218 TRANSFORMATION AND EQUIVALENCE OF FORCES. 



overcoming the affinities of carbon and hydrogen for the 

 oxygen united with them ; the re-composition effected by the 

 animal, is at the profit of these forces, which are liberated 

 during the combination of such elements. Thus the move- 

 ments, internal and external, of the animal, are re-appear- 

 ances in new forms of a power absorbed by the plant under 

 the shape of light and heat. Just as, in the manner above 

 explained, the solar forces expended in raising vapour from 

 the sea's surface, are given out again in the fall of rain and 

 rivers to the same level, and in the accompanying transfer of 

 solid matters ; so, the solar forces that in the plant raised cer- 

 tain chemical elements to a condition of unstable equilibri- 

 um, are given out again in the actions of the animal dur- 

 ing the fall of these elements to a condition of stable equi- 

 librium. 



Besides thus tracing a qualitative correlation between 

 these two great orders of organic activity, as well as between 

 both of them and inorganic agencies, we may rudely trace a 

 quantitative correlation. Where vegetal life is abundant, 

 we usually find abundant animal life; and as we advance 

 from torrid to temperate and frigid climates, the two de- 

 crease together. Speaking generally, the animals of each 

 class reach a larger size in regions where vegetation is 

 abundant, than in those where it is sparse. And further, 

 there is a tolerably apparent connexion between the quan- 

 tity of energy which each species of animal expends, and the 

 quantity of force which the nutriment it absorbs gives out 

 during oxidation. 



Certain phenomena of development in both plants and 

 animals, illustrate still more directly the ultimate truth 

 enunciated. Pursuing the suggestion made by Mr. Grove, 

 in the first edition of his work on the " Correlation of the 

 Physical Forces," that a connexion probably exists between 

 the forces classed as vital and those classed as physical, 

 Dr. Carpenter has pointed out that such a connexion is 

 clearly exhibited during incubation. The transformation of 



