GB191308923A - Improvements in Geographical Indicating Instruments. - Google Patents

Abstract

8923. Peck, W. April 16. Maps; planispheres. - A geographical apparatus designed for indicating for all latitudes of both hemispheres the times of sunrise, sunset, the length of twilight, the altitude of the sun, and the local apparent, mean, and sidereal times, comprises planispheres R, Fig. 1, mounted revolubly on a disk E which is rotatable about an horizontal axis, and a compound indicator, Fig. 3, consisting of a fixed graduated arm J, rotatable graduated arms K, S, and a sheet Z of transparent material such as celluloid having curved lines h, h, which indicate the times of sunrise and sunset, and curved lines t, t, which indicate the length of twilight. The disk E can be set at any suitable inclination in bearings r, r<1> and carries near its circumference fixed rings G bearing graduations of the hours and minutes before and after noon, and rotatable rings H bearing graduations of the hours and minutes of sidereal time graduations of minutes of the equation of time, and the days and months throughout the year. A curved line e, e<1> indicating the inclination of the ecliptic and containing graduations of degrees of the sun's longitude is marked upon the planispheres R, which are constructed on a known projection in which the poles P are central and equal angles on the terrestrial surface are represented by equal spaces on the planispheres. The arms K, S of the compound indicator are rotatable about a centre L, which is adapted to be positioned over either of the poles P. The arm S, which bears graduations representing the lengths of the longest and shortest days, is connected bv a link T to a rod V slidable on the arm K and carrying an index-pointer f. The rod V is graduated with a scale a of the degrees of meridian altitude of the sun and with a scale d of the sun's declination north or south of the equator. The latitude and longitude of any place can be read off respectively on the arm J and on the circumference of the planispheres R by rotating the planispheres until the place is beneath the edge of the arm J. When, by rotating the planispheres, the index f has been adjusted for any day of the year to the point of the curve c, e<1> which represents the sun's longitude, the sun's declination and meridian altitude for any latitude can be read off on the scales d, a respectively, the times of sunrise, sunset, and length of twilight are indicated by the lines h, h and t, t where they are crossed by the edge of the arm S, and the lengths of the shortest and longest days can be read off on the scale on the arm S.