within nearly fifty-seven millions of miles of the sun; and at its aphelion it is sixty times more

distant. On account of this extensive range, it must experience sixty times more light and heat when nearest to the sun, than in the remote point of its orbit. In the one position, the sun

will seem to be four times larger than he appears to us; and at the other, he will not be apparently larger than a star*.

In point of figure, and as seen by the naked. eye, or even by the help of ordinary telescopes, the appearance of this comet in 1835 and 1836, (for the same comet has different forms at its different appearances), had little that was remarkable; or, in other words, was of the more accustomed kind. But, to astronomers, both in the Northern and in the Southern hemispheres, it presented very peculiar and interesting sights.

On the first appearance of this comet, early in the month of August, 1835, it seemed merely a globular mass of dim vapour, without a tail. According to observations of M. Valz, at Nismes, this vapour-like or nebulous body, which was the comet, increased in magnitude as it approached the sun; but no other comet

* Somerville's Connexion of the Physical Sciences.

upon record ever exhibited such sudden and unaccountable changes of aspect. The nucleus,

the disc of a planet, was seen, upon one occasion, to grow apparently larger, as well as less bright, in the course of a few hours. But, more remarkable than even this, was its sudden display of luminous branches or sectors, diverging from the nucleus through the beard or nebulosity which surrounded it. M. Struve describes the nucleus, as seen by him in the beginning of October, elliptical in shape, and like a burning coal, out of which there issued, in a direction nearly opposite to that of the tail, a divergent flame, varying in intensity, form, and direction; appearing occasionally even double, and suggesting the idea of luminous gas bursting from the nucleus. On one occasion, M. Arago saw three of these divergent flames on the side opposite to the tail, which latter they greatly exceeded in brilliancy.

Hevelius describes an appearance of this comet precisely similar, at its approach to the sun in the year 1682; and something of the

same kind, in another comet, has been shown in the figure in my preceding chapter.

The appearances of Halley's comet in the Southern hemisphere, on its return from the sun in 1836, are described with very similar circumstances to those observed in the Northern, in the autumn of 1835.

"I am sure," says Sir John Herschel, (writing, in the middle of 1836, from the Cape of Good Hope, to M. Arago,) "you will be interested in learning that I have here been favoured with a long and beautiful exhibition of the comet, on its return from the sun. It was in sight from the 24th of January till the 5th of May [1836]. In its passage from its perihelion*, it must have been seen with great difficulty in Europe, for its physical aspect was

* Perihelion is the name of that point in the orbit of a planet which is nearest to the sun. It is formed from two Greek words; peri, near, and helios, the sun. Aphelion is the name given to the point exactly opposite to the perihelion; or that at which a planet or comet is furthest away from the sun, or at its greatest distance.