HISTORY OF GALVANISM. 37 



affected, but the zinc begins to decompose the 

 water, and to evolve hydrogen. If the plates be 

 now placed in contact, the silver discharges hy- 

 drogen, and the zinc continues, as before, to be dis- 

 solved. From these, and other analogous facts, Electricity 

 he concludes, that whenever a metal is dissolved 

 by an acid, electricity is disengaged. He extends 

 this principle to the action of the electrical ma- 

 chine, which he conceives has its power increased 

 by applying an amalgam to the cushion, into the 

 composition of which a metal enters which is rea- 

 dily oxidated. As a further illustration of the same 

 principle, he found the machine will not act when 

 immersed in carbonic acid gas. 



Nicholson had already suggested the opinion, Electricity 

 that the electricity of the pile differs from that " n f 

 of the machine, in consequence of the latter being 



in a state of higher intensity, but in less quantity ; tie intcnsi- 

 the former of course being in greater quantity, but 

 of low intensity. Dr. Wollaston coincided in 

 this idea, and supposed that it might explain the 

 difference between the operation of the two in- 

 struments. It had been long known that water 

 might be decomposed by the electric shock, but 

 v the effect differs from that of the pile, the two 

 gases being separated promiscuously from both 

 ends of the wire, not, as when the pile is employed, 

 the oxygen from one end, and the hydrogen from 

 the other. But Dr. Wollaston succeeded in pro- 

 ducing the galvanic effect on water by common 

 electricity, so as to keep the gases separate This 



