CLOSED BATTERY. 421 



The difference E - E represents the electromotive force of 

 polarization. If the polarization is independent of the current, 

 when this is beyond a certain limit, a series of equations will be 

 obtained, by varying the interpolar resistance, such that 



which give 



_ lr-l'r' Ir-Yr 



JX = 



I' - 1 I" - 1 



The identity of the different values thus obtained will serve as 

 a verification of the hypothesis of the constancy of the polarization. 

 When only two electromotive forces E and E-^ are to be compared, 

 we proceed in like manner for each of them, and we have 



If the resistances are adjusted so that the intensities are the 

 same in the two cases, the formula reduces to 



V 



the ratio of the electromotive forces only depends on the ratio of 

 the variations of resistances, and the galvanometer need not even 

 be graduated. This latter method was used by Wheatstone. 



1016. The following method, indicated by Poggendorff,* leads 

 to the same results in a more direct way. The two couples 

 E and E' (Fig. 208) are placed in the same circuit in such a 

 manner that their electromotive forces add themselves, and a 

 shunt AB is introduced between them containing a galvanometer. 

 The point A being arbitrary, the point B is displaced or the re- 

 sistances modified so that there is no current in the shunt. The 

 resistances R and R', of two portions AEB, AE'B of the total 

 circuit, are then as the electromotive forces (982). 



* See BOSSCHA. Pogg. Ann., Vol. xcvu., p. 172. 1851. 



