THERMAL EQUILIBRIUM 201
in remote space it can find embodiment only in exceedingly remote, rigid and inelastic solids. But in such solids is also embodied the quintessence of mechanical energy. The intensity and availability which has been lost to thermal forms has been regained in mechanical form.
Ultimately these remote, cold, hard solids must end their existence in collision, resulting in gasification, expansion and incandescence. The swing of the pendulum will have been reversed. The intensity and availability of mechanical energy which they embodied will have been lost, and in its place will reappear availability for radiation and elastic work-performance.
Thus there exist always and everywhere two great thermal tendencies, which are balanced against each other in cosmic equilibrium:
First: All heat tends always and everywhere to fall down-temperature, either by radiation or by work-performance. Nowhere in the universe has ever been observed any cessation or reversal of this tendency. Usually, the vast flood of radiant energy pouring outward into space from all the countless millions of suns finds its chance for direct radiation into remote space. This is true of the bulk of all sun-radiation; and in this form traveling outwardly at the inconceivable rate of 186,000 miles per second, it may exist for eons. Light is as permanent a form of energy as mechanical energy or heat. The universe maintains its stock of it as permanently as it does one of the space or motion-energy of celestial bodies.*
*Of the radiance emitted by our own sun, for instance, about one hundred millionth is arrested and degraded before the confines of its own system are reached and passed. Beyond those confines, apparently, is nothing to arrest it until the next solar system is reached. When that occurs, assuming the similarity of all solar systems to our own, wherein about one-fiftieth of all the surface presented is dark, about one-fiftieth of the radiation arrested would be degraded, by collosion with opaque bodies. The other forty-nine fiftieths would be arrested by the central sun and reflected without degradation.
But even these proportions are divisions of what is itself but a minute fraction of the whole. Assuming that the mean inter-stellar distance is but eleven light-years, the proportion of the entire radiation arrested by each solar system would be only a decimal fraction of the whole consisting of unity at the seventeenth decimal place. In other words, it would not be until 100,000,000,000,000,000 solar systems had been met, after II X IOIT years had elapsed, that all of the original radiation from our sun would have ceased its continuous existence, and been either reflectedow, as well as to Mr. Burgess: