360 PROCEEDINGS OP THE AMERICAN ACADEMY 



^ __ HA£ 



~ m^/(G/+ ^ ifl^> + &c.) ^" ' 



since g^ = 21, m g^' = M, and 



If the needle is at the centre of the coil z =^ y, x =z 0, and equa- 

 tions [XXI. A] become, if n equal the number of windings, 



r I — i^ /^i j_ A I: _ ^ ^"l . 



""^ — y 1,' "^ 12 y-^ 8 3/^ ' 

 C,' = ; 



' ~ y^V~^~2 y'^ 8 2/M ' 

 G*/ = 0. 



If we had but one turn, [XXXL] would become 

 C = -^ tan 0, 

 the ordinary equation for a galvanometer. 



