540 POPULAR LECTURES AND ADDRESSES. 



electric force or magnetic force being propagated 

 through and by a medium seemed as wild to the 

 naturalists and mathematicians of 100 years ago as 

 action-at-a-distance had seemed to Newton and 

 his contemporaries 100 years earlier. But a retro- 

 gression from the eighteenth century school of 

 science set in early in the nineteenth century. 



Faraday, with his curved lines of electric force, 

 and his dielectric efficiency of air and of liquid and 

 solid insulators, resuscitated the idea of a medium 

 through which, and not only through which but by 

 which, forces of attraction or repulsion, seemingly 

 acting at a distance, are transmitted. The long 

 struggle of the first half of the eighteenth century 

 was not merely on the question of a medium to 

 serve for gravific mechanism, but on the correct- 

 ness of the Newtonian law of gravitation as a 

 matter of fact however explained. The cor- 

 responding controversy in the nineteenth century 

 was very short, and it soon became obvious that 

 Faraday's idea of the transmission of electric force 

 by a medium not only did not violate Coulomb's 

 law of relation between force and distance, but 



