<5 9 a Col. roy’s Experiments for 
ice. If the barometer had not altered between the be- 
ginning and end of the experiment, the quicklilver al- 
ways became ftationary at or near the fir ft mark. If any 
fudden change had taken place in the weight of the at- 
mofphere during that interval, the fame was noted, and 
allowance made for it in afterwards proportioning the- 
fpaces.. 
Long tubes, with bores truly cylindrical or of any 
uniform figure, are fcarcely ever met with. Such how- 
ever, as were ufed in thefe. experiments, generally tapered 
in a pretty regular manner from one end to the other. 
When the bulb was downwards, and the tube narrowed 
that way, the column of quicklilver confining the air 
lengthened in the lower half of the fcale, and aug- 
mented the prefiure above the mean. In the upper half, 
the column being fhortened, the preflure was diminifhed 
below the mean. In this cafe, the obferved fpaces both 
ways from the center, were diminifhed in the inverfe 
ratio of the heights of the barometer at eachfpace, com- 
pared with its mean height. If the bore widened to- 
wards the bulb when downwards, the obferved fpaces, 
each way from the center, were augmented in the fame 
inverfe ratio; but in the experiments on air lefs denfe 
than the atmofphere, the bulb being upwards, the fame 
equation was applied with contrary ligns : and if any 
& extra- 
