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Herschel had the good fortune to be at the Cape on the occasion of the periodical return of Halley's great comet in 1833. To the study of this body he gave assiduous attention, and the records of his observations form one of the most interesting chapters in that remarkable volume to which we have just referred. Early in 1838 Sir John Herschel returned to England.
The last line of this specimen of Halley's poetic muse may be thus rendered: "Nor mortals nearer may approach the gods." The intimate friendship between the two greatest astronomers of the time continued without interruption till the death of Newton. It has, indeed, been alleged that some serious cause of estrangement arose between them.
When Halley's comet reappeared in 1835, Pontecoulant's computations for the date of perihelion passage were very exact, and afterwards he showed that, with more exact values of the masses of Jupiter and Saturn, his prediction was correct within two days, after an invisible voyage of seventy-five years!
Two of them, Ollier's Comet and Halley's, are known to return into sight after intervals of seventy-four and seventy-six years, during which they have visited portions of space a few hundred millions of miles further than the orbit of Neptune.
His observations of the eclipse of the sun, which occurred in 1715, added greatly to Halley's reputation. This phenomenon excited special attention, inasmuch as it was the first total eclipse of the sun which had been visible in London since the year 1140.
Halley's, and five other comets are thus related to Neptune; three connect themselves with Uranus, two with Saturn, above a score with Jupiter. Some form of dependence is plainly indicated, and the researches of Tisserand, Callandreau, and Newton of Yale College, leave scarcely a doubt that the "capture-theory" represents the essential truth in the matter.
In 1606 came a second treatise on the new star, discussing various theories to account for its appearance, and refusing to accept the notion that it was a "fortuitous concourse of atoms". This was followed in 1607 by a treatise on comets, suggested by the comet appearing that year, known as Halley's comet after its next return.
It is quite evident to any one who has studied these papers that Halley's friendship for Newton was as ardent as ever. The generous zeal with which Halley adopted and defended the doctrines of Newton with regard to the movements of the celestial bodies was presently rewarded by a brilliant discovery, which has more than any of his other researches rendered his name a familiar one to astronomers.
But the one known instance in point is against such a supposition. Halley's comet, the only great comet of which the returns have been securely authenticated and carefully observed, has preserved its "type" unchanged through many successive revolutions. The dilemma presented to astronomers by the Great Southern Comet of 1880 was unexpectedly renewed in the following year.
The earth in the circle of its orbit passed through the tail of Halley's comet in May, 1910, and we hadn't even a pyrotechnical display of fire rockets to celebrate the occasion. In fact there was not a single celestial indication of the passage and we would not have known only for the calculations of the astronomer.
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