THE MAGNETIC MEASUREMENT OF CURRENT. 31 

 Therefore 



T = ZIHr* 



=2n 

 sin 2 0- 

 . o 



dO 



(4) 



or 



T = ^ZIH (5) 



Note. When the field H is at right angles to the axis about 

 which the torque T is reckoned but inclined to the plane of 



e \ 



Fig. 27. 

 Top view of suspended coil. 



the coil as shown in Fig. 27, then H cos is the component of 

 the field which lies in the 

 plane of the coil, and substi- 

 tuting H cos <j> for H in 

 equations (i) or (5) we get 

 the correct expression for 

 T for the case shown in 

 Fig. 27. 



21. The Siemens elec- 

 trodynamometer. A gen- 

 eral view of a Siemens elec- 

 trodynamometer is shown 

 in Fig. 28, and the essen- 

 tial features of the instru- 

 ment are shown in Fig. 29. 

 A stationary coil A and 

 a suspended coil B are 



Fig. 28. 



"*"1 



