Forty-feet Refecting Telescope. 397 
The micrometer-motion which is required for sweeping the 
heavens, and indeed for viewing the planets or other objects, 
is obtained by means of the end of the rope B, fig. 37. which 
draws up the telescope. This goes down to a barrel. S', fig. 3. 
12 inches long, and 4, in diameter, joined upon the same axle 
with another barrel, 12 inches long, and 12 in diameter. A 
smaller rope goes from the largest barrel into the working- 
room, where it is fastened to the top of a thin vertical spindle, 
2 feet 6 inches long, and 3 inches in diameter, at a, fig. 43. 
Another rope of equal size is fastened to the bottom of the 
same spindle at b ; and when by turning the handle c d the 
rope a e is wound upon the spindle one way, the rope b f is 
wound off the contrary way. This second rope bf goes out of 
the work-room over a pulley, which leads it upwards to the top 
of the middle cross beam of the ladders, where it descends over 
another pulley, by a weight with shifters which is suspended to 
the end of it. In this manner a balance is obtained between the 
stress of the ropes a e and bf, which leaves the spindle at rest 
in any position where it may chance to stand, and conside- 
rably eases the labour of the workman, who turns this handle 
a certain number of times one way, and then the same number 
of times back again. By such a motion of the handle the te- 
lescope is alternately depressed and elevated ; and this being 
continued for as long a time as the observer chooses, enables 
him to review the heavens as they pass by the telescope. 
By the arrangement of the barrels, it is easy to see that the 
motion is sufficiently divided ; as many turns of the handle 
are wanted to pass over a small space of the heavens. The 
method of barrels and ropes is to be preferred to wheel- work, 
on account of the smoothness as well as silence of the motion, 
mdccxcv. 3 F 
