Forty-feet Reflecting Telescope . 393 
The first wheel in turning about carries a short pallet, of a 
shape similar to the long one. This must be placed low enough 
to let the long pallet pass freely, and high enough to clear the 
spring-lever in going over it. The pallet, on the appearance 
of the o, strikes a tooth of the second wheel, and brings the 
figure 1 into view, which with the other forms 10. The se- 
cond dial-plate has a blank, and the figures 1, 2, 3, 4, 3, 6 , 7, 
8, 9, 10, 11, 12, engraved upon its face, and presents thirteen 
teeth to the pallet on the first wheel, by which the blank and 
figures are successively brought into view, along with the suc- 
cession of the units on the dial-plate of the first wheel. 
In this manner the degrees are shewn from o to 129, which 
includes the whole range of north polar distance in this lati- 
tude ; while at the same time they are properly subdivided 
into minutes. A more minute division was not thought ne- 
cessary with this instrument, and indeed ought not to be 
aimed at. 
The cord which gives motion to the polar distance clock, is 
rendered a just representative, or true index, of the angular 
movement of the telescope in the following manner. 
On the machine which holds the right ascension roller, is an 
arm l m n, fig. 40. in an oblique direction, upon which is 
fastened a brass slider, 3 feet 1 inch long. A coarse screw 
passes from one end of it to the other, and is confined between 
its shoulders In. At 0 there is a handle, by which the screw 
being turned, a small sliding plate m, which carries a pulley, 
is drawn backwards or forwards at pleasure, along the whole 
range of the slider. 
On the telescope, near the bottom of the front edge of the 
