620 Mr. nairne’s Account of 
and its height from the furface of the quickfilver in the 
ciftern meafured thirty inches; which agreed exadfly 
with an open ciftern-barometer I had in the room. The 
quickfilver in the tube of this barometer was alfo boiled, 
and the meafure the fame. 
The quickfilver was then emptied out of this long 
tube, and the fealed end being cut off, it was then ce- 
mented to a piece of brafs,by which means it was fcrewed 
to the air-pump; and the lower end being immerfed in a 
cup of boiled quickfilver, it then made that kind of gage 
where the air is taken from the top of the tube, and 
which is called the long barometer-gage. This gage 
being fixed to the pump, and the fhort barometer-gage 
put on the plate of the pump under a receiver, the re- 
ceiver was cemented to the plate of the pump, and the 
pump worked for ten minutes as before. The quickfil- 
ver in the fhort barometer-gage fell now nearly to within 
one-twentieth or five hundredth parts of an inch of that 
in the ciftern, and the quickfilver in the long gage rofe 
nearly to within a twentieth or five hundredth parts of an 
inch of the height it was at when it was made as a com- 
mon barometer. 
Gages made with thefe precautions feem to me to be 
the moil to be depended upon, in determining the actual: 
diminution. 
