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the denfity at the level of the fea, in the tempera- 
ture 40 n, and height of the barometer, P -4- - P. 
Then the difference between A and D, or A — D,, 
will be D X — — rr- Where obferve, that b is 
pofitive or negative, according as n is pofitive or 
negative. 
By this problem, the denfities of the air at a given 
height, in different temperatures, are to be compared 
with each other. Even good writers have hitherto 
been generally run away with by a notion, that the 
air’s denfity, at a given elevation, at different times,, 
would be always truly meafured by the length of 
the mercurial column ; than which nothing can be 
more erroneous, as hath been at large explained 
in the 4th fed ion. 
PROBLEM FIFTH, 
The height of the quickflver in the Torricellian 
tube , and the temperature of the air being given , at 
a given elevation , above the level of the Jea, to com- 
pare the denfity of the air with that of the quick/ilver , 
at the time and place of obfervation , 
L ET TA reprefent the femi-diameter of the 
earth 5 T being the center, and A at the furface. 
Let B be a place at a given height, AB, above the 
furface. Let CD be the obferved length of the 
quicktiiver in the Torricellian tube, at the place B, 
in a given temperature of the air. It is required to 
find 
