Mr. cavallo’s Experiments , 8cc. 
389 
Experiments on Mr. yolta’s plates , commonly called a 
machine for exhibiting perpetual eledlricity. 
THE following experiments, which fhew how both 
lides of an eleCtric plate are affeCted in different circum- 
ftances, w r ere principally made with a plate which mea- 
fured fix inches and a quarter in diameter, and which 
confifled of a circular piece of thick glafs coated on one 
lide with fealing-wax 1 ^. 
If, after having excited the fealing-wax, I lay the plate 
with the wax upon the table, and the glafs uppermoft, 
that is, contrary to the common method; then, on 
making the ufual experiment of putting the metal plate 
on it, and taking the fpark, &c. I obferve it to be attended 
with the contrary electricity ; that is, if I lay the metal 
plate upon the eledtric one, and, while in that fituation, 
touch it with an infulated body, that body acquires the 
(a) Having conftru&cd feveral of thofe plates, with a view to difcover which 
iubftance would anfwer the bed for coating the glafs plate, I obferved that the 
ealieft to be made, and the flrongeil in power, are thofe made of the fecond fort 
of fealing-wax. It is remarkable, that fometimes they will not adf well at iirfb, 
but they may be rendered very good by fcraping with the edge of a knife their 
Alining or gloffy- fur face. This feems analogous to the well-known property of 
glafs, which is, that new cylinders or globes made for eledlrical purpofes are 
often very bad electrics at firft, but that they improve by being worked, that is, 
by having their furface a little worn. 
pofitive 
