270 HENRY A. EOWLAND 



The method adopted for determining the moment of inertia of the 

 suspended coil was that of passing a tube through its centre and placing 

 weights at different distances along it. In this way was found 



K = 82Q-Q c. g. s. units. 



The use of the electrodynamometer in the experiment was to determine 

 the horizontal intensity of the earth's magnetism at any instant in the 

 position of the ballistic galvanometer. This method was necessary on 

 account of the rapid changes of this quantity in an ordinary building 1 

 and also because a damping magnet, reducing the earth's field to about 

 J its normal value, was used. For this purpose the ballistic galvano- 

 meter was set up inside the large circle of 80 cm. diameter with one 

 turn of wire and simultaneous readings of the electrodynamometer and 

 needle of ballistic galvanometer were made. 



THEORY OF EXPERIMENT. 

 We have for the potential 



v 8*? , , , /-[", , -00021 



- * d ^w -- ed V w\ 1 H g 



For the magnetic intensity acting on the needle 



TT__ 2xnp"-c V 1C sin a 

 *(p 2 + J 2 )itan? 

 For the condenser charge 



Whence 



_ eGC (p^ + b^Z Nt i*l wd tan? P.. >* 



'"*V TV sin a 2 sin 0[_ ~ 2 



but 



and 2 sin $0 = I * |~1 i f * Y ~| nearly. 



ML \ us J " 



So that finally 



= eGC _.__ - __ 



A=0; -0011; -0030; -0056; -0090 for 1, 2, 3, 4, 5 discharges as inves- 

 tigated below. 



1 This experiment was completed before the new physical laboratory was finished. 



