the orbit of Mars from the sun; but, early in March, it appeared with a tail divided into six branches, all diverging, but curved in the same direction. Each of these tails was about 4° in width, and from 30° to 44° in length. The edges were bright and decided, the middle faint, and the intervening spaces as sombre as the rest of the firmament, the stars shining in them. This comet was repeatedly seen in Switzerland, with the nucleus below the horizon, and the six tails extending from twenty to thirty degrees above it. The scene presented by this remarkable body in the situation referred to was striking in the extreme when circumstances favoured the display. In the year 1770 a comet appeared which has acquired considerable notoriety from the alterations which its orbit has undergone. It was first observed by Messier, a man who united great simplicity of character with high scientific attainments. Louis XV. called him le furet des cométes, from his zeal in hunting after them. He had discovered twelve, every one of which, says Delambre, gained him admission to some foreign academy. While attending to his wife during her last moments, Montagne discovered another. This was a cutting stroke to Messier, and he exclaimed, "Alas, I had discovered twelve, and this Montagne has taken away my thirteenth!" Then remembering that it was his wife he should mourn for, he began to say, "ah! la pauvre femme!" and went on deploring his comet. The elements of the comet of 1770 were calculated by Lexel, who found for its orbit round the sun an ellipse of which the transverse diameter was only equal to three times the diameter of the earth's orbit, which corresponded with a period of revolution of five years and a half. It was deemed a singular circumstance that an object having so short a periodic time, whose greatest distance from the sun was not far beyond the orbit of Jupiter, and which shone with a vivid light, should not have been observed before; and the wits of the day made themselves merry, when, at the expiration of, the appointed term, the comet was not observed to return. It has not been seen since; and was popularly called Lexel's lost comet. But this sport was premature. The previous invisibility and subsequent disappearance of this body, after once presenting itself, have been sufficiently explained; and a confirmation of the laws of universal attraction has been drawn from circumstances apparently adverse to them. Its previous invisibility is accounted for by its orbit being altogether different prior to the year 1770, its nearest point to the sun being as distant as the path of Jupiter, corresponding, not to five, but to fifty years of revolution. Its appearance that year arose out of the fact that in 1767 it was in such close contact with the planet, moving in the same direction and in nearly the same plane, that the attraction of the sun upon it was not that of Jupiter. This entirely altered the form of the orbit, and caused the comet to wheel its path towards that of the earth, coming within our view, and executing the ellipse described by Lexel in the periodic time of five and a half years. But why has not the comet since been seen? Its passage to the point of perihelion in 1776 took place by day; and in 1779, before another return, it again encountered the vast body of Jupiter, and suffered a fresh orbital derangement, the attraction of the planet deflecting it into more distant regions. The comet therefore, though "lost" to us, is in existence, and in each instance of its change of route has faithfully obeyed the laws of gravitation. Those laws in 1770 introduced it as a bright and beautiful stranger to the notice of the human race, and again in 1779 stopped the fellowship, removing the comet into a remoter path, where it is hid from the gaze of man, and will be so unless some new perturbation directs its course towards the terrestrial orbit. *Another comet, exhibiting some remarkable features, presented itself in the year 1807. It was assiduously observed by Herschel in this country, and by the continental astronomers, Schroeter, Bessel, and Olbers. The drawings of the two former are here given, taken on two succeeding evenings, which show a divided tail, the separate branches having varied their aspects. Coruscations, flickering and vanishing like the northern lights, appeared to shoot out in an instant from the train to an immense extent. In the autumn of 1811, within the memory of many of the present generation, by far the finest comet suddenly appeared to adorn our heavens, that has been seen since the age of Newton. It was first beheld in this country in the beginning of September, and was visible for more than three months in succession to the naked eye, shining with great splendour, the observed of all observers. This was a comet of the first class in point of magnitude and luminosity. Its brilliant tail, at its greatest elongation, had an extent of 123 millions of miles, by a breadth of 15 millions; and thus, supposing the nucleus of the comet to have been placed on the sun, and the tail in the plane of the orbits of the planets, it would have reached over those of Mercury, Venus, the Earth, and have bordered on that of Mars. At its nearest approach to us, the comet was yet distant 141 millions of miles, so that even had the tail pointed to the earth, its extremity would have been 18 millions of miles away from its surface. The following are the calculations respecting its period of revolution: Years. 3056 3383 ment The mind is astounded at a journey requiring the least of these cycles for its accomplisha period equal to that extending from the fabulous age of Grecian story to the present; nor is the thought less wonderful, of the chain of solar influence following the traveller through the whole of its course, and preventing its elopement into the regions of immensity. The laws of the system, indeed, impose upon the long-period comets vast differences of velocity. The same body that rushes round the sun at the nearest point of contact with prodigious speed, will move but sluggishly through the remoter parts of its orbit. In computing the periodic time of the comet of 1811, Lemaur assigned 775 years to the half of the ellipse nearest the sun, and 3462 to the more distant half. But the space must be immense that has to be traversed by an object whose return is not expected, taking the lowest estimate given, till the year 4867. The appearance of this comet was strikingly ornamental to the evening sky. Many a reaper late in the harvest field stayed his hand, and many a peasant homeward-bound stopped in the way, to gaze upon the celestial novelty as it grew into distinctness with the declining day. The Ettrick shepherd has left a memorial of his impressions in the well-known lines :Stranger of heaven, I bid thee hail! 66 Shred from the pall of glory riven, Broad pennon of the King of Heaven! "Whate'er portends thy front of fire, And streaming locks so lovely pale; Those who were alive in 1811 will recollect the high temperature of that year- its bountiful harvest-its abundant vintage. Popular opinion assigned these blessings to the resplendent comet; and the wine of the comet was sold afterwards at high prices. No doubt, however, but that precisely different circumstances would have been connected, by the public mind, with the same cause; and this has literally been the case, for "a cold winter," and "meteors in Germany," are referred to the comet of 1680, by a writer in 1829. The following table, given by Arago, is valuable upon this point: From this table, it is clear that no conclusion can be drawn, to the effect that cometary appearances have any influence in raising the temperature. In 1828 and in 1831 no comets presented themselves, and the temperature was nearly at its maximum. In 1808 there were four, and it was nearly at its minimum. There was no inconsiderable amount of superstitious fear blended upon this occasion with the natural feelings of wonder and admiration that were excited. As the great comet of 1680 had been deemed a manifest presage of the revocation of the edict of Nantes, the persecution of the French protestants, and the long wars that ensued, so was the beautiful and transient visitor of 1811 abused in a similar manner. It was widely regarded as the herald of some awful terrestrial occurrence, and the particular event intended was not 1 doubtful to many minds when Napoleon led his legions from the West to perish amid the snows of Russia, and Moscow was in flames! Science has been more recently occupied with two cometary bodies, insignificant in their external aspect, but deeply interesting on account of the discovery that their orbital course is included within the bounds of our system, and their predicted returns fulfilled with unfailing punctuality. The first is known as the comet of Encke. It was observed in the year 1786, by Messier, traversing the constellation Aquarius; afterwards seen by Miss Herschel, in 1795, in Cygnus; and by M. Pons, in 1805, in Ursa Major; but no idea was entertained that these were appearances of the same body, till Encke, in 1819, established their identity, in consequence of which the comet has received his name. It passes at its perihelion within the orbit of Mercury, and has its aphelion midway between the paths of the telescopic planets and Jupiter, its greatest distance from the sun being twelve times its least distance, and its period of revolution 1203 days or 3 years. This object has now seven times answered to the announcements made respecting its course, incontestably establishing its character as a regular member of our system, moving in obedience to its laws. The comet appears as a small globular patch of vapour, without any starlike nucleus or tail, scarcely perceptible, and its dimness seems to be increasing. But this insignificant and shadowy thing exhibits a deeply interesting and important phenomenon, that of the gradual diminution of its periodic time, owing to a decrease in the size of its orbit, the supposed effect of a resisting medium in space, which is urging it nearer the sun, and may ultimately terminate its career as a separate body. The same conclusion is entertained with reference to the planets, founded upon this peculiarity of the comet of Encke. If the spaces in which they move is occupied by a resisting medium, that, it is conceived, will, in the long run of ages, diminish their actual velocity, decrease the centrifugal force, give more power to the solar attraction, draw them towards the centre, and thus end the system. Such a speculation is, to say the least, premature. We may admit the existence of an ethereal medium which shall perceptibly affect the movements of a small vapoury globule, and offer no appreciable opposition to the solid and weighty planetary masses. The proper course is to wait until such a medium is placed beyond all doubt, for it cannot be said yet to be demonstrated; and until we have some evidence of its action in the case of the planets, before we reason upon it as a fact. Besides the comet of Encke there is another whose periodicity has been ascertained, a discovery due to M. Biela, in 1826. This is entirely a telescopic object, and without tail or nucleus like the former. Its aphelion place is a little beyond the orbit of Jupiter, its perihelion within that of Venus, its time of revolution 2461 days, or 63 years. This was the comet which excited a large amount of apprehension for the safety of our terrestrial mansion, prior to its return in 1832. It was calculated that a little before midnight, on the 29th of October, it would cross the plane in which the earth revolves, near the point where our globe itself would be on the morning of the 30th of November following; and, undoubtedly, had the comet been delayed a month by any disturbance, a collision with its nebulosity would have taken place. The alarm was principally |