43 6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



ing ratio" by von Bezold, while the quantity of aqueous vapor 

 contained in 1 kilogram of moist air is "the specific moisture." 



If the precipitation separates from the moist air at a definite 

 altitude then the weight of x kilograms of aqueous vapor diminishes 

 to a smaller quantity, f, which is then to be introduced into the subse- 

 quent computations as the appropriate quantity of moisture. 



If we have a mixture of gases then the total pressure of the mix- 

 ture is equal to the sum of the partial pressures of the components, 

 while the volume of the mixture is the same as the volume of each 

 separate gas, since each gas expands as though the others were not 

 present. 



In computations relative to these changes of condition moist 

 atmospheric air is to be considered as a mixture of air and aqueous 

 vapor so long as the condition of saturation is not attained. 



The pressure of the saturated aqueous vapor is a function of the 

 temperature only; its values have been determined experimentally 

 by Regnault and expressed in numerical tables. " Since the specific 

 weight of aqueous vapor is 0.804 therefore the relative weight of 

 this vapor with respect to the air is 



E = 0804 - 0.622* 

 1.293 



If R represents the gas constant for dry air, then the constant for 

 aqueous vapor is R. L = R/e. 



We shall now proceed to consider the individual stages of adia- 

 batic expansion of moist air. 



§3. THE DRY STAGE AND THE SATURATION POINT 



Let the volume of the mass of moist air containing 1 kilogram 

 of dry air and x kilograms of aqueous vapor be V cubic meters; 

 the general temperature of the mass of gas be T = 273 + t on the 

 absolute Centigrade scale; the partial pressure of the dry air be 

 p' and the partial pressure of the aqueous vapor p", therefore the 

 total pressure of both is p = p' + p"\ then according to the equa- 



*The value of R = 29.272. R, = 47.061. The ratio k = 1.4025 for dry- 

 air, and other physical constants, especially the revised values of vapor pres- 

 sure for water and ice, will be found in the last edition of the Smithsonian 

 Meteorological Tables. — C. A. 



