Page:Collected Physical Papers.djvu/320

300 positive or negative, are first obtained; after the addition of reagent both are found to exhibit either an increase or a diminution. As has been said before a very high external resistance, varying from 1 to 5 megohms, is interposed in the external circuit, the slight variation of internal resistance of the cell due to the addition of the reagent being thus rendered quite negligible compared with the total resistance of the circuit. That there is no appreciable variation in the total resistance can be independently verified by applying a known electromotive force before and after the addition of the reagent, when the resulting deflection is found to be the same in the two cases. The deflections are thus simply proportional to the responsive electromotive variations.

Chemical Excitants.—The following record (fig. 81)