70

direction, is lessened : and that it is in an electro-positive state.

When the copper disc of the Voltaic pair is to beexamined, the positions of the metals are to be re-versed ; and also the positions of the discs whichform the condensor. The manipulation is preciselythe same as in the other experiment, and the goldleaf indicates electro-negation. A more conclusiveexperiment than this cannot be made, to show thedifferent electric conditions of the external surfacesof the Voltaic discs, when their inner surfaces are inintimate contact with each other ; and from this factwe can easily understand, that any two metals simi-larly united, are, and must of necessity be, electro-polar. The polar condition is maintained when thetwo metals are soldered together ; and even one, andthe self same mass, of an individual metal, is electro-polar on its opposite surfaces, when not of the samedegree of polish or texture. But these nice pointsof electricity we cannot pursue any farther in thisplace, as our present business is to explain the natureof Galvanic action in the simplest and clearest man-ner that the subject seems to admit of.

Having satisfied ourselves of the electro-polarityof a combined pair of metallic plates, we have littlemore than the functions of the condenser to bear inmind, to enable us to trace the combined electricactions of a series of pairs of metals, from one end tothe other, however extensive the series might be.Let us suppose, for instance, that we first place apair of copper and zinc plates upon a sheet of glass,or other insulator, with the zinc uppermost. In thispair we have a positive pole above, and a negativepole below. If now any plate of metal rested onthree small dots of sealing wax over the zinc, thesetwo would form a condenser, whose action would beincreased by uninsulating the upper plate, and agreater facility afforded for accumulation of fluid onthe zinc surface. If now, instead of a single discof metal, we were to place upon the zinc another