THE SMITHSONIAN INSTITUTION. 



389 



hence, 



e = E — E' =r 700. 



Here^ with a weaker current, the electro-motive opposing force ap- 

 peared sensibly less ; indeed, in this case it is less than the electro- 

 motive force of an element. 



For a battery of two elements tlie result was 



E =z 1G04. 

 After the insertion of the voltameter, 



E' = 984, 

 thus — 



e =z E — E' = 620. 



No claim to great accuracy is made for the numbers just given, but 

 that which is placed beyond doubt by them is what might have been 

 foreseen ; the electro-motive opposing force becomes gradually less 

 with the decrease of the strength of the current. Hence it is a func- 

 tion of the current, though the force of this function must be deter- 

 mined by more accurate experiments. 



That the magnitude of the electro-motive opposing force is depend- 

 ent on the strength of the current was first placed beyond doubt by 

 Poggendorff.— (P. A., LXI, 613.) Buff also (P. A., LXIII, 497) 

 found the electro-motive opposing force of a voltameter greater with the 

 current of three zinc and carbon elements than with that of only two ; 

 he found, moreover, the magnitude of the polari/.ation diminished by 

 the insertion of a greater length of wire in the closing arc. 



^'=- ^''' For the case in which the 



electrodes fill up the whole 

 section of a trough like that of 

 Fig. 27, the polarization ap- 

 peared somewhat greater, ac- 

 cording to Buff, when the de- 

 composing cell is less full. If 

 the electrodes are suspended in 

 the surrounding liquid, without 

 filling the whole section, the size 

 of the electrodes has no influence on the magnitude of the j)olari- 

 zation. 



§ 35. Numerical determination of polarization. — Lenz and Saweljev 

 have instituted a large series of experiments for determining galvanic 

 polarization in different cases. (Bull, de la Classe Phys. Math, de 

 I'acad. de Sci. de St. Peters, b. T. V., p. 1 ; P. A., LXVl'l, 497.) The 

 process which they used to determine the magnitude of polarization 

 in a decomposing cell was that of Wheatstone, viz: by determining 

 the electro-motive force of a battery, first with metallic closing con- 

 ductors, and afterwards with the decomposing cell inserted. The dif- 

 ference of these two numbers, gives the magnitude of the electro- 

 motive opposing force produced by the polarization in the decomposing 

 cell. 



The following example will explain the mode of observing. 



