HALLEY'S COMET.
HALLEY'S Comet is still an obscure object, and has confounded some of the rasher prophets who predicted hat by this time it wasid be conspicuous. It does not follow, however, that because it is not bright now it will not be in a few weeks' time as brilliant as ever it was in its history. Comets have a strange habit of gaining and lasing brilliance to an extraordinary degree within short periods. At present the comet is below and to the right of the planet Saturn in the Western sky, and is an evening star. Every evening the comet, although approaching the earth, is coming nearer to the point where it will be impossible to see it owing to the strength of the twilight. By April it will be a morning star. On April 18th it will reach its perihelion, or nearest point to the sun. It will reach its nearest point to the earth on May 20th; but as it and the sun will be in the same part of the sky, the comet will be invisible to us just when it should be particularly bright. The day before its nearest approach to the earth it will pass across the sun, and astronomers are looking forward with intense interest to this transit. There is no recorded case of a comet having been seen during transit, and it may be that the composition of comets is so nebulous that even the nucleus is not substantial enough to be projected on the sun. The tail, at all events, will be invisible ; the sun's rays will shine through it as through the lightest of vapours. After the transit the comet will be an evening star again, and will become more and more visible for a time, although it will be actually losing in brilliance.
When Halley first suggested that the comet now known by his name would return in 1758 he had compared only three sets of observations, in which he discovered such a striking similarity that he concluded that they must all refer to the same comet. These were the observations of 1531, 1607, and 1682, in which year be observed the comet for himself. He was then twenty-five years of age. He must have been pre- destined for the study of the stars. While he was still a schoolboy he had provided himself with an astronomical apparatus, and when he was an undergraduate at Oxford be erected a telescope and various instruments on the roof of his father's factory in Winchester Street, London. He left Oxford without taking a degree in order to study astronomy abroad, and when, after further calculations, he definitely predicted the return of the 1682 comet in 1758, he called upon " candid posterity to acknowledge that this was first discovered by an Englishman." We have read somewhere that Peter the Great when he was staying in England had a particular liking for the companionship of Halley, and that after carousing with him at Deptford one evening be wheeled him in a barrow through a yew hedge and did such damage that he had to pay handsome compensation to John Evelyn, the owner, which incident shows that Shakespeare was right in thinking that not every astronomer plucks his judgments from the stars. But it would be wrong to think of Halley's investigations as having a merely astronomical value ; it should never be forgotten that his prediction of the return of the comet known by his name depended upon and confirmed Newton's discovery of the law of gravitation. Newton was his close friend, and Halley paid for the publication of the " Principia" out of his own pocket. All Halley's calculations aasnmed the varying retardations by attraction which comets suffer daring their journeys through space. When his prediction was fulfilled, Newton's law could never again be disputel. In 1850 Mr. J. R. Hind read a paper before the Royal Astronomical Society in which be traced the appearances cf
Halley's Comet through the ages with.the help of the Chinese
annals. These had only recently become known in Europe. He believed that in them be had found credible references to Halley's Comet back to the year B.C. 11. He took it as certain that Halley's Comet reached its perihelion in 1378, and therefore, allowing the normal periodicity, he looked for some mention of it about the year 1301. The Chinese annals
definitely described a great comet in that year. But there was one European account of it, by Friar Giles, which was
not reconcilable with the Chinese record. If the Chinese were describing Halley's Comet, it seemed that Friar Giles certainly was not. Mr. Hind was led on to an examination of Friar
Giles's credibility. He discovered that his account of another comet in 1264 was so contradictory that he had no hesitation whatever in preferring the Chinese statements in 1301. He concluded that the comet of 1301 was Halley's Comet. He believed that the preceding return of the comet was in 1223, when in July, shortly before the death of Philip Augustus, a comet was seen for eight days in the evening twilight. The Chinese annals do not mention this comet, but they mention comets in the years 1222 and 1224, neither of which, Mr. Hind thought, closely resembled Halley's Comet. The comparison of all these old observations is rendered more difficult by the fact that other conspicuous comets appeared
about the same time as Halley's. That experience is in a way repeating itself, for during the present year two notable comets besides Halley's have appeared. The brilliant calcula- tions recently made by Messrs. Cowell and Crommelin of Greenwich have shown that Mr. Hind was wrong about the particularly bright comet of 1222, which was unquestionably Halley's Comet. Moreover, Messrs. Cowell and Crommelin have carried back the history of Halley's Comet to B.C. 210.
Every chronicler recorded a wonderful comet in 1066, the year of the Norman conquest of England. The representation of it in the Bayeux tapestry is familiar. The Chinese annals mention two comets in 837, and if it be assumed that there really were two comets that year, and that the copyists have not confused two accounts of the same comet, it is likely enough that one of them was Halley's. In 451 a comet was observed about the time of the battle in which Attila was defeated by Aetius. In the years 295 and 218 comets are mentioned in the annals. The latter was the comet that was seen in Europe shortly before the death of the Emperor Opilius Macrinus, and was described by Dion Cassius as a. very fearful star. Mr. Hind suggested that the so-called sword-shaped sign which was seen over Jerusalem in A.D. 65 when Titus began the war which ended in the destruction of the city may have been Halley's Comet. In the year B.C. 11 there was undoubtedly a remarkable comet which, according to Dion Cassius, seemed to be suspended above Rome before the death of Agrippa. As the Chinese annals also mention it, Mr. Hind believed that this too was Halley's Comet. Truly did Shakespeare write :—
" When beggars die there are no comets seen, The heavens themselves blaze forth the death of princes."
Not all Mr. Hind's "ascriptions," as art critics say, are reconcilable with Messrs. Cowell and Crommelin's latest calculations, but enough is established on all hands to prove that Halley's Comet has been appearing ever since the history of the skies has been written. The habit of associating comets with catastrophes and wonderful events has died hard. We remember a book published early in the nineteenth century in which the author, proudly equipped with all the latest scientific information, disposed of astrology as a base superstition, but added with a quaver of misgiving at the end of his treatise : " Comets, indeed, are like to bode no good." Professor Turner lately gave some amusing instances in a lecture. He humorously shook his head over the fact that when Halley's Comet was here in 1835 the General Election closely resembled that of 1910. Let us hope that the appearance of Halley's Comet in the beginning of the twentieth century will dispose finally of the superstition that the earth will be injured, if not con- sumed, by passing through a comet's tail. A comet was not discovered by photography till 1892, but the perfeetion to which astronomical photography has since been brought will make the observations of Halley's Comet infinitely more valuable than any that have ever been taken.
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