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When the reader has ſtudied and learnt the Principle and Conſtruction of the Planisphere, which is easy to accompliſh, he will find it is adapted, in the moſt eaſy and ready manner, for ſolving all the Problems to which it is applied, and I may venture to ſay, far more ſo than the Celeſtial Globe, it being inconvenient on the Globe to apply, and work the Hour Circle and the days of the months together, and to concentrate the Hour Circle and the Ecliptic is impoſſible; but, on this Planisphere, the Days of the Months and the Degrees of the Ecliptic are adjuſted together, by which means the Day of the Month being given, is the ſame as the Sun's place in the Ecliptic, or the contrary, ſo that theſe may become ſynonymous terms in the Planisphere, and as the Hour Circle on the Index turns concentrical with the Circle of Months, and juſt within it, ſo moſt of the Problems are ſolved at one remove of the Index, and the anſwer appears in an inſtant, by inſpection.
Having now deſcribed, and prepared the Planisphere for uſe, I ſhall next explain the motions of the Terraqueous Globe on which we live: and firſt, according to the true, or Copernican Syſtem of the Univerſe, this Globe is a Planet, revolving round the Sun in an orbit ſomewhat elliptical, and in the ſpace of 365 days, 5 hours, and 49 minutes, being accompanied with the Moon, and hath the Sun at reſt in the center of its orb.–Now, conceive at a vaſt distance, without this ſyſtem, the ſphere of the fixed Stars; and then imagine that on this, or ſome one day, the Sun appears to a be-
