to the Electrostatic Unit of Electricity. 293 



K = 826-6 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* and also because a damping 

 magnet, reducing the earth's field to about \ its normal value, 

 was used. For this purpose the ballistic galvanometer 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 



8tt<7 _ y - _ _ r -00021 



= -fdvw = e<V?o I l + ~J-\ 



For the magnetic intensity acting on the needle 



For the condenser charge 



Q = * ;jg *> 5 (•+»») = * -£ 



Whence 



v _ eGtC(p* + b *)% Nty/wd tan 99 r _ X 1 



2«VK^~ 'W^ 2 sin£0 L 1 " 2 + GtC J 



but to ^ = l5[ 1 ^(s)' + I©l 



and 2sin-0=-— 11 — — I nearly. 



So that finally 



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

 investigated below. 



2 

 -0002 



*This experiment was completed before the new physical laboratory was 

 finished. 



