in Eleffricity. 665 
a great deal of alkaline fait, is very apt to attract raoif- 
ture from the air, and therefore lefs proper for electri- 
city (which defedt they thought might be corredled by 
expo ling it to a violent and continued heat), took a pro- 
per advantage of this knowledge in the improvement of 
the machines with flat glades. He found, that glafles, 
which have been many years expofed to the warm air of 
a room, very old looking glafles for inftance, become 
by this means much harder, fo as better to refill the 
force of a file ; and are then much better for electrical 
machines: and that fuch glafles become ftill incompara- 
bly better, if they are expofed to a confiderable degree of 
heat during fome months : the heat forcing out of the 
glafs (at leafl: out of its furface) the alkaline fait, not vi- 
trified, which is to be found upon it, and may be known 
by the tafte. 
In December 1777 I faw one of thefe double-plated 
machines at Mr. cuyper’s houfe, and found it do admi- 
rably well, though the weather was at the time very 
damp, and the machine kept in a room in which there 
never was any fire made, and though the culhions had 
no amalgama upon them: they were made of yellow 
Turkifh leather, fluffed with fine lhavings of cork, ram- 
med in them ; and had been, prefled to give them . an 
equal frnooth furface. 
The 
