C 2 S9 ] 
XL VI. The Defcription of a New Hygro- 
meter , invented by James Fergufon, F.R. S. 
Read Nov. 8, t ]\f this machine (Tab. XVI. Fig. i. and 2 .) 
I7&4 ' 1 A AAA is a frame of wainfcot or ma- 
hogany, grooved in the innermoft edges of the two longeft 
fides, for holding a pannel BBBB of white deal-board, 
without pinching it. The pannel is about the thicknefs 
of a crown piece, and fifteen inches in length, crofs-wife 
,to the grain of the wood. The middle part projects out- 
ward from the upper and lower edges, at C and C, where 
it is faftened into the frame by two fcrews, to keep the 
middle part always in the fame place, whilft the reft of 
the pannel expands by moifl air toward both ends'of the 
frame, and contracts toward the middle when the air is 
dry. F is a pin fixt into the pannel near one of its ends, 
and a round pin is fixt near the other end of the pannel, 
on which the large pulley H turns, and alfo the fmall 
pully G which is fixed to H. One end of a fmall flexible 
cord DE is faftened to the pinF, and the other end goes 
round the pully G, and is fixt into the bottom of its groove, 
as at h. One end of another fmall cord I K is fixed into 
the bottom of the groove of the large pulley H, as at a , 
from which it goes round the part a i H ; and in its way 
thence to M it goes round a fmall pulley L, in which an 
axis is fixt, and turns in the piece O, which lies above the 
pulley, and is fcrewed to the upper fide of the frame at 
C. This cord goes over the pulley M (which turns cn a 
round pin fixt into the pannel) and has a flattifh weight N 
hung to it. — The pullies G and L are of equal diameters 
in their grooves, which is only equal to a tenth part of the 
diameter of the large pulley H in its groove. The pulley 
M may be of any convenient fize. 
Now it is plain, that as much as the pannel expands 
between F and G, fo much will the pully G be removed 
farther from the pin F; and juft fo much will the cord 
DE turn the pulley G backward ; and any point in the 
L 1 2 groove 
