399 
Forty-feet Reflecting Telescope. 
notice has been given of a star that was a little above or below 
the sweep ; for in some parts of the heavens known stars are 
scarce, and it becomes necessary to take in all those that may 
be come at 
The construction of the zone-clock is very simple and con- 
venient. The end of the axle which holds the double barrel, 
fig. 3. must be left projecting at T'. Upon this a small hollow 
cylindrical pipe is placed, which holds the end of the cord 
that is to move the zone-clock. The pipe must be guarded 
at both ends like a clock barrel, to keep on the cord, but re- 
main open at the end which goes upon the axle, upon which 
it must fit upon a square so as to keep firm. It should be 
about 1^ inches long, and 1 in diameter. 
From this piece the cord is made to pass to the work-room, 
where it rises up into the clock at a , fig. 44. It then passes 
over a large narrow barrel, bed, and by means of a weight 
w at its end, descends when the handle of the micrometer- 
motion turns the spindle and double barrel with which the 
pipe that holds this cord is connected. At c b are two levers 
that, in the usual way, occasion the hammers tf to strike the 
bells gh , when the pins quit the levers which they have lifted 
up. But these levers have spring joints, so as to permit the pins 
to pass back again without disordering the work. The pins 
which move the lever c are fastened to the barrel b c d. The 
lever b must be brought out so as to be before the front of the 
first frame-plate, and close to a dial- plate, which is to contain 
about 40 numbers. The dial- plate must be pretty thick, and 
be fixed upon a hollow arbor. The axle of the barrel, which 
should be jstrbng, must be long enough to come through the 
hollow arbor, and project a little way to receive a miked nut 
3 F 2 
