504 PARTICULAR CASES OF INDUCTION. 



hence, if r and / are two lengths, and m a magnetic mass, 



On the other hand, the electrical mass M is the product by a 

 time of an intensity of current, or of the magnetic power of a 

 shell, and we may also write 



M = \t = $t = h<rt = h > 



m' denoting a magnetic mass of suitable magnitude, and h and /' 

 lengths. We shall have then 





As the three first fractions are abstract numbers, it will be 

 seen that the resistance expressed in electromagnetic units is equal 

 to the quotient of a length by a time that is to say, a quantity 

 of the same order as a velocity. 



We may, indeed, easily discover in the experiment itself, a 

 physical representation of this velocity. Suppose, in fact, that 

 the cross-bar moved uniformly with a velocity u, and that the 

 intensity I of the current is measured by the action which it 

 exerts on a needle placed in the centre of a tangent galvanometer 

 (504) ; we shall have 



On the other hand, MR = HS, or 



it follows from this that 



tan 8 = - 



