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converted into the potential energy of food, and so is utilised by life. But the steam and oil engine also work by virtue of the energy of the sun, which, in bygone times, was stored up by great masses of vegetation, and is now preserved in coal and fuel. Potential energy, or energy on the leash, is not capable of being apprehended until it is converted into kinetic energy. Ignite coal and its potential energy—a form of chemical energy-turns, like that of a released spring, into kinetic, and the molecules of the burning coal are suddenly thrown into a state of intense chaotic motion, which we call heat. But vital energy or vital force, the energy of a man working or living, are not special and peculiar to life. They are one with the great flow of inanimate energy reaching us from the sun, which bears the whole world along.

Energy, someone may say, is a mere abstraction, a mere term, not a real thing. As you will. In this, as in many another respect, it is like another abstraction no one would deny reality to, and that abstraction is wealth. Wealth is the power of purchasing, as energy is the power of working. I cannot show you energy, only its effects. I cannot show you wealth, only its effects and its purely conventional symbol, money. Money is not wealth to a starving man in a deserted place. It is both a symbol and a measure of wealth earned, as work done is a measure of energy expended. Heat energy, mechanical energy, chemical energy, and so on, are different forms rather than different kinds of energy, just as coins, bank-notes, cheques, and so on, are forms of money. The bank-teller totals up a heterogeneous collection of coins, paper money, securities of various kinds and currencies, all as one sum of money, and then thinks of that sum, not of the sovereigns and shillings, notes and cheques he was

handling the moment before. So the scientific man looks into the processes of nature, sunshine and fire, storm and lightning and tempest, the battling of the elements, the rushing tumult of man and his machinery, the majestic circling of the moon and planets; stranger still, the silent, sleeping powers of coal, explosives, food and fertilisers. He is no more lost among them than the bank-teller is among his miscellaneous collection of monies. He totals them all in terms of energy, the power of working. The enormous variety of activities they display bother him not at all.

Now, just as strict watch as the bank-teller keeps on the credit and debit sides of the accounts of all his customers, nature keeps over the energy accounts of all its manifold processes. There is no work done for which the energy required does not have to be supplied, just as no money can be withdrawn from a bank into which none has been paid. Money cannot be spent twice, more must be forthcoming, and so it is with energy. It can only be spent once, and, whether spent usefully or uselessly, whether doing enduring work or dissipated doing nothing permanent, once spent it cannot be recovered. Very easy indeed it is to waste energy. The performance of any work demands so much energy, but any amount more may be demanded if the worker is inefficient. Abstraction or not, energy is as real as wealth, -I am not sure that they are not two aspects of the same thing. The one drives the commercial and industrial activities of men, and the other the whole physical activities of the entire universe.

Human beings and beasts of burden were at first almost the sole sources of useful energy, the only available labourers to overtake the heavy work of the world. For countless ages the inanimate energy of nature, of wind, waterfall and fire, proved too


difficult to harness and control. It is only a century since the new era of inanimate energy began, since science drilled the tumultuous rush of the swarms of molecules, too small to be seen, and out of their infinite variety of motions in all directions at onceout of heat-made the working motion of the steam engine. Animate energy, "brute force,” became dwarfed indeed beside the working giant whose food was fuel. What is more, it had to recognise that it indeed was no divinity, no “vital spark" of origin divine animating a mass of clay. It was just energy, no more no less, to that bank-teller keeping count, and it made a very humble sum compared with the accounts of his inanimate customers.

At once there came about an enormous increase in the world's work, done no longer by living workers but by the inanimate labourers, water-power, coal and oil, which science had enslaved. So that to-day a single machine puts forth a continuous round of labour which an army of men could not keep going for an hour.

Steam engines, locomotives, electric trams, and petrol-driven motor cars have made some of the main aspects of inanimate energy very familiar. We all know that if we want such energy or power in any form we have to pay for it, whether we get it as a finished product, as the electrical energy laid on to consumers' houses and paid for by the unit, or in a partially-inanufactured state as coal gas, or in its raw state as coal. In neither case do we care at all for the electricity or gas or coal we buy; we are buying energy, the power of doing so much work, the power of producing so much heat, light, and so on, as the case may be. We are all aware how largely this inanimate power has replaced animal labour. Whether at the docks or on ships or trains or cars, some animal-man, horse, mule or ox-has


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,

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