40$ Dr . Herschel's Description of & 
by a handle, on the axle of which is fixed a pinion of four 
leaves : this works in a wheel, on one side of the barrel, of 61 
teeth, and 18 inches in diameter. 
The barrels are 25-t inches long, and 12 inches in diameter, 
that the rope may not be doubled often, which might hurt the 
uniformity of drawing up the gallery. They are made exactly 
alike, and draw an equal length of rope at -every stroke of the 
handle ; but as one of the persons who draw the gallery might 
go on quicker than the other, each of the handles strikes a 
bell at every turn, going up as well as going down ; the dif- 
ferent tone of the bells easily shews, by sounding In regular 
alternate succession, when the gallery is properly moved; 
which therefore may be safely done in the dark. The mecha- 
nism of the bell-work at each handle is in a little box, to keep 
it dry, but sufficiently open at the side to throw out the sound. 
A single bell being suspended, as in fig. 45. upon a plate of 
iron, at a, there is a cock, be , planted upon it; between which, 
at d and e, are inserted two axles continued outwards. On the 
outside of the cock, and upon these axles, are two inverted 
hammers suspended, with lever arms, f g. These are made 
with spring joints, like those that have been described in the 
zone-clock. The axle which moves the barrel has a pallet 
upon it, and the plate with the bell apparatus being presented 
at rectangles to the axle, so as to make the pallet play in the 
notch of the plate between / and g , where the lever arms meet, 
it will make the bell give a stroke, either with one hammer 
going up, or with the other coming down. 
It is necessary to preserve the pliability of the ropes, for 
which reason no tar has been used with any of them that are 
about the telescope. To preserve them, however, they are 
