ON GALVANIC PHENOMENA. 273 



*' that the tinfoil of the electrometer was connected with the 

 ** Earth, while the copper plate, the wire, and the gold leaves, 

 *' were insulated, 1 brought, by means of an insulating 

 " handle, a zinc plate also of 5 inches in diameter, into contact 

 f* with the copper plate on the electrometer ; there was no 

 " visible divergence in the gold leaves* On separating the 

 "metals, the gold leaves immediately diverged. On again 

 " bringing them into contact, if the charge of the zinc plate 

 " had not been removed, the leaves returned to their natural 

 '* position. On again separating the plates, the divergence 

 ** took place as before. .. .If the charge of the zinc plate 

 *' had been removed after the separation, the second contact 

 " did not reduce the gold leaves to their natural state, but 

 *' left a slight divergence in them ; and when the plates 

 ** were again separated^ they diverged in a greater degree 

 '* than after the preceding separation.— Not, however* be- 

 ** yond certain limits, which apparently varied according to 

 " the state of the atmosphere as to moisture." This cause 

 of anomaly is possible, but very probably some other extra- 

 neous cause interfered in Dr. Maycock's operations; else 

 one single contact and separation of his plates could not have 

 produced a sensible divergence of the gold leaves. This is 

 an interesting object, which lam going to explain. 



Mr. Haiiy, the celebrated mathematician and experi- Hatty's expert- 

 mental philosopher* is the first who has proved, that, in the men t 3l ke first, 

 contact of zinc and silver (or copper), the former became 

 positive and the latter negative: but from the account I have 

 had of his experiments, it required about 10 repetitions of 

 the operation, applied to a condenser, to make it sensible to 

 the gold leaves. 



It is probable that Dr. Maycock has not had the oppor- These verified 

 tUnity of being acquainted with these first and original ex- bv the author, 

 periments, else he would have found that they contradicted 

 the results of his own : but, sir* he might have seen in 

 pages 26l and 262 of my paper in your Journal for August 

 1810, that I have repeated them with insulated plates of 

 zinc and silver 4 inches in diameter, and verified both parts 

 of their result. My first view was to ascertain the effect of 

 the contact of the two metals on their respective electrical 

 states ; an effect which appeared contradictory to my ob- 



Vol. XXXII, August, 1812. U servation. 



