OF ARTS AND SCIENCES. 141 



Equating the secoud members of (1) and (2) 



i:S= C,|^(r+ G)-lrB{S-\-r-\-G)'^ (3) 



When the battery shunt is removed, and a shunt put across the 

 terminals of the galvanometer, the whole current traversing the 

 circuit is 



Kirchoff's Laws give 



C = Ca-\- a and C^.G= Cg.G 

 therefore 



C = C, (^i^) (5) 



Equating the second members of (4) and (5) 



Ea= cJ^G<s^(r + B) {G-]-o)^ (6) 



Dividing (3) by (6) and cancelling, we have, since the current 

 passing through the galvanometer is the same in both cases, 



[f7(T + (r + i?) ( (? + o)-]S = \_S{r J^ G) -\- B{S -\- r Jr G)']a 

 or if 



(;._|_ G)8— G 



In practice, the terminals of r are connected to the galvanometer 

 and to the battery respectively by binding-screws with three wire 

 holes in each. One terminal of a Wheatstone's Rheostat is perma- 

 nently fastened to one pole of the battery, and the other terminal is 

 connected, first with the binding-screw on one side of r, and then with 

 that on the other side. The handle of the Rheostat is to be turned 

 until the galvanometer needle gives the same deflection in the second 



