of some of the principal fixed Stars, &c. 427 
weight of the moveable part of the instrument, which re- 
volves on an obtuse point at the bottom ; the upper part of 
this vertical axis is kept steady in a right angle, having two 
springs opposite the points of contact, which press it against 
its bearings, and it thus turns in these four points of contact 
with a very pleasant and steady motion. 
The bar, in which the vertical axis is thus centered, is 
acted on by two adjusting screws in directions at right angles, 
and perfectly independent of each other By these motions, 
the axis may be set as truly perpendicular, as by the usual 
method of the tripod with feet screws, which could not in this 
case have been employed. 
The frame, to which this apparatus is attached, is fixed to 
the corners of the hexagonal stone, by the conical tubes ; 
between which and the stone, the azimuth circle (which 
forms one piece with the vertical axis) turns freely. The 
azimuth circle of two feet diameter consists cf eight conical 
tubes, inserted in the vertical axis; and which are united at 
their ends by the circular limb ; this is divided and read off' 
exactly in a similar manner to the other circle. 
A level remains constantly suspended on the horizontal 
axis, which is verified in the same manner as in a transit in- 
strument. There are forcing screws for this purpose, which 
pass through the bar on which the vertical columns stand, 
and these by pressing against the long axis produce a small 
change in the inclination of the upper part of the instrument, 
without altering the position of the azimuth circle or its 
axis. 
The application of the plumb-line, as already described, is 
