new Nebulae and Cluflem of Stars . 461 
pullies was fuch that, while the telefcope t raver fed an arch of 
two degrees, the mark on the rope palled over about 24 inches of 
the index- board : but the exadl meafure was always to be de- 
termined experimentally, as it varied according to the fitua- 
tion of the inftrument. I perceived immediately that the 
quantity of rope ufed in the motion of the telefcope would 
be much better obferved by the affiftant, if the index’ were 
brought within doors near the writing delk : to effect this, I 
ufed a fmall cord, which, being led off from the great one, 
was carried over a pulley into the obfervatory, fo as to pafs 
over a fet of numbers, which I now divided into fuch parts 
as, in an equatorial fituation of the inftrument, would give 
nearly each equal to one minute. 
It would exceed the limits of this Paper to enumerate the 
various trials 1 made to bring the right afcenfion to greater per- 
fe&ion ; fuch as caufing the tube fometimes to hang inclining 
or rubbing againft a perpendicular plane ; at others, drawing 
it againft the fame by a fmall weight, faftened to a cord, 
palling over a fide pulley, &c. I fhall alfo pafs over the feveral 
changes in the form of the machine Ihewing the polar diftance, 
which, for convenience fake, was foon brought to an index 
moving over a dial, in the manner of a clock. 
By way of directing the perfon who gives motion to the 
telefcope, a fmall machinery was added, which ftrikes a bell 
at each extreme of the breadth of the fweep, and is adjuftable 
to any required number of turns of the handle. 
In June, 1784, I introduced a fmall quadrant of altitude, 
the ufe of which became foon after of the greateft confequence 
in determining the value of the numbers of the polar diftance 
piece. Hitherto I had fettled this value by caufing a ftar to 
pafs vertically through the field of the finder, which was very 
O 0 o 2 accurately 
