COMETS.—No. 1.

Most of our readers must have heard of the comet of Biela, which appears in the present year, and has caused no small alarm among those who are entirely ignorant of the nature of comets in general, and of the track of this particular one. We have met with an amusing little book on this comet of 1832, by Littrow, professor of astronomy at Vienna, from which we shall give the substance of a few extracts, that may not be uninteresting.

There are only four comets whose orbits are yet accurately known. That which appears in the present year is called Biela’s comet, from its having been discovered by an Austrian officer of that name in Bohemia in 1826. Its period of revolution round the sun is six years and two hundred and seventy days. Though it had been seen before in 1772 and 1805, it was not known to be a comet of so short a period. In the present year, 1832, we shall have its fourth visit. On the 27th of next November the comet will be nearest to the sun, but even then about seventy-two millions of geographical miles distant from that body: and on the 22d of this month (October) it will be nearest to the earth, and at the distance of about forty-four millions of miles from us.

The number of comets must be very great, for the appearance of near five hundred has been recorded; and if we consider how many must have passed unnoticed in the early history of the world for want of persons to observe them, we may form some idea of the prodigious quantity of these bodies. From 1769 to 1807 no comet appeared that attracted any attention from people in general, though astronomers during this period observed no fewer than thirty-six. There being then so many of these wanderers whose course is unknown, it may be supposed a possible thing that one of them should run foul of the earth; and supposing it to be a body of any considerable magnitude and density, such a shock would entirely put an end to the present order of existence. Setting aside however, the question as to the magnitude and real nature of comets, let us consider what chance there is of our knocking against the comet of the present year, which, from the position of its orbit, looks much more threatening than any other that is known.

On the 29th of the present month this comet of Biela will be distant from a certain point in the earth’s orbit only about 2⅓ of the earth’s diameters, or about twenty thousand miles in round numbers. If the earth were at this very point of its annual track on the same 29th of October, it might happen that we should feel such effects from the comet, or from the enormous mass of vapour composing it (computed to be more than one hundred and fifty times greater than the mass of our earth,) as to destroy all animal and vegetable life. But as the earth will not be at this dangerous point till the 30th of November, or thirty-two days later than the comet, we shall have nothing to fear from it this time. For the earth moving in its orbit at the rate of about 67,680 geographical miles in one hour, it will be 51,978,240 miles distant from the comet on the 29th of this month, and in no danger at all of being affected by it in any way that we can estimate.

Perhaps few people will trouble themselves about this comet any more, when they learn that they are quite safe for the present. But how, it may be asked, are we sure that on some future occasion we may not approach too near? If the comet should be in its nearest point to the sun on the 28th of December, instead of the 27th of November, then we should really approach it within the short distance above-mentioned. But this near approach cannot take place, unless the comet should be in its nearest point to the sun in the latter part of December; and this again will not take place till the year 1933, when the comet will be in its perihelion (i. e. nearest point to the sun) on the 31st of December, and again in the year 2115, on the 26th of the same month. But, should the comet’s period of six years and two hundred and seventy days be somewhat changed in the course of the next century, from the action of Jupiter and other planets, (which is far from improbable,) this would diminish still further the chance of any unpleasant proximity in the years 1933 or 2115. This we hope will console those who regard this visitor with more feelings of fear than curiosity.

It may be added that this comet is a very small one, and, though its vapour occupies so enormous a space, the real kernel or bright part of the comet is not more than sixty or eighty miles in diameter; and hence it is conjectured that if it really is a body properly so called, it must be very small indeed, and that, even in a near approach to the earth, any injury that it might do by its attraction would be hardly felt. Again, says Littrow—“as to the tail and its deadly vapours, which, as they say, threaten us with such dreadful consequences, we really have nothing at all to fear from them: and for the following plain, but quite satisfactory reason—the comet has no tail.”

The following conclusion will, we hope, remove whatever apprehension may still lurk in the minds of the most timid, as to the danger which they have to fear from this comet in the years 1933, 2115, and in subsequent years—should their lives be so far prolonged.

“We have already stated that Biela’s comet can only come near the earth when it is at its least distance from the sun, in the latter part of December. But since this proximity of the comet to the sun may just as well happen on every other day of the year as in December, and since its period is six years two hundred and seventy days, or about two thousand five hundred days, in round numbers,—after a lapse of two thousand five hundred years, a near approach (not an actual collision) to the comet is probable. I say merely probable, from which it must not be concluded that such an event actually 284will take place in two thousand five hundred years. This result merely means that a man might bet two thousand five hundred to ten, or to one hundred, that the comet will not come near the earth for the next ten or one hundred years. At the end of two thousand five hundred years there will be an equal chance that the comet will make this near approach, or that it will not. And after two thousand five hundred years the chance of its approaching the earth will go on increasing, but at so slow a rate that many thousands of years must elapse before the event can be really expected.”