r 199 ] 
ftored thereto, and In conrequence that any numbers 
of hygrometers, fimilarly conftrufted, might, like 
thermometers, be capable of fpeaking the fame 
language. 
The two points of heat, the more readily deter- 
nunable in a thermometer, are the points of freezing 
and boiling water. In like manner, to conflruff 
hygrometers which fliall be- capable of agreement, 
it is neced'ary to eftablifh 'two different degrees of 
a moiflure which fliall be as fixed in themfelves, and 
to which we can as readily and as often have re- 
courfe as poffible. One point is given by making 
the fubftance perfeftly wet, which Teems fufliciently 
determinable j the other is that of perfe<fl dry ; but 
which I do not apprehend to be attainable with the 
Tame precifion. A readinefs to imbibe wet, fo that 
the fuhftance may be foon and fully Taturated, and 
alfo a facility of parting with Its moiflure, on being 
.expofed to the fire to dry; at the fame time that 
neither immerfion in water, nor a moderate ex- 
pofition to the warmth of the fire, Tliall injure its 
texture; are properties requifite to the firfl mover 
of fuch an hygrometer, that in a manner exclude all 
fubflances that I am acquainted with, befides hempen 
and flaxen threads or cords, and what are com- 
pounded thereof. 
Upon thefe ideas, In the year 1758 I conflrudled 
two hygrometers, as near alike as poffible, in order 
that I might have the means of examining their 
ap-reement or difagreement on firnilar or diffimilar 
treatment. The interval or fcale between dry and 
wet, I divided into 100 equal parts, which I call 
the degrees of this hygrometer. The point of o 
denotes 
