Chap, i.] Water in Clouds. 383 



duced alrhoft to the flate of a permanently elaftic fluid 

 by mixture with air. 



We find that all fluids boil more eafily in proportion 

 as the prefiure of the atmofphere is removed; whether 

 this is effected by afcending a mountain, or making 

 ufe of the air pump. M. Lavoifier fays, that if the 

 weight of the atmofphere was only equal to between 

 twenty or twenty-four inches of a column of mercury, 

 inftead of twenty -eight inches, we fhould never be able 

 to obtain asther in a liquid ftate, at lead in fummer; 

 and that the formation of ssther muft confequentiy be 

 impofllble upon mountains of a moderate degree of 

 elevation, without employing extraordinary means of 

 compreflion for its condenfation. Upon the whole, in 

 appears mod probable that all bodies are capable of 

 exifting in a folid, a liquid, and an aeriform ftate ; that 

 the firft is tne moft fimple ftate of all bodies, and that 

 the two others depend on combinations with different 

 quantities of the matter of heat, of which the aeriform 

 ftate requires by far the moft. 



Vapour, as it firft rifes from boiling water, is irivifi- 

 ble, but as it mixes with the air it is deprived of part of 

 its heat, returns to its fluid form, and the very minute 

 dropr, of water which are produced, afcend in a co- 

 pious cloud of a white or light-grey-colour. Vapour 

 is the ' more readily difcernable in proportion to the 

 coldnefs and humidity of the atmofphere. The cloudy 

 appearance of fteam is occafioned by the difficulty with 

 which its particles are feparated and diflblved in the 

 atmofphere ; the difficulty is increafed in proportion 

 to the coldneis and humidity of the air, and this is the 

 reafon that the moifture exhaled with the breath, is 

 vifible in winter and not in fummer. 



It was ftated in a former volume, that the combina- 

 tion of the matter of heat or caloric, with the particles 



of 



