THEORY DEDUCED FROM PHYSICAL LAWS. 



its motion (provided it is large enough to remain en masse) 

 to the surface of the atmosphere ; unless it becomes colder 

 than the surrounding air, or enters into air of as high a dew 

 point. 



9. The latter case is not likely to happen ; for it is known 

 by observation that at great heights, the air becomes sud- 

 denly very dry, and the former cannot possibly occur, for 

 the following reason : as the air in question contains \ of 

 its weight in vapor, by calculating according to the prin- 

 ciples contained in articles 4 and 5 it will be found that 

 vapor contains, at the temperature of 12, latent caloric 

 enough to heat up forty-eight times its weight of air 100 

 Fahrenheit; and therefore, by the time it ascends high 

 enough to condense by refrigeration one half of its vapor 

 into water, it will be less cold by 50 than it would have 

 been, had it been dry air ascending to that height; and then, 

 according to article 3, it would be 50 warmer than the sur- 

 rounding air at that height. The diminution of bulk by 

 the condensation of this quantity of vapor would be by arti- 

 cle 1, ^y of the whole : and as it is known that air at 32 

 is expanded |<y of its bulk for every degree of Fahrenheit, 

 and as the mean temperature of the column would be about 

 32, its bulk would be increased by the evolution of 50 of 

 latent caloric, -gfo of the whole, or six times as much as it 

 was diminished by the condensation of the vapor to water. 

 And as the dew point of the ascending column would al- 

 ways be much higher than that of the surrounding atmos- 

 phere at the height to which the column had ascended, its 

 specific gravity would be less on this account ; and on the 

 whole, at the moment when one half its vapor was turned 

 to water, its specific gravity, when compared to that of the 

 surrounding air at the same height, would be about as seven 

 to eight. 



10. It thus appears that whenever a cloud is formed in 

 the atmosphere by refrigeration, the mass of air in which 



