ott- mthern Brand of the University of California Los Angeles FormL 1 QC This book is DUE on the last date stamped below JUL L-9-15m-8,'26 ^ SCIENCE FOR THE YOUNG; OR, THE FUNDAMENTAL PRINCIPLES OF "MODERN PHILOSOPHY EXPLAINED AND ILLUSTRATED IN CONVERSATIONS AND EXPERIMENTS, AND IN NARRATIVES OF TRAVEL AND ADVENTURE BY YOUNG PERSONS IN PURSUIT OF KNOWLEDGE. VOL. IV. FORCE. t/ SCIENCE FOR THE YOUNG. FORCE. BY JACOB ABBOTT, AUTHOR OF 'THE FRANCONIA STORIES," "MARCO PAUL SERIES," "YOUNG CHRISTIAN SERIES," "HARPER'S STORY BOOKS," "ABBOTT'S ILLUSTRATED HISTORIES," &c. WITH NUMEROUS ENGRA VINGS. NEW YORK: HARPER & BROTHERS, PUBLISHERS, FRANKLIN SQUARE. NOV Entered according to Act of Congress, in the year 1872, by HARPER & BROTHERS, In the Office of the Librarian of Congress, at Washington, A y) OBJECT OF THE WORK. THE object of this series, though it has been prepared with special reference to the young, and is written to a considerable extent in a narrative form, is not mainly to amuse the readers with the interest of incident and ad- venture, nor even to entertain them with accounts of cu- rious or wonderful phenomena, but to give to those who, though perhaps still young, have attained, in respect to their powers of observation and reflection, to a certain degree of development, some substantial and thorough instruction in respect to the fundamental principles of the sciences treated of in the several volumes. The pleas- ure, therefore, which the readers of these pages will de- rive from the perusal of them, so far as the object which the author has in view is attained, will be that of under- standing principles which will be in some respects new to them, and which it will often require careful attention on their part fully to comprehend, and of perceiving sub- sequently by means of these principles the import and significance of phenomena occurring around them which had before been mysterious or unmeaning. In the preparation of the volumes the author has been greatly indebted to the works of recent European, and especially French writers, both for the clear and succinct expositions they have given of the results of modern in- vestigations and discoveries, and also for the designs and engravings with which they have illustrated them. CONTENTS. I. RICK VAN DORN 13 II. CRANK MOTION 21 III. MECHANICAL FORCE 3C IV. TRANSFER OF FORCE BY PULLETS AND BANDS 50 V. TRANSFER OF FORCE BY GEARING 58 VI. THE MILL 73 VII. FALLING FORCE 90 VIII. HEAT 108 IX. THE FOUR CIRCUITS OF SOLAR ENERGY 123 X. THE FOUR CIRCUITS OF SOLAR ENERGY 146 XI. THE FOUR CIRCUITS OF SOLAR ENERGY 172 XII. THE FOUR CIRCUITS OF SOLAR ENERGY "191 XIII. SCIENCE AND SENTIMENT 223 XIV. THE SUN 236 XV. RICK AGAIN 264 XVI. DETONATIONS AND EXPLOSIONS 276 XVII. FORCE IN RELATION TO TIME 289 XVIII. CONCLUSION 302 ILLUSTRATIONS. Lawrence's Seat Frontispiece. Liquefaction 16 Force of the Wind 27 Crank Motion 30 Iron Shears 36 A Primitive Lathe 39 The Bow-lathe 42 Rick at the Lathe 47 Open Belt 52 Crossed Belt 52 Fast and loose Pulleys 52 Burnishing Marble Paper 53 Axis at right Angles. rA Pulleys of different Sizes 55 Means of varying Speed and Power. 56 Gearing 58 Variable Speed 59 Complicated Movement 60 Barrel and Fusee 61 Crown Wheel 62 Beveled Wheels 62 Hack and Pinion 63 Reciprocating Movement 63 Forward and Reverse Motion 63 Chain and Pulley 64 Another Form 64 Single-toothed Wheels 64 Eccentric, or Cam 65 Action of the Cam 65 Wipers 66 Wipers again 66 Crank-pin 66 The first Locomotive 67 Automatic Action 68 W T ings without Force to work them 70 More Wings without Force 71 Making a Sluice-way 78 Undershot Wheel 82 Overshot Wheel 85 Xll ILLTJSTKATIONS. Page The Pile-driver.. . 100 The Mill-pond 103 A King-post 106 Fire by Friction Ill Holy Fire 112 Work of the Sun 124 The Hurricane 134 The Anemometer 136 Pressure of twenty Pounds per Foot 140 Pressure of the Wind 141 The Water-spout 143 Clouds : Primary Forms T. .. r ,. . ' r 154 Clouds : Secondaiy Forms..?!! 1 . ,.M . ...7..? 158 Self-registering Pluviameter 166 Expenditure of Falling Force , 170 Contending Radiations 175 Field Ice ._ 178 Eifects of the Avalanche .-.r-.....' 186 Scenery on the Coast of Norway 188 Among the Icebergs after Seals and Whales 1 89 Stomata 193 Section of a Stoma 193 Solar Force restored 198 Contending Currents of Solar Energy. Victory easy 202 Victory doubtful 205 The Sun giving Help 216 The Sun sending Warning 219 Appearance during a total Eclipse 245 The Helioscope 248 General Appearance of Spots 249 Appearances indicating Cavities 250 Mottled Surface. Willow Leaves. Luminous Bridges 253 Changes of Form 255 The Meteor 261 The Zodiacal Light 262 We're resting 272 Measuring the Bursting Pressure 282 Transmitting an Impulse of Force 295 Oblique Action 298 The Torsion Balance ... .. 299 FORCE. / O CHAPTER I. KICK VAN DORN. " JOHN," said Lawrence one day, when John was with him in the shop watching some work at the lathe in which he was engaged, " are there any bad boys in your school ?" " Two or three," said John. "Is there any one that is really ugly," continued Law- rence, " so that every body dislikes him ? I want a really ugly boy." "There's Rick Van Dora," said John. "He's ugly enough. But what do you want of an ugly boy ?" " I wish to try some experiments upon him," said Law- rence. " Oh ho !" exclaimed John. " What an idea ! You can't try experiments upon a boy." " I want to see, at any rate, whether I can or not," said Lawrence. " How old a boy is Rick, as you call him?" " About twelve or fourteen," said John. 14 RICK VAN CORN. "How came he by such a name as Rick?" asked Law- rence. " I don't know," replied John. " His real name may be Richard, for aught I know. But the boys always call him Rick." "Is he a handsome boy?" asked Lawrence. " No," said John. " He looks as cross and ugly as he is. All the boys despise him and hate him. Besides, he is the poorest scholar in school. Pie don't study any, and he is always in some mischief or other." " Doesn't he do any thing well ?" asked Lawrence. "He plays ball pretty well," said John. "Yes, he's a good ball-player. They all like to have him on their side in playing ball, and I don't believe but that he might do well in other things if he only would try ; but he won't try." " Well, couldn't you ask him to come here and see me some day ?" said Lawrence. "He wouldn't come if I should ask him," replied John. " Why not?" asked Lawrence. " He would think that you had some design upon him," said John. " He is very suspicious when any body sends for him. He thinks, I suppose, that he is going to get a scolding for some of his misdeeds." "Tell him," said Lawrence, " that I have got a lathe, and am going to turn a bat, and that I want him to come and tell me about the best size and shape of it" "He may possibly come for that," said John, musingly; " but he is more likely to think that it is only a pretense to catch him." " Well, I must confess he would not be far from right in that supposition," said Lawrence. " But you can ask him, at any rate. Ask him to come next Saturday forenoon." " Well," said John, " I'll ask him, though it is very doubt- NATURE OF OUR KNOWLEDGE. 15 ful whether he will come. But what do you really want him for, any how ?" " I want to try an experiment upon him. I'm going to try to reform him." " To reform him !" repeated John. " I'm sure you won't succeed. Every thing has been tried already and failed. I should like to know by what means you expect to reform him." "By means of force," said Lawrence, quietly. "Force! Hoh !" exclaimed John, much surprised. "I don't think you have any authority to use force upon him. Besides, he won't stay. And then force has been used. He says that if there was any virtue in whipping to make a good boy, he should have been a saint before this time, for he has had nothing but whippings all his life." "I did not express myself quite right," said Lawrence. " It is not force itself exactly, but ideas offeree that I mean to employ. But you persuade him to come, and I'll try my experiment ; and I'll explain to you, in the end, how it worked." And here it must be said that there is one thing curious in respect to our ideas of every thing pertaining to the ex- ternal world, and that is, that we can not, strictly speaking, form any conception of what any thing really is, in its in- trinsic and real essence, but only how it acts. To show what I mean by this, let us take the case of lead as an example. "We say that lead is heavy. We mean by that that when we let it rest upon our hand, or upon any movable support, it weighs it down ; that is, it acts in a certain way. We say it is malleable ; we mean nothing more by that than that when it is struck by any hard sub- stance it yields, and becomes indented or flattened. It is fusible, which is only a word expressing how it acts when heated to a certain degree, namely, it sinks down from its 10 KICK VAN DOEN. EFAOT1ON. solid state and gradually becomes liquid. When we say it is of a bluish color, we mean simply that when it is held before our eyes it sends rays of light into them which produce in our minds a particular sensation. It is the same with all the other properties of lead. The names of these properties are only expressions of the manner in which the substance acts under different specified circumstances. As to the substance itself in its intrinsic and absolute nature we can have no idea whatever. Now it is not only so with lead and other metals, but with all the material substances, and all the agencies and powers of nature of every kind. What we call force forms LAWRENCE'S REFLECTIONS. 17 no exception to this universal rule. There is something in its inner and intrinsic nature that entirely eludes the efforts of the wisest philosophers to comprehend. All that we can really learn about it is how it acts. The young persons, therefore, who may read this book, must give up all idea of obtaining from it any conception of what force, in its hidden nature, is, and only hope to learn in what different forms it presents itself to us, and in what ways it acts in those dif- ferent forms. And so Lawrence, in saying that he was going to try to interest Rick Van Dorn in ideas of force, meant only that he intended to try to interest his mind in certain new trains of thought in respect to the different forms of force, and its various modes of action, and not at all in relation to its internal and absolute nature. The fact was, that Lawrence had become so accustomed, in his scientific studies, to consider all the substances and agencies in nature as governed by fixed laws, so that the way to change the action of any one of them was to change the circumstances under which it was placed, and not to get out of patience and fret at the wrong action as, for example, if he was trying to melt lead, and it would not melt as fast as he expected, not to denounce or find fault with the lead, but simply and quietly to give it more time, or apply more heat he had become so accustomed, I say, to act on these principles in dealing with material agencies, that he was quite inclined to look upon mental and moral processes in somewhat the same light. Or, rather, he was inclined to consider and inquire whether there might not be something analogous in the phenomena of mind to the regularity of sequence, in respect to cause and effect, that he knew so certainly every where prevailed in the world of matter. There can be no doubt, I think, that there is some truth 18 KICK VAN BORN. in this view of the subject, and that AVC should all act move philosophically, and get on much better, in dealing with the wrong doing that we witness around us in the world, if we would scold and fret about it less, and be less inclined to be made indignant by it, and try more to devise means for changing the influences that have been or are now oper- ating upon those that act badly. But we must return to Lawrence and John. "But really," said John, after a short pause, what kind of an experiment is it that you are going to try on Rick?" "I can't explain it very well," said Lawrence, " till after I have tried it. But I'll tell you a little story which per- haps you may think will throw some light upon it." So Lawrence began his story as follows : " There was once a farmer who was worried and plagued almost to death by a swampy place on his meadow. There was a little rill of water which came down from a spring on the upland, and, instead of finding a natural channel by which it could flow off into the river, it spread all over the ground in a certain spot, and killed out all the healthy grass, and caused hummocks of wild grass and weeds to grow in its place. It made the ground so soft and boggy that the farmer sank into it over his shoes, even when he went near the margin of it ; and his cattle often got mired in it. The farmer used to fret and scold every time he came that way, saying, ' Confound the vile brook !' " At one time he conceived the idea of curing the mis- chief, by stopping the water from coming into the meadow by a dam. So he hauled a great log across the little rill where it came down from the upland, and by packing sods against the upper side of the log he made quite a good dam. But of course the dam soon got full, the water ran over the top of the log, or, insinuating itself among the sods, oozed through, and soon made the matter worse than FOOLISH MANAGEMENT. 19 before. Then he tried another dam a little farther up, and afterward another a little farther down, but all to no effect." " What a silly man !" said John. "He used to complain in an impatient and fretful way to his wife and to his neighbors about the plaguy brook," continued Lawrence. " It was the torment of his life," he said. He did not dare even to let his children go into the field for fear that they should get swamped in that quag- mire. "At last one of his neighbors went with him to look at the place. "'Why, man,' said his neighbor, 'you don't go to work in the right way. You must not fight the mischief by damming up the flow of the water, but you must open a channel for it in a safe place where it will do no mischief.' "So his neighbor helped him to tear away one of the little dikes which he had made on one side, to prevent the water from spreading over a new place in the meadow, and dug a channel in the ground where the dam had been. They continued this channel down through the part of the ground most favorable till they reached the river. As soon as they had done this, the water began to flow freely through it. The farmer and his neighbor looked at the little rill a few minutes, and then the farmer turned toward the swampy place and said, ' It doesn't do a bit of good. The ground there is just as miry, and the grass as coarse and good for nothing as ever.' " ' My dear man,' said the neighbor, ' do you expect the mischief that has been years in growing can be repaired in an hour? Wait three months and then see.' " The farmer waited three months, and by that time the aspect of things had entirely changed. The swampy place had become of itself dry and hard, and the cultivated grasses, good for hay, had spread all over it again, and the 20 KICK VAN DOKN. water flowed quietly down toward the river through a pretty winding channel over a sandy bottom, and between banks of flowers, where the farmer's children used to like to come often to play." Lawrence paused as if he had finished his story. John also paused a moment or two, as if he were thinking of it. " It is a very good story," he said at length, " though I don't see what it has to do with your plan about Rick Van Dorn. You said it would throw some light on that sub- ject." " I said perhaps you would think that it threw some light on that subject," said Lawrence. " I don't think it does," said John. " At least I don't see any light." " Then I was mistaken," said LaAvrence. KICK ON HIS GUARD. 21 CHAPTER II. CRANK MOTION. LAWRENCE and John were at a town in New England, near the sources of the Connecticut River, where Lawrence was pursuing some scientific studies connected with his profession of civil engineer, and John was receiving in- struction at a certain institution in the vicinity, known as the Morningside school, at the time when the conversation described in the preceding chapter took place. Lawrence had fitted himself up a shop, where he had a bench and tools, and also a lathe, and where he was accus- tomed to work at leisure times, making apparatus of various kinds for his investigations and experiments. It was to this shop that he invited Rick to come. On the Saturday following the conversation narrated in the last chapter, John came into the shop where Lawrence was at work, and said that Rick had come to the gate, but would not come in. " "Why won't he come in ?" asked Lawrence. " I don't know," replied John. "He seems to think that you have some design upon him." So Lawrence went out to the door and called to Rick. " Rick," said he, " come in here." " What do you want of me ?" asked Rick. "I want you to give me some advice about making a bat," said Lawrence. Rick, who was standing just outside of a gateway, with his hand upon the gate, as if ready to start off at the least 22 CRANK MOTION. alarm, looked curiously upon Lawrence for a moment, and then said, " Upon honor ?" " Yes," said Lawrence, " upon honor." "You have got some secret design upon me, I believe," said Rick. "That's a fact," said Lawrence; " I have." Rick looked up surprised. "What is it?" said he. " To make you my friend," replied Lawrence, " so that you will come here often and help me." Rick looked surprised and puzzled. He gazed a moment at Lawrence as if uncertain what to do, and then, as if won by Lawrence's frank and open expression of countenance, and his honest and friendly manner, he came slowly toward him and entered the shop. He and Lawrence had, however,, scarcely entered the shop before a messenger came from the house to say that some visitors had called, and Lawrence and John were re- quested to go in and see them. So Lawrence asked Rick to excuse him for a few minutes. " You can amuse yourself," said he, " in looking about the shop while we are gone, and seeing the tools and things." So Lawrence and John went away. As they were going along the passage-way that led into the house, John said to Lawrence, " I don't think much of your sense in leaving such a boy as Rick among your nice tools." "Why what will he do?" asked Lawrence. " Oh, he'll do some mischief or other," replied John. "He'll break something, or dull some tool, or play some trick or other." " I hope he will," said Lawrence. "Hope he will !" exclaimed John, surprised. " Why do you hope he will ?" RICK'S DOINGS. 23 "Because then I shall know that he is really the kind of boy that I want to experiment upon," said Lawrence. Lawrence's wishes, thus expressed, were not, however, after all, exactly realized, for Rick, when left alone in the shop, did not undertake to do any actually malicious mis- chief, though he met with a mishap which for a moment greatly alarmed him. It happened that there was a grind- stone in the corner of Lawrence's shop which was turned by means of what is called a treadle. Such a treadle con- sists of a wooden bar placed near the ground parallel to the frame of the grindstone. The end which is farthest from the grinder when the stone is in use is pivoted to the frame by means of a wooden pin, and to the middle of it is attached an iron rod which extends upward, and by means of a hook at the upper end clasps a small crank formed upon the axle of the grindstone, while the other end extends forward near the place where the grinder stands. By this contrivance the grinder, working this outer end of the bar with his foot, can turn the grindstone himself, while holding the tool with his hands, so as to ob- viate the necessity of having two persons to do the work. Now Rick, in seeing this grindstone standing in the corner, went to it, and, as idle boys are always very prone to do in such cases, began turning it around by means of the treadle, by way of amusing himself, to see how fast he could make it spin. So he began to work the treadle with his foot, bearing hard upon the outer end of it with his whole weight every time the crank came round, thus imparting to it a rapidly increasing motion. In a short time the heavy stone was brought into a state of very swift rotation, and it revolved, moreover, with so much power that the crank, in turning, would lift the outer end of the treadle-bar so forcibly as to lift Rick off the ground when he rested his weight upon it, 24 CRANK MOTION. and give him what he called a ride. But the fun, as Rick called it, was soon brought to a very unexpected termina- tion by something suddenly giving way. The treadle-bar flew out of its place, the connecting rod became separated, and the different parts flew about in the most violent and alarming manner as the stone went whirling round with great apparent momentum. Rick was aghast with sur- prise and alarm. He seized hold of the stone and tried to stop its motion. But all his efforts were vain. It went furiously on, and seemed to be rattling and smashing every thing to pieces. It was just at this crisis that Lawrence and John came back into the shop. Rick was much alarmed. He looked up toward Lawrence as he saw him coming in, and said, "Dear me ! I've done some dreadful mischief!" "Oh no!" said Lawrence. "You may have done some damage, but I do not believe you have done any mischief. Mischief is harm done intentionally, and I am sure you can not have intended to do any harm to my things." Rick said that he would not do damage on purpose on any account. Lawrence then went to examine the grindstone, and after looking at it a moment as it gradually ceased its motion and came to a stand-still, he said, " You have not even done any damage at least, none of any consequence. There was only a pin that came out. It ought to have been fastened in more securely." Rick was quite reassured by hearing Lawrence speak of the damage which he had done in this way, and began at once to help Lawrence to repair it. The pin that had come out was in the farther end of the treadle-bar, and was the pivot on which that end turned in working the treadle, so as to cause the grindstone to revolve. "You have not only not done any damage," said Law- ACCUMULATION OF FORCE. 25 rencc, but you have performed an experiment that illus- trates a very fundamental principle in respect to the nature of force. I will explain the principle to you, and if you and John understand it, and remember it, you will gain a great deal more good from the accident than it will occa- sion me of trouble in repairing the damage." Lawrence went on to say that the principle which he referred to was this: That force was an agency that ex- isted always in definite and measurable quantities, such that, though it might be transferred from one place of de- posit to another, and so be accumulated or dispersed, it could not in any way be increased or diminished. " Yes," said John, " it can be increased ; for when your grindstone was spinning round very fast, it exerted a great deal more force than Rick did by the power of his foot," "It exerted more force in any one instant" said Law- rence, " than Rick could exert in that instant ; but the whole amount of all the impulses that Rick gave to it was equal to all that the grindstone could exert ; that is, there was in the stone an accumulation of a great many small forces, and not any increase of the whole amount. "It was like filling a pail with water by pouring in a great many mugsful from a spring," continued Lawrence. "It is true, you may increase the quantity that is in the pail, and in that sense we may say there is an increase; but there is no actual increase on the whole, for the amount that is in the pail, when it is full, is only made up of the separate amounts of all the dipperfuls. There can not be, absolutely, in the whole amount, any increase or dimi- nution." "There might be a diminution," said John, "for some of the water might be spilled." "True," replied Lawrence," a part might be spilled, and a part might dry up ; but none of it would cease to exist B 20 CRANK MOTION. on that account. Wherever it went when it was spilled, or wherever the vapor went of that which was turned into vapor, there it would be. There might be a diminution of the quantity in the pail, but there could be no diminution of the actual amount of water employed in the experiment. Precisely the same amount, neither any more nor any less, would exist somewhere at the end of the experiment that existed at the beginning. "And it is just so in respect to force," continued Law- rence. "Precisely the same quantity that we have at the commencement of any process, or at the entrance, so to speak, of any combination of machinery, exists somewhere at the end of the process ; or, in the case of machinery, must be stored in it, or must issue from it in some way. There can not possibly be any real gain or loss of force any more than there can be of water. A great many small or gentle forces may be combined to make a great one, and, on the other hand, a great one may be subdivided into many small ones, but there can not, in either case, be any absolute in- crease or diminution of the amount. "Take, for example, the case of wind blowing the trees, as shown in the engraving. Nothing can seem, at first view, more vague and indefinite than such a force as this, and yet nothing can be more strictly defined and determinate in its nature than the action of the breeze in such a case really is. For every leaf, and for the area of every branch and stem, there is a certain stream of particles of air, each moving with a certain definite velocity, and all consequent- ly striking against the leaf or the stem with a certain force ; so that, if the quantity of air in one of the streams, and the rate of its motion, were known, the precise amount of the force which it would exert would be determined. Each particle strikes with a definite force, depending upon its weight and its rate of motion, and this amount of force PERSISTENCE OF FORCE. 29 can not be made either less or more while those conditions remain unchanged. " Thus every force which we see acting in nature around us exists in precise and definite quantities, which can in- deed be made to pass from one body into another, and in that way can be accumulated, and can be made to change, too, from one form into another, as will be more fully ex- plained hereafter ; but the amount can never be increased in any other way than by uniting a great many small forces into a larger one, or diminished in any other way than by dividing a large one into many small ones, in neither of which cases is there any absolute increasing or diminishing of the absolute amount. " It results from this, that whenever we see any force, however great, in action, as, for example, in the case of a windmill turning with great speed, or a steam-engine driving a ship through the water with great power, and we wish to investigate it philosophically, the first question to be asked is, Where does the force come from? and in the same manner, when we see a force disappearing, as, for in- stance, when an express train that has been moving with great impetuosity is gradually brought to a stand, or a bullet in rapid flight through the air is stopped by a wall, we have to inquire, Where has the force gone to ? The idea that either, in the one case, it has been created or called into existence by any kind of contrivance or mechanism, or, in the other, that any portion of it, however small, can have come to an end, or ceased to exist, is wholly inad- missible ; and this principle of the absolute continuity and persistence of all the force which is in action in the visible universe around us lies at the foundation of all real knowledge on the subject." We have an excellent illustration of this principle, in one of its forms, in the rotation of the grindstone, as im- 30 CEANK MOTION. pelled by the efforts of Rick, which produced in the end such a violent result. The great force of rotation which the stone acquired consisted only of an accumulation of a great many small forces imparted to it by the pressure of Rick's foot upon the pedal, as may be seen in the action of a common grindstone in any farmer's yard. SANK MOTION. The grindstone, turning in the direction denoted by the arrow, whenever, at each rotation, it comes into the posi- tion represented in the engraving, the boy, bearing with his whole weight upon the end of the treadle, transfers all the force represented by the descent of that weight to the crank, and so to the stone. Of course, when the crank comes down to the lowest point, and then turns to go up on the other farther side, the boy raises his foot, and then, as soon as it passes over the highest point, and turns to come down on the hither side, he bears on again with all EXACT CALCULATIONS. 31 his force, and so adds another impulse to the motion of the stone ; that is, he sends in, as it were, an additional force to be added to what lie had imparted before. Thus he goes on sending in an addition to the force previously communicated to the stone, at every rotation of it, until the quantity accumulated becomes very large. The reader who likes to have precise ideas on any sub- ject of this kind will perhaps be interested in seeing how exact calculations are made in such cases as this, and how quantities of force can be measured and expressed numer- ically. Let us suppose, then, that Rick weighed ninety pounds, and that at the right moment of each revolution he bore with his whole weight on the pedal. Let us also suppose that the end of the treadle-bar on which his foot rested descended at the rate of six inches in a second. Then the force that he imparted would be that of ninety pounds moving at the rate of six inches a second. Now let us suppose that the stone weighed six times as much as Rick's body ; then the force which Rick imparted to it would be a motion one sixth as great that is, the motion of one inch a second. This means, of course, an average motion of all the parts of the stone. The parts near the circumference would evi- dently move much more rapidly than the parts near the cen- tre. Then, again, some portion of the force which Rick's weight would exert would be expended in overcoming the friction, and there would be many other considerations connected with the manner in which the pitman that is, the connecting rod between the crank and the middle of the treadle-bar* acts in the different parts of its course ; but the general principle is simple and plain, as Lawrence * A connecting bar of this kind in machinery, which acts in communi- cating force hy a reciprocating motion up and down, is called a pitman, from the analogy of its action to that which the man who stands in the 32 CKANK MOTIOX. presented it to the boys, namely, that the whole of the very considerable force with which the stone revolved at last was made up by the accumulation of comparatively small forces which Rick impressed upon it through the treadle as the crank went round; and that the whole amount of the greater force, together with the small portion which had been deflected through friction, was neither more nor less than exactly equal to the sum of all the smaller ones. A heavy wheel like this grindstone, moving with a force made up of the sum of a great many smaller ones, is not only an accumulator of force, but it acts also as an equalizer of its flow. The force imparted to it is intermittent; that is, it consists of a succession of impulses ; but the force with which the stone revolves is steady and uniform. This is of great importance in the case ^of the grindstone, be- cause it is necessary, in grinding, that the tool should be held upon the stone with a uniform and steady pressure ; and if the stone were not heavy that is, if it did not con- tain a large quantity of matter, to continue steadily in mo- tion when motion was once imparted to it it would be stopped by the friction of the tool when the crank had passed the lowest point at each revolution, and was as- cending on the farther side, during which part of its revo- lution no additional force could be imparted to it. All machinery which is moved by a succession of im- pulses such as those given by means of a crank must have some heavy wheel to receive and store, and thus equalize the force. When the machinery itself consists of heavy wheels, they serve this purpose themselves ; but when the machinery is light, as in the case of a sewing-machine, a heavy wheel must be expressly provided to accomplish this end. Such a wheel is called a fly-wheel, and is usually pit, in sawing, exerts in pushing up and pulling down the saw, by means of the handles on the lower end of it. UNIVERSAL PRINCIPLE. 33 made of iron, with the greatest portion of the weight in the rim, where the motion is swiftest, and where, of course, the greatest quantity of force can be stored. Such a wheel may be seen connected with the treadle beneath the table in any sewing-machine. In some cases these fly-wheels are of immense size, and are generally used as above ex- plained in receiving and storing large quantities of force received in intermitted impulses which is always the character of the force transmitted by a crank and deliv- ering it afterward to other parts of the machinery in a continued and equable flow. The principle which was thus illustrated by the case of the grindstone, that whenever we see force of any kind or in any quantity in action, we may be sure that it proceeds from some other force previously existing in the same or in some other form, and precisely equal to it in amount, and that when it ceases to act it is not annihilated that is, it does not cease to exist, but passes oiF into some other body in the same or in some other form, but without at all changing its amount, is universally true. The case of the grindstone does not, indeed, prove this principle. It is only one illustration of it. The case of the grindstone, more- over, only shows the operation of it in respect to the equal- ity between impulses of force communicated by Rick's foot, and the revolving force of the stone made up by the accumulation of these impulses. Lawrence did not show where and in what form the force existed before it ap- peared in the boy's foot, or where it went in its disappear- ing, as the grindstone gradually came to a state of rest. These points he reserved to be considered and explained another time. The principle itself has, however, been fully proved to be universally true, so fully that there is no longer any doubt of it in the minds of any scientific or even well-informed man. B2 34 CKANK MOTION. It would have been well for mankind if this great truth could have been earlier and more generally understood, for it would have saved many, many years of valuable time spent, and vast sums of money that have been wasted, in attempting to conti'ive means for the production of force, under the name of machines of perpetual motion. The phrase perpetual motion is an unfortunate one, in a philo- sophical point of view, inasmuch as we have perpetual mo- tion already all around us, every where, instead of its being any thing new yet to be discovered. The particles of all bodies that we know are in a state of incessant movement. The earth itself is in rapid rotation around the sun, and the most solid rocks are constantly undergoing internal changes produced by expansions, and contractions, and oth- er movements of the particles among themselves. Thus, instead of there being any difficulty in producing perpetual motion, it is impossible to escape from it. We can not by any conceivable means produce in any substance a condi- tion of absolute rest. The real object of the so-called perpetual-motion ma- chines is the creation of force, or the expanding of a single small force into a great one by means of some ingenious combination of levers and wheels, or other machinery effects which, by the very constitution of nature, can not possibly be produced. In all cases where a new machine is proposed for doing work, the first question to be asked in respect to it is, from what source is the force derived by which the machinery is driven ? If any adequate source offeree is pointed out, the machine may be a success. This source of force may be in the movement of the wind, the falling or running of water, the rising or falling of the tide, the combustion of wood or coal, as in a steam-engine, or that of zinc, as in an electro-magnetic engine. There must be a source offeree somewhere, external, in its nature, to FUNDAMENTAL LAW. 35 the machine which it sets in motion ; for no machinery can by any possibility create or produce its own force, or in- crease in the least degree the amount which is furnished by the source, whatever it is, from which it draws its sup- pty- Let every reader of this book, therefore, understand and fix indelibly this fundamental principle, namely, All force, as it exists in nature or in human contrivances, exists in fixed 'and definite quantities, which can not be in- creased in any other way than by accumulating many small forces to form a great one, or diminished in any other way than by being divided and dispersed. MECHANICAL FOKCE. CHAPTER III. MECHANICAL FOKCE. IN the case described in the last chapter, the function of the grindstone, in respect to its action as a fly-wheel, was this, namely, to receive the force in the form of a succession of impulses imparted by the weight of Rick at each revolu- tion of the crank, and then to deliver it, at the surface of the stone, in an equable and continuous flow. In some cases, however, the action of a fly-wheel is the reverse of this. It receives the motion in a continuous flow from the machinery by which it is driven, and delivers in a succes- sion of impulses, when such impulses that is to say, inter- mittent exertions of force are required by the nature of the woi-k to be done. Such intermittent action, for example, is required in the case of such an en- gine, as is shown in the accompanying engraving, for cut- ting off heavy iron bars into portions of a given length. It seems wonder- ful that bars of such thickness can be cut offin this manner at IKON till K A US. PONDEROUS SHEARS. 37 a single stroke by a pair of shears. But there is no diffi- culty in doing it, and that, too, with great rapidity, pro- vided that a sufficient force to overcome the cohesive strength of such a mass of iron is accumulated in the im- mense fly-wheel, which always forms a part of such ma- chinery, and is brought to the work by a band or some other connection, and that the jaws of the shears are made massive and solid enough to hold the force and deliver it all at the precise point or line in the iron bar where it is required. The iron is cut off in such a case as if the bar was one of wax. The portions are made equal by means of the gauge seen toward the right, against which the work- man, after each portion is cut off, pushes the bar, and thus measures another portion to be cut off at the next descent of the cutter. The portions thus cut forming short bars fall in a heap upon the floor below. In this case it is evident that the steady and equable force involved in the motion of the ponderous fly-wheel, or in that of other portions of the machinery not seen in the engraving, is delivered, not equally and steadily in doing its work, but in a series of prodigious though momentary impulses, each one taking effect during the instant that the jaw of the shears is coming down to cut off the bar. Dnring the time while the jaw is rising again, and the work- man is pushing the bar forward into the right position for a new cut, there is, of course, an intermission in the expend- iture of force, for it is plain that comparatively very little force is required for raising the jaw to its former position in order to bring it into readiness for a second stroke. Thus it is plain that in such a case as this the force that is stored in the fly-wheel of the machinery is delivered, not in a continuous flow, but in a succession of very powerful impulses. A curious example of the different modes of the trans- 38 MECHANICAL FORCE. mission of force is given in the accompanying engraving, from a drawing made by a French traveler of a primitive species of lathe which he observed in use among the na- tives of Algeria, in Africa. The cord, it will be observed, on which the man bears his foot, is passed once around the spindle which forms the axis on which the work is fixed, and the farther end of it is attached to the end of an elastic wooden spring. By this arrangement, of course, in bearing upon the cord with his foot, the workman causes the axis, with the work upon it, to revolve, and the top of the elastic rod to bend toward him. Thus a portion of the force which he impresses upon the cord is conveyed to the axis and to the work, and an- other portion is expended in bending the spring, thus stor- ing itself, as it were, in the elasticity of the wood. When the workman raises his foot, this stored force comes into action to turn the axis and the work upon it back to its former position. Thus the man turns the axis and the work back and forth by an alternating motion, turning it forward by the direct action of his foot, and back again by the force imparted to the wooden spring, and stored in it till it comes into action again when the pressure of the foot is relieved. In precisely what condition a force can be stored in this manner in the elasticity of a substance, so to speak, we shall see hereafter, so far, at least, as in the present state of our knowledge on the subject it can be explained. Although this engraving answers very well as an illus- tration of the points above referred to, it still represents a very awkward arrangement for any practical purposes of turning except the shaping of pottery, as there is no con- venient mode shown for supporting the tool, though the long bar seen between the workman and the work would serve this purpose for a certain part of the operation. The THE BOW-LATHE. 41 tool, in almost all cases in turning, requires a fixed and very firm support. Lathes for practical purposes are, however, not unfre- quently made on a principle substantially the same as is illustrated in this example, by farmers' boys and other per- sons who do not wish to incur much expense in their work. The spring, however, in these cases, instead of being set up perpendicularly in the floor, is placed horizontally above, over the bench, the fixed end of it being fastened to the beams or rafters, and the free end extending over the work. The work is held between two pivots set in blocks, Avhich blocks are set firmly in the bench. The cord from the free end of the spring is brought down, and, after being carried once round a part of the wood to be turned in a little groove made for it passes down through an opening in the bench made for the purpose to a treadle, constructed somewhat like the treadle of the grindstone, below, near the floor. Of course, the workman can cause the work to re- volve three or four times in the direction required for his tool by bearing down upon the treadle, and then, on rais- ing his foot, the spring draws the treadle up again, carry- ing the work round by a backward motion into its original position. There is a bar of hard wood, which passes across from one of the blocks to the other, to serve as a rest for the tool in turning. Such a lathe as this is called a spring lathe. This kind of lathe, though comparatively easy to make, is not very convenient, or, rather, efficient for work ; for, as the wood to be turned does not revolve continuously in the same direction, but turns and returns by a series of al- ternating movements, the tool must only be held up to the work while it is moving in the right direction. Of course, it is only half of the time that the tool is producing any useful effect. Then, moreover, as there is no flv-wheel to 42 MECHANICAL FOECE. steady and equalize the motion, the action is not so satis- factory in any respect. For such a lathe as this, some building which can be used as a shop is required, and a considerable degree of strength, and some experience and skill in doing such work, is necessary for the construction of it. There is another kind, however, in which the force is transmitted in a some- what analogous manner, that any ingenious boy can make, and which can be used on any table by the fireside. THE BOW-LATHE. It is called the bow-lathe, because it is worked by means of a bow held in one hand by the workman, while he man- ages the tool with the other. It consists, in its simplest form, of a board of any convenient size as, for example, a foot long and six or eight inches w T ide with two stand- ards near the two ends, as shown in the engraving. There is a bar extending horizontally from one of these standards to the other, at the proper height, for a " rest" to support the tool, l^ear the top of each standard is inserted a screw. The inner ends of both of these screws are carefully formed into smooth tapering points, to enter into the ends of the HOW TO MAKE A BOW-LATHE. 43 piece of wood to be turned. Common " wood screws,"* as they are called, will answer this purpose very well, but they should be of good size, and the ends should be prepared by filing off the threads for half an inch, and carefully form- ing a conical point at the end of each. These ends should be ground smooth, and then polished upon a whetstone, so as to prevent their wearing the wood. The tips should also be oiled a little when in use. The screw at one end, besides passing through the top of the stand, should also have a small block like a nut on the outside, as shown in the engraving, by means of which it can be held tight in its place while the work is going on. Any boy with ingenuity and skill enough to make a bow and arrow can make such a bow as is required for a lathe of this kind by taking the one represented in the engrav- ing as his guide as to the form. The string should be a very close and compact one ; cat-gut is best. The wood to be turned must be made of the right length, and then shaped roughly to the size and form required. Small holes must be made in each end to receive the piv- ots, and a quai'ter of a drop of oil put in each. The cord of the bow is to be wound once round the wood, and then, one end being fitted to the left-hand pivot, the right-hand screw is to be turned forward till the point enters the hole in the other end, so as to hold the wood in its place, and the binding nut at the end is to be tightened. The boy then, holding the bow in his left hand, and the tool which must be at first of the gouge form in his right, begins his work. The first thing to be done with the tool is to form a groove near the left-hand end of the piece of wood for the cord or bow-string to run in. In the engraving the bow- * So called because, though made of iron, they are intended to be used in wood. 44 MECHANICAL FORCE. string is represented as encircling the wood in the groove ; but the place which it must occupy while the workman is cutting the groove which must be done by holding the tool in the left hand is a little to the right of it. The drawing is made in this way the better to show the ulti- mate form and position of the groove. Of course, when the groove is finished, the bow-string must be run along to the left, into it, and then the work, with the gouge to the right, can go on regularly. If the young workman finds that lie can not manage the tool with the left hand very well in making the groove, he can, if he chooses, turn the piece of wood end for end be- tween the pivots, and so form the groove in what will be the right-hand end of it, and then reverse it again when the groove is made. However this may be, any boy, however ingenious, may depend upon finding this work for a time full of vexation and discouragement; for the great difficulty in the case of such a lathe as this is, not to make, it, but to acquire the skill to use it. It is difficult, in the first place, to attach the bow to the piece of wood to be turned, with the cord wound once around it iu such a manner as to bring the bow on the upper side of it ; though, after one learns to do this, nothing is more easy. Then it is difficult for a young workman to acquire the knack of moving the bow with one hand and holding the tool with the other, and of pressing the edge of the tool up to the work only while pulling the bow toward him, for it is only then that the wood is re- volving in the right direction. Then, after learning to work successfully with a gouge-shaped tool, it is very dif- ficult to learn the art of smoothing the work with a chisel, for it is almost impossible for a beginner to prevent the corners of the chisel from catching in the wood. Any intelligent boy, however, who has ingenuity, pa- JEWELERS' LATHES. 45 tience, and perseverance enough to surmount all these dif- ficulties, will be able to amuse himself a great deal with such a contrivance as this, and when he learns to manage it right, can turn small ninepins, and tops, and checker- men, and tool-handles, and other such things with it, and in so doing will learn practically a great deal about force, and the art of dealing with it, and the action of it upon different kinds of materials, and will acquire much other knowledge which will be of great use to him in helping him to understand machinery, and lead him to take an in- terest in it as long as he lives. In fact, lathes constructed on precisely this principle, but made neatly of iron and brass, are in constant use by me- chanics for light turning, as any one can see by inquiring at any jeweler's or watchmaker's, and watching one while it is in operation. The watchmakers turn arbors, and wheels, and screws, and other small work, sometimes of brass, and sometimes of softened steel, in such lathes. They secure the lathe itself firmly, while they are using it, by holding it in a vice which is secured to their bench. A wooden lathe of this kind, to be used upon a table, may either be made upon a plank base heavy enough to keep it steady, or, if the base- board is thin, it may be held to the table by clamps made of blocks of wood of the right size, with square notches cut in them, tightened by wedges crowded in either between the upper side of the notch in the clamp and the base-board above, or between the under side and the lower edge of the table below. But to return to our story. Lawrence explained to John and to Rick some of the principles here referred to in re- spect to the management of that form of force which con- sists in mechanical motion, in the course of conversation with them at the grindstone and at the lathe. After hav- 46 MECHANIC AT, FORCE. ing remedied the damage done to the treadle of the grind- stone, he went to the lathe, asking Rick, by the Avay, what was the best kind of wood for him to take to make the bat of. " The very hardest and toughest kind of wood that you can get," said Rick. " You see the balls are very hard, and we strike with all our might, and the bats, no matter how hard the wood is, soon get broken or battered to pieces." "Yes," said Lawrence. "You draw the bat back as far as you can, and then you concentrate in it all the force you can impart to it from your arms through the whole length of the swing of them, and deliver the whole in a single in- stant into the ball." "And send it spinning," said Rick. Lawrence asked how ash would do ; but Rick said that ash would not do at all. "It is tough and springy, and good enough for some things," he added, "but it soon splits into shivers if we use it for a bat." Lawrence finally made choice of a piece of seasoned ma- ple, and fixed it in the lathe. He asked Rick various ques- tions about the length and the other dimensions best for a bat, and followed his directions exactly in marking out the work. Then, when he was ready to begin, he took a gouge, and asked Rick if he would work the treadle for him Avhilc he turned. "Oh yes," said Rick; "I can do that well enough." Rick began, and, to show how well he could do it, he was soon driving the machinery so furiously that Lawrence was obliged to check him, telling him that a moderate and steady motion was Avhat was required. Rick watched the effect of the gouge upon the rapidly revolving wood, and soon began to be greatly interested in the operation. At last Lawrence put the gouge into his hands, and asked him to sec if he could not work the treadle KH'K AT WO UK. 47 ai:d manage the cutting too. Rick seemed at first to hesi- tate, but he soon became willing to make the attempt, Lawrence standing by and watching the operation. John *-as then in another part of the shop. KICK AT TUB LATHE. John had listened to Lawrence's explanations, and to his 48 MECHANICAL FOKCE. account of the bow-lathe, with much interest, and, although he had the use of Lawrence's lathe, which was, of course, much more convenient for actual use, he determined that he would make a bow-lathe for himself some time, "just for fun," as he said. Lawrence proposed to Rick that lie should make one too, promising to help him in doing it. But Kick replied somewhat churlishly that he did not want such a thing. He did not think that it would do him any good. However, when he came to the trial of the gouge in Law- rence's lathe, and found how easily and how well he suc- ceeded in bringing the rough piece of wood into an approx- imation to its true form for a bat, he became for a few min- utes somewhat interested in the operation, though it is probable that this interest depended altogether, or almost altogether, upon the fact that it was a bat that he was mak- ing, and extended very little to the scientific considerations in respect to the nature of force which were involved in the process of turning. After the bat had been brought substantially into its proper form by the gouge, Lawrence finished it with the chisel, and smoothed and polished it with sand-paper, while Rick worked the treadle, driving the machinery as it was proper to do in the process of polishing at great speed. When it was finished, Lawrence took it out of the lathe and handed it to Rick. " Now let us go out and try it, and, if you like it, you can have it. Or can you tell by handling it how it will work?" "I can tell pretty well by the feeling of it," said Rick, taking hold of it with his two hands, and holding it out as if about to strike a ball with it. " Yes," said he, " that will do pretty well. But I have got a ball in my pocket, and we will go out and try it. But do you say I may have it for my own?" RESULT OF TUB FIRST EXPERIMENT. 49 "Yes," replied Lawrence. "Only you must come back in a few days after you have tried it on the play-ground, and tell me how it works." So they went out upon the grass-ground behind the shop to try the bat. John remained in the doorway looking on. Rick took a ball out of his pocket, and tossing it a foot or two in the air, and bringing the bat into position in a moment so as to intercept it as it fell, he struck it fair and square, with tremendous force, at precisely the right instant of its descent. The ball soared to a great height. Rick followed it with his eyes, and then began to walk along rapidly in the direction it was going. He caught it as it came down, put it in his pocket, and walked off in the direction toward home without looking around at all to Lawrence and John, and without any word, either of thanks or of parting, at leaving them. Lawrence turned toward the door where John was stand- ing, and advanced with a very curiously expressive smile upon his countenance. John was writhing to and fro in convulsions of laughter, now stooping down with his hands upon his knees, and now holding his sides in desperate ef- forts to restrain himself within such bounds that Rick should not hear him. "A perfect failure !" he said, as soon as he recovered suf- ficient composure to speak articulately. " I told you you could not interest him in any thing beyond ball-playing." " Perfect success !" rejoined Lawrence. " I am entirely satisfied with the result of my first experiment." And so they went back into the shop. C 50 TRANSFER OF FORCE BY PULLEYS AND BANDS. CHAPTER IV. TRANSFER OF FORCE BY PULLEYS AND BANDS. THE word force, in common parlance, is used in a great many different senses, some of which are quite vague and indeterminate. As used by Lawrence in his conversation about wheels and machinery with John and Rick, as nar- rated in the last chapter, it relates solely to what is some- times designated as mechanical force that is, the visible motion of masses of matter. There are various other forms of force, which consist, as will hereafter be shown, of changes taking place, or of effects produced, in the inter- nal constitution of substances. These will be considered hereafter. We are now dealing only with mechanical force, or energy, which is compounded in respect to its quantity, and with reference to a certain important class of effects produced by it of the quantity of matter that is in motion, and the velocity with which it moves. But this kind of mechanical force, it is evident, may ex- ist in a great variety of forms, or rather, perhaps, condi- tions. It may be rectilinear and continuous, as in a block sliding upon ice ; it may be rectilinear and reciprocating, as, for instance, in the case of the piston of a steam-engine, which moves to and fro, or up and down, in successive al- ternations ; it may be uniformly accelerated, as when a grindstone is made to go faster and faster by uniform ad- ditions to its velocity every instant, or when a weight let fall from a height descends with steadily increasing veloc- ity to the ground ; and it may be intermittent that is, it may advance by a series of distinct impulses, with inter- MECHANICAL COMBINATIONS. 51 vals of rest between them. And so it may be rotary con* tinuous or rotary intermittent. In a word, the number and variety of kinds of motion which may be required in working of machinery is without end ; while all of them must be derived from one common source whatever that source may be whether the up and down motion of the piston in the steam-engine, or the slow revolving of the great water-wheel in the mill. Now nothing is more common than the number and va- riety of the contrivances by which mechanical force is transmitted, and modified in transmission, in the construc- tion of machinery. Of course the number of possible com- binations of this kind is, in theory, unlimited, and the num- ber of those that are actually in constant use is exceed- ingly great. We have before us a work describing and illustrating more than five hundred of such elementary movements.* Some of these, especially such as illustrate the most important and fundamental principles, will be de- scribed in this chapter. If the reader will study them at- tentively, they will not only afford him a clearer general insight into the nature and workings of mechanical force, but will aid him much in understanding the construction of such machinery as he may, from time to time, have op- portunity to examine, and will greatly increase his interest in it. One mode by which mechanical force is transferred from one revolving shaft to another is by a band. These bands are made sometimes of cords running in grooves, and some- times of broad belts of leather, or some similar substance, running upon the wide pulleys, being prevented from slip- ping upon them by friction. You will often see in large manufacturing establishments a long shaft placed near the * Brown's Five Hundred and Seven Mechanical Movements. Artisan Office, New York. 52 TEANSFEB OF FOBCE BY PULLEYS AND BANDS. ceiling, and extending the whole length of the apartment, with pulleys here and there along the whole extent of it, and bands bringing down the force, so to speak, to a great variety of different machines on the tables or bench- es of the workmen below. If, in such a case, the motion is communicated by what is called an open belt or band that is, one not crossed, as in Figure 1 the motion of the lower pulley, through the force transmitted from the up- per one, and consequently that of the shaft which the lower one carries, will be in the same direction as that of the upper one. On the other hand, if the belt be crossed, the direction of the motion will be reversed. Very often, of course, the workman at the shaft below will wish to stop his own particular machine without interrupting the movement of the shaft above, by which all the other machines are carried as well as his own. A contrivance is accordingly adopted by which the connection of his machine with the shaft above may be suspend- BELT - ed and restored at pleasure, which contriv- ance consists of what is called the fast and loose pulley. This is illustrated in the en- graving, Figure 3. The pulley on the upper shaft, it will be observed, is single, while the corresponding one on the lower shaft is double. The upper pulley is fixed firmly to its shaft, and must revolve with it, but the left half of FAST A 3 LoosB th 6 lower one is loose, while the right half POI.LEY. j g fasti Thus, by slipping the band from the loose pulley to the fast one, or from the fast one to the loose one below, the machine driven by the lower one may be stopped or set in motion at pleasure by the workman, A EOOM AT HAKPER S. 53 without interfering with the continued motion of tne great shaft above. The pulley on the upper shaft is made broad enough to take the band from either of the pulleys below. In Figure 3, the lower shaft is placed for convenience quite near the upper one, but in practice such connections are made by belts extending a considerable distance from BUBN16UINO MAUBLE PA 54 TRANSFER OF FORCE BY PULLEYS AND BANDS. the shaft above to the working machinery below, as is in- dicated by the break in the belt shown in the figure. A good example of this bringing down of the force by a long band from a shaft above is shown in the engraving of the process of burnishing marble papers as performed in Harper's establishment. The long band on the left is the medium by which force is communicated from the shaft above to the one below, near the work, the pulley below being double, one part be- ing fast and the other part loose, so that the operator can put in motion or stop the burnisher at pleasure. The burnisher is formed by a highly-polished surface at the lower end of the long bar hinged at the ceiling, and worked to and fro over the surface of the sheet of paper upon the table by means of the transverse bar seen near the middle of the pictui'e, which is made alternately to push and to pull the burnisher by means of the crank in- distinctly seen to the right of the small fly-wheel on the lower shaft. Thus this engraving, besides illustrating the form and functions of a band for conveying force, serves also as an example of the manner in which a continuous rotary motion is converted into a reciprocating rectilinear one. In the above-described cases, the two shafts one of them furnishing, and the other receiving the force are pai'allel to each other. The wheel, how- ever, which is to receive and be driven by the force, may have its axis at right angles, or at any other angle to the shaft from which its force is to be derived. All that is necessary in such a case as this is so to arrange the pul- leys that the band can take the direction indi- cated in Figure 4. ANGLES. The nature of the effect produced by the REGULATION OF SPEED. 55 transfer of force in these ways from one pulley to another upon different shafts depends greatly on the comparative dimensions in circumference of the two pulleys. In Figure 5, for example, the upper pulley, we will suppose, is of one half the diameter, and, of course, of one half the circumference of the lower one. Let us suppose that the cir- cumference of the upper one is two feet, and that of the lower four feet. Then the upper shaft, in one revolution, will only carry over two feet in length of the band. But two feet in length of the band will only carry the lower pulley through one half a revolution, so that it will take two revolutions of the upper shaft to produce one of the lower. On the same principle, if the upper pulley is larger than the lower one, the revolution of the lower will be propor- tionally greater in speed. If a wheel thirty feet in circum- ference upon one shaft drives one of three inches circum- ference on another, the latter will make one hundred and twenty revolutions for every one of the former. Or the process of producing the acceleration may be di- vided, as it were, by introducing an intermediate shaft. For example, the upper pulley may be ten times greater in circumference than the second one, which will cause the second one to revolve ten times as fast as the first ; and then there may be a pulley on this second shaft, with an- other band connecting it with the third shaft, the pulleys being in the same proportion that is, ten to one. Thus, the third shaft revolving ten times as fast as the second, and the second ten times as fast as the first, there will be a hundred revolutions of the third to every single revolu- tion of the first. It is very important to remember that there is no loss 56 TRANSFER OF FORCE BY PULLEYS AND BANDS. or gain whatever of force in these transmissions; for what is gained in speed is lost in power, and what is gained in power is lost in speed. In some cases, as, for instance, in polishing, great speed is required, with but little power. In others, as in the case of the shears for cutting iron bars, as shown in a former chapter, a slow motion, combined with great power, is the object to be attained ; and thus, in the construction of machinery, the relative sizes of the driving and driven wheels are determined by the comparative de- grees of speed and power required for the purposes in- tended. Sometimes there is a set of pul- leys of different sizes on the upper shaft, with a corresponding set in the reversed order on the lower one, so that the band can be shift- ed to any pair at the pleasure of the workman, according to the na- ture of the work that he has in Fig. c. hand. For instance, in the case of MEANS OF VABYING 6PEKD AND POWEE. a lathe, if he has iron to turn, he requires, while cutting away the iron, little speed and great power, and for this purpose he carries the band over the pair of pulleys on the right, as shown in the left-hand part of the engraving, Figure 6. But when he comes to the work of polishing the surface of the iron, after it is finished as to its form, he requires great speed and little power, and then he shifts the band toward the pulleys on the left. Sometimes these systems of wheels are blended into cones, as shown in the right-hand part of the engraving, the rel- ative speed of the two shafts depending upon the part of the conical surfaces which the band passes over for the time being. In the large manufacturing establishments of modern DIVISION AND DISTRIBUTION OF FORCE. 57 times, the quantity of force that is transmitted in this way by bands, and the magnitude of the pulleys and bands by which it is transmitted, are often enormous. There is an account in the newspapers, at the time of the writing of this chapter, of a pulley put up in a mill in Fall River, Mas- sachusetts, twenty- seven feet in diameter, and weighing over sixty tons, and also of a belt of leather used in a cer- tain mowing-machine factory of such dimensions as to con- sume one hundred and fifty fades in the manufacture of it, and weighing nearly a ton. The force conveyed by such machinery as this is sufficient, when divided and distribu- ted among the spinning-machines of the mill, to drive from fifty thousand to one hundred thousand spindles. 02 TRANSFER OP FORCE BY GEARING. CHAPTER V. TRANSFER OF FORCE BY GEARING. BUT, besides the use of bands, there is another mode of connecting shafts so as to communicate force from one to another, and that is by what is called gearing that is, by means of notched wheels, the teeth of which "engage" with each other, as shown in Fig. 7. In this case, as in that of the belt jor band, the relative speed of the two shafts will depend upon the rel- ative circumference of the two wheels, as measured by the number of teeth in each. For example, if in the figure the left-hand wheel is the driving one, and has thirty teeth, while the one on the right, which is driven, has forty, it is plain that when the former has made one revolution, its thirty teeth will only have engaged with and carried forward thirty of the teeth of the large wheel that is, will have carried it only through three quarters of a revolution ; or, in other words, that it will take four revolutions of the one to produce three revolutions of the other; but the power with which the shaft of the larger wheel revolves will be proportionally increased. Thus the proportion of speed to power, in the transmission of the force, can, in this case, as well as in that of force transmit- ted by a band, be regulated at pleasure by the comparative sizes of the wheels. But, what is still more curious, not only can the whole revolution of the shaft that is driven be accelerated or re- tarded by making the wheel by which the force is received CHANGE OF SPEED. 59 larger or smaller in circumference than the one from which it receives it, but its speed may be varied at different por- tions of the same revolution by varying the curvature of different portions of it. Of course the curvature of the driving-wheel must be varied to correspond, so that the distance from the centre of one shaft to that of the other through the two teeth which are engaged at the several successive moments of rotation shall be " constant" that is, always the same. In Fig. 8, for example, we have two oval-shaped wheels geared together. In the position in which they are shown in the engraving, that part of the right-hand wheel where the curva- ture is gnat as if it were a portion of a small wheel is engaged with a portion of the left-hand wheel where the curvature is small, like that of a portion of a large wheel. In this part of the rotation, therefore, if the left-hand wheel is the ther conditions favor, they tend to restore themselves to the former state ; and what is most remarkable, and most important to be un- derstood and remembered is, that in thus restoring them- selves, they give back, in returning to their former condi- tion, precisely the same amount of force as that which was expended in producing the original change; and, moreover, that this force, thus released, may be applied to any pur- pose for which man may wish to use it, and must be ex- pended in producing some effect or other. There is still a great deal of mystery about the precise nature of the changes which take place in the internal con- stitution of matter, which correspond in their effects to the raising and letting fall of weights in relation to gravita- tion. Some scientific men suppose that this up and down movement, so to speak, in chemistry, is very closely anal- ogous in its nature to that of raising and letting fall a weight that is to say, that the sun, in acting upon com- pound substances in plants, in some mysterious way sep- arates the elements to a certain distance from each other, and, still more mysteriously, places them in such a condi- tion in relation to each other that they are kept apart, until DECOMPOSITION AND EECOMPOSITION OF WATEK. 195 finally they are released from this coercion, and that then they come together again with prodigious force. This fall- ing together, as these philosophers imagine it, is precisely analogous in its nature to the coming together of the earth and the iron weight of the pile-driver when the weight is released from the lifters which hold it, only, of course, the distance through which the force acts is inconceivably minute in one case in comparison with the other. To show clearly what is meant by this, we can take the case of water. Water is composed of the two substances oxygen and hydrogen. In the form of water the two ele- ments are intimately united, and are held together with enormous force. There are various ways, however, by which this force can be overcome and the elements sepa- rated. The separation may be effected by the force of very great heat, or by that of electricity, or by the superior attraction for one of the substances of a third substance brought into action upon it. In some form or other, how- ever, very great force is necessary to separate these ele- ments from their combination with each other in water; and, moreover, after they are once separated, they have an extremely strong tendency to come together again, and, in coming together, to develop and redeliver, as it were, the same force that was expended in separating them. Still, this tendency to reunite is suspended and disguised while the two elements remain coW,just as the tendency of the pile-driving weight to fall is suspended and disguised so long as it is held by the grapple above. A child who should know nothing about the construc- tion and action of a pile-driver might look at one standing on the bank of a river, with the weight raised, and have no idea of the force stored in it and held in suspense by the brown mass of iron near the top of the guides; and when this mass is suddenly released by a slight movement of the 196 THE FOUR CIRCUITS OF SOLAR ENERGY. workman below, he is astonished, and perhaps alarmed, at the sudden and violent descent of it, and at the tremendous force with which it strikes upon the head of the pile. In the same manner, any one might see the two elements of oxygen and hydrogen brought into their gaseous form in their separation from each other, and, not knowing by what mysterious means they are held apart, would never imagine what an immense force is held in suspense by the condition in which they are placed in relation to each other; and when, at last, they are released from this distention, as they may be by raising the temperature of the smallest portion of them up to a certain point, we are astonished at the suddenness and violence of the force with which they rush into union again. This force, in all such cases, shows itself, in the first in- stance, in the form of heat ; and this is the reason why it is only necessary to raise a minute portion of the mixture to the temperature necessary for releasing them in order to release the whole ; for the heat developed by the union of the first set of particles affected raises the adjoining sets on every side to the right temperature for union, and these the next, and so on with amazing rapidity through the en- tire mass the solar force which had been stored in them by the separation being brought again into action by their union with such suddenness and rapidity as to produce, under certain circumstances, a violent explosion. In other cases, as in the burning of wood, for example, or the reunion of the separated elements in the bodies of animals, the process is more slow. The reason is, that while, in the case of two gases mingled together, the parti- cles of the substances Avhich tend to unite are in close jux- taposition to each other, in the case of solids, one of the substances is in a compact mass, and the other has no ac- cess to the interior portion any faster than the outer por- 3LAB FOECK KESTOBKD, PHILOSOPHY OP COMBUSTION. 199 tions are consumed and borne away. The chief substances which are separated from each other in vegetable growth are carbon and hydrogen from oxygen, and it is chiefly of carbon and hydrogen, in various forms and proportions, and in various modes of combination, that wood and nearly all other vegetable products are composed. Consequently, when wood is set on fire, or, to speak scientifically, when a portion of the wood is raised to such a temperature that the carbon and hydrogen can again be seized by the oxy- gen of the atmosphere, the process of reunion can go on only so fast as the outer layers of the wood are wasted away, so as to afford access for the oxygen to the interior portions. Thus, though the " falling together," as it is now generally considered, of the oxygen and the carbon, and the oxygen and the hydrogen, gives out all the force, ei- ther as heat or in some other form, which was expended by the sun in separating them, the process of reunion, even in the greatest forest conflagrations, proceeds in a regular and gradual, though sometimes very rapid manner. If there was enough oxygen at hand to supply at once all the carbon and hydrogen contained in the woods shown to be on fire in the engraving, the whole forest would flash into a flame in an instant with an inconceivably violent ex- plosion, sufficient not only to blow the horse and wagon to atoms, but to shake the whole country around with the force of the concussion. In the case of the animal organization, the liberation of the force stored in the food is so regulated, if the organs are in a healthy condition, as to supply heat and mechan- ical force just so fast as it is needed for maintaining the life and the movements of the animal ; for the food which the animal takes consists simply of substances containing heat and force from the sun, stored in them by the pro- cesses of vegetation, and brought into such a condition 200 THE FOUR CIRCUITS OF SOLAK ENERGY. as to be easily received and assimilated by the animal or- gans. In consequence of the form in which the solar force is thus stored, and the wonderful adaptation of the vital or- gans to the work of receiving and developing it, it is liber- ated within the body of the animal very gradually, as it is needed, and often large portions of it are retained and are not liberated at all, so that when one animal feeds upon the flesh of another, the stored force is transferred in an unex- pended condition from one organization to the other. Thus the insect receives its food that is, its supply of stored force from the juices of the plants in which a portion of the solar energy has been laid up by the processes of veg- etation. The insect expends a portion of this force in his creepings, or his leapings, or through his wings, but retains a large portion of it in the tissues of his body unexpended. The swallow, in devouring many insects, transfers the en- ergy to his own system, and expends large portions of it in giving the prodigious impulse to his wings necessary for his rapid and tireless flight ; he does not, however, expend all that he receives, but large portions of it are stored in his flesh, to be transferred to the body of the hawk or the eagle when the swallow is in his turn devoured. In the same manner, the ox, in a double sense, supplies force for the use of man ; he receives the solar energy that is stored up in the blades of grass into his system; a part of this energy he expends directly in drawing the loads or plowing the fields of man, and a part he stores in his mus- cles and in his flesh, which form the beef that man uses for food. In this way the force is transferred in an unexpend- ed form to the human system, and man proceeds to expend it in spading or hoeing the ground, or perhaps in guiding the labors of the successor of the ox that furnished him with his supply. Thus it is the solar force, in process of CONTENDING FORCES. 203 being stored, that forms the grass of the field. It is the same solar force, after it is thus stored and has been trans- ferred to the body of the ox, that impels the plow ; and it is the same that is, a portion of the same, after a double transfer that is exercised by the higher organs of man in superintending and directing the whole operation. Thus, in its circuit through the organs of vegetable and animal life, the solar force is brought by slow degrees into action in the animal system, in proportion as it is required, for the various purposes of life. It may be brought into action also in the same gradual manner without passing into any animal organization, for the carbon and hydrogen may be made to recombine with oxygen, and thus deliver out the force which the sun exercised in separating them in a great many other ways. The currents of solar energy, in the different circuits which they pursue, may and often do come into opposition and conflict the one against the other. We have innumer- able examples of this in the ordinary phenomena of nature as witnessed around us. A very familiar example of it is afforded in the spectacle of a steamer ascending a river against the current by the force derived from the combus- tion, under the boiler, of wood taken from the bank of the stream, as is shown in the engraving, and is seen every day on the Mississippi River. The flow of the stream is produced, as was shown in the preceding chapter, by the falling force of water raised into the air by the solar radiation that is, by that portion of the solar energy that performs its circuit through the wa- ter and the air. The force by which the engine of the steamer is driven is derived from the wood which grew upon the bank ; for the steam is in no sense, as is often sup- posed, the source of the impelling power, but only the vehi- cle of it. In other words, the force which carries the steam- 204 THE FOUR CIRCUITS OF SOLAR ENERGY. er against the current is the force set free by the combustion of the wood that is, by the reunion, with great eagerness, of elements separated from each other by the same amount of solar energy acting through the organs of vegetable life. The two forces shown in action in the engraving, one act- ing upon the water, and through it upon the bottom of the vessel, and tending to carry the vessel down the stream, and the other that of the revolving paddles driven by the action of the heat through the intervention of the steam, meet and oppose each other, and the strongest carries the day. In this case the contest is quite a gentle one, and the vic- tory is gained with very little manifestation of violence on either side ; but in other cases the struggle is often a fear- ful one, and the victory for a long time doubtful. The next engraving represents the struggle between the force evolved from coal and that of the sun acting through the air and water in the winds and waves, which is often ex- emplified in the passage of a French or English steamer in crossing the Atlantic. The scientific student must cease to regard the steam in these cases as in any sense the source of the power. It is only the vehicle by which the force is conveyed ; for the true source, as has already been said, is the coal. It is common to speak in popular language of the power of steam, but the power of steam is only a power of the kind that is exerted by one end of a pole when a man is push- ing at the other end that is, it is in all cases power im- parted to it, and transmitted through it. When the fires go out under the boiler, the ppwer of the steam comes to ah end. All its boasted energy ceases at once, and it be- comes as inert, and as helpless, and as incapable of carry- ing on any work by itself as the cranks, or piston-rods, or any other lifeless part of the machinery. FORCE IMPRISONED IN COAL. 207 Nor is the coal itself any more an original source of the power by which the machinery is worked. It is the source only in the sense of being the substance in which the force is stored, ready to be called into action by the will of man. The real source, and the original one, so far as we can at present trace it, is the sun. That is to say, as was explained in the last chapter, the sun, by its action upon the organs of vegetation in the leaves of plants, separates the carbon and hydrogen from their natural combinations, and fixes them mysteriously in some new combinations, without, however, at all diminish- ing the great strength of their tendency to come together again ; but, for some reason not understood, this tendency can only come into action very slowly under ordinary tem- peratures, though it bursts into great intensity of action when the temperature is raised above a certain point, pro- vided the oxygen with which the carbon and hydrogen wish to unite is at hand. If, however, the carbon and hy- drogen are kept beyond the reach of oxygen, they have, of course, no opportunity to reunite, and the store of re- served force will remain unexpended for an indefinite pe- riod. This happens when the wood, or any other vegetable product, is kept under water, for then there is no oxy- gen accessible to combine with the imprisoned elements. It is true that the water itself contains a large supply of oxygen, but it is oxygen which is not free. It is already combined with its full proportion of hydrogen, and can take no more. Wood, therefore, that is kept immersed under water will retain its reserved force for an indefinite period. Now it happens that there are various ways by which large quantities of wood and other products of vegetation are accumulated in vast masses, which are submerged in water and preserved, and in the end become beds of coal. 208 THE FOUR CIRCUITS OF SOLAR ENERGY. These beds of coal, of course, contain enormous stores of solar energy, which were deposited in the substance of them years ago, when they were formed. The traces of the an- cient vegetable origin of the beds are found very abundant- ly in the structure of the coal when examined by the mi- croscope and by other means. There are various natural processes by which such de- posits of vegetable matter are now being formed. One is by the " rafts," so called, formed by the floating trees which accumulate at or near the mouths of certain great rivers flowing through countries covered with for- ests. Immense quantities of this stored force are carried down every year by the Mississippi, and by the great riv- ers of Asia, until they reach the mouths of them, or the flat land near the mouths, where they become matted to- gether in vast masses which float upon the surface of the water, or, being sunk by the weight of the roots and of the earth adhering to them, become water-logged, and form the foundation of shoals, or even, in process of time, of islands. In other cases aquatic plants have grown up from the bottoms of shallow lakes, spreading their leaves over the surface of the water until the mud at the bottom is so filled in every part by the ramifications of the roots, that, in the end, the whole stratum in which they grow is made buoy- ant with them, and it rises to the surface, and covers the water with a floating field, as it were, on which, in time, mosses and lichens, and at last shrubs and bushes grow. The lake is thus transformed into a bog, the soil and the vegetation growing upon it being supported, in a some- what unstable and fluctuating condition, by the water be- low. As the thickness of this layer increases by earthy matter brought upon it by the wind, and by the decay of the vegetation which gathers upon it, the whole mass grad- ually subsides, until at length, in the course of ages, the FORMATION OF COAL DEPOSITS. 209 whole basin of the lake may be filled with vegetable mat- ter submerged in water and so preserved, thus holding the enormous store of solar force of which it is the custo- dian for the use perhaps of man in future, and often very distant ages. There is another mode still in which vast accumulations of vegetable matter are at the present day in the process of formation on the earth's surface, and that is by the slow growth and accumulation of peat in bogs. If this forma- tion takes place in a tract which is slowly subsiding, the peat may form to a great thickness in the course of ages, and the vegetable material so accumulating may be pre- served by the constant infiltration of water as the ground subsides, or even without subsidence by an increase of the deposit over an extensive area. In all these cases the tract in which these vegetable de- posits are formed may subsequently subside, and be cov- ered by strata of sand or gravel washed over them. If the subsidence goes on, new depressions may be formed and new deposits of vegetable matter produced above the oth- ers, and be separated from them by strata of sand, or grav- el, or clay hardened into strata of rock. Processes pre- cisely analogous to these are now slowly going on in va- rious parts of the earth, and there is abundant reason for believing that in former ages they went on on a vastly more extended scale than we witness at present, and the immense beds of coal alternating with strata of slate and sandstone formations which now constitute the "coal-meas- ures," so called, of England and America, as well as of vari- ous other portions of the earth, may have thus been formed. The quantity of reserved force thus stored among the strata beneath the surface of the ground, and the extent to which they are annually drawn upon for the purposes of man, are enormous. 210 THE FOUR CIRCUITS OF SOLAR ENERGY. Great Britain, it is estimated, brings out of the earth from her mines about 20,000,000 tuns of coal annually, and the stored force which she thus brings into action is equal to that which would be realized from the labor of about 133,000,000 of men, which is probably ten or twenty times, and perhaps fifty times the force of all the laboring men in the kingdom. This is one secret of the immense power to which England has attained. With only perhaps five mil- lion of laborers to feed and clothe, she enables these labor- ers, by means of the stored solar force in the coal, to do the work of more than a hundred and thirty millions. By means of the human energy thus re-enforced, she manufac- tures iron, and lays down railroads, and builds ships, and spins and weaves for half the world. The question of the amount of coal accessible to man contained in the geological formations of any country de- pends not only upon the extent laterally of the coal-bear- ing strata, but upon the depth to which they can be worked. And, singularly enough, the question of depth does not de- pend upon the difficulty of raising the weight through so great a distance, inasmuch as the coal itself; or, rather, the force that is stored in it, does that that is to say, the force developed by the combustion of a part of the coal serves to raise the other part, with all its store of force retained in it, up to the surface, whatever the depth may be. The real difficulty which puts a limit to the possible depth of these excavations is the heat ; for the heat is found to in- crease regularly, and so rapidly that at the depth of four thousand feet the temperature of the mine, through that of the rocks which it traverses at that depth, becomes about 105, and it is not possible for laborers to continue to work with the surrounding air at a higher temperature than that, even with all the relief which can be obtained by the best known means of ventilation. VAST STOKES OF FORCE. 211 So that the question for any country, in respect to its store of reserved force, is to determine how long the sup- ply of coal will last that is contained in all the strata un- derneath it down to the depth of four thousand feet. Many different calculations have been made within a few years past to determine how long the supply of coal buried in the bowels of the earth in England will last, and the results vary enormously from a few hundred to many thousand years. A commission of scientific men recently appointed to examine this question came to the conclusion that at the present rate of consumption the supply would last about thirteen hundred years; but with a consump- tion increasing in the future at the rate at which it has been increasing for a few years past, the supply would be exhausted in about two hundred and eighty years. Other estimates have been made, however, which give much lon- ger periods than these. The stores of coal held in reserve by the strata that un- derlie the continent of America are vastly greater even than those of England ; they are, indeed, practically incal- culable. It is only a very small beginning that has yet been made in bringing into use the immense supplies of stored force thus held in reserve for the present and future generations. There is something very interesting and curious in the principles which govern the redevelopment of the force held in reserve by combustible substances ; for a combus- tible substance is, in principle, one the particles of which have been separated by the sun from those of some other substance toward which they have an immensely powerful tendency of attraction. This tendency, inconceivably great as it is, takes effect through distances so minute that we can not directly perceive the action of it; we can only ob- 212 THE FOUR CIRCUITS OF SOLAK ENERGY. serve its effects ; and combustion is simply the reunion of these separated elements under favorable conditions by which the force with which they combine is fully devel- oped, and manifests itself in the evolution of intense light and heat. If the substance is a gas, the light and heat developed take the form of 'flame ; if a solid, the light and heat liber- ated give it the form of burning coals. The chief substances which are thus separated from each other, to combine again afterward with the evolution of light and heat, are hydrogen and carbon on the one hand, and oxygen on the other. It is found by careful experi- ments that the amount of heat, or, rather, of force in the form of heat which is developed by the combustion that is, by the reunion of the oxygen with the hydrogen and carbon is generally in proportion to the amount of oxy- gen so recombined; and consequently, as the elements above named, and others not so common, as in that of sulphur, for example, demand different quantities of oxygen to sat- isfy their different appetites, the heat furnished by the com- bustion of them is very different in the different cases, the combustion of hydrogen giving the greatest heat, that of carbon coming next, and that of sulphur least. Thus the force stored in different kinds of fuel varies in a considerable degree with the different proportions in which they contain the above elementary substances in their composition, and the quantity of heat that is, of force in the form of heat has been carefully ascertained. Some of the principal amounts are given in the following table. In order fully to appreciate the values expressed in the last column, the reader must remember that a unit of heat is the quantity required to raise a pound of water from its condition when just melted from ice one degree of Fahrenheit's thermometer. To raise it, consequently, from FOKCE DEVELOPED BY COMBUSTION. 213 the freezing to the boiling point that is, from 32 to 212, would require about 180 units of heat for each pound.* And each of such'units of heat is equivalent, as has al- ready been shown, to 772 foot-pounds that is, it repre- sents a force sufficient to raise a pound weight 772 feet into the air, or that which would be developed by the fall of a pound weight through that distance. The following table, then, shows the number of units of heat developed by the combustion of the several substances named in it. The letters in the second column denote the words carbon, hydrogen, and sulphur: TAHLE.f Substance. Composed of. Units of Heat. Hydrogen 11. f)C,000 Petroleum C. and H 22,000 Spermaceti C. and II 18,000 Charcoal C. 14,500 Anthracite Coal C. 14,000 Sulphur S. 3,500 These figures denote, of course, the total amount offeree which is stored in these several substances, or, rather, in their condition in relation to the oxygen which surrounds them, and which is actually brought into action when the * Not exactly, however, since it is found that the quantity required to produce an increase of one degree in the temperature varies slightly as the temperature increases. The amount also is very different for different substances ; that, however, which is required for water at a temperature of 32 is made the standard of measurement. t In such tables as these, the numbers given can, of course, only be con- sidered as approximations to the truth, since, in ascertaining values so ex- tremely difficult of precise determination, different experimenters will, of course, reach somewhat different results. The young student in science will also find in different books tables differing at the first view very de- cidedly from each other, owing to the fact that some use the degrees of Fahrenheit's thermometer, and others those of the Centigrade in desig- nating units of heat. 214 THE FOUR CIRCUITS OP SOLAR ENERGY. oxygen reunites with them. It is only a small part of this total amount that can be really utilized that is, made to serve a useful purpose by any of the contrivances of man. It is calculated that only from one twentieth to one tenth of the amount offeree stored in coal can be made effective for useful work in the best constructed steam-engines that have hitherto been employed, though a London firm, it is said, have recently made improvements by which they claim that one fifth of the whole amount can be utilized. Even at this rate far the largest portion is wasted, and a wide field is open for future engineers and inventors in devising arrangements for greatly increasing the benefit which generations to come may derive from the store of energy which nature has laid up in the beds of peat and coal for their use. Still, notwithstanding the imperfection of the appliances by means of which this stored force is used, the saving of human strength by the employment of it is immense. The stones used in the construction of the great pyramid of Egypt have been calculated to weigh, in all, about 12,000 millions of tons, and it required the labor, it is said, of 100,000 men for twenty years to raise them and put them in place. Dr. Lardner calculated that the force developed by the combustion of 480 tons of coal would have been suf- ficient to do the same work. And yet Great Britain employs for her various purposes the force contained in 20 millions of tons every year. It will assist the student to fix the principles above ex- plained in his mind, and to enlarge his conception of the extent to which all the manifestations of physical energy which he sees around him are effects derived ultimately from the radiation of the sun, if he should analyze some of these phenomena as he observes them, and trace back the THE BfN OITINQ 1IELP. VARIOUS RESULTS. 217 chain of causes that produce them to their origin in the sun. The results he will find in some cases quite curious. Take, for example, the case of the light-house upon a rock at sea. The light in the lantern conies from the combus- tion of oil, this combustion consisting simply in the libera- tion, in the form of light and heat, of the force stored in the oil. This oil was elaborated in the body of the whale from substances containing stores offeree which served the whale as food ; and these, if traced back to their origin, came from the agency of the sun in separating the carbon and the hydrogen from the oxygen in some vegetable or- ganization, or some organization on the confines of the vegetable and animal world, which fulfilled the ordinary functions of vegetation. In this forcible separation of these elements, a portion of the solar energy was absorbed and stored. Thus the light that beams from the lantern of the light-house is a light which may be traced back by a cir- cuitous route, and through various forms and disguises, to the sun. In the same manner, though by a very different path, the force by which the winds and the waves are impelled comes, as we have already seen, from the agency of the solar beams. Thus the solar force, coming by one path and reappearing in one form, sends help to the mariner to aid him in making his way through the perils with w r hich the same force in another form environs him. In other words, the force which the sun stores in the oil is used to guard against the mischief which might flow from that which he stores in the water and in the air. And even in cases where the force which comes through one circuit can not be made actually to help, it may be em- ployed to give warning. This is shown in the engraving of what is called a bell- buoy, which consists of a floating structure bearing a low K 218 THE FOUE CIRCUITS OF SOLAE ENEBGY. open tower or cage, within which is suspended a bell, which is rocked and swung incessantly by the motion of the sea, without the aid of any human attendant. These buoys are mainly useful in fogs, whether occurring by day or night, in either of which cases a light-house would be useless. Now the fog, as we have already seen, is produced by solar agencies acting through the water and air, and the motion of the waves, and the consequent rocking of the buoy and ringing of the bell, are the results of the same energy act- ing in a different portion of the same great circuit. In this case, accordingly, the sun, in one division of the same cir- cuit, applies his energy in giving warning and information to man to save him from dangers which he creates by his action in another division. Only one of the most simple of the forms in which the solar energy takes effect in the processes of vegetation, namely, the separation of carbon and hydrogen from oxy- gen, has been particularly dwelt upon in this chapter, inas- much as it is only the general principle of the storage of that energy in vegetable tissues which was to be here illus- trated. The real processes, as they take place in nature, are infinitely complicated. It is not even known in pre- cisely what way, nor in what proportions, the different kinds of solar radiation act in the processes of vegetation, though there is good reason to believe that the third of the three classes, namely, the actinic rays, act a very important, if not the most important part. The substances, moreover, both simple and compound, with which the sun has to deal, are infinite in number, and his modes of dealing with them in the different organizations of vegetable and animal life are infinitely varied. The forces brought into action, the. separations, the changes, the combinations and recom- binations which are produced, are absolutely without end. Though great numbers of scientific men have for the last RECAPITULATION. 221 quarter of a century been devoting their lives to the work of exploring this field, they all feel that the work is but just begun. The farther they advance, the more numerous are the vistas which open before them of regions of wonder and mystery into which they are not yet able to make their way. The general principle, however, as explained in this chap- ter, is well established, and it is one that every well-in- formed man should understand, namely, that the world of vegetable and animal life is, in respect to the physical phe- nomena which it manifests, a system for gathering, and storing, and afterward transmitting and expending in va- rious ways the energy derived from the sun. This energy is mainly received and stored by the action of vegetation, and is held in reserve in the tissues of plants. Through these tissues portions of it are transferred in the form of food to the organizations of animals, where it furnishes a supply offeree for the vital functions of the animal system, and for the locomotive organs which animals require to have constantly in readiness for action. Other portions of this force remain in the tissues of the plants, whence they gradually pass off into the surrounding air as the plants slowly decay, or are preserved through countless ages in the substance of peat, or coal, or petroleum, to be ultimately brought into action for the purposes of man. And what is very wonderful, if true, is, that even the or- gans of the brain, through which, in some mysterious way, the mind performs its functions, are, as is now supposed, dependent on supplies of this reserved force for their vig- orous and healthy action. In other words, not only the senses of seeing, hearing, and the like, but the more purely mental operations of thought, of reasoning, of imagination, and of memory are performed in some mysterious way through the agency of organs which, in their healthful 222 THE FOUR CIRCUITS OF SOLAR ENERGY. working, expend large portions of this force which has been received into the system with the food. This is won- derful, and it is a truth, if it is a truth, which is received at present with much caution by scientific men; but the evidence which is constantly coming into view strongly tends to establish it. Thus the force of the solar radiation, in entering into our atmosphere and acting upon the surface of the earth, di- vides itself into a thousand streams, and sets in motion a countless number of different agencies. It blows in the wind ; it falls in the rain ; it rolls in the waves of the sea ; it undermines and disintegrates the rocks along every shore ; it constitutes or, at least, sustains the strength of the lion, the fierceness of the tiger, the patient toil of the ox, and even the sagacity of the elephant and the cunning of the fox ; and in the mysterious mechanism of the or- gans through which alone the human mind can act, in the present state of its existence, it expends itself in producing the incessant and joyous activity of youth, and perhaps in sustaining the thoughtful reasonings and the far-reaching memories of age. It is thus the source and sustainer of almost every kind of action which we see taking place around us on the earth. In the dawn of human civiliza- tion, if the philosophers of those days had any glimpses of these truths, it would not, therefore, seem at all surprising that they established ceremonies of the nature of worship in honor of the Sun. MISS RANDOM'S COUSIN. 223 CHAPTER XIH. SCIENCE AND SENTIMENT. THOSE who have read the volume of this series entitled Water and Land will perhaps recollect that Lawrence had an acquaintance and friend named Theodora Random, a young lady of about sixteen years of age, who was gen- erally away at school at New York, though she spent her vacations at home in the town of Carlton, where Lawrence was now residing. Now this Miss Random had a cousin named Roundell, who was at this time a law student. Lawrence and Roun- dell were classmates in college, but after they left college their paths seemed to diverge, for Roundell commenced the study of the law, while Lawrence had chosen engineer- ing in some of its branches as his pursuit in life, and had gone to a scientific institute to study mathematics and physics. About the time that the incidents related in this volume were occurring, Roundell came to make a visit at Carlton, and he and Lawrence renewed their acquaintance with each other, and they took many walks, and held many conversa- tions together in regard to their plans of life, and the pro- fessions to which they had respectively devoted themselves. One pleasant morning, Dorrie, as Theodora was often called, conceived the idea of taking her pencils and paper, and her little sister Jenny, and going out into the woods to a place called the Cascade, on what she called a drawing excursion. Her plan was to find some pretty little object, 224 SCIENCE AND SENTIMENT. or group of objects, that would form the subject of a design for her sketch-book. Mr. Roundell, as it happened, came to the house to call upon his cousin just as she was setting out upon her ex- cursion, and when he learned where she was going, he said that he would accompany her. " Very good," said Dorrie ; " only I am not going to have you look over me while I am drawing." " And I will go and get Lawrence to go too," said Mr. Roundell, without noticing Dome's prohibition in respect to looking over her. "He likes such excursions." " If you do that," said Dorrie, " you will do it on your own responsibility. You must consider it as against my express orders." Mr.lloundell saw at once, by a certain sly and significant look upon Dome's face, that she was not in earnest in this ; so he proposed that she should go on till she reached a certain place which he designated, and wait there until he and Lawrence came and joined her. " Well," said Dorrie, " if you will go, you must, I suppose ; but I hope you won't find him at home." Mr. Roundell paid no attention to this, but went in search of Lawrence, while Dorrie, with a small portfolio under her arm, and her pencils in their case in her pocket, set off with her little sister to walk by another Avay toward the ap- pointed place of meeting. This place of meeting was a very pretty spot near a stream, where Lawrence had made a seat some time before, which seat had become a favorite resting-place for all the young persons of the village when walking in that direc- tion. The seat was formed in a somewhat curious way. Lawrence had observed two young trees growing pretty near together, upon a smooth grass-plot in a place shelter- ed by quite a little grove growing behind it, and had con- LAWRENCE'S SEAT. 225 ceived the idea of using those trees as a support for the back of a seat. So he bent the trees into the right inclina- tion for such a purpose, and confined them in that position till they had become fixed in it. Then he put two short posts in the ground, one in front of each tree, and at the proper distance to form the breadth of the seat. He nailed cleats across from the top of these supports to the lower part of the trees, arranging the whole so that the plank which was to serve for the seat, when placed upon the cleats, should be at the right distance above the ground. He then procured a piece of plank long enough to afford room for two or three persons to sit upon it, and, after smoothing it and rounding the edges, he fastened it to the cleats. He also nailed a narrow board against the trees at the proper height to form a support to the back for per- sons not quite full grown. Thus he formed a very comfortable and quite a durable seat ; and as it was in a very pleasant spot, pretty open, though sheltered by a grove in the background, and not far from the stream at a spot where the water fell over the rocks in the bed of it in quite a picturesque manner, it is not at all surprising that " Lawrence Wollaston's seat," as it was called, soon became a favorite resting-place for young people making excursions in that region. The trees, moreover, notwithstanding the nails driven into the stem of them, continued to grow, and, as Law- rence watched the growth of the new shoots from the top from time to time, and trimmed them a little as occasion required, he gradually aided the trees to form a sort of canopy of foliage over the seat, which greatly added to the attractiveness of the place, especially in warm and sunny days. It was at this place, as has already been said, that Miss Random and her sister were to wait for Mr. Roundell and K2 226 SCIENCE AND SENTIMENT. Lawrence, and there the two young men in due time found her. When they came to the spot, however, although they saw Miss Random upon the seat, they did not see Jenny any where near. As they approached toward her, Dome nodded to them. Lawrence bid her good morning, and said, " I am very glad to see you. How do you do this morn- ing ? " Pretty well," said Miss Random, " only cross." She said this with something like a pout upon her lips, and something still more like a twinkle in her eye. At any rate, there was something in the expression of her face that led Lawrence to think that her vexation was pretended rather than real. " What makes you feel cross ?" asked Mr. Roundell. " Why, I came away from home," said Dorrie, " and for- got my India-rubber, and so I had to send Jenny back for it, and she has been gone ever so long; and that makes me feel cross and contrary. I hope that one or the other of you will say something that I can have a chance to con- tradict especially Mr.Wollaston," she added, looking up to Lawrence with a half smile upon her face. " Why, I thought you liked Mr.Wollaston," said her cous- in, " or else I should not have brought him." " I like him well enough," said Dorrie, " if he wasn't so dreadfully scientific." " You don't like science, then ?" said Mr. Roundell. "No," said Dorrie. "I think it is horrid. It makes every thing in the world so matter-of-fact like and commonplace. Look, now, at this beautiful stream. Before people knew any thing scientific about it, what a charming thing it was. They followed it back till they found it coming out of the ground in a fountain, boiling up in a most mysterious and wonderful manner. They imagined it the work of nymphs MISS RANDOM'S IDEAS OF SCIENCE. 227 and naiads, that had magic power over it, and gave all sorts of wonderful virtues to the water. All its sparkles were their smiles, and its ripples, and bubbliugs, and whirl- ings were their play, and its murrnurings and purlings their fairy talk. It was all charming. But now all this is gone. The fountain is nothing but an outlet for the rain that has soaked down into the ground among the moun- tains, with grass and weeds growing round it, and the stream itself only a big drain, to drain off the rain-water into the sea." Mr. Roundell and Lawrence both laughed here, being somewhat amused at Miss Random's idea of the belittling effect of scientific knowledge in respect to our conceptions of the grand phenomena of nature. "And then thunder and lightning," continued Dorrie, with a triumphant look and tone, and turning toward her cousin. " He explained it to me the other day ; and what do you think he made it out to be ? Why, nothing but a big spark of electricity, precisely such as he makes by rub- bing a long Cologne bottle with a silk handkerchief only a little larger and brighter." "A little larger and brighter?" repeated Lawrence, in an interrogative tone. " Well, a good deal larger and brighter, if you please," said Dorrie; "but just the same thing, in fact, as any little snap from his electric machine, or like the sparkles we see when we rub a cat's. back in a dark closet. Think of mak- ing it out that a bright flash of lightning, dazzling your eyes and setting the whole sky in a blaze, with a tremen- dous peal of thunder coming immediately after it, and frightening you half out of your senses, is really nothing different from the sparkles you see in a silk stocking when you take it off in the dark." Dorrie said all this in a jocose and good-humored way, 228 SCIENCE AND SENTIMENT. showing that she was talking for the sake of talking rather than to express any serious opinion that she really enter- tained. "Now, you see," she continued, "before the scientific men came in to discover and explain every thing, people often had grand and sublime ideas in respect to the wonders of nature, and the sublimity and grandeur were greatly in- creased by the very mystery of them." "Yes," said Lawrence, "that is a very fair statement of the case. It is a question between the pleasure of ignorant wonder and intelligent understanding." Miss Random paused a moment on hearing these words, and seemed to be thinking of them. " There is one thing I should like to know, at any rate," said Miss Random, after a moment's reflection, " for I think it goes against your theory of lightning and electricity be- ing the same. We get electric sparks most easily in cold and dry weather, as, for example, in cold and clear winter nights ; but we never have thunder-storms at such times ; they always come in warm days and in showers of rain. This shows that they are different things." Now it is always very important, when we are convers- ing with persons younger than ourselves, and they ask a question, to determine, before we attempt to answer it, whether the inquiry which they make is really a request for information or an argument in disguise. If it is really a request for information, your answer will be listened to, and, if satisfactory, will be understood and received. If it is an argument in disguise, your answer will scarcely be heard, and, if heard, will be very little attended to. In such cases, the question is asked with the expectation and hope that it is unanswerable, and if you attempt to answer it, the mind of the person who asked it is shut up against re- ceiving the explanation that you give. It is usually better, LAWRENCE'S FOKBEAKANCE. 229 therefore, not to attempt to answer such difficulties at all, but to admit whatever of force, or of seeming force, there may be in them, and leave the point in question without any attempt to explain it. It is a very difficult thing for us to make people see a thing when they do not wish to see it, and especially when their seeing it would deprive them of a triumph over us, which they had anticipated, and would give us a triumph over them. Teachers of classes in Sunday-schools have often occasion to observe this distinction, for their pupils often ask them questions, not from an honest desire to have a difficulty removed, but to show off their own acumen in discovering it, and pointing it out, and sometimes even with a secret wish to embarrass and perplex the teacher with the insu- perableness of it. Of course, a mind that is in that state will receive no benefit from any instruction or explanation offered to it, and any attempt to offer instruction would be vain. It would be met by resistance more or less open, and the conversation would end either in a sullen silence on the part of the inquirer, or in perfectly useless discus- sion. Now Lawrence, like other young men of his age, some- times did very foolish things, but he very seldom did any thing quite so foolish as to get into a discussion of this sort Avith a lady. So, when Miss Random argued that the thunder and lightning of the heavens could not be of the same nature as with the electric cracklings produced by friction, from the fact that the phenomena of the latter kind are more commonly produced in clear, cold winter weather, while the former are almost entirely confined to the hottest season of summer, and when, moreover, the whole atmosphere is filled with the falling rain, he offered no counter argument in reply, but rather fell in with the view which she had expressed. 230 SCIENCE AND SENTIMENT. " That is true," said he. " I never thought of it before in the precise light in which you now present it. Dryness and cold seem most favorable for producing electricity by friction, while we seldom have lightning except after a hot day and in the midst of pouring showers. Dr. Franklin was the man who first proved, as he thought, that the two things were the same, and if he were alive now, and I knew him, I would go and ask him what he had to say in respect to that difficulty." Miss Random had been perfectly good-humored in all that she had said, and she was confirmed in this amiable frame of mind by finding her difficulty treated with so much respect. While they had been talking in this way at the seat, Theodora's sister Jenny, who had been sent back for the India-rubber, had returned, and, finding the party engaged in conversation, had very discreetly taken care not to in- . terrupt them, but had come and laid the India-rubber down gently in her sister's lap, and had gone down to play on the bank of the stream. So Theodora rose from her seat, and said that, as Jenny had come, they might as well go on.* "And when I come to a place where I see any thing pretty to draw," she said, " you shall find or make me a seat somehow, and while I am drawing you can go and collect your specimens of botany or geology." So the whole party began to walk on. "And if you find any pretty flowers," added Dome, "you may bring them to me, only don't bring me any of the bar- barous Latin names of them. I don't see what the use is of the Latin names, anyhow. "Look, now, at that pretty little white clover," she added, pointing down to the side of the path ; " what do you call a white clover, now ?" * See Frontispiece. BOTANICAL NAMES. 231 " The botanical name of it, I believe, is trifolium repens" said Lawrence. " And what is the use of calling it by such a name as that ?" said Dorrie. " Why not call it white clover and done w r ith it ? I am sure it is a great deal prettier name than trifolium repens." "That is true," said Lawrence. "I like the name white clover better for some purposes." " For what purposes ?" asked Dorrie. " Why, when I am talking about the plant to farmers or to children, because they know it by that name, and do not know it by any other; but when I am thinking of the plant myself, I like best to think of it as trifolium re- pens, for that is the name that it is known by all the world over. In thinking of it by the name that educated men know it by in France, and Germany, and Italy, and India, I put myself, as it were, in a kind of relation to them, and in imagination make myself one of them, as it were, and form a part of their company. It is a mere imagination, I admit." " Yes," said Dorrie, " I think it is." " But it is a very pleasant feeling, for all that. A great many of our pleasures are those of the imagination. They depend upon the form in which ideas lie in our minds." Dorrie was silent. She felt that there was some force in w r hat Lawrence was saying, but she did not think there was much force in it, after all. " Well," she said, presently, after a short pause, " you must not think, cousin, that I quarrel a great deal with Mr. Wollaston about his science. I think there is some sense in it." She said this with a sly smile upon her face, which plain- ly indicated that she was speaking jocosely. "It is all a question," replied Lawrence, " as I said be- 232 SCIENCE AND SENTIMENT. fore, between the pleasure of wondering ignorance and in- telligent understanding. When a child sees a magician put a rabbit under a box, and then, in a moment, lift the box and finds that Bunny has mysteriously disappeared, his as- tonishment and wonder are excited, and they are feelings which give him pleasure. When, however, the manner in which the trick is performed is explained to him, the won- der is all gone, and another pleasant feeling comes in to take its place that of understanding the process by which the feat is performed. If, now, another child, who knows nothing about it, goes with him to witness the performance, and they sit together and see the rabbit disappear, one has the pleasure of wondering at the mystery, and the other that of understanding the secret. I don't know which you would consider the greatest." " I think the pleasure of wondering is the greatest," said Dorrie. "Very likely," said Mr. Roundell; "but the pleasure of understanding is the highest. The child that knows how the trick is performed feels that he stands on a higher level than the other, who only wonders at the inexplicable mystery of it." I think that Mr. Roundell was right in this opinion. It is often a very pretty thing for a child to stand upon the shore of a brook, and see the water flow by, and play with the pebbles and flowers upon the brink. And I do not deny that there may be a certain feeling of pleasure in his wondering at the mystery of such a stream, in not knowing where it comes from and where it is going to. But when the child is afterward taken to the summit of a neighboring hill, and traces the course of the brook in its meanderings down the mountain ravines to the place where he had stood upon the bank, and follows it below as it goes on gradually widening and receiving other brooklets on its way, till it MAGICAL EFFECT OF NON-RESISTANCE. 233 finally flows out into the river or into a lake, the pleasure which he feels is of a higher kind, if not greater in degree, than that which he felt before. His field of view is en- larged, his ideas are expanded, and he has raised himself to a higher position, intellectually, by the new knowledge which he has acquired. It is substantially such a change as this that we pass through at every step we take in becoming acquainted with the true character and significance of the natural phenomena which we see taking place around us. " But you think," said Mr. Roundell, resuming the con- versation after a moment's pause, " that the pleasure of wondering about a mystery is greater than that of under- standing the explanation of it ?" " Why no not exactly," replied Dora ; "and you must not think that I seriously have any fault to find with Mr.Wollaston's science. I like it well enough. Indeed, I have learned a great many things that I like very much to know." " She's a charming pupil, at any rate," said Lawrence. Dorrie would not have been by any means so ready to make this acknowledgment, which was, indeed, a half re- traction of what she had said before, if Lawrence had re- sisted her, and allowed himself to get into an argument with her on the subject. It was one of the numerous cases in which the quickest and most effectual way to disarm your antagonist, and lead him to yield, is to cease your resistance to him. " I take a much greater satisfaction, for instance," con- tinued Miss Random, " in looking at the telegraph wires along the roadside now that I know, as Mr.Wollaston ex- plained it to me, that nothing passes along them, but a succession of impulses some kind of electrical impulses. I used to think that letters and words passed along some- 234 SCIENCE AND SENTIMENT. how or other, and I wondered how it could possibly be. It was nothing but ignorant wonder, as Mr.Wollaston says. " But he explained to me that there are really no letters, or words, or any thing of the kind that pass along the line, but only a series of electric pulsations, in sets, each set de- noting a particular letter, and they make out the letters and the words at the end of the line." " How do they make them out ?" asked Mr. Roundell. Mr. Roundell was a very intelligent and well-informed young man, but there are a great many intelligent and well-informed men who have no clear idea of how the elec- tric pulses that pass along the wires are translated into intelligible words and sentences at the end of it. " Why, the wire at the end is coiled round an iron rod," said Miss Random, " and every time a pulsation passes it it makes the rod a magnet, and it pulls a little clapper, and the instant that the flow is past it lets the clapper drop again, and so, by hearing or seeing the motions of the clapper, they know what sets of pulsations are passing, and so can make out the letters and words." " I should think it would be very difficult," said Mr. Roundell. "It is very difficult," replied Lawrence, " and it requires a great deal of instruction and a great deal of practice to make a good telegraphic operator." " But there is one thing I don't understand," asked Miss Random, " and that is, how the electricity makes the iron a magnet just by passing round it through a coiled wire. It is electricity in the wire, and magnetism in the rod. Does the electricity turn into magnetism, or does it wake up the magnetism that is in the iron already, or how ?" " Ah !" replied Lawrence, " there you pass beyond the bound of our present knowledge at any rate of mine. All we know is the fact that, in some mysterious way, a LIMITS OP HUMAN KNOWLEDGE. 235 current of electricity, in passing across a bar of iron, tends to develop a magnetic force in it ; and if it passes across it a great many times, as it does in being wound around it in a coil, the development of magnetism is all the stronger. Nobody has found out yet what the secret working of the process is." " So there's where the ignorant wonder comes in again," said Dorrie. " That's a fact," said Lawrence. " I don't see, then, that you gain much, after all," said Miss Random. " We certainly do not gain any thing," said Lawrence, " in the way of reducing the number of the subjects of mystery and wonder in the phenomena of nature around us. We gain the advantage of an intelligent understand- ing of some parts of the process for a certain distance. The satisfaction which this affords increases as our inves- tigations go on and our horizon enlarges. But we are sure in the end, whatever the path which we follow, to find our- selves on the verge of a region of mystery and wonder that we can not penetrate. Intelligent understanding is better, as far as we can go with it ; but, in whatever di- rection we may go. we are sure to come to a region where there is nothing for us but wondering ignorance at last." 236 THE SUN. CHAPTER XIV. THERE is perhaps no case in which, in our attempts to investigate the phenomena of nature around us, we are brought sooner into the condition of wondering ignorance than that of the sun. We know it, it is true, as the source of almost all the forces of every kind which we see in op- eration in the earth around us. This force comes from it in a perpetual, an enormous, and, apparently, an undimin- ished supply; but on the principles now admitted, that force can not be increased or diminished, and can by no possibility come into existence out of nothing, the question at once arises, What is the source of this supply ? And here we have to enter at once into the region of ig- norant wonder that Lawrence and Miss Random spoke of in their conversations; for it is a remarkable fact that, though the sun may perhaps be considered as in some sense the most conspicuous object in nature, and the most open to the observation and even to the full scrutiny of man, it is yet the object which of all others is involved, in re- spect to its constitution and the character of the various phenomena which it presents, in the most absolute and im- penetrable mystery. The point, however, which we have to consider in this chapter is simply whence the sun derives the enormous supply of force which he is now and has long been radia- ting. The quantity of this force, like most of the quanti- ties with which astronomy and other sciences connected with it are concerned, wholly transcends the powers of hu- SOLAR RADIANCE INTERCEPTED BY THE EARTH. 237 man conception, so that the numerical statements concern- ing them are rather matters of curiosity than means of conveying any definite ideas to the mind. The distance of the earth, then, from the sun being about ninety millions of miles, the sun's rays must, of course, be diffused at that distance over the surface of a sphere one hundred and eighty millions of miles in diameter, and this, it is found by computation, comprises an area of thousands of millions of millions of square miles a space so vast that the portion of heat and light which would be inter- cepted by so small a body as the earth would be inconceiv- ably minute. Herschel made a calculation to determine what the proportion would be, and he found that the quan- tity of solar force received by the earth was so exceeding- ly small, when compared with the whole amount emitted by the sun, that the fraction expressing it conveys no idea to the mind of the general reader. The fraction is UTTT.oo 0,0 o o- What an enormous reservoir of power, then, the sun must contain, if so exceedingly minute a portion of it can produce all the effects which we see taking place around us on the globe ! And thus, while it is very difficult for us to comprehend how extremely minute a portion of the solar force falls upon the earth relatively to the whole amount emitted, it is equally difficult to appreciate how immense the amount is, absolutely, that the earth does thus receive. The most careful observations and calculations have been made to determine this amount, and it has been ascertained that the total quantity emanating from the sun, and received and expended upon every acre of the earth's surface, or in the atmosphere above it, is equal to that represented by the continuous labor of one thousand horses ! A large portion of this force is employed in evaporating 238 THE SUN. water and producing changes in the atmosphere. Another large portion is absorbed by the organs of vegetation and stored in the tissues of plants ; and a third remains as heat in the surface of the ground, to be radiated again into space when night comes or when the season changes. But no practical method has yet been devised for intercepting and utilizing this force at once on its arrival by applying it to mechanical purposes. Many scientific men, however, and especially the naval engineer, Ericsson, believe that this will some day be done, and that we shall then cease to be dependent, as we are now, on the stored force of coal received from the sun in former ages. Several experiments have, in fact, been made with a view to ascertain the present practicability of so gathering and concentrating the solar radiance as to make it applicable to the purpose of driving machinery ; such concentration is necessary; for, though a force equal to that of a thousand horses is received within the area of an acre, that which would be included in any small area, like that occupied by the fixtures and appurtenances of a steam-engine, would be too small to produce any useful mechanical effect. A French mechanician, however, succeeded a few years ago in so concentrating the sun's rays by means of reflectors as to drive a small hot-air engine by the heat derived from them. Now, when we consider that a force is continually flow- ing from the sun equal to that of a thousand horses on every acre of the earth's surface, and yet that the amount that is intercepted by the whole earth is only about one two hundred millionth of the quantity that is emitted by the sun, and that this immense emission has now been going on not only for the six thousand years of history, but, as there is every reason to believe, for millions upon millions of ages before, we see at once that there must be DIFFERENT THEORIES. 239 some mysterious source of supply of a magnitude tran- scending all possible human conception. What is the na- ture of this source of supply no one knows. In the absence of any thing like positive proof of what the origin of this vast and inexhaustible energy actually is, all the light we have upon the subject consists of conjectures and specula- tions as to what it may be. The principal theories that have been advanced are these : 1. That the sun is a hot body cooling. 2. That it is a combustible body burning. 3. That it is an inert mass heated and kept hot by a suc- cession of blows. 1. That the sun is a hot body cooling. This was the most obvious thought, and the one first adopted. It is true, it only removed the difficulty one step farther back ; for, even if there could be heat enough contained in such a mass as that of the sun to endure for so many ages, the question would arise, By what process could such a hot body have been formed in the centre of the solar system? But then this is the final result of all our discoveries and explanations of natural phenomena. We only remove the difficulty one or more steps back. We can never, by mere scientific investigation, arrive at any beginning. This theory is, however, in its original form, now gener- ally abandoned ; for it has been shown that radiation from such a mass at the rate at which the radiation from the sun is now going on would, according to all known laws of radiation, exhaust the supply so rapidly as to produce a total change in the effects of it in the course of a far short- er period than even the six thousand years of history. A theory, however, which is in some respects a modifi- cation of this original idea, has been recently advanced, and that is, that the sun may be a vast mass of gaseous matter enormously compressed, it is true, but still retain- 240 THE SUN". ing its gaseous condition which is in the process, as it cools, <& gradually liquefying. In such a process it would, of course, give out in radiation not only its heat of temper- ature, but also its heat of vaporization. This is substan- tially the same process that takes place in warming a house by means of steam. The steam from the boiler car- ries into the pipes not only the heat of its temperature, but also that of its vaporization, and this, as well as the other, it gives out by its condensation in the pipes. If it were air instead of steam that was conveyed into the pipes, though it might be of precisely the same temperature, it would give out comparatively little heat, namely, only that of its temperature that is, the amount necessary to cool it; but the pipes must abstract from the steam not only enough to cool it, but also the enormous additional quan- tity necessary to condense it an amount equal, as we saw in a previous chapter, to not far from a thousand units to the pound. This supposition, that the body of the sun is composed of a gas in the process of being liquefied by the radiation of both its sensible and latent heat, would account for the continuance of the radiation for an immensely longer pe- riod than would be required for the cooling of a body with- out any change of state, but the origin of the supply would remain as great a mystery as ever. 2. The second of the three theories I have named is that the sun is a combustible body burning. Now combustion is the name we give to certain kinds of chemical action so intense, in respect to the degree of force with which the elements concerned come together, as to produce an abundant evolution of light and heat that is, offeree in those forms. Now the quantity offeree thus liberated is that which has been already described as the heat of dissociation, which, as we have seen, is vastly GREAT I1EAT PRODUCED BY COMBUSTION. 241 greater than that of vaporization ; that is, the heat re- quired for separating the particles of water from each oth- er so as to convert the substance from the liquid to the gaseous state, though very great, is enormously surpassed by that required for separating the particles of oxygen and hydrogen from each other in decomposing the water. It requires, as we have seen, nearly 1000 units of heat per pound to vaporize water, and something like 50 or 60 thou- sand to separate the particles of the vapor into their orig- inal elements. Thus, instead of regarding the sun as a hot body, cooling itself by radiating its sensible and its latent heat giving out in the latter its heat of vaporization this second theory views it as a combustible body burning ; that is, as a mass of different substances having so strong a chemical affinity for each other that they combine with great intensity of action, so as to give out, in the form of light, heat, and actinism, the whole of the immense force required to separate such substances in decomposition, and thus provides an immensely more copious source of sup- ply. By this latter supposition a vastly greater and more enduring heat is provided for than by the former, just as a mass of coal in burning will give out a vastly greater quan- tity of heat than a mass of iron would, of the same weight, in simply cooling from the same temperature. But the quantity, after all, would not be enough to ac- count for so long-continued and so enormous a supply of force as that which has been coming for so many ages from the sun. The most careful calculations have been made, and it has been shown conclusively that if the sun were a mass of coal, the combustion of it would not afford force enough to account for the solar radiation for but a very small portion of the long period during which we know that the sun has been shining with at least the present fer- vency of its beams. L 242 THE SUN. 3. The third theory which has been advanced is that the sun is an inert mass kept hot by a perpetual succession of blows. These blows are supposed to be given by masses of meteoric or other matter constantly falling upon it, and striking with prodigious violence as they fall. It has been shown in a former chapter that whenever two masses of matter strike each other, the extinguishment of the motion thus resulting is accompanied by a develop- ment of heat, and also, when the collision is sufficiently vi- olent, of light, and perhaps of electricity, and of other forms of energy. Thus a blacksmith can heat a bar of iron red hot by simply hammering it upon an anvil, and a ball from the gun of a siege train, when it strikes the wall of the fort attacked, is so heated by the sudden extinction of its motion as at night to emit a flash of light that is plain- ly visible. It is calculated that the heat produced by the impact of a leaden bullet upon a solid wall would be suffi- cient to melt the lead, if it could all be imparted to the bullet, instead of being divided between the bullet and the wall. Nor does it make any difference in the proportional ef- fect whether the bodies impinging against each other are large or small, or whether the force with which they strike is violent or gentle. The quantity of heat which is evolved depends simply upon the quantity of motion extinguished, so that a flake of snow descending ever so gently upon the grass, and stopped by the collision, warms itself and the grass by the extinction of its motion, just as much, in pro- portion to its weight and the velocity of its descent, as a 500- pound iron ball in crashing against an iron-clad wall of ma- sonry. Now there is every reason for believing that the region of space included within the preponderating influence of the sun, and within which the planets move, is very far FOREIGN BODIES FALLING INTO THE STJN. 243 from being occupied solely by these visible orbs. The hun- dreds of minor planets that have recently been discovered, the thousands of millions of meteors and comets for a dis- tinguished astronomer proved that there were more comets in the space within the influence of the sun than there were sands upon the sea-shore show that there is revolving about the sun at all times a quantity of matter, in various forms, wholly inconceivable in amount. And if the space through which these masses move is filled, as there is every reason for believing that it is, with some resisting medium, they must be gradually drawn nearer and nearer to the sun in their orbits of revolution, and there must be all the time vast numbers of them falling into it, and in thus fall- ing into it, their motion, by its extinction, must be convert- ed into heat. The only question would seem to be w r heth- er there can be a sufficient quantity of such matter falling into the sun to develop, by the resulting concussion, the quantity of heat necessary to supply the enormous emana- tions. There is one important thing to be considered in respect to this point, and that is, that it makes no difference in re- gard to the amount of heat that would be evolved by a body falling upon the sun, whether it strikes upon a solid surface or plunges into a liquid or a gaseous one, for we may even suppose the sun to be composed of a gaseous sub- stance enormously compressed. In the case of a solid, the motion would be almost instantaneously extinguished. In the case of the foreign body plunging into a liquid or a gas, the extinction of the motion would be more gradual; but in both cases the amount of extinction of motion, and the whole quantity of heat resulting from it, would be the same ; only, in the former case, the heat would be more suddenly produced, and would appear more directly at the spot on the surface where the impingement took place, 244 THE SUN. whereas in the other it would be more gradually devel- oped, and would be diffused more generally through the mass. Another thing to be considered is that a body falling into the sun would fall with a very much greater force than one descending from a corresponding height upon the earth ; for, on account of the immense mass of the sun, the effect of gravitation on its surface is between twenty and thirty times as great as that exercised at the surface of the earth; so that the force with which a falling body would strike that is, the amount of motion that would be ex- tinguished by the collision and, consequently, the amount of heat that would be generated, would be vastly greater than that which would be produced by the fall of a simi- lar body upon the surface of the earth. Now the most laborious calculations have been made by certain German mathematicians and astronomers, based on very careful and long-continued observations, to determine what the probability is in respect to the quantity of mat- ter that is thus continuously arriving at and falling into the sun, the velocity with which it would be moving at the time of collision, and the quantity of heat which would be developed, and the result is very strongly confirmative of the theory in the minds of a great number of scientific men. It has been shown by very careful computations that the velocity with which a revolving body, large or small, would ultimately sink into the sun, would be not less than 400 miles in a second, and that the quantity of matter that would be required to maintain the present radiation from the sun for 2000 years would form a layer upon his surface of less than twelve miles in thickness, which would increase the diameter of that orb by an amount that would be whol- ly imperceptible under the nicest observations at this dis- tance. (5ORUSCATIONS AROUND THE SOLAR DISK. 245 There are, however, many scientific men who are far from being satisfied with this explanation, so that the ques- tion must be considered as still in doubt. All we have to do at present, therefore, is to make ourselves acquainted with such facts in regard to the constitution and condition of the sun as have been observed, and hold our minds somewhat in suspense in regard to the true explanation of the phenomena until more light shall be obtained. It is well ascertained that it is only the central and brighter portion of this body which is directly observable by us, and this gives it the appearance of a well-defined spherical mass, excessively brilliant, but in a state of calm- ness and repose. But it has been found within a few years, and especially by means of observations during periods of total eclipse, when the whole of this central portion is con- 246 THE SUN. cealed from view, that instead of having a distinct and de inite quiescent boundary, the whole vicinity of what has been supposed to be the boundary is filled, to the height of many thousands of miles, with a boiling, flaming, furious mass, in a state of the most intense and violent action. And the indications of this and similar action are seen extending themselves over the whole surface of the orb, which seems to be furrowed with incandescent billows in a state of incessant motion. Enormous flame-like corus- cations, in masses larger than this globe on which we dwell, rise, and glow, and wave, and then melt away and disap- pear. Some of these blazing radiations appear to project themselves forty or fifty thousand miles into the surround- ing space, though, on account of the immense magnitude of the body of the sun, and his vast distance from us, they do not perceptibly affect the smoothness of the contour of his disk, as it appears from the earth to our unassisted vis- ion ; but the real violence and rapidity of the action thus taking place are inconceivable. On the one hand, cavities of appai'ently absolute darkness, and, on the other, vast pro- tuberances of extraordinary and special brightness, form and fluctuate over the surface, increasing and diminishing at the rate of thousands of miles in extent in very brief periods of time. Thus the sun, instead of existing in the calm, placid, and unchanging condition which it appears to assume, is in re- ality a mass of seething and surging incandescence, deform- ed by incessant and tempestuous agitations of surface, pro- duced by contests among forces the nature of which elude our research as completely as the enormous magnitude and extent of their effects surpass our powers of conception. Among all the phenomena denoting the incessant dis- turbance and change which is taking place in the condition of the solar surface, what are known as the spots, or mac- MACULAE AND FACUL^E. 247 tt&e, as they arc termed by astronomers, which are some- times large enough to be seen by the naked eye, first at- tracted the attention of mankind, and have been a very fruitful subject of speculation in all ages.* It was for some time a matter of doubt whether the ap- pearance of spots was due to something actually attached to and forming a part of the sun's surface, or whether they were caused by opaque bodies revolving in space at a dis- tance from the sun, and passing across his disk from time to time, so as to intercept a portion of his light. That the former supposition was the true one soon seemed to be proved by the fact that when the spots disappear on one side, and then afterward reappear again on the other, which often happens, the interval of disappearance is always the same as the time that they continue in sight. This evi- dently could not be the case if the phenomena were due to bodies revolving at a distance from the sun, since it would be only a small portion of the orbit of such bodies that would come between us and the disk in the course of its revolution, and, consequently, the times of appearance and disappearance would be very unequal. The spots on the sun are sometimes, though not very oft- en, of such magnitude that they can be seen by the naked eye. To make it possible to look directly at the dazzling surface, astronomers employ darkly-colored glasses to in- tercept a portion of the rays. By ordinary observers, glass covered with a film of smoke, by being held in the flame of a lamp or candle, is used. The smoked glass answers the purpose sufficiently well for sudden and temporary emergencies ; but for permanent use astronomers employ a helioscope, which is much more * In addition to the macula, there are certain lines of superior and ex- cessive brilliancy often seen in the vicinity of the spots, which are termed faculce, from a Latin word signifying a small torch. 248 THE SUN. convenient. This instrument consists of two wedge-shaped plates of glass one of a very dark color, and the other perfectly transparent made to fit each other very exactly, and set together in a suitable frame, as shown in the en- graving. The frame is rectangular in form, and of a width and length conven- TUB IIKLIOSOOPK. j ent foj. ^Q Q y g ^ and is provided with a handle. The plates of glass are so fitted together (as shown in the second figure, which pre- sents a sectional view of them) that the thick part of one plate, ABC, lies upon the thin part of the other, CBD. The thickness of the glass, therefore, through which the rays have to pass is the same every where, and there is, therefore, no refraction to distort the image, while by mov- ing the instrument along before the eyes the image may be made more bright or more obscure at pleasure. At SE, for example, the rays pass through a greater portion of the dark glass than at S'E'. These simple contrivances answer very well for viewing the sun with the naked eye; but great difficulties have been encountered by astronomers in devising effectual and convenient means of enfeebling the rays in the use of pow- erful telescopes. Some kinds of colored glass, it was found, intercepted the rays of light, but allowed the heat to pass freely ; while others, which absorbed the heat, did not sen- sibly diminish the dazzling intensity of the light. With- out great care, moreover, the plate or plates of colored glass, by a more or less irregular refraction of the rays, af- fected unfavorably the distinctness of the image. These difficulties have at length been in part avoided SPOTS ON THE SUN. 249 and in part overcome in the use of an arrangement by which a magnified image of the sun is received upon a white screen, like the picture in a camera obscura, where it can be studied in all its aspects and peculiarities by the observer at his leisure, and drawings and photographs taken with great facility. The spots, some of which are almost always to be seen GENERAL Al'I'EAKANCK OF THE SPOTS. L2 250 THE SUN. by means of powerful telescopes, are of the most fantastic forms ; but, with few exceptions, each one consists of an apparently black central portion, surrounded by a gray or semi-luminous border, which is called the penumbra ; and usually, like clouds floating in the sky, they change their form from day to day as they are borne slowly along by the revolution of the sun. They are sometimes small and circumscribed in form, at others extremely irregular, spreading into the most fantastic forms, but always, or nearly always, bordered by the penumbra. Many of these spots, though occupying but a small space apparently upon the sun's disk, are really of immense mag- nitude. Vast numbers of them are so large that if, as has often been supposed, they are cavities in a luminous enve- lope surrounding the sun, a body of the magnitude of this earth might be dropped into them without touching the sides ; and some, that have been observed and measured, would admit in this manner bodies of from fifty to a hun- dred times the bulk of this globe. The evidence which led many astronomers to conclude APPEARANCES INDICATING CAVITIES. THE PHOTOSPHERE. 251 that the spots are of the nature of cavities, and not of pro- tuberances upon the surface of the sun, is derived from cer- tain peculiar changes in the form of the spot, which take place as it passes away from the centre of the disk, where it is presented directly to view, toward the limb, where it is seen obliquely. These changes are rudely represented in the preceding engraving. It is plain that if the spots were protuberances the pe- numbra surrounding them forming the sides the portion of the penumbra lying to the right of the spot would grad- ually become concealed, while that on the left side would come more and more directly into view, as the spot moved from the centre toward the right limb of the sun as view- ed by the spectator. The contrary is, however, generally found to be the fact, as shown in the engraving. This phenomenon is often referred to as proving satisfactorily that the spots are of the nature of cavities opening in some kind of bright gaseous or liquid envelope surrounding the sun, and disclosing a view of something dark, or at least of something having the effect of a dark object on our vis- ion. It is not, however, considered absolutely certain that there is not some illusion about these appearances. How- ever this may be, the vast luminous envelope which the sun presents to our view, endued with such exceeding bril- liancy, and in a state of the most intense and violent com- motion, is the source from which the heat and light that emanate from the sun seem to be derived, and is called the photosphere. The photosphere, as this supposed igneous envelope forming the radiant surface of the sun is called, is popu- larly conceived of as existing in a calm, tranquil, and unchanging condition, though constantly pouring forth streams of heat and light of such intense and dazzling bril- liancy. As seen without any scientific aids to the vision, 252 THE SUN. this is the aspect which it presents; but, when viewed through powerful telescopes, this seeming quiescence and uniformity disappears, and the whole surface, as has al- ready been said, is found to be in a state of the most vio- lent action and agitation. The surface becomes variega- ted, too, by forms and figures of different degrees of bril- liancy, which are continually varying in contour and posi- tion, and melting into each other in changes which, to be seen at all at such a distance, must be produced by move- ments of enormous magnitude, and of vast rapidity of ac- tion. The general surface is every where mottled with a kind of brilliant efflorescence, and in the vicinity of the spots a mysterious configuration appears called the willow leaves, from the resemblance to a group of willow leaves lying on the ground. In some parts these leaves lie min- gled confusedly, crossing each other in every direction. In other parts, especially in the penwnbrce of the spots, there is a tendency to regular arrangement, and especially to a convergent direction toward the centre of the spot. Some- times lines of these figures extend out across a spot, form- ing what Nasmyth, the astronomer who first observed them, named luminous bridges. The engraving represent- ing these appearances is not a fancy sketch, but an exact copy of a group of spots, and of the surrounding surface of the sun, as seen by Nasmyth on the 5th of June, 1864. The mottled appearance of the photosphere, as observed by the aid of the most powerful telescopes, is still more distinctly shown in the next engraving, which records an observation made by Huggins. The granulations of light which form the mottling of the surface are of a form some- what resembling grains of rice, to which they have some- times been compared, and are very curiously grouped. The nature and the cause of them, as of every thing else re- MOTTLED SUBFACE. WILLOW LEAVES. LUMINOUS BBIDOI CHANGES IN THE SPOTS. 255 lating to the physical constitution of the sun, is enveloped in unfathomable mystery. It is remarkable that the spots in the sun do not appear indiscriminately in all parts of the disk ; they are chiefly confined to a zone extending, some 30 or 40 on each side of the equator. It is true that those existing at a distance from the equa- tor toward either pole would be seen more or less oblique- ly, and would consequently come less distinctly into view. The smaller ones, situated far to the northward or south- ward, might, from this cause, especially if it should be true that the spots are of the nature of excavations or openings in a liquid or gaseous envelope, entirely escape observa- tion ; but, making all necessary allowances for this, it re- mains certain that the spots are due to some action among the constituents of the sun which is mainly confined to the equatorial regions of his surface. Spot as seen Oct. 13, 1865. Spot as seen Oct. 14, 1865. CHANGES OV FORM. 256 THE SUN. The changes of form and the movements of the spots may be very exactly observed and recorded by means of cross-lines in the field of view of the telescope. The en- gravings representing this mode of observation show the changes of form and position of a spot which passed over the disk of the sun in the fall of 1865, from drawings made by the English astronomer Howlet. On the upper margin of each figure, the divisions, in seconds, are marked for one angular minute of the surface ; and by noting the relation of the spot to these marks, and to the lines drawn through them, the reader will perceive the changes, both in the forms of the spots and in their position, on the different days specified. It has been shown, by careful observations made in this manner, that the spots do not occupy a fixed position, as if pertaining to any solid portion of the orb, but that they have a comparatively slow motion upon the surface of it, as well as a motion with the surface in its reg- ular rotation. These changes of form and position, not only of the dark spots, but also of the bright lines and spaces which diver- sify the general surface of the sun, though seemingly grad- ual and slow, as they appear to us at the enormous dis- tance from which we view them, are really effected with prodigious rapidity, and imply a continual and inconceiv- ably intense action of some nature or other among the constituents of the photosphere. But the most striking proofs of the prodigious intensity of the action which is taking place in the sun, and the enor- mous magnitude of the movements induced by it, are af- forded, as has already been said, by the views which are presented at the time of a total eclipse. If the surface of the orb were really bordered by the smooth, well-defined, and quiescent, though dazzling envelopment which it seems to present to view in ordinary vision, the intervention of CORUSCATIONS AND COKON^E. 257 the moon, when the disk was entirely covered, would com- pletely suppress the light from it during the brief period of totality, and, as it were, blot it out entirely from the heavens. But this is far from being the case. Although the whole body of the sun is covered, the figure of the moon intervening is surrounded by a remarkable halo of bright light, with protuberances, and radiations, and corus- cations breaking out on every side, like vast volcanoes, or, rather, like rolling mountains of liquid fire. These incandescent emanations are observed to be in a state of incessant movement. The changes of form and position are, of course, as seen from this enormous distance, apparently slow; the actions, however, in reality, take place on an inconceivably vast scale, and with enormous power and rapidity. In one instance an extremely brilliant cor- uscation was observed to surge across the disk at a rate which carried it, in the space of five minutes, over a dis- tance of more than thirty thousand miles. How inconceiv- ably vast must be the force of an agency which such a movement as this implies ! These coruscations and corona?, formed of luminous em- anations rising high above the surface of the sun, were ob- served very distinctly during the eclipse of the year 1869, and more perfect and exact representations of them were secured than has ever been possible before, on account of the very complete arrangements for photographing the eifects which the observers had made. In various parts of the margin of the disk, rose-colored protuberances, like surging waves of fire, and coruscations shooting out for thousands of miles, like gigantic jets of flame, were seen by the eye and photographed by the instruments. In addition to the knowledge which has thus been ac- quired by astronomers of the physical characteristics of the sun by observation with the telescope, a great deal of 258 THE SUN. information has been obtained within a few years in re- spect to its chemical composition by means of what is called the spectrum analysis. A few words must be said in respect to this subject, though it is not very directly, or, at least, not very obviously connected with the subject of this volume. A spectrum is a colored image produced by the separa- tion of the light from any luminous source into its com- ponent colors by means of a prism, the effect of the prism being to refract the rays in different degrees, and thus to separate them from each other. Now the light, coming from different sources as, for instance, from the sun, from a star, from an incandescent metal, from the electric spark, from the combustion of iron, or hydrogen, or zinc is found, when separated in this manner by a prism, to pro- duce spectra very different in appearance from each other ; and when a peculiar apparatus is employed that is con- structed with great delicacy and precision, certain lines ap- pear sometimes dark, sometimes bright crossing it in great numbers and in a great variety of positions in re- spect to the length of the prism and to each other. This subject has been somewhat more fully explained in the vol- ume of this series entitled Light. It is sufficient for our present purpose to say that the number, character, and rel- ative position of these lines vary according to the nature of the incandescent substance which emits the light, its condition of aggregation that is, whether it is in a solid, liquid, or gaseous state and the character of the media through which it passes in coming to the place of observa- tion. Many thousand of these lines are now known, and their significance understood. To the uninitiated observer, a map of any spectrum would exhibit only a succession of bands of bright color alternating with dark lines, forming a combination which, though exceedingly beautiful, would LANGUAGE OF THE SPECTRUM. 259 appear hopelessly complicated and unmeaning to a person first observing them, and yet to the spectroscopic scholar every portion of it speaks a language perfectly precise and clear. To him every bright band and dark line has a mean- ing, depending both on its character and on its position, which he readily and perfectly understands, while to all others it seems almost inconceivable that there can be any meaning in them, just as it would seem impossible to a savage, when shown a printed book, that such a compli- cated and interminable aggregation of apparently mean- ingless characters could possibly be the vehicle of commu- nicating intelligence of any kind to any human mind. And it is, indeed, a great study, that required to read and understand the language of the spectrum. Many men are employing themselves almost exclusively in these in- vestigations. A society has now, at the time of this writ- ing, been formed in Italy which is to be devoted entirely to the work of perfecting the spectroscopic apparatus and pursuing investigations by means of it, especially in rela- tion to the constitution of the sun, and they have com- menced the publication of a periodical for the sole purpose of communicating to the scientific world the results of their investigations. The results that have been attained thus far show con- clusively that many of the same substances that go to com- pose the mineral strata and the atmospheric envelope of the earth are found to exist in the sun, and also in many of the stars ; and that the same laws which govern the ac- tion of light upon this planet are still in force at distances so enormous that, while light moves at the rate of 192 mil- lions of miles in a second, it must have required, in some cases, 1000 years to traverse the distance between the place of its emission in some of these distant orbs to the spot where it enters the spectroscope and comes under the ob- 260 THE SUN. servation of man. What a proof this fact affords us of the vast extent, both in respect to space and duration, over which the same system of law which is now observed to be in action upon this earth exercises its dominion ! It is to be inferred from this that the same fundamental principles in respect to the nature and the action offeree which prevail here prevail every where, and that the solar force, after passing through all the changes in form and character which we see exemplified in its various circuits over the earth, continues to be controlled in its action, aft- er it is radiated away from the earth into the surrounding space, by the same laws which governed it while subject to our observation here. We can not follow it into these regions, nor discover the mysterious paths by which it finds its way back at last to the source from which it flows to us. We are somewhat in the situation of half-instruct- ed inquirers into the philosophy of the river's flow. They trace the stream back to its source in a fountain issuing from the ground, which seems to furnish mysteriously a never-ceasing supply. They follow it in its downward course till it is lost in the boundless sea, but they know nothing of the wondrous way by which it or its equivalent finds its way back through invisible evaporation, and drift- ing clouds, and falling rain on the mountain tops, and infil- tration through pervious strata, to begin its course through the fountain again. They have glimpses, it is true, of the clouds, and some ideas of their connection with evapora- tion from the sea, and with the fall of rain, but they have not yet learned to connect these phenomena together, and to see them as parts of the grand system provided by na- ture for the circulation of the waters of the globe. In the same manner we trace back the continuous and unchanging flow of force which we see passing before us to its unfailing fountain in the sun. We follow it on- VARIOUS COSMICAL PHENOMENA. 261 ward in the same way through all its circuitous paths, through the air, the water, and the organs of animal and vegetable life, until it finally passes off into the great ocean of space around us, but we can not yet see by what means, or through what paths, it or its equivalent finds its way back to replenish the great fountain of supply. We have glimpses, it is true, of the action of force of some kind and in some forms in the meteors, the comets, the auroral and zodiacal light, and other mysterious celes- tial phenomena. Meteors are seen at night, and even by day, shooting through the sky ; and sometimes they seem THE .MKTr.OK. 262 THE SUN. to enter the earth's atmosphere, where they are heated to incandescence by the friction of the air, and burst with frightful explosions, throwing down large fragments to the ground. The zodiacal light is a luminous track or space seen in THE ZODIACAL T.IGUT. MYSTERIES UNSOLVED. 263 certain seasons of the year, following the sun in the even- ing when he goes down, or preceding him in the morning when he rises. There have been various surmises as to the cause and the nature of this phenomenon, but there is little known of it except that it is one of various forms in which the forces existing in the interstellar spaces are embodied. We have not yet learned to interpret the significance of these various phenomena, still less to connect them togeth- er, or to understand what part they bear in the grand sys- tem provided by nature for the circulation offeree through- out the universe a circulation which moves on in a per- petual flow of grandeur and majesty, never ending and never beginning. 264 KICK AGAIN. CHAPTER XV. KICK AGAIN. THERE arc various avenues through which the knowl- edge of external realities can enter the mind. When any thing is told us, the truth, so affirmed, enters through the ear, and the organs connected with the ear, in the brain. When we read it in a book, it enters through the eye. When we see it illustrated in a diagram or in a pictorial representation, it enters still through the eye, but through a different set of organs in the brain from those which take cognizance of the signification of words. Now, when a truth enters the mind by any two of these or other ave- nues, even if it is not apprehended any more clearly, it makes a much stronger and more lasting impression than when it enters only by one. This is one secret of the great efficiency of illustrations on the blackboard, or demonstrations by experiments. Many persons imagine that these aids are mainly useful in conveying a clear understanding of the subject to the pu- pil's mind. But in many cases the great advantage is, not in enabling the pupil to understand the subject any better, but to deepen, and strengthen, and make more permanent the impression which the truth makes upon him. For example, to take a very simple case, if in a school of young children you tell them that when a four-sided figure, with square corners, has all its four sides equal, it is called a square, and that when two of the pairs of sides are lon- ger than the other two, so as to make it longer in one direc- tion than it is in the other, it is called an oblong, they may TWO AVENUES FOB KNOWLEDGE. 265 all perfectly understand the explanation, but the impres- sion which it will make will be very faint and evanescent. But if now the teacher draws the figure of a square, and also one of an oblong upon the blackboard, and writes the name of each in a legible and careful manner under it, so as to convey to the children the same truth which had be- fore entered by words through the ear, now, by means of vision through the eye, it is not improbable that it would make an impression upon them so strong that it would never be effaced. It is not so much the superior efficacy of one of these modes over the other upon which the results in such cases depends, but upon the conjoint action of the two. For if the teacher had merely drawn the two figures, with the names under them, upon the board, and had then only ask- ed the children to look upon them long enough to observe the forms and to read the names, the impression would probably have been as faint and evanescent as before. The visible forms must be accompanied with the verbal expla- nation to secure the result. And now for the application of these principles to our present purpose. These truths in respect to the origin of almost all terrestrial forces in the agency of the sun, which have been presented in a somewhat methodical and con- nected manner in the preceding chapters, had been explain- ed and illustrated in a much more simple and familiar way by Lawrence to John and Rick Van Dorn, in various cas- ual conversations that he held with them in their walks or fishing excursions. John had comprehended the sub- ject pretty fully, and Rick had been much interested in some of the details of facts which Lawrence presented to his mind from time to time, though he had not made much progress in comprehending the full import of the general principles which were at the foundation of them. So Law- M 266 KICK AGAIN. rence contrived a plan to present somewhat directly, in a visible form, the general truth that the sun stores force in plants which may be afterward evoked and made active by man. Among his other articles of apparatus Lawrence had a small toy steam-engine, which was intended to be worked by means of an alcohol lamp placed under the boiler. He had had this engine for some time, it having been given to him when he was quite young. Connected with this he had a number of mechanical toys, some of which he had made himself. One was the figure of a man sawing wood, another represented a shoe-maker hammering upon his lap- stone, and there were several others. These were connect- ed with the piston-rod of the engine in such a manner that the engine, when in operation, set them all at work. Now Lawrence told Rick and John one day that he had a plan for drawing force from the sun to work his little men, though he told them it would take some time to gath- er enough to do it. In saying this, he took some peas and beans, and planted them in a sunny place in the garden. Rick looked on while he did this, somewhat interested it is true, but much puzzled. He did not see at all what con- nection there could be between planting peas and beans, and gathering force from the sun to keep toy carpenters and shoe-makers at work. Lawrence did not make much explanation at the time when the planting was done, but simply said, when the seed was in the ground, " There ! Now, as soon as they come up, the sun will begin to lay in force for me to run my engine." So they all went away, and Rick thought no more of the subject for two or three w r eeks. At length, one day, when Rick was in the shop, Lawrence said, " Let us go out into the garden, and see how my store of force is going on." STORED FORCE BROUGHT INTO USE. 267 So they went into the garden, and found that the peas and beans were up, and growing quite large. " Yes," said Lawrence, " every thing is going on very well. The sun is storing force in all these leaves and stems." " I don't see any force," said Rick. " They are nothing but common peas and beans." " And yet you'll see how I get the force out of them one of these days," said Lawrence. The next time that Rick came, which was about a week afterward, Lawrence went with the two boys into the gar- den again. " Yes," said he, " the experiment has gone on very well. I think there is force enough gathered." So he cut off all the plants close to the ground, and car- ried the vines to a place where he could let them dry in the sun. This was necessary, for if he had evolved the force which was contained in the tissues, in the state they were then in, it would have been chiefly absorbed in the work of evaporating the water which was also contained in them, and the vapor which would thus be formed he had no means of confining so as to make it work his engine. So he left the vines to be dried by the sun that is, he call- ed, as it were, upon the sun to furnish the additional force necessary to evaporate the water, in order that he might have the use of all that was stored in the tissues for the work which he wished it to perform. At length, some time afterward, when the vines had had time to become thoroughly dry, he made a somewhat com- plicated arrangement of apparatus for bringing this latent force into action in a manner to attract Rick's attention, and fix the truth which he was attempting to elucidate in his mind. He took a gun-barrel, which he kept among his apparatus to serve the purpose of an iron retort, and, 268 RICK AGAIN. gathering his dry vines in a paper, he crowded and ram- med them into it until that part of the barrel that was to go into the fire was full. Then he connected a flexible tube at one end with a cap which fitted over the muzzle of the gun-barrel, and at the other end with a small metallic pipe which he fitted in the place of the lamp under the boiler. By this arrangement, and by means of some other precautions not necessary to be described here since this book is not intended to ex- plain the details of chemical manipulations the hydrogen gas, brought out by the heat from the dried vines, with all the stored force contained in it, derived from its forcible separation from oxygen, and its prodigiously strong tend- ency to reunite with it so soon as it should have an oppor- tunity, was conveyed under the boiler of the little steam- engine, and there allowed to come out into contact with the air, and, of course, with the oxygen which the air con- tained. Still the hydrogen, notwithstanding this very strong tendency to unite with oxygen, for some mysterious reason can not do so while both are cool. While the hydrogen was in the gun-barrel, although it was very hot there, it did not combine with oxygen, for there was none there. All oxygen was, of course, entirely excluded from the in- terior of the barrel. And when the hydrogen issued from the pipe, and so came into contact with the oxygen of the outer air, it could not even then begin to combine, because it was not now any longer hot, having become cooled in passing through the tube. But if ever so small a portion of it could be heated to the right point, when it was in con- tact with the oxygen, the two would immediately combine with great force, and this force would appear in the form of heat, which would immediately act, too, in raising the portions of the gases next to it to the right temperature, SUCCESSFUL RESULT. 269 and so the union would continue to go on with great ener- gy as fast as the hydrogen issued from the mouth of the pipe- Such is the philosophy of the burning of gas issuing from a tube. The energy, in the form of heat, which is furnished by the reunion of the oxygen and hydrogen, separated previ- ously by the action of the sun, is far greater than is neces- sary for carrying on the process of combustion. In the case of Lawrence's experiment, a great portion of the heat that is, of the force in that form passed up through the bottom of the boiler, and transferred itself to the water, converting it into steam. The steam, in its turn, deliver- ed the force to the piston in the little cylinder, and this communicated it to the piston-rod, and this to the wheels and bands connected with the mechanism of the figures, and in a very short time all the little men were as busy at their work as if they had been alive. " There !" said Lawrence, as his experiment arrived at this successful result ; " see how I make the men work by the force I gathered from the sun by means of my peas and beans." "It is not the peas and beans at all," said Rick; "it is your steam-engine." " But where does the force come from to make the en- gine work?" " It don't come from any where," said Rick. " All you have to do is to make a fire under the boiler. That's the way with all steam-engines." Thus it appeared that, after all, Rick had not very clear- ly comprehended the principles which this experiment was intended to illustrate. But the lesson was not lost upon him by any means. The visible embodiment of the prin- ciple which the experiment presented to him remained pic- 270 KICK AGAIN. tured in his imagination for years. It gave him a glimpse of the truth at the time, and the memory of it aided him greatly in perceiving the full force and extent of it long years afterward. It happened very frequently, in the various interviews which took place between Lawrence, John, and Rick, and in the conversations which Lawrence held with the two boys, that Rick very imperfectly comprehended what Law- rence explained, while John, whose mind was more mature in respect to the reception of general truths, understood them much more fully. For example, one day, when the thi'ee were returning from an excursion which they had been making together, they came to a place where an old man and his grandson were at work making hay. The old man had proposed that morning, at dinner, that he and Jo- sie should go down and work a little upon the hay that afternoon. " We can not do much," said he to himself, " for he is too young, and I am too old. But we can do something ; and after every half hour of work we will take a little time for rest." Just as Lawrence and his party came along, the two hay-makers had come to a recess, as Josie called it, and had just gone to sit down upon a log, near the field, to rest. Now Lawrence had been explaining to Rick and John that very afternoon that all the strength that we exercise in the action of all our bodily organs, whether of the limbs or of the brain, is derived from the stored force laid up in the food which we take, and this force tends to expend it- self in young animals through the organs of motion, lead- ing them to take pleasure in all kinds of rapid bodily move- ment, while in the old a larger portion of it comes into ac- tion through the organs communicating more immediate- ly with the mind. Now he and the two boys came by the FUNNY RESTING. 273 place where the hay-makers had been working just at the time when the old man and Josie had gone to take their seat on the log. Josie had asked his grandfather, just before they had sat down, whether it was not time for them to take a rest, for he said he was so tired he could not possibly do any more ; and so they had sat down together on the log. But they had not been there more than two minutes before Josie, having recovered his breath a little, jumped up and began to climb the gnarled and misshapen old oak, under the shadow of which the log which his grandfather had taken for a seat was lying. His grandfather had remonstrated at first, asking him why he wanted to climb that tree. It would be a great deal better, he said, for him to sit still and rest. But Josie said that he was rested already, and so went on climbing. It was when he had reached a con- siderable height upon this tree that Lawrence and the two boys came along by a path on the other side of it. " Hi-yo ! Josie," said Rick, calling out to him, " what are you doing there ?" ""We're resting," said Josie. "Grandfather and I have been making hay, and we're resting." The truth is, that the supply offeree introduced into the system in the food, while it must always reappear in some way, makes itself manifest in very different forms in the same system, and the proportions in which it appears in these different forms vary very much at different periods of life. A portion of it develops itself as heat, and is em- ployed in keeping the body warm. Another portion is ex- pended in giving strength to the muscles and limbs, and another still in maintaining the action of the vital organs, and even, as is now generally believed, those of the brain, through the instrumentality of which, in some mysterious way, the mind performs its functions. In childhood and M2 274 KICK AGAIN. youth the force expends itself, in most of these ways in a rapid and fitful manner, changing from one to another in- cessantly, the different limbs and organs becoming easily fatigued, and also being very soon and very easily restored by a brief period of repose. In age the action in all these modes is more steady and slow, and the change from one form of expenditure to another is much less frequently de- manded. So Josie, in the case referred to, had not remained five minutes upon the log before he felt rested, and the force within him had begun to accumulate and to demand fresh outlets through which to expend itself. It found these outlets in the exercise of his limbs in climbing the tree, and in those movements in his brain that w r ere concerned in the curiosity which he felt in seeing whether there was a bird's nest or a squirrel's nest among the branches, or in the ex- citement and pleasure which the strange appearance of ev- ery thing beneath and around him would assume when viewed from his lofty position. In the mean time Law- rence and the two boys came to the place, and Lawrence, being acquainted with the old man, took a seat beside him on the log and began to talk with him about old times, and the old man soon became greatly interested in recall- ing and relating the incidents of his early youth, when all that part of the country was in so different a condition. Josie soon came down from the tree, and stood for a mo- ment listening to the conversation between Lawrence and his grandfather, but very soon he and Rick set off to run down toward a little brook which flowed near, and where, he said, he thought there were some fishes. Josie went dancing and capering backward along the path before Rick as if he had not done any work for a week. John preferred to stay under the tree, and very soon he took a seat upon the log by the side of Lawrence. He sat EVOLUTION OP FORCE FROM FOOD. 275 there for a long time listening with Lawrence to the old man's stories. When afterward, in continuing their walk, Lawrence ex- plained to the boys that the force which sustained all the activity that they had observed in the two cases that of the mind in the man, and of bodily motion in the boy was derived from the effect of the food which they had taken, in bringing with it into their systems force stored in it by the sun, Rick said that, in respect to Josie, he did not believe it was any thing that he ate that made him act so, but only his love of fun ! 276 DETONATIONS AND EXPLOSIONS. CHAPTER XVI. DETONATIONS AND EXPLOSIONS. WHEN a certain degree offeree is very suddenly set free, there is often produced what we call a detonation or an explosion, using the one term or the other according to the quantity of force which is brought into action. Thus the quantity of force produced by the sudden com- bustion or other chemical action taking place in the com- position contained in a boy's torpedo, when thrown upon the pavement, is small, and we call the result a detonation. In the case of the powerful torpedoes inclosed in iron cases, and used for blowing 'up hostile ships at the entrance to a harbor, a precisely similar effect, and one produced, too, by similar means, though vastly more powerful, is called an explosion. The noise that is produced both by detonations and explosions is due altogether to the action of the liber- ated force upon the air. The sudden heat that is developed expands and drives back the air in all directions, and the sudden return of it produces a shock attended with a vari- ety of concussions which sends abroad in every direction through the surrounding atmosphere that kind of confused medley of vibrations which in their effect upon the ear constitute what we call noise. If there were no air, the most tremendous explosion that can be conceived would produce no sound. The most rapid mode by which force can be developed that is, brought out from a latent into an active state is by some kind of chemical action, usually combustion, which EXPLOSIVE SUBSTANCES. 277 word, in fact, only denotes that kind and degree of chem- ical action which is so rapid as to be attended with the evolution of light and heat ; but, even by this means, the force would not be ordinarily evolved with the degree of rapidity necessary to produce an explosion without anoth- er condition which will be hereafter explained. The most effective substances in ordinary use to produce explosive force are gunpowder, gun-cotton, nitro-glycerine, dynamite, and the like, all of which act on substantially the same principle, namely, that of producing an extremely rapid combustion by bringing large quantities of oxygen on the one hand, and of carbon and hydrogen on the other, into close juxtaposition with each other, so that they may rapidly combine. For one of the great fundamental facts in the economy of nature, as we observe it, is this : that far the greater portion of the action which we see taking place around us on this globe consists in the energy put forth by the sun in separating carbon and hydrogen from oxygen, and then, as the counterpart and correlative of this, the intense ea- gerness manifested between the oxygen, and the carbon, and hydrogen in coming together again. Now the whole philosophy of the explosive force mani- fested by gunpowder and the other substances above named consists in their composition being such as to bring quantities of carbon and hydrogen on the one hand, and of oxygen on the other, into close juxtaposition, so that they may unite, and thus liberate and restore, as it were, the force that was expended in separating them, with the. greatest rapidity. To illustrate this, suppose we have a large and solid log of dry wood. Now the wood of such a log contains carbon and hydrogen, but no oxygen. The oxygen is in the air around it. When the substances are raised to the right 278 DETONATIONS AND EXPLOSIONS. temperature to bring their tendency to combine into action, the log begins to bui'n that is, the oxygen combines with all that portion of the carbon and hydrogen which lies on the surface of the log, which is all that is accessible to it at first; and it can only gain access to the inner portions as fast as the outer ones are burned away. If now the log is split up into small and slender portions, and, still more, if it is converted into shavings by a plane, the air that is to say, the oxygen that is in it gains a much more ready access to the substance of the wood, be- ing able to introduce itself into the interstices of the heap of sticks or shavings, and the combustion will be greatly accelerated ; and, ponsequently, the force that is developed, though it will be no greater in the total amount, will come forth from its latent into an active state in a much more rapid manner. And if it were possible to reduce the wood to dust by a rasp or a saw, and then to keep the particles suspended in the air, and near enough to each other to furnish to each portion of carbon and hydrogen a portion of oxygen, nei- ther more nor less than it required, close at hand, the whole mass would flash, as it were, into a flame with almost the suddenness of gunpowder. Indeed, the dust of wood or of coal mingled thus with air is sometimes blown into furnaces, and is found to pro- duce a wonderful effect, through the rapidity and the force of the combustion which results. Now the oxygen in the air, being a gas, can not be kept mingled in this way with any powdered substance. If it could be obtained in a solid form, and could be pulverized, and in that form mingled intimately with any powdered compound of carbon and hydrogen, then, when a portion of the mass was raised to the right temperature, an almost instantaneous combination, accompanied with a sudden de- NATURE OP NITROGEN. 279 velopment of force in the form of heat, and having the ef- fect of an explosion, would result. But oxygen can not be made to exist by any means now known in a solid form, except in combination with some oth- er substance. The best, therefore, that can be done is to use it in combination with some other substance for which it lias the weakest possible affinity that is, the one which will most easily and readily let go its hold, so as to allow the oxygen, with the least hinderance, to enter into combi- nations with the hydrogen and carbon. This substance is nitrogen. The great distinguishing characteristic of nitrogen is the weakness of its affinity for other substances, just as the strength of its affinity is the great characteristic of ox- ygen. Now nitrogen will combine with oxygen in various ways and in many different proportions, the two elements being at all times ready to let go at once their hold upon each other whenever any other substance is presented for which oxygen has a stronger attraction. Nitrogen is usually described in books as one of the most inert substances in nature, and yet the compounds which it forms with other elements, and especially with oxygen, are the most violent in their action of all known substances. Nitric acid is perhaps the principal of these combinations, and is one of the most powerful and destruct- ive agents that exist. It consists essentially of a large quantity of oxygen held in combination with a smaller quantity of nitrogen, united to it by a very feeble force. People are often surprised that a substance so inert should form compounds so active and violent ; but, instead of its being a matter of surprise that this should be the case, it is the very inertness of this element on which the violence of the action of the compound depends that is, it holds the oxygen committed to its keeping with so feeble a grasp, 280 DETONATIONS AND EXPLOSIONS. and releases it so readily, that this last immensely power- ful agent is always at once set free, and enabled to act with its full force upon other substances. It is the oxygen which is really the agent in all the violent action which results, the nitrogen only serving the purpose of holding it weakly, and releasing it readily, when the time for action comes. Still, however rapidly the process of combustion may be made to proceed by this arrangement in the case, for ex- ample, of gunpowder the force is not developed with suf- ficient suddenness and in sufficient quantity to produce all the effects of an explosion without being restrained and allowed to accumulate its energy. Thus an ounce of gun- powder, ignited in the open air, burns with a flash indeed, but the combustion of it requires a perceptible period of time, and the force developed has time to pass off into the air without any very sudden or violent action; but let the same quantity be inclosed in the cast-iron shell of a hand-grenade, or rammed into a gun-barrel, or into a hole drilled into a rock, and confined there with wadding or tamping, so that the force which results from the begin- ning of the burning, can be held in restraint until the com- bustion is completed, then, when it at last breaks away, and the whole accumulated force comes into action in a single instant, a very violent explosion is the result. There are many other ways in which force, developed gradually, may be accumulated and allowed to act all at once so as to produce an explosion. The bursting of a steam-boiler is one example of this, and the accumulation of some mysterious force in the case of a volcano, until it acquires energy sufficient to burst the barriers that confine it, is another. In the case of the steam-engine, the force gradually pro- duced by the heat from the coal, acting upon the steam, MEASOTIINO THE BURSTING PEKBSX7EE. EXPERIMENTS ON PRESSURE. 283 works itself off, when all is right, through the machinery ; or, if there is any tendency to accumulation, the safety valve allows the surplus to escape. When, from any cause, the force accumulates too rapidly to pass off through these avenues, it increases in tension until it becomes sufficient to overcome the cohesive strength of the iron of the boiler, and an explosion is the result. The precise degree of this tension may be exactly meas- ured. It is obviously of the nature of a, pressure, and it is measured and estimated sometimes by the number of pounds to the square inch, and sometimes by what are call- ed atmosphere*. The pressure of the atmosphere is about fifteen pounds to the square inch, so that a pressure of two, three, or ten atmospheres would be that of thirty, forty- five, or one hundred and fifty pounds to the square inch respectively. In locomotive engines, the pressure employ- ed is often from fifty to sixty pounds to the square inch. Great as the pressure is, in many cases, which acts upon the interior surface of a large boiler, it can be conveyed very easily, by small pipes, to a great distance, and there observed and measured safely. In this way some experi- ments were made during the last year, under the direction of the Navy Department of the United States, to ascertain certain points in respect to the amount of pressure realized in large boilers when raised to the bursting point. The experiments were made upon Sandy Hook, at a place far removed from any dwelling. The engraving shows the ef- fect produced by one of the explosions. In the middle distance is seen the inclosure where the boilers to be experimented upon were stored, and a repre- sentation of the result of one of the explosions. In the foreground is also the place where the observers were sta- tioned. Pipes are seen lying upon the ground, and form- ing a communication between the boiler experimented 284 DETONATIONS AND EXPLOSIONS. upon and the station. These, being connected with the boiler at one end, and with the gauges at the station at the other end, afford the means of determining the pressure in the boiler at each different stage of the experiment. There were several boilers tested. In one of them, when the pressure reached fifty pounds to the inch, one of the interi- or braces gave way ; and when, at length, the index of the gauge marked fifty-three pounds to the inch, the boiler burst with a terrific explosion, and portions of it, and of the shell connected with it, weighing about four tons, were hurled high into the air, and thrown to a distance of 500 feet from the inclosure. The great violence of the effect, in cases like this, where force is held in restraint for a time after being brought into great tensile action, arises from its being converted into heat by the compression, the prevention of motion seeming to operate in some sense in the same way as the extinguish- ment of it. In the case of gunpowder, the gases produced by the combustion, of the carbon and sulphur, by means of the oxygen in the nitre, are found to occupy about 500 times the space occupied by the gunpowder itself. This is an enormous expansion ; but if this expansion is pre- vented for a moment from taking effect by the resistance of the sides of the gun-barrel, or of rock, within which the combustion goes on, the gases become heated so as to de- mand 2500 times the original space ; and this is the cause of the enormous increase in the violence of the effect pro- duced by the combustion of such substances when it takes place under confinement. With some of the immense guns now manufactured by the English and American govern- ments, balls weighing 500 pounds are thrown with such force as completely to penetrate a target consisting of a plate of solid iron eight inches thick, backed by six inches of the very hardest kind of wood, behind which is another THE EFFECT HOW PRODUCED. 285 plate of iron Jive inches thick, with another thickness of six inches of hard wood beyond it, and a one and a half inch plate of iron in the rear the whole all firmly riveted to- gether ! Besides gunpowder, there are various other explosive substances, such as gun-cotton, nitro-glycerine, dynamite, and others, the properties of which depend upon a consti- tution substantially the same in principle with that of gun- powder, namely, the combining of a substance consisting chiefly of carbon and hydrogen with some other substance containing a large quantity of oxygen in a state of conceal- ment or disguise, as it were. In gunpowder, the combusti- ble substances the sulphur and carbon are finely pulver- ized in a mill, as is also the nitre which contains the oxygen. In gun-cotton, on the other hand, nature divides the com- bustible material by forming the long, slender filaments of the cotton, and the oxygen is added by means of a combi- nation of acids containing it, which infiltrates itself into the substance of the fibre, and thus brings the two ele- ments into a much closer connection with each other than can possibly be effected by any mere mechanical means. It is substantially the same with nitro-glycerine, and with a composition called dualin, which are estimated to exert by their combustion ten times the force of gunpowder ! These, and perhaps most other explosive substances now used, depend for their effect on the very energetic manner in which oxygen, when held weakly by nitrogen, under certain conditions lets go its hold and seizes upon any car- bon or hydrogen that is within its reach. And not only these, but a great many of the most remarkable phenomena of nature depend upon this relation which the action of ni- trogen and that of oxygen have to each other. The read- er should bear this principle distinctly in mind, namely, That the counterpart of oxygen in the economy of nature, 286 DETONATIONS AND EXPLOSIONS. in respect to the strength of affinity for other substances, and its tenacity of hold when in combination with them, is nitrogen. Nitrogen is the great weak-holder. It is as remarkable for the feebleness of its tendency to unite with other substances, and the readiness with which it gives them up to other affinities, as oxygen is for the contrary qualities. And a very large proportion of the processes going on all the time in the natural world, and of the phenomena of animal and vegetable life, are dependent upon the mutual play and interaction of these two elements in relation to themselves and to other substances, as determined by the weak affinities of the one, and the strong affinities of the other. Thus, as we saw in the preceding chapter, the forcible separation of oxygen from its strong combinations, by the power of the sun, in the leaves of plants, and the delivery of it to the weak custody of nitrogen, and, finally, the sur- rendering of it back, under new circumstances, to its strong combinations again, is the secret of a very large portion of the phenomena of vegetable and animal life. It is in ac- cordance with this view that plants have comparatively little need of air, and that chiefly for the sake of the carbon which the air contains ; but animals have great need of it, on account of the oxygen which they use for the sake of the heat-force which they obtain by letting it fall into combination with the carbon again. Some persons are, at first thought, surprised that, since this is the state of the case that is, since oxygen has so strong an affinity for other substances, and as so large a quantity of it is held in the air, and in a peculiarly weak union with nitrogen for the air is chiefly composed of those two elements that the action of the air is not more instantaneous and violent than it is. The explanation is, OTHER VIOLENT CHEMICAL ACTION. 287 that the oxygen in the air can not act with very great ra- pidity or energy on account of the wide diffusion and ex- treme dilution of it. The proportion in the atmosphere is only about one quarter of its bulk, and the substance of it is so minutely divided and so much diffused that the in- tensity of its action is greatly diminished in consequence of the limited supply of it which any given current of air can bring into action in any given time. There are many other examples of chemical action so en- ergetic as to produce detonations and explosions, the ef- fect of which is dependent upon the powerful attraction of certain other substances possessing in some degree the characteristics of oxygen. There are also certain metals that have so ardent an affinity for oxygen that they seize it with even greater avidity than that which is manifested by the action of carbon or hydrogen upon it. They seize it wherever they find it, no matter how strong its existing combination may be. Two very conspicuous examples of these are the metals potassium and sodium the bases re- spectively of potash and soda. These metals have so ex- cessively strong an affinity for oxygen that they decom- pose water to obtain it ; and they can not be retained in a metallic state without very special and effectual precau- tions to protect it from the water existing in the atmos- phere, and in almost all substances around them. And the action, moreover, is so violent that all the phe- nomena of combustion are produced when they are brought into contact with water. It is very wonderful to see a globule of either of these metals burst into a blaze when thrown into water, or placed on a wet surface of any kind. The great heat developed by this intense action is made use of to produce explosive effects by arranging the ma- terials in such a way as to allow them suddenly to com- bine in any confined space. This has been tried especially 288 DETONATIONS AND EXPLOSIONS. with sodium, by inclosing a portion of it, and also a por- tion of water, in two glass tubes connected together by a narrow neck or division, somewhat like that of an hour- glass. This neck is closed by a division formed of some substance soluble in water, such as sugar, or salt, or a film of gum, or glue. The charge, thus prepared, is placed, for example, in the hole drilled in a rock, and closely confined there by a wadding or tamping rammed in. After the lapse of a certain time, which can be calculated with some accuracy beforehand, the dividing substance is dissolved by the water which is in contact with it on one side, and the water and the sodium rush together. The water is de- composed. The oxygen of it combines with the sodium and forms soda. The other element of the water that is, the hydrogen, is set free in the form of a gas, and is so in- tensely heated by the energy of the chemical action that an explosive force is generated sufficient to rend the rock in pieces. Thus the philosophy of detonations and explosions is, in general, simply this, namely, that substances having a very powerful tendency to combine are brought together un- der such conditions that this tendency may be suddenly set free to act ; then the particles of which the substances are composed fall together, as it were, with enormous force, though it is a force acting through very minute distances as estimated by our senses. In thus falling, and by the sudden arrest of the force with which they fall, they gen- erate very intense heat, and this heat, acting through the gases which are likewise usually also set free by the ac- tion, develop an enormous expansive force, which, sudden- ly breaking loose from the restraints confining it, produces the disruptive effect, while the shock communicated to the air produces the sound ; these together constitute the ex- plosion. HOW TIME IS TO BE TAKEN INTO ACCOUNT. 289 CHAPTER XVH. FORCE IN RELATION TO TIME. THERE are some very interesting and important consid- erations involved in the relation between time and force considerations which are necessary to be taken into ac- count in order to the attainment of clear and correct ideas of the fundamental principles involved in the subject. In estimating absolute quantities of force, the element of time is not necessarily to be taken into account at all, though at first thought people are generally apt to imag- ine it otherwise. But the amount of force expended in raising one pound one foot is an absolute and definite quantity, whether more or less time is expended in produ- cing it. A gallon of water is the same quantity whether it falls drop by drop and is half a day in accumulating, or flows in a gushing stream so as to fill the measm-e in a minute. In the same manner a foot-pound is a foot-pound, neither more nor less, whether it is the work of a squirrel raising the pound slowly and laboriously by a cord wound round an axle connected with his revolving cage, or is a part of the immense energy expended in raising, in five seconds, by steam, a trip-hammer weighing many tons. When we say that a horse is five or seven times stronger than a man, we mean that he can exert a force in one hour equal to that which a man can exert in five or seven hours. The theoretical horse-power that by which the efficiency of powerful engines is estimated is 33,000 foot-pounds per N 2UO FORCE IK RELATION TO TIME. minute ;* bat every one of those foot-pounds represents a quantity of force precisely equal to that exerted by the squirrel in raising a pound weight one foot, or an ounce weight sixteen feet, or, if we can imagine such a thing, that exerted by a flea trained to work in a mimic tread- mill, and raising thereby a weight of one grain as many feet as there are grains in a pound. Thus, in simply estimating quantities of force, the ele- ment of time is not at all concerned, just as in estimating any absolute quantity of water we have nothing to do with the time that was required for it to flow through a particu- lar faucet ; but in estimating the amount offeree which can be obtained from particular sources of power, we have to consider the element of time, in order to determine the ef- fectual value of the results. Just as in the case of water, though a gallon is a gallon, neither more nor less, however slowly or rapidly it may come, we have to consider how many gallons a given source will supply in a given time, in order to make our calculations correctly in respect to what can be done with it. There are two respects in which the element of time comes into the account in calculations relating to the em- ployment of force. First, the rapidity with which the force is either brought into action from its latent state, or can be delivered to the control of man ; and, secondly, the ra- pidity with which it can be transmitted from place to place. In respect to the first point, in the burning of coal under the boiler of a steam-engine, force is developed by coming from a latent into an active state ; and in the case of a mill- wheel carried by a stream of water, the force is already in action, but is delivered, or, rather, a portion of it is deliv- * This would be about what he would do by walking off at the rate vf one step two feet long for every second, and raising by means of a rope passing over pulleys a weight of 270 pounds. VARIOUS BATES OF TRANSMISSION. 291 ered through the mill-wheel to the control of man. It is, of course, important to consider how much force such sources of supply would furnish in a given time. And, secondly, if the force so furnished is to be trans- mitted from one place to another, either by water-pipes, or air-pipes, or wires, or bands, it is often necessary to con- sider the time which will be required for such transmission. It is surprising ho\v great a difference there is in the ra- pidity with which force, in its various forms and through different media, can be transmitted. We have a good il- lustration of this in the case of the eruptions of Vesuvius which are taking place on so remarkable a scale at the time of this present writing. Let us see at what different rates of speed the forces that are set in motion by any one of the explosions that take place are transmitted to differ- ent distances from the spot. First, if we suppose the dis- tance from the crater to Naples through the air is ten miles, a bird, frightened by the thundering report and the burst of vapor and flame, would fly to the city in ten min- utes, the sound of the explosion would traverse the inter- vening air in perhaps a minute and a half, and the light of the flash in about T^.WTT f one second, a speed that is altogether inconceivable to us. And yet all these different modes of communication are only examples of the transmission of force in different forms, the first impulse being given in each case by the explosion. It is impossible for us to form any conception of the velocity of such a motion as that of light, nor picture to our imagination any kind of undulation as moving at such a rate. We can, however, gain some idea of the nature of such a motion by attempting to form some definite conception of the manner in which motion must pass through any 292 FOKCE IN RELATION TO TIME. elastic substance. Suppose, for instance, we have a long elastic cord or line, like an India-rubber tube, except that its being hollow would be of no consequence, and that two persons are experimenting with it, one having hold of each end. Now if the person at one end gives a sudden pull, the motion will be communicated from that end to the other in this way, as is supposed, namely, the particles of the India-rubber next the person's hand that pulls will, by their attraction for those next beyond, draw them in the direction in which they themselves have been pulled, and they the next, and so on by a kind of wave or undulation of motion from one end of the line to the other. It would be substantially the same in the case of pushing, provided that the line could be prevented from bending laterally. It is supposed that the motion is communicated in a somewhat similar way, only with inconceivably greater rapidity, in the case of a pull or a push communicated through an iron wire, or through any other solid sub- stance that is, that one set of particles communicates its motion to the next, and the second set to the third, and so on to the end ; and, of course, that all such transmissions of motion require a certain portion of time, however minute, and that the period required is in proportion to the distance passed over. The reader will perceive, on a moment's reflection, that undulations or vibrations of this kind are very different from those of waves in water, in this respect, namely, that the direction of the motion of the particles is backward and forward instead of being upward and downward. There is, however, a striking analogy between the two different modes. If this is the true theory of the transmission of the solar radiation, for example, we may well be amazed at the in- TRANSMISSION OF ELECTRIC FORCE. 293 conceivable capabilities of nature in respect to the phe- nomena of force. The distance from the earth to the sun is so great that it would require 300 years for a railroad train at full speed to traverse it, and yet the undulations of light pass over it in eight minutes and a half. And then, on the other hand, the magnitude of the dis- tances that the human mind has to take cognizance of in the visible universe is not less amazing than the rapidity of the action taking place in it ; for, though light would pass in less than ten minutes from the sun to the earth, there are stars known to be so remote that it would require something like a thousand years for the light coming from them to reach us when proceeding at the same rate of mo- tion that is, at a rate which would traverse a distance in about eight minutes which it would take a railroad train 300 years to pass over, though going at full speed. Electricity, as it manifests itself in passing along the tele- graph wire, is supposed to be a force in process of being transmitted in the form of some kind of vibratory or un- dulatory motion, either of the substance of the wire itself, or of some subtle medium contained in it. This is inferred from the fact that a certain amount of force in some form or other must be expended at one end of the wire, and the same amount in some other form is, or may be, developed from it at the other end. The force thus necessary at the beginning is usually generated by a process something like combustion, in w r hich zinc, or some other metal, takes the place of fuel ; that is to say, the process is like combustion in the fact that it consists of a powerful recombination of the metal with oxygen previously separated from it, only the combination takes place under such circumstances that the liberated force reappears in the form of electricity in- stead of in that of light and heat. But there must always be an expenditure of force in 294 FOBCE IN RELATION TO TIME. some form to set the electric current in motion. This force, as has already been said, is supplied generally by a battery at one end of the line ; but when a special current has to be sent from any intermediate point, for any special pur- pose, a new force must be imparted by an apparatus for consuming an additional quantity of zinc fuel, if it may be so called. The engraving represents the manner in which this is done, or was formerly done, in some countries in Europe. An accident has happened to the train, and the official wishes to communicate the knowledge of the fact to the next station. He has in his hand a small battery inclosed in a box. By a slight movement of the handle he sets the battery in action. The oxygen begins to com- bine with the zinc, thus restoring, as it were, the force with which the two elements were originally separated from each other. This force appears in the form of electricity, and the man, by means of a conductor attached to a long, slender pole, communicates the force to one of the wires, and thus can send a series of impulses to the nearest station. He can not communicate a message of words convenient- ly in this way, but he can call attention and procure help somewhat as a person sick in a chamber can call for help by knocking on the floor under circumstances in which he would not be able to communicate any information in words. This method, however, is now seldom used on any rail- road, other more convenient ones having superseded it ; but it will illustrate the principle which I have been ex- plaining. The word force is used in several very different senses in common parlance. The import of the word, for example, is very different as used in the phrases force of gravitation, force of cohesion, and other similar expressions, from that which is implied when we speak of the force of a current TRANSMITTING AN IMPULSE OF FOECE. EE ACTION. 297 of water or of wind. Indeed, some writers have maintained that, on account of this ambiguity, the word force ought to be banished from all scientific discussions, and the word energy substituted, to denote that form offeree which com- municates itself in some kind of motion from one body to another, and expends itself in the one just in proportion as it passes into the other. It is force in this sense which has been chiefly treated of in this volume that is, force in the sense of energy, which is diminished in one body just in proportion as it is imparted to another. And the portion, too, it must be remembered, which is lost by one is precisely that which is gained by the other. Let a log be rolled from the bank of a river into the water, and the flow of the current will soon set it in motion down the stream ; but just so far as motion is imparted to the log, just to that precise degree that of the water that impinges upon it is diminished ; that is, the motion of the water is retarded just as much as the log is impelled, so that the whole amount of motion is the same as before. And, in the same manner, a vessel at sea is driven forward only so fast as the wind itself is kept back by it ; that is, the wind can not give up its energy and keep it too. This is true in cases of oblique as well as of direct action, as, for example, in the case of a windmill, or a vessel sailing on a wind, as they say, in which cases the wind strikes the sails obliquely, and moves them forward by an indirect reaction. It is only just so far as the wind itself, or a portion of it, is retarded in its motion in one direction that the vessels are made to move in another ; that is, the force or energy is not produced; it is only parted with by one body to be received by another. It is thus only a small part of the moving force or energy that man withholds from the wind by the sails of his ships, or of his windmills by his sails, or from the current of a FOKCE IN RELATION TO TIME. OBLIQUE ACTION. river by his water-wheels. Perhaps the greatest force that man has wholly under his control is that drawn from coal, and kept under subjection and guidance in the large steam- engines that he builds. The British government have re- cently constructed some war steamers of a very large class, one of which, the Devastation, has engines of 5600 horse power. Think of a team of horses four abreast, and more than two miles long for that would be about the space that such a power represented by horses would require and all entirely under the perfect control and management of one man, so that it can be made to obey orders commu- nicated by the slightest signals of the officer of the deck MINUTE FOKCES. 299 signals made by the motion of the fingers of his hand to " Ease her," " Back her," " Stop her," and the like with the promptness, and, at the same time, with the self-restraint of the most docile dog ; and then again, at the word, or, rather, the touch of command, can be made to urge the mighty mass of the ship, with its immense weight of iron plating, and its enormous guns, and its hundreds of work- ing population, against the strongest gales and through the heaviest surges with irresistible energy. On the other hand, the smallest forces which man takes definite cognizance of and measures are perhaps those de- veloped by the faintest currents of electricity. The instru- ment by which such feeble forces are measured is called the Torsion Balance. 300 FOECE IN KELATION TO TIME. It is called the Torsion Balance because the force with which that of the current is brought into comparison is the resistance to the torsion or twisting of some very delicate fibre, usually a single filament of a spider's or a silk-worm's spinning. The engraving shows the form and general ap- pearance of the instrument. It is inclosed in glass, to pro- tect the needle within from currents of air. It stands on a tripod furnished with screws to secure a perfectly level position for it. The current of electricity is brought by one of the wires on the left, and carried away by the other. The receiving wire, after entering beneath the instrument, is wound round a coil, a portion of which is visible in the engraving. By this means the magnetic effect which such a current is capable of producing is greatly increased. This magnetic influence, acting, through the circular plate above it, upon the needle suspended by the filament, causes it to turn in one direction or the other, its turning being resisted by the torsion of the filament, and the degree of it, as marked by the gradation of the circle, denoting the strength of the current. By this instrument forces inconceivably minute may be measured and compared. The doctrine that lies at the foundation of the science of force that, namely, which it has been the main object of this book to explain and illustrate, is this : that no force, in the sense of energy, can ever be generated, but can only, when already existing, either in an active or suspended form, be transmitted or released, each particular movement of it requiring a certain lapse of time. The cases which seem at first view to be exceptions to this principle are all illusory, as, for example, that of the explosion of a blast of gunpowder rending rocks in pieces by the communica- tion of a very small force through an electric wire. Here the great force which the small one seems to produce is THE KOW OP BRICKS. 301 not generated) but only catted out into action. The true source of the disrupting power is in the sun, which sepa- rated the oxygen from the carbon by the actinic force of its rays when the wood which furnished the carbon for the gunpowder was growing. The carbon and the oxygen being placed side by side in the gunpowder, with an im- mensely strong tendency to come together which tenden- cy can, however, for some mysterious reason, only come into action when a portion of them is raised to the right temperature the spark produced by the electric discharge acts, not to generate the force, but only to release it from its suspense and detention. It is in principle a case precisely analogous to that of a child who sets to falling a long row of bricks by a touch upon one of them at the end. The whole amount of force with which the bricks fall is very great compared with that of the touch with which the whole movement was begun ; but it is force which was accumulated in the bricks, as it were, by the labor of the child in setting them up one by one in lifting each one up far enough to set it on the end. Thus the force with which the bricks fell was only an accumulated force released, and not a new force generated by the slight touch which set the train in motion. And just as in the movement transmitted through such a train a certain time is required for the movement to pass onward to the end of it, so in all cases a definite lapse of time is expended in every mode by which force is trans- mitted sound passing through the air requiring but lit- tle, electricity through a wire very much less, and light through the luminiferous ether, which is supposed to be the medium that conveys it, the least of all. CONCLUSION. CHAPTER XVIIL CONCLUSION. THE concluding limit of the space within which the dis- cussion of each subject in these volumes is necessarily con- fined now draws near, and warns me that I must bring what I have to say upon Force to a close. This is not, however, because the subject is exhausted. All that has been said in this volume, and, indeed, all that man has yet learned, and, in fact, all that is possible, in this state of be- ing, for him to know, forms but the merest beginning of knowledge in this boundless field. Every young man who reads this book attentively will find that he knows less, not than he actually did know, but than he imagined that he knew before he began it; for the field of knowledge on this subject is unbounded. The farther we enter into it, the wider the region beyond us expands, but then the stronger becomes our desire to go on and explore the mys- teries that remain, so that the effect of such incipient studies as these is to discourage self-conceit, not weary out the love of knowledge. It almost always surprises the learner when he is first informed that the subject of force really includes almost, if not all the phenomena of nature that are subject to our cognizance. But this is strictly true, for every thing that takes place is a manifestation of force of some kind, except, perhaps, the phenomena involved in mental operations. Many scientific men would not even except those, on the ground that even mental operations, so far as they mani- fest themselves to the human observation, whether they ENERGY AND PRESSURE. 303 are our own or those of others, act through and by means of bodily organs, which in all their actions are dependent entirely on some form of material force communicated to the system in the food. However this may be, it is certain that all which takes place in the visible universe around us consists of move- ment of some kind, produced by some previous movement, and thus forming a part of the grand circuit which the vast amount of cosmical force that is, the force that is in action in the universe, constantly describes. Besides this moving and acting force called energy, which expends itself, or rather transmits itself in its action, there is what is sometimes called a force, namely, pressure, which, so long as it produces no motion, undergoes no change. For example, if a heavy weight is supported in the air on the top of a tall pillar of wood, like a mast, and remains at rest, it will continue to exert the same pressure upon the fibres of the wood forever without any change. So long as there is no movement there is no expenditure, and the pressure remains undiminished. But if the pillar be suddenly removed, the weight begins to descend, pass- ing through space and occupying time; and the force be- gins to be expended that is, transmitted to the surround- ing objects which it meets on its way, or encounters at the end of its descent. It is this force, acting in time and through distance, which is called energy, and has been the main subject of discussion in this volume. Lawrence explained all these things pretty clearly and fully to John in his various conversations with him, and somewhat more in detail than they have been stated here. He also, from time to time, stated and explained particular facts to Rick, as he had occasion to see him, but without much attempt to make him understand abstract principles or extended generalizations. Such a boy must be taught 304 CONCLUSION. particulars in respect to the phenomena of nature for a long time before he is prepared to see the analogies which connect them together, or to comprehend the general prin- ciples that underlie them all. Lawrence had too much knowledge of the nature and movements of a mind like Rick's, which is in process of formation, to attempt too much with it, so he was satisfied with calling Rick's at- tention to such points as could be made obvious through the senses. A boy of his age can much more easily under- stand, and will much more fully appreciate what he can see, or picture to his imagination in the form of a visible phenomenon, than things which exist in his mind only as a thought. But the great effect produced on Rick's mind by Law- rence's instructions was, after all, a moral one that is, it was the influence of them upon his feelings and affections. While he hated most of the teachers under whose care he had been successively placed teachers who took appar- ently no notice when he did right, but scolded or whipped him when he did wrong he soon began to form a strong attachment for Lawrence, whom he readily learned to con- sider as his friend ; and though it is true that the knowl- edge which he obtained was comparatively slight, and of course, like the beginnings of all knowledge, was very su- perficial, still what there was of it was knowledge ; and, what was better than all, it was knowledge acquired with pleasure, and was the beginning of a change in him, which, if it should be followed by measures and treatment of a similar character by the teachers of theMorningside School, would probably, in time, make him a good and happy boy. There never was a more false or unphilosophical senti- ment expressed than that conveyed by Pope's celebrated distich, FINAL REFLECTIONS. 305 " A little learning is a dangerous thing ; Drink deep, or taste uot the Pierian spring." If such a doctrine were believed and obeyed, it would put an effectual stop to all acquisition of knowledge, for it is only a " little learning" on any conceivable subject that it is possible for any one in the present condition of the human mind to attain. We must learn all we can, be it little or a great deal, on every subject that comes within our view. We may, indeed, make a choice among the dif- ferent subjects which lie open before us in regard to the degree of time and attention which we will devote to each, but no knowledge is useless simply because it is but a be- ginning. There are thus two lessons taught by this book, or, rath- er, two truths to be learned from it : First, that physical force is a very curious and interest- ing subject of study ; and, Secondly, that it may be made one excellent means of changing the heart and the character of a bad boy ; but that the way to employ it for this end is to make it a sub- ject of curious study for his mind, and not by the personal application of it to his body. TUB END. VALUABLE AND INTERESTING WORKS FOR PUBLIC & PRIVATE LIBRARIES, PUBLISHED BY HARPER & BROTHERS, NEW YORK. Cf~ For a full List of Books suitable for Libraries published by HABPKB A BBOTHKKB, sec HABPEB'B CATALOGUE, which may be had gratuitously on application to the publishers personally, or by letter enclosing Ten Cents in postage stamps. ABPKB & BBOTUEKS will send their publications by mail, postage pr* paid, on receipt of the price. MACAULAY'S ENGLAND. The History of England from the Accession of James II. By THOMAS BABINGTON MACAULAT. 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