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vii Spheres; and what further benefit and pleasure may we not expect to accrue among these respective classes, when this plain, easy, and familiar Treatise, (with the Planiphere) falls into their hands? when, by only turning the hour and minute given, and found on the Index, to the day of the month, the Planiphere stands rectified for that time, and represents the true situation of the Heavens, and the Problem is performed in a quarter of a minute of time, or less; and, by continuing to move the Index to a good regulated clock or watch, not only the relative positions and situations of the Celestial Bodies with respect to each other, and to the prime Circles of the Sphere, but their Horary Progressive Motion from East to West, is most beautifully seen by day and night perpetually; which, with the extensive variety of uses that this Planiphere is applicable to, cannot fail to enlighten and enlarge the understandings of every possessor of it, in the most rapid degree; and I humbly conceive and flatter myself, that if this little Work should be made an auxiliary Study in our Finihing Schools, great benefit will be derived therefrom in the education of the rising generation; as the precepts and examples are easy, pleasing and engaging, and are calculated to allure, rather than to deter the minds of Youth from the study thereof; which, if this should be the case, my utmost wishes will be answered, and my labour amply rewarded.

It will appear obvious to every one, that the Want of such a Planiphere, as an easy and sure Guide by which to demonstrate the Theory of Astronomy, hath always been the grand obstacle, the fatal check to the Study of