The stifling air.

Fine comets.

yesterday evening. As the night advanced there were many who insisted that they could detect a change in the atmosphere. The air, they said, was stifling. It was wonderful to see how

many persons gathered from different sections of the city around the newspaper offices, with substantially the same statement. As a consequence many families of the better class kept watch all night, in order that if the worst came they might be awake to meet it. The orgies

around the colored churches would be laughable, were it not for the seriousness with which the worshipers take the matter. To-night (Saturday) they are all full, and sermons suited to the terrible occasion are being delivered.

So great is the number of splendid comets the histories of which are written in astronomical annals, that it would be a hopeless task

to enumerate the thousands of interesting details about them.

We pay brief attention to a few.

The great comet which appeared in September, 1882,

It was

of 1882.

was the most magnificent one of recent years. bright enough to be visible in full daylight, close to The comet the sun. On September 17 it passed across the sun, coming within 300,000 miles of the photosphere. Though it thus dashed directly through the corona, and may indeed have encountered some of the solar prominences, its speed was unabated. But the intense heat to which it was exposed, together with the strain caused by the tidal action of the sun, apparently disrupted the nucleus. In less than a month it exhibited two centers of condensation. As the days rolled by still further changes took place, until the nucleus had become 50,000 miles long, and was ornamented by a number of centers of condensation, the largest of which was 5,000 miles in diameter.

The tail, at its best, was 100,000,000 miles in length, and stretched across the sky as a splendid golden bar. Along its track were scattered filmy débris, in the form of companion comets six or more in number. For nearly two months there projected in front of its head a luminous sheath, as though the comet were a sword which was being thrust into its scabbard.

The spectrum was very bright, and indicated the presence of hydro-carbons, sodium, and iron; calcium and manganese were also suspected. The comet was not lost to view till it had reached a distance of nearly 500,000,000 miles from the sun. Its orbit is a very elongated ellipse, and it is expected to return in the middle of the twenty-seventh century.

Encke's comet was discovered in 1786, and was found to be making its round trip in only three years and a quarter, the shortest known cometic period of revolution. It is insignificant in appearance, but made trouble for astronomers as soon as they had obtained a fair grip

Filmy débris.

Encke's comet.

Biela's comet.

Twins.

A meteoric shower.

on it. No matter how carefully they predicted its successive returns, it always outran the figures, and arrived at perihelion ahead of time. Such an effect would be produced by encounter with meteoric bodies, which offered a resistance to its motion. For a body which is retarded loses "centrifugal force," and is consequently pulled nearer to the sun, and compelled to describe a smaller orbit, in which it goes more rapidly than before. Should the resistance continue, Encke's comet must inevitably be drawn into the fiery embrace of the sun.

Biela's comet was discovered in 1826, and was soon proven to be one of short period; it should come around once in six and three fourths years. In 1832 this harmless object gave rise to a comet-scare; for the fact became noised abroad that it crossed the path of the earth, and people jumped to the conclusion that there would be a collision. But when the comet crossed the earth's orbit our planet was many millions of miles away.

Thirteen years afterward the comet split in twain, under the very eyes of the watchers. The operation occupied several days, and after the parts had separated to a distance of nearly 150,000 miles, tails were shot out, and nuclei blazed up in rivalry. The original comet had possessed neither of these marks of cometic blue blood. They interchanged cometary compliments by alternately brightening and fading out. In 1852 they were seen again, the distance between them being then ten times as great as before. They were still exchanging compliments, and thus politely bowed themselves out; for they have never been seen since.

On November 27, 1872, the earth, when crossing the orbit of the missing comet, encountered a fine meteoric shower. The comet should have been millions of miles

FIG. 128.-PHOTOGRAPH OF RORDAME'S COMET, SHOWING MASSES OF MATTER DRIVEN OFF INTO THE TAIL.

The motion of the comet causes the stars to appear as streaks on the negative.

Lexell's comet.

Supposed returns.

beyond on that date. Perhaps the earth did not dash. into the comet, but into a mass of meteoric matter which was following in its wake. In 1885 there was another shower, and again in 1892; these were probably due to the same group of bodies. Either the comet has become invisible, or has met with some accident, which has disintegrated it.

Lexell's comet is perhaps the most tantalizing one with which astronomers have had to deal. It was first seen in 1770, and Lexell found that it was moving in an elliptical orbit, with a period of five and one half years. It did not reappear in 1776, but the earth was not then in a favorable position with reference to it and the sun. In 1781 circumstances were favorable, but the comet was a truant. Lexell and Laplace investigated the matter, and detected Jupiter in the rôle of mischiefmaker. Before 1767 the comet had come so near this planet that its previous orbit had been transformed in the five and a half years ellipse. In 1779 it came altogether too near to Jupiter, and was tangled up among his moons; the moons moved on with their accustomed serenity, but the comet's orbit was so altered that it was given up for lost. But in 1843 a comet appeared whose orbit was somewhat similar to that of the long-lost Lexell. Leverrier went to the bottom of the question, and decided against their identity.

In 1889 Mr. W. R. Brooks* found a comet which has already been mentioned as accompanied by four companions. It too had been troubled by Jupiter, and had skirmished with his moons. Surely this was the returned prodigal; but months of tedious calculation rendered its identity with Lexell's doubtful. Six more

*Of Geneva, N. Y.; director of the Smith Observatory.