126 



Specific Gravities of Aqueous Vapour^ SfC. 



[Jan. 



IX, — Table of the Specific Gravities of Aqueous Vapour, Dry Air, 

 and Saturated Air. — By Lieutenant Campbell, Assistant Surveyor 

 General. 



Daniel in his essay on the Hygrometer, at page 177 of his Essays, 

 has given a table of the specific gravity of air saturated with moisture, 

 but has incorrectly computed the expansion produced by the moisture 

 absorbed. Galbraith, at page 213 of his tables, gives a table of the 

 specific gravity of dry and saturated air, computed for Dalton's expan- 

 sion of air, and as I am not aware that a correct table on Gay Lussac's 

 expansion has been published, I have therefore re-computed Daniel's 

 table correctly. In Daniel's table the first column headed " Alteration 

 of volume from heat," the quantities given are, 



~ 480 



T being the temperature of the air. 



The second headed " Alteration of volume from vapour.'* 



30 



30 — FT 



FT being the elastic force at the temperature. 



The third headed " Increase of density from weight" is the speci- 

 fic gravity of aqueous vapour, and 



FT 



= 10.113 X 



448 -f T 



the specific gravity in the fourth volume is 



1 



z=i w 



I-{-yT-f?;V 



V T the alteration of volume for heat. 



V V the alteration of volume for vapour. 

 w the increase of density from weight. 



Thus the expansion of air from the freezing point to the given tern, 

 perature is made. 



