14 



♦ KNOWLEDGE ♦ 



[November 1, 1887. 



However, at that time no very special attention was 

 directed to the resemblance between the paths of the comets 

 of 1843 and 1668. It was not regarded as anything very 

 new or striking that a comet should return after making a 

 wide excursion round the sun ; and those who noticed that 

 the two comets really had traversed appreciably the same 

 path around the immediate neighbourhood of the sun, simply 

 concluded that the comet of 1008 had come back in 1843, 

 after 175 years, and not necessarily for the first time. 



It must be noticed, however, before leaving this part of 

 the record, that the comet of 1843 was suspected of be- 

 having in a rather strange way when near the sun. For 

 the tirst observation, made rather roughly, indeed, with a 

 sextant, by a man who had no idea of the interest his obser- 

 vation might afterwards have, could not be reconciled by 

 mathematicians (including the well-known mathematician, 

 Benjamin Pierce) with the movement of the comet as sub- 

 sequently observed. It seemed as though when in the sun's 

 neighbourhood the comet had undergone some disturbance, 

 possibly internal, which had in slight degree affected its 

 subsequent career. 



According to some calculations the comet of 1843 seemed 

 to have a period of about thirty-five years, which accorded 

 well with the idea that it was the comet of 1068, returned 

 after five circuits. Nor was it deemed at all surprising that 

 the comet, conspicuous though it is, had not been detected in 

 1713, 1748, 1783, and 1818, for its path would carry it where 

 it would be very apt to escape notice except in the southern 

 hemisphere, and even there it might quite readily be missed. 

 The appearance of the comet of 1668 corre.-iponded well with 

 that of the comet of 1843. Each was remarkable for its 

 extremely long tail, and for the comparative insignificance 

 of its head. In the northern skies, indeed, the comet of 

 1843 showed a very straight tail, and it is usually depicted 

 in that way, whereas the comet of 1668 had a tail showing 

 curvature. But pictures of the comet of 1843, as seen in 

 the southern hemisphere, show it with a curved tail, and 

 also the tail appeared forked towards the end during that 

 part of the comet's career. 



However, the best observations, and the calculations 

 based on them, seemed to show that the period of the comet 

 of 1843 could not be less than 500 years. 



Astronomers were rather startled, therefore, when, in 

 1880, a comet appeared in the southern skies, which 

 traversed appreciably the same course as the comets of 

 1668 and 1843. When I was in Australia, in 1880, a few 

 months after the great comet had passed out of view, I met 

 several persons who had seen both the comet of that year 

 and the comet of 1843. They all agreed in .saying that the 

 resemblance between the two comets was very close. Like 

 the comet of 1843, that of 1880 had a singularly long tail, 

 and both comets were remarkable for the smallness .and 

 dimness of their heads. One observer told me that at 

 times the head of the comet of 1880 could barely be 

 discerned. 



Like the comets of 1665 and 1843, the comet of 1880 

 grazed close past the sun's surface. Like them it was but 

 about two hours and a half north of the earth's orbit-plane. 

 Had it only resembled the other two in these remarkable 

 characteristics, the coincidence would have been remark- 

 able. But of course the i-eal evidence by which the associa- 

 tion between the comets was shown was of a more decisive 

 kind. It was not in general character only but in details 

 that the path of the comet of 1880 resembled those on 

 which the other two comets had travelled. Its path had 

 almost exactly the same slant to the earth's orbit-plane as 

 theirs, crossed that plane ascendingly and descendingly at 

 almost exactly the same points, and made its nearest 

 approach to the sun at very nearly the same place. To the 



astronomer such evidence is decisive. Mr. Hind, the 

 Superintendent of the " Nautical Almanac," and as sound 

 and cautious a student of cometic astronomy as any man 

 living, remarked so soon as the resemblance of these comets' 

 1 paths had been ascertained, that if it were merely accidental 

 the case was most unusual; na}', it might be described as 

 unique. And, be it noticed, he was referring onl}' to the 

 resemblance between the comets of 1880 and 184.3. Had 

 he recalled at the time the comet of 1668, and its closely 

 similar orbit, he would have admitted that the double 

 coincidence could not possibly be merely casual. 



But this was by no means the end of the matter. Indeed, 

 thus far, although the circumstances were striking, there 

 was nothing to prevent astronomers from interpreting them 

 as other cases of coincident, or nearly coincident, cometic 

 paths had been interpreted. Hind and others, mvself in- 

 cluded, inferred that the comets of 1880, 1843, aiid 1668 

 were simph' one and the same comet, who.se return in 1880 

 probably followed the return in 1843 after a single revo- 

 lution. 



In 1882, however, two years and a half after the appear- 

 ance of the comet of 1880, another comet came up from the 

 south, which followed in the sun's neighbourhood almost the 

 same course as the comets of 1668, 1843, and 1880. The 

 path it followed was not quite so close to those followed by 

 the other three as these had been to each other, but yet was 

 fai" too close to indicate possibly a mei'e casual resemblance ; 

 on the contrary, the resemblance in regard to shape, slope, 

 and those peculiarities which render this family of comets 

 unique in the cometai-y system, was of tlie closest and most 

 striking kind. 



Man}' will remember the startling ideas which were sug- 

 gested by Professor Piazzi Smyth respecting the portentous 

 significance of the comet of 1882. He regarded it as con- 

 firming the great pyramid's teaching (according to the views 

 of orthodox pyramidalists) respecting the approaching end 

 of the Christian dispensation. It was seen under very 

 remarkable circumstances, blazing close by the sun, within 

 a fortnight or three weeks of the precise date which had 

 been announced as marking that critical epoch in the his- 

 tory of the earth. 



Moreover, even viewing the matter from a scientific stand- 

 point. Professor vSmyth (who, outside his pyramidal para- 

 doxes, is an asti'onomer of well-deserved repute) could 

 recognise sufficient reason for regarding the comet as por- 

 tentous. 



Many others, indeed, both in America and in Europe, 

 shared his opinion in this respect. A very slight retardation 

 of the course of the comet of 1880, during its passage close 

 by the surface of the .sun, would have sufficed to alter its 

 period of revolution from the thirty-seven years assigned on 

 the supposition of its identity with the comet of 1843, to 

 the two and a half j'ears indicated by its apparent return in 

 1882, and if this had occurred in 1880, a similar inter- 

 ruption in 1882 would have caused its return in less than 

 two and a half years. 



Thus, circling in an ever narrowing (or rather shortening) 

 orbit, it would present!}', within a quarter of a century or so 

 perhaps, have become so far entangled among the atmo- 

 spheric matter around the sun, that it would have been 

 unable to resist absolute absorption. What the conse- 

 quences to the solar system might have been none ventured 

 to suggest. Newton had expressed his belief that the 

 effects of such absorption would be disastrous, but the 

 phj'sicists of the nineteenth century, better acquainted with 

 the laws associating heat and motion, were not so despondent. 

 Only Professor Smyth seems to have felt assured (not being 

 despondent but confident) that the comet portended, in a 

 very decisive way, the beginning of the end. 



