of a Comet . j OI . ; 
Box A, which confifts of two parts incloGng the eye lens. This 
figure alfo fliews how the piece C pafles through D, and is held 
by the ring E : the brafs work, confi fling of a hollow cylinder, 
a. wheel and pinion, and index plate, is there reprefented in its 
place. F is the body of the brafs work, being a hollow cylin- 
der with a broad rim c at the upper end ; this rim is partly 
turned away to make a bed for the wheel d. The pinion e 
turns the wheel d , and carries the index plate a . One of its 
pivots moves in the arm f fcrewed upon the upper part of c r 
which arm ferves alfo to confine the wheel d to its place 
upon c. The other pivot is held by the arm g fattened to F. 
Fig. III. Is a plan of the brafs work. The wheel d, which 
Is in the form of a ring, is laid upon the upper part of F or r, 
and held by two final! arms f tnd h y fcrewed down to e with 
the fcrews /, /. 
Fig. IV. Is a plan of the brafs work, a \ d 9 is the wheel 
placed upon the bed or focket of the rim of the cylinder c r c 9 
and is held down by the two pieces/*, /a, which are fcrewed upon 
r, c . The piece f projects over the center of the index plate 
to receive the upper pivot of the pinion m, n , is the fixed wire 
fattened to c, c. o , p , the moveable wire fattened to the annu- 
lar wheel J, d . The index plate a is divided into 60 parts, 
each fub-divided into two, and milled upon the edge. When 
the finger is drawn over the milled edge of the index plate 
from q towards r, the angle m r r, o r will open, and if drawn 
from r towards q 9 it will Ihut again. The cafe C, C, mutt 
have a (harpcorner /, which ferves as a hand to poin out the 
divifion on the index plate. 
