CHAPTER VII Why is there not more intelligence? When we allow for dexterity and power of association, when we recognize a certain amount of instinctive capacity and a capacity for profiting by experience in an intelligent way, we must admit a certain degree of disappointment when we take a survey of the behavior of mammals, especially of those with very fine brains, from which we should naturally expect great things. Why is there not more frequent exhibition of intelligence in the stricter sense? The answer is that most mammals have become in the course of time very well adapted to the ordinary conditions of their life and tend to leave well alone. They have got their repertory of efficient answers to the ordinary questions of everyday life and why should they experiment? In the course of the struggle for existence, what has been established is efficiency in normal circumstances, and therefore even the higher animals tend to be no cleverer than is necessary. So while many mammals are extraordinarily efficient, they tend to be a little dull. Their mental equipment is adequate for the everyday conditions of their life, but it is not on sufficiently generous lines to admit of, let us say, an interest in nature or adventurous experiment. Mammals always tend to play for safety. We hastened, however, to insert here some very interesting saving clauses. A glimpse of what mammals are capable of, were it necessary, may be obtained by watching those that are playful, such as lambs and kids, foals and calves, young foxes and others. For these young creatures, let themselves go irresponsibly, they are still un-stereotyped, they test what they and their fellows can do. The experimental character of much of animal play is very marked. It is now recognized by biologists that play among animals is the young form of work and that the playing period, often so conspicuous, is vitally important as an apprenticeship to the serious business of life and as an opportunity for learning the alphabet of nature. But the playing period is much more. It is one of the few opportunities animals have of making experiments without too serious responsibilities. Play is nature's device for allowing elbow room for new departures, behavior variations, which may form part of the raw materials of progress. Play, we repeat, gives us a glimpse of the possibilities of the mammal mind. Other Glimpses of Intelligence. A squirrel is just as clever as it needs to be, and no more, and of some vanishing mammals, like the beaver, not even this can be said. Hum-drum non-plastic efficiency is apt to mean stagnation. Now we have just seen that in the play of young mammals there is an indication of unexhausted possibilities, and we get the same impression when we think of three other facts. A. In those mammals, like dog and horse, which have entered into active cooperative relations with man, we see that the mind of the mammal is capable of much more than the average would lead us to think. When man's sheltering is too complete, and the domesticated creature is passive in his grip, the intelligence deteriorates. B. When we study mammals like the otter, which live a versatile life in a very complex and difficult environment, we get an inspiring picture of the play of wits. C. Thirdly, when we pass to monkeys, where the forelimb has become a free hand, where the brain shows a relatively great improvement, where words are much used, we cannot fail to recognize the emergence of something new, a restless inquisitiveness, a desire to investigate the world, an unsatisfied tendency to experiment. We are approaching the dawn of reason, the mind of monkeys. There is a long gamut between the bushy-tailed, almost squirrel-like marmosets and the big-brained chimpanzee. There is great variety of attainment at different levels in the Simeon tribe. Keen Census. To begin at the beginning, it is certain that monkeys have a first-class sensory equipment, especially as regards sight, hearing, and touch. The axes of the two eyes are directed forwards as in man, and a large section of the field of vision is common to both eyes. In other words, monkeys have a more complete stereoscopic vision than the rest of the mammals enjoy. They look more and smell less. They can distinguish different colors, apart from different degrees of brightness in the colored objects. They are quick to discriminate differences in the shapes of things, for instance boxes similar in size, but different in shape. Or if the prize is always put in a box of the same shape, they soon learn, by association, to select the profitable one. They learn to discriminate cards with short words, or with signs printed on them, coming down when the yes card is shown, remaining on their perch when the card says no. Bred to a forest life where alertness is a life or death quality, they are quick to respond to a sudden movement or to pick out some new feature in their surroundings. And what is true of vision holds also for hearing. POWER OF MANIPULATION Another quality which separates monkeys very markedly from ordinary mammals is their manipulative expertness, the coordination of hand and eye. This great gift follows from the fact that among monkeys the foreleg has been emancipated. It is ceased to be indispensable as an organ of support.  The forelim has become a free hand, and everyone who knows monkeys at all is aware of the zest with which they use their tool. They enjoy pulling things to pieces, a kind of dissection, or screwing the handle off a brush and screwing it on again. ACTIVITY FOR ACTIVITY'S SAKE Professor Thorndike hits the nail on the head when he lays stress on the intensity of activity in monkeys, activity both of body and mind. They are pent up reservoirs of energy, which almost any influence will tap. Watch a cat or a dog, Professor Thorndike says. It does comparatively few things and is content for long periods to do nothing. It will be splendidly active in response to some stimulus such as food or a friend or a fight, but if nothing appeals to its special makeup, which is very utilitarian in its interests, it will do nothing. Watch a monkey and you cannot enumerate the things he does, cannot discover the stimuli to which he reacts, cannot conceive the raison d'être of his pursuits. Nothing appeals to him, he likes to be active for the sake of activity. This applies to mental activity as well, and the quality is one of extraordinary interest, for it shows the experimenting mood at a higher turn of the spiral than in any other creature, save man. It points forward to the scientific spirit. We cannot indeed believe in the sudden beginning of any quality, and we recall the experimenting of playing mammals, such as kids and kittens, or of inquisitive adults like Kipling's Mongoose, Rikki Tikki Tavi, which made it his business and life to find out about things. But in monkeys the habit of restless experimenting rises to a higher pitch. They appear to be curious about the world. The psychologist whom we have quoted tells of a monkey which happened to hit a projecting wire so as to make it vibrate. He went on repeating the performance hundreds of times during the next few days. Of course he got nothing out of it, save, fun, but it was grist to his mental mill. The fact of mental life is, to monkeys, its own reward. The monkey's brain is tender all over, functioning throughout, set off in action by anything and everything. Sheer quickness. Compared with the quality of restless inquisitiveness and delight in activity for its own sake, there is the quality of quickness. We mean not merely the locomotor agility that marks most monkeys, but quickness of perception and plan. It is the sort of quality that life among the branches will engender, where it is so often a case of neck or nothing. It is the quality which we describe as being on the spot, though the phrase has slipped from its original moorings. Speaking of his bonnet monkey, an Indian macaque, second cousin to the kind that lives on the Rock of Gibraltar, Professor S. J. Holmes writes, For keenness of perception, rapidity of action, facility informing good practical judgments about ways and means of escaping pursuit, and of attaining various other ends, Lizzie had few rivals in the animal world. Her perceptions and decisions were so much more rapid than my own that she would frequently transfer her attention, to sign upon a line of action, and carried into effect before I was aware of what she was about. Until I came to guard against her nimble and unexpected maneuvers, she succeeded in getting possession of many apples and peanuts, which I had not intended to give her except upon the successful performance of some task. Quick to learn. Right fundamental to any understanding of animal behavior is the distinction so clearly drawn by Surrey Lancaster between the little-brain type, rich in inborn or instinctive capacities, but relatively slow to learn, and the big-brain type, with a relatively poor endowment of specialized instincts, but with great educability. The little-brain type finds its climax and ants and bees, the big-brain type in the horses and dogs, elephants and monkeys. And of all animals, monkeys are the quickest to learn, if we use the word learn to mean the formation of useful associations between this and that, between a given sense presentation and a particular piece of behavior. The Case of Sally. Some of us remember Sally, the chimpanzee at the zoo with which Dr. Romanes used to experiment. She was taught to give her teacher the number of straws he asked for, and she soon learned to do so up to five. If she handed a number not asked for, her offer was refused. If she gave the proper number, she got a piece of fruit. If she was asked for five straws, she picked them up individually and placed them in her mouth, and when she had gathered five she presented them together in her hand. Just to teach her to give six to ten straws were not very successful. For Sally, above six meant many, and besides, her limits of patience were probably less than her range of computation. This was hinted at by the highly interesting circumstance that when dealing with numbers above five, she very frequently doubled over a straw so as to make it present two ends, and thus appear as two straws. The doubling of the straw looked like an intelligent device to save time, and it was persistently resorted to in spite of the fact that her teacher always refused to accept a doubled straw as equivalent to two straws. Here we get a glimpse of something beyond the mere association of a sound, five, and that number of straws. The Case of Lizzie The front of the cage in which Professor Holmes kept Lizzie was made of vertical bars which allowed her to reach out with her arm. On a board with an upright nail as handle there was placed an apple out of Lizzie's reach. She reached immediately for the nail, pulled the board in, and got the apple. There was no employment of the method of trial and error. There was direct appropriate action following the perception of her relation to board, nail, and apple. Of course, her ancestors may have been adepts at drawing a fruit-laden branch within their reach, but the simple experiment was very instructive. All the more instructive because, in many other cases, the experiments indicate a gradual sifting out of useless movements, and an eventful retention of the one that pays. When Lizzie was given a Vaseline bottle containing a peanut enclosed with a cork, she had once pulled the cork out with her teeth, obeying the instinct to bite at new objects. But she never learned to turn the bottle upside down and let the nut drop out. She often got the nut, and after some education she got it more quickly than she did at first, but there was no indication that she ever perceived the fit and proper way of getting what she wanted. In the course of her intent efforts her mind seemed so absorbed with the object of desire that it was never focused on the means of attaining that object. There was no deliberation and no discrimination between the important and the unimportant elements in her behavior. The gradually increasing facility of her performances depended on the apparently unconscious elimination of useless movements. This may be called learning, but it is learning at a very low level. It is far from learning by ideas. It is hardly even learning by experiment. It is not more than learning by experience. It is not more than fumbling at learning. Trial and error A higher note is struck in the behavior of some more highly endowed monkeys. In many experiments, chiefly in the way of getting into boxes difficult to open, there is evidence, one, of attentive, persistent experiment, two, of the rapid elimination of ineffective movements, and three, of remembering the solution when it was discovered. Kinneman taught two macaques, the Hampton Court maze, a feat which probably means a memory of movements, and we get an interesting glimpse in his observation that they began to smack their lips audibly when they reached the latter part of their course, and began to feel, dare one say, we are right this time. In getting into puzzle boxes and into combination boxes, where the barriers must be overcome in a definite order, monkeys learned by the trial and error method much more quickly than cats and dogs do, and a very suggestive fact emphasized by Professor Thorndike is a process of sudden acquisition by a rapid, often apparently instantaneous abandonment of the unsuccessful movements and selection of the appropriate one, which rivals in suddenness the selections made by human beings in similar performances. A higher note still was sounded by one of Thorndike's monkeys which opened a puzzle box at once, eight months after his previous experience with it, for here was some sort of registration of a solution. Imitation Two chimpanzees in the Dublin Zoo were often to be seen washing the two shelves of their cupboard and wringing the wet cloth in the approved fashion. It was like a caricature of a washerwoman, and someone said, what mimics they are? Now we do not know whether that was or was not the case with the chimpanzees, but the majority of the experiments that have been made do not lead us to attach to imitation so much importance, as is usually given to it by the popular interpreter. There are instances where a monkey that had given up a puzzle in despair returned to it when it had seen its neighbor succeed, but most of the experiments suggested that the creature has to find out for itself. Even with such a simple problem as drawing food near with a stick, it often seems of little use to show the monkey how it is done. Placing a bit of food outside his monkey's cage, Professor Holmes poked it about with a stick so as to give her a suggestion of how the stick might be employed to move the food within reach, but although the act was repeated many times, Lizzie never showed the least inclination to use the stick to her advantage. Perhaps the idea of a tool is beyond the bonnet monkey, yet here again we must be cautious, for Professor L. T. Hobhouse had a monkey of the same macaque genus which learned in the course of time to use a crooked stick with great effect. The Case of Peter Perhaps the cleverest monkey as yet studied was a performing chimpanzee called Peter, which has been generally described by Dr. Leitner Whitmer. Peter could skate and cycle, thread needles and untie knots, smoke a cigarette and string beads, screw in nails and unlocked locks, but what Peter was thinking about all the time it was hard to guess, and there is very little evidence to suggest that his rapid power of putting two and two together ever rose above a sort of concrete mental experimenting, which Dr. Romanes used to call perceptual inference. Without supposing that there are hard and fast boundary lines, we cannot avoid the general conclusion that, while monkeys are often intelligent, they seldom, if ever, show even hints of reason, that is, of working or playing with general ideas. That remains man's prerogative. The Bustle of the Mind In mammals like otters, foxes, stoats, hares and elephants, what a complex of tides and currents there must be in the brain mind. We may think of a stream with currents at different levels. Lowest there are the basal appetites of hunger and sex, often with eddies rising to the surface. Then there are the primary emotions, such as fear of hereditary enemies and maternal affection for offspring. Above these are instinctive aptitudes, inborn powers of doing clever things without having to learn how. But in mammals these are often expressed along with, or as it were, through, the controlled life of intelligent activity where there is more clear-cut perceptual influence. Higher still are the records or memories of individual experience and the registration of individual habits, while on the surface is the in-streaming multitude of messages from the outside world, like raindrops and hailstones on the stream, some of them penetrating deeply, being, as we say, full of meaning. The mind of the higher animal is in some respects like a child's mind, in having little in the way of clear-cut ideas, in showing no reason in the strict sense, and in its extraordinary educability. But it differs from the child's mind entirely in the sure effectiveness of a certain repertory of responses. It is efficient to a degree. Until at last arose the man. Man's brain is more complicated than that of the higher apes, Gorilla, Orang, and chimpanzee, and it is relatively larger. But the improvements and structure do not seem in themselves sufficient to account for man's great advance in intelligence. The real of inner life has become a swift stream, sometimes a rushing torrent. Besides perceptual inference or intelligence, a sort of picture logic which some animals likewise have, there is conceptual inference or reason, an internal experimenting with general ideas. Even the cleverest animals it would seem to not get much beyond playing with particulars. Man plays an internal game of chess with universals. Intelligent behavior may go a long way with mental images. Rational conduct demands general ideas. It may be, however, that percepts and concepts differ rather in degree than in kind, and that the passage from one to the other meant a higher power of forming associations. A clever dog is probably a generalized percept of man, as distinguished from a memory image of the particular men it is known, but man alone has the concept man, or mankind, or humanity. Experimenting with concepts or general ideas is what we call reason. Here, of course, we get into deep waters, and perhaps it is wise as not to attempt too much. So we shall content ourselves here with pointing out that man's advance in intelligence, and from intelligence to reason, is closely wrapped up with his power of speech. What animals began, a small vocabulary, is carried to high perfection. But what is distinctive is not the vocabulary so much as the habit of making sentences, of expressing judgments in a way which admitted of communication between mind and mind. The multiplication of words meant much. The use of words as symbols of general ideas meant even more, for it meant the possibility of playing the internal game of thinking. But perhaps the most important advance of all was the means of comparing notes with neighbors, of corroborating individual experience by social intercourse. With words also, it became easier to in-register outside himself the gains of the past. It is not without significance that the Greek lojos, which may be translated the word, may also be translated mind. Looking Backwards When we take a survey of animal behavior, we see a long inclined plane. The outer world provokes simple creatures to answer back. The animal creatures act experimentally on their surroundings. From the beginning this two-fold process has been going on, receiving stimuli from the environment and acting upon the environment, and according to the efficiency of the reactions and actions living creatures have been sifted for millions of years. One main line of advance has been opening new-gateways of knowledge, the senses which are far more than five in number. The other main line of advance has been in the most general terms, experimenting or testing, probing and proving, trying one key after another till a door is unlocked. There is progress in multiplying the gateways of knowledge and making them more discriminating. And there is progress in making the modes of experimenting more wide awake, more controlled and more resolute. But behind both of these is the characteristically vital power of in-registering within the organism, the lessons of the past. In the life of the individual these end registrations are illustrated by memories and habituations and habits. In the life of the race they are illustrated by reflex actions and instinctive capacities. BODY AND MIND We must not shirk the very difficult question of the relation between the bodily and the mental side of behavior. A. Some great thinkers have taught that the mind is a reality by itself which plays upon the instrument of the brain and body. As the instrument gets worn and dusty the playing is not so good as it once was, but the player is still himself. This theory of the essential independence of the mind is a very beautiful one. For those who like it when applied to themselves are not always so fond of it when it is applied to other intelligent creatures like rooks and elephants. It may be, however, that there is a gradual emancipation of the mind which has gone furthest in man and is still progressing. B. Some other thinkers have taught that the inner life of thought and feeling is only, as it were, an echo of the really important activity, that of the body and brain. Ideas are just foam bells on the hurrying streams and circling eddies of matter and energy that make up our physiological life. To most of us this theory is impossible because we are quite sure that ideas and feelings and purposes which cannot be translated into matter and motion are the clearest realities in our experience and that they count for good and ill all through our life. They are more than the ticking of the clock. They make the wheels go round. C. There are others who think that the most scientific position is simply to recognize both the bodily and the mental activities as equally important and so closely interwoven that they cannot be separated. Perhaps they are just the outer and the inner aspects of one reality, the life of the creature. Perhaps they are like the concave and convex curves of a dome, like the two sides of a shield. Perhaps the life of the organism is always a unity, at one time appearing more conspicuously as mind-body, at another time as body-mind. The most important fact is that neither aspect can be left out. By no jugglery with words can we get mind out of matter and motion. And since we are in ourselves quite sure of our mind, we are probably safe in saying that in the beginning was mind. This is in accordance with Aristotle's saying that there is nothing in the end which was not also in kind present in the beginning, whatever we mean by beginning. In conclusion, what has led to the truly wonderful result which we admire in a creature like a dog or an otter, a horse or a hare? In general we may say just two main processes. One, testing all things, and two, holding fast that which is good. New departures occur and these are tested for what they are worth. Adiosyncrasies crop up and they are sifted. New cards come mysteriously from within, into the creature's hand, and they are played for better or for worse. So by new variations and their sifting, by experimenting and registering the results, the mind is gradually evolved and will continue to evolve. Chapter 8. Foundations of the Universe. The World of Atoms. Most people have heard of the Oriental race which puzzled over the foundations of the universe and decided that it must be supported on the back of a giant elephant. But the elephant? They put it on the back of a monstrous tortoise, and there they let the matter end. If every animal in nature had been called upon, they would have been no nearer a foundation. Most ancient peoples indeed made no effort to find a foundation. The universe was a very compact little structure, mainly composed of the earth and the great canopy over the earth which they called the sky. They left it as a hole, floating in nothing. And in this the ancients were wiser than they knew. Things do not fall down unless they are pulled down by that mysterious force which we call gravitation. The earth, it is true, is pulled by the sun, and would fall into it. But the earth escapes this fiery fate by circulating at great speed round the sun. The stars pull each other, but it has already been explained that they meet this by traveling rapidly in gigantic orbits. Yet we do, in a new sense of the word, need foundations of the universe. Our mind craves for some explanation of the matter out of which the universe is made. For this explanation we turn to modern physics and chemistry. Both these sciences study, under different aspects, matter and energy, and between them they have put together a conception of the fundamental nature of things which marks an epic in the history of human thought. The Bricks of the Cosmos More than two thousand years ago the first men of science, the Greeks of the cities of Asia Minor, speculated on the nature of matter. You can grind a piece of stone in dust. You can divide a spoonful of water into as many drops as you like. Apparently you can go on dividing as long as you have got apparatus fine enough for the work. But there must be a limit, these Greeks said, and so they supposed, that all matter was ultimately composed of minute particles which were indivisible. That is the meaning of the Greek word Adam. Like so many other ideas of these brilliant early Greek thinkers, the Adam was a sound conception. We know today that matter is composed of atoms. But science was then so young that the way in which the Greeks applied the idea was not very profound. A liquid or a gas, they said, consisted of round, smooth atoms which would not cling together. Then there were atoms with rough surfaces, hooky surfaces, and these stuck together in form solids. The atoms of iron or marble, for instance, were so very hooky that, once they got together, a strong man could not tear them apart. The Greeks thought that the explanation of the universe was that an infinite number of these atoms had been moving and mixing in an infinite space during an infinite time, and had at last hit by chance on the particular combination which is our universe. This was too simple and superficial. The idea of atoms was cast aside only to be advanced again in various ways. It was the famous Manchester chemist John Dalton who restored it in the early years of the 19th century. He first definitely formulated the atomic theory as a scientific hypothesis. The whole physical and chemical science of that century was now based upon the atom, and it is quite a mistake to suppose that recent discoveries have discredited atomism. An atom is the smallest particle of a chemical element. No one has ever seen an atom. Even the wonderful new microscope which has just been invented cannot possibly show us particles of matter which are a million times smaller than the breadth of a hair, for that is the size of atoms. We can weigh them and measure them, though they are invisible, and we know that all matter is composed of them. It is a new discovery that atoms are not indivisible. They consist themselves of still smaller particles, as we shall see. But the atoms exist all the same, and we may still say that they are the bricks of which the material universe is built. But if we had some magical glass by means of which we could see into the structure of material things, we should not see the atoms put evenly together as bricks are in a wall. As a rule, two or more atoms first come together to form a larger particle, which we call a molecule. Single atoms do not, as a rule, exist apart from other atoms. If a molecule is broken up, the individual atoms seek to unite with other atoms of another kind, or amongst themselves. For example, three atoms of oxygen form what we call a low zone. Two atoms of hydrogen, uniting with one atom of oxygen, form water. It is molecules that form the mass of matter. A molecule, as it has been expressed, is a little building of which atoms are the bricks. In this way we get a useful first view of the material things we handle. In a liquid the molecules of the liquid cling together loosely. They remain together as a body, but they roll over and away from each other. There is cohesion between them, but it is less powerful than in a solid. Put some water in a kettle over the lighted gas, and presently the tiny molecules of water will rush through the spout in a cloud of steam and scatter over the kitchen. The heat has broken their bond of association and turned the water into something like a gas, though we know that the particles will come together again as they cool and form once more drops of water. In a gas the molecules have full individual liberty. They are in a state of violent movement, and they form no union with each other. If we want to force them to enter into the loose sort of association which molecules have in a liquid we have to slow down their individual movements by applying severe cold. That is how a modern man of science liquefies gases. No power that we have will liquefy air at its ordinary temperature. In very severe cold, on the other hand, the air will spontaneously become liquid. Some day when the fires of the sun have sunk very low, the temperature of the earth will be less than minus 200 degrees centigrade. That is to say, more than 200 degrees centigrade below freezing point. It will sink to the temperature soon. Our atmosphere will then be an ocean of liquid air, 35 feet deep, lying upon the solidly frozen masses of our water oceans. In a solid the molecules cling firmly to each other. We need a force equal to 25 tons to tear us under the molecules in a bar of iron, an inch thick. Yet the structure is not solid in the popular sense of the word. If you put a piece of solid gold in a little pool of mercury, the gold will take in the mercury between its molecules as if it were porous like a sponge. The hardest solid is more like a latticework than what we usually mean by solid, though the molecules are not fixed like the bars of a latticework but are in violent motion. They vibrate about equilibrium positions. If we could see right into the heart of a bit of the hardest steel we should see millions of separate molecules at some distance from each other all moving rapidly to and fro. This molecular movement can, in a measure, be made visible. It was noticed by a macroscopist named Brown that in a solution containing very fine suspended particles the particles were in constant movement. Under a powerful microscope these particles are seen to be violently agitated. They are each independently darting hither and somewhat like a lot of billiard balls on a billiard table, colliding and rebounding about in all directions. Thousands of times a second these encounters occur, and this lively commotion is always going on. This incessant colliding of one molecule with another is the normal condition of affairs. Not one of them is at rest. The reason for this has been worked out, and it is now known that these particles move about because they are being incessantly bombarded by the molecules of the liquid. The molecules cannot of course be seen, but the fact of their incessant movement is revealed to the eye by the behavior of the visible suspended particles. This incessant movement in the world of molecules is called the Brownian motion, and is a striking proof of the reality of molecular motions. The Wonder World of Atoms The exploration of this Wonder World of Atoms and molecules by the physicists and chemists of today is one of the most impressive triumphs of modern science. Quite apart from radium and electrons and other sensational discoveries of recent years, the study of ordinary matter is hardly inferior, either in interest or audacity to the work of the astronomer. And there is the same foundation in both cases, marvellous apparatus, and trains of mathematical reasoning that would have astonished Euclid or Archimedes. Extraordinary, therefore, as are some of the facts and figures we are now going to give in connection with the minuteness of atoms and molecules, let us bear in mind that we owe them to the most solid and severe processes of human thought. Yet the principle can in most cases be made so clear that the reader will not be asked to take much on trust. It is, for instance, a matter of common knowledge that gold is soft enough to be beaten into gold leaf. It is a matter of common sense, one hopes, that if you beat a measured cube of gold into a leaf six inches square, the mathematician can tell the thickness of that leaf without measuring it. As a matter of fact, a single grain of gold has been beaten into a leaf 75 inches square. Now the mathematician can easily find that when a single grain of gold is beaten out to that size, the leaf must be one 367 thousandth of an inch thick, or about a thousand times thinner than the paper on which these words are printed. Yet the leaf must be several molecules thick. The finest gold leaf is, in fact, too thick for our purpose, and we term with a new interest to that toy of our boyhood the soap bubble. If you carefully examine one of these delicate films of soapy water, you notice certain dark spots or patches on them. These are the thinnest parts, and by two quite independent methods, one using electricity and the other light, we have found that at these spots the bubble is less than three million seven inch thick. But the molecules in the film cling together so firmly that they must be at least twenty or thirty deep in the thinnest part. A molecule, therefore, must be far less than the three millionths of an inch thick. We found next that a film of oil on the surface of water may be even thinner than a soap bubble. Professor Perrin, the great French authority on atoms, got films of oil down to the fifty millionth of an inch in thickness. He poured a measured drop of oil upon water. Then he found the exact limits of the area of the oil sheet by blowing upon the water a fine powder which spread to the edge of the film and clearly outlined it. The rest is safe and simple calculation as in the case of the beaten grain of gold. Now this film of oil must have been at least two molecules deep, so a single molecule of oil is considerably less than a hundred millionth of an inch in diameter. Innumerable methods have been tried, and the result is always the same. A single grain of indigo, for instance, will color a ton of water. This obviously means that the grain contains billions of molecules which spread through the water. A grain of musk will send a room, pour molecules into every part of it for several years, yet not lose one millionth of its mass in a year. There are a hundred ways of showing the minuteness of the ultimate particles of matter, and some of these enable us to give definite figures. On a careful comparison of the best methods we can say that the average molecule of matter is less than the one one hundred and twenty-five millionth of an inch in diameter. In a single cubic centimeter of air, a globule about the size of a small marble, there are thirty million trillion molecules. And since the molecule is, as we saw, a group or cluster of atoms, the atom itself is smaller. Atoms, for reasons which we shall see later, differ very greatly from each other in size and weight. It is enough to say that some of them are so small that it would take four hundred million of them in a line to cover an inch of space, and that it takes at least a quintillion atoms of gold to weigh a single gram. Five million atoms of helium could be placed in a line across the diameter of a full stop. The energy of atoms. And this is only the beginning of the wonders that were done with ordinary matter, quite apart from radium and its revelations, to which we will come presently. Most people have heard of atomic energy and the extraordinary things that might be accomplished if we could harness this energy and turn it to human use. A deeper and more wonderful source of this energy has been discovered in the last twenty years, but it is well to realize that the atoms themselves have stupendous energy. The atoms of matter are vibrating or gyrating with extraordinary vigor. The piece of cold iron you hold in your hand, the bit of brick you pick up, or the penny you take from your pocket is a colossal reservoir of energy, since it consists of trillions of moving atoms. To realize the total energy, of course, we should have to witness a transformation such as we do in atoms of radioactive elements, about which we shall have something to say presently. If we put a grain of indigo in a glass of water, or a grain of musk in a perfectly still room, we soon realize that molecules travel. Similarly, the fact that gases spread until they fill every empty available space shows definitely that they consist of small particles travelling at great speed. The physicist brings his refined methods to bear on these things, and he measures the energy and velocity of these infinitely minute molecules. He tells us that molecules of oxygen, at the temperature of melting ice, travel at the rate of about five hundred yards a second, more than a quarter of a mile a second. Molecules of hydrogen travel at four times at speed, or three times the speed with which a bullet leaves a rifle. Each molecule of the air, which seems so still in the house on a summer's day, is really travelling faster than a rifle bullet does at the beginning of its journey. It collides with another molecule every twenty-thousandth of an inch of its journey. It is turned from its course five billion times in every second by collisions. If we could stop the molecules of hydrogen gas and utilize their energy as we utilize the energy of steam or the energy of the water at Niagara, we should find enough in every gram of gas, about two-thousandth of a pound, to raise a third of a ton to a height of forty inches. I have used for comparison the speed of a rifle bullet, and in an earlier generation people would have thought it impossible even to estimate this. It is, of course, easy. We put two screens in the path of the bullet, one near the rifle, and the other some distance away. We connect them electrically and use a fine time recording machine, and the bullet itself registers the time it takes to travel from the first to the second screen. Now, this is very simple and superficial work in comparison with the system of exact and minute measurements which the physicist and chemist use. In one of his interesting works Mr. Charles R. Gibson gives a photograph of two exactly equal pieces of paper in the opposite pans of a fine balance. A single word has been written in pencil on one of these papers, and that little scraping of lead has been enough to bring down the scale. The spectroscope will detect a quantity of matter four million times smaller even than this. And the electroscope is a million times still more sensitive than the spectroscope. We have a heat measuring instrument, the Bolo, which makes the best thermometer seem early Victorian. It records the millionth of a degree of temperature. It is such instruments multiplied by the score which enable us to do the fine work recorded in these pages. The Discovery of X-rays and Radium Discovery of Sir William Crooks But these wonders of the atom are only a prelude to the more romantic and far-reaching discoveries of the new physics, the wonders of the electron. Another and the most important phase of our exploration of the material universe opened with the Discovery of Radium in 1898. In the Discovery of Radioactive Elements a new property of matter was discovered. What followed on the Discovery of Radium and of the X-rays we shall see. As Sir Ernest Rutherford, one of our greatest authorities, recently said, the new physics has dissipated the last doubt about the reality of atoms and molecules. The closer examination of matter which we have been able to make shows positively that it is composed of atoms. But we must not take the word now in its original Greek meaning, an indivisible thing. The atoms are not indivisible. They can be broken up. They are composed of still smaller particles. The Discovery that the atom was composed of smaller particles was the welcome realization of a dream that had haunted the imagination of the 19th century. Chemists said that there were about eighty different kinds of atoms, different kinds of matter, but no one was satisfied with the multiplicity. Science is always aiming at simplicity and unity. It may be that science has now taken a long step in the direction of explaining the fundamental unity of all the matter. The chemist was unable to break up these elements into something simpler, so he called their atoms indivisible in that sense. But one man of science after another expressed the hope that we would yet discover some fundamental matter of which the various atoms were composed, one primordial substance from which all the varying forms of matter have been involved or built up. Prute suggested this at the very beginning of the century, when atoms were rediscovered by Dalton. Father Secchi, the famous Jesuit astronomer, said that all the atoms were probably evolved from ether, and this was a very favored speculation. Sir William Crookes talked of protheal as the fundamental substance. Others thought hydrogen was the stuff out of which all the other atoms were composed. The work which finally resulted in the discovery of radium began with some beautiful experiments of Professor, later Sir William, Crookes, and the 80s. It had been noticed in 1869 that a strange coloring was caused when an electric charge was sent through a vacuum tube. The walls of the glass tube began to glow with a greenish phosphorescence. A vacuum tube is one from which nearly all the air has been pumped, although we can never completely empty the tube. Crookes used such ingenious methods that he reduced the gas in his tubes until it was 20 million times thinner than the atmosphere. He then sent an electric discharge through and got very remarkable results. The negative pole of the electric current, the cathode, gave off rays which faintly lit the molecules of the thin gas in the tube and caused a pretty fluorescence on the glass walls of the tube. What were these rays? Crookes at first thought they corresponded to a new or fourth state of matter. Hitherto we had only been familiar with matter in the three conditions of solid, liquid, and gaseous. Now Crookes really had the great secret under his eyes, but about 20 years elapsed before the true nature of these rays was finally independently established by various experiments. The experiments proved that the rays consisted of a stream of negatively charged particles traveling with enormous velocities from 10,000 to 100,000 miles a second. In addition, it was found that the mass of each particle was exceedingly small, about one-eighteen hundredth of the mass of a hydrogen atom, the lightest atom known to science. These particles, or electrons, as they are now called, were being liberated from the atom. The atoms of matter were breaking down in Crookes' tubes. At that time, however, it was premature to think of such a thing, and Crookes preferred to say that the particles of the gas were electrified and hurled against the walls of the tube. He said that it was ordinary matter in a new state, radiant matter. Another distinguished man of science, Leonard, found that when he fitted a little plate of aluminum in the glass wall of the tube, the mysterious rays passed through this as if it were a window. They must be waves in the ether, he said, the discovery of X-rays. So the story went on from year to year. We shall see in a moment to what it led. Meanwhile, the next great step was when, in 1895, Wrenchin discovered the X-rays, which are now known to everybody. He was following up the work of Leonard, and he one day covered a Crookes' tube with some black stuff. To his astonishment, a prepared chemical screen which was near the tube began to glow. The rays had gone through the black stuff, and on further experiments he found that they would go through stone, living flesh, and all sorts of opaque substances. In a short time the world was astonished to learn that we could photograph the skeleton in a living man's body, locate a penny in the interior of a child that had swallowed one, or take an impression of a coin through a slab of stone. And what are these X-rays? They are not a form of matter. They are not material particles. X-rays were found to be a new variety of light with a remarkable power of penetration. We have seen what spectroscope reveals about the varying nature of light wavelengths. Light waves are set up by vibrations in ether, and, as we shall see, these ether disturbances are all of the same kind. They only differ as regards wavelengths. The X-rays, which Wrenchin discovered then, are light, but a variety of light previously unknown to us. They are ether waves of very short length. X-rays have proved a great value in many directions, as all the world knows, but that we need not discuss at this point. Let us see what followed Wrenchin's discovery. We refer throughout to the ether, because although modern theories dispense largely with this conception, the theories of physics are so inextricably interwoven with it that it is necessary, in an elementary exposition, to assume its existence. The modern view will be explained later in the article on Einstein's theory. While the world wondered at these marvels, the men of science were eagerly following up the next clue to the mystery of matter which was exercising the mind of crooks and other investigators. In 1896 Becquerel brought us to the threshold of the great discovery. Certain substances are phosphorescent. They become luminous after they have been exposed to sunlight for some time, and Becquerel was trying to find if any of these substances gave rise to X-rays. One day he chose a salt of the metal uranium. He was going to see if, after exposing it to sunlight, he could photograph a cross with it through an opaque substance. He wrapped it up and laid it aside to wait for the sun, but he found the uranium salt did not wait for the sun. Some strong radiation from it went through the opaque covering and made an impression of the cross upon the plate underneath. Light or darkness was immaterial. The mysterious rays streamed night and day from the salt. This was something new. Here was a substance which appeared to be producing X-rays. The rays emitted by uranium would penetrate the same opaque substances as the X-rays discovered by wrenching. Discovery of Radium Now at the same time as many other investigators, Professor Curie and his Polish wife took up the search. They decided to find out whether the emission came from the uranium itself or from something associated with it, and for this purpose they made a chemical analysis of great quantities of minerals. They found a certain kind of pitch blend which was very active, and they analyzed tons of it, concentrating always on the radiant element in it. After a time, as they successively worked out the non-radiant matter, the stuff began to glow. In the end they extracted from eight tons of pitch blend about half a teaspoonful of something that was a million times more radiant than uranium. There was only one name for it—radium. That was the starting point of the new development of physics and chemistry. From every laboratory in the world came a cry for radium salts, as pure radium was too precious, and hundreds of brilliant workers fastened on the new element. The inquiry was broadened, and as year followed year, one substance after another was found to possess the power of emitting rays—that is, to be radioactive. We know today that nearly every form of matter can be stimulated to radioactivity, which as we shall see means that its atoms break up into smaller and wonderfully energetic particles which we call electrons. This discovery of electrons has brought about a complete change in our ideas in many directions. So instead of atoms being indivisible, they are actually dividing themselves spontaneously and giving off throughout the universe tiny fragments of their substance. We shall explain presently what was later discovered about the electron. Meanwhile, we can say that every glowing metal is pouring out a stream of these electrons. Every arc lamp is discharging them. Every clap of thunder means a shower of them. Every star is flooding space with them. We are witnessing the spontaneous breaking up of atoms—atoms which have been thought to be indivisible. The Sun not only pours out streams of electrons from its own atoms, but the ultraviolet light which it sends to the Earth is one of the most powerful agencies for releasing electrons from the surface atoms of matter on the Earth. It is fortunate for us that our atmosphere absorbs most of this ultraviolet or invisible light of the Sun—a kind of light which will be explained presently. It has been suggested that, if we receive the full flood of it from the Sun, our metals would disintegrate under its influence and this steel civilization of ours would be impossible. But we are here anticipating we are going beyond radium to the wonderful discoveries which were made by the chemists and physicists of the world who concentrated upon it. The work of Professor Madame Curie was merely the final clue to guide the great search. How it was followed up, how we penetrated into the very heart of the minute atom and discovered new and portentous minds of energy, and how we were able to understand not only matter but electricity and light will be told in the next chapter. The discovery of the electron and how it affected a revolution in ideas. What the discovery of radium implied was only gradually realized. Radium captivated the imagination of the world. It was a boon to medicine, but to the man of science it was at first a most puzzling and most attractive phenomenon. It was felt that some great secret of nature was dimly unveiled in its wonderful manifestations, and they are now concentrated upon it as gifted a body of men, conspicuous among them, Sir J. J. Thompson, Sir Ernest Rutherford, Sir W. Ramsey, and Professor Soddy, as any age could boast, with an apparatus of research so far beyond that of any other age as the Aquitania is beyond a Roman galley. Within five years the secret was fairly mastered. Not only were all kinds of matter reduced to a common basis, but the forces of the universe were brought into a unity and understood as they had never been understood before. The Discovery of the Electron Physicists did not take long to discover that the radiation from radium was very like the radiation in a crook's tube. It was quickly recognized, moreover, that both in the tube and in radium and other metals the atoms of matter were somehow breaking down. However the first step was to recognize that there were three distinct rays that were given off by such metals as radium and uranium. Sir Ernest Rutherford christened them after the first three letters of the Greek alphabet, the alpha, the beta, and gamma rays. We are concerned chiefly with a second group and purpose here to deal with that group only. The alpha rays were presently recognized as atoms of helium gas shot out at the rate of 12,000 miles a second. The gamma rays are waves like the x-rays, not material particles. They appear to be a type of x-rays. They possess the remarkable power of penetrating opaque substances. They will pass through a foot of solid iron, for example, and a footnote. The beta rays, as they were at first called, have proved to be one of the most interesting discoveries that science ever made. They proved what crook said surmised about the radiations he discovered in his vacuum tube. But it was not a fourth state of matter that had been found, but a new property of matter, a property common to all atoms of matter. The beta rays were later christened electrons. They are particles of disembodied electricity. Here spontaneously liberated from the atoms of matter, only when the electron was isolated from the atom was it recognized for the first time as a separate entity. Electrons, therefore, are a constituent of the atoms of matter, and we have discovered that they can be released from the atom by a variety of agencies. Electrons are to be found everywhere, forming a part of every atom. An electron, Sir William Bragg says, can only maintain a separate existence if it is travelling at an immense rate from one three hundredth of the velocity of light upwards, that is to say at least six hundred miles a second, or thereabouts. Otherwise the electron sticks to the first atom it meets. These amazing particles may travel with the enormous velocity of from ten thousand to more than one hundred thousand miles a second. It was first learned that they are of an electrical nature because they are bent out of their normal path of a magnet as brought near them. And this fact led to a further discovery, to one of those sensational estimates which the general public is apt to believe to be founded on the most abstruse speculations. The physicist set up a little chemical screen for the beta rays to hit, and he so arranged his tube that only a narrow sheaf of the rays poured on to the screen. He then drew this sheaf of rays out of its course with a magnet, and he accurately measured the shift of the luminous spot on the screen where the rays impinged on it. But when he knows the exact intensity of his magnetic field, which he can control as he likes, and the amount of deviation it causes, and the mass of the moving particles, he can tell the speed of the moving particles which he thus diverts. These particles were being hurled out of the atoms of radium, or from the negative pole in a vacuum tube, at a speed which in good conditions reached nearly the velocity of light, that is nearly 186,000 miles a second. Their speed has, of course, been confirmed by numbers of experiments, and another series of experiments enabled physicists to determine the size of the particles. Only one of these experiments need be described to give the reader an idea how men of science arrived at their more startling results. Fog, as most people know, is thick in our great cities because the water vapor gathers on the particles of dust and smoke that are in the atmosphere. This fact was used as the basis of some beautiful experiments. Artificial fogs were created in little glass tubes by introducing dust in various conditions for super-saturated vapor to gather on. In the end it was possible to cause tiny drops of rain, each with a particle of dust at its core, to fall upon a silver mirror and be counted. It was a method of counting the quite invisible particles of dust in the tube, and the method was now successfully applied to the new rays. Yet another method was to direct a slender stream of the particles upon a chemical screen. The screen glowed under the cannonade of particles, and a powerful lens resolved the glow into distinct sparks which could be counted. In short, a series of the most remarkable and beautiful experiments checked in all the great laboratories of the world settled the nature of these so-called rays. They were streams of particles more than a thousand times smaller than the smallest known atom. The mass of each particle is, according to the latest and finest measurements, 1,845th of that of an atom of hydrogen. The physicist has not been able to find any character except electricity in them, and the name electrons has been generally adopted. The key to many mysteries. The electron is an atom of disembodied electricity. It occupies an exceedingly small volume, and its mass is entirely electrical. These electrons are the key to half the mysteries of matter. Electrons in rapid motion, as we shall see, explain what we mean by an electric current, not so long ago regarded as one of the most mysterious manifestations in nature. What a wonder, then, have we here, says Professor R. K. Duncan, an innocent-looking little pinch of salt and yet possessed of special properties, utterly beyond even the fanciful imaginings of man of past time. For nowhere do we find in the records of thought even the hit of the possibility of things which we now regard as established fact. This pinch of salt projects from its surface bodies, that is, electrons, possessing the inconceivable velocity of over 100,000 miles a second, of velocity sufficient to carry them, if unimpeded, five times around the earth in a second, and possessing with this velocity masses a thousand times smaller than the smallest atom known to science. Furthermore, they are charged with negative electricity. They pass straight through bodies considered opaque with a sublime indifference to the properties of the body, with the exception of its mere density. They cause bodies which they strike to shine out in the dark. The effect of photographic plate. They render the air a conductor of electricity. They cause clouds and moist air. They cause chemical action and have a peculiar physiological action. Who to-day shall predict the ultimate service to humanity of the beta rays from radium? Chapter 8 Part 2 This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. This recording has been Mark Smith of Simpsonville, South Carolina. The Outline of Science, Volume 1 by J. Arthur Thompson Chapter 8 Part 2 The Electron Theory or the New View of Matter The Structure of the Atom There is general agreement amongst all chemists, physicists, and mathematicians upon the conclusions which we have so far given. We know that the atoms of matter are constantly, either spontaneously or under stimulation, giving off electrons or breaking up into electrons, and they therefore contain electrons. Thus we have now complete proof of the independent existence of atoms and also of electrons. When, however, the man of science tries to tell us how electrons compose atoms, he passes from facts to speculation, and very difficult speculation. Take the letter O as it is printed on this page. In a little bubble of hydrogen gas no larger than that letter there are trillions of atoms, and they are not packed together but are circulating as freely as dancers in a ballroom. We are asking the physicists to take one of these minute atoms and tell us how the still smaller electrons are arranged in it. Naturally he can only make mental pictures, guesses, or hypotheses which he tries to fit to the facts and discards when they will not fit. At present, after nearly twenty years of critical discussion, there are two chief theories of the structure of the atom. At first Sir J. J. Thompson imagined the electrons circulating in shells, like the layers of an onion, round the nucleus of the atom. This did not suit, and Sir E. Rutherford and others worked out a theory that the electrons circulated round a nucleus rather like the planets of our solar system revolving round the central sun. Is there a nucleus then round which the electrons revolve? The electron as we saw is the disembodied atom of electricity, we should say, of negative electricity. Let us picture these electrons all moving round in orbits with great velocity. Now it is suggested that there is a nucleus of positive electricity attracting or pulling the revolving electrons to it, and so forming an equilibrium. Otherwise the electrons would fly off in all directions. This nucleus has been recently named the proton. We have thus two electricity in the atom. The positive equals the nucleus. The negative equals the electron. Of recent years Dr. Langmuir has put out a theory that the electrons do not revolve round the nucleus, but remain in a state of violent agitation of some sort at fixed distances from the nucleus. But we will confine ourselves here to the facts, and leave the contending theories to scientific men. It is now pretty generally accepted that an atom of matter consists of a number of electrons or charges of negative electricity held together by a charge of positive electricity. It is not disputed that these electrons are in a state of violent motion or strain, and that therefore a vast energy is locked up in the atoms of matter. To that we will return later. Here, rather, we will notice another remarkable discovery which helps us to understand the nature of matter. A brilliant young man of science who was killed in the war, Mr. Mosley, some years ago, showed that when the atoms of different substances are arranged in order of their weight, they are also arranged in the order of increasing complexity of structure. That is to say, the heavier the atom, the more electrons it contains. There is a gradual building up of atoms containing more and more electrons from the lightest atom to the heaviest. Here it is enough to say that as he took element after element from the lightest hydrogen to the heaviest uranium, he found a strangely regular relation between them. If hydrogen were represented by the figure one, helium by two, lithium three, and so on up to radium, then uranium should have the figure ninety-two. This makes it probable that there are in nature ninety-two elements. We have found eighty-seven, and that the number Mr. Mosley found is the number of electrons in the atom of each element. That is to say, the number is arranged in order of the atomic numbers of the various elements. The new view of matter. Up to the point we have reached then, we see what the new view of matter is. Every atom of matter, of whatever kind throughout the whole universe, is built up of electrons in conjunction with a nucleus. From the smallest atom of all, the atom of hydrogen, which consists of one electron rotating round a positively charged nucleus to a heavy complicated atom such as the atom of gold constituted of many electrons and a complex nucleus, we have only to do with positive and negative units of electricity. The electron and its nucleus are particles of electricity. All matter, therefore, is nothing but a manifestation of electricity. The atoms of matter, as we saw, combine and form molecules. Atoms and molecules are the bricks out of which nature is built up everything. Ourselves, the earth, the stars, the whole universe. But more than bricks are required to build a house. There are other fundamental existences such as the various forms of energy which give rise to several complex problems. And we have also to remember that there are more than 80 distinct elements, each with its own definite type of atom. We shall deal with energy later. Meanwhile, it remains to be said that although we have discovered a great deal about the electron and the constitution of matter, and that while the physicists of our own day seem to see a possibility of explaining positive and negative electricity, the nature of them both is unknown. There exists the theory that the particles of positive and negative electricity which make up the atoms of matter are points or centers of disturbances of some kind in a universal ether, and that all the various forms of energy are in some fundamental way aspects of the same primary entity which constitutes matter itself. But the discovery of the property of radioactivity has raised many other interesting questions besides that which we have just dealt with. In radioactive elements such as uranium, for example, the element is breaking down. In what we call radioactivity we have a manifestation of the spontaneous change of elements. What is really taking place is a transmutation of one element into another, from a heavier to a lighter. The element uranium spontaneously becomes radium, and radium passes through a number of other stages until it in turn becomes lead. Each descending element is of lighter atomic weight than its predecessor. The changing process, of course, is a very slow one. It may be that all matter is radioactive, or can be made so. This raises the question whether all matter in the universe may not undergo disintegration. There is, however, another side of the question which the discovery of radioactivity has brought to light, and which has affected a revolution in our views. We have seen that in radioactive substances the elements are breaking down. Is there a process of building up at work? If the more complicated atoms are breaking down into simpler forms, may there not be a converse process of building up from simpler elements to more complicated elements? It is probably the case that both processes are at work. There are some 80-odd chemical elements on the earth today. Are they all the outcome of an inorganic evolution, element giving rise to element, going back and back to some primeval stuff from which they were all originally derived infinitely long ago? Is there an evolution in the inorganic world which may be going on parallel to that of the evolution of living things? Or is organic evolution a continuation of inorganic evolution? We have seen what evidence there is of this inorganic evolution in the case of the stars. We cannot go deeply into the matter here, nor has the time come for any direct statement that can be based on the findings of modern investigation. Taking it altogether, the evidence is steadily accumulating, and there are authorities who maintain that already the evidence of inorganic evolution is convincing enough. The heavier atoms would appear to behave as though they were evolved from the lighter. The more complex forms it is supposed to have evolved from the simpler forms. Mosley's discovery, to which reference has been given rise, points to the conclusion that the elements are built up one from another. Other New Views We may hear referred to another new conception to which the discovery of radioactivity has given rise. Lord Kelvin, who estimated the age of the earth at twenty million years, reached this estimate by considering the earth as a body which is gradually cooling down, losing its primitive heat, like a loaf taken from Kelvin, at a rate which could be calculated, and that the heat radiated by the sun was due to contraction. Uranium and radioactivity were not known to Kelvin, and their discovery has upset both his arguments. Radioactive substances which are perpetually giving out heat introduce an entirely new factor. We cannot now assume that the earth is necessarily cooling down. It may even, for all we know, be getting hotter. At the 1921 meeting of the British Association, Professor Rayleigh stated that further knowledge had extended the probable period during which there had been life on this globe to about one thousand million years, and the total age of the earth to some small multiple of that. The earth he considers is not cooling, but contains an internal source of heat from the disintegration of uranium in the outer crust. On the whole, the estimate obtained seemed to be in agreement with the geological estimates. The question, of course, cannot in the present state of our knowledge be settled within fixed limits that meet with general agreement. As we have said, there are other fundamental existences which give rise to more complex problems. The three great fundamental entities in the physical universe are matter, ether, and energy. So far as we know, outside these there is nothing. We have dealt with matter, there remain ether and energy. We shall see that just as no particle of matter, however small, may be created or destroyed, and just as there is no such thing as empty space, ether pervades everything. So there is no such thing as rest. Every particle that goes to make up our solid earth is in a state of perpetual unremitting vibration. Energy is the universal commodity on which all life depends. Separate and distinct as these three fundamental entities, matter, ether, and energy, may appear, it may be that after all they are only different and mysterious phases of an essential oneness of the universe. The future. Let us, in concluding this chapter, give just one illustration of the way in which all this new knowledge may prove to be as valuable practically as it is wonderful intellectually. We saw that electrons are shot out of atoms at a speed that may approach 160,000 miles a second. Sir Oliver Lodge has written recently that a 70th of a grain of radium discharges at a speed a thousand times that of a rifle bullet 30 million electrons a second. Professor LeBon has calculated that it would take 340,000 barrels of powder to give a bullet the speed of one of these electrons. He shows that the smallest French copper coin, smaller than a farthing, contains an energy equal to 80 million horsepower. A few pounds of matter contain more energy than we could extract from millions of tons of coal. Even in the atoms of hydrogen, at a temperature which we could produce in an electric furnace, the electrons spin round at a rate of nearly 100 trillion revolutions a second. Every man asks it once, will science ever tap this energy? If it does, no more smoke, no mining, no transit, no bulky fuel. The energy of an atom is of course only liberated when an atom passes from one state to another. The stored up energy is fortunately fast bound by the electrons being held together as has been described. If it were not so, the earth would explode and become a gaseous nebula. It is believed that some day we shall be able to release, harness, and utilize atomic energy. I am of opinion, says Sir William Bragg, that atom energy will supply our future need. A thousand years may pass before we can harness the atom, or tomorrow might see us with the reins in our hands. That is the peculiarity of physics. Research and accidental discovery go hand in hand. Half a brick contains as much energy as a small coal field. The difficulties are tremendous, but as Sir Oliver Lodge reminds us, there was just as much skepticism at one time about the utilization of steam or electricity. Is it to be supposed, he asks, that there can be no fresh invention, that all the discoveries have been made? More than one man of science encourages us to hope. Here are some remarkable words written by Professor Sadi, one of the highest authorities on radioactive matter in our chief scientific weekly, Nature Magazine, November 6, 1919. The prospects of the successful accomplishments of artificial transmutation brighten almost daily. The ancients seemed to have had something more than an inkling that accomplishment of transmutation would confer upon men powers hitherto the prerogative of the gods. But now we know definitely that the material aspect of transmutation would be of small importance in comparison with the control over the inexhaustible sores of internal atomic energy to which its successful accomplishment would inevitably lead. It has become a problem no longer redolent of the evil associations of the age of alchemy but one big with a promise of a veritable physical renaissance of the whole world. If that promise is ever realized, the economic and social face of the world will be transformed. Before passing on to the consideration of ether, light, and energy, let us see what new light the discovery of the electron has thrown on the nature and manipulation of electricity. What is electricity? The nature of electricity. There is at least one manifestation in nature and so late as twenty years ago it seemed to be one of the most mysterious manifestations of all, which has been in great measure explained by the new discoveries. Already at the beginning of this century we spoke of our age of electricity yet there were few things in nature about which we knew less. The electric current rang our bells, drove our trains, lit our rooms, but none knew what the current was. There was a vague idea that it was a sort of fluid that flowed along copper wires as water flows in a pipe. We now suppose that it is a rapid movement of electrons from atom to atom in the wire or wherever the current is. Let us try to grasp the principle of the new view of electricity and see how it applies to all the very electrical phenomena in the world about us. As we saw, the nucleus of an atom of matter consists of positive electricity which holds together a number of electrons or charges of negative electricity. Footnote. The words positive and negative electricity belong to the days when it was regarded as a fluid. A body overcharged with the fluid was called positive. The undercharged body was called negative. A positively electrified body is now one whose atoms have lost some of their outlying electrons so that the positive charge of electricity predominates. The negatively electrified body is one with more than the normal number of electrons. This certainly tells us to some extent what electricity is and how it is related to matter, but it leaves us with the usual difficulty about fundamental realities. But we now know that electricity, like matter, is atomic in structure. A charge of electricity is made up of a number of small units or charges of a definite constant amount. It has been suggested that the two kinds of electricity, that is, positive and negative, are right-handed and left-handed vortices or whirlpools in ether or rings in ether. These are very serious difficulties, and we leave this to the future. What an electric current is. The discovery of these two kinds of electricity has, however, enabled us to understand very fairly what goes on in electrical phenomena. The outlying electrons, as we saw, may pass from atom to atom, and this on a large scale is the meaning of the electric current. In other words, we believe an electric current to be a flow of electrons. Let us take to begin with a simple electrical cell in which a feeble current is generated such a cell as there is in every house to serve its electric bells. In the original form, this simple sort of battery consisted of a plate of zinc and a plate of copper immersed in a chemical. Long before anything was known about electrons it was known that if you put zinc and copper together they would produce a mild current of electricity. We know now what this means. Zinc is a metal, the atoms of which are particularly disposed to part with some of their outlying electrons. Why? We do not know, but the fact is the basis of these small batteries. Electrons from the atoms of zinc pass to the atoms of copper, and their passage is a current. Each atom gives up an electron to its neighbor. It was further found long ago that if the zinc and copper were immersed in certain chemicals which slowly dissolved the zinc and the two metals were connected by a copper wire the current was stronger. In modern language there is a brisker flow of electrons. The reason is that the atoms of zinc which are stolen by the chemical leave their detachable electrons behind them and the zinc has therefore more electrons to pass on to the copper. Such cells are now made of zinc and carbon immersed in salamoniac but the principle is the same. The flow of electricity is a flow of electrons, though we ought to repeat that they do not flow in a body as molecules of water do. You may have seen boys place a row of bricks each standing on one end in such order that the first, if it is pushed, will knock over the second, the second, the third, and so on to the last. There was a flow of movement all along the line but each brick moves only a short distance. So an electron merely passes to the next atom which sends on an electron to a third atom and so on. In this case however the movement from atom to atom is so rapid that the ripple of movement, if we may call it so, may pass along at an enormous speed. We have seen how swiftly electrons travel. But how has this turned into power enough even to ring the bell? The actual mechanical apparatus by which the energy of the electron current is turned into sound or heat or light will be described in a technical section later in this work. We are concerned here only with the principle which is clear. While zinc is very apt to part with electrons copper is just as obliging in facilitating their passage onward. Electrons will travel in this way in most metals and copper is one of the best conductors. So we lengthen the copper wire between the zinc and the carbon until it goes as far as the front door and the bell which are included in the circuit. When you press the button at the door two wires are brought together and the current of electrons rushes round the circuit and at the bell its energy is diverted into the mechanical apparatus which rings the bell. Copper is a good conductor, six times as good as iron and is therefore so common in electrical industries. Some other substances are just as stubborn as copper is yielding and we call them insulators because they resist the current instead of letting it flow. Their atoms do not easily part with electrons. Glass, vulcanite and porcelain are very good insulators for this reason. What the dynamo does. But even several cells together do not produce the currents needed in modern industry and the flow is produced in a different manner. As the invisible electrons pass along a wire they produce what we call a magnetic field around the wire. They produce a disturbance in the surrounding ether. To be exact it is through the ether surrounding the wire that the energy originated by the electrons is transmitted. To set electrons moving on a large scale we use dynamo. By means of the dynamo it is possible to transform mechanical energy into electrical energy. The modern dynamo as Professor Soddy puts it may be looked upon as an electron pump. We cannot go into the subject deeply here. We would only say that a large coil of copper wire is caused to turn round rapidly between the poles of a powerful magnet. That is the essential construction of the dynamo which is for generating strong currents. We shall see in a moment how magnetism differs from electricity and we'll say here only that round the poles of a large magnet there is a field of intense disturbance which will start a flow of electrons in any copper that is introduced into it. On account of the speed given to the coil of wire its atoms enter suddenly this magnetic field and they give off crowds of electrons in a flash. It is found that a similar disturbance is caused though the flow is in the opposite direction when the coil of wire leaves the magnetic field and as the coil is revolving very rapidly we get a powerful current of electricity that runs in alternate directions and alternating current. Electricians have apparatus for converting it into a continuous current where this is necessary. A current therefore means a steady flow of the electrons from the atom. Sometimes however a number of electrons rush violently and explosively from one body to another as in the electric spark or the occasional flash from an electric tram or train. The grandest and most spectacular display of this phenomenon is the thunderstorm. As we saw earlier a portentous furnace like the sun is constantly pouring floods of electrons from its atoms into space. The earth intercepts great numbers of these electrons. In the upper regions of the air the stream of solar electrons has the effect of separating positively electrified atoms from negatively electrified ones and the water vapor which is constantly rising from the surface of the sea gathers more freely round their positively electrified atoms and brings them down as rain to the earth. Thus the upper air loses a proportion of positive electricity or becomes negatively electrified. In the thunderstorm we get both kinds of clouds. Some with large excesses of electrons and some deficient in electrons and the tension grows until it lasted as relieved by a sudden and violent discharge of electrons from one cloud to another or to the earth an electric spark on a prodigious scale. Magnetism We have seen that an electric current is really a flow of electrons. Now an electric current exhibits a magnetic effect. The surrounding space is endowed with energy which we call electromagnetic energy. A piece of magnetized iron attracting other pieces of iron to it is the popular idea of a magnet. If we arrange a wire to pass vertically through a piece of cardboard and then sprinkle iron filings on the cardboard we shall find that on passing an electric current through the wire the iron filings arrange themselves in circles round it. The magnetic force due to the electric current seems to exist in circles round the wire on ether disturbance being set up. Even a single electron when in movement creates a magnetic field as it is called round its path. There is no movement of electrons without its attendant field of energy and their motion is not stopped until that field of energy disappears from the ether. The modern theory of magnetism supposes that all magnetism is produced in this way. All magnetism is supposed to arise from the small whirling motions of the electrons contained in the ultimate atoms of matter. We cannot here go into the details of the theory nor explain why, for instance, iron behaves differently from other substances but it is sufficient to say that here also the electron theory provides the key. The theory is not yet definitely proved but it furnishes a sufficient theoretical basis for future research. The earth itself is a gigantic magnet, a fact which makes the compass possible and is well known that the earth's magnetism is affected by those great outbreaks on the sun called sunspots. Now it has been recently shown that a sunspot is a vast whirlpool of electrons and that it exerts a strong magnetic action. There is doubtless a connection between these outbreaks of electronic activity and the consequent changes in the earth's magnetism. The precise mechanism of the connection, however, is still a matter that is being investigated. Ether and Waves This material universe is supposed to be embedded in a vast medium called the Ether. It is true that the notion of the Ether has been abandoned by some modern physicists but whether or not it is ultimately dispensed with, the conception of the Ether has entered so deeply into the scientific mind that the science of physics cannot be understood unless we know something about the properties attributed to the Ether. The Ether was invented to explain the phenomena of light and to account for the flow of energy across empty space. Light takes time to travel. We see the sun at any moment by the light that left it eight minutes before. It has taken that eight minutes for the light from the sun to travel that 93 million miles odd which separates it from our earth. Besides the fact that light takes time to travel it can be shown that light travels in the form of waves. We know that sound travels in waves. Sound consists of waves in the air or water or wood or whatever medium we hear it through. If an electric bell be put in a glass jar and the air be pumped out of the jar the sound of the bell becomes feebler and feebler until when enough air has been taken out we do not hear the bell at all. Sound cannot travel in a vacuum. We continue to see the bell, however, so that evidently light can travel in a vacuum. The invisible medium through which the waves of light travel is the Ether and this Ether permeates all space and all matter. Between us and the stars stretch vast regions empty of all matter. But we see the stars. Their light reaches us even though it may take centuries to do so. We conceive then that it is the universal Ether which conveys that light. All the energy which has reached the earth from the sun and which stored for ages in our coal fields is now used to propel our trains and steamships to heat and light our cities to perform all the multifarious tasks of modern life was conveyed by the Ether. Without that universal carrier of energy we should have nothing but a stagnant lifeless world. We have said that light consists of waves. The Ether may be considered as resembling, in some respects, a jelly. It can transmit vibrations. The waves of light are really excessively small ripples measuring from crest to crest. The distance from crest to crest of the ripples in a pond is sometimes no more than an inch or two. This distance is enormously great compared to the longest of the wavelengths that constitute light. We say the longest for the waves of light differ in length. The color depends upon the length of the light. Red light has the longest waves and violet the shortest. The longest waves, the waves of deep red light, are seven two hundred and fifty thousandths of an inch in length. This is nearly twice the length of deep violet light waves which are one sixty thousandths of an inch. But light waves, the waves that affect the eye, are not the only waves carried by the Ether. Waves too short to affect the eye can affect the photographic plate, and we can discover in this way the existence of waves only half the length of the deep violet waves. Still shorter waves can be discovered until we come to those excessively minute rays, the X-rays, below the limits of visibility. But we can extend our investigations in the other direction. We find that the Ether carries many waves longer than light waves. Special photographic emulsions can reveal the existence of waves five times longer than violet light waves. Extending below the limits of visibility, our waves we detect as heat waves. Radiant heat, like the heat from a fire, is also a form of wave motion in the Ether, but the waves our senses recognize as heat are longer than light waves. There are longer waves still, but our senses do not recognize them. But we can detect them by our instruments. These are the waves used in wireless telegraphy, and their length may be in some cases measured in miles. These waves are the so-called electromagnetic waves. Light, radiant heat, and electromagnetic waves are all of the same nature. They differ only as regards their wavelengths. End of this part of Chapter 8