of the Cumulus Cloud. 141 



tainly have a tendency to prevent further condensation ; but 

 the temperature of the gases would also be raised, and their 

 elastic force increased : they would therefore rise higher, and 

 the remaining steam would be mechanically carried up with 

 them sufficiently high to produce further condensation. That 

 the liberated caloric would expand the gases enough to cause 

 them to rise in the atmosphere is apparent, as it requires but 

 little caloric to give considerable additional elasticity to the 

 atmospheric gases. And on the condensation of steam much 

 latent caloric is given out, there would therefore be an ade- 

 quate supply of caloric to produce the effects named. It has 

 been computed that the evolution of heat from the condensa- 

 tion of a pound of steam would be sufficient to raise the tem- 

 perature of 3657 cubic feet of air 10°. Every pound of rain or 

 cloud that is formed, will consequently raise the temperature 

 of the atmosphere to that proportional extent. 



This view, thowever, does not rest entirely on theoretical 

 reasoning; that there are beds of warm air mixed with floating 

 particles of water occasionally found in the atmosphere, is 

 known from the experience of aeronauts, as well as from others 

 who have ascended mountains. Mr. Green found such a bed 

 at a height of nearly 10,000 feet from the earth, where the dew- 

 point was at 64-°, the same as at the surface of the earth at the 

 time. At 1 1,060 feet, only 1*060 feet higher, the dew-point had 

 fallen to 32°, only one half the temperature ; because, there is 

 no doubt, he had then got above the warming influence of 

 condensation of steam. The effect of condensation in raising 

 temperature, is seen also in the method practised of heating 

 water by passing steam into it. It is found that one pound 

 of steam will raise the temperature of 1000 pounds of water 

 1°. And Mr. Espy has shown, in the instrument he called 

 " a Nephelescope," that rarefaction of the air, effected by re- 

 moving pressure from it, cooled it after a certain rate or law ; 

 but this law of cooling was disturbed as soon as condensation 

 took place. Condensation counteracted the cooling effect of 

 expansion about one half, showing that if a column of air, in 

 which steam had been recently condensed, were to be exami- 

 ned, it would be found that the temperature would be reduced, 

 as we ascended in that column only one half of what it would 

 be in a neighbouring column where no condensation had taken 

 place. Suppose in the latter column the temperature to di- 

 minish 1° for every one hundred yards of elevation, as before 

 shown, then, in the former column, where condensation had 

 taken place, the temperature would be diminished only half a 

 degree for every one hundred yards of height. If the foregoing 

 facts and reasonings be admitted, it will follow that on con- 



