THE ASTRONOMICAL COMPASS.—The utilisation of the heavenly bodies as a means of determining direction has attracted considerable attention since the outbreak of war, and various attempts to simplify the problem for general use have been made. Simplified azimuth tables, in conjunction with maps of the stars, have mostly been employed, but it is evident that such tables may be replaced by graphical projections of the circles of the celestial sphere. Under the title of the “Rev. William Hall's Visible Astronomical Compass,” an arrangement for the direct solution of the chief problems depending upon the diurnal motion of the heavens has been published by Mr. J. D. Potter, 145 Minories, E.C. (price is. net, post free). A circle 6 in. in diameter, on a card 10 in. x8 in., contains a stereo-graphic projection on the plane of the horizon, for latitude 50° N., showing the circles of each even degree of declination, and hour circles at intervals of ten minutes. Circles of azimuth and altitude are not drawn, but the outer edge of the horizon circle is graduated for true bearings, and altitudes may be read off on a scale provided, after measurement with dividers along a travelling thread fixed at the zenith point. Given the time, or an approximate measurement of altitude, the bearing of any object is, of course, readily determined, and the “compass” can then be adjusted so as to show true directions. No new principle is involved, but the arrangement provides a stereographic projection in a convenient form, and the necessary instructions for its use are given. It should be understood, however, that a star map and an almanac are also requisite, and that some means of measuring altitudes would greatly extend the usefulness of the projection.