The great comet of 1882.-It is very seldom that any discovery unites in itself so many and such important points of interest as has been the case with the great comet now engaging so much attention. The report of the discovery by M. Cruls of a new naked-eye comet was in itself enongh to arouse a keen degree of interest; for as three such objects had already been observed within the last twelve months, that a fourth should follow in such quick succession was quite an unprecedented event. M. Cruls' discovery had scarcely been published in England before a yet more unusual observation was made. Mr. Common, of Ealing, who ever since the accidental discovery of the comet "Tewfik," during the total eclipse of May 16 last, had persistently examined the neighborhood of the sun with what might well have appeared to be the forlorn hope of detecting some comet wandering there, was at length rewarded, on Sunday, September 17, by the sight of a splendid comet close to the sun, of which he obtained observations. In the extreme south of Europe more favorable conditions prevailed; and the comet was seen on September 18 at a large number of places in Italy, Spain, and Algeria in full daylight, when only 40 from the sun. And, indeed, Mr. Common was not the only person who was fortunate enough to see it on September 17, before perihelion; for a dispatch from Reus, near Tarragona, announced that there the inhabitants were astonished to see a comet close to the sun, so that, though only 10.5 distant from it, it was bright enough to catch the eye of casual gazers. Indeed, it was so bright that it could be seen even through light cloud. Its tail could readily be detected by means of an operaglass furnished with a dark glass. On the following day, however, M. Thollon, at Nice, was able to detect some portion of the tail without even this assistance, for he says: "The coma aud part of the tail visi ble to the naked eye were nearly 20' in length. Their outer contour took the shape of a half-ellipse of eccentricity about 4, and the fairly large and very brilliant nucleus occupied a position intermediate between the apex and the focus." The same cloud-bank which baffled English observers on this and the following days covered the north of France likewise, and in despair of its breaking up, M. de Fonvielle resolved to rise above it, and on Friday, September 22, prepared for a balloon ascent. Fearing, however, that his own sight was not sufficiently good, he resigned his place in the car to M. Maurice Mallet, whom he duly instructed as to the observations to be obtained. The small dimensions of the car greatly hampered the adventurous astronomer, who, however, succeeded in making a sketch, and in obtaining a rough estimation of the distance from the sun and position-angle of the comet. The cloudy weather rendered it difficult to obtain sufficient observations to form an orbit; but Mr. S. C. Chandler, jr., of Harvard College, at length succeeded in deducing approximate elements, which showed a remarkable resemblance to those of comet I, 1880, and I, 1843. Per. pass. = 1882, September, 17.38, G. M. T. Long. node...... Inclination ...... = 342 29 Mean equinox, 1882.0. = 140 17 = 7.54407. The resemblance of the orbit of the great comet of 1880 to that of the still finer one of 1843 had attracted the earnest attention of astronomers at the time, and most had been led to consider them one and the same body. And now the appearance of a third magnificent object on the same, or nearly the same, track revived the discussion which took place in 1880. Then three leading theories had been started. The first, of least probability and but little received, saw in the comet of 1843 a return of the comet of 1668, and supposing the comet of 1702 to have been another return of the same object, considered that we had here a comet with a period of about 35 years, which had been apparently slowly increased to one of 37 years. But this theory rested on but very slender foundations; and, if true, it is obvious that our present visitor can claim no identity with his predecessors in the same path. Professor Weiss, of Vienna, holding a somewhat similar view, ascribed to the comet a constant period of about thirty-seven years, and identified it with those of 1106. 1179, 1363, 1511, and 1695, but not with that of 1668. A second theory suggested that the comets of 1843 and 1880 might now be independent comets traveling on the same track, the original parent comet having suffered disruption at some much earlier visit, and the fragments having become so widely separated that an interval of thirty-seven years now takes place between their perihelion passages. In any case it was felt that the hypothesis that so brilliant an object could have frequently returned without any observation having been made of it was quite incredible. A third and more popular theory regarded, indeed, the comets of 1668, 1843, and 1880 as one and the same object, but supposed that its period was gradually being shortened through the resistance experienced by the comet whilst passing through the solar atmosphere at perihelion. M. Meyer went further back, and regarded Aristotle's comet, B. C. 371, as the next earlier appearance to that of 1668. This theory seemed to receive strong confirmation by the apparition of the present comet, and further information seemed to lend it greater force. The great comet which had borne the names of Thollon, Common, and Cruls, who had each in turn discovered it independently, now proved to have been still earlier discovered by Mr. Finlay, first assistant at the Cape Observatory, who remarked it at five o'clock in the morning of September 8, and who obtained the following place for it on the fol lowing day: Cape mean time. September 8, 17h 23m 58 R. A. Decl. -0° 45′ 30.0 Mr. Finlay had been more fortunate than the subsequent discoveiers, not only in thus anticipating them by several days, but in being able to retain his hold on the comet right up to its conjunction with the sun; and Mr. Gill was able to inform the Astronomer Royal that, "on Sunday, September 17, the comet was followed by two observers with separate instruments, right up to the sun's limb, where it suddenly disappeared at 4h 50m 588 Cape mean time." This observation is wholly unprecedented in the history of astronomy, and proved most valuable as showing how exceedingly unsubstantial the comet was, for the sun's bril liancy could not, as some have supposed, account for the disappearance. Had it been so bright as to have become invisible, neither bright nor dark. in the center of the sun's disk, it would have appeared as a bright object when seen against the comparatively dull background of the regions near the limb. Had it harmonized with the degree of splendor of the limb, it would have looked dark on the disk. There was not, therefore, enough solid matter, or that matter was not sufficiently aggregated, for it to appear as a spot or a cloud, bright or dark, whilst in transit. Mr. Hind had meanwhile computed an orbit, which compares as follows with those which Mr. Tebbutt obtained for the 1880 comet, and those of Professor Plantamour for the comet of 1843: But this orbit would give the comet's distance from the center of the sun at the time of Dr. Gill's remarkable observation, on September 17, as only 10'.9; that is to say, it should have been far on the disk, and fully 5' from the limb at the time when it was actually seen to be only just entering the limb. Mr. Hind cannot think this discrepancy due to faults in the elements, for they represent the middle position within 1', and the first observation was taken only twenty hours after the one at the Cape with which the elements are in so little accord. There is, therefore, strong reason to believe that the comet's speed received con siderable alteration whilst in the immediate neighborhood of the sun, and Mr. Hind suggests the probability of its return in October, 1883. Mr. Chandler, using the above-mentioned Dun-Echt observation, with one made at Washington, September 23, and Cambridge, United States, September 30, found that a parabolic orbit gave considerable deviations in the middle place, and deduced therefore the following elliptic elements. The elliptic elements obtained by Professor Plantamour, for the comet of 1843, and by M. Meyer, for that of 1880, are given for comparision: A comparision of the orbit with whatever observations were available seemed to Mr. Chandler to confirm the periodical nature of the comet, although further observations will be necessary to fix the period with precision. The physical appearance of the comet which, like that of 1843, and unlike that of 1880, showed at first a decided nucleus, together with the above intimation of a period very considerably greater than that of the internal from 1830, January 27, the date of perihelion of the 1880 comet, suggest that perhaps the 1843 comet suffered disintegration when at its nearest approach, and that the 1880 comet was a portion of its less condensed material, whilst the body of the comet, with the prin cipal nucleus, suffering less retardation than the separated part, has taken two and a half years longer to perform a revolution. The remarkable discovery made by Professor Schmidt, of Athens, on October 8, of a second comet only 40 S. W. of the great comet, and having the same motion, would seem rather to confirm this view. The spectroscopic observations of the comet have only been less interesting than the questions of its orbit and identity. M. Thollon, who examined its spectrum on September 18, with a Steinheil spectroscope, having one prism of 60° of dense flint, in conjunction with a horizontal telescope of 9 inches aperture, into which the light of the comet was reflected by means of a siderostat, gives the following description of it: "Although working in full daylight, the spectrum of the comet was very bright; its leading characteristic was the presence of the bright lines of sodium. We at once saw in the field of the instrument a tolerably distinct spectrum, due to the scattered light of our atmosphere, in which the dark Fraunhofer lines could be distinguished. Upon the background of this spectrum a narrow and much more brilliant continuous spectrum, given by the nucleus of the comet, was seen clearly detached. From the height of the spectrum we estimated the apparent diameter of the nucleus as about 15". This spectrum stretched very far into the violet. The bright lines of sodium D, and D2 were given at the same time both by the nucleus and by the neighboring regions. From their length we estimated the apparent diameter of the part of the comet which displayed them at 1.5. They were neither diffused nor broadened, but narrow and perfectly separated, and exceedingly bright, especially in the spectrum of the nucleus. They were nearly of the same brilliancy, however, the most refrangible seemed a little the brighter, and they were, in short, exactly like the lines given by a flame moderately charged with sodium, both in brightness and in their essential characteristics. Of their identity there can be doubt, for besides the characteristics which we have just pointed out, we compared their positions with those of the Fraunhofer lines D, and D, given by the spectrum of the diffused daylight. We ascertained that the bright lines of the comet were not exactly superposed on the Fraunhofer lines, but were both displaced towards the red by a very small amount, the same in each case, equal perhaps to or of the interval between D, and D. We therefore concluded that the comet was traveling away from the earth at that moment. We intended to measure this displacement the next day, and prepared a more powerful spectroscope for this purpose; but the state of the sky did not give us the opportunity. No part of the comet showed us the bands of carbon, nor any band or line other than those of sodium, perhaps on account of the diffused light, which would be able to mask bands of small brilliancy. "The singular analogy between the spectrum of this comet and that of comet Wells, observed some months ago, will doubtless appear the more remarkable, as preceding comets have never shown the lines of sodium." But as the comet has receded from the sun, the ordinary cometary hydrocarbon bands have made their appearance, and the ordinary yellow, green, and blue bands had become very conspicuous on October 1, whilst the sodium lines were very much fainter. M. Ricco, at Palermo, observing up to October 11, found the spectrum of the tail perfectly continuous, and could trace it right to the end. The three hydrocarbon bands were only given by the nucleus and a region of some 5′ radius round it. These changes in the spectrum, as the comet recedes from perihelion, combined with the reverse changes witnessed in that of comet Wells as it approached it, seem to render it not unlikely that sodium would appear in the spectrum of any comet which should approach the sun sufficiently nearly; that it is, in fact, an indication of excessively high temperature, as the hydrocarbon bands are of one not quite so great. An intermediate spectrum of which no definite details have yet been sup plied seems to have been observed at Dun-Echt and elsewhere. M. Ricco speaks of having seen many lines up to September 27, a band in the red, a line in the yellow near and after D1, two others in the green, |