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XXXVIII. Account of a new Hygrometer * 
By M. J. A. De Luc, Citizen of Geneva, 
ft. R. S. and Correfpond . Member of the 
Academies of Paris and of Montpellier, 
Read June i o, JN laying before the Royal Society an 
177 J ' account of my attempts to find out a 
method for meafuring themoiftureof the air, I think 
myfelf obliged to relate the gradual fteps of my mind, 
the obftacles I met with, the means by which I en- 
deavoured to overcome them, the degree at which I 
flatter myfelf to have arrived, the hopes that may be 
entertained of farther advances, and the ufes which 
may be derived from my firft experiments. 
Attempts to invent an Hygrometer. 
t. In order to proceed regularly in this inveftiga- 
tion, I began by examining the effential requifites in a 
machine intended to meafure humidity, which I found 
to be the three following : 
1 ft, The fettling of a fixed point, from which 
every meafure of the fame kind ftiould be taken, 
fuch., for inftance, as that of boiling water in a ther- 
mometer, when the barometer is at a certain height. 
2d, Degrees equally determined, or comparable, 
m different hygrometers, fuch as are in the thermo- 
meter. 
