618 Mr. nairne’s Account of 
he had done. I therefore determined, for greater cer- 
tainty, to fee if the fault might not be in the gages; and 
for that purpofe I repeated the experiment with the 
fyphon-gage, and both the long and fhort barometer- 
gages, and found that the feveral degrees of exhauftion 
indicated by thefe, were very different from that which 
the pear-gage had indicated: no conclufion, therefore,, 
could be drawn from this experiment. 
I determined next to compare again this pear-gage 
with the long and fhort barometer-gages with all the ac- 
curacy I was matter of: and firft, left the tubes of thefe 
barometer-gages might not be perfectly clean and free 
from moifture, I had fome tubes made at the glafs houfe ;> 
and as foon as they were brought home, which was 
within an hour after they were made, two of them, which 
were of the fame fize, were filled with diftilled quickfil- 
ver; and then the quickfilver was carefully boiled in the 
tubes the whole length, which was about thirty-fix inches : 
I then cut off about fix inches from the fealed end of one 
of the tubes, and took care to keep it perfectly full of the 
boiled quickfilver; it was then inverted into a glafs cittern 
containing boiled quickfilver; and a piece of very thin 
ivory, about half an inch in length, with divifions on its 
edge, was- put over the tube, fo as to float on the fur face 
of 
