![]() If any machine were produced whose source of energy could not at once be traced, a man of science (complete freedom of investigation being supposed) would in the first place try to trace its power to some hidden source of a kind already known or in the last resort he would seek for a source of energy of a new kind and give it a new name. Consequently, on any one who calls it in question is thrown the burden of proving his case. The principle of the conservation of energy, which in one sense is simply denial of the possibility of a perpetual motion, rests on facts drawn from every branch of physical science and, although its full establishment only dates from the middle of the 19th century, yet so numerous are the cases in which it has been tested, so various the deductions from it that have been proved to accord with experience, that it is now regarded as one of the best-established laws of nature. No such spirit has ever existed, save in the imagination of his describer, and no such machine has ever been known to act, save in the fancy of its inventor. There was a time when wise men believed that a spirit, whose maintenance would cost nothing, could by magic art be summoned from the deep to do his master’s work and it was just as reasonable to suppose that a structure of wood, brass and iron could be found to work under like conditions. It had not then been proved that energy is untreatable and indestructible in the ordinary course of nature even now that proof has only been given by induction from long observation of facts. ![]() ![]() Before that analysis of the action of ordinary machines which led to the laws of dynamics, and the discussion of the dynamical interdependence of natural phenomena which accompanied the establishment of the dynamical theory of heat, there was nothing plainly unreasonable in the idea that work might be done by the mere concatenation of machinery. There was a time when the problem of the perpetual motion was one worthy of the attention of a philosopher. Just as some of the most interesting branches of modern pure mathematics sprang from the problem of squaring the circle, as the researches of the alchemists developed into the science of modern chemistry, so, as the result of the vain search after the perpetual motion, there grew up the greatest of all the generalizations of physical science, the principle of the conservation of energy. Still, like these others, it retains a great historical interest. Like the exact quadrature of the circle, the transmutation of metals and other famous problems of antiquity, the perpetual motion has now become a venerable paradox. Most of the perpetual motionists, however, had more practical views, and explicitly declared the object of their inventions to be the doing of useful work, such as raising water, grinding corn, and so on. The energy created by such a machine would simply be the work done in overcoming the friction of its parts, so that its projectors might be held merely to have been ignorant of the laws of friction and of the dynamic theory of heat. The earlier seekers after the “perpetuum mobile” did not always appreciate the exact nature of their quest for we find among their ideals a clock that would periodically rewind itself, and thus go without human interference as long as its machinery would last. ![]() Briefly, a perpetual motion usually means a machine which will create energy. PERPETUAL MOTION, or Perpetuum Mobile, in its usual significance, not simply a machine which will go on moving for ever, but a machine which, once set in motion, will go on doing useful work without drawing on any external source of energy, or a machine which in every complete cycle of its operation will give forth more energy than it has absorbed.
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