1886.] 



A Theory of Voltaic Action. 



311 



negatives this view. It was thought, however, the results might 

 throw light on questions as to the molecular nature of any electro- 

 chemical polarisation of the condensed films as a cause of the static 

 voltaic effect, and for that reason they are here shortly stated. The 

 condenser, fig. 3, was provided with a pair of zinc plates faced up 

 together. The difference of potential of their films after metallic 

 contact of the plates was tested qualitatively by a quadrant electro- 

 meter in the usual way. A very small value was found, due doubtless 

 to some slight difference in the state of their surfaces. The plates 

 were then separated to a small distance, and joined to the opposite 

 poles of a battery of 100 Daniell cells. After Vl\ days the battery 

 was removed, and the difference of potential of the films on the plates 

 again tested. It was supposed that if any greater oxidation of the 

 positively electrified plate, as compared with the other, was caused 

 by polarisation of the films, there would be a greater difference of 

 potential than before ; the film on the tarnished plate being negative. 

 If anything, the reverse was the case, but the effect was very slight, 

 and may have been due to some kind of storage cell action in the 

 supports of the plates. A second trial with the Daniell battery 

 joined the reverse way gave a like negative result. Probably the 

 effect suggested does not take place, or it is masked by local actions 

 in the film. 



34. An old experiment of Gassiot (' Phil. Mag.,' vol. 25, 1844, 

 p. 283), where electrical disturbance is produced by altering the capacity 

 of a Yolta condenser without contact between its copper and zinc 

 plates, which are merely connected to the gold disks of an electroscope, 

 is assumed by some authors (Yon Zahn, ' Untersuchungen fiber 

 Contactelectricitat,' p. 55 ; Wiedemann, ' Lehre von der Elektri- 

 citat,' vol. 2, p. 988) to be difficult or incapable of explanation by the 

 contact theory, though I think wrongly so, as there is contact of 

 dissimilar metals, viz., copper-gold and zinc-gold on the connexions 

 to the gold disks of the electroscope used. (Yon Zahn's inability to 

 repeat the experiment so as to get Gassiot's result seems to me 

 unaccountable.) 



35. In order to exclude any uncompensated contact of dissimilar 

 metals, as in Gassiot's experiment, I modified it by joining the copper 

 plate of the condenser, fig. 3, to the copper quadrant in the electro- 

 meter, fig. 1, and the zinc plate to the zinc quadrant. The latter 

 connexion was made by a copper wire, but the dissimilar contacts 

 thereby introduced compensate one another. 



On altering the capacity of the condenser a very decided alteration 

 of the potentials near the quadrants was observed. The following 

 table gives the results :— Column I gives the sign of the electrification 

 of the needle. II, the position of the index with condenser plates 

 apart. Ill, the point to which the index swings on closing them to 



vol, xli. y 



