Chapter X. The periodital Divisions of Time（续 8）

will be at P, distant from R (also on the 8th house) about 76 equatorial degrees.

By taking the trouble to calculate the distances between the several positions given by Ptolemy, the Reader may satisfy himself of the sufficiency of this Planisphere for the purpose for which it was first projected ; viz. for the more expeditious’ measurement of the arcs of direction. The Tables of Ascensions, extracted from the Almagest, in p, 223, will shew that the arcs, as measured in Figs. 1 and 2 of the plate, exactly tally with the amounts of distance obtained by calculating arithmetically, according to the respective latitudes, as quoted in the Tables.

The slight view which has been here given of the Zodiacal Planisphere invented by Mr. Ranger, must not be considered as pretending to offer a complete idea of its powers: they are so manifold and various, that another volume would be

required to detail them fully ; ‘and it has now been used only in order to give a better illustration of Ptolemy’s examples of the spaces of prorogation than mere words can do. To persons conversant with the mathematical part of astronomy, the facility with which a complete representation of zodiacal latitude, declination, the poles of position, crepusculine circles, and other phenomena, may be made by this Planisphere, will be sufficiently obyious from the accompanying Figures.

a a a a ad Davis and Dickson, Printers, St. Martin’s-le-Grand, Londou.