Still another fixed eyepiece telescope of daring and successful design is the turret telescope of the Hon. J. E. Hartness of which the inventor erected a fine example of 10 inch aperture at Springfield, Vermont. The telescope is in this case a refractor, and the feature of the mount is that the polar axis is expanded into a turret within which the observer sits comfortably, looking into the ocular which lies in the divided declination axis and is supplied from a reflecting prism in the main beam from the objective Figure 96 shows a diagram of the mount and observatory. Here _a_ is the polar turret, _bb_ the bearings of the declination axis, _c_ the main tube, d its support, and _e_ the ocular end. Optically the telescope is merely an ordinary refractor used with a right angled prism a little larger and further up the tube than usual. The turret is entered in this instance from below, through a tunnel from the inventor’s residence. The telescope as shown in Fig. 96 has a 10 inch Brashear objective of fine optical quality, and the light is turned into the ocular tube by a right angled prism only 2¾ inches in the face. This is an entirely practicable size for a reflecting prism and the light lost is not materially in excess of that lost in the ordinary “star diagonal” so necessary for the observation of stars near the zenith in an ordinary equatorial. The only obvious difficulty of the construction is the support of the very large polar axis. Being an accomplished mechanical engineer, Mr. Hartness worked out the details of this design very successfully although the moving parts weighed some 2 tons. The ocular is not absolutely fixed with reference to the observer but is always conveniently placed, and the performance of the instrument is reported as excellent in every respect, while the sheltering of the observer from the rigors of a Vermont winter is altogether admirable. Figure 97 shows the complete observatory as it stands. Obviously the higher the latitude the easier is this particular construction, which lends itself readily to large instruments and has the additional advantage of freeing the observer from the insect pests which are extremely troublesome in warm weather over a large part of the world. This running account of mountings makes no claim at completeness. It merely shows the devices in common use and some which point the way to further progress. The main requirements in a mount are steadiness, and smoothness of motion. Even an alt-azimuth mount with its need of two motions, if smooth working and steady, is preferable to a shaky and jerky equatorial. Remember that the Herschels did immortal work without equatorial mountings, and used high powers at that. A clock driven equatorial is a great convenience and practically indispensable for the photographic work that makes so large a part of modern astronomy, but for eye observations one gets on very fairly without the clock.