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.”*

9. 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.

10. 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 upon record ever exhibited such sudden and unaccountable changes of aspect. The nucleus, which had become clear and well-defined, like 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 sur

* Somerville's Connexion of the Physical Sciences.

rounded 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

ing 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.

11. 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.

12. 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.

13. "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 quite changed [from what it presented on its approach]. For a long time it had no

*

* 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.

tail; the parabolic envelope of the head was formed with such astonishing rapidity, that its visible volume more than doubled in the space of twenty-four hours. I may say, without exaggeration, that I saw it augment; for, on the morning of the 26th of January, on repeating my micrometric observations of the well-defined part, after an interval of three hours, I found an increase in its linear dimensions equal to a sixth-part of the whole! This extraordinary dilatation continued, and the paraboloïd became so large and lustreless, that it at length entirely disappeared, leaving only the nucleus and the tail of the star.t Another, and a singular peculiarity, was the existence of a very small interior comet, having a head and tail complete-its nucleus was that of the general mass. This cometic nucleus dilated less rapidly than the envelope; and at the end of the period of being visible the tail itself became imperceptible."

14. This, then, is the first comet of which at least the moderns have established the reality of the periodical returns. It is also the first comet of which the elements or distinguishing characters have been determined from observations made in Europe; for, although the comets which appeared in the years 240, 539, and 887,

* Micrometric observations are observations made with a micrometer, an instrument for measuring small spaces; of which the name is derived from the Greek micros, small, and metron, a

measure.

The word nucleus properly means a kernel or nut; but also anything about which other things are gathered.

of the Christian era, are the most ancient of those whose orbits have been traced, their elements were computed from Chinese observations.

15. Authentic records of Halley's comet extend backward only to the year 1456; but there are traces that are probable, though not absolutely certain, to periods before the Christian era.

CHAPTER LVII.

ABOUT SHOOTING OR FALLING STARS. ENLARGED IDEAS OF THE SOLAR SYSTEM. THE NOVEMBER ASTEROIDS.

The

1. WE might now think that we had done with our outline of the bodies composing the Solar System; and this, till very lately, would have been the case. sun, the primary planets, secondary planets, satellites, or moons, and the long list of comets: these, till very lately, composed what was regarded as the entire assemblage of the Solar System. Much more, however, is at present talked of; and, as it is always my wish to make my little readers acquainted with the very newest, as well as oldest particulars of knowledge, or of what is received as knowledge, I have some remarkable statements to make, though without answering that at least part of them will not hereafter be disputed, if not entirely rejected. In natural history, as in natural philosophy, and in many other branches of human science, it is right that those little ones should know, how often