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rated for a while, at ro o’clock there was feme dew, 
and the hygrometer fell fenfibly till eleven : but af- 
terwards the clouds doling again, the heat encreafed, 
and the humidity evidently diminifhed. 
"102. I take it for granted here, that the moft 
common and moft plentiful dew proceeds from the 
air, and not from the earth, as fome philofophers 
have imagined. I fhould produce the proofs I have 
collected of this fadt from a multitude of experi- 
ments, if it had not been done in an excellent paper, 
written by Profeffor le Roi, On the elevation and 
JuJpenfion of water in the air *. Thefe phasnomena 
of the dew become very interefting examined with 
the help of the hygrometer, and joined toobfervations 
of the degrees of faturation of the air with reipect to 
water, which have been fo ingenioufly imagined, 
and begun by the author of this memoir. If this 
part of natural philofophy is ever cleared up, as I 
hope it will be, we (hall be much indebted for it to 
the fagacity of this true philofopher. 
103. I fhall only mention one more obfervation 
I have endeavoured to make with my hygrometer, 
which ought not to be omitted, as it is connected 
with the principles upon which the inftrument is 
conftrudted. It has likewife a reference to medicine, 
in as much as one of the objedts of that fcience, in 
its inquiries to preferve our health, is to determine 
the effedts of water at different degrees of heat upon 
our organs. Ivory being an animal fubftance, the 
effects produced upon it by water at different degrees 
* Mem. de 1’Ac. des Sc. de Paris, for the year 1751. 
of 
