The class of phenomena we are about to describe are those produced by the interposition of celestial objects; for we know well that inasmuch as many of the heavenly bodies are constantly in motion, it follows that the direction of lines drawn from one to another will vary from time to time; and it must occasionally happen that three will come into the same line. “ When one of the extremes of the series of 3 bodies, which thus assume a common direction, is the Sun, the intermediate body deprives the other body, either wholly or partially, of the light which it habitually receives. ”When one of the extremes is the Earth, the intermediate body intercepts, wholly or partially, the other extreme body from the view of observers situate at places on the Earth which are in the common line of direction, and the intermediate body is seen to pass over the other extreme body, as it enters upon or leaves the common line of direction, and the intermediate body is seen to pass over the other extreme body, as it enters upon or leaves the common line of direction. The phenomena resulting from such contingencies of position and direction are variously denominated ‘Eclipses’ ‘Transits’ and ‘Occultations’ according to the relative apparent magnitudes of the interposing and obscured bodies, and according to the circumstances which attend them.“ We shall proceed to consider the several phenomena in detail, beginning with Eclipses.

Variation in the Obliquity of the Ecliptic. — Although it is sufficiently near for all general purposes to consider the inclination of the plane of the ecliptic as invariable; yet this is not strictly the case, inasmuch as it is subject to a small but appreciable change of about 48″ per century. This phenomenon has long been known to astronomers, on account of the increase it gives rise to, in the latitude of all stars in some situations, and corresponding decrease in the opposite regions. Its effect at the present time is to diminish the inclination of the two planes of the equator and the ecliptic to each other; but this dimimition will not go on beyond certain very moderate limits, after which it will again increase, and thus oscillate backwards and forwards through an arc of 1 ° 21 ′: the time occupied in one oscillation being about 10,000 years. One effect of this variation of the plane of the ecliptic—that which causes its nodes on a fixed plane to change—is associated with the phenomena of the precession of the equinoxes, and undistinguishable from it, except in theory.

Precession.—The precession of the equinoxes is a slow but continual shifting of the equinoctial points from East to West.

The early origin of the telescope, like that of most other important inventions, is lost in obscurity, and it is now impossible to determine who was the first maker. It is certain that some time prior to the end of the 13th century lenses were in common use for assisting in procuring distinctness of vision. A certain Vitello, a native of Poland, seems to have done something in this line; and Eoger Bacon, in one of his works, employs expressions which show that even in his time (he died in 1292), spectacles were known.

Seeing that this was the case, it is almost certain that some combination of 2 or more lenses must have been made in the interval which elapsed between Bacon's time and the commencement of the 17th century, when telescopes are usually considered to have been invented. Dr. Dee mentions that though some skill is required to ascertain the strength of an enemy's force, yet that the commander of an army might wonderfully help himself by the aid of “perspective glasses,” a phrase which must refer to some kind of optical instrument then in use

One of the most important total eclipses of the Sun. that has occurred within the last few years was that of July 28, 1851. Though not visible in England, it was seen to great advantage in Sweden, to which country astronomers flocked in great numbers. From the numerous observations that were made, and subsequently published, we select some extracts which will doubtless interest the reader. The following remarks are from the pen of Mr. G. B. Airy, the Astronomer Royal, who observed it at Göttenberg: —

Around the Sun as a centre, certain bodies, called planets, revolve, at greater or less distances: they may be divided into two groups, (i.) The inferior planets, comprising Vulcan, Mercury, and Venus; and (ii.) the superior planets, including Mars, the Minor Planets, Jupiter, Saturn, Uranus and Neptune, the Earth being the boundary between the two. If viewed from the Sun, all the planets, inferior and superior, would appear to spectators placed on the Sun, to revolve round that luminary in the order of the zodiacal signs; such, however, is not the case when the motions of the planets are watched from one of their number itself in motion; it consequently happens that the apparent motions of the inferior planets on the one hand, and the superior on the other, differ considerably. The former are never seen in those parts of the heavens in opposition to the Sun, but are sometimes to the east and sometimes to the west of it. Twice in every revolution an inferior planet is in conjunction with the Sun (Fig. I); in inferior conjunction, when it comes between the Earth and the Sun, and in superior conjunction when the Sun intervenes between the Earth and the planet. When it attains its greatest distance from the Sun, east or west, it is said to be at its greatest elongation—east or west, as the case may be.