The optical axis of the telescope is now parallel to the polar axis, but the latter may be slightly out of position in spite of the preliminary adjustment. Now reverting to the polar field of Fig. 170, swing from position _A_ to _B_ and back again, correcting any remaining eccentricity of the star arcs around the pole by cautious shifting of the polar axis, leaving the telescope clamped in declination. The first centering is around the pole of the instrument, the second around the celestial pole by help of a half dozen small stars within a half degree on both sides of it, magnitudes 9 and 10, easily visible in a 3” or 4” telescope, using the larger field of the finder for the coarse adjustment. If the divided circles read to single minutes or closer, which they generally do not on instruments of moderate size, one can use the readings to set the polar axis and the declination circle, and to make the other adjustments as well. In default of this help, the declination circle adjustment may be set to read 90° when the optical axis is brought parallel to the polar axis, and after the adjustment of the latter is complete, the R. A. circle can be set by swinging up the telescope in the meridian and watching for the transit of any star of known R. A. over the central cross wire, at which moment the circle should be clamped to the R. A. thus defined. Two possible adjustments are left, the perpendicularity of the polar and declination axes, and that of the optical axis to the declination axis. As a rule there is no provision for either of these, which are supposed to have been carried out by the maker. The latter adjustment if of any moment will disclose itself as a lateral wobble in trying to complete the adjustment of optical axis to polar axis. It can be remedied by a liner of tinfoil or even paper under one end of the tube’s bearing on its cradle. Adjustment of the former is strictly a job for the maker. For details of the rigorous adjustments on the larger instruments the reader will do well to consult Loomis’ _Practical Astronomy_ page 28 and following.[31] The adjustments here considered are those which can be effectively made without driving clock, finely divided circles, or exact knowledge of sidereal time. The first and last of these auxiliaries, however, properly belong with an instrument as large as Fig. 168, on a fixed mount. [31] See also two valuable papers by Sir Howard Grubb, _The Observatory_, Vol. VII, pp. 9, 43. Also in Jour. Roy. Ast. Soc. Canada, Dec., 1921, Jan. 1922. There are several rather elegant methods of adjusting the polar axis to the pole which depend on the use of special graticules in the eyepiece, or on auxiliary devices applied to the telescope, the general principle being automatically to provide for setting off the distance between Polaris and the pole at the proper hour angle. A beautifully simple one is that of Gerrish (_Pop. Ast._ =29=, 283).