measuring Heights with the Barometer. 733 
it appears, that when the temperature of the air is 2 8°. 2, 
the ratio of its weight, with refpeft to that of quickfil- 
ver, is as 1 to 10552: hence the increafe of the weight 
of air, on every degree of difference of temperature be- 
tween 2-8°. 2 and 5 2°. 5, amounts to 34.4; and hence we 
have 5 2 0 .5-4°.2=4&°.3 for the temperature of the air 
in Britain, when its weight would be rn-jr of that of 
quickfilver ; and confequently agree with Mr. de lug’s, 
though the heat would differ from his 21 0 . It will no 
doubt be remarked, that the equation for the air, refult- 
ing from the operations of the barometer, falls fhort of 
that given by the manometer. Part of the difference, I 
apprehend, may arife from the fmall number of baro- 
metrical obfervations obtained in- extreme temperatures., 
I fhall, neverthelefs, adduce reafons hereafter for hippo- 
ling, that it really fhould diminifh, becaufe of the drier 
and lefs elaitic flate of the fuperior air, compared with 
that taken into the manometer at the earth’s furface. In 
the mean time, fihce both inftruments agree in the equa- 
tion for 5 2 0 , which is a heat that the barometer will very 
frequently be ufed in, itfeems beft to adhere to the mean 
manometrical refult 2.45, in fixing the zero of the fc'alej, 
which is obtained in the following manner. 
Divide the excefs or defect, expreffed in x oooth parts' 
of the logarithmic refult, by 2.45, the mean expanfion or 
air; 
