[ +49 ] 
92. The firft circumftance in thefe obfervation^ 
that deferves to be noticed, is the difference in the 
finking of the two hygrometers when they were: 
expofed to the air, before the fun fhone in the gar- 
den. They both of them fell confiderably, but one- 
of the two 7 degrees and a half lefs than the other... 
One of the caufes of this difparity is probably in 
the inftruments themfelves, and is owing to their 
being differently atfeded by the action of the humor.. 
There is a difference of the fame kind obfervable in 
the thermometers, which are likewife more or lefs 
fenfible to the impreffions of the heat even when 
the bulk of their liquid is the fame; that is to fay,, 
they are aded upon more or lefs quickly by the de- 
gree of heat which furrounds them, according to the- 
thicknefs, or even according to the nature of the glafs. 
of which the ball is made. Confequently it is pof- 
iible that the different thicknefs or porofity of the 
ivory may have had feme influence on the going of 
the hygrometer in this obfervation (66 and 6 g\ 
93. But thefe differences in the. ivory pipes muff 
produce a much greater difference in the fenfihility 
of the hygrometers, than thofe of the glafs balls 
can produce in the thermometers ; becaufe it is much 
more difficult for the humor to penetrate the ivory,., 
than for the heat to get through the glafs. So that 
any encreafe of the obflacles retards the introdudion 
of the humor, much more than that of' the heat ; 
and confequently the difference of fenlibllity muft 
be more difficult to be prevented in. the hygrometers, 
than it is in the thermometers.. 
This flownefs of the humor in- pervading the- 
bodies into which it infinuates itfelf, makes it a de~ 
5. finable 
