514 CONSTANTS OF COILS. 



branch b of Wheatstone's bridge, and the adjustment made for 

 the permanent state. During the variable period the bridge is 

 traversed by a current (949) 



_ 



~ 



and the discharge, when the principal current is made, is 



'V 



The intensity /? of the permanent current is equal to - (948), 

 which gives 



m = E. 



MN 



On the other hand, if the resistance b is made to vary by S, 

 the permanent current, which traverses the galvanometer, is (947) 



ab' a' 



A A ' 



or, replacing A by the value - , which represents equilibrium of 

 the bridge, 



aa' 



MN i 

 consequently 



m _ 



If a be the swing for the discharge m, y the deflection produced 

 by the permanent current *, which corresponds to the defect of 

 adjustment, we deduce 



TT tan y 



