424 MEASUREMENT OF ELECTROMOTIVE FORCES. 



from which is deduced 



R 



g 



Rf I+-1+* 



n 



If the ratio is itself very small, the two currents I and ^ are 



o 



sensibly equal; and unless the differences V and Vj, are extremely 

 small, which would represent a very special case, they are virtually 

 equal. 



1019. MEASUREMENT OF POLARIZATION. When a battery of 

 electromotive force <? and resistance r is closed by a circuit of 

 resistance /o, too weak for the polarization to attain its maximum 

 value, the new values e and r give a current of strength 



_ 

 " 



and the difference of potential V of the two poles is 



If the method of compensation (1012) be applied in the two 

 cases by joining each time one pole of the battery to the point A 

 (Fig. 205) and determining the position of the point C which 

 corresponds to no current in the galvanometer, we get the ratios 

 m Q and m of the differences of potential e Q and V to the electro- 

 motive force E of the principal battery. We shall thus have 



m 

 > 



an equation which gives the ratio of the electromotive force of the 

 polarized battery to its initial electromotive force.* 



* PAALZOW. Pogg. Ann., Vol. cxxxv., p. 326. 1868. 



