i66 
Dr. LONGFIELp’S 
SIR, 
Corke, 
Feb. 1 8, 1774. 
I HAVE now had a full trial of sM eaton’s hygro- 
meter, and think it a very taleful and agreeable inftru- 
ment. It is capable of a confiderable degree of exadt- 
nefs, but not fufficient for any thing which requires great 
accuracy. It abforbs the moifture of the air much more 
readily than it parts with it ; and I have great reafon to 
believe, that, as the gravity of the air differs, it will point 
to different degrees on the fcale, the degree of moifture 
or drynefs being the fame. If the cord is too much 
twifted it will require frequent adjuftments, and I know 
that the extreme degree of moifture is very uncertain 
(though that of drynefs is not fo) and different perfons 
will adjuft it very differently at that point. 
My telefcope I have found, by theory and experiment, 
to magnify 134 times. 
My friend, whom I mentioned to you, has been mak- 
ing obfervations for thefe thirty years. He has -a good 
clock, with a common pendulum ; a quadrant of two feet 
radius; a five feet telefcopeof two glaffes, with a common 
micrometer; an excellent refledtor of short’s, of eigh- 
teen inches focus; and is getting a tranfit inftrument. His 
obfervations 
