96 Traces of Unity in the Various 



Grove himself, lies through an experiment of M. 

 Karstan, which is this. A coin is placed on a pack of 

 thin plates of glass and then electrified. On removing 

 the coin, and breathing on the glass plate, an impres- 

 sion of the coin, which cannot be removed by polishing, 

 is perceptible. And this is not all : for, on separating 

 carefully the glass plates, images of the coin may be 

 developed (by breathing it is to be presumed) on each of 

 the surfaces of each one of them a proof that a mole- 

 cular change has been transmitted through the substance 

 of the glass, and a reason for supposing that a piece of 

 glass or other dielectric body, if it could be split up 

 while under the influence of electric induction, would 

 exhibit some molecular change at each side of each 

 lamina, however minute the subdivision. The spark, or 

 brush, or voltaic arc, also points, with not less certainty, 

 to a change in ponderable matter in connection with 

 the electrical phenomenon. The colour of the light, 

 and the lines in the spectrum, show that the material of 

 the electrodes, or that between the electrodes, one or both, 

 is mixed up in the phenomenon ; and other considera- 

 tions make it certain that this light is more than that 7 of 

 combustion. If it were only due to the latter cause it 

 could not happen, as it does do, in vacuo. In point of 

 fact the material of the electrode is volatilized. Thus : 

 " If a voltaic discharge be taken between zinc terminals 

 in an exhausted receiver, a fine black powder of zinc is 

 deposited on the side of the receiver : this can be col- 

 lected and takes fire readily in the air by being touched 

 with a lighted match or ignited wire, instantly burning 

 into white oxide of zinc. To an ordinary observer the 

 zinc would seem to be burned twice first in the re- 

 ceiver where the phenomenon presents all the appearance 

 of combustion, and secondly in the real combustion in 



