330 Prof. A. Anderson on 



terminals of the galvanometer, and p, q, and s are mercury- 

 cups connected respectively with A, C, and B. A rocking- 

 key can simultaneously connect Gj with p and G 2 with q, or 

 G x with r and G 2 with s, the galvanometer heing in the 

 former case in the branch AG and in the latter in BD, in 

 series with the condenser. The branches AB AD are equal 

 inductionless resistances, and DC, which is also inductionless, 

 is adjusted till as perfect a balance as possible is obtained. 

 When the battery- circuit is made or broken, the galva- 

 nometer being in the branch AC, there is a throw of the 

 needle due to the passage through this branch of a quantity 



of electricity equal to L( -=- -J , where L denotes the coefficient 



of self-induction of E, and c the current in the galvanometer, 

 when an additional resistance x is put in the branch BC. 

 The current c is equal to Ebx/A, E being the E.M.F. of the 

 battery, and A the determinant 



a + 2B, + x, — K— x, — R 



— R— x, b + Gt+~R+x, — G 

 -R, -G, 6 + G + R 



in which a is the resistance of the battery, R of the coil, and 

 G of the galvanameter. Since 



/dc\ _ (W> \ 



we easily find 



fdc\ _ M 



\dx) x=0 " (b + 2G + R) [a(b + R) + 26R]' 



and therefore the quantity of electricity is 



LE6 



(b + 2G + R) [a(b + R) + 26R] * 



If, by means of the rocking-key, the galvanometer be put 

 in BD, and the battery-circuit made or broken as before, a 

 quantity of electricity will pass through the galvanometer 

 equal to K(Y 1 — V 2 ), where K is the capacity of the condenser 

 and Vi— V 2 the final difference of potential between the 

 points B and D. If the capacity K be adjusted till the 

 throw of the needle is the same as before, we have 



L = K Vl ^ Vg - ( J> + 2G + R) [a (h + R) + 2 AR] , 



