CfORY. XLE UNIVERSITY OF CALIFORNIA AT LOS ANGELES SCIENCE PRIMERS, edited by Professors HUXLEY, ROSCOE, and BALFOUR STEWART. IN TROD UCTOR Y . INTRODUCTORY. BY PROFESSOR HUXLEY, F.R.S. NEW YORK : CINCINNATI : CHICAGO: AMERICAN BOOK COMPANY. SCIENCE PRIMERS. EDITED BY PROFESSORS HUXLEY, ROSCOE, AND BALFOUR STEWART. INTRODUCTORY ........ T. H. HUXLEY CHEMISTRY H. E. ROSCOE PHYSICS BALFOUR STEWART PHYSICAL GEOGRAPHY A. GEIKIE GEOLOGY A. GEIKIE PHYSIOLOGY AND HYGIENE M. FOSTER AND R. S. TRACY ASTRONOMY J. N. LOCKYER BOTANY J. D. HOOKER LOGIC W. S. JEVONS INVENTIONAL GEOMETRY . . . . W. G. SPENCER PIANOFORTE FRANKLIN TAYLOR POLITICAL ECONOMY W. S. JEVONS NATURAL RESOURCES OF THE UNITED STATES J. H. PATTON W. P. 3 TABLE OF CONTENTS. H ART. SECT. I. NATURE AND SCIENCE. PACK I. ,, Sensations and Things S . Causes and Effects 3 3. ,, The reason Why. Explanation 6 4. Propert.es and Powers . . 7 5. Artificial and Natural Objects. Nature .... 8 6. Artificial Things are only Natural Things shaped and brought together or separated by Men . 8 7. ,, Many Objects and Chain* of Cau.es and Effects in Nature are out of our reach . ... 10 8. The Order of Na ure : nothing happens by Accident, and there is no such thing as Chance . . r , . .10 9. ,, Laws of Nature ; Law* are not Causes 12 10. i, Knowledge cf Nature is the Guide of Practical Conduct . 14 11. Science: the Knowledge of the 1-aws of Nature obtained by Observation, Experiment, and Reasoning . . .16 II. MATERIAL OBJECTS.-(A.) MINERAL BODIES. 12. ,, The Natural Object Water 19 13. A Tumbler of Water . ao 14. ,. Water occupies Space ; it offers Resistance i it has Weight ; and is able to transfer Motion which it has acquired ; it is therefore a form of Matter 20 15. Water is a liquid 21 16. Water is almost incompressible 22 17. ,, The Meaning of Weight 24 18. Gravity and Grav.tation 25 19. The cause of We ght : Attraction: Force . . . .27 20. ,, The Weight of Water is Proportioned to its Bulk. . . 28 21. 'I he Measuring of Weights. The Balance .... 29 22. The Weight of the same Bulk or Volume of Water is Con- stant under the same conditions. Mass. Density . . ;o 23. ,, Equal Volumes of Different Things under the same circum- stances, have Different Weights : the Density of Different Bodies is Different . 32 24. ,, The Meaning of Heavy and Light Specific Gravity . . 33 25. ,, Things of greater Specific Gravity than Water sink in Water ; Things of less Specific Gravity float . . 34 *6. ,, A Body which Floats in Water always occupies as nuich Space beneath the level of the Surface of the Water as is equal to the Volume cf Water which weighs as much as that Body ; in other words, it d splaces its own Weight of Water 36 27. ,, Water Presses in all Directions 37 28. The Transference of Motion by Moving Water : the Momen- tum of Moving Water 40 29. ., The Energy of Moving Water 43 30. ,, The Properties of Water are Constant 47 31. ,, Increase of Heatat first causes Water to Increase in Volume 48 32. ,, Increase of Heat at length causes Water to become Steam . 50 33. ,, The taking away of Heat from Steam causes the Steam to change into Hct Water 51 34. When Water is changed into Steam, its Volume becomes about 1.700 times greater than it was at first . . 51 35. Gases or Elastic Kh:i Is. Air 52 36. Steam is an Elastic FiuiJ or Gas 54 37. ,, Gases and Vapours 55 38. '1 he Evaporat ion of Water at ord nary Temperatures . . 56 39- ii When Hot Water is cooled, it Contracts to beg n with, but after a time Kxp.inHs 57 TABLE OF CONTENTS. ART. SECT. PAGE 40. - II. Water cooled still further becomes the transparent brittle solid Ice .... 58 41. Ice has less Specific Gravity than the Water from which it was formed 59 42. Hoar Frost is the Gaseous Water which exists in the Atmos- phere, condensed and converted into Ice Crystals . . 60 43. When Ice is warmed it begins to change back into Water as soon as the Temperature reaches 32 61 44. ., Ice the solid, Water the liquid, and Steam the gas, are three states of one natural object; the condition of each state being a certain amount of Heat ..... 62 45. The Phenomena of Heat are the Effects of a rapid Motion of the Particles of Matter 63 46. The Structure of Water 65 47. Suppositions or Hypotheses ; their Uses and their Value . 67 48. The Hypothesis that Water is composed of Separate Parti- cles (Molecules) ....... .68 49. All Matter is probably made up either of Molecules or of Atoms 70 50 Elementary Bodies are neither destroyed nor is their Quantity increased in Nature 72 51. Simple Mixture "... 73 52. Mixture followed by Increase of Density: Alcohol and Water 74 53. Solution: Water Dissolves Salt ;6 54. ,, Quicklime and Water : Plaster of Paris and Water : Com- bination 79 55. , f Mineral bodies may take on definite shapes and grow, or increase in iize, by the addition of like parts . . .82 (B.) LIVING BODIES. 56. ,, The Wheat Plant and the substances of which jt is composed 83 57. ,, The common Fowl and the Substances of which it is com- posed 85 58. Certain Constituents of the Body are very similar in the Wheat Plant and in the Fowl 86 59. Proteid Substances are met with in Nature only in Animals and Plants; and Animals and Plants always contain Pro- 60. ,, What is meant by the word Living ? 61. The Living Plant increases in Size, by adding to the Sub- stances which comp se its Body, like Substances; these, however, are not derived fro:n without, but are manufac- tured within the Bxly of the Plant from simpler Materials 62. ,, The Living Plant, after it has grown up, detaches part of its S_ubstance, which has the Power of developing into a similar Plant, as a Seed 63. The Living Animal increases in Size by adding to the Sub- stances which compose its Body, like Substances ; these however are chiefly derived directly from oiher Animals or from Plants 64 The Living Animal, after it has grown up, detaches part of its Substance, which has the Power of growing into a similar Animal, as an Egg 65 ,. Living Bodies differ from M.neral Bodies in their Essential Composition, in the manner of their Growth, and in the fact that they are reproduced by Germs .... III. IMMATERIAL OBJECTS. 66. ,, Mental Phenomena 67. The order of Mental Phenomena : Psychology SCIENCE PRIMERS. INTRODUCTORY. i I. NATURE AND SCIENCE. 1. Sensations and Things. All the time that we are awake we are learning by means of our senses something about the world in which we live and of which we form a part ; we are constantly aware of feeling, or hearing, or smelling, and, unless we happen to be in the dark, of seeing ; at intervals we taste. We call the information thus obtained sensation. When we have any of these sensations we com- monly say that we feel, or hear, or smell, or see, or taste, something. A certain scent makes us say we smell onions ; a certain flavour, that we taste apples ; a certain sound, that we hear a carriage ; a certain appearance before our eyes, that we see a tree ; and we call that which we thus perceive by the aid of our senses a thing or an object. 2. Causes and Effects. Moreover, we say of all these things, or objects, that they are the causes of the sensations in question, and 6 SCIENCE PRIMERS. [NATURE AND that the sensations are the effects of these causes. For example, if we hear a certain sound, we say it is caused by a carriage going along the road, or that it is the effect, or the consequence, of a carriage passing along. If there is a strong smell of burning, we believe it to be the effect of something on fire, and look about anxiously for the cause of the smell. If we see a tree, we believe that there is a thing, or object, which is the cause of that appearance in our field of view. 3. The reason Why. Explanation. In the case of the smell of burning, when we find on looking about, that something actually is on fire, we say indifferently either that we have found out the cause of the smell, or that we know the reason why we perceive that smell ; or that we have explained it. So that to know the reason why of anything, or to explain it, is to know the cause of it. But that which is the cause of one thing is the effect of another. Thus, suppose we find some smouldering straw to be the cause of the smell of burning, we immediately ask what set it on fire, or what is the cause of its burning ? Perhaps we find that a lighted lucifer match has been thrown into the straw, and then we say that the lighted match was the cause of the fire. But a lucifer match would not be in that place unless some person had put it there. That is to say, the presence of the lucifer match is an effect produced by somebody as cause. So we ask why did any one put the match there ? Was it done carelessly, or did the person who put it there intend to do so ? And if so, what was his motive, or the cause which led him to do such a thing ? And what was the reason for his having such SCIENCE. ] IN TROD UCTOR Y. a motive? It is plain that there is no end to the questions, one arising out of the other, that might be asked in this fashion. Thus we believe that everything is the effect of something which preceded it as its cause, and that this cause is the effect of something else, and so on, through a chain of causes and effects which goes back as far as we choose to follow it. Anything is said to be explained as soon as we have discovered its cause, or the reason why it exists ; the explanation is fuller, if we can find out the cause of that cause ; and the further we can trace the chain of causes and effects, the more satisfactory is the explanation. But no explanation of anything can be complete, because human knowledge, at its best, goes but a very little way back towards the beginning of things. 4. Properties and Powers. When a thing is found always to cause a particular effect, we call that effect sometimes a property, sometimes a power of the thing. Thus the odour of onions is said to be a property of onions, because onions always cause that particular sensation of smell to arise, when they are brought near the nose ; lead is said to have the property of heaviness, because it always causes us to have the feeling of weight when we handle it; a stream is said to have the power to turn a waterwheel, because it causes the waterwheel to turn ; and a venomous snake is said to have the power to kill a man, because its bite may cause a man to die. Properties and powers, then, are certain effects caused by the things which are said to possess them. 8 SCIENCE PRIMERS. [NATURE AND 5. Artificial and Natural Objects. Nature. A great many of the things brought to our knowledge by our senses, such as houses and furniture, carriages and machines, are termed artificial things or objects, because they have been shaped by the art of man; indeed, they are generally said to be made by man. But a far greater number of things owe nothing to the hand of man, and would be just what they are if mankind did not exist, such as the sky and the clouds; the sun, moon and stars ; the sea with its rocks and shingly or sandy shores ; the hills and dales of the land ; and all wild plants and animals. Things of this kind are termed natural objects, and to the whole of them we give the name of Nature. 6. Artificial Things are only Natural Things shaped and brought together or separated by Men. Although this distinction between nature and art, between natural and artificial things, is very easily made and very convenient, it is needful to remember that, in the long run, we owe everything to nature ; that even those artificial objects which we commonly say are made by men, are only natural objects shaped and moved by men ; and that, in the sense of creating, that is to say, of causing something to exist which did not exist in some other shape before, man can make nothing whatever. Moreover, we must recollect that what men do in the way of shaping and bringing together or separating natural objects, is done in virtue of the powers which they themselves possess as natural objects. SCIENCE.] INTRODUCTORY. 9 Artificial things are, in fact, all produced by the action of that part of nature which we call mankind, upon the rest. We talk of "making " a box, and rightly enough, if we mean only that we have shaped the pieces of wood and nailed them together ; but the wood is a natural object and so is the iron of the nails. A watch is " made " of the natural objects gold and other metals, sand, soda, rubies, brought together, and shaped in various ways ; a coat is " made " of the natural object, wool ; and a frock of the natural objects, cotton or silk. Moreover, the men who make all these things are natural objects. Carpenters, builders, shoemakers, and all other artisans and artists, are persons who have learned so much of the powers and properties of certain natural objects, and of the chain of causes and effects in nature, as enables them to shape and put together those natural objects, so as to make them useful to man. A carpenter could not, as we say, " make " a chair unless he knew something of the properties and powers of wood ; a blacksmith could not " make " a horseshoe unless he knew that it is a property of iron to become soft and easily hammered into shape when it is made red-hot; a brickmaker must know many of the properties of clay ; and a plumber could not do his work unless he knew that lead has the properties of softness and flexibility, and that a moderate heat causes it to melt. So that the practice of every art implies a certain knowledge of natural causes and effects; and the improvement of the arts depends upon our learning more and more of the properties and powers of natural io SCIENCE PRIMERS. [NATURE AND objects, and discovering how to turn the properties and the powers of things and the connections of cause and effect among them to our own advantage. 7. Many Objects and Chains of Causes and Effects in Nature are out of our reach. Among natural objects, as we have seen, there are some that we can get hold of and turn to account. But all the greatest things in nature and the links of cause and effect which connect them, are utterly beyond our reach. The sun rises and sets ; the moon and the stars move through the sky ; fine weather and storms, cold and heat, alternate. The sea changes from violent disturbance to glassy calm, as the winds sweep over it with varying strength or die away ; innumerable plants and animals come in being and vanish again, without our being able to exert the slightest influence on the majestic procession of the series of great natural events. Hurricanes ravage one spot ; earthquakes destroy another ; volcanic eruptions lay waste a third. A fine season scatters wealth and abundance here, and a long drought brings pestilence and famine there. In all such cases, the direct influence of man avails him nothing ; and, so long as he is ignorant, he is the mere sport of the greater powers of nature. 8. The Order of Nature : nothing happens by Accident, and there is no such thing as Chance. But the first thing that men learned, as soon as they began to study nature carefully, was that some events take place in regular order and that some causes SCIENCE.] INTRODUCTORY. " always give rise to the same effects. The sun always rises on one side and sets on the other side of the sky ; the changes of the moon follow one another in the same order and with similar intervals ; some stars never sink below the horizon of the place in which we live ; the seasons are more or less regular ; water always flows down-hill; fire always burns; plants grow up from seed and yield seed, from which like plants grow up again; animals are born, grow, reach maturity, and die, age after age, in the same way. Thus the notion of an order of nature and of a fixity in the relation of cause and effect between things gradually entered the minds of men. So far as such order prevailed it was felt that things were explained ; while the things that could not be ex- plained were said to have come about by chance, or to happen by accident. But the more carefully nature has been studied, the more widely has order been found to prevail, while what seemed disorder has proved to be nothing but complexity ; until, at present, no one is so foolish as to believe that anything happens by chance, or that there are any real accidents, in the sense of events which have no cause. And if we say that a thing happens by chance, everybody admits that all we really mean is, that we do not know its cause or the reason why that particular thing happens. Chance and accident are only aliases of ignorance. At this present moment, as I look out of my window, it is raining and blowing hard, and the branches of the trees are waving wildly to and fro. It may be that a man has taken shelter under one of these trees; perhaps, if a stronger gust than usual comes, a branch will break, 12 SCIENCE PRIMERS. [NATURE AND fall upon the man, and seriously hurt him. If that happens it will be called an "accident," and the man will perhaps say that by " chance " he went out, and then " chanced " to take refuge under the tree, and so the " accident " happened. But there is neither chance nor accident in the matter. The storm is the effect of causes operating upon the atmosphere, perhaps hun- dreds of miles away ; every vibration of a leaf is the consequence of the mechanical force of the wind acting on the surface exposed to it 5 if the bough breaks, it will do so in consequence of the relation between its strength and the force of the wind ; if it falls upon the man it will do so in consequence of the action of other definite natural causes ; and the posi- tion of the man under it is only the last term in a series of causes and effects, which have followed one another in natural order, from that cause, the effect of -which was his setting out, to that the effect of which was his stepping under the tree. But, inasmuch as we are not wise enough to be able to unravel all these long and complicated series of causes and effects which lead to the falling of the branch upon the man, we call such an event an accident. 9. Laws of Nature ; Laws are not Causes. When we have made out by careful and repeated observation that something is always the cause of a certain effect, or that certain events always take place in the same order, we speak of the truth thus dis- covered as a law of nature. Thus it is a law of nature that anything heavy falls to the ground if it is SCIENCE.] INTRODUCTORY. 13 unsupported ; it is a law of nature that, under or- dinary conditions, lead is soft and heavy, while flint is hard and brittle ; because experience shows us that heavy things always do fall if they are unsupported, that, under ordinary conditions, lead is always soft and that flint is always hard. In fact, everything that we know about the powers and properties of natural objects and about the order of nature may properly be termed a law of nature.. But it is desirable to remember that which is very often forgotten, that the laws of nature are not the causes of the order of nature, but only our way of stating as much as we have made out of that order. Stones do not fall to the ground in consequence of the law just stated, as people sometimes carelessly say ; but the law is a way of asserting that which in- variably happens when heavy bodies at the surface of the earth, stones among the rest, are free to move. The laws of nature are, in fact, in this respect, similar to the laws which men make for the guidance of their conduct towards one another. There are laws about the payment of taxes, and there are laws against stealing or murder. But the law is not the cause of a "man's paying his taxes, nor is it the cause of his abstaining from theft and murder. The law is simply a statement of what will happen to a man if he docs not pay his taxes, and if he commits theft or murder ; and the cause of his paying his taxes, or abstaining from crime (in the absence of any better motive) is the fear of consequences which is 'the effect of his belief in that statement. A law of man tells what we may expect society will do under certain circumstances; and a law of nature tells us what we may expect 14 SCIENCE PRIMERS. [NATURE AND natural objects will do under certain circumstances. Each contains information addressed to our intelligence, and except so far as it influences our intelligence, it is merely so much sound or writing. While there is this much analogy between human and natural laws, however, certain essential differences between the two must not be overlooked. Human law consists of commands addressed to voluntary agents, which they may obey or disobey ; and the law is not rendered null and void by being broken. Natural laws, on the other hand, are not commands but assertions respecting the invariable order of nature ; and they remain laws only so long as they can be shown to express that order. To speak of the violation, or the suspension, of a law of nature is an absurdity. All that the phrase can really mean is that, under certain circumstances the assertion con- tained in the law is not true ; and the just conclusion is, not that the order of nature is interrupted, but that we have made a mistake in stating that order. A true natural law is an universal rule, and, as such, admits of no exceptions. Again, human laws have no meaning apart from the existence of human society. Natural laws express the general course of nature, of which human society forms only an insignificant fraction. 10. Knowledge of Nature is the Guide of Practical Conduct. If nothing happens by chance, but everything in nature follows a definite order, and if the laws of nature embody that which we have been able to learn SCIENCE.] INTRODUCTORY. about the order of nature in accurate language, then it becomes very important for us to know as many as we can of these laws of nature, in order that we may guide our conduct by them. Any man who should attempt to live in a country without reference to the laws of that country would very soon find himself in trouble ; and if he were fined, imprisoned, or even hanged, sensible people would probably consider that he had earned his fate by his folly. In like manner, any one who tries to live upon the face of this earth without attention to the laws of nature will live there for but a very short time, most of which will be passed in exceeding discomfort ; a peculiarity of natural laws, as distinguished from those of human enactment, being that they take effect without summons or prosecution. In fact, nobody could live for half a day unless he attended to some of the laws of nature ; and thousands of us are dying daily, or living miserably, because men have not yet been sufficiently zealous to learn the code of nature. It has already been seen that the practice of all our arts and industries depends upon our knowing the properties of natural objects which we can get hold of and put together ; and though we may be able to exert no direct control over the greater natural objects and the general succession of causes and effects in nature, yet, if we know the properties and powers of these objects, and the customary order of events, we may elude that which is injurious to us, and profit by that which is favourable. Thus, though men can nowise alter the seasons or change the process of growth in plants, yet having it SCIENCE PRIMERS. [NATURE AND learned the order of nature in these matters, they make arrangements for sowing and reaping accord- ingly ; they cannot make the wind blow, but when it does blow they take advantage of its known powers and probable direction to sail ships and turn wind- mills ; they cannot arrest the lightning, but they can make it harmless by means of conductors, the con- struction of which implies a knowledge of some of the laws of that electricity, of which lightning is one of the manifestations. Forewarned is forearmed, says the proverb ; and knowledge of the laws of nature is forewarning of that which we may expect to happen, when we have to deal with natural objects. ii. Science: the Knowledge of the Laws of Nature obtained by Observation, Experi- ment, and Reasoning. No line can be drawn between common knowledge of things and scientific knowledge ; nor between com- mon reasoning and scientific reasoning. In strictness all accurate knowledge is Science ; and all exact reasoning is scientific reasoning. The method of observation and experiment by which such great results are obtained in science, is identically the same as that which is employed by every one, every day of his life, but refined and rendered precise. If a child acquires a new toy, he observes its characters and ex- periments upon its properties ; and we are all of us constantly making observations and experiments upon one thing or another. But those who have never tried to observe accu- rately will be surprised to find how difficult a business it is. There is not one person in a hundred who can SCIENCE.] INTRODUCTORY. \1 describe the commonest occurrence with even an ap- proach to accuracy. That is to say, either he will omit something which did occur, and which is of im- portance ; or he will imply or suggest the occurrence of something wltich he did not actually observe, but which he unconsciously infers must have happened. When two truthful witnesses contradict one another in a court of justice, it usually turns out that one or other, or sometimes both, are confounding their in- ferences from what they saw with that which they actually saw. A swears that B picked his pocket. It turns out that all that A really knows is that he felt a hand in his pocket when B was close to him ; and that B was not the thief, but C, whom A did not observe. Untrained observers mix up together their inferences from what they see with that which they actually see in the most wonderful way; and even experienced and careful observers are in constant danger of falling into the same error. Scientific observation is such as is at once full, precise, and free from unconscious inference. Experiment is the observation of that which hap- pens when we intentionally bring natural objects together, or separate them, or in any way change the conditions under which they are placed. Scien- tific experiment, therefore, is scientific observation per- formed under accurately known artificial conditions. It is a matter of common observation that water sometimes free/es. The observation becomes scien- tific when we ascertain under what exact conditions the change of water into ice takes place. The com- monest experiments tell us that wood floats in water. 18 SCIENCE PRIMERS. [NATURE AND Scientific experiment shows that, in floating, it displaces its own weight of the water. Scientific reasoning differs from ordinary reason- ing in just the same way as scientific observation and experiment differ from ordinary observation and ex- periment that is to say, it strives to be accurate ; and it is just as hard to reason accurately as it is to observe accurately. In scientific reasoning general rules are collected from the observation of many particular cases ; and, when these general rules are established, conclusions are deduced from them, just as in every-day life. If a boy says that " marbles are hard," he has drawn a conclusion as to marbles in general from the marbles he happens to have seen and felt, and has reasoned in that mode which is technically termed induction. If he declines to try to break a marble with his teeth, it is because he consciously, or un- consciously, performs the converse operation of de- duction from the general rule " marbles are too hard to break with one's teeth." You will learn more about the process of reasoning when you study Logic, which treats of that subject in full. At present, it is sufficient to know that the laws of nature are the general rules respecting the be- haviour of natural objects, which have been collected from innumerable observations and experiments ; or, in other words, that they are inductions from those observations and experiments. The practical and theoretical results of science are the products of deductive reasoning from these general rules. Thus science and common sense are not opposed, as people sometimes fancy them to be, but science is SCIENCE.] INTRODUCTORY. 19 perfected common sense. Scientific reasoning is simply very careful common reasoning, and common knowledge grows into scientific knowledge as it be- comes more and more exact and complete. The way to science then lies through common know- ledge ; we must extend that knowledge by careful ob- servation and experiment, and learn how to state the results of our investigations accurately, in general rules or laws of nature ; finally, we must learn how to reason accurately from these rules, and thus arrive at rational explanations of natural phenomena, which may suffice for our guidance in life. II. MATERIAL OBJECTS. A. MINERAL BODIES. 12. The Natural Object Water. One of the commonest of common natural objects is water ; everybody uses it in one way or another every day ; and consequently everybody possesses a store of loose information of common knowledge about it. But, in all probability, a great deal of this knowledge has never been attended to by its pos- sessor ; and certainly, those who have never tried to learn how much may be known about water, will be ignorant of a great many of its powers and properties and of the laws of nature which it illustrates ; and consequently will be unable to account for many things of which the explanation is very easy. So we may as well make a beginning of science by studying water. 20 SCIENCE PRIMERS. [MATERIAL 13. A Tumbler of Water. Suppose we have a tumbler half-full of water. The tumbler is an artificial object (5); that is to say, certain natural objects have been brought together and heated till they melted into glass, and this glass has been shaped by a workman. The water, on the other hand, is a natural object, which has come from some river, pond, or spring; or it may be from a water-butt into which the rain which has fallen on the roof of a house has flowed. Now the water has a vast number of peculiarities. For example, it is transparent, so that you can see through it ; it feels cool ; it will quench thirst and dis- solve sugar. But these are not the characters which it is most convenient to begin with. 14. Water occupies Space ; it offers Resist- ance; it has "Weight; and is able to transfer Motion which it has acquired ; it is therefore a form of Matter. The water, we see, fills the cavity of the tumbler for half its height, therefore it occupies that much space, or has that bulk or volume. If you put the closed end of another tumbler of almost the same size into the first, you will find that when it reaches the water, the latter offers a resistance to its going down, and unless some of the water can get out, the end of the second tumbler will not go in. Any one who falls from a height into water will find that he receives a severe shock when he reaches it. Water therefore offers resistance. If the water is emptied out, the tumbler feels much OBJECTS.] INTRODUCTORY. lighter than it was before ; water, therefore, has weight. And. finally, if you throw the water out of the tum- bler at any slightly supported object, the water hitting against it would knock it over. That is to say, the water being put in motion is able to transfer that motion to something else. All these phenomena, as things which happen in nature are often called, are effects of which water, under the conditions mentioned, is the cause, and they may therefore be said to be properties ( 4) of water. All things which occupy space, offer resistance, possess weight and transfer motion to other things when they strike against them, are termed material substances or bodies, or simply matter. Water, therefore, is a kind, or form, of matter. 15. Water is a liquid. You will easily observe that, though water occupies space, it has no definite shape, but fits itself exactly to the figure of the vessel which holds it. If the tumbler is cylindrical; the contour of the surface of the water will be circular when the tumbler is held vertically, and will change, without the least break or interruption, to more and more of an oval when the tum- bler is inclined ; and, whatever the shape of the vessel into which you pour it, the sides of the water always exactly fit against the sides of the vessel. If you put your finger into the water you can move it in all direc- tions with scarcely any feeling of obstacle. If you pull your finger out there is no hole left, the water on all sides rushing together to fill up the space that was occupied by the finger. You cannot take up a handful of 22 SCIENCE PRIMERS. [MATERIAL water, for it runs away between your fingers, and you cannot raise it into a permanent heap. All this shows that the parts of water move upon one another with great ease. The same fact is illustrated if the tumbler is inclined, so that the level of the surface rises above the edge of the tumbler on one side, and the water is therefore to some extent unsupported by the tumbler at this point. The water then flows over in a stream and falls to the ground, where it spreads out and runs to the lowest accessible place, or gradually soaks up into crevices. Nevertheless, although the parts of the water thus loosely slip and slide upon one another, yet they hold together to a certain extent. If the surface of the water is just touched with the finger, a little of it will adhere ; and if the finger is then slowly and carefully raised, the adjacent water will be raised up into a slender column which acquires a noticeable length before it breaks. So, in the early morning, after heavy dew, you may see the water upon cabbage-leaves and blades of grass in spherical drops, the parts of which similarly hold together. Material substances, the parts of which are so movable that they fit themselves exactly to the sides of any vessel which contains them, and which flow when they are not supported, are called fluids ; and fluids the parts of which do not fly off from one another, but hold together as those of water do, are called liquids. Water therefore is a liquid. 16. Water is almost incompressible. It has been seen that water, like every other OBJECTS.] INTRODUCTORY. 2 3 material substance, resists the intrusion of other mat- ter into the place which it occupies. But many things, though they resist, can be easily squeezed or com- pressed into a smaller volume. This, however, is not the case with water, which like other liquids, is almost incompressible : that is to say, an immense pres- sure is needful to cause its volume to diminish to any appreciable extent. It may seem strange that anything so apparently yielding as water should yet be almost as difficult to squeeze as so much iron ; but the apparent yieldingness of water is due to the ease with which it changes its shape ; and, if water is prevented from changing its shape, it is very difficult to drive its parts closer together. It has been ascertained that if water is confined in a closed space, a pressure amounting to fifteen pounds on the square inch diminishes its volume by only ^ Tr ^ TJ th part. Take a common syringe, and having seen that the plug or piston fits the cylinder of the syringe well, put the nozzle into water and draw the piston up. Then turn the nozzle upwards and push upon the piston till a little of the water squirts out, so as to make sure that the cylinder contains nothing but water. Now put your finger on the opening of the nozzle firmly, so as to stop any water from passing out, and then try to push the piston down. You will find that you cannot make it stir without great force ; and, if the piston moves appreciably, it will be because some of the water has escaped by the sides of the piston. In fact, if the piston presented a square inch of surface, and fitted accurately, and the column of water in the cylinder were one inch long, it must be pressed down by a weight of 30,000 pounds (about thirteen tons) to make it move one-tenth of an inch. 3 24 SCIENCE PRIMERS. [MATERIAL 17. The Meaning of Weight. Let us next consider the property of weight. We say that anything has weight when, on trying to lift it from the ground, or on holding it in the hand, we have a feeling of effort. Or again, if anything which is sup- ported at a certain height above the ground, falls when the support is taken away, we say that it has weight. Now the ground merely means the surface of the earth ; and, as all bodies which possess weight fall directly to- wards the surface of the earth when they are not kept away from it by some support, we may say that all bodies which have weight tend to fall in this way. And it does not matter on what part of the surface of the earth you make the experiment. Rain consists of drops of water, and it does not matter whether we watch a shower in calm weather here, or in New Zealand ; the drops fall perpendicularly towards the ground. But we know that the earth is a globe and that New Zealand is at our antipodes, or on the opposite side of the globe to England. Hence if two showers are falling at the same time, one in New Zealand and one here the drops must be falling in opposite directions, towards one another; that is, towards the centre of the earth which lies between them. In fact, all bodies which have weight tend to fall towards the centre of the earth that is to say they fall in this way if there is nothing to prevent them ; and when we speak of weight we mean this tendency to fall. To call anything heavy, is the same as saying that we fully expect that, if there is nothing to support it, it will fall to the ground; or that if we support it ourselves we shall be conscious of effort. OBJECTS.] INTRODUCTORY. 25 1 8. Gravity and Gravitation. The word gravity, when it was first used, had ex- actly the same meaning as weight ; and a body which has weight is said to gravitate towards the centre of the earth. But gravity has now acquired a much wider sense than weight. For an immense number of careful observations and experiments have estab- lished the general rule, or law of nature, that every material substance tends to approach every other material substance, just in the same way as a drop of rain falls towards the earth; and, in fact, that any two portions of matter, whatever the nature of that matter may be, will move towards one another if there is nothing to prevent them from doing so. To make this clear, let us suppose that the only material bodies in the universe were two spherical drops of water, each a tenth of an inch in diameter. Each of these drops would have the same bulk as the other, and would be a quantity of matter exactly equivalent to the other. Then, however great the distance which separated these two drops, they would begin to approach one another ; and, each moving with gradually increasing swiftness, they would at length meet in a point exactly half-way between the positions which they at first occupied. But if the bulk of one drop were greater than that of the other drop, then the larger, would move more slowly, and the point of meeting would be by so much nearer the larger drop. It follows that, if the one body of water were as big as the earth and the other remained of its original size, no bigger than a rain-drop the motion of the large mass towards the small one would be an inconceivably minute fraction of the total 26 SCIENCE PRIMERS. [MATERIAL distance travelled over. It would appear as if the large body were perfectly still and drew the small body to itself. This is just what happens when a single drop of water falls from a cloud, say through a distance of a mile, to the earth. The earth really moves towards it, just as it moves towards the earth, on the straight line which joins the centres of the two. But the length of this line which each travels over is inversely proportional to the quantity of matter in each, that is to say is the less the bigger the quan- tity. So that we have a rule-of-three sum. As the quantity of matter in the earth is to that in a rain- drop, so is a mile to the distance travelled over by the earth. And if any one worked out this sum, he would find that the fourth term of the proportion would be an inconceivably minute fraction of an inch. For all practical purposes, therefore, we may consider the earth to be at rest in relation to all falling bodies, inasmuch as the quantity of matter in any filling body is insignificant, in comparison with that contained in the earth. What is true of water is true, so far as we know, of all kinds of matter, and we therefore say that it is a law of nature that all kinds of matter possess gravity ; that is to say, that of any two, each tends to move towards the other, at a speed which is the slower the greater the quantity of matter it contains in propor- tion to that which the other contains ; and this speed gradually becomes quicker as the two bodies approach. What is usually called the law of gravitation is a statement of the same observed facts in another and more complete fashion. (See Physics Primer.) OBJECTS.] INTRODUCTORY. 27 19. The cause of Weight: Attraction: Force. We know nothing whatever of the reason why bodies possess weight. Bodies do not fall on account of the law of gravitation ( 9) ; nor does their gravity explain why they fall. Gravity, as we have seen, is only a name for weight, and the law of gravitation is only a statement of how bodies approach one another, not why they do so. It is often said that gravitation is attraction, and that bodies fall to the earth because the earth attracts them. But the word " attract " simply means to " draw towards," and "attraction" means nothing but "draw- ing towards ; " and to say, when two bodies move to- wards one another, that they are " drawn towards " one another, is simply to describe the fact and makes us no whit wiser than we were before. On the contrary, unless we take great care, it may make us a little less wise. For the words " drawing towards " are so closely associated with ropes and hooks and the act of pulling, that we are easily led to fancy the existence of some analogous invisible machinery in the case of mutually attractive bodies. Again, gravitation is spoken of as a force ; and as the word force is in vory common use, let us try to make out what we mean by it. A man is said to exert force when he pushes or pulls anything so as either to exert pressure upon it or to put it in motion. A wrestler's force is proved by his hug ; a bowler's force is shown by the swiftness of motion of the ball. Force, then, is the name which we give to that which causes or, in the case of pressure, tends to cause, motion. The force of gravity therefore means 28 SCIENCE PRIMERS. [MATERIAL the cause of the pressure which we feel when bodies which possess gravity are supported by our bodies, and the cause of their movement towards the centre of the earth, when they are free to move. But it is exactly about the cause of these phenomena that we know nothing whatever. A good deal of mischief is done by the inaccurate use of such words as attraction and force, as if they were the names of things having an existence apart from natural objects, and from the series of causes and effects which are open to our observation ; while they are, in reality, merely the names of the unknown causes of certain phenomena. And it is worth while to take pains to get clear ideas on this head at the outset of the study of science. Let us remember then that, so far as we know, it is a law of nature, that any two material bodies, if they are free to move, approach one another with gra- dually increasing swiftness ; and that the space over which each travels before the two meet, is inversely pro- portional to the quantity of matter which it contains. Attraction of gravitation is a name for this gene- ral fact ; weight is the name for the fact in the case of terrestrial bodies ; force is a name which we give to the unknown cause of the fact. The fact is that which it is important to know. The names are of no great consequence so long as we recollect that they are merely names and not things. 20. The Weight of Water is Proportioned to its Bulk. We must next consider, not weight in general, but the weight of water. We say that a tumbler full of OBJECTS.] INTRODUCTORY, 29 water is heavier than an empty tumbler, because the full tumbler gives us a greater feeling of effort when we lift it than the empty tumbler does. The more water there is in the tumbler the greater is the effort. A pail full of water requires still more effort, though the empty pail feels quite light ; and, when we come to deal with a large tub full of water, we may be unable to stir it, though the empty tub could be lifted with ease. Thus it seems that the greater the bulk of water the more it weighs, and the less the bulk the less it weighs. But then a single drop of water in the palm of the hand seems to weigh nothing at all. However, this clearly cannot be, for the drop falls to the ground readily, and therefore it must have weight. Moreover, a few thousand drops would fill the tumbler, and if a thousand drops weigh something, each drop must have a thousandth of that weight. The fact is that our feeling of effort is a very rough measure of weight, and does not enable us to compare small weights, or even to perceive them if they are very small. To know anything accurately about weight we must have recourse to an instrument which is contrived for the purpose of measuring weights with precision. 21. The Measuring of Weights. The Balance. Such an instrument is the balance or scales, which you may see in every grocer's shop. It is composed of a beam which moves easily on a pivot fixed to its middle, and which has a scale-pan attached to each end. So long as both scale-pans are empty the beam is horizontal; but if you put anything which has 30 SCIENCE PRIMERS. [MATERIAL weight into one, that one goes down and the other rises. If now you either pull or push the empty scale downwards, the beam may be brought into the horizontal position again, and the effort required to bring it into the horizontal position will be the greater, the greater the weight of the body in the opposite scale. An ounce in the one scale is easily raised by the pressure of a finger in the other. A pound requires more effort; ten pounds needs put- ting out the strength of the arm ; to raise fifty pounds involves still more exertion ; while a couple of hundred- weight will not be stirred by the strongest push or pull upon the empty scale. Suppose that, instead of pressing down the empty scale, you put something that has weight into it; then, as soon as this weight is equal to that in the other scale, the beam will become horizontal. In fact, one scale has just as much tendency to move towards the centre of the earth as the other has, and as neither can go down without pulling the other up, they neu- tralise one another. It comes to the same thing, as if two boys of equal strength were pulling one against the other ; so long as the pulls in opposite directions are equal, of course neither boy can stir ; while the smallest addition of strength to one enables him to pull the other over. 22. The Weight of the same Bulk or Volume of Water is Constant under the same conditions. Mass. Density. Now let two graduated thin glass measures be put into the two scales, and made to counterpoise one another exactly. Then, if even a single drop of OBJECTS.] INTRODUCTORY. 3' water is put into the one measure the scale will descend, if the balance is a good one ; showing that the drop has weight. If the measures are graduated accurately, then whatever volume of water is put into one, an exactly similar volume of the same water must be put into the other to make the beam level. This obviously means that the same volume of water under the same circumstances always has the same weight. In 18 it was said that bodies tend to move to- wards one another with a relative velocity l which is inversely proportional to the quantity of matter which they contain. But how are we to measure quantity of matter? Is it to be estimated by the space which it occupies ; that is, by its volume ? or are we to esti- mate the quantity of matter in a body by its weight ? You will soon learn that the volume of all bodies is constantly changing in correspondence with the changes in the pressure exerted by other bodies, but more especially in correspondence with the changes of temperature to which they are subjected ; while the weight of the same body, at the same point on the earth's surface, never alters. Hence we may take the weight of a body as a measure of the quantity of matter which it contains ; and it follows that, for the same weight, the larger the volume of a body the less matter it contains proportionally to its volume, and the less the volume, the more matter it contains. The 1 Velocity, or swiftness, is measured by the distance over which a body travels in a given time. Of two bodies, one of which travels through one foot in a second, while the other travels through two feet, the latter has the greater relative velocity 3* 32 SCIENCE PRIMERS. [MATERIAL proportion of its weight to its volume gives us the density of a body. Now what is true of water is true of all other bodies or material substances. Suppose that one of the measures is emptied and replaced, the beam may be brought to the horizontal position again by means of a piece of lead cut to exactly the right size. The piece of lead will thenceforth furnish an exactly cor- responding or equivalent weight for so much water ; and pieces of iron or brass, which counterpoise the lead, will also be equivalents of the weight of the water, or of the lead, or of one another. But the pieces of lead, iron, or brass will obviously be of much less volume or bulk than the water which they counterpoise. Here it follows that the densities of these metals, or the quantity of matter contained in the same volume, must be much greater than in the case of water. What are called weights in commerce are pieces of lead, or iron, or brass exactly equivalent in weight to a certain bulk of water under certain conditions. An imperial gallon of water thus weighs ten pounds, and therefore an imperial pint weighs a pound and a quarter. 23. Equal Volumes of Different Things under the same circumstances, have Different Weights : the Density of Different Bodies is Different. The important fact which has just been alluded to must be considered more fully. We have seen that an imperial pint measure gives us the space which is taken up by as much water as weighs a pound and a quarter ; and this space is the bulk or volume of that OBJECTS.] INTRODUCTORY. 33 weight of water. But if you take an ordinary pound weight and a quarter-pound weight, and put them into an imperial pint measure, you will find that, instead of filling it, they take up only a very small portion of the space in its interior, or in other words, of its capacity. Thus the volume of a pound and a quarter of lead, or of iron, or of brass, is very much less than the volume of the same weight of water ; that is to say, the metals are denser than water ; the same volume has greater mass or more gravity. Or, to put the case in another way, fill the tumbler with which we began half full of water, making a mark on the side exactly at the level of the top of the water. Then place it in one scale of a balance, and counterpoise it with weights in the other. Next, pour out the water, and after drying the tumbler, fill it with fine sand carefully up to the mark. The volume of sand will be equal to the volume of water. But now the same weights will no longer counterpoise it, and you will have to put more weights in the opposite scale. Volume for volume, therefore, sand is heavier than water. Throw out the sand, and put in sawdust in the same way, and you will find that a less weight than was necessary to counterpoise the water counterpoises the sawdust. Volume for volume, therefore, sawdust is lighter than water. Experiment in the same way with spirit and oil, and they will be found to be lighter than water, while treacle will be heavier, and quicksilver very much heavier than water. 24. The Meaning of Heavy and Light Specific Gravity. We are in the habit of using the words heavy and 34 SCIENCE PRIMERS. [MATERIAL light rather carelessly. We call things that are easily lifted light, and things that are hard to lift, heavy. We say that sand, which is blown about by the wind, is light, and that a block of wood is heavy, and yet we have just seen that sand is heavier, bulk for bulk, than wood. In order to get rid of this double meaning, the weight of a volume of any liquid or solid, in proportion to the weight of the same volume of water at a known temperature and pressure, is called its specific gravity. Water being taken as i, anything a volume of which is twice as heavy as the same volume of water is said to have the specific gravity 2 : if three times, 3 ; if four and a half times, 4-5, and so on. Thus the specific gravity of any liquid or solid expresses its density in pro- portion to that of water under the same conditions. Sawdust, oil, and spirit have a less specific gravity than water, while treacle, sand, and quicksilver have a greater specific gravity. In this sense, the former three substances are light, while the latter three are heavy. 25. Things of greater Specific Gravity than "Water sink in "Water ; Things of less Specific Gravity float. Here are two tumblers of water. Throw some sand into one and some sawdust into the other. What happens ? The sand sinks to the bottom, the sawdust floats at the top. We may stir them up as we like, but the sand will tumble to the bottom and the sawdust, as obstinately, rise to the top. Thus that which is lighter than the water floats, and that which is heavier (bulk for bulk) sinks. So, if we pour OBJECTS.] INTRODUCTORY. 35 some oil into the water, it floats, and if we pour some coloured spirit in carefully, it also floats ; while treacle and quicksilver sink to the bottom, just as the iron- filings do. We saw that the iron-filings sank, because iron is heavier than water. Here is a piece of the thin tinned sheet-iron that they make tin boxes of. What will happen if we drop it into the water? It is heavier than water, bulk for bulk, and therefore it will sink as you see it does. But now here is a " tin" canister made of this very same tinned sheet-iron. We drop that into the water, and you see it does not sink at all, but floats at the top as if it were made of cork. Here is a perplexity. We were sure just now that iron is heavier than water, and here is an iron box floating ! Is this an exception to the law ? Not at all ; for what we said was that a thing would float if it were lighter, bulk for bulk, than water. Now let us weigh the tin box, and having weighed it let us next try to find out how much the same bulk of water weighs. This may be done very simply, for the walls of the box are very thin, so that the inside of the box is very nearly as large as the whole box. Consequently, if we fill the box with water, and then weigh the water, we shall find out, very nearly, what is the weight of a bulk of water as great as that of the box. But if we do this, we shall find that the water which was contained in the box, weighs very much more than the box does. So that, bulk for bulk, the box, although it is made of iron, is really lighter than water, and that is why it floats. You will all have heard of the iron ships which are now so common, and you may have wondered how it 36 SCIENCE PRIMERS. [MATERIAL is, that ships made of thick plates of iron riveted together, and weighing many thousand tons, do not go to the bottom. But they are nothing but our tin canisters on a great scale, and they float because each ship weighs less than a quantity of water of the same bulk does. It is because of this property of water to bear up things lighter than itself, and because of that other property of being easily moved which the particles of water have, that the sea, and rivers, and canals, are such great highways for mankind. For there is nothing so heavy that it may not be made to float in water, if the box which holds it is large enough to make the weight of the whole less than the weight of the same bulk of water. And then, having once got the weight to float, the particles of water are so easily moved, that the force of the winds, or of oars, or of paddles, readily causes it to slip through the water from one place to another. 26. A Body which Floats in Water always occupies as much Space beneath the level of the Surface of the Water as is equal to the Volume of Water which weighs as much as that Body ; in other words, it displaces its own Weight of Water. A cubic inch of water weighs about 252 grains and a half. Suppose that the tin box in the previous experi- ment was square, and had the bulk of 100 cubic inches, then the weight of a corresponding volume of water would be 25,250 grains. If the box weighed 8,416 grains, just a third of its bulk would be immersed; if OBJECTS.] INTRODUCTORY. 37 12,625 grains, half; if 16,832 grains, it would sink two- thirds of its volume, and so on. Or, if, when the box is floating, you make a mark upon its side at the exact level of the surface of the water, the bulk of that portion of the box which lies below the water-level can be ascertained. Suppose it to be thirty cubic inches, then the weight cf the box will be 30 x 252-5 or 7575 grains. Hence it may be said that the im- mersed part of a floating body takes the place of the water which it displaces, and, as it were, represents it. If you press downwards upon the floating box, there is a feeling of resistance as it descends, and when the pressure is taken off, the body immediately rises again. Hence the water presses upwards against the bottom of the floating body. But it also presses against the sides, for if the sides of the box are very thin they will be driven in. If a thin empty bottle is tightly corked and lowered into deep water the cork will be driven in, or else the bottle will be crushed. 27. Water Presses in all Directions. Thus water presses in all directions upon things which are immersed in it. If a long wooden or metal pipe, placed vertically, has its lower end stopped with a cork which does not fit very tightly, and water is poured into the top of the tube, the water will at first fill the part of the tube above the cork, and its weight will exert a certain pressure on the cork. In fact, if the end of the tube is stopped by applying the palm of the hand closley against it, the downward pressure of the water will have to be overcome by a certain amount of effort As the water accumulates, this downward 3 8- SCIENCE PKIMERS. [MATERIAL pressure will become greater and greater until the hand is driven away, or the cork is forced out, and the water falls to the ground. The pressure in this case is the same as the weight of the water, and the cork would have been driven out equally well by a rod of lead of the same weight. Suppose the tube to be square, and that the inside of the square measures exactly one inch each way. Then an inch of height of the tube will hold exactly one cubic inch of water. Since one cubic inch oi water weighs 252 grains and a half, as much water as will fill the tube about two feet three inches and a half high, will weigh a pound (7,000 grains), and fifteen pounds of water will fill such a tube between thirty-three and thirty-four feet high. And these respective weights measure the pressure of two columns of water, one twenty-seven and a half inches high, and the other nearly thirty-four feet high, on a square inch of the surface on which they rest. The specific gravity ( 24) of lead is n'455 in other words it is about eleven and a half times denser than water. Therefore if a bar of ltdd cut square and one inch in the side, and rather less than T \th of the height of a column of water, is slipped into the tube in place of the water, it will exert the same pressure on the bottom. And now comes a difference between the lead and the water, which depends on the fluidity of the latter. The lead exerts no pressure on the sides of the tube, but the water does. If a small hole is cut in the side of the tube close to the bottom, and stopped with a cork, the lead will not press upon the cork. But if the column of water is high enough, OBJECTS.] INTRODUCTORY. 39 the cork will be driven out with as much force as before, so that the water presses just as much side- ways as downwards. It is easy to satisfy oneself of this by inserting a long glass tube, with its lower end bent at right angles and fitted with a cork, into the side of the wooden pipe. The water will at once rise in the tube to the same height as it has in the pipe. Whence it is obvious that the pressure of the water on any point of the side is exactly equal to the vertical pressure at that point; for the pressure outwards is exactly balanced by that of the vertical column in the tube inwards. The water in a watering-pot always stands at the same level in the can and in the spout. If a glass tube is bent into the shape of a Q> an ^ water is poured into it, the water will always stand at the same level in the two legs of the tube, whatever the shape of the bend may be, or the relative capa- cities of the two legs, or the inclination of the tube. And this must needs be so, for the force with which the water tends to flow out of the one half of the arrangement depends on the vertical height 1 of the sur- face of the water above the aperture of exit ; so that any column of equal vertical height must balance it. That a column of watei will stand at exactly the same level as any other with which it communicates, may be seen still more simply by placing a glass tube, open at each end, in a basin of water. However the tube may be inclined or bent, whether its lower end is 1 Vertical height is the height measured along a line drawn from the surface of the water perpendicularly to the