194 A Physicist on Evolution. 



I was not prepared to see this theory received as it has been by 

 the best intellects of our time. Its success is greater than I could 

 have thought possible." 



lu our day great generalizations have been reached. The theory 

 of the origin of species is but one of them. Another, of still wider 

 grasp and more radical significance, is the doctrine of the Conserva- 

 tion of Energy, the ultimate philosophical issues of which are as 

 yet but dimly seen — that doctrine which "binds nature fast in 

 fate " to an extent not hitherto recognized, exacting from every 

 antecedent its equivalent consequent, from every consequent its 

 equivalent antecedent, and bringing vital as well as physical pheno- 

 mena under the dominion of that law of causal connection which, as 

 far as the human understanding has yet pierced, asserts itself 

 everywhere in nature. Long in advance of all definite experiment 

 upon the subject, the constancy and indestructibility of matter had 

 been affirmed ; and all subsequent experience justified the affirma- 

 tion. Later researches extended the attribute of indestructibility to 

 force. This idea, applied in the first instance to inorganic, rapidly 

 embraced organic nature. The vegetable world, though drawing 

 almost all its nutriment from invisible sources, was proved incom- 

 petent to generate anew either matter or force. Its matter is for 

 the most part transmuted air; its force transformed solar force. 

 The animal world was proved to be equally uncreative, all its 

 motive energies being referred to the combustion of its food. The 

 activity of each animal as a whole was proved to be the transferred 

 activities of its molecules. The muscles were shown to be stores of 

 mechanical force, potential until unlocked by the nerves, and then 

 resulting in muscular contractions. The speed at which messages 

 fly to and fro along the nerves was determined, and found to be, 

 not as had been previously supposed, equal to that of light or 

 electricity, but less than the speed of a flying eagle. 



This was the work of the physicist : then came the conquests 

 of the comparative anatomist and physiologist, revealing the 

 structure of every animal, and the function of every organ in the 

 whole biological series, from the lowest zoophyte up to man. The 

 nervous system had been made the object of profound and continued 

 study, the wonderful and, at bottom, entirely mysterious controlHng 

 power which it exercises over the whole organism, physical and 

 mental, being recognized more and more. Thought could not be 

 kept back from a subject so profoundly suggestive. Besides the 

 physical life dealt with by Mr. Darwin, there is a psychical life 

 presenting similar gradations, and asking equally for a solution. 

 How are the different grades and orders of mind to be accounted 

 for ? What is the principle of growth of that mysterious power 

 which on our j)lanet culminates in Keason ? These are questions 

 which, though not thrusting themselves so forcibly upon the atten- 



