30 



Meteorological Observations on Parisnath Hill. [No. 1 



With the tensions obtained on the third I have computed the 

 values of S for air mixed with vapour, at the respective hours. 

 Adapting the formula for that purpose, and taking 0.622 as the 

 specific gravity of vapour, that of air of the same temperature and 

 pressure being unity, it becomes 



S = A -J— (b — 0.378 el 

 a-f t I J 



where e stands for the mean tension of vapour between the two 

 stations. The values for e were obtained by taking the arithmeti- 

 cal means of the tensions observed at the corresponding hours on 

 the hill and at Calcutta. (Mean tension, Table VIII.) 



An error of 0.04 or 0.05 inches in the value of e would produce a 

 difference of about 0.003 inches in the resulting weight ; but in the 

 opposite direction to that of the error in the moisture. 



Table IX. of barometrical differences for moist air on the 3rd. 



Time. 



S. 



S. 



Deviation or 





Observed. 



Calculated. 



error. 



9 A. M. 



3.876 



3.873 



— 0.003 



10h. 10m. 



3.873 



3.869 



— 0.004 



2 



3.837 



3.836 



— 0.001 



3 



3.839 



3.838 



— 0.001 



4 



3 843 



3.838 



— 0.005 



5 



3.844 



3.840 



— 0.004 



6 



3.846 



3.842 



— 0.004 



Average, . , 







— 003 



The computed values of S are now closely approaching the 

 observed values. The small differences still remaining are easily ac- 

 counted for by the probable errors in the height and in the tensions 

 of moisture. A series of experiments which I made for comparing 

 the indications of the wet bulb, at temperatures from 28o to 31°, 

 and with tensions from 0.3 to 0.8 inches, with those of Eegnault's 

 Dew point apparatus gave this result : the tensions obtained by 

 August's formula were always higher than those derived from the 

 direct observation of the Dew point. The difference was on an 

 average 0.05 inches and varied from 0.006 to 0.08 inches. It 

 was smallest with lower tensions and increased as they became 

 greater. Kegnault's formula gave still greater differences. 



