S80 TENTH ANNUAL REPORT OF 



A voltameter was tlien inserted. Without any "urtlier addition, the 

 deflection was 



31°. 8. 



Wlien an iron wire, whose resistance was equal to 49 metres of the 

 standard wire, was inserted in addition, the deflection was 



20°. 6; 

 conseciucntlj'' 



E' = 3320. 



After exchanging this iron wire for the ahove mentioned hrass wire, 

 (= 29.2 metres of standard wire,) the result was 



E = 3520, 

 and the mean 



E' =z 3420. 



Tliese experiments show clearly that the electro-motive force is di- 

 minished by inserting the voltameter, and diminished not a little ; 

 for A\e have 



e=E — E' = 1000. 



Hence, if a decomposing cell he introduced in the circuit, two causes 

 come into action diminishing the strength of the current — fi^'st, the 

 electro-mo tive force, which sets the current in motion, is diminished ; 

 and second, the resistance is ^'ncreased. The strength of the current 

 in this case is to he computed hy the formula 



Daniell was the first, to my knowledge, who proved the existence of 

 galvanic polarization, simply hy using Ohm's law, (Philos. Trans. ^ 

 1842, Ft. II, Pogg. Arn., LX, 387,) and he did it in a very ingenious 

 way, without using any other instrument than the voj^ameter itself. 

 An instrument of this kind was inserted in the closing arc of a hat- 

 Fi-, on tery of 5 D.aiiell ele- f\-.^x 



ments r>s sho»vn in Eig. 

 ^ — " — -V. 22 ; 6 cubic ir'ches of 

 N»-9-o-»-V deionauing gas were 

 evolved in 5 minutes. 

 If there was no electro- 

 motive opposing force 

 present, the same voltameter, placed in the closing arc of 10 double 

 elements, sbonld yield double the quantity of gas in the same time ; 

 for in the first case the strength of the current was ' 



5E ^ 



in the second, 



10 E 10 E 



y R + r 5 Pt + r' 

 hence in th'^ hast case we should obtain 12 cubic inches of gas in five 

 minutes. The experiment, however, did not give 12, but 20 cubic 



