344 COMPARISON OF RESISTANCES. 



When the diagonal r is open, or r=oo, this expression becomes 



I I 



+ 



a + b a' + V 



which was evident. 



The resistance p has still the same value when the bridge is 

 in equilibrium, the diagonals r and R being conjugate, for the 

 current is then null and the resistance r does not come into the 

 equations. 



948. If we indicate by the index zero the values corresponding 

 to the equilibrium of the bridge, and putting for brevity 



we have 



a + a a 



from this follows 



(22) *.< 



a = = E-, 



949. Suppose now that there are electromotive forces in all 

 the branches, but that the diagonals R and r are conjugate; we 

 may put 



Equations (20), or the sums of equations (21) relative to all 

 the electromotive forces considered separately, give then, if we 



