Uygroinetry* t g 
jew proceeds to its maximum, the hygrofcope moves from So to 
ioo (and fometimes a little farther, § 27.)- Then we have 
alfo a certain proof that extreme moijlure exifts in the air ; foe 
every folid body expofed to it is wet . But it is only at that 
moment that we can depend on extreme moijlure exifting; for, 
if in the other defcribed ftages of the phenomenon, the ap- 
pearance of Water Oh the furface of fome folids had proceeded 
from a fpontaneous precipitation in the air^ all the other folids 
ought to have been wet ; but they only become wet in a certain 
fucceffion, and ih the mean time the flip of quill, and all the other 
above-mentioned bygrofcopes , move more and more towards their 
point 100, in fign of moijlure increafiitg ih the air. Confe- 
quently (as I had concluded from my firft obfervations), in- 
jftead of having in dew an hygrofcopic ftandard for the hygrome- 
ter, we have in its phenomena many circumftances which 
will only be explained with the affiftance of that inftrument. 
29. Some previous obfervations had alfo warned me againfl 
the general idea, that moijlure was to be extreme in the air , 
when there was a fufficient quantity of water in the fpace, 
even though that air might be fuppofed to be filled with evapo- 
rated water to its maximum ; and the doubts I entertained in 
that refped: were the caufe of the difficulties I expreffed in the 
beginning of my firft Paper, which I only got over when I 
thought of water itfelf, to obtain the point of extreme moijlure 
on my hygrometer . This was alfo the reafon why, as foon as 
my'firft hygrometer was finifhed, I placed it in a cellar, the walls 
and ground of which were wet , and where it continued two 
months, without ever attaining its point of extreme moijlure . I 
have related that experiment in § 54. et feq. of my firft Paper.^ 
30. When alfo I had the hygrojcopes mentioned above in 
the obfervations on dew , I undertook a very long courfe of 
various forts of experiments on that important point of hy- 
D 2 * grology* 
