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been emancipated and his place taken by his tireless competitor. But it will be less familiar to some of you that this energy can not only displace, it can replace animate energy, and as time goes on it will more and more replace it. Conceivably, some future race of men, instead of sitting down to dinner, will attach themselves to something akin to an electric lamp-socket and draw thence from the public mains the supply of pure physical energy required for the day's work without any necessity of absorbing at the same time the useless husks-the material wrappings in which this energy is done up-that constitute our present food.

Now, though less generally appreciated at its true human significance than other scientific developments of the nineteenth century, this is probably the most fundamental and important. The doctrine of organic evolution cut away some of our most cherished notions about ourselves on the biological side. Fallen man-a discredited creature-with eyes ever turned backwards into his alleged more glorious past, a feeble and ineffective imitator of bygone days, dressed up by myth and poetic fancy to appear divine, gave place to the truer and more robust conception of man ascending from the animal world, a creature of hope and promise, with eyes ever forward on the future, and with reason gradually growing and developing to the point of comprehending the terms on which he stands with universal nature. Simultaneous with this profound reversal of mental outlook came the realisation that the physical strength in which he gloried was, even less than his body, of divine origin, but was borrowed from the inanimate world and could be augmented therefrom without the agency of life at all. Never before in his long history had any fundamental factor of his existence so suddenly and completely changed.



His physical necessities became a problem completely apprehended, a problem of energy, pure and simple. Life, the mystifier, scarcely complicated it. The pale, pursuing spectre which has dogged the ages and dragged them down is to be exorcised, not by mystical philosophy and religions, but by physics, chemistry and engineering.

But even on the purely philosophical side the gain is not inconsiderable. In constructing a machine which will run and perform continuous work, the scientific man has most nearly approached an imitation of the living body. Conversely, the living body has been often likened to a machine. If we regard merely the physical attributes of life and ignore the moral, æsthetic and spiritual aspects, then, undoubtedly, the body is a machine. Especially during sleep is the parallel exact. It is a machine set to run automatically whilst the engineer, the brain, has for the time being vacated the controlling platform. The pumping of the blood by the heart, the pumping of air by the lungs, the digestion of food, with their attendant sub-conscious regulations and adjustments, go on in the living body, both asleep and awake, in a definite round of themselves, much as a machine runs in its appointed cycles by virtue of its automatic valves and regulators. Awake and alert, it is a machine with the engineer at the helm, continually opening and closing non-automatic valves, making it vary in its actions, not over one or two, or possibly a dozen different combinations of motion, but over a practically infinite variety. But, whatever the complexities introduced by wakefulness, the sub-conscious regulation of the human machine does not cease for an instant. If we go further, beyond the physical realm of motion and forces, and trespass upon the intellectual activities of the brain, and the still finer moral, æsthetic and spiritual activities of the soul,

then, in spite of these further complexities, the mechanical aspect of the body can still no more be ignored than can the prime mover of a loom producing the most wonderful and artistic textiles. For good or ill, that machine has as much or little a right to be considered the man as his soul or brain. The attempt to amputate the spiritual from the physical world paralyses both.

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The mechanistic notion of life, the representation of the body as primarily and fundamentally a machine, is often bitterly and not very intelligently opposed. We are told that the machine-the scientist's imitation of life is not merely a purely inanimate mechanism. In its cunning combination of valves and regulators it has a brain, part of the brain of its designer. The partial likeness is that of the machine to the man, of the limited imitation to the original ; not the other way about, which is true enough. But let us bear in mind one essential and undeniable fact. Machine or man, inanimate mechanism with the mechanical imitation of a brain, or brain controlling an animate mechanism, what of the power? The power to live, the power to do work, is not in the brain nor in the body, not in the valves nor the moving parts. The power, whether of life or of mechanism, is external. That is the real ground of the analogy.

Inanimate energy, which before ran to waste or lay in the ground unused, began to be guided by human intelligence and shaped for human ends. What this energy can do for good and evil the world is everywhere now the witness. Primitive man froze on the site of what are now coal mines, and starved within the sound of the waterfalls that now are working to provide our food. The energy was there, the knowledge to utilise it was not. So while we are leading cramped lives and fighting among ourselves,



whether in peace or war, for a modicum of the means of existence, science tells us that, in the commonest materials that make up the framework of the world, there is energy of a magnitude of which we have no experience, and the means of livelihood upon a scale of which we have no standard. The energy is there. The knowledge that can utilise it is not-not yet.

If the nineteenth century is destined to be remembered in history on account of the establishment of the doctrine of energy, to the twentieth, young as it still is, belongs the credit of elevating and extending that doctrine to the extent that makes it of universal human interest. One simple question concerning the source of energy the nineteenth century quite failed to answer. Divorcing from the problem everything but its purely physical aspect, and putting it in its widest form, there remained unanswered the problem of its origin. How is it that the world is not yet grown old and "dead," though geologists dispute among themselves whether its history, in much the same condition as at present, can be traced back a hundred million or a thousand million years? Or, look up on a clear night at the same stars as those that greeted the gaze of the cavedweller and the mastodon when man was young. How can nature, the bank-teller, account for such a large expenditure of energy, over so prolonged a period, without long ago having become bankrupt? The sun and stars do not burn coal. Even if they did, Lord Kelvin computed that the combustion of a mass of coal the size of the sun would only suffice for 5000 years of the present rate of output of solar energy. Though, without any new source of energy, it was found by him to be possible to account for solar radiation over a period of some millions of years, the claims of the geologists for hundreds or thousands of millions could not be satisfied. What

is the origin of the stream of energy pouring out into space from stars so numerous that every living person in the world might claim a separate one as his own? That is the problem that has stared us in the face since we began to understand the laws of energy, an academic problem, perhaps, until it is realised that it is necessary for us to be able to get our hands on the levers controlling the primary sources of energy, or, when our fuel supplies are exhausted, relapse into barbarism.

At the close of the nineteenth century an extraordinary series of discoveries in physics and chemistry put into our hands a scrap of a material called radium, which asked us precisely the same question as the stars, but at point-blank range. It is a new element discovered by M. and Mme. Curie in a uranium - containing mineral, pitchblende. It possesses the outstanding property of emitting energy, in relatively large amount, and in new and surprising forms, spontaneously and continuously. All we have learned of this new property, radioactivity, shows that this steady emission of energy is going on in the rocks, from which the radium is extracted, at precisely the same rate as from the radium after it has been extracted, and has been going on for hundreds of millions of years. The explanation follows from the discovery that these radioactive elements are undergoing slow changes into other elements, changes of precisely the same kind as the alchemist sought to effect when he strove in vain to transmute the base metals into gold. Modern chemistry is unable to achieve such changes, but they are now known to be going on slowly and spontaneously in the radioactive elements. We can at present only watch and follow them. We have not yet succeeded in interfering with them or quickening their rate.

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