RESISTANCE OF A BATTERY. MANGE'S METHOD. 



359 



The variation of resistance necessary to produce an appreciable 

 change in the intensity of the current is determined experimentally. 



Another defect of the method in the case of the resistance of 

 an element, is that delicate galvanometers cannot be used unless 

 they are shunted on the diagonal R. 



963. Professor Lodge* gets rid of part of the inconveniences 

 of Mance's method by inserting a condenser Q in the galvano- 

 meter circuit (Fig. 189). This arrangement amounts to making 

 R = oo and therefore 1 = 0. 



As soon as the condition of equilibrium of the bridge is 

 satisfied, the two diagonals are conjugate; the changes in resistance 

 in one of them CD, are without effect on the difference of 

 potential at the ends A and B of the second, and therefore on 

 the charge of the condenser. The needle of the galvanometer 



Fig. 189. 



remains therefore at zero when the key is worked ; but it is 

 necessary, this time, that the effects of induction be entirely 

 eliminated, for no permanent deflection is observed. 

 The general equations give then 



-E, 



IT 



* LODGE. Phil. Mag. [5], Vol. in., p. 515. 1877. 



