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87. As, in mentioning the particular purport of. 
the foregoing obfervations, I have not explained my 
fyftem concerning vapours, I (hall not here flop to 
draw the confequences that may be deduced from 
them in favour of this fyftem. Indeed, to fay the 
truth, I think them too few and too imperfect to 
conclude any thing from them as yet. I have only 
related them, as 1 declared at firft, to give a general 
notion, both of the going of my hygrometer, and of 
the inquiries that may be purfued with its affiftance. 
It is with the fame intention that I proceed to relate 
fome obfervations of another kind. 
88. Some accidental obfervations had made me 
fufpedt that the immediate aflion of the fun upon 
my hygrometer produced a drying, which might not 
be wholly occafioned by the real ftate of the air with 
refpeft to the humor, but might depend in fome 
meafure upon fome fingular property of the folar 
rays, which we fee produce effe&s upon fome bo- 
dies, not immediately to be accounted for by the or- 
dinary laws of heat. This firft remark induced me, 
as I have taken care to mention, always to obferve 
the hygrometer in the fhade upon the mountains of 
Sixt. At my return, I determined to examine more 
accurately whether my conjecture in this refpeft had 
any foundation. 
89. The firft thought that occurred to me for this 
purpofe was, tc obferve two hygrometers at the fame 
time, one in the fhade and the other in the fun,, very 
near each other, that the fame air might circulate 
freely round them. The air of the country having 
appeared to me more proper for this obfervaticn than 
M m m 2 that 
