fame 'Experiments made with an Air-pump. 617 
to hold the quickfilver for it, was put under a receiver; 
which receiver was placed on a leather foaked in oil and 
tallow, on the plate of the pump. 
I muft obferve here, that the foot of the glafs cup, 
which held the quickfilver for the pear-gage, being 
broken off by an accident, another foot, made of a piece 
of box-wood, was cemented to it. The reafon of men- 
tioning this circumftance, which may feem trifling, will 
appear in the fixth experiment. The pump was then 
worked, and the pear-gage was pufhed down till its 
open end was immerfed in the quickfilver in the cup : 
the air being then let into the receiver, it forced the 
quickfilver into the gage till it was filled within a 4000th 
part of the whole, fo that by this gage the pump ap- 
peared to have expanded the air 4000 times. To what 
it might be owing that this pump, which was on Mr. 
smeaton’s principle, fhould expand the air 4000 times 
inftead of only iooq as Mr. smeaton’s, I could not even 
furmife. 
Having the pleafure of knowing Mr. smeaton, and 
being well acquainted with his great abilities in practice 
as well as theory, I could not imagine that this apparent 
fuperiority could proceed from our having executed the 
various parts of the pump in a more perfect manner than 
Vol. LXVII. 4 L he 
