MEMOIRS 



or THX 



HCtaratrg antr ^jaoso^piftwal Societg of 



I. — On the Separate Pressures of the Aqueom and the 

 Gaseous portions of the Atmosphere, 



By Mr. Alderman Hopkins. 



{Read October l^tk and November 2nd, 1852.] 



Meteorologists generally consider that it is desirable to 

 separate the whole of the pressure of the atmosphere on 

 the surface of the earth, into the two pressures of which 

 it is made up ; that is, the pressure of the gases, and 

 of the aqueous vapour that is diffused through them. To 

 accomplish this object, the dew-point or point of condensa- 

 tion of the vapour is found, each dew-point having a certain 

 amount of tension or expansive force, which causes the vapour 

 when it is at that point to press on the surface of the earth 

 or against a column of mercury, with the precise amount of 

 force due to that tension. And this pressure of the vapour 

 being subtracted from the total amount of atmospheric pres- 

 sure as ascertained by the barometer, leaves, it is said, that 

 which belongs to the gases alone. 



But the dew-point of vapour is found to be different at 

 different times, as well as in different places ; and the amount 

 of vapour pressure will consequently vary accordingly. Near 



B 



