HISTORY OF GALVANISM. 99 



contained only -^ part of sulphuric acid, a platina 

 wire of 3 ' of an inch in diameter, and from 

 ^ to -jV of an mcn m length was readily fused.* 

 In the formation of his minute apparatus, this sa- 

 gacious experimentalist made an observation of 

 great importance in enabling us to produce as 

 much effect as possible from the smaUest quantity 

 of materials. He remarks that the zinc plate 

 should have a counterpart of copper opposed to 

 each side of it ; for in the usual arrangement, 

 although both sides of the zinc are oxidated, that 

 side only is efficient which has a copper surface 

 opposed to it. 



This principle, which Dr. Wollaston had used children's 

 with so much success in his elementary battery, tery. 

 was applied by Mr. Children with proportionate 

 success, to the formation of the most powerful 

 galvanic instrument which has hitherto been con- 

 structed. The plates were six feet long by two 

 feet eight inches, so as to present 32! square feet 

 of surface ; each zinc plate was supended between 

 two copper plates, and they were connected to- 

 gether by lead. Each of these sets or triads of 

 plates was immersed in the separate cell of a trough, 

 which was filled with a properly diluted mixture of 

 the sulphuric and nitric acids, and the plates were 

 all attached to a beam, and so adapted to a coun- 

 terpoise as that they could be readily lifted up 

 out of the trough and again immersed in it at 



* Ann. of Philosophy, vi. 209. 

 H 2 



