420 Mr. de Luc on 
therefore I (hall confine myfelf to the defcription of fome par- 
ticulars. The flip of whalebone is reprefented by a, b\ and at 
its end a is feen a fort of pincers , made only of a flattened 
bent wire, tapering in the part that holds the flip , and prefled 
•by a Aiding ring. The end b is fixed to a moveable bar r, 
which is moved by a fcrew for adjufting at firft the index. The 
end a of the flip is hooked to a thin brafs wire; to the other 
end of which is alfo hooked a very thin filver gilt lamina , that 
has at that end pincers fimilar fo thofe of the flip, and which 
is fixed by the other end to the axis by a pin in a proper hole. 
The jpring d, by which the Jlip is ftretched, is made of filver 
gilt wire; it ads on the flip as a weight of about 12 grains, 
and with this advantage over a weight fbefides the avoiding 
force other in-eon veniencies of this) that, in proportion as the 
flip is weakened, in its lengthening by the penetration of 
moifture, the Jpring , by unbending at the fame time, lofes a 
part of its power. The axis has very fmall pivots , the 
Jhoulders of which are prevented from coming againfl: the frame, 
by their ends being confined, though freely, between the flat 
bearing of the heads of two flcrews , the front one of which is 
feen near f. The fedion of that axis, of the fize that belongs 
to a flip of about 8 inches, is reprefented in Jig. 2. ; the flip 
ads on the diameter a , a, and the Jpring on the fmaller dia- 
meter b , b. 
100. Another conftrudion of the fame inftrument is repre- 
fented, of half its dimenfions, by jig. 3. (Tab. X.) The eflential 
parts of that hygrometer are the fame as in the other ; therefore I 
fiiall only mention the differences adapted to the ufe of fixing it 
out of a window. Th z figure reprefents the manner in which 
it is fixed, with its dial turned half-way towards the obferver, 
by a proper head of the hooks which hold it at the top and the 
bottom. 
