of the Equatorial Instrument. 83 
star that is to be observed. This light, as was said before, 
being reflected down the tube to the wires, the stars are seen 
upon a beautiful pale green field, the wires appearing black. 
The centre D being of necessity full two inches in diameter, 
in order to admit of the aperture and lens i, rests on three fric- 
tion wheels, and by this means the motion is as easy as on the 
centre C. At k, /, ?n, n, is a small sliding door, to close up 
the lantern from the wind, but which is here removed to shew 
the inside. 
(15.) Tab. X. figure 2, represents the refraction piece. 
AB is a portion of the telescope; C the eye tube; a, b, c , 
a divided semicircle; d its nonius fixed to AB, shewing the 
angle of the horary and verticle circles ; e , a small spirit 
level, attached to the plate on which this semicircle is en- 
graved, and moving with it by means of the screw f which 
turns a pinion, that works in a toothed wheel, that turns the 
whole plate, together with the exterior eye tube, round its 
centre, but without moving the tube that carries the cross 
wires. From hence it may be understood, that by turning 
the screw f till the level e stands true, the index d, which 
represents a point in the horary circle, will mark how much 
the division zero, (0) which represents the vertical, is in- 
clined thereto. /, k , is a small quadrant of altitude, that, by 
means of the level g, and screw and pinion h, turning on a 
centre at m, gives the elevation above the horizon of any ob- 
ject in the field of the telescope, i, is a small aperture through 
which a key is fixed on, to give a lateral motion to the wires 
to adjust them ; and near / is another screw, to adjust them 
parallel to the equator and declination circle. 
Ms 
