206. Planets are opaque bodies, similar to our earth, which move round the sun in certain periods of time. They shine not by their own light, but by the reflection of the light which they receive from the sun. The planets are distinguished into primary and secondary.

207. The primary planets regard the sun as the centre of their motion. There are eleven primary planets, distinguished by the following characters and names: Mercury, Venus, the Earth, Mars, Ceres, Pallas, Juno, Vesta, Jupiter, Saturn, Georgium Sidus or Herschel.

208. Since the 1st of January, 1801, four new planetary bodies have been discovered, between the orbits of Mars and Jupiter, to which the names Ceres, Pallas, Juno, and Vesta have been given. They are apparently at such equal distances from the sun, that it is not yet decided with certainty, which of them is the nearest or the most remote. Their orbits are not confined within the limits of the zodiac. Neither of them is visible to the naked eye, or appears, through a telescope, larger than a star of the fifth magnitude. They are generally called Asteroids.

209. The secondary planets, satellites or moons, regard the primary planets as their centres of motion; thus, the moon revolves about the earth, the satellites of Jupiter move round that planet, &c. There are eighteen secondary planets. The Earth has one satellite, Jupiter four, Saturn seven, and the Georgium Sidus six satellites.

210. The orbit of a planet is the imaginary path which it describes round the sun. The earth's orbit is represented by the ecliptic.

211. Nodes are the two opposite points, where the orbit of a planet seems to intersect the ecliptic. The node in which the planet appears to ascend from the south to the north side of the ecliptic, is called the ascending Node, and is marked thus, ; and the opposite point, where the planet appears to descend, from the north to the south side of the ecliptic, is called the descending Node, and is marked thus, &.

212. Aspect of the stars and planets is their situation with respect to each other. There are five aspects, viz. o Conjunction, when they are in the same sign and degree; Sextile, when they are two signs or a sixth part of a circle distant;

Quartile, when they are three signs, or a fourth part of a circle from each other; A Trine, when

they are four signs or a third part of a circle from each other; Opposition, when they are six signs

or half a circle apart.

213. The conjunction and opposition (particularly of the moon) are called the Syzygies; and the Quartile aspect, the Quadratures.

214. Direct. A planet's motion is said to be direct, when it appears, to an observer on the earth, to go forward in the zodiac, according to the order of the signs.

215. Stationary. A planet is said to be stationary, when, to an observer on the earth, it appears for some time in the same point of the heavens.

216. Retrograde. A planet is said to be retrograde, when it apparently goes backward, contrary to the order of the signs.

or

217. Digit. The twelfth part of the sun's or moon's apparent diameter.

218. Disc. The face of the sun or moon, such as it appears to a spectator on the earth; for though the sun and moon be really spherical bodies, they appear to be circular planes.

219. Geocentric latitudes and longitudes of the planets, are their latitudes and longitudes, as seen from the earth.

220. Heliocentric latitudes and longitudes of the planets, are their latitudes and longitudes, as they would appear to a spectator situated in the

sun.

221. Apogee, or Apogeum, is that point in the orbit of a planet, the moon, &c. which is farthest from the earth.

222. Perigee, or Perigeum, is that point in the orbit of a planet, the moon, &c. which is nearest to the earth.

223. Aphelion, or Aphelium, is that point in the orbit of the earth, or of any other planet, which

is farthest from the sun. This point is called the higher Apsis.

224. Perihelion, or Perihelium, is that point in the orbit of the earth, or of any other planet, which is nearest to the sun. This point is called the lower Apsis.

225. Line of the Apsides, is a straight line joining the higher and lower apsis of a planet, viz. a line joining the Aphelium and Perihelium.

226. Eccentricity of the orbit of any planet, is the distance between the sun, and the centre of the planet's orbit.

227. Occultation is the obscuration, or hiding from our sight,of any star or planet, by the interposition of the body of the moon, or any other planet.

228. Transit is the apparent passage of any planet over the face of the sun, or over the face of any other planet. Mercury and Venus, in their transits over the sun's disc, appear like dark specks. Transit is also the passage of the sun, moon, or any other planet, over the meridian, horizon, or some other line or circle of the heavens.

229. Eclipse of the sun is an occultation of part of the disc of the sun, occasioned by an interposition of the moon, between the earth and the sun; consequently, all eclipses of the sun happen at the time of the new moon. Sometimes the whole disc is hidden, and then the eclipse is said to be total.

230. Eclipse of the moon is a privation of the light of the moon, occasioned by the interposition of the earth, between the sun and the moon; consequently, all eclipses of the moon happen when she is full.

231. Elongation of a planet is the angle formed by two lines drawn from the earth, the one to the sun and the other to the planet. It is the apparent distance of a planet from the sun, as seen from the earth.

232. Diurnal arch is the arch described by the sun, moon, or stars, from their rising to their setting. The sun's semi-diurnal arch it that which he describes in half the length of a day.

233. Nocturnal arch is the arch described by the sun, moon, and stars, from their setting to their rising.

234. Aberration is an apparent motion of the celestial bodies, occasioned by the earth's annual motion in its orbit, combined with the progressive motion of light.

235. Centripetal force is that force with which a moving body is perpetually urged towards a centre, and made to revolve in a curve, instead of proceeding in a right line; for all motion is naturally rectilinear. Centripetal force, attraction, and gravitation are terms of the same import.

236. Centrifugal force is that force with which a body, revolving about a centre, or about another body, endeavours to recede from that centre or body. There are two kinds of centrifugal force, viz. that which is given to bodies, moving round another body as a centre, usually called the projectile force; and that which bodies acquire by revolving upon their own axes. Thus, for example, the annual orbit of the earth round the sun, is regulated by the action of the centripetal and projectile forces; and the diurnal rotation of the earth on its axis, gives to all its parts a centrifugal force, proportional to its velocity.

237. The orbit of the earth, and of the other planets, is not a circle, but is of an eliptical form, having the sun in one of its foci*-nor is the mo

It

To understand the true meaning of the term fuci, a knowledge of Geometry and Conic Sections is necessary. will be sufficient, in this place, for the young pupil to know, that if a thread, with its ends united, be laid on a piece of paper, and two pins be fixed at any distance on a line, within