166 JAMES CLERK MAXWELL 



though in an incomplete form, his first statement ot 

 those equations of the electric field which are so in- 

 dissolubly bound up with Maxwell's name. 



The great advance in theory made in the paper is 

 the distinct recognition of certain mathematical 

 functions as representing Faraday's eleetrotonic-statc, 

 and their use in solving electro-magnetic problems. 



The paper contains no new physical theory of 

 electricity, but in a few years one appeared. In his 

 later writings Maxwell adopted a more general view 

 of the electro-magnetic field than that contained 

 in his early papers on "Physical Lines of Force." It 

 must, therefore, not be supposed that the somewhat 

 gross conception of cog- wheels and pulleys, which wo 

 are about to describe, were anything more to their 

 author than a model, which enabled him to realise 

 how the changes, which occur when a current of 

 electricity passes through a wire, might be represented 

 by the motion of actual material particles. 



The problem before him was to devise a physical 

 theory of electricity, which would explain the forces 

 exerted on electrified bodies by means of action 

 between the contiguous parts of the medium in the 

 space surrounding these bodies, rather than by direct 

 action across the distance which separates them. A 

 similar question, still unanswered, had arisen in tho 

 case of gravitation. Astronomers .have determined 

 tho forces between attracting bodies; they do not 

 know how those forces arise. 



Maxwell's fondness for models has already been 

 alluded to; it had led him to construct his top to 

 illustrate the dynamics of a rigid body rotating about 



