INDUCTION. 51 



potential be found the same as before it was brought 

 within the sphere of inductive influence, showing that 

 no permanent effect has resulted. 



Hence it will be seen that the effect of induction is 

 opposite to that of contact; the latter producing perma- 

 nent equilibrium between conductors, while the former 

 produces temporary disturbance of equilibrium. 



SPECIFIC INDUCTIVE CAPACITY. It has already been 

 stated that electric induction takes place through all 

 substances, but in different degrees ; and, since it 

 is found that each has an inductive power peculiar 

 to itself, this property is called its specific inductive 

 capacity. 



The importance of this subject will be understood 

 when it is considered that it affects enterprises in- 

 volving large capital, public convenience, and public 

 safety ; as in the transmission of electric energy by 

 insulated conductors, as telegraph and telephone wires, 

 ocean cables, and electric light wires ; including the 

 important question of underground transmission in 

 cities. 



Hence, for the last forty years, it has engaged the atten- 

 tion of such men as Faraday, Boltzmann, and many 

 others, including the earlier researches of Cavendish, 

 who seems to have been the first to investigate it, but 

 whose experiments on this subject have only recently 

 been published. 



The general method of investigation is as follows: 

 The inductive capacity of dry air at the barometric 

 pressure of 760 millimeters (29.92 inches) and at the 

 temperature of C. (32 Fahrenheit) is made the 

 standard unit by which the inductive capacities of all 

 other substances are estimated. 



