Appendix II.

40

a Nonius Index for subdividing into everythree Minutes.

Above this Declination-Semicircle isFastened a Reflecting Telescope L L, of the’Gregorian Construction, the focal Length ofits great Speculum being 18 Inches.

In order to adjust the Instrument forObservation, the first thing to be done, is'to make the Horizontal Plates level or ho-rizontal, by means of the two Spirit-Levels,and the four Screws in the Cross-Pedestal.This being done, you move the MeridianSemicircle, by means of the Meridian Han-dle, so as to raise the Equatorial Plates tothe Elevation of the Equator of the Place;which is equal to the Complement of theLatitude (and which, if not known, maylikewise be found by this Instrument, as (hallbe afterwards shewn). And thus the Instru-ment is ready for Observation.

T0 find the Hour of the Day , and Meridianof the Place.

First find, from astronomical Tables,the Sun’s Declination for the Day, and sotthat particular Time of the Day; then setthe Declination-Semicircle to the Declina-tion of the Sun, taking particular Noticewhether it rs North or South, and set theDeclination-Semicircle accordingly.

Vol. III. Dd You