most prominent of which is §, arranged in a line slightly curved. The tail may be easily traced by a series of stars which winds around through the Milky Way in a beautiful manner.*

MYTHOLOGICAL HISTORY.-This is the scorpion that sprang out of the earth at the command of Juno, and stung Orion. Scorpio and Orion are so placed among the constellations that they never appear in the heavens together.

Sagittarius, the archer, is represented as a centaur with his bow bent, as if about to let fly an arrow at Scorpio.

μ

PRINCIPAL STARS.-A row of stars from u to ẞ marks the bow another from y eastward points out the arrow and the right arm drawn back in bending the bow. North of 7, two stars of the fourth magnitude denote the head of the centaur. The Milk Dipper, so called because the handle lies in the Milky Way, is a very striking figure.

MYTHOLOGICAL HISTORY.-This constellation is named in honor of Chiron, one of the centaurs. These monsters were represented as men from the head to the loins, while the remainder of the body was that of a horse -the ancients having so high an opinion of that animal that the union was not considered in the least degrading.

Chiron was renowned for his skill in music, medicine, and prophecy. The most distinguished heroes of mythology were among his pupils. He taught Esculapius physic; Apollo, music; and Hercules, astronomy.

Capricornus contains no very conspicuous stars. The Southern Fish (No. 6) has one star of the first magnitude, Fomalhaut (a, No. 7), which on a clear summer evening may be seen in the south, midway to the zenith. Antinous and the Eagle is a double

*Antares (anti, like; Ares, Mars) was so named because it rivalled Mars in brightness and color.

constellation. It contains a beautiful star of the first magnitude, Altair. This is conspicuous, as being the center one in the row of three bright stars. A similar row denotes the tail of the eagle; the first star of which is named 5, and the last star lies in Cerberus. The Dolphin contains a pretty cluster in the form of a diamond. It is sometimes called Job's Coffin.

Cygnus, the swan, is a remarkable group of stars, the principal ones being so arranged as to form a large and beautiful cross. The upright piece lies along the Milky Way. It is composed of four stars, three of which, Deneb (a), y, and P, are bright, while the fourth is a variable star. No. 61, a minute star, scarcely visible to the naked eye, is noted as being the nearest to the earth of any of the fixed stars in the northern hemisphere (p. 241).

Lyra, the harp, contains one brilliant blue star, Vega (p. 217). Close by it is a parallelogram of four smaller stars, by which it may be easily recognized.

MYTHOLOGICAL HISTORY.-This is the celestial lyre upon which Orpheus discoursed such ravishing music that wild beasts forgot their fierceness and gathered about him to listen, while the rivers ceased to flow, and the very rocks and trees stood entranced.

III. Southern Constellations.-We now imagine ourselves viewing the stars visible to a person far

south of the equator. The constellations are reversed with reference to the horizon. The two stars which, in the northern hemisphere, compose the base of the parallelogram in Orion, form here the upper side. Sirius is above Orion. All the northern circumpolar constellations are hidden from view. At the southern pole there is no conspicuous star, but the richness and number of the neighboring stars compensate this deficiency, and give to the heavens.

an incomparable splendor. Here is the magnificent constellation Argo, in which we find Canopus, looked upon anciently as next to Sirius in brilliancy: 7, a variable star, now surpasses it in brightness.

Nearly at the height of the south pole, blazes the Southern Cross; below is the Centaur, containing two stars of the first magnitude and five of the second; and above is Hydrus, where shines Achernar, another beautiful star of the first magnitude.

1. Double Stars.-To the naked eye, all the stars appear single. With the telescope, over 10,000 have been found to be double. Thus, Polaris consists of two stars about 18" apart; Rigel has a companion about 10" from it; and Sirius, one distant 7". A

good opera-glass will separate & Lyræ into two components.

In case two stars happen to lie in the same straight line from us, though at immense distances from each other, their light will blend. They will be seen by the naked eye as a single star, and by the telescope as a double star. They are called optical double stars. Many, however, of the double stars have been found to be physically connected. Each double star of this class forms a binary system of two suns revolving in an elliptical orbit about their common center of gravity, like the planets in the solar system, in accordance with Newton's law of gravitation. In a few instances, there are combinations of triple, quadruple, and even septuple stars. Thus & Lyræ is a double-double star, while 0 Orionis is a system of six suns. The components of a double star commonly differ in brightness; so that frequently the fainter one is nearly lost in the brilliancy of its companion sun.

THE PERIODS of some systems have been ascertained. Thus, § Ursa Majoris is a double star, and the two stars of which it is composed have performed an entire revolution about each other since they were found to be connected. There are only eleven binary stars now known whose periods are less than a century, while the others have periods which seem to extend, in some cases, beyond a thousand years.

ORBITS.-It is not possible to estimate the dimensions of the orbits of the double stars, until their dis tances from us are definitely known. "Taking the