Indeed, the Law of the Dissipation of Energy is an intelligent and well-supported denial of the chimera of perpetual motion. There is a loose idea that perpetual motion is impossible to us, because we can not avoid friction with its consequent loss of energy, but that nature works without friction, or that, in general, friction entails no loss, and so here perpetual motion is possible; but nature no more works without friction than we do, and friction entails a loss of available power. The supply of invisible molecular energy in the sun is no more infinite than the quantity of matter in the sun is infinite. The sun is daily lifting huge masses of water from the sea to the skies, yearly lifting endless vegetation from the earth, setting breezes and hurricanes in motion, dragging the huge tidal wave round and round the earth; performing, in short, the great bulk of the endless labor of this world and other worlds, so that the energy of the sun is continually being given away without any corresponding restoration. The loss of force in the shape of radiant light and heat can never be weaned back to any other mode of available energy. Carnot, Clausius, Thomson, and Rankine have all from different points of view been led to the same conclusion. We can make no use whatever of the energy represented by equally diffused heat. If one body is hotter than another, as the boiler of a steam-engine is hotter than the condenser, then we can make use of the difference of temperature to convert some of the heat into work; but if two substances are equally hot, even though their particles contain an enormous amount of molecular energy, they will not yield us a single unit of work. Energy is thus of different qualities, mechanical energy being the _best_, and universal heat the _worst_; in fact, this latter description of energy may be compared to the waste heap of the universe, in which the _effete_ forms of energy are suffered to accumulate without any further conversion.[166] If, then, when mechanical force passes into heat, _some_ of the heat can never be brought back to be mechanical force, and if the change from mechanical force to heat be ever going on, all the force in the universe must at last take the form of radiant heat. But if that be so, then at last all differences of temperature must disappear, and every thing end in a universal death. "We are come," says Adolph Fick, "to this alternative: either in our highest, most general, most fundamental abstractions, some great point has been overlooked, or the universe will have an END, and must have had a BEGINNING; it could not have existed from Eternity, but must at some date, not infinitely distant, have arisen from something not forming a part of the natural chain of causes--that is, IT MUST HAVE BEEN CREATED."[167]