putation gives at 100,000,000, a number from which, if our globe and system were stricken they would no more be missed than a unit taken from

"the autumnal leaves that strew the brooks

In Vallambrosa."

There are several parts of the firmament in which stars appear to the naked eye closely packed together, and others which present a general indivisible luminosity to the unassisted vision. The chief of these are the Pleiades, Hyades, the Milky Way, and Presepe. The latter is a region faintly gleaming in the sombre districts of Cancer, which may be easily found by running a line through Castor and Pollux and continuing it to the southeast about three times the distance between those stars. The ancients were acquainted with Presepe, a speck of light which they supposed to be the general effect of three stars, as it is not resolvable into component parts by the unaided gaze; but Galileo with his imperfect means discovered it to be a congress of thirty-six. The Hyades appear to consist of five stars, but between thirty and forty are readily discernible under a moderate instrumental power. The Pleiades also yield a similar result, their optical number, six or seven, being largely multiplied by the application of a telescope. The constituents of the group are thus stated in modern catalogues :

But the cluster easily resolves into about forty constituents. Of the Milky Way the Roman poet wrote, as the path leading to great Jupiter's abode, whose "groundwork is of stars." Milton, likewise, speaks of that "broad and ample road, whose dust is gold, and pavement stars." These poetical conceptions become verities when an instrument sufficiently powerful is directed to the zone in question. It is found to be composed of stars which assume the appearance of a tortuous consecutive girdle of light, owing to their grouping and distance. Some idea may be formed of their profuseness from the fact that Herschel was led to the conclusion, when examining this wonderful region, that in some parts of it no less than fifty thousand were included within a zone two degrees in breadth, which passed under his review in a single hour's observation. Yet this is but a specimen of countless combinations which are discoverable in the concavity of the heavens, so remote from us as to escape the observation of the eye, yet recognised by its aided vision, forming clusters of various shapes, as rich in stars as the zone which we can analyse proves to be.

That luminous celestial highway which the Greeks called the Galaxy, and the Romans the Via Lactea, from its whiteness, is more or less visible at all seasons of the year; but in northern latitudes it is seen to. the best advantage in the interval between the close of July and the beginning of November. It varies in breadth from four to eighteen

degrees, and also in brightness, being most resplendent in the southern hemisphere, about the constellations Argo Navis, Robur Carolinum, and the Cross. "The general aspect," says Sir John Herschel, "of the southern circumpolar region, including in that expression 60° or 70°, is in a high degree rich and magnificent, owing to the superior brilliancy and larger development of the Milky Way; which from the constellation of Orion to that of Antinous, is in a blaze of light, strangely interrupted, however, with vacant and almost starless patches, especially in Scorpio near a Centauri and the Cross; while to the north it fades away pale and dim, and is in comparison hardly traceable." This vast zone is a sensible annulus in the heavens, and most probably really of that shape. It passes from the head of Cepheus about 30° from the North Pole, through Cassiopeia, nearly covering Perseus, over part of Auriga, and crossing the ecliptic between the feet of Gemini and the horns of Taurus, proceeds over the equinoctial into the southern hemisphere to within 20°

of the South Pole. It then takes a northerly direction, and divides into two branches before again passing the ecliptic into the northern hemisphere. The eastern branch streams over the bow of Sagittarius, through Aquila and part of Cygnus. The western branch passes over the tail of Scorpio, the right side of Ophiucus to Cygnus. The two branches unite in that constellation, and pass on to Cepheus, the point from whence we started, where the stream has its greatest breadth for a considerable space.

By some of the pagan philosophers the Via Lactea was regarded as an old disused path of the sun, of which he had got tired, or from which he had been driven, and had left some faint impression of his glorious presence upon it. Its stellar composition was however suspected long before it was proved, but its multitudinous host of stars remained a secret till Herschel turned his mighty instrument at Slough upon the silvery belt. In a

single spot he counted between five and six hundred without moving his telescope; and in a space of the zone not more extensive than 10° long by 21° wide, he computed that there were no fewer than 258,000. "What Omnipotence!" was the involuntary exclamation of Schroeter of Lilienthal, upon examining a part of the same magnificent girdle. It is not easy to convey to popular apprehension the opinion generally held by astronomers respecting the cause of this singular and lucid tract, but the following statement will perhaps be sufficiently intelligible. It is conceived on good grounds that all the stars in the universe are arranged in clusters or groups, each of which may have millions of constituents, and that the Milky Way is the remote and elongated part of our cluster or group, to which all

the visible stars belong, forming one of many thousands of starry schemes or nebula which the firmament exhibits, as we shall hereafter see. It is a fair supposition, that stars which are classed as belonging to the inferior orders of magnitude only appear to be so generally because of their greater distance. Now it is observable, that those of the superior magnitudes are pretty equally distributed through the sky, and those of the inferior appear in crowds towards the margin of the Milky Way, while that zone is plainly demonstrated to be an enormous aggregation of the smaller sizes. The theory has therefore presented itself, that the stars of our firmament are the constituents of a layer, comparatively thin, but extended to an immense distance, somewhat after the semblance of the top of a round table, to use a homely illustration, or a millstone, or a cheese, the thickness of which is vastly surpassed by its diameter. If our position therefore is towards the central regions of this layer, we shall obviously see a great gathering of stars, agglomerated into one mass, looking towards the circumference, forming an appearance answerable to that of the Milky Way; but looking along the surfaces of the layer, we shall see a far lesser number of stars, appearing also more distinct and scattered, answering to the aspect of the other parts of the heavens. Supposing likewise the layer, on one side, to be split down the middle, the appearance in that direction will be that of the Milky Way, divided through a certain extent into two branches. The diagram may help to illustrate this view of the architecture of the visible stellar universe, and our own place in it, occupying a space in the neighbourhood of the sun at S. Sir John Herschel, after visiting the

southern hemisphere, struck with the superior brilliancy of that part of the Milky Way

which traverses the southern sky, remarks:-"I think it is impossible to view this splendid zone, with the astonishingly rich and evenly distributed fringe of stars of the third and fourth magnitudes, which form a broad skirt to its southern border like a vast curtain, without an impression, amounting to a conviction, that the Milky Way is not a mere stratum, but an annulus; or at least that our system is placed within one of the poorer and almost vacant parts of its general mass, and that eccentrically, so as to be much nearer to the parts about the Cross than to that diametrically opposed to it."

Though the whole number of stars which the naked eye discerns on an ordinary night is small, yet, leaving the common haunts of men, and gazing upon the celestial vault at a high elevation in the atmosphere, largely improves the appearance of old familiar stellar faces, and many are caught sight of which were before wholly invisible. Visiting the peaks of lofty mountains, at night forms fresh acquaintances among the stars, and its friends of long standing glitter with a brilliance which the denser regions of the atmosphere render obscure to the dwellers below. The son of Marshal Ney remarks, in a personal narrative of the ascent of one of the Pyrenean summits: "How glorious were the heavens on that night! Ye who have never bivouacked on the Cardal know not what a fine night is." Brydone observes of the top of Mount Etna:-"We had now time to pay our adorations in a silent contemplation of the sublime objects of nature. The sky was clear, and the immense vault of the heavens appeared in awful majesty and splendour. We found ourselves more struck with veneration than below, and at first were at a loss to know the cause; till we observed, with astonishment, that the number of stars seemed to be infinitely increased, and the light of each of them appeared brighter than usual. The whiteness of the Milky Way was like a pure flame that shot across the heavens, and with the naked eye we could observe clusters of stars that were invisible in the regions below. We did not at first attend to the cause, nor recollect that we had now passed through ten or twelve thousand feet of gross vapour, that blunts and confuses every ray before it reaches the surface of the earth. We were amazed at the distinctness of vision, and exclaimed together, 'What a glorious situation for an observatory! Had Empedocles possessed the eyes of Galileo, what discoveries must he not have made!' We regretted that Jupiter was not visible, as I am persuaded we might have discovered some of his satellites with the naked eye, or at

M

66

Surely," he adds in another

least with a small glass which I had in my pocket." passage, "the situation alone is enough to inspire philosophy."

To measure the distance of the stars, is a task which has baffled the ablest men, armed with the best instruments for the purpose, and using them with the utmost nicety and perseverance. Until our own day, the conclusion arrived at had only been negative. It could merely be demonstrated, that the nearest of these bodies must at the least be removed from us a certain space, the extent of which requires the billions of our arithmetic to express. It is clearly ascertainable, that the enormous interval intervening between us and that remote wanderer in our system, Uranus, is but a narrow chasm compared with the interval between him and the most contiguous of the stellar orbs. On observing the same star, lying in the plane of the earth's orbit, from the two extremities of the orbit, at the end of six months, no perceptible alteration in the apparent size of the star can be discerned, notwithstanding this vast change of situation. The inference therefore is, that the diameter of the earth's orbit, the immense line of 190 millions of miles, bears no sensible proportion to the real distance of the stars. But another method adopted to measure the great gulf, and most laboriously pursued for upwards of a century, has been the detection, if possible, of an annual parallax of the stars, or apparent change of place caused by being viewed from opposite extremities of the earth's orbit. All the planets, even the remotest, appear in very different places when viewed at the vernal and autumnal equinoxes, or at any two extreme points of our globe's path; and if the angle subtended be given, the distance may be calculated. But no parallax of a star amounting even to a single second has been detected, and Bradley makes the observation, which Sir John Herschel confirms, that if such an amount of parallax existed, it could not possibly have escaped notice. Supposing, however, a parallax of one second perceptible, that, by the rules of trigonometry, would give a distance from us of more than 19 billions of miles; but as there is no such quantity detectible, there is no star lying within that range they all lie beyond it!

Parallax is the apparent change of place which an object undergoes through an observer shifting his own position. The traveller in journeying marks a great change in the same scenery, in the disposition of its various features, by the alteration of his own point of view. He observes the trees, fields, and hedgerows, which appeared in a direct line between him and some distant hill, at one station, making an angle with the eminence as seen from another station. Suppose we stand at a, and have two trees before us in

b

d

the direct line a bc, both will be projected to the same point d, but if we shift our position to e, then the nearest tree will be seen in the direction f, and the farthest in the direction g. By measuring the base line a e, and the angles a b e, and a ce, or the parallax, the mathematician readily arrives at the distance of the trees from the points of observation. Now, with reference to estimating the distances of the stars, we have the diameter of the earth's orbit as a capital base line to work upon, a real change of place occurring annually on our part in relation to them amounting to 190 millions of miles. Yet, notwithstanding this vast alteration of position, no angle of the value of a second, has been found with certainty in the case of any star.

The diagram now subjoined, exhibits the earth at two extreme points of its orbit. Let the reader keep in mind the 190 millions of miles between those points, and

then he may form some idea of the awful gulf between us and the stars, from the fact, that the triangle formed by lines drawn from the extremes of the orbit to a star at the vertex, has defied the most perfect instruments of human invention to measure, so inappreciable is it. Supposing the whole of that orbit filled with a globe resplendent as the sun, it would have a circumference of 600 millions of miles, and yet have only the appearance of a twinkling atom as seen from the nearest of the stars.

Previous to the determinations of Newton, the discovery of an annual parallax of the stars was a point of great interest in order to confirm the Copernican doctrine of the earth's motion in space. Though not so important on that ground now, it is an object which modern astronomers have pursued with great zeal, though not with success until our own time. Dr. Brinkley, the Bishop of Cloyne, conceived that he had succeeded in the case of a Lyræ, the star Vega of the first magnitude in that constellation; but improved instruments have lessened the amount of parallax he assigned, and Mr. Airy has pronounced it too small to be sensible. The grand problem of stellar remoteness has however been solved by Professor Bessel, and has been justly called a magnificent conquest.

Bessel commenced this great achievement in the month of September 1834, at Konigsberg, and was employed upon it during the four following years, communicating the result in a letter to Sir John Herschel in 1838. "After so many unsuccessfulattempts to determine the annual parallax of a fixed star," he remarks, "I thought it worth while to try what might be accomplished by means of the accuracy which my great Fraunhofer heliometer gives to the observations. I undertook to make this investigation upon the star 61 Cygni, which by reason of its great proper motion, is perhaps the best of all, which affords the advantage of being a double star, and on that account may be observed with greater accuracy, and which is so near the pole, that, with the exception of a small part of the year, it can always be observed at night at a sufficient distance from the horizon." This star, now one of the most interesting in the heavens, is in the right wing of the Swan, about 74° S. by E. of Dened, a second class star in that constellation. It is of the fifth magnitude, and in our latitude passes the meridian near the zenith. As intimated in the preceding extract, 61 Cygni has long been known by a motion of its own in space, so extraordinary, independent of that which its constituents may have about each other, that Arago supposes its velocity to exceed that of Mercury, the most rapid body of the solar system, sixty thousand times. In watching this star, Bessel commonly took observations sixteen times every night. Without detailing the course he pursued, which would be uninteresting and unintelligible to most readers, it will be sufficient to state, that our Astronomical Society testified its confidence in his researches and their result, by awarding to him its gold medal. His determination of the annual parallax of the star is 03136, or somewhat less than one third of a second, which places it from us at the astonishing distance of 657,700 times the radius of the earth's orbit, or nearly 624 billions of miles. To aid the imagination in forming some idea of this interval, it may be stated, that the conflagration of the star would not be announced to us under a period of ten years, for a ray of light, which darts to us from the sun in eight minutes, would require that time to travel through the space between us and it. As to that standing example of velocity in terrene regions, a cannon ball, with its rush of five hundred miles an hour, it must be allowed to travel some fourteen millions of years to compass such a space. One delicate thread of a spider's web, placed before the