216 G. Th. Fechner*s Justification of the Contact Theory. 



tioned the development of electricity between gold and silver, 

 which may be demonstrated in a weak degree even without 

 a condenser. If, indeed, De la Rive even in all these cases 

 supposes (supponirt) a chemical action, I have only to observe, 

 that it must also be allowed me to suppose in all cases an 

 electrical action, where it cannot be demonstrated, where 

 further it agrees better with the contact theory. 



6. Biot long ago convinced himself that piles constructed 

 of an equal number of pairs of plates, with fluids of very dif- 

 ferent chemical action, as water, solution of common salt, of 

 sal ammonia, of chloride of potassium, of sulphate of iron, in- 

 dicated at the electrometer the same intensity of the poles. 

 If other fluids, such as solution of soda, showed exceptions 

 (which become explicable according to the theory of contact 

 by a change of the metallic surface), these are certainly not 

 of the kind that can speak in favour of the chemical theory. 

 De la Rive himself performed similar experiments {Recherch., 

 p. 142) and found that piles constructed of an equal number 

 of plates with river water, solution of Glauber's salts and greatly 

 diluted nitric acid, indicated an equal power of electricity at 

 the insulated pole, where (as was also the case in Biot's ex- 

 periments) the other pole stood in connexion with the ground ; 

 if on the other hand both poles are insulated, a difference 

 occurs, and the diluted nitric acid gives the weakest, often 

 quite imperceptible electrical signs. 



In order now to explain the equality of power, (for the first 

 appearance is evidently opposed to the chemical theory) by 

 construction of the pile with different fluids (in the case of 

 non-insulation) De la Rive supposes that there is, it is true, 

 more electricity developed by the liquids which attack more 

 strongly, but that always one part of the developed opposite 

 electricities reunites even through the members of the pile. 

 But since fluids of stronger chemical action possess in general 

 also a better conducting power, they would allow of a quicker 

 reunion, and with this would be explained how the free portion 

 of electricity is not stronger with them than with fluids which 

 act less powerfully. Disregarding however other objections 

 which might easily be raised against this view, it were yet 

 very curious, if this compensation in the various fluids should 

 amount exactly to the equality of the actions, and the more 

 so, since the conducting power of the fluid members of the 

 pile also depends in some degree on their dimensions ; conse- 

 quently the compensation could only be exact with one single 

 thickness of the fluid layers. With the theory of contact the 

 equality of the intensity of non- insulated piles in the con- 

 struction with various fluids (in so far as they do not charge 



