MEASUREMENT OF RESISTANCES IN ABSOLUTE VALUE. 



1105. INDUCED DISCHARGES. In a circuit which contains no 

 permanent electromotive force, the current / induced by the varia- 

 tion of the flow of magnetic force Q satisfies the differential 

 equation (518) 



The quantity of electricity m= \idt which traverses the circuit 

 in the time / 2 - / x is defined by the equation 



When the current is zero at the two limits, or if it has resumed 

 the same value as well as the coefficient of self-induction, we get 

 simply 



m 



We may, first of all, displace the circuit in an invariable magnetic 

 field ; the difference Q x - Q 2 represents then the difference of the 

 flow of magnetic force across the surface of the circuit in the two 

 extreme positions. 



Suppose, for instance, that the circuit is movable about an axis 

 in a uniform field ; if H is the component of the field perpendicular 

 to the axis, S the maximum projection of the surface of the circuit 

 on a plane passing through the axis, x l and x 2 the angles of the 

 surface S with the meridian of the field in the two extreme positions, 

 we have 



Q! - Q 2 = HS (sin x l - sin x z ) . 



If x l = , and x 2 = , that is to say, if the circuit is displaced 

 through 1 80 from a position in which it is perpendicular to the 

 field, we get 



*=? 



Instead of displacing the circuit, we may displace the field itself. 

 Suppose a magnet, of magnetic moment M, is placed in the centre 

 of a frame. When the axis of the magnet makes an angle x with 



