EVOLUTION THE MASTER-KEY 



hotter than another, we can make it do work. 

 But when the water has fallen from the height, or 

 the heat has distributed itself, no more work can 

 be got out of it. The energy is still there, but it 

 is no longer available. At present there is a great 

 difference of heat potential between the different 

 parts of the solar system, one consequence of 

 which is the presence of life upon the earth. But 

 in time to come the heat will have distributed it- 

 self so that what corresponds to the solar system 

 of to-day will be all of one temperature, and life 

 will be impossible. 



Now if energy, as represented by heat, is ever 

 seeking its own level, the time must come when, if 

 there be no compensatory process, all the energy 

 in the universe ceases to be available. To state 

 the case broadly, the heat will still be there the 

 dead universe will have a certain temperature 

 but there will be no difference of potential, and the 

 cosmic life will have run its course. If the law of 

 the dissipation of energy be the whole truth, the 

 universe is certainly comparable, in this connection, 

 to a watch that is running down. Furthermore, 

 there is within it if this law be the whole truth 

 no possibility of being wound up again, for it is a 

 prime character of natural processes, as Lord Kel- 

 vin was the first to point out, that they are irre- 

 versible. "This remarkable property of all nat- 

 ural processes," as Dr. Merz says, "seems to lead 

 us to the conception of a definite beginning and to 

 shadow forth a possible end the interval, which 

 3>4 



