388 An Account of the Measurement 
sufficiently firm. Inside this hollow stand is erected another 
frame, of the same substance, strong and well made, within 
which is suspended the sector; its frame being supported at top 
in every lateral direction, and sustained at bottom by a cone 
resting in a metallic concavity, the figure of which may be ima- 
gined, by supposing an arch of a circle to revolve round a 
tangent to one of its extremities. A cylinder, in the upper part 
of the interior stand, finds its place in an opening of an octa- 
gonal shape in the exterior frame, and, by a simple contrivance, 
is retained in that situation, while the sector and apparatus re- 
volves on the cone. Thus, a ready means presents itself of 
turning the instrument round, with the face of its divided arch 
towards the east or west. It may be steadily retained in any 
position, by clamping it to the brass work of an azimuth circle, 
attached to the bottom of the external frame. 
The direction of the meridian, at the place of observation, 
having been previously obtained from double azimuths of the 
pole star, this instrument admits of being placed in that direction 
very accurately. A telescope, twenty-nine inches in length, is 
attached to the side of the great tube, or rather, may be occa- 
sionally placed on a frame permanently fastened to it, having 
its axis in the plane of the divided arch, and very nearly at right 
angles to its radius. On the divided azimuth circle below, the 
angular bearing of any proper object may be set off, by turning 
the- sector round till that object bisects the cross wires in the 
little telescope, and then noting the vernier. If the axis of the 
sector be horizontal, and the interior frame set perfectly upright, 
the instrument may be turned round from one point of the 
compass to the other, and properly adjusted for observation, in 
# few minutes. 
