The
PRINCIPLE AND USES
of the new
CELESTIAL PLANISPHERE.
Take any Sector, or Gunter's Rule, (but the Sector is the beſt, becauſe it can be set to any Radius) and, with a pair of compaſſes, take the parallel diſtance of 60°, and 60° in the Chords, or the parallel diſtance of 45° in the Semi-Tangents, opening the Sector to any Radius as will beſt ſuit your Plane; with this diſtance ſweep a circle in the middle of your Plane, which is the Equinoctial, and muſt be divided into 360 equal parts, or degrees; and alſo into 24 hours, at the rate of 15° per hour; beginning where the degrees do; this circle is the Right Aſcenſion in time, and degrees—in this caſe, the center of the Sector is the pole of the projection, and the parallel of 45° is the radius of the Equinoctial; and, as the Tropic of Cancer is 23° 28' from the Equinoctial towards the Pole, take the parallel diſtance of theſe degrees (counting them doubly)
