388 TENTH ANNUAL REPORT OF 



§ 34. Galvanic polarization varies ivith the magnitude of the force of 

 the current. — Many physicists, and among others Lenz, (Fog. Ann., 

 LIX, 234.) have expressed the opinion that the electro-motive opposing 

 force of a voltameter is independent of the strength of the current. 



In Daniell's memoir, mentioned above, (Pogg. Ann., LX, 387,) 

 this opinion is adopted, and the attempt is made to establish it by 

 a series of experiments with the voltameter. These measurements, 

 however, are not exact enough for this purpose. Wheatstone also 

 entertains this opinion, and is thereby led to a further false conclu- 

 sion. He determined the electro-motive force of a battery of three 

 Daniell's elements, then the electro-motive opposing force in a volta- 

 meter, which was inserted in the closing arc of the same battery. He 

 found 



E=:90 e=69. 



When batteries of four, five, and six elements were used, almost ex- 

 actly the same value tor e was found ; hence Wheatstone inferred 

 that the electro-motive opposing force may be considered as constant. 

 E is here the electro-motive force of three combined cups, consequently 



the electro-motive force of one cup is — - = 30, a value less than e. 



Wheatstone thinks that the phenomenon may be explained by sup- 

 posing that'a single element cannot effect the decomposition of water 

 in a voltameter. 



But tliis is erroneous. The electro-motive opposing force can never 

 become stronger than the original cause which produces it ; hence we 

 must suppose that the electro-motive oppposing force is dependent 

 upon the strength of the current. But then the current of a single 

 element can certainly decompose water, though at a very small rate. 

 For instance, when a voltameter was inserted in the closing arc of a 

 Daniell's element, its plates being about two square inches, 1 obtained 

 a very sensible development of gas. 



That the electro-motive opposing force in a voltameter actually de- 

 pends upon the strength of the current, appears very strikingly in a 

 series of experiments which I made for this purpose. As already 

 mentioned above, I found the electro-motive force of a battery of six 

 zinc and carbon elements to be — 



E =: 4422, 

 and the electro-motive opposing force, 



e = 1000. 



The electro-motive force of each single element was H^ = 737, 

 thus decidedly less than the electro-motive opposing force in the vol- 

 tameter. 



The electro-motive force of a battery of four such elements (zinc 

 and carbon) was next determined ; the result w^as 



E = 3124. 



After inserting the voltameter the electro-motive force was only 



El = 2427 ; 



