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



course of their hourly changes remains always the same. The suc- 

 cession of the hourly increase and decrease is always gradual, and 

 never suddenly interrupted, as that of the moisture, and the turn- 

 ing points fall invariably upon nearly the same hours. 



On comparing the regular course of the curve of the hourly baro- 

 metrical pressures of single days with that of the so-called pressure 

 of the dry atmosphere and considering that the change observed 

 in the latter is produced by deducting the tension of moisture from 

 the former, it would appear, that the daily course of the pressure of 

 the dry atmosphere was naturally irregular, and that the vapour 

 was always present in the exact quantity required to restore the 

 uniformity of the barometrical curve. In fact, it would seem as if 

 the supply of vapour was at all times and solely governed by the 

 greater or smaller irregularity of the curve of the so-called pressure 

 of the dry air. 



Knowing the laws which regulate the supply of watery vapour, 

 and knowing also how many accidental circumstances may alter the 

 curve of its tension for single days, so as to make it entirely unlike 

 its monthly or yearly mean, and observing at the same time that 

 the curve of the hourly barometrical pressures never alters its shape 

 for one single day, such a conclusion would, to say the least, appear 

 very improbable. 



Assuming, on the other hand, that the course of the pressure of 

 the dry atmosphere were regular and uniform in itself, we should, 

 from a knowledge of the frequently altered course of the moisture, 

 expect to find this regularity disturbed by the casual admixture 

 of more or less watery vapour. We see, however, that such is not 

 the case in reality, the barometrical curve being quite independent 

 of the changes in the tensions of moisture, and never irregular. 



The process of obtaining the so-called pressure of the dry atmo- 

 sphere by deducting the tension of vapour near the surface of the 

 ground from the barometrical column is based upon the supposition, 

 that the tension of vapour near the surface would, practically, not 

 differ much from the tension which would be produced by the 

 weight of the column of watery vapour, diffused through the whole 

 height of the atmosphere, if it were separated from the latter, and 

 sustained its own pressure. This would involve another assumption, 



