The first step in this direction is a very simple one indeed. Suppose one were to tilt the azimuth axis so that it pointed to the celestial pole, about which all the stars appear to revolve. Then evidently the telescope being once pointed, a star could be followed merely by turning the tube about this tilted axis. Of course one could not easily reach some objects near the pole without, perhaps, fouling the mount, but in general the sky is within reach and a single motion follows the star, very easily if the original mount had a slow motion in azimuth. This is in fact the simplest form of equatorial mount, sometimes called parallactic. Figure 73 shows the principle applied to a small reflector. An oblique block with its angle adjusted to the co-latitude of the place drops the vertical axis into line with the pole, and the major part of the celestial vault is then within easy reach. It may be regarded as the transition step from the alt-azimuth to the true equatorial. It is rarely used for refractors, and the first attempt at a real equatorial mount was in fact made by James Short F. R. S. in mounting some of his small Gregorians.[15] As a matter of record this is shown, from Short’s own paper before the Royal Society in 1749, in Fig. 74. [15] Instruments with a polar axis were used by Scheiner as early as 1627; by Roemer about three quarters of a century later, and previously had been employed, using sights rather than telescopes, by the Chinese; but these were far from being equatorials in the modern sense. [Illustration: FIG. 73.—Parallactic Mount for Reflector.] A glance shows a stand apparently most complicated, but closer examination discloses that it is merely an equatorial on a table stand with a sweep in declination over a very wide arc, and quite complete arrangements for setting to the exact latitude and azimuth. The particular instrument shown was of 4 inches aperture and about 18 inches long and was one of several produced by Short at about this epoch. [Illustration: FIG. 74.—Short’s Equatorial Mount.] In the instrument as shown there is first an azimuth circle _A A_ supported on a base _B B B B_ having levelling screws in the feet. Immediately under the azimuth circle is mounted a compass needle for approximate orientation, and the circle is adjustable by a tangent screw _C_. Carried by the azimuth circle on a bearing supported by four pillars is a latitude circle _D D_ for the adjustment of the polar axis, with a slow motion screw _E_. The latitude circle carries a right ascension circle _F F_, with a slow motion _G_, and this in turn carries on four pillars the declination circle _H H_, and its axis adjustable by the slow motion _K_.