554 



PROCEEDINGS OF THE AMERICAN ACADEMY 



ing temperature in these to a minimum). The binding posts, etc., 

 should also be protected against temperature changes. 



In order to prevent gross variations in the electric current from 

 variations in the battery, which might vitiate the results slightly by 

 affecting the differential current, there is introduced in the circuit 

 leading to the Wheatstone's Bridge, W, a shunted galvanometer, cf, 

 whose deflection indicates the amount of current passing through the 



FiGUEE 3. 



latter. This can be varied within certain limits by altering the resist- 

 ance of a battery shunt, R (see Fig. 3). Knowing this current, we 

 can easily compute the differential current flowing through the sensitive 

 "bridge" galvanometer, for any given change in either arm of the 

 bridge, by using the following approximate formula : — 



Designating by a Resistance of one arm of Wheatstone's Bridge. 

 „ na „ other „ „ 



(n being in practice very slightly greater than unity.) 

 „ X Resistance of each of the other arms. 



„ g „ galvanometer. 



„ b „ one cell of battery (resistance of line 



wire neglected). 

 „ £1 The electromotive force of one cell. 



„ c „ differential current. 



"We find for the value of the current produced in the galvanometer 

 through the bridge, in terras of the whole current C (making n = 1 

 in the denominator), — 



