378 G. Th. Fechner on the Contact Theory of Galvanism. 



wood. These signs of electricity were negative, when I held 

 between the fingers the brass point of that zinc plate, the other 

 end of which was fastened in the less moist part of the wood. 

 For the success of this experiment, it is necessary that the 

 wood be somewhat moist ; the moisture which it attracts from 

 the air is perfectly sufficient; care must also be taken that the 

 one end of the wood be kept drier than the other." 



The truth of the result of the following, certainly interest- 

 ing experiment, has been doubted, but it is certainly correct, 

 as I have often convinced myself by a frequent and more care- 

 ful repetition of it in the following easy manner. 



Upon the zinc surface of a soldered zinc and copper plate 

 were laid three or four equally large or somewhat larger leaves 

 of air-dried writing paper, the top one moistened with distilled 

 water, and upon this was placed, by the zinc surface, a 

 second soldered zinc and copper plate ; so that a system of 

 the following order was formed : copper, zinc, dry paper, 

 moist paper, zinc, copper. The zinc and copper were filed 

 quite bright, and I had convinced myself that if I tried the 

 system omitting the moist paper, at the copper condenser no 

 development of electricity could be detected. When, however, 

 I now applied the system with the inserted moist paper to the 

 condenser in such a manner that the double plate lying on the 

 moist paper came into connexion with it, while the other 

 double plate stood in connexion with the earth by means of 

 the fingers, either air-dried or sprinkled with distilled water, 

 there was obtained, in accordance with De la Rive, a negative 

 divergence, and a positive one on the contrary by reversion of 

 the system. The same phaenomena took place, if instead of 

 distilled water I employed water acidulated by nitric acid for 

 the purpose of moistening. 



These experiments I have also varied and simplified in the 

 following way: 



Between two zinc plates, without copper, were arranged 

 several layers of air-dried writing paper, and the one extreme 

 layer on which lay the zinc plate was moistened with distilled 

 or nitric-acid ulate water. Sometimes the zinc plate situated 

 on the dry, sometimes that situatedon the moist layer of paper 

 was put in connexion with a condenser of zinc. This expe- 

 riment, still more simplified, may be performed as follows : 

 let a zinc rod be wound round at one end with air-dried 

 blotting paper; at the other, with blotting paper which has 

 been moistened with spring or with distilled water. Accord- 

 ing now to the circumstance whether the dry or wet paper is 

 discharged at the (brass) condenser, while at the same time 

 the other paper is held with the fingers, do we obtain a posi- 



