( 293 ) 
ON THE 
‘ THEORIES 
OF THE 
EXCITEMENT 
GALVANIC ELECTRICITY ; 
BY 
WILLIAM HENRY, M.D.F.R.S, &c. 
~<<<@>>>- 
| Severat theories have been framed to 
account for the origin of the electricity, which 
is excited by the Galvanic pile, and by simi- 
lar arrangements. Of these, the first in the 
order of time was proposed by the distin- 
guished philosopher* to whom we are in- 
debted for some of the earliest, and therefore 
the most difficult, steps in this department of 
science. The hypothesis was suggested by a 
fact, which may be considered, indeed, as 
fundamental to it. It had been observed by 
Mr. Bennett, so long ago as the year 1788, 
and afterwards confirmed by Volta himself, 
that electricity is excited by the simple appo- 
sition of different kinds of metals. The best 
way of exhibiting this fact is to take two discs 
or plates, the one of copper, the other of zinc; 
* Signor Volta, in Nicholson’s Journal, 8yo. i. 1335, 
