power of so feeble a gravitating force as would correspond to the minute mass of the nucleus; and it is therefore very conceivable that a comet may lose, at every approach to the sun, a portion of that peculiar matter, whatever it be, on which the production of its tail depends, the remainder being of course less excitable by the solar action, and more impassive to his rays, and therefore, pro tanto, more nearly approximating to the nature of the planetary bodies." Laugier has recently presented two memoirs* to the French Academy on ancient appearances of Halley's comet. He made use for this purpose of the description of comets which E. Biot obtained from the Chinese historians, and presented to the French Board of Longitude. Thus the comet can now be traced back through nine perihelion passages. Its disturbed period of revolution has varied from 77.58 to 74.91 years. Bessel calculated that if the mass of the comet had experienced a loss of one 23,000th of the whole quantity, the period of the comet would be diminished by 1,607 days. The history of the discovery of Encke's comet,† its orbit, its very short period of a little more than three years, and the speculations to which its premature return has led, are well known, and are recorded in other volumes of this Almanac. This comet came to its perihelion, for the seventh time since its period was computed, on the 12th of April, 1842. ‡ At that return, it was seen by Galle at Berlin on the 9th of February; on the 12th of March by Laugier and Mauvais at Paris; and on the 10th of March by Valz at Marseilles. § It was also seen at Philadelphia on the 28th of March by Professor Kendall, and was observed there by him and by Mr. S. C. Walker in March and April. | It was seen at Cambridge by Mr. B. A. Gould, Jr. on the 10th of April, this being the first fair evening after the comet was seen in the United States. T Encke's comet was observed at Hudson by Professor Loomis from March 28 to April 11. Encke did not expect that this comet, which he calls Pons's comet, but which all other astronomers call Encke's comet, would be visible in the northern hemisphere. As it had never been missed since 1819, he was anxious it should be observed in the southern hemisphere, and sent an ephemeris to England to be distributed among the Australian colonies of Great Britain. Encke's comet returned again to its perihelion on August 9, 1845.** But only five observations were made upon it; two at Rome, where it was first seen by De Vico,tt July 9, and again on the 14th; two at Washington, where it was seen July 10; and one at Philadelphia,‡‡ by S. C. Walker, on July 4, who therefore had the first sight of it. Encke's comet returned again to its perihelion on the 26th of November, * Compt. Rend., XVI. p. 1006, XXII. and XXIII. 1846; and Astron. Nachr., XXIII. 377. † Astron. Nachr., XXI. 113-128. 1 Ibid., XIX. 185. § Compt. Rend., XIV. 172. || Astron. Nachr., XXI. 231. Astron. Nachr., XXII. 203; Phil. Mag., XX. 137. **Astron. Nachr., XXIII. 84-92. tt Ibid., XXIII, 255. #Ibid., XXIV. 131; Gould's Astron. Journ., I. 56, 134; Compt. Rend., XXVII. 343, 1848.* It was seen at Cambridge, by Mr. Bond, August 28, and continued to be observed until the 25th of November. Captain Smyth remarked in 1844, "It has since been very generally observed at its successive epochs, and, though never yet seen by the naked eye, is, astronomically speaking, a well-known object.”† In 1848, however, Mr. Bond says of October 8, "The comet is just visible to the naked eye"; and of November 3, "It is plainly visible to the naked eye." Humboldt observes in his Cosmos, "Encke's comet has several times, although with difficulty, been observed by the naked eye, as in Europe in 1819, and, according to Rümker, in New Holland in 1822."§ Encke's comet was also observed at Washington from the 1st of September to the 15th of November. || The comet appears to have been first seen in Europe by Mr. Hind of London, on the 3d and 4th of September. It was afterwards observed at most of the foreign observatories. Colla T at Rome saw it on the 20th of September. On the 22d of November the comet came very near to Mercury, that is, within a distance equal to fifteen times the moon's distance from the earth.** This is not so near an approach as the comet of 1770 made to the earth. Encke's comet came once more to its perihelion on the 14th of March, 1852.tt At Biela's comet was discovered by Biela in 1826; its orbit was calculated by Gambart. Santini has given particular attention to it, and done for Biela's comet what Encke did for the comet which bears his name. its perihelion return, in 1832, there was an intense popular apprehension, particularly in France, that it would run down the earth.‡‡ It was invisible in its next return to the perihelion, in 1839. Its last passage through that point of its orbit was within four hours of the time calculated by Santini. At this appearance it was first seen at Berlin on the 29th of November, 1845, and at Cambridge, England, on the 1st of December. On the 19th of December, Mr. Hind of Bishop's Observatory, near London, thought it appeared unusually elongated and pear-shaped. On the 13th of January, 1846, it was first discovered to be double. This observation, originally made at the Washington Observatory, was confirmed on the 15th of the same month by another witness, Mr. Challis of Cambridge, England. §§ The distance between the two parts of Biela's comet increased, till, finally, it was too large to allow of any sensible attraction being exerted by one upon the other. The new offshoot from the old comet, though faint at first, began to increase in size and brightness till it equalled the old comet, and finally eclipsed it. Afterwards it grew faint again, and disappeared entirely from sight on March 15. The comet continued single from this time until it ceased, on the 22d of April, to be seen at all. The distance between the comet and its strange companion and * Astron. Nachr., XXVII. 115. † Cycle, I. 250, 251. 1 Astron. Nachr., XXXI. 39; Proc. Amer. Acad., II. 139. § I. 92. Annuaire des Longitudes, 1832. Compt. Rend., XXVII. 3432. tt Astron. Nachr., XXXIII. 405, 245; XXXIV. 17. SS Phil. Mag., XXVIII. apparent offspring, from February 10 to March 15, was about two thirds of the moon's distance from the earth. Much of the change in distance was apparent, and not real. Professor Plantamour of Geneva has investigated the motions of the separate parts on the supposition that they were independent bodies. From his elements, it would appear that there must be a difference of sixteen days in their next return to the perihelion. This comet, with all its singularities, was carefully observed at Washington.* Professor Coffin has given separate orbits for the two parts, which differ even more in the time of revolution than those of the astronomer of Geneva. Mr. Herschel closes the case of this comet, in his Outlines, as follows: "And it will be, therefore, necessary, at their next reappearance, to look out for each comet as a separate and independent body, computing its place from these elements as if the other had no existence. Nevertheless, as it is still perfectly possible that some link of connection may subsist between them (if, indeed, by some unknown process the companion has not been actually reabsorbed), it will not be advisable to rely on this calculation to the neglect of a most vigilant search throughout the whole neighborhood of the more conspicuous one, lest the opportunity should be lost of pursuing to its conclusion the history of this strange occurrence." Mention is said to be made in the Chinese annals of a comet with three heads. On the duality of Biela's comet Mr. Herschel has this note: § "To say nothing of a singular surmise of Kepler, that two great comets seen at once in 1618 might be a single comet separated into two, the following passage of Hevelius, cited by M. Littrow (Nach., 564), does really seem to refer to some phenomenon bearing at least a certain analogy to it. In ipso disco,' he says (Cometographia, 326), 'quatuor vel quinque corpuscula quædam sive nucleos reliquo corpore aliquanto densiores ostendebat.'" Santini, after estimating the disturbing action of Jupiter and Saturn, has calculated the next perihelion passage of Biela's comet for September 28th, 1852. || In the year 1556 a comet appeared, the elements of which were computed by Halley, and found to agree with those of another comet which was seen in Europe and China in the summer of 1264, with a tail exceeding,100° in length. Pingré and Dunthorne computed the elements of the comet of 1264, and Pingré insisted on the identity between this comet and that of 1264. Hind has gone over again the calculation of Halley for the comet of 1556, and reached the same conclusion. The interval between 1264 and 1556 would give to the comet which appeared at both of these times a period of 292 years. Hence this comet might return again in 1848.** Hind also supposed that the comet visible in 975 gave indications of being another yet earlier appearance of the same body. tt The *Gould's Astron. Journ., I. 135, 136; Astron. Nachr., XXIV. 135-140. † Amer. Alm. for 1847, p. 92. § Outlines, p. 359; Compt. Rend., XX. 334; XXII. 644. Compt. Rend., XXXI. 496; Astron. Nachr., XXXII. 95. ¶ Cometographie, I. 411. **Lalande, 3185; Astron. Nachr., XXI. 193; Phil. Mag., XXXI. 50. 1 Pp. 361, 362. On the Expected Return of the Great Comet of 1264 and 1556. By J. R. Hind. 1848. Chinese annalists describe comets which were visible in the years 395 and 104. If all these cometary appearances are exhibitions of one body returning at these various periods to its long deserted perihelion, the average duration of its revolution falls short of 292 years. It is obvious, however, that the period of a comet will be disturbed from time to time by the perturbations of the planets, which, as they are never encountered by the comet under the same relative configuration, will never twice produce precisely the same effect. Mr. Mädler calculated the disturbances of the comet of 1556.* Mr. Barber found that from 1556 to 1592 Jupiter and Saturn together diminished the period of the comet by 263 days, and between 1592 and 1806 Jupiter alone increased it by 751 days, so that the period was in the long run increased by 488 days. The whole effect of Uranus and Neptune, and a part of Saturn's also, were neglected. Mr. Bomme of Middleburg, Netherlands, has published a complete memoir on the subject † He takes into account the influence of the four exterior planets since 1264, and that of the Earth and Venus while the comet was near them in 1556, and he calculates that the orbit in which the comet was moving in 1264 corresponded to a period of 302.922; that the orbit in which it moved in 1556 had a period of 308.169; that the perturbations suffered since that time will diminish the current period by 2166 days, so as to leave it 302.25. The comet will pass through its perihelion, therefore, on the 2d of August, 1858, and will be describing then an orbit of 112785 days. If Halley's elements are taken in place of Hind's, the approaching perihelion passage will be on the 22d of August, 1860. If the true elements lie between those of Hind and those of Halley, the comet must make its appearance between 1858 and 1860. Thus the long-continued delay of this comet, which was first expected in 1848, and of which Herschel was almost ready to despair some time ago, is satisfactorily explained; and its return is postponed for at least six years longer. A prize has been offered by the Academy at Modena for the best discussion of the observations of the comets of 1264 and 1556. Professor Peirce's catalogue, already quoted, gives the elements of the four new comets which were seen in 1840. The first was discovered by Galle, December 2, 1839, and passed its perihelion January 4, 1840. The second, discovered by Galle on the 25th of January, has a period assigned to it of 2423 years. The third was discovered by Galle, March 6, and passed its perihelion April 2. The fourth, discovered by Bremiker, October 26, has received a period from Götze § of 360 years. It passed its perihelion November 13. A single comet graced the sky in 1842, the elements of which are also given in the same catalogue. It was discovered on the 28th of October, by Laugier, of Paris. The year 1843 was highly favored. First came the great comet of that year, || in all respects as remarkable as any on record. It was distinguished by its great length of tail, its brightness, its periodicity, and its small perihelion distance. Mac * Astron. Nachr., XXI. 337. † Proeve eener Berekening der Steringen in die Loopbaan der Komeet van 1264-1556. Amsterdam. 1850. Outlines, p. 356. § Astron. Nachr., XXII. 247. Ibid., XX. 289, 397. lear, who remembered the great comet of 1811, says it was not half as brilliant as that of 1843. The latter was visible almost at noonday; it had sometimes a tail 69° in apparent length, or 108,000,000 miles. Bessel said that it seemed to have exhausted its head in the manufacture of its tail. Clerihew observed, at Calcutta, that on the 11th of March it shot off a secondary tail 100° in length in one day, fainter than the primitive tail, and making an angle of 18° with it on the southern side.* Many computed orbits brought it within 60,000 miles of the sun's surface, so that the apparent diameter of the sun exceeded 120°, and the area it covered on the sky was from forty to fifty thousand times as great as the apparent disc of the sun to us. Herschel estimates the heating power of the sun at this propinquity twenty-four times as great as that in the focus of Parker's great lens, which melted carnelian, agate, and rock-crystal. This comet hurried round the sun at the rate of 366 miles a second; it occupied only 2 hours in going from its ascending to its descending node, and it described 291° of anomaly in a single day. Walker at one time thought the comet must have struck the sun, and Plantamour believed that at least it must have grazed the sun's atmosphere. This comet was first seen by Captain Ray, at Conception, on the 27th of February, and east of the sun. It was observed at the Cape of Good Hope on the 3d of March, at Trevandrum,‡ India, on the 6th, and at Cambridge, U. S., on the 9th of March. In Europe, it was first seen at Rome and Naples on the 17th. It was observed at Philadelphia till the 10th of April, and was possibly seen by Encke on the 15th of the same month. Circumstances were not favorable to good observations, from which a correct orbit could be deduced. The comet was visible for a very short time, during which it moved over a small arc, and that near to the horizon. Moreover, before all the observations came to hand, other new and interesting comets had been discovered, which distracted the attention of astronomers. The volume of this Almanac for 1844 contains a list of 38 different orbits, calculated by different astronomers, and accompanied by an able discussion of the whole subject by Professor Peirce. Recently, Professor J. S. Hubbard of the Washington Observatory has subjected to rigid examination all the observations, amounting to 140, and deduced a new set of elements.§ Some astronomers supposed the comet of 1843 identical with that of 1668, and assigned to it a period of about 175 years. Henderson, who adopted this view, stated that he had in his possession a map representing the apparent track of the comet of 1668, as seen at Goa in the East Indies. Others thought the comet of 1843 identical with that of 1668, and also with that of 1689. Professor Peirce discovered a mistake in Pingré's calculation of the latter, which changed the inclination of its orbit from 69° to 30°. Vogel has recently recomputed the orbit, and, by a new construction of the language in which one observation is described, has changed the inclination back again to 59°.¶ Various ellipses have been as * Astron Nachr., XXI. 199. Smyth's Cycle, I. 247. † Outlines, pp. 369, 370. § Astron. Journ., I. 153. Astron. Nachr., XXXIV. 387-389. |