228 Mr Anderson's Corrections for the Effects of Humidity 
tion is 41°, whereas that of the moistened thermometer was 
Sir- 
According to my formula, the greatest difference that can take 
place between a dry and moistened thermometer, will evidently 
be when f— o. In this case F 
. . 1080 F 
180 
ih 
from which we de- 
rive 
inches, # —■ 
30 + 1 .572 
Hence, in air absolutely dry at the tempera- 
ve, when the barometer stands at 30 
~ 17°. 9, being the greatest possible 
6 + 8F 
ture of 60°, we should have, when the barometer stands at 30 
1080 x *524 _ 
depression of the moistened thermometer that can occur when 
the temperature of the air is 60°, and barometrical pressure 30 
inches. 
Having thus furnished a simple and accurate method of de- 
termining the elasticity of atmospheric vapour, I now resume the 
consideration of the corrections which I proposed to apply to the 
barometrical formula, for the measurement of heights. The 
first correction I noticed, had for its object to reduce the pres- 
sures at the two stations, to what they would be, if no vapour 
were present, and then to apply a coefficient, adapted to the ex- 
pansion of dry air, viz. 1 -f *002086 — 32^ ? instead of 
the one commonly employed, 1 -f *00244 — 82 V By 
this mode of proceeding, the pressure of the vapour being dis- 
engaged from that of the dry air, the geometrical progression, 
which only applies to the latter, will be restored to the strata of 
the aerial columns, and a corresponding coefficient for the devi- 
ation from the standard temperature, introduced into the for- 
mula. Let f therefore, denote the elastic force of vapour at the 
lower station* where the pressure is h ; andjf' that at the higher, 
where the pressure, corrected for temperature, is / 3 . Since the 
weight of vapour is to that of dry air, under the same pressure 
as 5° to 8°, the weight of a certain volume of vapour will be to 
that of an equal volume of air, at the lower station, as — fto b . 
o 
This relation would hold through the whole length of the at- 
mospherical column, if the moduli of the vaporous and aerial 
