66 



THE i>Ko<;i:i:ss <>F SCIKNVK 



I have said that our epoch can produce achieve- 

 ments in physical science of greater moment tlian 

 any other has to show, advisedly ; and I think 

 that there are three great products of our time 

 which justify the assertion. One of these is that 

 doctrine concerning the constitution of matter 

 which, for want of a better name, I will call 

 " molecular ; " the second is the doctrine of the 

 conservation of energy ; the third is the doctrine 

 of evolution. Each of these was foreshadowed, 

 more or less distinctly, in former periods of the 

 history of science ; and, so far is either from being 

 the outcome of purely inductive reasoning, that it 

 would be hard to overrate the influence of meta- 

 physical, and even of theological, considerations 

 upon the development of all three. The peculiar 

 merit of our epoch is that it has shown how these 

 hypotheses connect a vast number of seemingly 

 independent partial generalisations ; that it has 

 -ivt-n them that precision of expression which is; 

 necessary for their exact verification ; and that) 

 it has practically proved their value as guides toj 

 the discovery of new truth. All three doctrines! 

 are intimately connected, and each is applicable to 

 the whole physical cosmos. But, as might have 

 been expected from the nature of the case, tlu 

 first two grew, mainly, out of the consideratior 

 of physico-chemical phrnomrn.-i: while the thii 

 in great measure, owes its rehabilitation, if not it 

 origin, to the study of biological phenomena. 



