399

Appendix II.

Optical Science, and become equally inContempt and Disuse; while the VisualGlasses will approve themselves the genuineResult of Optical Philosophy, and be usedat least by all the prudent and thinkingPart of Mankind. Those who would seea larger Account of this Matter may con-fual my Essay on Visual Glasses , which haspassed through four Editions.

VIII. Description and Uses of the E qua to-ri al Telescope, <?r Port able Obser-vatory, by Mr. James Short, F. R. S.whofirs adapted aFdescope to this Machinery.

T HIS Instrument consists of two cir-cular Planes or Plates, marked A A,Which are supported upon four Pillars ; andthese are again supported upon a Cross-foot, or Pedestal, moveable at each End bythe four Screws B B B B : The two circularElates A A are moveable, the one abovethe other, and are called the horizontalPlates, as representing the Horizon of thePlace; and upon the upper one are placedtwo Spirit-Levels, to render them at alltimes horizontal: These Levels are fixed atRight-Angles to one another : This upperPlate is moved by a Handle C, which is

called