2 PHILOSOPHY OF STORMS. 



by the velocity of sound, that when air is expanded by di- 

 minished pressure, it becomes colder at a rate not differing 

 very widely from that which obtains in the atmosphere ; so 

 that if dry air were to ascend in the atmosphere, it would, 

 by expansion, cool down about one degree for every hundred 

 yards of its ascent ; or perhaps a little more. 



4. It has been. shown by many experimenters, particularly 

 by Berard and Delaroche, and also by Clement and De- 

 sormes, that the specific caloric of atmospheric air under a 

 mean pressure, is about one quarter, that of water being 

 one. 



5. It is also known that the latent caloric of the vapor of 

 water at zero, is 1212 Fahrenheit, and that as the tem- 

 perature of the vapor increases, the latent caloric diminishes 

 in the same proportion, so that the latent and sensible calo- 

 ric of vapor, when added together, will always make 1212. 



6. It is known also that the caloric of liquidity of water 

 is 140 Fahrenheit; or that water, on freezing, gives out 

 140 of caloric. 



7. As the specific gravity of steam or vapor is about T 6 oV<r 

 of that of the air at the same temperature, if a portion of 

 air near the earth's surface should have a dew point of the 

 temperature of 80, when by article 1 the quantity of vapor 

 would be one forty-eighth of the whole weight, it will 

 be readily perceived by calculation that its specific gravity 

 will be to that of dry air, as seventy-nine to eighty. And 

 if a column of air eighty feet high, with such a dew point, 

 could be introduced into a surrounding atmosphere of the 

 same temperature absolutely dry, it would, by the principle 

 of spouting fluids, begin to move upwards with a head of 

 pressure of one foot, or with a velocity of eight feet per 

 second. 



8. If the surrounding air should not be absolutely dry, 

 but have some lower dew point, this column would still 

 move upwards, though with a less velocity, and continue 



