observations had been made, twenty-four in number, for the purpose of comparing their elements a work of immense labour and difficulty, of which the present Astronomer Royal has remarked, that in all probability he was the only person then in existence who could have performed it. He found the elements of two comets to coincide with tolerable exactness with those of the comet of 1682, as follows: :

a. Year of the comet. b. Longitude of ascending node. c. Inclination of the orbit. d. Longitude of the perihelion. e. Perihelion distance from the sun, that of the earth being 100,000. f. Time of the comet arriving at its perihelion distance. g. Distance from perihelion to ascending node. h. Direction of the comet's motion.

The general elements here are pretty closely analogous. With reference to the periodic time, there is, from

a difference of about fifteen months. This Halley conjectured might arise from the disturbing action of the planets, a correct idea, and one of great sagacity, as the theory of planetary disturbance was but then in its infancy. Upon these data, therefore, he ventured the conclusion that the three appearances were returns of the same comet, which would reappear after the lapse of a similar interval. His words are: 66 Nothing seems to contradict this my opinion, besides the inequality of the periodic revolutions, which inequality is not so great neither, as that it may not be owing to physical causes; for the motion of Saturn is so disturbed by the rest of the planets, especially Jupiter, that the periodic time of that planet is uncertain for some whole days together. How much more, therefore, will a comet be subject to such like errors, which rises almost four times higher than Saturn, and whose velocity, though increased but a very little, would be sufficient to change its orbit from an elliptical to a parabolical one? This, moreover, confirms me in my opinion of its being the same comet, that in the year 1456, in the summer time, was seen passing retrograde, between the earth and the sun, much after the same manner; which, though nobody made observations upon it, yet, from its period and the manner of its transit, I cannot think different from those I have just now mentioned. Hence I dare venture to foretell that it will return again in the year 1758." Subsequently his tone grew more decided. Historical records supplied some further links to the chain of cometary appearances after nearly the same interval. Thus: :

The pro

The astronomer was confirmed by this evidence in the accuracy of his prediction, and called upon all posterity to remember that an Englishman had announced it. phecy was no random guess. It was not founded merely upon the coincidence of the dates, but a result obtained, in the case of the last three comets, from the close agreement of the elements of their orbits.

Great curiosity was excited as the year 1758 approached, to ascertain whether the prediction would be verified. No doubt existed upon the subject in the scientific world, but some apprehension was felt lest circumstances should be unfavourable to a perception of the phenomenon. "We cannot doubt," observed Lalande, in 1757, "that it will return; and even if astronomers should not see it, they will not be the less persuaded of

its return. They know that the faintness of its light, and its great distance, perhaps even bad weather, may keep it from our view; but the public will find it difficult to believe us; they will put this discovery, which has done so much honour to modern philosophy, among the number of predictions made at hazard. We shall see dissertations spring up again in the colleges, contempt among the ignorant, terror among the people, and seventy-six years will elapse before there will be another opportunity of removing all doubt." Lalande engaged with Clairaut and Madame Lepaute in calculating the attractive influence of Jupiter and Saturn upon the comet, which might change to some extent its time of perihelion. "During six months," he remarks, we calculated from morning till night, sometimes even at meals; the consequence of which was, that I contracted an illness which changed my constitution for the remainder of my life. The assistance rendered by Madame Lepaute was such, that without it we never could have dared to undertake this enormous labour, where it was necessary to calculate for every degree, and for 150 years, the distance and force of each of the two planets with respect to the comet." They finally announced in November 1758, just as astronomers began to look out for its return, that the comet would employ 618 days more to return to the perihelion than on the preceding revolution; namely, 100 days from the effect of Saturn, and 518 days from the action of Jupiter. The perihelion was placed therefore about the middle of April 1759, but Clairaut distinctly forewarned the world, that being pressed for time, he had neglected small values, which collectively might amount to, more or less, about a month in the seventy-six years. The event realised the anticipation of Halley, and answered as nearly as possible to the calculations of the French philosophers. The comet was first seen from the neighbourhood of Dresden by George Palitzch, a farmer by profession, but a self-educated astronomer. This was on Christmas day 1758, with an eight-feet telescope. It was afterwards seen at Paris, Leipsic, Lisbon, and Cadiz. It passed its perihelion on the 12th of March 1759, exactly a month before the time announced, but within the assigned limit of divergence from that date. The elements of its orbit proclaimed it to be the comet of the former periods by their similarity. The following is Lalande's deduction, the letters indicating the particulars connected with the table already given :

Another period of revolution has transpired since the time to which we are referring. Dating seventy-six years forward, we are brought to the year 1835. After estimating the action of the planets, Damoiseau, of the French Board of Longitude, fixed the perihelion passage on Nov. 4th of that year, and Pontécoulant on Nov. 13th, a difference of nine days. Both agreed that the first appearance of the comet would be in the early part of August, and the perihelion certainly about the middle of November. The comet was seen at Rome Aug. 5th, and passed its perihelion Nov. 16th. The fictitiousness of the representation,

"A pathless comet, and a curse,

The menace of the universe;
Still rolling on with innate force,
Without a sphere, without a course,"

has thus been demonstrated, and these bodies proved to be constituent members of our system, obedient to the law of gravitation, which keeps them within prescribed limits and in definite orbits, as with bit and bridle.

We may now glance at some of the appearances of this comet at its successive returns, as far as historical records supply information.

The comet of 1006 is conceived on good grounds to have been identical with that of

1682. Its first recorded appearance was thus immediately prior to the Danish invasion of England, and during the declining days of the empire of the caliphs. Hali-ben-Rodoan mentions the immense curved tail in the form of a scythe. The head appeared four times as large as Venus. The second visit, which must have been about 1082, in the reign of the Conqueror, is unrecorded: and the third and fourth, in 1155 and 1230, are merely mentioned by the annalists, without any detail. Its fifth return was in the year 1305, when the papal chair was removed to Avignon, the Swiss cantons were effecting their independence, and Edward I. tyrannising over Scotland. At the season of Easter, this "great and fearful star," as it was called, was perceived, but so far from raising the temperature, a supposed cometary effect in later times, a general cold prevailed over Europe, and a severe frost in England at Midsummer destroyed the corn and fruits. History gives no particulars of its next visit in 1380, but in 1456 its appearance filled all Christendom with consternation. It passed very near to the earth, and swept the heavens with a tail extending over sixty degrees, in the form of a sword or sabre. The Turks had just become masters of Constantinople, and threatened an advance into the heart of Europe.

The comet variously excited hope or fear, according as it was deemed

the friend of the crescent or the cross. At Constantinople, the occurrence of a coincident lunar eclipse increased the portentousness of the event. Phranza, grand-chamberlain and principal secretary to the last head of the Greek Roman empire, reports:

"Each night, soon after sunset, a comet was seen like a straight sabre, approaching the moon. The night of the full moon having arrived, and then by chance an eclipse having taken place, according to the regular process and circular orbits of the celestial lights, as is cus

tomary-some persons seeing the darkness of the eclipse, and regarding the comet in form of a long sword which arose from the west, and travelled towards the east, approaching the moon, thought that the comet in shape of a long sword thus designated, with regard to the darkness of the moon, that the Christians, inhabitants of the West, had agreed to march against the Turks, and would gain the victory; but the Turks, also considering these things, became not a little fearful, and had great discussions." The pope, however, Calixtus III., regarded the comet as in league with the Moslems, and ordered the Ave Maria to be repeated by the faithful three times a day instead of two. He directed the church bells to toll at noon, a custom which still prevails in Catholic countries. To the Ave Maria the prayer was added, "Lord save us from the Devil, the Turk, and the Comet;" and once each day these three obnoxious personages were regularly excommunicated. There was perhaps as much worldly policy as superstition in sounding this note of alarm, for fees accumulated to the priesthood from the increase of confessions. The comet at length, after patiently enduring some months of daily excommunication and cursing, showed signs of retreat, and Europe breathed freely when it vanished from the skies. At the eighth return in 1531, the New World had been discovered, and by the invention of printing the foundation had been laid for the intellectual and religious

reform of the Old. The comet as then seen in Cancer was of a bright gold colour. In 1607, the ninth visit, the Copernican system had been broached, and Galileo and Keppler were labouring to establish it. The course of the comet was observed through Ursa Major, Boötes, Serpentis, and Ophiuchus. Its light was pale and watery. The tail is described as long and thick, like a flaming lance or sword. The apparent magnitude of the head was greater than that of any of the fixed stars, or Jupiter; and, say the chronicles of the age, of its direful effects "the Duke of Lorraine died"-"a great war between the Swedes and the Danes." "The comet does me much honour," was the remark of Cardinal Mazarine on his death-bed, when informed by his servile attendants that one had made its appearance. It is happily said in Shakspeare, in allusion to this sycophancy,

"When beggars die there are no comets seen."

The tenth return brings us to the time of Newton and Halley. Cassini calls it then as clear and round as Jupiter, referring to the nucleus. At the eleventh revolution in 1759, it was a pale and feeble object. Messier was obliged to use a powerful reflecting telescope. Palitzch, indeed, caught it with the naked eye once, but no one else appears to have done so. In 1835, the twelfth advent, it was much more distinct, and was frequently seen without a telescope presenting the annexed appearance.

Its thirteenth return will occur in 1911, when the present generation shall have passed away, and the few remaining infants of to-morrow be bending under the infirmities of age.

The later apparitions of Halley's comet have thus been far less brilliant and conspicuous than its earlier exhibitions. At its four last periodic returns, it bore no resemblance to the comæta horrenda magnitudinis of the year 1305. Arago conjectures that the comets, in describing their immense orbits, disseminate in space at each revolution all the matter which when near the perihelion is detached from the nucleus and forms the tail. It is clearly possible, therefore, that some of them may in process of time completely waste away, unless by travelling through similar detached trains, they recover a quantity of matter sufficient to compensate for their own losses. We may believe, also, that dissipation occurring, the same body that now presents an insignificant appearance, exhibited a bolder front in days of yore, though the early annalists and artists have undoubtedly borrowed largely from imagination in describing these bodies. In a celestial atlas published

It is evident that these artistic efforts are not true to nature, however true to such wild and distorted descriptions as the following, from the " Exempla Cometarum" of Rossenburg, a contemporary of Newton :- "In the year 1527, about four in the morning, not only in the Palatine of the Rhine, but nearly over all Europe, appeared for an hour and a quarter a most horrible comet, in this sort. In its length it was of a bloody colour, inclining to saffron. From the top of its train appeared a bended arm, in the hand whereof was a huge sword in the instant posture of striking. At the point of the sword was a star. From the star proceeded dusky rays, like javelins or lesser swords, as if imbrued in blood, between which appeared human faces of the colour of blackish clouds, with rough hair and beards. All these moved with such terrible sparkling and brightness, that many spectators swooned with fear!"

Before we finally take leave of the comet of Halley, some notice may be bestowed upon his claim to the distinction of being the first to foretell the precise periodical return of one of these bodies. This has been disputed, and assigned to Newton, on evidence recently detailed in one of the leading journals, but which certainly cannot be admitted to invalidate his pretensions. It is affirmed that previously to the appearance of the comet of 1736, Colonel Guise told Whiston that Sir Isaac Newton had said in his presence, that "though he would not say he was sure of it, nor would publish it, he had some reason to believe that a comet would return about the latter end of 1736." Another witness also, Mr. Howard, is cited, as having heard him make a similar remark; and upon being questioned concerning it, it is stated that "he seemed to draw back, as sorry that he had said so much, but still could not deny that he had such an expectation." Whiston therefore says:-"As far as we yet know, Sir Isaac is the very first man, and this the very first instance, where the coming of a comet has been predicted beforehand, and has actually come according to that prediction, from the beginning of the creation to this day." Thomson seems to fall in with this idea in panegyrising the great philosopher:

-:

This is all the evidence that can be arrayed in favour of Newton; and obviously its hearsay source, with the dubious tone of the testimony reported, cannot weigh a feather in the scale against the claims of Halley, whose prediction was the result of careful comparison, and as such boldly published to the world.

The next most remarkable comet of modern times appeared about the middle of December, 1743, and continued visible during the spring of the year following. On the 1st of February, according to Chizeaux, it was more brilliant than Sirius, the brightest star in the heavens. On the 8th it equalled Jupiter, and was visible in the presence of the sun at the beginning of the next month. By selecting a convenient situation many persons saw it at mid-day without glasses. Several instances of similar brilliancy are on record. Justin mentions a comet which appeared at the birth of Mithridates, and overcame the brightness of the sun by its splendour; and, however this may be an exaggeration, there are many well-attested cases of these bodies being seen by broad daylight. The Cæsarian comet, two others in 1402, with one in 1532, were thus visible. The fine comet of 1577 was seen with the naked eye by Tycho Brahe before sunset. On account of its brightness and peculiar form the comet of 1744 excited great attention and interest. It exhibited no train until within the distance of