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cover the means of predicting their future return. The Principia of Newton, which laid the foundation of all sound astronomical science, had appeared soon after the middle of the seventeenth century; and Halley, the contemporary and friend of Newton, had his attention naturally directed to the physical enquiries which that immortal book suggested. One of the most curious and interesting of these questions was that to which we now allude. Halley, referring to the records of all former observers, with a view to obtain means of determining, as far as possible, the course of former comets, succeeded in identifying one which he had himself observed in 1682, with comets which had appeared on several former occasions; and found, that the interval between its successive returns was from 75 to 76 years. This discovery has since been fully confirmed, and the comet has received the name of Halley's comet. We now propose to lay before the reader the history of this celebrated comet.

In retracing the history of a body of this nature, so far as we can collect it from ancient chroniclers and historians, it is necessary to bear in mind that the terror which the appearance of comets inspired, had a tendency to produce an exaggeration of their effects. The propensity to ascribe to supernatural causes effects which the understanding fails to account for, has rendered comets peculiarly objects of superstitious terror. They have been accordingly regarded in past ages as the harbingers of war, pestilence and famine, and of all the greatest scourges which have visited the human race. But more especially they have presided at the birth and death of the most celebrated heroes. Thus, a conspicuous body of this kind appeared for seven days succeeding the death of Julius Cæsar, and was regarded as the soul of that illustrious person transferred to the Heavens. Another was seen at Constantinople in the year of the birth of Mohammed. It is obvious, that under the influence of such powerful prejudices, the circumstances attending these appearances would naturally be amplified and exaggerated; and the probability of exaggeration is increased by the fact that since science has shed its light upon the civilized world, these terrible objects have, in a great degree, disappeared, and comets have dwindled for the most part into very insignificant appearances. One of the ill consequences of this exaggeration is, that it greatly increases the difficulty of identifying the bodies which have been described with those which have appeared in more recent times. In fact, we have little more to guide us than the epochs of the respective appearances; and, antecedently to the fifteenth century, we possess absolutely no other evidence of the identity of these bodies except the record of their appearance at

the times at which we know, from their woerantes peus the ought to have appeared. As the fine, I VOL seem at least probable that the first recorded appearates of Ear ley's comet was that which was supposed to seize the 1071 of Mithridates, one hundred and tiny pan bare the bora vẻ Christ. It is said to have appeared fe re-for sa light is described to have surpassed that of the su: remar tude to have extended over a fourth part of the framer: a r is stated to have occupied oonsequely abox for DOTS I ISIT and setting.

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In the year 323, a comet appeared in the syn Trg Amie according to the historians of the Lover Engre, acerret n the year 399, seventy-five years after the last the net minemi being the period of Haley's comes

The interval between the birth of Musicians and dep 323 was four hundred and fity-three years were volt de P valent to six periods of 75 years The ivot seem to

in the interim there were fre returns of this comet those or at least unrecorded. The appearance in the Tear Che was attended with extraordinary érénszuers In the TheZen. Cometarum of Lubieniets, it is described as cometa proagiosa magnitudinis, horritalis arports, coman ad terran wagne demittere risus. The next recorded appearance of a comet agreeing with the ascertained period marks the taking of home by Totila in the year 550; an interval of 151 years, or two periods of 754 years, having elapsed. One unrecorded return must therefore, have taken place in this interima. The next appearance of a comet coinciding with the assigned period is 340 years afterwards, viz. in the year 930, five revolutions having been conpleted in the interval. The next appearance is recorded in the year 1005, after an interval of a single period of seventy-fre years. Three revolutions would now seem to have passed unrecorded, when the comet again makes its appearance in 1239. In this, as well as in former appearances, it is right to state once more, that the sole test of identity of these comets with that of Halley, is the coincidence of the times of their appearances, as nearly as historical records enable us to ascertain, with the epochs at which the comet of Halley might have been expected to appear. That such evidence, however, must needs be imperfect will be evident, if the frequency of cometary appearances be considered; and if it be remembered that hitherto we find no recorded observations, which could enable us to trace even with the rudest degree of approximation the paths of those comets, the times of whose appearances raise a presumption of their identity

with that of Halley. We now, however, descend to times in which more satisfactory evidence may be expected.

In the year 1305, one of those in which the comet of Halley may have been expected, a comet is recorded of remarkable appearance; cometa horrenda magnitudinis visus est circà ferias Paschatis, quem secuta est pestilentia maxima. Had the horrid appearance of this body alone been recorded, this description might have passed without the charge of great exaggeration; but when we find the Great Plague connected with it as a consequence, it is impossible not to conclude that the comet was seen by its historians through the magnifying medium of the calamity which followed it. Another appearance is recorded in the year 1380, unaccompanied with any other circumstance than its mere. date. This, however, is in strict accordance with the ascertained period of Halley's comet.

We now arrive at the first appearance at which observations were taken, possessing sufficient accuracy to enable subsequent investigators to determine the path of the comet; and this is accordingly the first comet, the identity of which with the comet of Halley, can be said to be conclusively established. In the year 1456, a comet is stated to have appeared of unheard of magnitude;' it was accompanied by a tail of extraordinary length which extended over sixty degrees (a third of the heavens,) and continued to be seen during the whole of the month of June. The influence which was attributed to this appearance renders it probable that in the record there exists more or less of exaggeration. It was considered as the celestial indication of the rapid success of Mohammed II., who had taken Constantinople, and struck terror into the whole Christian world. Pope Calixtus II. levelled the thunders of the church against the enemies of his faith, terrestrial and celestial, and in the same Bull exorcised the Turks and the comet; and in order that the memory of this manifestation of his power should be for ever preserved, he ordained that the bells of all the churches should be rung at midday, a custom which is preserved in those countries to our times. It must be admitted that, notwithstanding the terrors of the church, the comet pursued its course with as much ease and security as those with which Mohammed converted the Church of St Sophia into his principal mosque.

The extraordinary length and brilliancy which was ascribed to the tail upon this occasion, have led astronomers to investigate the circumstances under which its brightness and magnitude would be the greatest possible; and, upon tracing back the motion of the comet to the year 1456, it has been found that it was then actually under the circumstances of position with respect

to the earth and sun most favourable to magnitude and splendour. So far, therefore, the results of astronomical calculation corroborate the records of history.

The next return took place in the year 1531. Pierre Appian, who first ascertained the fact, that the tails of comets are usually turned from the sun, examined this comet, with a view to verify his statement, and to ascertain the true direction of its tail. He made accordingly numerous observations upon its position, which, though, compared with the present standard of accuracy, they must be regarded as of a rude nature, were still sufficiently exact to enable Halley to identify this comet with that observed by

himself in 1682.

The next return took place in 1607, when the comet was observed by the celebrated Kepler. This astronomer, on his return from a convivial party, first saw it on the evening of the 26th September; it had the appearance of a star of the first magnitude, and, to his vision, was without a tail; but the friends who accompanied him having better sight, distinguished the tail. Before three o'clock the following morning the tail had become clearly visible, and had acquired great magnitude. Two days afterwards the comet was observed by Longomontanus; he describes its appearance, to the naked eye, to be like Jupiter, but of a paler and more obscure light; that its tail was of considerable length, of a paler light than that of the head, and more dense than the tails of ordinary comets. He states, that on the 24th of September following, the comet was not apparent; that on the 24th of October it was seen obscurely, and some days afterwards disappeared altogether.

The next appearance, and that which was observed by Halley himself, took place in 1682, a little before the publication of the Principia. A comet of frightful magnitude had appeared in 1680, and had so terrified all Europe, that the subject of our present enquiry, though of such immense astronomical importance, excited comparatively little popular notice. In the interval, however, between 1607 and 1682, practical astronomy had made great advances; instruments of observation had been brought to a state of comparative perfection; numerous observatories had been established, and the management of them had been confided to the most eminent astronomers of Europe. In 1682, the scientific world was, therefore, prepared to examine the visitor of our system with a degree of care and accuracy before unknown. It was observed at Paris by Lahire, Picard, and Dominique Cassini; at Dantzic, by Hevelius; at Padua, by Montonari; and in England, by Halley and Flamstead.

In 1686, about four years afterward, Newton published his Principia, in which he applied to the comet of 1680 the general principles of physical investigation first promulgated in that work. He explained the means of determining, by geometrical construction, the visible portion of the path of a body of this kind, and invited astronomers to apply these principles to the various recorded comets,-to discover whether some among them might not have appeared at different epochs, the future returns of which might consequently be predicted. Such was the effect of the force of analogy upon the mind of Newton, that without awaiting the discovery of a periodic comet, he boldly assumed these bodies to be analogous to planets in their revolution round the sun.

In the third book of his Principia, he calls them a species of planets revolving in elliptic orbits, of a very oval form, and even remarks an analogy observable between the order of their magnitudes and those of the planets. He says,- As among planets without tails, those which revolve in less orbits, and nearer to 'the sun, are of less magnitude, so comets which in their perihelia approach still nearer to the sun than the planets, are much less than the planets, that their attraction may not act too strongly on 'the sun. But,' he continues, I leave to be determined by others the transverse diameters and periods, by comparing comets 'which return after long intervals of time in the same orbits.'

It is interesting to observe the avidity with which minds of a certain order snatch at generalizations, even when but slenderly founded upon facts. These conjectures of Newton were soon after adopted by Voltaire :-Il y a quelque apparence,' says he, in an Essay on Comets, 'qu'on connaitra un jour un cer'tain nombre de ces autres planetes qui sous le nom de comètes tournent comme nous autour du soleil, mais il ne faut pas espérer ' qu'on les connaissent toutes.'

And again, elsewhere, on the same subject:

Comètes, que l'on craint à l'égal du tonnere,
Cessez d'epouvanter les peuples de la terre ;
Dans une ellipse immense achevez notre cours,
Remontez, descendez près de l'astre des jours.'

Extraordinary as these conjectures must have appeared at the time, they were soon strictly realized. Halley undertook the labour of examining the circumstances attending all the comets previously recorded, with a view to discover whether any, and which of them, appeared to follow the same path. Antecedently to the year 1700,

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