Mr. Pond on the Declinations 
426 
horizontal position ; and it is easy to comprehend, that by 
this valuable improvement, all errors of division may be 
completely done away, without any of the manifest inconve- 
niences of the French circle of repetition ; which, though a 
very ingenious instrument, and admirably adapted to some 
particular operations, will, I think, never be adopted for 
general use in our observatories. 
The plumb-line, a very material part of this instrument, is 
suspended from a small hook at the top of the tube at the left 
hand of the figure. It passes through an angle, in which it 
rests in the same manner as the pivot of a transit instrument 
does on its support. At the lower end of the tube which pro- 
tects it, a smaller tube is fixed at right angles, which contains 
microscopic glasses so contrived, that the image of a lumi- 
nous point, like the disc of a planet, is formed on the plumb- 
line and bisected by it. Great attention should be given to the 
accurate bisection of this transparent point by the plumb-line at 
the moment of observation. It is absolutely essential in instru- 
ments of this construction to consider the observation, as 
consisting in two bisections at the same time : the one of the 
star by the micrometer, the other of the plumb-line-point by 
the plumb-line. The least negligence in either of these bisec- 
tions will render the observation unsuccessful. 
The two strong pillars, which support the axis of the ver- 
tical circle, are firmly united at their bases to a cross bar; to 
which also the long vertical axis is affixed, and which may be 
considered as forming one piece with them. The stone 
pedestal is hollow, and contains a brass conical socket, firmly 
fastened to the stone, and reaching almost to the ground. 
This socket receives the vertical axis, and supports the whole 
