342 



TRANSACTIONS OF THE 



THEORY OF RAIN, HAIL, SNOW AND THE WATER SPOUT, 

 DEDUCED FROM THE LATENT CALORIC OF VAPOUR AND 

 THE SPECIFIC CALORIC OF ATMOSPHERIC AIR. By J. 

 P. Espy, Esquire. 



It is demonstrated by the air pump, that if air satu- 

 rated with vapour is suddenly rarefied, some of the va- 

 pour is condensed by the refrigeration which is produced 

 by the rarefaction. 



It follows from this principle, that if air saturated with 

 vapour should be made to ascend in the atmosphere, the 

 vapour condensed in so ascending would in quantity be 

 proportionate to the height to which it ascended ; for 

 the higher it ascended, the more it would be rarefied and 

 cooled, and so more and more of its vapour would be 

 condensed. 



Now if any cause exists in nature to produce an up- 

 ward motion of air highly charged with vapour, and to 

 continue that motion for some considerable time, the 

 quantity of vapour so condensed would be very great, 

 and a rain w^ould be thus produced which would continue 

 as long as very moist air continued to ascend. 



When it is recollected that air is lighter the more 

 moisture it contains, it will readily be perceived that 

 there is a cause to produce an upward motion of air, 

 containing a large portion of vapour. 



Indeed nothing is more certain than that a column of 

 air lighter than surrounding columns would be forced to 

 rise, and that with a velocity proportionate to the supe- 

 rior weight of surrounding columns. 



It might be supposed that the equilibrium would soon 

 be restored, more especially if upon the condensation of 



