lvi INTRODUCTION. 



water vapor tabulated by Marks & Davis l from the most recent determina- 

 tions of the specific volume of water vapor. However, owing to the paucity 

 of data, and its inaccuracy for the range of atmospheric temperatures and 

 conditions, the values derived from densities given by Marks and Davis 

 between io° and 50 are probably too low and require revision. The basis on 

 which this assertion is made is the generalization that the theoretical value 

 0.6221 is probably a minimum specific gravity towards which actual values 

 asymptotically tend at low temperature and low relative humidity in the 

 meteorological sense, or high super heats in the steam engineering sense. 

 This generalization affords a very helpful "control" in harmonizing and 

 combining experimental determinations of specific volume. It was thus 

 employed in a recomputation, from the original experimental data on speci- 

 fic volumes, of the accompanying table of specific gravities, 8, of saturated 

 water vapor. 



a is the weight of a cubic meter of dry air (free from carbonic acid) 



at temperature o°C, and pressure of 760 millimeters of mercury 



of standard density under standard gravity: a - 1.29278 kg. 



(Bureau International des Poids et Mesures: Travaux et Memoires, 



t. I, p. A 54.) 



5 is the density of aqueous vapor relative to dry air: 8 = 0.6221. 



While, as stated above, there is reason for believing that this value is too 



low, for atmospheric temperatures the error is less than one per cent. For 



practical work in meteorology and at moderate temperatures, it seems best 



to retain the theoretical value until the actual value has been determined 



1 Marks, Lionel S., and Davis, Harvey N. Tables and diagrams of the thermal properties 

 of saturated and superheated steam. New York, 1909. 



