diately above the horizon at sunrise and sunset, such is not actually the case; but the effect proceeds from the bending of his rays towards the part where we happen to be. Again, the density of the atmosphere occasions the sun and moon to appear larger than when their rays descend to us less obliquely; and owing to the difference in density which often prevails in a small space, the lower and upper portions of the discs of the sun and moon assume a compressed or oval form. When the former appearance is presented by the moon, about the end of the second and third quarter, it is generally indicative of rain or wind. The boat-like form is, nevertheless, extremely pleasing, when seeming to float through trackless ether, or urging its way amid innumerable clouds, light, fleecy, and fantastic. Such is the supposed cause of twilight; and yet, to borrow the remark of Humboldt, the extraordinary lightness of the nights during the summer of 1831, occurring in the latitudes of Italy and northern Germany, when small print could be read at midnight, was in manifest contradiction to all that had been taught on the theory of twilight, and the height of the atmosphere. A few additional stars are added to those of last month; but twilight, at this season, is too strong to admit of noticing them very particularly, more especially as they have not risen far above the horizon. The sun enters this interesting constellation on the 21st of June, the first day of summer, the longest in the northern hemisphere, mid-day at the North Pole, and midnight at the South. Macrobius, who ingeniously explained the origin and intent of all such figures as were anciently associated with the constellations, considers them as part of the hieroglyphic language which the ancients inscribed on the heavens. They placed, said he, the Crab and Goat, Cancer and Capricorn-not by chance, nor yet without designat the two corners of the sun's CANCER. course, but at once to mark the points, and to convey the knowledge of certain celestial phenomena. When the sun arrived at an assigned limit, they perceived that he began to move backwards, and to descend obliquely; and in order to mark the place where this occurred, they took note of the stars that shone in its vicinity; and for the purpose of rendering these familiar to the mind, they associated with them different kinds of living creatures. The Crab, which moves backward and obliquely, afforded an apt symbol of the sun's retrograde movement. And although the constellation of the Goat had reference to pastoral occupations, it also marked the opposite natural barrier of the sun's progress, that part of the ecliptic where, having quitted his lower path, he begins to ascend higher and higher. The wild goat, therefore, an animal which delights in climbing the loftiest mountains, was selected as the figure under which to arrange a symbolic constellation. The "neighbour stars" that surround the Crab are those of the Lynx, the Lion, and the Twins, the Unicorn, the Little Dog, Hydra, and the Lesser Lion. The Greater Lion is stationed immediately before it. Hence it happens that the harmless Crab, and the monarch of Libyan wastes, appear as if looking earnestly at each other; that the hind feet of the Lynx come very near to the side of Cancer; that the Twins are close behind; and that, further, Unicorn, the Dog, and Hydra form a line between the lower portion of the Twins and Lion. Cancer exhibits a group of stars called Præsepe, or the Bee-hive, or rather a cluster of very minute stars, not separately distinguishable by the naked eye, but sufficiently luminous to be seen as a nebulous speck, somewhat resembling the nucleus of a comet, and for which it has occasionally been mistaken by casual observers. Præsepe is situated in a triangular position, with regard to Castor and Procyon, or the Little Dog: a line drawn from the latter in a north-easterly direction meets with this nebulous cluster at the distance of twenty degrees, and if extended in a north-westerly_direction from the same, meets Castor at an equal distance, forming, altogether, nearly a right angle, of which the angular point is in Præsepe. It may also be discovered by means of two stars of the fourth magnitude, lying one on either side, at the distance of two degrees. When contemplated with a three-and-a-half-feet achromatic, and a power of ninety-five, it is scarcely possible to imagine any kind of celestial scenery more brilliant or more beautiful. Fifteen or twenty of the most conspicuous among its clustering stars present admirable configurations; one is nearly an equilateral triangle; another, an isosceles; a third resembles a cone; a fourth presents parallel lines. In more than two instances three bright stars appeared in a straight line, similar to the belt of Orion, while a considerable number were extremely minute. The word "nebula," applied by astronomers to denote certain fixed and apparently whitish clouds in the heavens, literally signifies a cloud or mist, consisting of innumerable stars, so thickly studded together that their combined light presents the thin luminous appearance by which they are distinguished. Sir William Herschel conjectures that however widely dispersed, they yet encompass the whole starry sphere of heaven, like the Milky Way, which is undoubtedly composed of fixed stars. He mentions that nebulæ are more general in some parts than in others; that spaces in their vicinity are often starless; and that luminous clouds, or mists, are more frequently among stars of considerable magnitude than among those of minor importance. Various forms and classes may be noticed, although reducible into two great divisions-viz., such as are composed of countless stars, though discoverable only by the aid of powerful telescopes, and such as the highest magnifiers have not been able to reveal otherwise than as merely luminous clouds. In former times about one hundred nebula were known to astronomers; since then the unwearied exertions of Sir William Herschel have brought to light at least two thousand more. Their different places were afterwards computed from his observations, and arranged in a catalogue, in the order of right ascension, by his sister, Caroline Herschel, a lady distinguished for her astronomical knowledge and discoveries. Her illustrious nephew, Sir John Herschel, added five hundred nebula to those discovered by his father, as also the same number in the southern hemisphere, among which the Magellanic clouds are the most beautiful and conspicuous. These dim and wondrous nebulæ, whether containing a bright assemblage of glorious stars, or whether bearing only the appearance of a far-off cloud, are often most singularly varied. Herschel speaks of several as presenting equally eccentric and curious forms. Among these is one resembling a luminous hour-glass, surrounded by a thin, hazy atmosphere; another, consisting of a nucleus, bright and circular, having a nebulous ring; a third, faint and branching, of a milky whiteness, and diversified with bright spots. A remarkable nebulosity appears in the constellation of Orion, discernible without the assistance of a glass, and occupying a middle distance in the sword. Huggins observed the appearance, and remarked concerning it that astronomers had noticed three NEBULOSITY IN ORION. stars close to each other in the sword, but that when he examined the middlemost with a telescope he readily perceived twelve other stars; three that nearly touched each other, and four that seemed to twinkle dimly, as through a cloud. This nebulosity exhibited an indefinite foggy appearance, brighter, yet more diffuse when a telescope was used; but the whole power of Herschel's forty-feet reflector could not resolve it into distinct stars. Nothing, however, deterred, Huggins continued to observe it with the greatest interest; and at length, having perfected his forty-feet telescope, discovered that it possessed such a magnitude and brilliancy as fully to warrant him in believing that it was the nearest of its brethren, and consequently likely to afford much valuable information. Apparently it was composed of little flocky masses, or wisps of clouds, adhering to small stars at its outskirts, and could not, perhaps, be more aptly described than by comparing it to a curdling surface strewed over with small locks of wool, or the breaking up of a mackerel sky, when the clouds assume a wavy appearance. Whatever the filmy mass might be, its dimensions were enormous. "We know not," wrote the astronomer, "what the immense looming mass portends; time may, however, develope it, and, with the passing on of years, facts may be elicited that will astonish the world." And so it has been. The telescope of which we are about to speak has discovered the revolution of this stupendous nebula. When Dr. Nichol visited Parsonstown he saw the nebula through its mighty tube. It was the first time that the grand instrument had been directed towards that mysterious object, and though Lord Rosse warned him that circumstances connected with its examination did not admit of a final conclusion with regard to existing theories, the narrator went with breathless interest to its inspection. Not the slightest trace of a star was discoverable: "looming unintelligible as ever, appeared the nebula; but how brilliant its brightest portions! How broken the interior of its mass! How innumerable the streams that seemed attached to it on every side! How strange, especially a large horn northward, rising in bold relief, amid the darkness of the night, like a cumulous cloud!" Truly had Lord Rosse remarked, that one observation would not suffice with regard to a number of sparkling points, small as those of a needle, nearly as close as grains of sand, the more especially when any sudden gust of wind, or momentary irregularity in the instrument, might cause the light of each to mingle, and present the aspect of a luminous cloud. Throughout the winter did the noble constructor of an unrivalled telescope seize every favourable opportunity to ascertain, if possible, the constitution of the nebula. He plainly saw that all about the trapezium was a mass of stars, the remainder of the nebula also abounding with stars; consequently that such appearances might be regarded as stellar groups, infinitely remote, and yet so vast as to be discernible across those spaces in the heavens of which the magnitude is overpowering to the mind. SPIRAL NEBULA. This extraordinary nebula is justly considered as one of the most wondrous objects in the starry heavens. It was discovered by Lord Rosse, and is termed Lord Rosse's Whirlpool, or Spiral Nebula. When examined through an eighteen-inch reflector, a bright and globulous nebula becomes apparent, surrounded by a ring at some considerable distance, of unequal lustre, and subdivided through about two-fifths of its circumference into separate laminæ, one of which appears as if turned upwards out of the plane of the other. When regarded through the sixfeet reflector of Lord Rosse's, the interior, or the seeming upturned portion of the ring, assumes the character of a nebulous coil, tending in a spiral form towards the centre: a similar tendency in the streaks of nebula connecting the ring and central mass is further developed, and forms a striking feature. A narrow curved band of nebulous light also beautifully connects the encircling nebula with the ring, and the whole, though not obviously formed of innumerable stars, yet doubtless owes its origin to them. The position of this Spiral Nebula is near the ear of the Northern Greyhound, below eta of the Great Bear. Its singular form indicates the action of some powerful and controlling law; it resembles a scroll gradually unfolding, or the evolution of a gigantic shell." 66 CHAPTER VII. JULY. "With hieroglyphics older than the Nile The heavens are studded. Those who read aright, SUCH of the northern constellations as were resplendent in the heavens during winter now occupy very different positions. Most of the southern have disappeared, and even those which seem to traverse the immensity of space are scarcely discernible, however brilliant, in the light nights of the present month. Their positions, however, are as follow:-Westward of the meridian shine the Northern Crown, Libra, and the Serpent. At a considerable elevation, and some distance from the meridian, Arcturus may be dimly discerned. Far below this beautiful constellation beams the Spica Virginis, very near the S.W. by W. point of the horizon. Cor Caroli may be seen north by west of Arcturus, occupying a high and distant position: immediately beneath, and nearly due west, is Denebola. Westward of the meridian the Great Bear holds an exalted station, his two pointers directed eastward to the Pole star. Castor and Pollux have recently descended below the horizon, towards the north-west; and Capella, a star which never sets in this latitude, is very near the north point, a few degrees above the horizon. Cassiopeia lifts up her head in the north-eastern quarter of the heavens; a Lyræ looks down from a great height. Eastward of the meridian, and in the same direction, though at a lower altitude, is Denebe, one of the principal stars in the Swan. The Square of Pegasus, formed of four stars, may be faintly discovered, a little northward of the east point, nearly opposite to the place they held in January. Antares, a star of the first magnitude in |