HYGROLOGY, AND ITS CONNECTION WITH METEOROLOGY- 301 



open air, what are the quantities of evaporated water in one swered by ti- 

 cubicfoot of that air, at any given temperature ? ^^* '^• 



II. The points of the hygrometer and thermometer having 

 been observed, what is the quantity of evaporated water in one 

 cubic foot of that part of the atmosphere ? 



III, The points of both instruments having been observed, to 

 what degree ought the therviometer to fall, in order that the 

 hygrometer should arrive in that air at 100 ; which point it 

 must attain before there is any precipitation of water P 



25. The answers to these questions, from the immediate re- j^^ degree of 

 suits of my experiments, led to this first conclusion ; that cold in the air 

 no diminution of heat in the atmosphere could occasion in it cU'udraiid*^ 

 the precipitation of such a quantity of water as to produce rain. 

 clouds pouring rain ; which confirmed me in the opinion 

 already expressed in my work, Idees sur la Meteorologie, that 

 the aqueous vapour, constantly ascending in the atmosphere, Aqueous va- 

 ceased in great part to act on the hygrometer, being converted ^""oj^'^^jj^g^ hy*^ 

 into an aeriform fluid, namely, the atmospheric air, and that grometer from 

 clouds and rain were produced by the decomposition of this ''^j^g|i"|^j°"* 

 fluid. atmospheric 



1Q. Such was the conclusion of all the above hygroscopic ^t. 

 experiments 3 and with respect to a/moip Aerie phenomena, it ^j.^^JJyg°J_ 

 coincided with the observations of Mr. de Saussureand myself scopic experi- 

 in the high regions of the atmosphere. Having both long in- JJIfthVe^atmc- 

 faabited our mountainous country near the Alps, we had sepa- spheric pheno- 

 rately followed the same meteorological observations with our ^j"^* "'^ ^^^® 

 hygrometers, and we had absolutely ascertained these two 

 points.— 1. That the more we ascend in the atmosphere, the .^.j,^^ ^^^^ j^_ 

 dryer the air is observed _; and that even, in clear weather, it is ductions form- 

 dryer in the night than in the day. 3. That clouds, rain, hail, ^^ ^^^^^^^J,. 

 and thunder, are produced in certain strata of the atmosphere and Mr. de 

 which were cZe«r a moment before, and in which one cubic foot Saussure. 

 of air did not contain above two grains of water. Having 

 both separately, at different times, and also in different parts of 

 the mountains, made the same observations, and published them 

 separately, I cannot suppose, that their results can be contested. 

 Thus it is certain, that raia is not produced by a moisture exist- 

 ing in the atmosphere j and consequently that it proceeds from 

 a decomposition of the air itself. 



27. From what I have said so far. it may be judged, that the Proofs, that 



whole 



