servation of energy itself, and of this principle it behooves us now to speak. Joule, we have said, proved the law according to which work may be changed into heat; and Thomson and others, that according to which heat may be changed into work. Now, it occurred to Thomson that there was a very important and significant difference between these two laws, consisting in the fact that, while you can with the greatest ease transform work into heat, you can by no method in your power transform all the heat back again into work. In fact, the process is not a reversible one; and the consequence is that the mechanical energy of the universe is becoming every day more and more changed into heat. It is easily seen that if the process were reversible, one form of a perpetual motion would not be impossible. For, without attempting to create energy by a machine, all that would be needed for a perpetual motion would be the means of utilizing the vast stores of heat that lie in all the substances around us, and converting them into work. The work would, no doubt, by means of friction and otherwise, be ultimately reconverted into heat; but if the process be reversible, the heat could again be converted into work, and so on forever. But the irreversibility of the process puts a stop to all this. In fact, I may convince myself by rubbing a metal button on a piece of wood how easily work can be converted into heat, while the mind completely fails to suggest any method by which this heat can be reconverted into work. Now, if this process goes on, and always in one direction, there can be no doubt about the issue. The mechanical energy of the universe will be more and more transformed into universally diffused heat, until the universe will no longer be a fit abode for living beings. Although, therefore, in a strictly mechanical sense, there is a conservation of energy, yet, as regards usefulness or fitness for living beings, the energy of the universe is in process of deterioration. Universally diffused heat forms what we may call the great waste heap of the universe, and this is growing larger year by year. At present it does not sensibly obtrude itself, but who knows that the time may not arrive when we shall be practically conscious of its growing bigness? It will be seen that we have regarded the universe, not as a collection of matter, but rather as an energetic agent,-in fact, as a lamp. Now, it has been well pointed out by Thomson, that, looked at in this light, the universe is a system that had a beginning and must have an end; for a process of degradation cannot be eternal. If we could view the universe as a candle not lit, then it is perhaps conceivable to regard it as having been always in existence; but if we regard it rather as a candle that has been lit, we become absolutely certain that it cannot have been burning from eternity, and that a time will come when it will cease to burn. We are led to look to a beginning in which the particles of matter were in a diffuse chaotic state, but endowed with the power of gravitation, and we are led to look to an end in which the whole universe will be one equally heated inert mass, and from which everything like life or motion or beauty will have utterly gone away. From "The Conservation of Energy." |