENTIAL OILS? Oils which form essences, and are found in the flowers, seeds, and fruits of plants. 1054. Mention some of the essential oils. The oils of roses, lemons, pepper, turpentine, etc. 1055. What is the composition of the above essential oils? They are composed of carbon and hydrogen; and, in the case of many of them, in precisely the same proportion (958). 1056. From what is the oil of turpentine prepared? From the pitch of pine trees; when this material is distilled with water, the oil of turpentine passes off with the steam and is afterward condensed, while ordinary rosin remains behind. 1057. What is "burning fluid," so called? A solution of camphene or purified turpentine, in alcohol. 1058. Why may not turpentine alone be employed for the purpose of illumination? For the reason that it burns with too much smoke. 1059. Is "burning fluid" explosive? It is not. 1060. How is this proved? It is proved by the fact that the fluid burns without explosion from the wick of a lamp. 154 CIHEMISTRY. 1061. Why, then, do: fluid lamps and cans" so frequently explode? Because a mixture of air and the vapor of burning fluid is as explosive as gunpowder, and such a mixture is always contained in half filled cans, or lamps partially burned out. 1062. What are artificial essences? Essential oils prepared by chemical processes. 1063. Mention some of these essences that may be artificially prepared. Pear oil, apple oil, oil of wintergreen, and oil of grapes. 1064. Mention a remarkable fact in connection with these oils. It is remarkable that, though possessed of very delicate flavors, the most of them are prepared from extremely nauseous substances. The butyric acid which exists in rancid butter, and gives it its disagreeable odor, is one of the ingredients of pine-apple oil. 1065. What does this fact illustrate? It is another illustration of the fact that chemical combination often entirely changes the properties of substances. CAMIPEORS AND RESINS. 1066. What are CAMIPHORS? White crystalline solids, which separate by cold from certain of the natural essential oils. 1067. What happens when small bits of ordinary gum camphor are thrown upon warm water? The particles sail about as if they were possessed of life. RESINS. 155 1068. What produces this effect? The camphor is gradually converted into camphor vapor, which pushes them along as it escapes. 1069. What effect is produced on India rubber by heating it with sulphur? It is changed in its nature, and is no longer stiffened by cold or softened by heat. 1070. What is it then called? V-lcanized rubber. This is the material out of which most India rubber goods are now made. 1071. What are the properties of GUTTA PERCHA? It is much tougher and less elastic than India rubber, but, like that material, can be vulcanized, by heating with sulphur. 1072. What are its uses? It is employed as a substitute for India rubber where great elasticity is not required. 1073. What are RESINS? Substances formed from the essential oils by the action of oxygen. 1074. Give an example of a resin. Common rosin; one of the constituents of the pitch of pine trees (1056). 1075. What are some of the uses of rosin? It is employed in making brown soap, and in sizing certain kinds of paper. 1076. How are ship-pitch and shoemaker's wax made? By heating and partially decomposing ordinary rosin by heat. 156 CHEMISTRY. 1077. Mention some other resins. Copal, shellac, mastic, amber, and Venice turpentine are also resins. 1078. What are their uses? They are principally used for making varnishes. 1079. Of what is ordinary sealing-wax composed? Of shellac and Venice turpentine, colored with vermilion. 1080. What is CAOUTCHOUC or India rubber? It is formed from the milky juice of certain trees, which grow in Asia, Africa, and South America. This juice has the property of hardening into the solid gum by simple exposure to the air. PROTEIN BODIES. 1081. What remains when dough is kneaded in water till all the starch is removed? A gray substance called gluten, or vegetable fbrin. 1082. In what does it differ from all the organic matter hitherto described? In containing nitrogen, with small quantities of sulphur and phosphorus. 1083. What other similar substances are found in the vegetable world? Vegetable albumen, contained in the juices of fruits and trees; and vegetable casein, found in many seeds, as, for example, in peas and beans. PUTREFACTION. 157 1084. What name has been applied to these animal and vegetable substances to designate them as a class? They are called 2rotein bodies. 1085. What do these substances resemble? Animal fibrin, albumen, and casein. 1086. Mention a common property of the protein bodies which distinguishes them from substances which contain no nitrogen. When burned they give off an odor like that of burning wool. 1087. Mention a still more important distinction between such substances and those not containing nitrogen. They undergo putrefaction, with the emission of gases of offensive odor. 1088. What substances are produced during putrefaction? The putrefying substance is decomposed, forming, besides other substances, ammonia, carbonic acid, phosphuretted and sulphuretted hydrogen. 1089. To which of these gases is the offensive smell of putrefying bodies chiefly due? Principally to the phosphuretted and sulphuretted hydrogen. 1090. Mention an important difference between the PUTREFACTION of nitrogenous bodies and the FERMENTATION of non-nitrogenous substances already described. Putrefaction, once begun, continues spontaneously; but the process of fermentation requires the constant presence of a ferment. 158 CHIEMISTRY. 1091. What is a ferment? Yeast, or any other nitrogenous body in a state of decomposition, acts as a ferment. 1092. How does a ferment start, and afterward maintain the process of fermentation? The motion of its own atoms, which occurs in decomposition, is supposed to impart motion to the atoms of the fermenting body, and thus cause their re-arrangement. 1093. What is the first action that takes place in raising bread with yeast? Under the influence of the yeast, a portion of the starch of the flour is converted into sugar. 1094. What afterward occurs? The sugar ferments, yielding alcohol and carbonic acid; the bubbles of the latter become entangled in the dough, and thus raise the sponge. 1095. What becomes of the alcohol? It escapes into the oven during the process of baking. 1096. By what other means than fermentation can we produce the gas needed to make bread light? By employing soda or saleratus with sour milk or tartaric acid, as before described (914). 1097. What advantage is derived by the use of these materials for raising bread.? A light sponge is produced without the loss of starch and sugar, as occasioned by the use o? yeast. PRElSICs ACID. 159 1098. What is the great objection to the use of the above-mention ed substances? The difficulty of employing them in just the proper proportion to neutralize each other. 1099. What bad result follows the use of an excess of alkali? It neutralizes the acids of the stomach, thereby interfering with digestion. PRUSSIC ACID, ETC. 1100. What is the composition of the substance known in commerce as YELLOW PRUSSIATE OF POTASH? It is composed of iron, potassium, and cyanogen. 1101. What is CYANOGEN? A colorless compound gas, containing nitrogen and carbon, and nearly twice as heavy as the air. 1002. Mention some of its properties. It has the odor of peach pits, and burns with a beautiful purple flame. 1003. What occurs when yellow prussiate of potash is distilled with sulphuric acid? The salt is decomposed and _pr2usic acid produced. 1004. What is the appearance of prussic. acid? It is a colorless liquid, giving off a strong odor of peach pits. 160 CHEMISTRY. 1105. Wh.lat are the properties of this acid? It is intensely poisonous; a drop of the concentrated liquid, if placed upon the tongue of a dog, produces immediate death. ALTAILOIDS. 1106. What are the ALKALOIDS? A class of organic bodies resembling in certain properties the alkalies of inorganic chemistry. 1107. Mention some of the points of resemblance. Their action upon vegetable colors is the same, and, like the alkalies, they unite with acids to form salts. 1108. What is the composition of the alkaloids? ~Most of them are composed of carbon, hydrogen, oxygen, and nitrogen. 1109. Mention some of the more important alkaloids. Strychnine,.Xorphine, Quinine, and Nivcotine. 1110. What is STRYCHNINE? An alkaloid obtained from hnwu vomica; it is the most dreadful of poisons. 1111. Whence are MORPHINE and QUININE obtained? The former is extracted from opium, the latter from Peruvian bark. 1112. What is said of NICOTINE? It exists in tobacco; it is a most energetic poison, ranking scarcely below prussic acid. COLORING MATTER. 16 1113. What are the uses of the alkaloids? Some of them are much used in medicine. Excepting in small doses they are all highly.poisonous. COLORING MATTERS. 1114. Mention some of the more important vegetable dye-stuffs. Indigo, madder, and logwood. 1115. What is INDIGO? A blue substance deposited from the colorless juice of certain plants by simple exposure to the air. 1116. What is the principal use of indigo? It is employed for dyeing woolen and cotton cloth blue. 1117. What is MADDER? The ground root of a plant extensively grown in India and Europe for the sake of its red coloring matter. i118. Why is it so highly prized as a dye? Because it is the only dyestuff which will produce a perfectly fast red upon cotton. 1119. What is LOGWOOD? A wood obtained from Spanish America containing a red coloring matter. 1120. Mention a property of this coloring matter. It combines with the oxide of iron, producing a jet black color. 1121. What are the uses of logwood? It is much employed in dyeing. Most silk and woolen goods are dyed black by means of logwood. 162 AGRICULTURAL CHEMIISTRY. CHAPTER XIV. AGRICULTURAL CHEMISTRY. THE RELATIONS OF THE PLANT TO THE SOIL. 1122. WHENCE do plants obtain their nourishment? In part from the air and in part from the soil. 1123. What does the air supply? Carbonic acid and ammonia. 1124. What does the soil supply? Carbonic acid, ammonia, and mineral matter. 1125. Do plants take mineral matter from the soil without refereree to its composition? They do not. They take the kind and variety which is especially suited to their growth. 1126. What are the substances which they take from the soil? They consist of several oxides and acids. The oxides are potassa, lime, magnesia, and oxides of manganese and iron. These are found combined with silicic, sulphuric, and phosphoric acids, and are accompanied by a small portion of common salt. All plants need these substances, and they may therefore be called the mineral food of plants. 1127. Do all plants contain these substances in the same proportion? They do not. The phosphates predominate in grains, 'COMPOSITION OF SOILS. 163 lime exists in'large proportion in grasses, potash in root crops, and silica in straw. 1128. Of what are soils principally composed? Of vegetable matter, sand, clay, and carbonate of lime. Soils contain the other substances above mentioned in small proportion. The mechanical character of soils depends on the proportion of these ingredients. They have besides their special uses, to be hereafter mentioned. 1129. What is the use of the VEGETABLE MATTER in the soil? It furnishes to the soil, as it gradually decays, carbonic acid, ammonia, and the mineral matter which it originally derived itself from the soil. 1130. What is the use of the CARBONATE OF LIME Carbonate of lime neutralizes the acidity of soils. It has also the effect of hastening the decomposition of both vegetable and mineral matter, and thus prepares food for the plant. And besides this it is itself a constituent of the mineral food of plants. 1131. What is the use of the cLAY? It retains by chemical affinity much of the prepared food of plants which would otherwise be washed away. It also gives tenacity to the soil. 1132. What is the effect of taking off many crops from the soil without the addition of fertilizing material? It gradually exhansts the soil. 1133. How does the soil become exhausted? By giving up all of its material which is in a fit state to nourish plants, or all of some one essential constituent. 1t 164 AGRICULTURAL CHEMISTRY. 1134. How is the soil improved by rest? Through the influence of change of temperature, air, water, and carbonic acid, the mineral matter of the soil decomposes, and becomes fitted to nourish the plant. 1135. How is this improvement hastened, and poor land brought under cultivation? By plowing in, while yet green, such a growth of clover, rye, or buckwheat as can be obtained from the poor soil. The same object is accomplished by the use of peat and muck. 1136. In what way does this improve the soil? The vegetable matter thus added serves in its decay as gaseous food for future plants. It also hastens the decomposition of the soil itself, and thus increases the supply of mineral food. 1137. Why is stable manure and animal matter of all kinds a highly valuable addition to the soil? Because in its decay it yields both mineral matter and a very large proportion of ammonia. 1138. What is the most perfect system of farming, though not always practicable? That in which a large part of the crops raised is consumed by animals on the farm. 1139. Why is this system superior to one in which all of the crops are sold? Because it retains a large portion of the material taken from the soil to be returned to it again in the form of manure, LIME, ASHES) AND GYPSUM. 165 1140. Why is burned LIiE a valuable application to heavy soils? Because it hastens decomposition of both animal, vegetable, and mineral matter, and thus prepares material for the plant. Chalk, marl, and shells have these effects in a much lower degree, but are valuable fertilizing material. 1141. Why is ASHES a valuable addition to the soil? For the same reasons as lime, and, besides, because it supplies in itself the various constituents of the food of plants. 1142. How are both lime and ashes likely to prove injurious to light soils? By exhausting their store of fertility. Where they are used on such soils, this effect must be compensated by more abundant manuring. 1143. What purpose does gypsum serve as a fertilizer? It furnishes lime and sulphuric acid, two important constituents of the food of plants, and besides serves to fix and retain the ammonia of the air. 1144. What are COMPOSTS? Composts consist of vegetable and animal matter heaped together for fermentation and partial decay, in order to prepare them for application to the soil. A covering of vegetable mold or peat prevents the escape of ammonia. 1145. What other material is more effectual for retaining ammonia in composts and in the manure heap? Gypsum or plaster. A sprinkling of dilute sulphuric acid is also sometimes used for the same-pu'rpose. 166 AGRICULTURAL CHIEMISTRY. 1146. What is GUANO? It consists of the droppings of birds, partially decomposed and hardened by time. 1147. Where is it found? The best guano is brought from certain islands of the rainless region along the coast of Peru. It is found in some instances accumulated to the depth of a hundred feet. 1148. In what does the principal value of guano as a fertilizer consist? In the large proportion of ammonia which it contains. Phosphoric acid and potash are other important constituents, but of less value. 1149. Has the fact that the region referred to is rainless any thing to do with the quality of Peruvian guano? It has. When guano is exposed to rain, its ammonia is dissolved and carried away. Other guanos than the Peruvian contain, for this reason, little of value excepting phosphate of lime and magnesia. 1150. When phosphates are wanted, in what form are they most cheaply supplied? In the form of bone dust, which furnishes at the same time a certain portion of animal matter. The value of bone dust is greatly increased by the addition of sulphuric acid, which converts the phosphate of lime into "superphosphate," and renders it easily soluble (940). 1151. What caution is to be observed in employing lime or ashes with decomposed stable manure! or any other fertilizer containing ammonia? Lime or ashes expel ammonia from eguano and other de AMMONIACAL FERTILIZERS. 167 composed manures, and should therefore never be applied with them unless with large admixture of peat or other absorbent material. 1152. As nitrogen is abundant in the air, and hydrogen in water, why can not ammonia, which is so valuable a fertilizer: be artificially produced? In the first place, its elements can not be cheaply separated from air and water; and, again, when obtained, they refuse to combine with each other. We are, therefore, principally dependent on the decay of animal and vegetable matter for ammonia. 1153. What other source of ammonia exists? The distillation of coal and wood in the making of gas is another source of ammonia. The gas liquor of gas works is, therefore, a valuable fertilizer. 1154. What other substance serves the same purpose as ammonia as a fertilizer? Nitre or saltpetre, which is, however, much more expensive than the other substances employed to furnish nitrogen to the soil. 1155. Why do ammonia and saltpetre serve the same purpose as the food of plants? Because both contain nitrogen, which is the constituent which gives them their value as food for plants. 168 PHYSIOLOGY AND PHYSIOLOGICAL CHIEMISTRY. CHAPTER XV. PHYSIOLOGY AND PHYSIOLOGICAL CHEMISTRY. 1156. WHAT is the relation of the animal to the vegetable world? The animal lives on food which the vegetable has prepared out of earth and air. 1157. Is this true even of animals that feed on flesh? It is also substantially true of these, for the animals which are consumed as food have derived their support from the vegetable world. 1158. Can not the animal, like the vegetable, also live on earth and air? It can not; these materials must have undergone a change, and taken the form of vegetable matter, before they can serve as the food of animals. 1159. H[ow, then; may all animal matter be regarded? As vegetable matter modified or entirely transformed by the processes of the animal body. 1160. What is the first great step in this transformation? The conversion of the food into blood. Out of this fluid all parts of the animal body are formed. 1161. How may the blood be figuratively regarded? As the rivers on which all the materials for building the body are floated to their destination. DIGESTION. 169 1162. What are the first steps in the conversion of food into blood? After being ground up by the teeth, and moistened by the saliva, it is conveyed to the stomach, and there submitted to the action of the gastric juice. 1163. How is the food effected by the gastric juice? The food is converted by the action of the gastric juice into a uniform greyish semifluid mass called chyme. 1164. What becomes of the chyme? It is pushed forward into the intestines, where minute absorbent vessels draw off from it its useful portion, in the form of a milky elastic liquid called chyle. 1165. What is the next step in the process? The chyle is poured into the blood, and then becomes blood itself. 1166. Into what distinct parts may blood be separated? Into an alkaline liquid called the serum, a fibrous material called fibrin, and minute red globules. 1167. How may this separation be effected? By simply beating fresh blood with a branched stick. The fibrin adheres to the stick, and the globules after a time settle from the serum. 1168. What is the FIBRIN? It is analogous to gluten in the vegetable world, and to muscle or flesh in the animal world. 1169. What is the sERUM? It is principally albumen, analogous to the vegetable albumen in the juices of plants, and especially so to the white of an egg. 8 170 PHYSIOLOGY AND PIIYSIOLOGICAL CHIEMISTIRY. 1170. Of what are the red globules composed? They consist principally of albumen, with a small portion of red coloring matter. 1171. Are not these materials at the same time quite analogous to one another? They are; animal fibrin, albumen, and the casein of the milk are analogous to each other and to the same substances in the vegetable world, both in chemical composition and character. 1172. Are they not probably capable of conversion into one another? Under the influence of the vital force they are probably readily converted into one another. 1173. What does the blood contain besides the substances above mentioned? Water, fat, phosphate of limfe, and certain other salts. 1174. What is evident from the preceding paragraphs? That the blood contains, ready formedl, much of the mlaterial required to build up the animal body. 1175.; Illustrate this further. Flesh is fibri forom the blood. Bones are phosphates from the blood. Tallow is fat from the blood. The egg is calbumen from the blood. 1176. What is the power which selects the material of the blood to build up the organs, and to produce the different fluids of the body? The power resides in innumerable minute cells which are distributed throughout the body. CIRCULATION OF TIIE BLOOD. 171 1177. What organs serve to propel the blood through the body? The heart acts as a forcing pump, to force the blood through the arteries to all parts of the body. 1178. How are the ARTERIES situated? They are, for the most part, deeply imbedded, that they may be safe from injury. 1179. Into what vessels does the blood pass from the arteries? Into minute branches of the arteries, which again communicate with the branches of the veins. 1180. How is the blood returned again to the heart? It returns through the veins, to renew its circuit. 1181. Does it commence, without interruption, a new circuit through the arteries to all parts of the body? It does not, but first makes a passage through the lungs, and returns again to the heart. 1182. How is the heart arranged to serve these two purposes, of sending all the blood on one circuit through the lungs, and in another to all parts of the body? It consists of two distinct compartments, of which the right one controls the passage through the lungs, and the other the general circulation. Each of these compartments is double, consisting of an auricle, which receives the blood, and a ventricle, which I I forces it on its way. 172 PHYSIOLOGY ANtD PHYSIOLOGICAL CHEMISTRY. 1183. What does the preceding figure represent? A human heart, with the lungs lifted away on either side to expose it more distinctly to view, etc. 1184. Of what do BONES consist? Of a framework of mineral matter, which is principally phosphate of lime, filled in with a cartilaginous matter commonly known as gelatine. 1185. Are these found separate in different parts of the bone? They are not; they penetrate each other so perfectly in every part that if the one is removed the other retains its perfect shape. 1186. How may the animal matter or cartilage be removed without affecting the mineral matter? It may be burned out, leaving the bone in a porous condition, but still perfect in form. 1187. How may the mineral matter be removed without affecting the cartilage? It may be dissolved out by muriatic acid, leaving a mass of the original shape so flexible that it may actually be tied into a knot. 1188. Why are the bones of the old more brittle than those of young persons? Because they contain a smaller proportion of cartilage. 1189. How are the bones held in their places in the body? By firm ligaments, which allow them to move on each other, but not to become displaced. 1190. How are the bones moved? By muscles, which contract at the will of the individual. THE MUSCLES. -173 1191. Are the muscles always in contact with the part they move? They are not; but are often connected with it by longer or shorter cords called tendons. Thus the muscles that move the fingers lie just below the elbow in the arm. 1192. What is the appearance of the muscles? Their color is red-they form the principal part of lean flesh. 1193. What proportion of fluid matter does animal muscle contain? The fluid matter amounts to nearly four fifths of the whole. 1194. What name is given to this fluid? It is called ftesh fluid, and contains besides water various organic substances, which are the occasion of the high flavor of meat broth. 1195. What is the chemical composition of dried muscle? It consists principally of animal fibrin, quite analogous in composition to vegetable gluten, before described. 1196. How does the cartilage of bones, the material of the skin, -tendons, and ligaments, differ from fibrin in chemical composition? They contain rather more oxygen and nitrogen. 1197. Are all of these materials very nearly the same in animals as ill man? The bones and other materials above mentioned are the same in animals as in man. 1198. Of what are the brain and nerves of animals composed? Of albuminous matter, with certain peculiar acids and fats. ~17-4 PHYSIOLOGY AND PHYSIOLOGICAL CHEMISTRY. 1199. Does a knowledge of the composition of the brain throw any light on its office as the organ of the mind? It does not; this is a mystery which no science can explain. 1200. What are the NERVES? The nerves are minute branches of the brain, extending to all parts of the body. 1201. What is their office? They form a sort of telegraphic communication between the brain, which is the seat of the mind, and-the various organs of the body. 1202. Name two classes of nerves. There are nerves of sensation and nerves of motion. 1203. Illustrate the action of the first by an example. If the hand is accidentally burned, a nerve of sensation communicates the fact of the injury to the brain, and gives us consciousness of pain. 12~04. Illustrate the action of the nerve of motion. A nerve of motion sends a return message to the proper muscle, and the hand, in obedience to it, is instantaneously withdrawn. 1205. Why is more food needed when the body is once fully formed? Because it is constantly wearing out and needs repair. 1206. Illustrate this further. The brain wears out by thinking and the muscles by physical exertion, and new particles must take the place of the old. FOOD. 175 1207. How are these supplied? New matter is constantly supplied by the blood. 1208. What becomes of the old matter? It is carried away by the blood, and drawn off from this fluid as refuse matter in the course of its circulation. 1209. What kind of matter is always required to supply the place of the worn-out muscle and brain? Substance like albumen, fibrin, and casein, containing nitrogen. Such material is called plastic food, to indicate its capacity of being formed or modded into organs. 1210. What kind of food do working animals require? Food rich in the plastic material above mentioned, that their waste of muscle may be rapidly repaired. 1211. What office is served by those constituents of the food which, like starch and sugar, contain no nitrogen? They are the floating fuel which sails along in the blood, and is slowly consumed in every part of the body to keep it warm. On account of its relation to respiration, such material is called respiratory food. 1212. How does it happen that no starch or sugar are found in healthy blood? They seem to be changed to fat or something similar as soon as they enter the circulation and before they are consumed. 1213. How are these materials burned up inside of the body where there is no air? The-blood contains oxygen, which is all that is essential to combustion. 176 PHYSIOLOGY AND PHYSIOLOGICAL CHEMISTRY. 1214. Whence does it derive this oxygen? It absorbs it as it passes through the lungs. 1215. Describe the structure of the lungs which makes this absorption possible. The lungs contain innumerable air cells, which are filled at every breath. Outside of these the blood flows in minute vessels, with nothing but a thin membrane to separate it from the air of the cells. As it passes it takes in the oxygen which is required to burn up the starch and sugar of the food. 1216. Will not flesh and other plastic food answer for fuel in the animal body? It will, but it is poor fuel; and at the same time more expensive. 1217. Where does this combustion take place? The combustion does not occur in the main channels of the blood, but in the minute branches of the blood-vessels which exist in every part of the body. 1218. What happens if the burning oxygen of the blood does not find sufficient fuel? It begins to burn up the body itself. 1219. Why does a starving man or animal become emaciated? For the reason above suggested; that his body is gradually burning up. 1220. Why is more of the combustible food above referred to needed when breathing is quickened by cold weather or exercise? Because the blood takes in more oxygen, which must have something to burn. ANIMAL IIEAT. 17 1221. What follows from the greater amount of combustion which takes place? The body grows warmer, or in cold weather is able better to resist the external cold. 1222. To what is the case analogous? To that of a stove with increased draft. 1223. In what seasons and what climates is most food required, for the above reasons? In cold seasons and in cold climates. 1224. In wood, starch, sugar, fat, and similar material in a stove, smoke or at least gases and vapors are produced; why is not this the case in the blood? It is the case in the blood also. 1225. What gases are produced in the blood? Carbonic acid and vapor of water. 1226. How are these disposed of? The blood absorbs them and carries them to the lungs, where it gives them off into the air at the same time that it takes in oxygen from the air. 1227. How does this vENovs BLOOD) which always comes to the lungs with this load of carbonic acid, appear? It has a dark purplish color. 1228. What is the appearance of the ARTERIAL BLOOD, which has parted with its carbonic acid and taken oxygen instead? It is bright red or scarlet. 1229. What kind of food is best adapted to fattening animals? Food containing a large proportion of starch and sugar. 8* 178 PHYSIOLOGY AND PHIYSIOLOGICAL CHEMISTRY. 1230. How does this conduce to the formation of fat? The surplus of starch and sugar over and above what is required to sustain the animal heat, takes the form of fat. 1231. What is the composition of MIL? Milk is composed of water, cheese or casein, globules of oil, certain salts, and a peculiar kind of sugar called sugar of milk. 1232. Why is butter produced by churning milk or cream? The agitation causes the small particles of oil to unite into larger masses. 1233. What keeps the cheesy portion or curd dissolved in the milk? The small portion of free soda which milk contains enables it to keep the curd dissolved. 1234. Why does the curd separate from the other portions when milk is long exposed to the air? Because the sugar of milk turns to acid, and the acid then neutralizes the soda, which before kept the curd dissolved. 1235. Will vinegar or any other acid poured into milk have the same effect? Any acid poured into milk has the same effect. 1236. What other means are employed to precipitate the curd? In making cheese, rennet, which consists of the infusion of the lining membrane of the calf, is used with the same -effect. GELATINE. 179 1237. How may milk be converted into a solid form and be kept sweet for months? By adding to it a little soda and gum, and then evaporating it to dryness by gentle heat. 1238. What effect have the gum and soda? The gum surrounding each particle protects it from the air, and the soda neutralizes any little acid which may begin to form, and so checks its formation. 1239. How is milk reproduced from such solidified milk? By simple solution in warm water. 1240. What is the GELATINE used in the preparation of jellies? It is identical in composition with the cartilage of bones and the skin of animals, and is produced from such material by simple boiling and evaporation. 1241. Upon what property does its use depend? On the property of a hot solution of the substance to stiffen or gelatinize on cooling. 1242. Hiow does it differ from ordinary glue? It is a purer kind of glue. 1243. What is ISINGILASS? It is a pure gelatine obtained from a species of sturgeon. Ordinary gelatine is often called by the same name. 1244. Why is gradual heating to be recommended in the preparation of soups? Because sudden and high heating coagulates the albumen which the flesh fluid contains, and by stopping up the pores on the outside, prevents the escape of the fluid. 180 PHYSIOLOGY AND PHYSIOLOGICAL CHEMISTRY. 1245. Why does sudden heating yield more nutritious and highly flavored meats? Because it operates, as above explained, to imprison the highly flavored juices of the meat. 1246. How are the skins of animals converted into leather? By steeping them for a long time in all infusion of bark. 1247. What chemical action takes place during the process? The tannin of the bark combines with the gelatine of the hide, securing it against decay and rendering it impervious to water. 1248. Mention another method of preparing skins. Soft leather for gloves and similar uses is made by impregnating skins with alum and oil. 1248*. For what is refuse leather sometimes employed? Refuse leather is used in the preparation of the prusslate of potash (1100), a salt much used in dyeing and calico and paper printing. 1248t. How may it be otherwise turned to account? The tannin may be extracted from it and used in tanning new leather, while the gelatine which remains may be converted into glue. CIRCULATION OF MATTER. 181 CHAPTER XVI. CIRCULATION OF MATTER. 1249. WHAT is the principal agent in the circulation of matter upon the globe? Water. 1250. How does it act to produce this circulation? Descending in rain, it dissolves the materials of the soil and of rocks, and supplies them for the growth of plants, crystals, and innumerable varieties of shell-fish in the ocean. It then rises again by evaporation to commence its round anew. 1251. What further circulation of mineral matter does it help to produce? That which takes place in plants. Every tree is a sort of mineral fountain. The material of the soil rises in the sap, and, falling again in the dead leaves and branches, is returned to the earth. 1252. What circulation of other material of vegetable life is constantly occurring? The ammonia and carbonic acid absorbed by plants and converted into their substance are reproduced and returned to the atmosphere again through decay and decomposition. 1253. Give a brief statement of the relations of vegetable and animal life. Plants produce food for animals out of the materials of 182 CIRCULATION OF MATTER. the earth and air. Animals consume it, and return in their breath and death tile same materials to the atmosphere and earth. 1254. How is the sun shown to be the source of all mechanical power? The cwater that drives the mill-wheel in its descent has been previously lifted by the sun's heat in the form of cloud and vapor. The steam that propels our engines is produced by the use of fuel which the sun's rays helped to form out of earth and air. The muscles that move our bodies are repaired by food which the sun's rays have also assisted to produce. 1255. In what sense may the sun be regarded as the source of the life of the globe? The sun moves the winds and lifts the vapors which are the life of our globe, and his genial rays call forth the vegetable life on which all animal life is sustained. 1255*. How does the accompanying cut illustrate the circulation of. matter? It indicates to the eye that all forms of life are pro duced out of Earth, Air, and Water, and are in perpet. ual process of reconversion into the same materials. I __ ~-. —.-{-:.._-:.,..._..... GEOLOGY. 113 CHAPTER XVII. GEOLOGY. 1256. IN what condition have we reason to believe that the earth existed originally? It was "without form and void," and probably existed as a thin vapor or nebula, like that of which comets are composed. 1257. What was probably its next condition? It cooled down to a fluid form, as steam condenses to water. 1258. What fact in nature shows that the earth was once fluid? It is bulged out at the equator, just as a fluid globe would come to be by revolving on its axis. 1259. Mention another fact that confirms the belief that the earth was once entirely fluid. The interior of the earth is probably now in a molten or fluid condition, as will be hereafter shown. 1260. What was the third step in the earth's history? The process of cooling continued until a crust formed upon the surface of the fluid sphere, as ice forms on water. 1261. Why did not the process continue until the whole mass became solid? Because the crust was a poor conductor, and served to keep in a good part of the remaining heat. 184 GEOLOGY. 1262. What change followed the formation of the crust? As the cooling still proceeded, the water which had before existed as steam, condensed and covered the whole earth. 1263. What was the next step toward the present condition of the earth? As the globe contracted by cooling, the crust bulged out in certain parts and sank in others, and the dry land appeared above the universal ocean. 1264. What effects would rains and ocean tides and currents have upon the crust, both above and below the water? They would gradually wear it away, and leave it as a sediment on the bed of the ocean, to harden again in the course of ages into rock. 1265. What class of rocks have thus been formed? The rocks which have been thus formed are called aqueous or sedimentary rocks. 1266. What is the foundation rock, on which these sedimentary rocks rest, called? Primitive or igneous rock, of which granite is an example. 1267. How is it known that the sedimentary rocks have been formed as above stated? It is inferred from the fact that they are stratified, or made up of layers, like the leaves of a book, as deposits from water always are. It is also known from the fact that they contain buried within them various shells and other animal and vegetable remains. GEOLOGY. 185 1268. How is their formation. as above stated, on the bed of the ocean, consistent with the fact that such stratified rocks, containing animal and vegetable remains, cover whole regions which are high above the ocean? Strata originally formed on the bed of the ocean have been subsequently lifted to their present position by the further bulging of certain parts of the earth, which has elevated continents. The figure represents such strata partially elevated above the ocean from which they were deposited. -- I I I II -- - 1269. What observed fact confirms ihis view? The fact that changes of elevation in different parts of the earth's surface are going on at the present day. 1270. Mention an instance of such elevation. The coast of Sweden is at present rising at the rate of about two feet in a century, as is shown by the gradual emergence of rocks which were once covered by the sea, and by the fact that ancient sea-ports have become inland towns. 1271. Mention an instance of sudden elevation. In the year 1823 an earthquake occurred in Chili which is said to have lifted up an area of nearly 100,000 square miles. 1272. Mention an instance of subsidence. The subsidence of certain portions of the coast of England, Scotland, and New England is proved by the fact 186 GEOLOGY. that rooted stumps of trees are found under water on these coasts. 1273. What may we infer from these and other similar facts? That there were causes in operation. in the earlier periods of the earth's history sufficient to have lifted up continents and mountain chains. 1274. What is the evidence that the interior of the earth is at present in a molten or fluid condition? It is found in the fact that wherever the crust is deeply perforated, as in the case of volcanoes, molten matter issues fromn its interior. It is also proved by the fact that in earthquakes successive portions of the crust of the earth actually bend and roll along in a wave, as they could not if the earth were solid tO tthe centre.'. i c-=!!!2EYSER i - I C ~~In~~~~~GBIBPE B IBIT GEYSEPRS OF ICELAN'D. GEOLOGY. 187 1275. What other facts strongly confirm this view? The existence of hot springs like the Geysers of Iceland, and the fact that the earth grows hotter the farther we bore into its crust. The increase is about one degree for every 50 to'70 feet. This observation makes it probable that at the depth of 50 to 100 miles all rocks are in a molten condition. 1276. What is the thickness of the stratified rock which forms the outer layer of the crust above this molten mass? Stratified rock is entirely absent in many places, and where it occurs varies from a few feet to several miles in thickness. 1277. Is the stratified portion of the earth's crust the same in charaoter throughout its whole thickness? It is not. The rocks which form the strata are of very various character. Limestones, sandstones, and slates of different kinds form the principal varieties. 1278. Into what two classes may the stratified rocks be subdivided? Into fossiliferou8 rocks, so called from the fact that they contain fossils, or the remains of vegetable and animal life, and the mon-fossiliferous, which are destitute of fossils. 1279. Mention the principal non-fossiliferous stratified rocks. Gneiss, mica slate, and clay slate are the principal nonfossiliferous stratified rocks. Clay slate is also found as a fossiliferous rock. 18 188 GEOLOGY. 1280. How are gneiss and mica slate supposed to have been formed? They are supposed by many geologists to have been formed from the ruins of granite rock. Others suppose them to have been originally fine grained, like the slates, and to have become crystalline after their deposition through the agency of heat. 1281. Why are the non-fossiliferous stratified rocks also called METAMORPHIC rocks? Because of the change to a crystalline structure which the last-mentioned view supposes them to have undergone after their deposition. 1282. How do gneiss and mica slate differ from each other and from granite in their structure? The original stratification is entirely distinct in mica slate, in gneiss it is less apparent, and in granite there is no appearance of stratification. All of these rocks are highly crystalline. GRANITE. GNEISS. MICA SLATE. 1283. What general term is applied to all rocks destitute of fos. sils? They are called azoic rocks. 1284. How have the fossiliferous rocks been subdivided? They have been subdivided into groups or systems, which, proceeding from the non-fossiliferous rocks upward, are named as follows: the Lower Silurian, Upper Silurian, GEOLOGY. 189 Old Red Sandstone, Carboniferous, New Red Sandstone, Oolitic, Cretaceous, Tertiary, and Diluvium. To these are to be added the alluvial deposits which are still in process of formation. 1285. What is said of the time when the different systems were deposited? The rocks of each system were deposited during a distinct period in the history of the globe. 1286. What is the most important means of distinguishing rocks of the different systems? They are distinguished principally by the animal and vegetable remains they contain, which are, to a great extent, different in each. 1287. Why does this difference exist in the organic remains? It arises from the fact that different races of plants and animals inhabited the world during different periods of its history. 128:8. What does the great thickness of the stratified rocks suggest as to the age of our globe, or, in other words, as to the time required for the deposition of all the formations? The process of deposition must, from the nature of the case, have proceeded with extreme slowness, and it is obvious that very long periods of time, amounting to hundreds of thousands of years, must have been required for its completion. 1289. What other fact may be cited as proof of the correctness of this view? Limestone strata exist hundreds of feet in thickness, 190 GEOLOGY. which are entirely composed of the remains of shell-fish, of which innumerable successive generations must have had time to live, grow, and die before such accumulations could have taken place. 1290. Are the strata of all the systems above mentioned found piled one upon the other in all parts of the earth? They are not. In some places the primitive rock is bare, at other points but a single formation covers it, and in other cases the rocks of several systems rest one upon another. 1291. How is this illustrated in the geology of North America? Much of the northern portion first lifted from the sea is crusted with azoic rocks only. The central portions of the United States remained long enough under water to receive the deposits of the Silurian period, which now form their surface. Much of the region between the Mississippi and the Rocky Mountains was still submerged, and in rising brought with it the later cretaceous formation. The region about the Gulf of Mexico, and as far as New Jersey alongthe Atlantic coast, being the last which the earth won from the sea, lifted with them the deposits of the ter tiary period. 1292. Explain the figure. The figure represents North America at the coal epoch. The white portions represent the part of the continent which was above water at that period. The remaining black and shaded portions taken together represent the GEOLOGY. 191 ocean at the same period, while the black alone represents the present ocean. The detached shaded portions indicate the localities of our present coal fields. AMERICA AT THE COAL EPOCH. 1293. Illustrate the formation of coal fields in general by those in North America. When the middle portions of the country were elevated, at the close of the Silurian period, they inclosed a portion of the former ocean waters, forming inland seas. 192 GEOLOGY. These first received a lining of the old red sandstone, and afterward of limestone, and were then filled up with the successive layers of coal clay, iron ore, and limestone, which form the coal measures. 1294. What rocks do we meet with in proceeding outward from a coal basin in any direction? The outcropping edge of the sandstone lining forms a margin of many miles, and sometimes of scores of miles, in extent on all sides of the coal fields. From this we step off upon the Silurian, which forms the general remaining surface of these portions of the country. From these again we pass to on the north to the older rocks of New England and the Canadas, and in the south and west to the later cretaceous and tertiary formations.* 1295. When strata of different formations occur one above the other, are they always contiguous formations of the series before given? The strict order is always observed in all formations which occur, but one or more formations may be entirely wanting, and distant members of the series may thus be brought into contact. 1296. How is this to be accounted for? The portion of the earth where this is observed must have been submerged to receive the deposits of the earlier periods, again elevated to escape others, and again submerged to receive the later. *For the origin of coal, see Chemistry, page 143 GEOLOGY. 193 1297. As the series of formations at all places is imperfect in one or another of the ways above mentioned, how is it possible to decide to what formation any stratum belongs? There are certain differences in the structure and composition of the, rocks of, different ages, which enable the geologist to form an opinion, but the fossils which the stratum contains are by far the surest guide. 1298. What fact proves that such elevations as are above mentioned, preceded and followed by submergence, have taken place? One proof is found in the existence of coal beds in Europe, formed, as all coal is, from plants which have grown on the land, and occurring between stratified rocks which could only have been formed by deposition from water. 1299. Are the strata of the different systems always found in their original horizontal or nearly- horizontal -.<,lposition? By no means; they ~~ have been often broken -~ by upheaval from beneath, and lifted into an z inclined position, as represented in the figure.* 1300. What advantage does this fact give us in the study of geology? Large portions of the history of the globe, which would * The dark lines crossing the strata represent veins or lodes of metallic ores. 9 194 GEOLOGY. otherwise be inaccessible, are thus turned up to be pried open by the geologist's pick and hammer, and read in course. 1301. How may the relative age of mountains and mountain chains be determined by the geologist? The relative age of mountains and mountain chains may be determined by the age of the rocks which they have lifted up with them in their elevation. 1302. What is the relative age of the Alleghanies of North America and the Andes of South America as determined by this reasoning? The Andes are much the younger, as is proved by the fact that they have lifted the tertiary strata with them. The Alleghanies are patriarchs in comparison, as is shown by the horizontal position of the new red sandstone, tertiary, and cretaceous formations at the base of the range. 1303. What other irregularities occur in rocks besides inclined position? Strata of all formations are found, not only lifted and broken, but also bent and folded, where they have been subjected to lateral pressure. The operation of such causes has produced great confusion in the position and form of rocks all over the world. 1304. Are the strata of different overlying formations always ":conformable" or parallel with each other? They are not; the strata of more recent formations are often found lying upon the inclined and worn-off edges of those of earlier date, as is shown in the accompanying figure. GEOLOGY. 195 _ Id,2, Li p 1305. How is this occasioned? By an upheaval which lifted the earlier rocks into an inclined position before the later were deposited. 1306. How might the later deposit of stratified rock come to be inclined also? By a later upheaval, which should lift it from its original horizontal position with the earlier strata on which it rests. 1307. What inference might be made from such an arrangement in nature? It could be inferred with certainty that the elevation of the mountain had taken place at two different epochs. It has recently been shown by this reasoning that the Alps of Switzerland have been thus lifted at different points of time, with intervening periods of rest. 1308. How have stratified rocks often been changed at a period subsequent to their deposition? They have, in many cases, been softened and even melted down by the encroachment of the molten mass beneath. 1309. How have they become permanently changed in consequence? They have been changed on cooling into crystalline rock. 196 GEOLOGY. 1310. What has been the result in the case of limestones and sandstones? The limestones have been converted into crystalline marble, and the sandstones into quartz rock. 1311. What has been the effect on clay slates? They have passed into the condition of mica slate, gneiss, and probably even into granite, according to the degree of heat to which they have been exposed. (Compare 1280.) 1312. How would the original stratified appearance of the rock be modified in this process? It would be more or less obliterated, according to the degree of heat (1282). 1313. In the changes of stratified rocks above mentioned, how are their fossils affected? They are destroyed by heat. 1314. Where this is the case, how can the age of the rock be ascertained? In many cases it can not be ascertained. In others it may be inferred from fossils in another part of the same stratum which has been subjected to less heat. 1315. How does it happen that primitive rock is often found in veins in the stratified Iocks, or entirely overlying them? This occurs where the crust has been ruptured by subThis occurs where the crust has been ruptured by sub GEOLOGY. 197 terranean forces, and the molten mass beneath has risen to fill the fissures, or overflowed and hardened above. 1316. What similar process is taking place at the present day? The overflow of lava from the craters of existing volcanoes. 1317. How does the lava of modern volcanoes differ from more ancient igneous rocks? It is not so crystalline in its structure, nor so compact and dense. MOUNT ETlA., 1318. How many volcanoes, active at the present time, are known? Not far from 300. 1319. What class of rocks; besides modern lava, is supposed to be of volcanic origin? Trap rock, of which the Palisades on the Hudson River, and the Giant's Causeway on the coast of Ireland, are examples. This kind of rock is sup- posed to consist of the lava of ancient submarine volcanoes, which has been subsequently elevated from the sea. - 1320. What remarkable character has this CHEESE OGROTTO. kind of rock? Its columnar structure. The whole mass is often found 198 GEOLOGY. cracked into regular prismatic columns, which are again divided, so as to stand one upon another. The preceding figure represents a grotto in Germany which is formed of this kind of rock. 1321. What purpose does the study of the rocks subserve besides giving us the history of the globe itself and the changes which it has experienced? The rocky strata of the earth furnish not only a history of the globe itself; but give us, in their fossil remains, an account of the various races of plants and animals which have inhabited it before man existed. Each formation or system may be regarded as a separate volume, containing the natural history of the period during which it was deposited. 1322. Give some general idea of the difference of the plants and animals which existed on the earth during successive periods of its history. TRILOBITES. The plants and animals of the lower or older strata belong to the lower divisions of the several classes of animals. There is, in general, a progress to higher forms of animal and vegetable life as we ascend to the dilu GEOLOGY. 199 vial or last completed formation, or, in, other words, as we come to a later period in the earth's history. 1323. State the order of succession of animals. Marine animals alone occur in the "Silurian." Trilobites, the first among the crustacea, are represented in the preceding figure. In addition to fishes, and other marine animals, insects and scorpions only, among land animals, are ICTHYOSAURUS. PLESIOSAURUB. found in the " Carboniferous." Gigantic reptiles are added in the "New Red Sandstone" period, and are also found in abundance in the two which succeed. Two species of these reptiles are represented in the preceding figure. In the "Tertiary," among a great variety of land animals as well as marine, occur huge thick-skinned species of the PALEOTHERIUM. ANOPLOTHERIUM. forms represented in the last figure. In the still more recent tertiary deposits and remains, the monkey, the mammoth, and the mastodon are found. Last of all, in the alluvial deposits, which are still in progress of formation, occur the remains of man. 200 GEOLOGY. 1324. What is said of the vegetable fossils? In the forms of vegetable life there is a similar progression, from the flowerless plants of the earlier formations to the fruit and forest trees of the present period. The introduction of many of these preceded by only a short time the creation of man, and constituted the last adornment of the world for his reception. The succeeding figure represents a gigantic fern of the carboniferous period, one of the plants which contributed to the formation of the immense deposits of coal which have already been mentioned. TREE FERN. 1325. What is said of the scenery of the earth in past ages? We know of an insular period when only the highest portion of the continents had emerged —we know also of GEOLOGY. 201 periods of great convulsions and upheavals, of others characterized by inland lakes and luxuriant vegetation. And finding in the rocks such perfect remains of plants and animals, we can even form a tolerably correct idea of the dscaes of the most ancient periods. The figure rep landscapes of the most ancient periods. The figure represents an imaginary landscape of the Reptilian Age, which embraces the three systems which succeed the carboniferous. 1326. How are the periods above referred to proved to have been of great duration? From the immense thickness of the rocky strata which were deposited during each period. 1327. How does it happen that no remains or implements of man are found in all these formations preceding the alluvial. It must be because no human beings existed during the immense periods which these formations represent. 1328. How is the great age of the world before man was created, which geology requires, consistent with the Bible account that the work of creation was begun and completed in six days? The days of the Mosaic account should probably be 9* 202 GEOLOGY. regarded as long "periods" (an interpretation which the original language of the Bible admits), and the evenings and mornings as the beginnings and endings of these periods. 1329. Show that the leading results of geology are in manifest harmony with the Bible. According to the Mosaic account of the creation, the earth was once entirely submerged, and the "dry land" afterward appeared. Geology leads to the same independent conclusion. According to the Bible the nobler races of animals were created last. Geology gives its corresponding testimony. The Bible makes the appearance of man the crowning act of the creation. Geology leads to the same result. The Bible leads us to believe that the world will be destroyed by fire. Geology furnishes us evidence that the earth carries in her own bosom the sufficient means of such a catastrophe. 1330. What may we infer from these points of agreement? In these points of agreement we may find the assurance that God's written word and the volume of creation serve each to illustrate the other, in proportion as we understand them, and that both will finally be found in perfect harmony. THE END.