INDUCTION. 49 



runs through the substance of the medium till it reaches 

 the object, and the continued stress produces continued 

 strain. Something analogous to this, it is assumed, 

 takes place in the transmission of electric energy by 

 induction. 



This hypothesis has the sanction of eminent author- 

 ity, and may assist us in arriving at a solution of the 

 problem. Gordon says: "If electric induction were a 

 4 direct action at a distance,' we should expect that it 

 would be transmitted equally through all insulators. 

 One of the strongest arguments for supposing it to be 

 a strain of the particles of the insulator is found in the 

 fact that different insulators transmit it with very differ- 

 ent strengths." 



"Induction, so far from being a 'direct action at a 

 distance,' is most certainly transmitted by the particles 

 of the dielectrics, and is affected by almost every molec- 

 ular change which may occur in them." 



And he defines strain, as here used, to mean " an 

 alteration of size or shape," including "all alterations 

 of volume," " all twistings and bendings, and all vibra- 

 tory motions other than those of a rigid body as a 

 whole." 



The wave theory agrees with the views here expressed ; 

 for we have only to conceive that this " strain " consists 

 in a " vibratory motion," that is, in undulations of the 

 medium. 



It is also in accordance with the analogy of similar 

 transmission of other forms of radiant energy. And, if 

 all energy has a common origin, it is reasonable to sup- 

 pose that the transmission of its different forms would 

 present striking analogies. 



INFLUENCE OF DIELECTRIC. In order to observe 



