106 ELEMENTS OF ELECTRICITY AND MAGNETISM. 



rH' 

 I, = ~ - tan <f>. 



(0 



Then the other current 7 2 is sent through the galvanometer and 

 the corresponding deflection <j> 2 is observed, giving 



Dividing equations (i) and (ii), member by member, we have 



7j tan <f> l 

 7 ~~ tan <f> 



(37) 



Figure 70 is a general view of a tangent galvanometer. The 

 divisions on the large horizontal circle are not used. 



Fig. 70. 



58. The action of a uniform magnetic field upon a suspended 

 coil in which an electric current is flowing, (a) Simple case of a 

 rectangular coil with two of its edges parallel to the field. Figure 7 1 

 represents a rectangular coil of wire suspended between the poles 

 N and 5 of a large magnet. Let H be the intensity of the 

 magnetic field (assumed to be uniform), let b be the breadth of 

 the coil, let a be the height of the coil, and let Z be the 



