ELECTROMAGNETIC SYSTEM. 59 1 



Strength of magnetic shell [<]. Strength of the current [I]. As 

 the magnetic strength of a shell is the product of a surface density 

 by the thickness, we have 



These dimensions are the same as those of potential, as could be 

 foreseen (329). 



The dimensions and the value of current strength, are the 

 same as the magnetic power of a shell. 



Quantity of electricity [Q]. The quantity of electricity being 

 the product of a current strength by a time, we have 



These dimensions are the same as those of the quantity of 

 magnetism in the electrostatic system ; hence, in the electromagnetic 

 system, the surface density, the force, and the electrical potential will 

 have the same dimensions as the corresponding magnetic quantities 

 in the electrostatic system. 



Specific inductive capacity [K]. The specific inductive capacity 

 (126) is inversely as the coefficient of electrical elasticity of the 

 medium that is to say, proportional to the ratio of the displacement 

 to the corresponding force; which gives 



it is therefore equal to the inverse of the square of a velocity. 



Resistance [R]. The resistance of a conductor may be defined 

 by Joule's law (244), which gives 



from which is deduced 



The electromagnetic resistance is therefore a velocity ; we have 

 obtained this result directly (407). Suppose that the two rails, and 

 the bar in the experiment assumed in this paragraph, are without 



