8o 
Sir George Shuckburgh's Account 
while the graduated circle will possess those of a meridian 
quadrant. For this purpose l, m, is a stout brass tube, inclos- 
ing a stiff' iron rod, turning upon two fine steel points, ad- 
justed, by proper screws, parallel to the line of sight of the 
telescope ; this rod is attached to a spirit level of great sen- 
sibility, lying below it, which, with the rod, turns round 
upon the steel points just mentioned, and is in fact a hanging 
level of the best construction. At the eye end of the tele- 
scope S, is a peculiar apparatus to correct the effects of re- 
fraction and parallax, when an observation is made out of the 
meridian : it is composed of two levels, a small quadrant of 
altitude n, o, and a semicircle divided, with its nonius, to 
every 5', on the breech plate of the telescope, the exterior eye 
tube having a circular motion, by a wheel and pinion at 0, in- 
dependent of the tube that carries the cross wires ; by this 
means, the angle of the horary and vertical circles may at 
any time be found, together with the altitude of the object, 
and then, by the resolution of two right angled triangles, the 
refraction and parallax, in right ascension and declination, will 
be obtained, t, u, are two handles to a Hook's joint at x, x> 
which, turning an endless screw at w, w, give a gradual mo- 
tion to the telescope in right ascension or declination ; and 
this motion can at any time be restrained by a clamp at q» 
The handles t, u, are hung on to any part of the instrument, 
by means of the line and wire v, v, and are thus kept within 
the observer's reach, r and s are two microscopes, placed on 
opposite sides of the circle QR, and at right angles to the 
line of sight of the telescope, of use only when the plumb 
line is used in preference to the level /, m, above described, 
