254 CONNECTION OF ELECTRICITY AND MAGNETISM. 



ACTION AT A DISTANCE. 



By Professor Clerk Maxwell. 



[From the Proceedings of the London Institution.] 



I have no ne.w discovery to bring before you this evening. I must ask 

 you to go over very old ground, and to turn your attention to a question 

 which has been raised again and again ever since men began to think. 



The question is that of the transmission of force. We see that two 

 bodies at a distance from each other exert a mutual influence on each 

 other's motion. Does this mutual action depend on the existence of 

 some third thing, some medium of communication, occupying the space 

 between the bodies, or do the bodies act on each other immediately 

 without the intervention of anything else? 



The mode in which Faraday was accustomed to look at phenomena of 

 this kind differs from that adopted by many other modern inquirers, 

 and my special aim will be to enable you to place yourselves at Fara- 

 day's point of view, and to point out the scientific value of that con- 

 ception of lines of force which, in his hands, became the key to the 

 science of electricity. 



When we observe one body acting on another .at a distance, before 

 w^e assume that this action is direct and immediate we generally inquire 

 whether there is any material connection between the two bodies ; and 

 if we find strings or rods, or mechanism of any kind, capable of account- 

 ing for the observed action between the bodies, we prefer to explain the 

 action by means of these intermediate connections rather than to admit 

 the notion of direct action at a distance. 



Thus, when we ring a bell by means of a wire, the successive parts of 

 the wire are first tightened and then moved till at last the bell is rung 

 at a distance by a process in which all the intermediate particles of the 

 wire have taken part one after the other. We may ring a bell at a dis- 

 tance in other ways, as by forcing air into a long tube, at the other end 

 of which is a cylinder with a piston which is made to fly out and strike 

 the bell. We may also use a wire; but instead of pulling it we may 

 connect it at one end with a voltaic battery and at the other with an 

 electro-magnet, and thus ring the bell by electricity. 



Here are three different ways of ringing a bell. They all agree, how- 

 ever, in the circumstance that betiveen the ringer and the bell there is 

 an unbroken line of communication, and that at every point of this line 

 some physical process goes on by which the action is transmitted from 

 one end to the other. The process of transmission is not instantaneous 

 but gradual : so that there is an interval of time after the impulse has 

 been given to one extremity of the line of communication, during which 

 the impulse is on its way, but has not reached the other end. 



It is clear, therefore, that in many cases the action between bodies at 

 a distance may be accounted for by a series of actions between each 

 successive pair of a series of bodies which occupy the intermediate space; 



