35 COMPARISON OF RESISTANCES. 



955. When near equilibrium,* the current *", which corresponds 

 to an error e in the value of ^', is expressed by 



,-Ef, 



We may replace A by the value A , corresponding to the equili- 

 brium of the bridge (928), which gives 



Eliminating the resistance a' from the expression of A by the con- 

 dition of equilibrium, we have 



if we put 



the value of K may be written 



ST V Sr 



(29) 



b b a 



The minimum of absolute error e is that value which corresponds 

 to the feeblest current /, which the galvanometer will measure. The 

 absolute error is then 



and the relative error 



representing by H the function . 



b 



956. It is interesting to investigate the conditions of adjustment 

 which correspond to the maximum sensitiveness. 



* See SCHWENDLER, Phil. Mag. [4], Vol. xxxi., 1866, and Vol. xxxin., 

 1867; HEAVISIDE, Phil. Mag. [4], Vol. XLV., p. 114, 1873; GRAY, Phil. Mag. 

 [5], Vol. XIL, p. 283, 1881. 



