Now comes adjustment 3, the alignment of the polar axis to the meridian. One can get it approximately by setting the telescope tube roughly parallel with the polar axis and, sighting along it, shifting the equatorial head in azimuth until the tube points to the pole star. Then several methods of bettering the adjustment are available. At the present date Polaris is quite nearly 1° 07′ from the true pole and describes a circle of that radius about it every 24 hours. To get the correct place of the pole with reference to Polaris one must have at least an approximate knowledge of the place of that star in its little orbit, technically its hour-angle. With a little knowledge of the stars this can be told off in the skies almost as easily as one reckons time on a clock. Fig. 169 is, in fact, the face of the cosmic clock, with a huge sweeping hour hand that he who runs may read. [Illustration: FIG. 169.—The Cosmic Clock.] It is a clock in some respects curious; it has a twenty-four hour face like some clocks and watches designed for Continental railway time; the hour hand revolves backward, (“counter-clockwise”) and it stands in the vertical not at noon, but at 1.20 Star Time. The two stars which mark the tip and the reverse end of the hour hand are delta Cassiopeæ and zeta Ursæ Majoris respectively. The first is the star that marks the bend in the back of the great “chair,” the second (Mizar), the star which is next to the end of the “dipper” handle. One or the other is above the horizon anywhere in the northern hemisphere. Further, the line joining these two stars passes almost exactly through the celestial pole, and also very nearly through Polaris, which lies between the pole and δ Cassiopeæ. Consequently if you want to know the hour-angle of Polaris just glance at the clock and note where on the face δ Cassiopeæ stands, between the vertical which is XXIV o’clock, and the horizontal, which is VI (east) or XVIII (west) o’clock. You can readily estimate its position to the nearest half hour, and knowing that the great hour hand is vertical (δ Cassiopeæ up) at I^h 20^m or (ζ Ursæ Majoris up) at XIII^h 20^m, you can make a fairly close estimate of the sidereal time. A little experience enables one to make excellent use of the clock in locating celestial objects, and knowledge of the approximate hour angle of Polaris thus observed can be turned to immediate use in making adjustment 3. To this end slip into the plane of the finder cross wires a circular stop of metal or paper having a radius of approximately 1° 15′ which means a diameter of 0.52 inch per foot of focal length.