[ 209 1 
defirous of having an inftrument made on the fame 
plan, they may have recourfe thereto. 
It appears from the foregoing obfervations, that, 
in the compafs of 1 1 months, the cords had ftretch- 
ed the value of 5° : and I alfo obferved that they 
both had contraded their compafs about 10°. I 
would, therefore recommend, that an hygrometer 
fhould from its firft adjuftment, be readjufted at the 
end of three months, and again, at the end of fix 
months from the firft; after that, at the interval of 
about fix months, to the end of two years from the 
beginning ; and after that, I apprehend that once a 
year will fuffice ; the beft time of adjuftment, being 
' in the dry and warm weather of July or Auguft: 
and by thefe means, I apprehend the inftrument 
will be always kept within 2° of its proper point. 
Refpeding the fenfibility of this inftrument, it 
has that in a greater degree than its conftancy to 
its fcale can be depended upon, which was all 
that I intended ; where greater degrees of fenfibility 
are required, to make comparifons at fmall intervals 
of time, the beard of a wild oat, and other con- 
ftrudlions may be ufed, with advantage ; this inftru- 
ment being confidered as a cheque upom them as to 
more diftant periods. 
General Condujion, 
I am aware that an hygrometer actuated by any 
principle of the kind here made ufe of may not be 
a meafurer of the quantity of moifture, adlually dif- 
folved in, and intimately mixed, with the air; but 
only indicates the difpofition of the air to part with, 
VoL. LXI. E e or 
f 
