24 Meteorological Observations on Parisnath Hill. [No. 1. 



the temperature changes from t' to t" and the pressure from b' to b", 

 is expressed by the following equation : 

 ?! _ q-f-t/ V' 



¥ ~ a + t"' b' 

 Where S' and S" stand for the weight of the same volume of air 

 at the respective temperatures t', \!' and under the pressure b', b''. 



The constant a == 272.85 ; - = 0.003665 being the increase in 



a 



volume of a quantity of air measured at 0° C. for every degree Centi- 

 grade above zero. 



This equation expresses at the same time the ratio of the variation 

 in the specific gravity of the air. 



Applying this equation to the present case, we find that the 



b" 

 factor — , within a period of 24 hours, changes in narrower limits 

 b 



a -f t" 

 than the factor r , which is dependent on the hourly variation 



a-ft 



of the temperature during the day. The latter therefore will pre- 

 ponderate in determining the value of the equation, and we may 

 expect to find the hourly weight of the air between the two stations 

 following a similar course as the real hourly mean temperatures, 

 but in an inverse ratio, the smallest barometrical difference falling 

 upon 2 p. m., and the highest upon 7 A. M. The following table, in 

 Col. II., gives the hourly differences as found by deducting the pres- 

 sure at Parisnath from that at Calcutta. For the corrected hours 

 the differences obtained from the original readings on the hill have 

 been placed opposite, in Col. I. 



