The Evolution of the Sciences 



amount of work required to restore it to its 

 original level; it will continue falling until, 

 sooner or later, some obstacle arrests it, and then 

 its stability will be great in proportion to its 

 proximity to the bottom of the ravine, that is 

 to say, to the portion of its energy expended. 



The thermo-chemists took this analogy for 

 their starting-point; they compared a system 

 of bodies in reaction to a falling stone and con- 

 cluded that the direction of the transformation 

 must always be of a nature to cause loss of 

 energy in the system that is to say, it must 

 release heat; and the most stable transforma- 

 tion, the one most likely to occur, will be the 

 transformation which causes the release of the 

 greatest possible quantity of heat. This principle, 

 which owed its origin to Thomsen, received at 

 the hands of Berthelot all the development 

 necessary to determine its meaning and its 

 consequences. This very precision, however, 

 enables us to subject it to severe criticism. 



One may remark, first of all, that the ap- 

 plication of the principles of thermo-chemistry 

 is meaningless unless all the conditions of the 



problems are carefully defined; the amount 



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