104 POPULAR LECTURES AND ADDRESSES. 



the assumption of atoms. But there can be no 

 permanent satisfaction to the mind in explaining 

 heat, light, elasticity, diffusion, electricity and 

 magnetism, in gases, liquids, and solids, and de- 

 scribing precisely the relations of these different 

 states of matter to one another by statistics of 

 great numbers of atoms, when the properties of 

 the atom itself are simply assumed. When the 

 theory, of which we have the first instalment in 

 Clausius and Maxwell's work, is complete, we are 

 but brought face to face with a superlatively grand 

 question, What is the inner mechanism of the 

 atom ? 



In the answer to this question we must find the 

 explanation not only of the atomic elasticity, by 

 which the atom is a chronometric vibrator accord- 

 ing to Stokes's discovery, but of chemical affinity 

 and of the differences of quality of different 

 chemical elements, at present a mere mystery in 

 science. Helmholtz's exquisite theory of vortex- 

 motion in an incompressible frictionlcss liquid has 

 been suggested as a finger-post, pointing a way 

 which may possibly lead to a full understanding 



