Electromagnetic to the Electrostatic Unit of Electric Quantity. 2 87 



G the magnetic galvanometer-constant, 

 H the horizontal intensity of the uniform magnetic 

 field in which the needle moves ; 



then n H . *, 



(J = -p tan % approximately. 



Let Y be the difference of potentials maintained by the 

 battery at the points A and Bj then 



Y 



C = 



s+g r x + r 2 R sg 



s+g 

 n sV 



r x + r 2 (s+g)U + sg 



Let K be the capacity of the air-condenser in absolute elec- 

 tromagnetic units (gramme, centimetre, second); then if a 2 is 

 the angular swing produced by the discharge in the second 

 case, and P the periodic time in seconds of the needle swinging 

 freely, 



YK= Hj Sln 2 ; 



. Go 



... K= F n g - 



7r r 1 J tr 2 (s + g)H + sg tan% 



= I n + r,(«+yJB -+5 £k *W*™™^y, 

 a result quite independent of the electromotive force or resist- 

 ance of the battery. 



If a is the area of the lower plate of the condenser in square 

 centimetres, 

 t the distance in centimetres between the plates, 

 k the electrostatic capacity in absolute units (gramme, 

 centimetre, second), 

 A 



but 



k=v 2 K; 



V; 



A it i\ + r 2 (s + g)~R + sg M x 

 4nrt P r x s d 2 



d 2 is supposed to be the undamped deflection of the galvano- 

 meter ; but as there was always some slight damping even in 

 our ballistic galvanometer, the following correction must be 

 introduced : for cl 2 we must write (1 + \ \)d 2 , where X is the 

 logarithm to the base e, or 2*71828, of the decrement. 



