Clerk Maxwell 31 



expenditure of work, raise the temperature of B and lower 

 that of A, in contradiction to the second law of thermo- 

 dynamics." 



In the history of electrical science Maxwell (1831-1879) 

 stands in very much the same relative position to Faraday 

 as Lord Kelvin occupied towards Joule in the domain of 

 heat. They both brought pre-eminently mathematical minds 

 to bear on the results of experimental discoveries, and saw 

 more clearly than the original discoverers the important 

 consequences which flowed from their researches. Neither 

 Faraday nor Joule were experimentalists pure and simple, 

 they were indeed guided mainly by theoretical considera- 

 tions; but it lay beyond their object or powers to enter 

 fully into the wider generalizations, though Faraday showed 

 in the passages we have quoted that his imagination went 

 far beyond his immediate experimental results. 



The theory of electrostatics which deals with electric 

 charges at rest, their distribution on conductors, and their 

 mutual attractions or repulsions, is explained in the simplest 

 manner by assuming the existence of two kinds of electricity, 

 for which it is convenient to retain the old names, positive 

 and negative electricity. The mechanical effects of the 

 charges may be dealt with mathematically very much as 

 we do in the case of gravitational attractions. There is 

 also a formal analogy between magnetic and electric actions, 

 so that independent magnetic fluids were sometimes intro- 

 duced to facilitate the treatment of magnetic problems. 



Faraday saw that, if we wish to grasp the relationship 

 between the action of electric charges at rest and the electro- 

 dynamic effects produced by electricity in motion, and 

 more especially, if we wish to include in the same field of 

 enquiry the electric effects produced by moving magnets, 

 we must take a more comprehensive view. We must cease 

 to look at the centres or origin of the forces, and fix our 

 attention on the medium between them. This, as has already 

 been explained, was Faraday's outlook. Further, if the 

 effects of light and electricity are both transmitted through 

 a medium, our natural distaste to add unnecessarily to 

 the number of hypotheses inclines us to the belief that the 

 same medium serves bo:h purposes. But here a formidable 



