Forty-feet Reflecting Telescope. 395 
straight away to O', fig. 3. where it is bent over a small pul- 
ley to one just close to it, which leads it in a direct line to P', 
under the polar distance clock, where it rises up to the barrel. 
The barrel is of such a diameter as to answer as nearly as 
possible to the length of the cord which is drawn by the mo- 
tion of the telescope over one degree of polar distance ; but 
as the utmost accuracy could not have been obtained in the 
make of the barrel, the loop at the telescope which draws the 
end of the cord, as we have described, may be slipped back- 
wards or forward upon its bar, which will either lengthen or 
shorten the radius of its motion, and occasion its drawing 
more or less of the cord. 
As there is a good quadrant upon the telescope, there re- 
mains nothing else to obtain a just position of this loop than 
to compare the indication of the polar distance piece with that 
of the quadrant ; and when the former is regulated to a per- 
fect agreement with the latter, we may safely rely upon the 
truth of its report. 
The time and polar distance pieces are placed so that the 
assistant sits before them at a table, with the speaking-pipe 
rising between them ; and in this manner observations may 
be written down very conveniently. The place of new objects 
also may directly be noted, as their right ascension and polar 
distance is before the assistant upon the table, where nothing 
is required but to read them off, on the signal of the observer. 
By a catalogue in zones the assistant may guide the ob- 
server, who is with his back to the objects he views, and who 
ought to have notice given him of such stars as have their 
places well settled, in order to deduce from their appearance 
the situations of other objects that may occur in the course of 
