96 SCIENTIFIC THOUGHT. 



ficient to cover the whole field. The law of gravitation 

 embraced cosmical and some molar phenomena, but led to 

 vagueness when applied to molecular actions. The atomic 

 theory led to a complete systematisation of chemical com- 

 pounds, but afforded no clue to the mysteries of chemical 

 affinity. And the kinetic or mechanical theories of light, 

 of electricity, and magnetism, led rather to a new dualism, 

 the division of science into sciences of matter and of the 

 2. ether. The unification of scientific thought which was 



Insuffici- 

 ency of the grained by any of these three views, the astronomical, the 



astronoim- 



Sd kinetic' atomic, and the mechanical, was thus only partial. A 

 more general term had to be found under which the 

 different terms could be comprised, which would give a 

 still higher generalisation, a more complete unification 

 of knowledge. One of the principal performances of 

 the second half of the nineteenth century has been to 

 find this more general term, and to trace its all-pervad- 

 ing existence on a cosmical, a molar, and a molecular 

 scale. It will be the object of this chapter to complete 

 the survey of those sciences which deal with lifeless 

 nature by tracing the growth and development of this 

 s. greatest of all exact generalisations the conception of 



The concep- 

 tion of energy. 



eneigy. 



The complex of ideas and the manifold courses of 

 reasoning which are centred in this conception form 

 such an intricate network, the interests involved are so 

 great, the suggestions which led up to it so numerous, 

 the consequences which resulted for science and practice 

 so far-reaching, that the historian has no little difficulty 

 in laying bare the many lines of thought which appa- 

 rently cross and re -cross each other. Accordingly the 



