354 COMPARISON OF RESISTANCES. 



ACB and ADB arranged in parallel, and for the galvanometer that 

 of the two branches CAD and CDB. 



The conditions of maximum sensitiveness relative to the battery 

 and the galvanometer are then 



ii i 



+ 



R a + b a' 

 T i 



_ _ __ i __ 

 r a + a! b + b' 1 



or, allowing for the condition of equilibrium, 



(34) 



b + b' 



it follows that 



(35) Rr = ab' = ba'. 



All the branches are then conjugate in pairs. 



If we wish to satisfy at the same time all conditions of the 

 maximum, both for the battery and galvanometer, as well as for 

 the branches of the bridge, equations (32), (33), and (35) give 



or 



from this follows 



a a' = b = b' = 



that is to say, that the four branches of the bridge are equal. 

 Equations (34) give also 



the six resistances are then equal to each other. 



960. USE OF THE ELECTROMETER OR ELECTRODYNAMOMETER. 

 The electrometer might be substituted for the galvanometer in 

 using Wheatstone's bridge. The needle should remain at zero 



