three columns of aurora borealis shooting upwards in the north; and in a short time after a complete arch, like those already de scribed, though somewhat different in its position. It arose between the E. and N. and N. E. points, passed obliquely to the south below Arcturus, and descended in the west through Orion, having almost the same direction through that constellation which the equator has. Its light was the most faint about the vertex of the arch. Its most dense parts were continually varying in the intensity of their light. The larger stars were visible through its densest parts. It varied its position, and it continued visible about half an hour; but there was nothing which could be called a shooting, or quick corruscation. There was a steady northern light all the evening, or at least till the arch had disappeared.

The grandest specimen of this phenomenon which Mr. H. had seen, appeared on the 12th of April, between nine and ten in the evening. He perceived a broad arch of a bright pale yellow, aris ing between Arcturus and Lyra, about the right leg of Hercules, and passing considerably to the south of the zenith, its northern border being a little south of Pollux, and descending to the horizon near Orion, which was then setting. This arch seemed to be about 15° in breadth, and was of such a varied density, that it appeared to consist of small columns of light, which had a sensible motion. After above ten minutes he saw innumerable bright corruscations, shooting out at right angles from its northern edge, which was con cave, and elongating themselves more and more till they had nearly reached the northern horizon. As they descended, their extremities were tipped with an elegant crimson, such as is produced by the electric spark in an exhausted tube. After some time this aurora borealis ceased from shooting, and formed a range of beautiful yellow clouds, extending horizontally about a quarter of a circle. The greatest part of the aurora borealis which darted from this arch towards the north, as well as the cloud-like and more stationary aurora, were so dense that they hid the stars from view. The moon was eleven days old, and shone bright during this scene, but did not eclipse the brightness of these corruscations. The wind was at north, or a little inclined to the east.

The last phenomenon of this kind which Mr. H. saw, was on the 26th of April. About a quarter before ten in the evening, he

observed in the W. a luminous appearance, of the colour of the most common aurora borealis. From this mass or broad column of light issued three luminous arches, each of which made a different angle with the horizon. That nearest to the south seemed to arise at right angles with the horizon; while that nearest to the north made the smallest angle, and passed towards the N. E. through the constellation Auriga, having Capella close to its upper edge. He had not viewed them many minutes when they were rendered invisible by a general blaze of aurora borealis, which possessed the space just before occupied by these arches. He was soon satisfied that where the aurora borealis was dense, it entirely hid from view the stars of the second magnitude. He observed this particularly with respect to the star 6 m the left shoulder of Auriga. But the corruscations were never so dense as to render Capella invisible. The wind was between the N. and N. E. this evening.

After comparing the phænomena above described with each other, and with those observed by Mr. Cavallo, in London; by Mr. Swinton, at Oxford; by Dr. Huxham, at Plymouth; and by Mr. Sparshal, at Wells, in Norfolk; Mr. II. cannot entertain a doubt, that these arches had all the same origin; and that they ought to be considered as a species of that kind of meteor called aurora borealis.

[Phil. Trans. Abr. Vol. xvi, year 1790.

CHAP. XLVI.

BLAZING BALLS AND BURNING STONES.

SECTION I.

General Remarks.

THERE is a very extraordinary class of atmospheric bodies, usually known by the name of fiery or luminous meteors, which yet remains to be described, and which has never hitherto been satis. factorily accounted for. They are of all sizes, from a smail shooting star of the fifth magnitude, to a cone or cylinder of two or three miles in diameter. They differ in consistency as much as in dimensions, and in colour as much as in either. They are sometimes a subtle, luminous, and pellucid vapour; sometimes a com. pact ball or globe, as though the material of which they are formed, were more condensed and concentrated. And not unfrequently they have been found to consist of both, and consequently to assume a coinet-like appearance, with a nucleus or compact substance in the centre or towards the centre and a long thin pellucid luminous main, or tail, sweeping on each side. They are sometimes of a pale white light; at others of a deep igueous crimson; and occasionally iridescent and vibratory. The rarer meteors appear frequently to vanish all of a sudden, as though abruptly dissolved or extinguished in the atmospheric medium; their flight is accompanied with a hissing sound, and their disappearance with an explosion. And the most compact of them, or the nuclei of those that are rarer have often descended to the sur. face of the earth, and with a force sufficient to bury them many feet under the soil; generally exhibiting marks of imperfect fusion and considerable heat. The substance, in these cases, is for the most part metalline; but the ore of which they consist is no where to be met with, in the same constituent proportions, in the bowels of the earth. Under this form the projected masses are denominated meteoric stones or aërolites.

Yet, however these extraordinary bodies may differ in colour, shape, dimensions, or consistency; they seem to agree with great exactness, in their transient appearance, velocity, and elevation, when first discovered. It is seldom they have been capable of being traced longer than from a single moment to two or three minutes; their height has been pretty fairly and concurrently calculated at from fifty to sixty miles above the surface of the earth; and their velocity, from similar calculations, at from twenty to thirty miles in a second; consequently in the lowest computation exhibiting a rapidity more than ninety times that of sound, and nearly approaching to that of the earth in her annual orbit.

Dr. Halley calculated that the meteor seen throughout England in 1718-19 (as the reader will find in his own very instructing description in the subjoined section) must have been sixty miles high, and have passed over three hundred geographical miles in a minute. It exploded with a great report.

Lerry computed that the extensive meteor which appeared to have originated over the coasts of England, in 1770, was from the first more than eighteen leagues high; and described more than sixty leagues in ten seconds.

The prodigious meteor that appeared nearly in the same direction, in 1783, was calculated by Dr. Blagdon (as we shall perceive presently) to have formed at a height of fifty miles; to have been about two miles in length; and to have moved at the rate of about twenty miles in a second. It rushed with a hissing noise, and exploded with a report. Mr. Cavallo computed that at the time of the explosion it was 56 miles high, 1070 yards in diameter, and its path immediately over Lincolnshire.

Amidst the numerous hypotheses that have been successively advanced, to account for these extraordinary phænomena, and we may add, as successively abandoned, we shall content ourselves with enumerating the following, as those which have possessed the greatest number of advocates.

1. It was contended by Sir J. Pringle, and various other philoso phers, that they are revolving bodies, or a kind of terrestrial

comets.

2. Dr. Halley conjectured them to consist of combustible va pours, accumulated and formed into concrete bodies on the out skirts, or extreme regions of the atmosphere, and to be suddenly

set on fire by some unknown cause: and this opinion, has since been maintained, with little difference, by Sir W. Hamilton and Dr. King.

3. Dr. Blagdon regarded them as altogether electrical phæno

mena.

4. M. Izarn believed them to consist of volcanic materials, pro pelled into the atmosphere in the course of explosions of great violence.

5. M. Chladui threw out the hypothesis that they consist of substances existing exterior to the atmosphere of the earth, and other planets, which have never incorporated with them, and are found loose in the vast ocean of space; combined and inflamed by causes unknown to us.

6. The latest, and, at this moment, the most favourite hypothe sis, is that the whole, or at least, the more compact division of them, consists of materials thrown from immense volcanos in the moon, concerning which we shall speak more at large in a subsequent section. This idea was first started by M. Olbers, in 1795, (Zach's Mon. Corr. vii. 148, as also Phil. Mag. xv. 289.) and has since been very plausibly supported by M. Laplace.

This last hypothesis does not, however, very well apply to the smaller and less substantial meteors of shooting stars: and hence the philosophers who advocate it endeavour to derive these latter phænomena from some other cause, as electricity, or terrestrial exhalations: and observe in support of the distinction they find it necessary to make, that shooting stars must be of a different nature from fire-balls, since they sometimes appear to ascend as well as to fall: an observation that has especially been dwelt upon by Benzenberg and Chladni,

[Editor.

SECTION II.

Account of several extraordinary Meteors, or Lights in the

Sky.

By Dr. Edmund Halley, F. R. S.

THE theory of the air seems now to be perfectly well understood, and its different densities at all altitudes, both by reason and expe-riment, are sufficiently defined; for, supposing the same air to