CONTRIBUTIONS TO SCIENCE. 543 



emanating from two pipes, each of which is supplying water 

 to a tank, would be curved round, and would avoid one another. 

 The lines of displacement, and consequently the lines of force 

 which coincide with them, will therefore be bent in exactly 

 the same manner as the magnetic lines of force represented 

 in Tig. 10, p. 533, and the pressure in the medium at right 

 angles to these lines will cause an apparent repulsion of the 

 bodies. 



For the same displacement, that is, for the same charges 

 of the little bodies, the repulsion will be proportional to the 

 elasticity of the medium. It is also proportional to the 

 product of the charges, or, since they are equal, to the 

 square of one of them. Suppose then that the medium is 

 exchanged for one of greater elasticity. If we wish to keep 

 the repulsion between the bodies the same, the displace- 

 ments and therefore the charges must be diminished, the 

 product of these charges, that is, the square of either charge, 

 being made inversely proportional to the elasticity of the 

 medium. The magnitude of each charge must therefore 

 vary inversely as the square root of the elasticity of the 

 medium when the dielectric is changed. Hence, if we 

 define the electrostatic unit of electricity as " that quantity 

 of positive electricity which, acting on an equal quantity at 

 unit distance repels it with unit force," it follows that the 

 unit will vary with the character of the dielectric, being 

 inversely proportional to the square root of its elasticity. 



But the attraction or repulsion between two given 

 charges of electricity varies inversely as the specific induct- 

 ive capacity of the dielectric, so that the electrostatic unit 

 of electricity varies directly as the square root of the specific 

 inductive capacity, and thus the specific inductive capacity 

 is a quantity which varies inversely as the elasticity of the 

 medium. 



Suppose we have two parallel wires conveying equal 

 electric currents in the same direction. Other things re- 

 maining unchanged, the velocity of the molecular vortices 

 at any point is proportional to the strength of the currents. 

 The attraction between the wires we know to be propor- 



