COMPARISON OF RESISTANCES. 



R being conjugate, the changes of resistance of the former could 

 have no influence on the current which traverses the second. 



If we wish to discuss the experiment more completely, we 

 need only retain the electromotive force E 6 in the general formulas ; 

 we have then 



and we get 



a 

 M 



[V ar~\ 

 PljrtJ' 



a = 



+ tf' 



(3 6 > (fl'^-Rr) 



a=E& ~^iN~ 



M 



tf ' 



P ^b 



MN 



According to the conventions as to the signs made above (937), 

 the currents in the different branches have the directions indicated 

 by the arrows in Fig. 188; the only ambiguity is as to the 

 current of the branch AD, the direction of which corresponds to 



the upper arrow or to the lower one, according as a'b^Rr, and 



it may happen that this branch is not traversed by any current. 



It will be seen that of changes its direction according as 

 r=0 or r=oo that is to say, when the key is opened or closed. 

 The current being modified in all the branches, except that of the 

 galvanometer, by the breaks in the bridge, the needle can only be 

 stationary provided the effects of induction are negligable or are 

 counteracted; we should then, in general, wait until it comes to 

 rest after each operation. 



The changes in the battery current may have the effect of 

 modifying the electromotive force E fc , which we have supposed to 

 be constant. On the other hand there is no object in endeavouring 

 to attenuate these variations, for on them the sensitiveness of the 

 method depends. 



