J. Herschel, during his late sojourn at the Cape of Good Hope, is said to have discovered in the southern skies binary stars, whose periods of revolution are even shorter than those now stated, their change of position having been quite perceptible during the three or four years of his residence in that quarter. Sir W. Herschel, in the paper to which I have already referred, states observations which furnish us with a phenomenon which is new in astronomy, namely, the occultation of one star by another. With a power of 460, in July, 1782, the stars of Zeta Herculis were then half the diameter of the small star asunder; in 1795 he found it difficult to perceive the small star with the same power; in 1802 the small star could no longer be perceived, but the apparent disc of the large star seemed to be a little lengthened one way. With his ten feet telescope, and a power of 600, he found it to have the appearance of a wedge-formed star. On the 11th of April, 1803, he examined the apparent disc with a power of 2140, and found it, as before, a little distorted, but there could not be more than about three fourths of the apparent diameter of the small star wanting to a complete occultation. "Most probably," he observes, "the path of the motion is not quite central; if so, the disc will remain a little distorted during the whole time of the conjunction." This phenomenon evidently demonstrates the fact of circular orbital motion, performed in a plane nearly parallel to our line of vision.

The star Gamma Virginis has presented phenomena nearly similar to that of Zeta Herculis. This star is remarkable both for the length of its period, the rapid increase of the angular motion of the two stars of which it is composed, and particularly the great diminution of their apparent distance. It has been known as a double star for at least 120 years. The two stars of which it is composed, and which are nearly equal, were so far apart about the middle of the last century that they were marked in Mayer's catalogue as two distinct stars, so that any moderately good telescope would have shown their separation, being at that period about seven seconds distant from each other. Since that time they have been constantly approaching, and in 1833 were scarcely more than a single second asunder; so that a common telescope was insufficient to show their separation, and even telescopes of very superior power could show them no otherwise than as a single star somewhat elongated. According to Sir J.

Herschel's computations, the small star must have arrived at its perihelion on the 18th of August, 1834. He also determined the inclination of the orbit to the visual ray to be 22° 58', and the angle of position of the perihelion projected on the heavens 36° 24'. The small star of Eta Coronæ reached its perihelion in 1835; and it is calculated that the revolving star of Castor will reach the same point during the year 1855.

From the observations that have been made on binary stars, it now appears demonstrable that the law of gravitation extends its influence to the starry regions; that the same laws of motion which direct the planets in their courses, and connect them with the sun as their centre, likewise operate in these binary systems in carrying one star around the centre of gravity of another. It has often been surmised that gravitation is a power which is universal in its influence; and here we have a proof that it extends not only beyond the range of the planetary system and the orbits of the most eccentric comets, not only to stars reckoned the nearest to our globe, but to those of the third, fourth, and even tenth magnitudes, which may be supposed many hundreds of billions of miles farther distant; thus rendering it highly probable that it is a fundamental law of matter, and extends its energies throughout the amplitude of creation, combining in one vast system all the operations of the Eternal.

The orbits in which the one star moves around the other are found to be elliptical, which is the same kind of curve in which the earth and the other planets move round the sun, and in which the satellites of Jupiter, Saturn, and Uranus perform their revolutions round their respective primaries; another proof that the same general law operates in both cases. Some of these orbitual motions are retrograde and others are direct, or in the same direction as the motions of the planets of our system. In some cases it happens that the edge of the orbit of the revolving star is presented to the earth, or in a line parallel to that of our vision, as is found in the star π Serpentarii; in which case the star appears to move in a straight line, and to oscillate on each side of the larger star around which it revolves, in a manner similar to that of the satellites of Jupiter, which appear to pass from the one side to the other of the planet in nearly straight lines, because the plane of their orbits is nearly in a line with our eye. At the time when Sir W. Herschel first observed this binary system,

the two stars were distinctly separate; but at present the small star is so completely projected on the other that even Struve, with his powerful telescope, cannot now perceive the least separation between the two bodies; a fact which evidently demonstrates that to our eye the one is passing across the disc of the other, and that a number of years hence it will appear on the other side of the larger star. On the other hand, the two stars of Zeta Orionis are now separated by a small interval, although they appeared as one star in the time of Sir W. Herschel; all which phenomena demonstrate a motion in a circular or elliptical orbit, the plane of which lies oblique to our eye; and it has been calculated, from the apparent motions of these bodies, that the ellipses in which they move are in general more elongated than the orbits of the solar planets. On the whole, to use the words of Sir John Herschel, "we have the same evidence of their rotations about each other that we have of those of Uranus and Saturn about the sun; and the correspondence between their calculated and observed places in such very elongated ellipses must be admitted to carry with it proof of the prevalence of the Newtonian law of gravity in their systems, of the very same nature and cogency as that of the calculated and observed places of comets round the central body of our own."

Having stated the above general facts respecting binary stars, I shall now present to the reader a few telescopic views of these objects.

Fig. 15 represents a telescopic view of Epsilon Bootis, with a magnifying power of about 200 times. This is reckoned a very beautiful double star, on account of the different colours of the stars of which it is composed, and has an appearance somewhat similar to a planet and its satellite, both shining with innate but differently coloured light. The small star is of a bluish colour, and is separated from the other by a space equal to the diameter of the larger star, and its apparent size is one third of the other. It is sometimes called Mirac, and is situated about ten degrees northeast of Arcturus. The large star has a reddish tinge.

Fig. 16 is a Herculis the small star is of a bluish colour, separate from the other two diameters of the large star; the blue star is one third the size of the other. It is situated in the head of Hercules, about thirty degrees southwest from the bright star a Lyræ, and six degrees northwest from Ras

Fig. 15-31.

Alhague, a star of nearly the same magnitude. It comes to the meridian about the middle of July, at nine o'clock in the evening, at an elevation of about fifty-two degrees. This

star is also distinguished by the name Ras Algethi, and may be seen marked in Plate II., which contains a map of stars which are seen near the meridian about the beginning of September.

Fig. 17 is a view of y Andromeda : the small star is of a fine greenish-blue colour, separate from the large star about Aine seconds, or four diameters of that star; the larger star is of a reddish white. It is situated in the left foot of Andromeda, and is distinguished by the name of Almaach. It is a star of the second magnitude, about forty-two degrees of north declination, and passes the meridian, in the beginning of December, about half past ten in the evening, about ten degrees south from the zenith. It is about twelve degrees nearly due west from the variable star Algol.

Fig. 18 is Zeta Cygni : the smaller star is blue, and they are separated about ten diameters. This star is situated in the eastern wing of the Swan; right ascension, 21h 4', north declination twenty-eight degrees, and is about twenty degrees southeast of Denib, the principal star of this constellation.

Fig. 19 represents Zeta Aquarii. The two stars are nearly equal in apparent magnitude, and one diameter and a half separate from each other; both stars are of a whitish colour. It is in the middle of other three stars, which together form a figure resembling the letter Y. Its right ascension is 22h 20', and its south declination about two degrees. It is a star of about the third magnitude, and comes to the meridian at nine o'clock in the evening about the middle of October.

Fig. 20 represents the Pole-star. The accompanying star is a very faint point, and requires an accurate telescope with considerable power to distinguish it. The large star is white, and the small star somewhat of a ruddy appearance, and is distant from the larger seventeen seconds, or about three or four of its diameters.

Fig. 21 is the double star Castor. The smaller star is nearly half the size of the larger, and they are distant about five seconds, or two diameters of the principal star. They are both of a whitish colour. Their situation may be found on Plate I. Castor and Pollux lie to the northwest of Orion, at a considerable distance from it. They are very conspicuous, are within five degrees of each other, and rise to a very