INDEX.

Imperfection and Error in the common refractingTelescope, in. 55 n. &seq. The periodical Timesof the primary Planets stated by, iii. 105 n. Firstinvestigated the conical Motion of the Earth’s Axisiii. 170 n. His astronomical Principles of Chrono-logy, iii. 248. Determined the Æra of the Argo-nauts, iii. 269, its seq. _ 6

Newtonian System, that of Copernicus should be socalled, iii. 103 n. Cometography, a Compendiumof, iii. 203 n.

Nonius , what, and why so called, ii. 131 n. Describedibid. *

Notes, Musical, Number of exhibited, and their Na-ture accounted for in a Harpsichord, ii. 254.Notiometer. See Hygrometer.

Nychtbemeron , what, iii. 223.

O.

(~\B']e£ls of the simple Colours, what, ii. 322, andvV ^3 n. The Images of, in various Glasies deter-mined, iii. 12 n.

Obscura, Camera, what, in. 78.

Occultatrn of Venus and Mercury, Use of, m. 140 n.Opacity of Bodies accounted for, ii. 291 n. Where,

Opake, why a Body is so called, ii. 285, seq.^Optics, Subject of what, iii. 2. Division of, in. 2 n.Principal Parts of, iii. 3•

Orrery what, i. 202. , An adequate Representation ofthe Solar System, iii. 154- D of ’ s l 6 5 ";

Principal Uses of, iii. 166. By Pcjsidonius, describedby Cicero, iii. 166 n. Contrived by Sevennus Boe-thinus iii. 167 n. Hemispherical,' described, iii.168 n. Large one by Mr. 'Rowley, iii. 168 n. WhatSort, the best, iii. 169 n. The Circles on, explain-ed iii. 178 n. Shows the Variety of Seasons, iii.179 tef seq. The various Phases of the Moon, iii.192! Eclipses of the Moon, iii. 192. Transits ofMercury, and Venus, ibid. by Mr. J. Neale, i. 204 n.Oscillation, Centre of in a Pendulum,, i. 122.

OtacouJHcs, Instruments, why so called, ii. 246.