146 HOUSTOX, KEXNELLY — THE PATH OF A CURKENT. [Mar. 19, 



the mathematical processes of astronomy at the present time tacitly 

 assume the same law, without pretending to explain the mechanism by 

 which such action may be conveyed. Consequently, it was only too 

 easy for students to imbibe, with the mathematical ideas for study- 

 ing quantitative electromagnetic facts, the fundamental hypoth- 

 esis of action at a distance upon which this idea was based. Thus 

 the mechanical forces existing between charged electrified bodies, 

 between magnet poles, between electric currents, or between elec- 

 tric currents and magnets, were all referred to the mutual actions of 

 elementary portions of imaginary electric or magnetic substances, 

 each of which exerted an influence proportional to its quantity, and 

 inversely proportional to the square of its distance from the element 

 acted on. About the middle of the present century, Faraday first 

 paved the way for a change in our views on these questions. He 

 suggested the theory that an electrified body or a magnet did not 

 emit any material effluvium, but exerted an influence on the invisi- 

 ble medium in its vicinity ; namely, the universal ether ; that 

 this influence was of the nature of a stress, and that the ether sur- 

 rounding an electrified or magnetized substance was in some 

 manner strained along certain directions which he called lines of 

 force. Consequently, an electrified body produced lines of electric 

 force along which the ether was strained, while a magnetized body 

 similarly produced lines of magnetic force along which the ether 

 was strained, but in a manner different from electric strain. It was 

 this strained ether that connected the electrified or magnetized 

 bodies with bodies in their neighborhood, and permitted attraction 

 and repulsion to be set up between them without necessitating any 

 action at a distance. 



Clerk Maxwell developed the ideas of ether strains and stresses 

 mathematically. While retaining the original methods of quanti- 

 tatively determining the mechanical actions between electric and 

 magnetic bodies, by summing up the effects of all the elements of 

 those bodies on each other, in reference to the inverse squares of the 

 distances, he developed, at considerable length, the action of the 

 intervening medium, and showed how the strain in such medium 

 could produce the mechanical effects observed. In the treatment 

 of this subject he noticed that a disturbance of the electric or mag- 

 netic condition of the ether was controlled by a formula similar to 

 that which controls a disturbance in an elastic solid. He was, 

 therefore, led to believe that electromagnetic disturbances in the 



