260 THE FITNESS OF THE ENVIRONMENT 



riety, and complexity of phases and compo- 

 nents, and for constancy of temperature, while 

 equally important and unique relationships 

 between the properties of water and carbonic 

 acid and their vapor or gas pressures exist, 

 and exert much influence upon the meteoro- 

 logical cycle. 



Thus, judged by the phase rule, the actual 

 characteristics of the environment may be 

 shown to contribute the factors which make for 

 complexity and regulation of material sys- 

 tems. Now there can be no doubt that, when 

 feasible, the ideal method — from the physico- 

 chemical point of view — to describe a ma- 

 terial system is in the terms of the phase 

 rule. 1 Hence the characteristics which that 



1 "Ten years after the law of mass action was propounded 

 by Guldberg and Waage, Willard Gibbs, Professor of Physics 

 in Yale University, showed how, in a perfectly general manner, 

 free from all hypothetical assumptions as to the molecular 

 condition of the participating substances, all cases of equi- 

 librium could be surveyed and grouped into classes, and how 

 similarities in the behavior of apparently different kinds of 

 systems, and differences in apparently similar systems, could 

 be explained. 



" As the basis of his theory of equilibria, Gibbs adopted the 

 laws of thermodynamics, a method of treatment which had 

 first been employed by Horstmann. In deducing the law of 

 equilibrium, Gibbs regarded a system as possessing only three 

 independently variable factors — temperature, pressure, and 

 the concentration of the components of the system — and he 

 enunciated the general theorem now usually known as the 



