50 ELEMENTS OF STATIC ELECTRICITY. 



induction there must be two or more bodies at differed 

 potentials placed in each other's vicinity, and these must 

 be separated by an insulator; for, if separated by a con- 

 ductor, equilibrium would at once be restored, and in- 

 duction could not take place. 



Insulators through which induction takes place are 

 called dielectrics, from the Greek &, through. Air was 

 the dielectric between the electroscope and electrified 

 body, and between the spheres and cylinder, in the ex- 

 periments already given. 



Now, since conductors permit electricity to pass 

 through them easily, while insulators resist its passage, 

 there must be some peculiarity in the nature or arrange- 

 ment of the molecules which makes two bodies of the 

 same class similar in this respect, while two of opposite 

 classes are dissimilar. 



Hence we can easily conceive that when two insulated 

 conductors, at different potentials, are brought into con- 

 tact, the undulations of their molecules would assume 

 the same phase, and equilibrium take place; but that 

 when those undulations are transmitted through a die- 

 lectric, they undergo such a change that, the phases of 

 the undulations not being the same, there is a repulsion 

 instead of an intermingling, which results in creating 

 opposite potentials in adjacent parts, on either side of 

 the dielectric, the negative of one being equal to the 

 positive of the other. 



And since in the transmission, part of the energy is 

 consumed in overcoming the resistance, difference of 

 potential, on opposite sides, must result from this cause 

 also. 



If either conductor be removed, still remaining insu- 

 lated, the equilibrium of each will be restored, and its 



