370 On the PROGRESS of HEAT, &e. 
. (b— bre)” 
3mr Log 6 ~ 
6— — * Log b, and therefore (§ 19.), 4” 
bz Log d 
ome r Jee abe 
3 mr Log b = amr? hence when z is very 
a 
Whe 
3mr° 
fmall, 4=T — 
22. THEREFORE when 2, or the height above the furface is 
fmall, ) diminifhes in the fame proportion that the height in- 
creafes, which is conformable to experience. 
2 ° 
In our climate, when. z= 280 feet, BOEVATEE bx 26 =1°; fo 
3mr 
that the co-efficient ame et = a and therefore 
z 
Fata PTS ess Te 
b=T 280° 
Wuen the conftant quantities are thus determined, the for- 
mula agrees nearly with obfervation. In the rule for barome- 
trical meafurements, it is implied, that the heat of the atmo- 
{phere decreafes uniformly; but the rate for each particular 
cafe is determined by actual obfervation, or by thermometers 
obferved at the top and bottom of the height to be meafured. 
XI. 
