Theorem of the Mechanical Theory of Heat. 419 



librium will be attained even between the radiant beat existing 

 in the aether and the heat existing in material bodies. Lastly, 

 in relation to their molecular arrangement, material bodies will 

 get nearer to a certain condition in which, regard being had to 

 the existing temperature, the total disgregation is the greatest 

 possible. 



I have endeavoured to express the whole of this process by 

 means of one simple theorem, whereby the condition towards 

 which the universe is gradually approaching is distinctly charac- 

 terized. I have formed a magnitude which expresses the same 

 thing in relation to transformations that energy does in relation 

 to heat and ergon — that is, a magnitude which represents the 

 sum of all the transformations which must have taken place in 

 order to bring any body or system of bodies into its present 

 condition. I have called this magnitude Entropy. Now in 

 all cases in which the positive transformations exceed the nega- 

 tive an increase of entropy occurs. Hence we must conclude 

 that in all the phenomena of nature the total entropy must be 

 ever on the increase and can never decrease ; and we thus get 

 as a short expression for the process of transformation which is 

 everywhere unceasingly going on the following theorem : — 

 The entropy of the universe tends towards a maximum. 



The more the universe approaches this limiting condition in 

 which the entropy is a maximum, the" more do the occasions of 

 further changes diminish; and supposing this condition to be at 

 last completely attained, no further change could evermore take 

 place, and the universe would be in a state of unchanging- 

 death. 



Albeit the present condition of the universe is still very far 

 removed from this limiting condition, and the approach to it is 

 so slow that all such periods as we speak of as historical are but 

 a very short span in comparison with the immeasurable periods 

 that the universe requires for comparatively very slight modifi- 

 cations, it yet remains an important result that a law of nature 

 should have been discovered which allows us to conclude with 

 certainty that everything in the universe does not occur in cycles, 

 but that it changes its condition continually in a certain direc- 

 tion, and thus tends towards a limiting condition. 



