their discoveries; they contented themselves with ascertaining their existence, and noting six or eight in their charts. When, however, the thoughts of Sir William Herschel were directed to the subject, and his telescope swept the starry heavens, no less than five hundred double stars were added, having their situations and relative positions distinctly marked. The son of this illustrious astronomer discovered many more: his unwearied labours, with those of Sir James South, produced an additional list of three hundred and eighty. Subsequently Sir J. Herschel formed a distinct catalogue of 3,300 double and even triple stars, the result of his own observations, accompanied with precise measurements of their distances and angles of position; and Sir James South identified four hundred and eighty, the result also of his own labours. Since then further discoveries have increased their numbers. The celebrated astronomer, Struve, makes mention of no fewer than 3,000 double stars, in the progress of identifying which he examined about 120,000. of those sparkling luminaries which gem the vault of heaven.

The southern hemisphere reveals two hundred and fifty stars of the same description, according to the testimony of Mr. Dunlop; and during a late residence at the Cape of Good Hope, Sir James Herschel added considerably to their list. It is, therefore, conjectured that 6,000 have been made the subject of accurate research.

Connected with the mention of double stars is that important discovery which realizes the fact of a progressive and regular change, bearing in some stars chiefly on their position, in others on their distance, and which results from the smaller star revolving round the larger in an elliptical or circular orbit, although occasionally both stars revolve around some central point. Those who narrowly observe the heavens by aid of a high magnifier may readily ascertain the fact of a revolving motion in such stars as are called double. At one time the satellite or smaller star disappears, in consequence of becoming obscured while passing behind the other, as Jupiter or Venus is occasionally invisible when on the opposite side of the sun, or the satellites of Jupiter, if similarly circumstanced with regard to that planet. Three stars have occasionally been seen revolving about a common centre, and even four or five.

The orbits in which one star circles round another are generally elliptical, similar to the path described by the earth and other planets when revolving round the sun, as also those in which the satellites of Jupiter, Saturn, and Uranus perform their revolutions. These orbicular motions are either retrograde or direct, or in the same direction as the movements of our own planets; and very curious is the fact with regard to the star Serpentarii, in common with many others, that the revolving star appears to move in a straight line, and to oscillate on either side of the larger star, around which it revolves in a manner similar to the satellites of Jupiter, which pass apparently from one side to the other of the planet in nearly straight linesan effect resulting from the plane of their orbits being nearly in a line with the eye of the observer. When Sir William Herschel first directed his attention to the subject of double stars, the two stars to which we have referred were distinctly separate. At the present time the lesser star is so completely projected on the other, that even the most powerful telescope cannot reveal any separation; and why? Because one star is passing across the disc of the other, and will not again be visible till after the lapse of many years.

In our next chapter we shall instance several binary, or double stars, belonging to such of the constellations as have already been regarded in a legendary or historic point of view.

Taurus, one of the zodiacal constellations, pertains to this month, and may readily be discovered near Perseus and Orion. It is needful to remark that the sign or figure, as represented in the earliest charts, and retained to the present day, is merely the front portion of the animal.

THE zodiacal light is rarely visible in this country, excepting during the months of April and May, when it may be seen in clear and cloudless evenings soon after sunset, or, at the opposite season, before sunrise. It resembles a cone of light extending from the horizon obliquely upwards, and is conjectured to be a rotating ring of finely-divided or nebulous matter, situated, perhaps, between the orbits of Venus and Mars, but certainly extending beyond that of the earth.

Though faint and dimly defined in the northern regions of the globe, and totally distinct from any atmospheric meteor or aurora borealis, those who have resided in the zone of palms must ever retain a pleasing remembrance of the mild radiance of this beautiful phenomenon, which rises pyramidically, and illumines a portion of the unvarying length of the tropical nights. Humboldt speaks of it with enthusiasm, as occasionally shining with greater brightness than that of the Milky Way, near the constellation of Sagittarius; and this not only in the dry and highly-rarefied atmosphere of the Andes, at elevations of thirteen or fifteen thousand feet, but also in the vast grassy plains of Venezuela, and on the sea-coast, under the ever-clear sky of Cumana. The same great traveller speaks of the zodiacal light as a phenomenon of unrivalled beauty, more especially when a small fleecy cloud floats across it, and seems as if detached from the illuminated background. A passage in his journal, during a voyage from Lima to the west coast of Mexico, especially refers to such a beauteous incident, when night after night the zodiacal light appeared with a magnificence he had never before seen; and, judging from the brightness of the stars and nebulæ, it was evident that the transparency of the atmosphere in that part of the Pacific Ocean which lay between 10° and 14° of north latitude must have been extremely great. Humboldt delighted to observe the glorious aspect of the heavenly luminaries; he mostly slept on deck, and watched with intense interest those celestial phenomena which are especially conspicuous in the southern hemisphere. During three whole nights, from the 14th to the 16th of March, and during a very regular interval of three-quarters of an hour after the sun had set, no trace of the zodiacal light was visible,

although the darkness was great; but scarcely had an hour elapsed before it became suddenly apparent, extending in great brightness between Aldebaran and the Pleiades, and on the 18th of March attaining an altitude of 39° 5'. Long, narrow clouds, scattered over the lovely azure of the sky, appeared at a small height above the horizon, as if in front of a golden curtain; somewhat higher up were ranged other clouds, varied with changing tints of the greatest beauty, and presenting the appearance of a second sunset. Nor was the phenomenon itself of that mild radiance which seems to possess little reality; its diffused light equalled that of the moon in her first quarter; moreover, a mild reflected glow was visible in the east. Floating over the waters of the Pacific, with measureless depth beneath, and immensity above, it seemed impossible to close the eyes in sleep while the light of which we speak continued to illumine the heavens; it suddenly be came visible, but did not long continue; towards ten o'clock it gradually diminished in lustre, and at midnight scarcely a trace remained.

While exploring also the tropical regions of South America, the same enterprising traveller noticed with astonishment variations of intensity in the zodiacal light. Having passed his nights during several months in the open air, and under a serene sky, on the banks of great rivers, or in the midst of vast savannahs, he had frequent opportunities of carefully observing it; at one moment shining with a steady light, and then seeming to fade away; again suddenly re-appearing in full brilliancy, with an undulating motion. Madame Marian, who watched this beautiful phenomenon with the deepest interest, mentions having once observed a reddish tinge connected with it. Processes, therefore, were conjectured by Humboldt to be going on in the nebulous ring itself; or else that, although in the lower region of the atmosphere, condensations were taking place at a higher elevation, which modified the transparency of the air, or rather its reflecting power, in some peculiar and unknown manner.

Strange it seems that such an attractive spectacle should have failed to excite the attention of astronomers before the middle of the seventeenth century; or, to borrow the language of the author of Cosmos, "that it should have escaped the observant Arabs in ancient Bactria, or the Euphrates, and in southern Spain." Such, however, is the fact; and although, even in this our obscurer sky, the zodiacal light is distinctly visible in the beginning of spring, after evening twilight, above the western horizon, and at the end of autumn, before the dawn of day, as if heralding the sun's rising in the east, the earliest description of it is contained in Childrey's Britannia Baconica of the year 1661 :-"I have observed," said he, "several years together, when twilight hath almost deserted the horizon, a plainly discernible ray of the twilight striking up towards the Pleiades, and seeming almost to touch them; but what the cause of it in nature should be, I cannot yet imagine, but leave it to further inquiry." The same phenomenon was farther noticed by Dominic Cassini about twenty years later.

Humboldt mentions also that most probably the remarkable light, rising pyramidically from the earth, as described in an ancient Alex. manuscript now in the royal library at Paris, and seen in the eastern part of the sky during forty nights successively from the high table-land of Mexico, was that same beauteous light which is now visible in the temperate zone.

This phenomenon, doubtless of primeval antiquity, but first discovered in Europe by Childrey and Dominic Cassini, cannot be regarded as the lumi

nous atmosphere of the sun itself; it is rather attributable, as already mentioned, to an extremely oblate ring of nebulous matter, revolving freely in space between the orbits of Venus and Mars. No certain judgment can be formed concerning the true dimensions of the supposed ring; but, according to the opinion of Humboldt, the nebulous particles of which the ring consists, and which revolve around the sun according to the same laws as the planets, may either be themselves luminous, or may reflect the solar light. The first supposition is not inadmissible: even a terrestrial fog showed itself, about the middle of the eighteenth century, at the time of the new moon, and in the middle of the night, so phosphorescent, that objects could be distinctly recognized at a distance of above six hundred feet.

Thus far we are indebted to the accurate observation of Baron Humboldt in his Physical Description of the Universe; and, before dismissing this portion of our subject, we earnestly recommend our readers to watch carefully for the appearance of the wonderful phenomenon, which few, perchance, have, seen.

Several of the more brilliant constellations have disappeared. Orion has sunk beneath the western horizon, and among the stars which held such prominent stations during the past months, Betelgeux is alone visible. Aries is seen no longer; the Pleiades and Aldebaran, Caput Medusa and Taurus, verge on the borders of the north-western horizon; and Sirius is completely set. Southward gleams the Hydra's head, with Alphard, its chief star; and considerably to the west of Alphard, though nearly at the same altitude, are Canis Minor and Procyon. Castor and Pollux may be readily discerned northward of Procyon, nearly midway between the zenith and the western point of the horizon. Nearer the north-western horizon than the zenith, though widely separate, is Capella. Cassiopeia has descended from her elevated position, and taken a humbler place near the northern quarter of the heavens. The Great Bear, on the contrary, shines not far from the zenith; his two pointers seem directed downwards to the Pole-star. Regulus is about 22° west of the meridian, at a commanding elevation; Denebola, pertaining also to the Lion, is on the meridian, somewhat higher than Regulus; Arcturus looks down from his place in heaven, in the direction of E.S.E.; and 26° to the north-west of this bright star is Cor Caroli, near the zenith. You

may readily discern the Northern Crown due east, midway between the zenith and the horizon; and a Lyra shines in perfect beauty. Near the north-east, about 234° above the horizon, in the N.N.E. quarter, gleams the Swan; and one of its chief stars, Denebola, is about 14° above the horizon. Draco is somewhat higher—at least 20° above a Lyræ, and nearly in the same direction.

Now look towards the eastern and south-eastern portions of the sky. Virgo, Libra, Taurus, Poniatowski, Serpentarius, and Hercules are all visible. Spica Virginis, a bright star of the first magnitude, is 24° above the horizon, occupying a direction S.S.E.; it is 35° south-east of Denebola, and nearly the same distance S.S.W. of Arcturus: these three stars form a large equilateral triangle, pointing to the south. A similar triangle next engages the attention, inclining northward, and consisting of Arcturus, Denebola, and Cor Caroli. Direct your attention, in the next place, nearly due west, at a small elevation above the horizon. Ras Algethi, chief star in Hercules, beams there; as also Ras Alhague, 5° distant, in the head of Ophiuchus the former is the brightest. Southward of Serpentarius, and eastward of Virgo, shines Libra, of which the two most prominent stars are of the second magnitude; the one named Zubeneschamali, 21° eastward of Spica Virginis, but at a lower altitude; the other Zubenesgemabi, about 91° higher, towards the north-east, although occupying a position in the southeast quarter of the heavens, and slightly elevated above the horizon. Serpentarius extends between Corona Borealis and Libra; its principal star, Unuk, is of the second magnitude, but is readily discerned by observing that it is nearly in the middle, between two lesser stars, the lower being 210, the upper 51° distant; moreover, it is in a direction E.S.E., about 24° above the horizon.

This pleasing constellation, although containing fewer stars than many others, is yet of considerable importance, and may be readily distinguished. In order, therefore, to facilitate its recognition, the learner will do well to observe that when Gemini is on the ecliptic, the back of the right-hand figure is towards Cancer, and the face of the left towards Taurus. The Lynx appears as if galloping over them, the hinder feet coming near the Crab. Auriga approaches the right-hand figure; the head of the Unicorn is beneath their feet, near which is seen Orion, with Canis Minor immediately behind him.

The orbit of the earth, or the apparent circle described by the sun in his annual course, passes through the midst of this constellation, from the 21st of June till the 23rd of the following month, but the brightness of the solar rays renders the stars of which it is composed invisible. At other times the two brilliant stars demoninated Castor and Pollux shine pre-eminent: the first, the northernmost of the two, is a star of the first magnitude; the second, situated a little to the south-east, is considerably less brilliant. Castor is a double star, the smaller being invisible to the naked eye, yet revolving around the larger with a slow motion. About 20° south-west of Castor and Pollux are three small stars, nearly in a straight line, and about three or four degrees apart. The southernmost lies parallel with Pollux and the star Betelgeux, pertaining to Orion, but somewhat nearer to the former than the latter. These stars form the feet of the Twins. We have already mentioned that the division of the zodiac into constellations originated in Chaldea, and that the design of such an important