DOUBLE, OR BINARY STARS.

146. Many of the stars which appear single to the naked eye, or when viewed through an inferior telescope, appear double through a telescope of greater power; that is to say, the single star is separated into two, which appear very near each other.

This singular fact cannot be accounted for by supposing one star situated behind the other at an immense distance, inasmuch as the number of double stars, which amounts to some thousands, precludes the idea of their being merely optically double; while other circumstances remarked by observers, which we are about to explain, clearly prove that these stars are physically double-united to each other, that is to say, by gravity, the cause which unites the planets and the sun.

Castor is one of the most remarkable double stars. In the year 1759, Dr. Bradley communicated to his friend Dr. Maskelyne the following memorandum respecting the position of the two stars of which it consists: "No change of position in the two stars; the line joining them at all times of the year parallel to the line joining Castor and Pollux in the heavens, seen by the naked eye." Sir William Herschel watched these stars for many years preceding 1803, and found that during that period of time, from 1759 to 1803, the small star, so far from retaining the position indicated by Dr. Bradley in the above memorandum, had a gradual motion round the other. Since the year 1803 other observers, including Sir John Herschel, have attentively measured the increasing angle of position, and found it still progressing. From a comparison of all

Fig. 19,

the observations on this double star, it may be concluded that, in a period of somewhat more than 250 years, the smaller will have completely circulated round the larger; so that about the year 2000, the two stars will be situated just as they were when Bradley made his observations. Most wonderful are the truths which double stars, similar to the one now described, open to our view: here we see, not a sun with its attendant planets, but two suns, selfluminous and massive, revolving round their common centre of gravity. Whether or not they have

an accompaniment of attendant Double Star, Castor. bodies it is impossible to say: certain it is, that the distance of the two stars from each other must be far greater than the distance between any two bodies of our system; so that a retinue of planets might attend each sun, and yet neither system would interfere with the movements of the other.

The labours of Sir J. Herschel, Sir James South, Professor Struve of Dorpat, Dawes, Smyth, and others, have brought to our knowledge at least 4000 of these binary systems. Although, in the present state of the science, observations are yet wanting to prove that each and all these revolve round the centre of gravity, like the two composing the star Castor, yet many others have been marked with accuracy, and their periods calculated. The following table will shew a few of the results of observations in this department of the science :

147. Many of these double stars present the beautiful phenomenon of contrast in the colours of the two stars composing the system. Cancri is one of these: the larger star is of a yellow colour; the smaller is blue. The larger of the two composing y Andromeda is crimson; the other a beautiful green. n Cassiopeia discloses a combination of a large white star, and a small one of a purple colour. In a Leonis, 3 Orionis, and a Serpentis, the large star is white and the small bluish. In 59 Andromedæ, the two stars are of a bluish colour, and equal in size: the same occurs in the star & Serpentis.

TRIPLE AND MULTIPLE STARS.

148. In studying the starry heavens wonders multiply upon us at every turn. What can be more unlike any combination we could have conceived, from the contemplation of our own system, than a complicated arrangement of three or more suns revolving round the centre of gravity of the whole? Yet instances of these remarkable combinations are scattered throughout the heavens, and indicate a complexity and diversity unknown in that portion of the universe which has been appointed as our abode, as well as the wonderful intelligence of that Almighty Being who has summoned into existence so great a variety in the material universe, and who has imposed upon the whole such laws as insure the utmost regularity amidst seeming complexity. The

star Cancri is a triple star, which, under favourable circumstances, may be seen with a good telescope magnifying 300 or 400 times.

149. & Lyræ is a double double star; it may be found 2° N.E. of Vega, and clearly seen through a good 31-feet achromatic; it consists of two pairs of stars, each pair revolving apparently round the centre of gravity of the two, and both pairs revolving round the centre of the whole system.

The annexed cut represents the double star Polaris, the quadruple star & Lyræ, and the triple star & Libræ.

ε

The first

ε or 4 or 5 Libræ is a double double star. pair consists of stars considerably unequal; the larger is very white, the other reddish. The second pair is white, and equal in size.

☛ or 48 Orionis, a little below the three stars which form the belt, is a double triple star, or two sets of triple stars, almost similarly situated. R. A. 5 hours 30 min.,

Orionis, in the centre of the sword of Orion, is a quadruple (or rather sextuple) star, forming a trapezium in the middle of the nebula.

44 Orionis, 5° E. by N. from the bright star Rigel,

K

or 51 Libra appears

is another double triple star. generally double; but the larger, through a superior telescope, may be again divided, and found to consist of two stars, as represented in the drawing. Between and ẞ Delphini, but nearer ß, may be found a triple

star.

In the Unicorn's Head is a multiple star, consisting of one star with about twelve round it. It may be found 16° west of Procyon.

THE MILKY WAY.

150. During the autumnal and winter months we cannot fail to remark a bluish-white zone stretching all across the heavens from one side to the other; this is the Milky Way. It may be traced through the constellations Cepheus, Cassiopeia, Perseus, Auriga, part of Orion and Gemini, and through the southern groups, the Cross, the Altar, Scorpio, Sagittarius, Ophiuchus ; here it separates into two branches, which again unite in the neck of the Swan.

.

151. The conjecture of the ancients that this milkwhite zone was an assemblage of stars, was confirmed on the invention of the telescope; for no sooner was it directed to the Milky Way than thousands of stars became visible; and as, in the progress of time, the telescope has undergone improvement, so many more have been brought to light, that it would be utterly impossible to enumerate or classify the myriads which compose it. Direct the telescope at random to any part of this luminous zone, and its field will be filled with scores of stars, some shining brightly, and others fading away in every degree of faintness. It is almost impossible to