COMETS. 



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twice as near, exposed to a heat of proportionate greater intensity. Sir John Herschel 

 computed that the heat received by its surface during the passage of the perihelion was 

 equal to that which would be received by an equal portion of the earth's surface, if it were 

 exposed to the influence of 47,000 suns, placed at the common distance of the actual sun. 

 It is difficult to conceive how a flimsy body could have resisted such a temperature so as 

 not to have been entirely dissipated. This comet is also remarkable as one of the few on 

 record which have been visible in broad daylight. 



Comets have been observed to undergo remarkable transformations on their approach to 

 the perihelion, breaking up into two or more separate parts, evidently owing to the action 

 of the sun. Seneca reports an instance of dissolution of this kind ; Hevelius witnessed 

 another ; and Biela's comet exhibited the strange phenomenon on the occasion of its third 

 re-appearance, in the year 1846. It then separated into two distinct comets, which moved 

 side by side, in distinct and independent orbits, as long as visible. One of these objects was a 

 little fainter than the other, but both had tails, and exhibited the distinctive features of a 

 comet. The change of constitution seems to have taken place very suddenly. It was first 

 observed in Europe on the 15th of January, by Mr Challis of Cambridge, and M. Wickmann 

 of Konigsberg ; but it was afterwards found to have been seen on the 1 2th by Lieutenant 

 Maury, at the Observatory of Washington, in the United States. The separation has 

 probably been permanent, and become more decided. In 1852, on the occasion of the 

 fourth re-appearance, Biela's comet was preceded by another, a fainter object, which may 

 have been the companion separated from it, removed to a greater distance. The annexed 

 cut represents some of the various appearances presented by Hallcy's comet in 1835 in 

 different parts of its orbit a, b, c, in approaching the sun ; d, e, in retreating. 



It is probable that a great comet, revolving round the sun in the long period of nearly 

 three centuries, was observed in the years 975, 1264, and 1556. This is the opinion of 

 Gauss of Gottingen, Mr Hind, and other astronomers. Assuming the comets of those years 

 to be three apparitions of the same body, its return to the sun may be anticipated after 

 the lapse of a corresponding interval. The wanderer is now overdue, as full three centuries 

 have elapsed since the last period ; but as its time of revolution may be lengthened by 

 planetary perturbations, it will be looked for till the year 1860. In 1264, the comet was 

 visible many months, and very conspicuous. All Europe regarded it as intimating the 

 death of Pope Urban IV. "Its apparition," says Thierri, "boded his illness, and its 

 disappearance his death, as events have proved." Historians relate that it was last seen 

 on the night of the pontiffs decease. In 1556, the comet was also a striking object, and 

 similarly interpreted as signifying terrestrial changes. It was noticed that " the tail was 

 always at first turned towards Spain." The emperor Charles V. was greatly alarmed at 

 its appearance ; and looked upon it as a sign of his approaching death. He is said to have 

 been induced by the impression to cede the imperial crown to his son. 



The leading features of the chief cometary appearances of modern times have now been 

 sketched. There are various inquiries which naturally suggest themselves with reference 

 to these bodies. What is their physical constitution ] What their origin and office in 



