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2d, Another particular caufe, lefs obvious though- 
notlefs probable than the preceding, is the difference 
in the mutual attraction of parts, in the concrete and 
difcrete humor, and confequently in their refpedtive 
facility to feparate, and get one by one through the 
narrow pores. When this entrance is attempted by 
the humor, under the form of water, the mutual at- 
traction of its parts, being greater than in dew, occa- 
fions a greater refiltance to their introduction, than 
when they are already divided by fome other caufe, 
viz. when the humor is reduced to fmall drops, or 
vapor. 
14. This phenomenon, therefore, does not con- 
tradict my principle ; it is only a particular faCt ; and 
it remains true, that bodies furrounded with water 
are expofed to the extreme of humor. To remove 
this caufe of exception from my hygrometer, it was 
fufficient to provide outlets for the air, and not to 
increafe too much the thicknefs of the body, upon 
which the humor was to aCt. 
1 5. Another difficulty, which prefented itfelf, was 
that water might probably aCt with more or lefs 
energy in proportion to its heat. But this did not 
flop me long. As my prefent objeCt was a fixt point 
for the hygrometer, and not the greateft power of 
water, confidered as a caufe of humidity, it was 
enough to employ it conftantly at the fame degree 
of heat; and, to fix this with greater precifion, 
I determined to ufe water at the inftant that it ceafes 
to be ice. The bafis therefore of my hygrometrical 
fcale was to be the foaking power of melting ice. 
1 6. This principle, being thus unfolded, appeared 
fo fimple, that I was at firft furprifed how it could 
have 
