ioB Sir George Shuckburgh’s Account 
deduced ; and when found, must be corrected by the screws* 
at one end of the declination axis. I have been rather dif- 
fuse in the account of this adjustment, because it is one of the 
most important in the whole instrument, and does not readily 
present itself. 
It has now been seen that, ist, the level and its axis are 
parallel to the axis of the declination circle. 2dly, the line of 
sight at right angles to this axis, and parallel to the polar 
axis; and consequently the declination axis at right angles to 
the polar axis. 3dly, the polar axis parallel to that of the 
earth. These are the chief requisites in the adjustment of 
this instrument. Those that remain are secondary, and I 
shall take them in the following order, ist. The adjustment 
of the cross wires to the focus of the telescope. 2dly. The 
hanging level. 3dly. The line of collimation, north and 
south, as well as east and westward. 4thly. The index wires 
in the microscopes, ^thly. The refraction apparatus. And, 
6thly, the power and scale of the microscopes. 
(25.) First, the cross wires. Let the eye tube be adjusted 
to distinct vision for parallel rays by some distant object, such 
as Jupiter, Saturn, or Venus, by daylight; that done, ob- 
serve, while one limb of either of these planets appears run- 
ning along the equatorial wire, whether any motion of the 
eye, upwards or downwards before the eye glass, alters the re- 
lative place of the image and the wire ; if a motion of the 
eye upwards moves the planet in the same direction, the 
wires are too near the eye glass, and must be pushed in ; and 
vice versa , till the image become fixed upon the wire, what- 
* The heads of these screws being divided into 10 parts, and the value of each 
known, any given correction is easily applied. 
