ARTICLES 407 



P increase toward a maximum, while certain other such func- 

 tions decrease toward a minimum. 



When we pass on to biological systems evolving^under 

 the complex conditions presented to us in nature, we may, if 

 we choose, apply the same language in a discussion of their 

 history, and state empirically that their evolution is an irre- 

 versible process, 1 or make the guess that here also certain 

 functions increase toward a maximum. 2 But no attempt 

 seems to have been made to give explicitly the form of these 

 functions, or even as much as to indicate just what are the 



1 " The second law (of thermodynamics) is the law of evolution of the world 

 accessible to our observation" (Chwolson, Lehrbuch dcr Physik, 1905, vol. iii, 

 p. 499 ; Scientia, 1910, vol. iii, p. 51. 



"... the second law of the theory of energy is now generally regarded as 

 essentially a statistical law. So viewed, the second law of energy becomes a 

 principle stated wholly in terms of the theory of probability. It is the law that 

 the physical world tends, in each of its parts, to pass from certain less probable to 

 certain more probable configurations of its moving particles. As thus stated the 

 second principle . . . becomes a law of evolution " (Josiah Royce, Science, 1914, 

 vol. xxxix, p. 551). 



" Un systeme isole ne passe jamais deux fois par le meme etat. 



" Le second principe affirme un ordre n£ce"ssaire dans la succession de deux 

 phenomenes, sans retour possible aux etats deja traverses. 



" C'est pourquoi j'ai cru expressif d'appeler ce principe un principe devolution. 



" II se trouve qu'en proposant ce nom je suis fidele a la pensee de Clausius, car 

 le mot (vrpoTrrj, d'ou il a tire entropie, signifie precisement evolution " (J. Perrin, 

 Traite de Chitnie Physique, 1903, vol. i, pp. 142-43). 



Compare also : 



" II est hautement improbable qu'un systeme isole passe deux fois par le meme 

 e"tat ; cela est d'autant plus improbable que la complication du systeme est plus 

 grande, et pratiquement il serait insense de se placer dans cette hypothese d'un 

 retour a l'etat initial " (J. Perrin, Traite de Chimie Physique, 1903, vol. i, 

 pp. 145-46). 



The following is also of interest : 



M The book of Nature is the book of Fate. She turns the gigantic pages — 

 leaf after leaf, never re-turning one. . . . The face of the planet cools and dries, 

 the races meliorate, and man is born. But when a race has lived its term, it 

 comes no more again" (Emerson, The Conduct of Life). 



The mere statement that a system " never twice passes through the same 

 state" is, in itself, insufficient to distinguish between evolution as a " progress," or 

 merely a " changeful sequence," to use the apt phrase of Prof. J. A. Thomson in 

 The Wonder of Life, 1914. It is insufficient to define the direction of evolution. 

 This direction is indicated by the more definite statement that the system passes 

 from less probable to more probable states. A rigorous proof of this latter 

 principle seems to be given only for certain special kinds of systems. 



2 " Un corps vivant qui reste vivant, suit toujours, quel que soit le 

 derangement qu'il a subi, la loi qui defini l'equilibre stable. II est done en 

 e"tat d'equilibre stable ; la stabilite de cet equilibre resulte de ce qu'une certaine 

 fonction de ces elements est a un maximum" (Le Dantec, La Stabilite de la Vie, 

 1910, p. 25). 



