70 



SCIENTIFIC THOUGHT. 



to Cavendish, that in the case of electric attraction and 

 repulsion, the nature of the intervening medium was of 

 importance : it played a part in the electric phenomena 

 in the same way as in the propagation of light and heat 

 the intervening medium played a definite part. This 

 part had been entirely overlooked by Continental philos- 

 ophers, who worked on the hypothesis of an immediate 

 action at a distance, based upon the analogy of gravi- 

 tation. Their researches, carried on by methods similar 

 to those invented by Laplace and his school for the cal- 

 culation of the combined effect of gravitational forces at 

 various points in space, entirely ignored the question how 

 such effects were brought about. As time did not seem 

 to enter as an appreciable factor, the investigation of the 

 mechanism by which action at a distance was communi- 

 cated was set aside as unnecessary or impossible : the 

 astronomical view of the phenomena sufficed. For 

 Faraday, the intervening medium, which as in the com- 

 munication of light and heat took an active part, the 

 question of its nature and mode of action was very 

 important; he accordingly first of all gave it a name. 

 As in optics the term luminiferous ether had been 

 recently revived, and had become familiar through 

 Young and Fresnel, so through Faraday were intro- 

 duced the terms " dielectric " and " magnetic field," 

 as the carriers of electric and magnetic action ; and 

 though for a long time used only by himself, they 



tween gravity and electricity." On 

 the failure of this attempt he fully 

 reported in his Bakerian Lecture, 

 November 1850 ( ' Exp. Res.,' vol. 

 iii. p. 161). But the former results 

 were sufficient to ripen gradually 



in his mind the idea of the physical 

 nature of the lines of force, which 

 he expounded with increasing pre- 

 cision from 1851 onward. (See 

 ' Exp. Res.,' 28th series, vol. iii. p. 

 328 ; also pp. 402, 438.) 



