Theories of Electricity 139 



scope, which figured so prominently in the development 

 of electrostatics more than a century ago is in use 

 throughout the world as the most reliable instrument for 

 investigations in radioactivity. 



We have seen that at the beginning of the nineteenth 

 century the subject of electrostatics had been developed 

 on a purly mathematical basis of forces acting at a dis- 

 tance, and that but little physical significance was at- 

 tached to the conception of the electric fluids. It re- 

 quired the genius of Faraday to attract attention again 

 to the physical character of the fluids themselves and to 

 combat the then almost universal notion of forces acting 

 at a distance. To a man of the keen physical insight of 

 Faraday, the idea that the attraction and repulsion of 

 bodies was due merely to forces acting at a distance was 

 very repugnant, and he strenuously championed the ne- 

 cessity of a medium, by means of and through which 

 forces could be transmitted, also emphasizing the great 

 importance of considering the medium as the seat of the 

 electrical and magnetic forces instead of the fluids them- 

 selves. 



In illustration of these ideas, Faraday introduced the 

 conception of lines of electric and magnetic force, with 

 which we are now so familiar. The old notion of action 

 at a distance, which had done such great service in 

 formulating the mathematical theory of electrostatics, 

 died hard, but its fate was sealed by the development of 



