AXD MODERN PHYSICS. 150 



attraction is proportional to the product of the charges, 

 and inversely proportional to the square of the 

 distance between them. 



The action between two charges is action at a 

 distance taking place across the space which separates 

 the two. 



Faraday, in 1837, in the eleventh series of his 

 " Experimental Researches," published his first paper 

 on " Electrostatic Induction." He showed as indeed 

 Cavendish had proved long previously, though the 

 result remained unpublished that the force between 

 two charged bodies will depend on the insulating 

 medium which surrounds them, not merely on their 

 shape and j>osition. Induction, as he expresses it, 

 takes place along curved lines, and is an action of 

 contiguous particles ; these curved lines he calls the 

 " lines of force." 



Discussing these researches in 1845, Lord Kelvin 

 writes* : 



"Mr. Faraday's rc.scnrchc.-j . . . were undertaken with a 

 view to tc.st an idea which he had long possessed that the 

 forces of attraction and repulsion exercised by free electricity 

 arc not the resultants of actions exercised at a distance, but are 

 projKi^atcd by means of molecular action among the con- 

 tiguous particles of the insulating medium surrounding the 

 electrified bodies, which he therefore calls the dielectric. I5y 

 this idea he has been led to some very remarkable views UJKM 

 induction, or, in fact, uj>on electrical action in general. As it 

 is impossible that the phenomena observed by Faraday can be 

 incompatible with the results of experiment which constitute 

 Coulomb's theory, it is to be expected that the difference of 

 his ideas from those of Coulomb must arise solely from a 

 different method of stating and interpreting physically the 



* Tapers on 4< Electrostatic*," etc., r> 20. 



