G. Th. Fechner's Justification of the Contact Theory. 205 



long and half an inch wide, wetted with the solution under 

 examination previously acidified. Allow a portion of the paper 

 to project beyond the tube and secure it by inserting a cork. 

 Warm the bottom of the tube over a spirit-lamp. The action 

 of the gas on the solution is manifested by the change pro- 

 duced in the colour of the paper. As in Nos. 10 and 11, 

 Table I. you have only to distinguish between black and yel- 

 low, and in Nos. 14 — 17, between no change, black, yellow, 

 and orange, all of which are easily perceived upon white 

 paper, this method of testing accomplishes the object equally 

 as well as the more operose and disagreeable methods in com- 

 mon use. 



Glasgow, May 1, 1838. 



XXVII. Justification of the Contact Theory of Galvanism. 

 By G. Th. Fechner.* 



T^HE present memoir was already complete before I re- 

 ceived Pfaff's late work ^* Revision der Lehre vom Gal- 

 vano-Voltaismus" which has in general the same object in 

 view. As I find that Pfaff's experiments refer rather to other 

 points of the subject than to my own, I think that this paper 

 will not have been rendered superfluous by that work, but 

 that the one may serve as the completion of the other. 



The chief arguments which can with any appearance of 

 weight be brought to bear against the theory of contact, and 

 in favour of the chemical theory, have lately been brought 

 together by the zealous supporter of the latter, De la Rive, in 

 a separate work " Recherches sur la Cause de VElectr. Volt. 

 1 836." I shall chiefly refer to this, especially since the parti- 

 sans of the chemical theory rest principally on De la Rive's 

 experiments. Faraday's late experiments militate not so 

 much against the voltaic theory as (at least apparently so) 

 against a theory which seeks for the origin of electricity 

 solely in the contact of metals with each other, on which sub- 

 ject I shall at the conclusion have occasion to add a few 

 words. Moreover they have been, together with the experi- 

 ments of Karsten, which may be considered in the samfe light, 

 treated of in detail by Pfaff; I can therefore pass them over 

 at present. I have myself my own opinion on the subject, 

 which I would rather produce at another time and with experi- 

 ments, than at present with words. As to the following ex- 

 periments, I have frequently repeated and varied them, in order 

 to derive the expression from facts, not from accidents, from 



* From Poggendorff's Annalen, vol. xlii. p. 48). Translated by Mr. 

 W. Francis. 



