On November 12th, 1837, at eight o'clock in the evening, the attention of observers in various parts of Great Britain was directed to a bright luminous body, apparently proceeding from the north, which, after making a rapid descent, in the manner of a rocket, suddenly burst, and scattering its particles into various beautiful forms vanished in the atmosphere. This was succeeded by others all similar to the first, both in shape and the manner of its ultimate disappearance. The whole display terminated at ten o'clock, when dark clouds. which continued up to a late hour, overspread the earth, preventing any further observation. In the November of 1838, at the same date, the falling stars were abundant at Vienna: and one of remarkable brilliancy and size, as large as the full moon in the zenith, was seen on the 13th by M.Verusmor off Cherburg, passing in the direction of Cape La Hogue, a long luminous train marking its course through the sky. The same year, the non-commissioned officers in the island of Ceylon were instructed to look out for the falling stars. Only a few appeared at the usual time; but on the 5th of December, from nine o'clock till midnight, the shower was incessant, and the number defied all attempts at counting them.

Professor Olmstead, an eminent man of science, himself an eye-witness of the great meteoric shower on the American continent, after carefully collecting and comparing facts, proposed the following theory :- The meteors of November 13th, 1833, emanated from a nebulous body which was then pursuing its way along with the earth around the sun; that this body continues to revolve around the sun in an elliptical orbit, but little inclined to the plane of the ecliptic, and having its aphelion near the orbit of the earth; and finally, that the body has a period of nearly six months, and that its perihelion is a little within the orbit of Mercury. The diagram represents the ellipse supposed to be

M

Ν

described, E being the orbit of the earth, м that of mercury, and N that of the assumed nebula, its aphelion distance being about 95 millions of miles, and the perihelion 24 millions. Thus, when in aphelion, the body is close to the orbit of the earth, and this occurring periodically, when the earth is at the same time in that part of its orbit, nebulous particles are attracted towards it by its gravity, and then, entering the atmosphere, are consumed in it by their concurrent velocities, causing the appearance of a meteoric shower. Arago has suggested a similar theory, that of a stream or group of innumerable bodies, comparatively small, but of various dimensions, sweeping round the solar focus in an orbit which periodically cuts that of the earth. More recently, a very complete catalogue of aerolite falls, amounting to 175, has been analysed with a curious result. By far the greater number are registered for the months of June and July, as compared with the opposite months, December and January. The earth is then at the greatest distance from the sun; and it appears probable, from Leverrier's investigations, that the mean mass or system of the planetoids is at the same time at its perihelion, and therefore nearest the earth. The conjecture is hence indulged, that aërolites are minute outriders of that remarkable family. Though great obscurity rests upon the subject which may never be dissipated, it is agreed on all hands, that shooting stars, meteoric showers, and aërolites, are identical phenomena

E

manifested in different ways; that independently of the great planets and satellites of the system, there are vast numbers of bodies circling round the sun, both singly and in groups, some also moving as minute moons round the earth; and that in the course of their revolutions these "starlets," or "meteor-planets," as they have been called, come within the sphere of the earth's attraction, and ere precipitated upon its surface, "as weary and forlorn birds of passage, far out at sea, are entangled in the rigging of vessels, and fall helpless on deck."

CHAPTER VII.

A GLANCE AT THE STARS.

have been chiefly occupied hitherto with those celestial bodies, which from their conspicuous appearance or changes of position, and some of them from their obvious connexion with the convenience and existence of the human race, have in all ages been objects of special attention. Most of these bodies are situated within the limits of the zodiac, an imaginary zone or girdle extending round the heavens, of about sixteen degrees in breadth. It includes the sun and moon, and also all the planets, with the exception of the planetoids. But in the zodiac, and throughout the whole celestial concave, we see scattered every where a number of radiant points of varying brightness, which appear to have always the same position with regard to each other. This has originated the title of the fixed stars, by which they are popularly known. The term, in an absolute sense, is inaccurate; for recent observations have detected changes in the mutual relations of many of these bodies, and it is probable that all of them are subject to translation. Owing to their vast distance, their motions appear exceedingly slow to us, requiring the finest instruments to be perceptible; and hence they have a character of permanence in contrast with the planets, and the term "fixed" becomes comparatively applicable. The apparent immobility of these objects renders them of immense use in geography, navigation, and planetary astronomy; and hence the observation of the sidereal host, and the formation of accurate catalogues of its members, are among the most important of the labours of science. Sir J. Herschel, in magnificent language, before the Astronomical Society, thus referred to the catalogue of Piazzi, published in 1805, containing the places of no less than 7646 stars:- "For what has a Piazzi worn out his venerable age in watching? The answer is, not to settle mere speculative points in the doctrine of the universe; not to cater for the pride of man, by refined enquiries into the remoter mysteries of nature, -to trace the path of our system through infinite space, or its history through past and future eternities. These, indeed, are noble ends; the mind swells in their contemplation, and attains in their pursuit an expansion and hardihood which fit it for the boldest enterprise. But the direct practical utility of such labours is fully worthy of their speculative grandeur. The stars are the landmarks of the universe; and, amidst the endless and complicated fluctuations of our system, seem placed by its Creator as guides and records, not merely to elevate our minds by the contemplation of what is vast, but to teach us to direct our actions by reference to what is immutable, in His works. It is indeed hardly possible to over-appreciate their value in this point of view. Every well-determined star, from the

moment its place is registered, becomes to the astronomer, the geographer, the navigator, the surveyor, a point of departure which can never deceive or fail him, the same for ever and in all places, of a delicacy so extreme as to be a test for every instrument yet invented by man, yet equally adapted for the most ordinary purposes; as available for regulating a town clock, as for conducting a navy to the Indies; as effective for mapping down the intricacies of a petty barony, as for adjusting the boundaries of trans-Atlantic empires. When once its place has been thoroughly ascertained and carefully recorded, the brazen circle, with which that useful work was done, may moulder, the marble pillar totter on its base, and the astronomer himself only survive in the gratitude of his posterity; but the record remains, and tranfuses all its own exactness into every determination which takes it for a groundwork, giving to inferior instruments, nay, even to temporary contrivances, and to the observations of a few weeks or days, all the precision attained originally at the cost of so much time, labour, and expense."

In the earliest times of which we have any account, mankind appear to have been acquainted with the use of the stars as celestial guideposts in their travels by land and We voyages on the deep. Te may conclude their observance in the former circumstances to have had the precedence. Without being aware of some safe and sure method of directing their course by night, acquired in journeys on shore, men would hardly venture upon a night voyage at sea. It is likely that in the great Oriental deserts, those immense plains with few natural landmarks, the useful discovery was made how accurately the traveller may direct his footsteps by a cultivated acquaintance with the stars, which stimulated enterprize upon the pathless waters, and laid the foundations of maritime expeditions. Diodorus Siculus expressly states that travellers in the sandy deserts of Arabia were accustomed to direct their course by the Bears, the two constellations of that name, a fact which the Koran recognises in the passage: "God has given you the stars to be guides in the dark both by land and sea." The honour of inventing nautical astronomy is usually assigned to the Phenicians, but some knowledge of it prevailed among the Greeks as early as the time of the Trojan war. Ulysses is represented sailing on his raft, sitting at the helm, and watching the stars through the night. While, however, the Greek sailors chiefly confined their observations to Ursa Major, the Phenician navigators made a closer approximation to the north. Aratus tells us, referring to Ursa Minor :—

"Observing this, Phenicians plough the main."

The renowned pilot of the Trojan fleet, Palinurus, through intently watching the face of the nocturnal heavens at the helm, fell overboard, and for a time was lost to his companions. The Pleiades are supposed to derive their name from λéu, to sail, because, during the winter months, they were of high importance to the benighted Greek mariner. It must appear marvellous in the extreme to the uninformed, that now the skilful navigator, on a before unvisited ocean, can determine positively where he is, to within a few miles, by means of the stars; and ascertain his distance from, and true course to, any known meridian or harbour of the globe. From the deck of his ship he has merely to measure the moon's apparent distance from certain stars, to compare the result with their true places as given in the Nautical Almanack for every day in the year, and he finds his longitude. There are nine conspicuous stars which are chiefly used for this purpose, owing to their position being contiguous to the moon's path in the heavens;—a Arietis, Aldebaran, Pollux, Regulus, Spica Virginis, Antares, Altair, Fomalhaut, and Markab. The late Captain Basil Hall on one occasion was at sea for eighty-nine days, passing in the interval through a distance of eight thousand miles, without once making land or seeing a single sail on the voyage, but with unerring precision he came direct to his destination. His course lay from San Blas on the west coast of Mexico, through the Pacific Ocean,

round Cape Horn, and across the South Atlantic to Rio Janeiro. Arrived within a few days' sail of Rio, he took a set of lunar observations, to ascertain his true position, and the bearing of the harbour, and shaped his course accordingly. Afterwards, as he remarks, "I hove to, at four in the morning, till the day should break, and then bore up; for, although it was hazy, we could see before us a couple of miles or so. About eight o'clock it became so foggy, that I did not like to stand in farther, and was just bringing the ship to the wind again, before sending the people to breakfast, when it suddenly cleared off, and I had the satisfaction of seeing the great Sugar-loaf rock, which stands on one side of the harbour's mouth, so nearly right ahead that we had not to alter our course above a point in order to hit the entrance of Rio. This was the first land we had seen for three months, after crossing so many seas, and being set backwards and forwards by innumerable currents and foul winds." The crew might well cheer their skilful commander upon entering the port.

On a clear night in winter, when the moon is absent, the heavens exhibit an aspect of great brilliancy, attractive to the eye of childhood and maturity. But to see the stars to advantage, in the utmost of that glory which they reveal to the gaze of man, we must cruise in tropical seas, or wander with the Bedouins in their deserts. There, through a more transparent medium, the lesser lights of heaven shine with a lustre and vivacity of which we have no conception, who are only familiar with a denser atmosphere. Known to be at a distance from us, in comparison with which the interval between us and the farthest planet is but a hand-breadth, the stars far surpass that planet in their light, and hence it follows that they are not like him dependent upon the central luminary of our system, but self-luminous bodies, independent suns. This is rendered unquestionable by the fact, that while every reflected light is susceptible of polarisation, the light of the stars, like that of the sun, is incapable of it. The tremulous emission of the stellar light, the scintillation or twinkling of the stars, is a remarkable feature, and was long a puzzle to philosophers. It is now generally supposed to arise from the molecules of the atmosphere constantly undergoing sudden compressions and dilatations, which produce changes in its refractive power, and consequent changes in the direction of the rays of light,

apparently every moment displacing the stars. The effect is not so sensible in the case of the planets because of their disks. These, though small, are of sufficient magnitude to bear without so much disturbance the minute agitations of the atmosphere, whereas the stars, being only brilliant points, without any perceptible diameter, are completely displaced. It has been observed, that in serene climates, and on the tops of high mountains, the twinkling of the stars is much less powerful than when viewed from other situations, which tends to confirm the preceding explanation as the true one.

On directing the eye to the celestial vault, the impression made upon the mind is that of an incalculable number of stars being visible - that of the army of heaven consisting of a host which our arithmetic will not suffice to reckon. It is well known that this is an optical illusion. Their twinkling and disorderly position in the sky confuse and deceive the sight. They are so scattered as not to be included at once in the field of vision. Hence arises the idea, that the visible number, which is really very limited, is, on the contrary, immense. This is the popular notion, and it is borne out by our first optical impressions. But an ordinary eye will not be able to discern much above a thousand in our firmament under the most favourable circumstances; and including both hemispheres, three thousand will be the outside number which a keen and experienced gaze will reach. The Greek and Arabian astronomers distinguished some of the brightest stars by particular names, which are recognised in our nomenclature of the heavens, as Sirius, Aldebaran, Rigel, Arcturus, Capella, Canopus, and Fomalhaut, though a different mode of proceeding is now adopted, having become necessary by the large additions made to the ancient catalogues. To distinguish the stars in a constellation, the letters of the Greek alphabet are now employed; when these are exhausted, those of the Roman are used; and when these fail, numerals are resorted to. Thus a designates the most brilliant star of a group, ẞ the next most conspicuous, y the third, and d the fourth. In this way, the relative brightness of the members of particular constellations is indicated, not that of the stars in general, for y Virginis is equal in brightness to a Aquarii. This method was first introduced by John Bayer of Augsburg, in his "Uranometria,” in 1603; who thus ranged the stars in the order of brilliancy, as they then appeared to the naked eye, and it has been adopted by most succeeding astronomers. Referring to the whole host of heaven, the stars are divided into classes, according to their apparent magnitudes, which range from those of the first magnitude, or the brightest, down to the sixteenth; but all after the sixth are invisible to the naked eye, and are hence called telescopic objects. Of the stars in both hemispheres, within reach of a practised gazer, which in round numbers may be stated to be three thousand, the following are about the proportions belonging to the different classes:

From direct experiments with the photometer, an instrument for measuring the intensity of light, Sir W. Herschel inferred as follows:

Light of a star of the average first magnitude

second

100 = 25

The intensity of the light, therefore, of a first class star, according to this estimate, is a hundred times greater than that of one belonging to the sixth. Sir John Herschel has arrived at a different conclusion, having found the light of Sirius, the brightest star in the heavens, about 324 times that of an average star of the sixth magnitude.

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