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 small 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 compact ball or globe, as though the material of which they are formed, were more condensed and concentrated. And not un. frequently they have been found to consist of both, and consequently to assume a comet-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 igneous 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 disap pearance with an explosion. And the nost 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 mi. nutes; 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 10 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 ex. ploded with a report. Mr. Cavallo computed that at the time of the explosion it was 564 miles high, 1070 yards in diameter, and its path immediately over Lincolnshire.

Ausidst 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, propelled into the atmosphere in the course of explosions of great violence.

5. M. Chladni 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 hypothesis, 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 Bens zenberg 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 experiment, are sufficiently defined; for, supposing the same air to

occupy spaces reciprocally proportional to the quantity of the supe rior or incumbent air, I have elsewhere proved, that at forty miles high the air is rarer than at the surface of the earth about 3000 times; and that the utmost height of the atmosphere, which reflects light in the crepusculum, is not fully forty-five miles. Notwithstanding which, it is still manifest, that some sort of vapours, and those in no small quantity, rise nearly to that height. An instance of this may be given in the great light the society had an account of (vide Trans. Srpt. 1676) from Dr. Wallis, which was seen in very distant counties almost over all the south part of England. Of which, though the Doctor could not get so particular an account as was requisite to determine its height, yet from the distant places it was seen in, it could not but be a great many miles high.

So likewise that meteor which was seen in 1708, on the 31st of July, between nine and ten o'clock at night, was evidently between forty and fifty miles perpendicularly high, and as near as I can gather, over Sheerness and the Buoy on. the Nore. For it was seen at London moving horizontally from E. by N. to E. by S. at least fifty degrees high, and at Redgrave in Suffolk, on the Yarmouth road, about twenty miles from the east coast of England, and at least forty miles to the eastward of London, it appeared a little to the westward of the south, suppose S. by W. and was seen about thirty degrees high, sliding obliquely downwards. I was shown in both places its situation, but could wish some person skilled in astronomical matters had seen it, that we might pronounce concerning its height with more certainty; yet, as it is, we may securely conclude, that it was not many miles more westerly than Redgrave; which, as I said before, is above forty miles more easterly than London. Suppose it therefore, where perpendicular, to have been thirty-five miles east from London, and by the altitude it appeared at in London, viz. at fifty degrees, its tangent will be forty-two miles, for the height of the meteor above the surface of the earth; which also is rather of the least, because the altitude of the place shown me, is rather more than fifty degrees; and the like may be concluded from the altitude it appeared in at Redgrave, near seventy miles distant. Though at this great distance, it ap peared to move with an amazing velocity, darting, in a very few seconds of time, for about twelve degrees of a great circle froin north to south, being very bright at its first appearance; and it dieri

away at the end of its course, leaving for some time a pale whiteness in the place, with some remains of it in the track where it had gone; but no hissing sound as it passed, or explosion, was heard.

It may deserve the honourable Society's thoughts, how so great a quantity of vapour should be raised to the very topof the atino. sphere, and there collected, so as upon its accension, or otherwise illumination, to give a light to a circle of above 100 miles diameter, not much inferior to the light of the moon; so as one might see to take a pin from the ground in the otherwise dark night. It is hard to conceive what sort of exhalations should rise from the earth, either by the action of the sun or subterranean beat, so as to surmount the extreme cold and rareness of the air in those upper regions: but the fact is indisputable, and therefore requires a solution.

Like to this, but much more considerable, was that famous me teor which was seen to pass over Italy, on the 21st of March. O. S. Anno 1676, about an hour and three quarters after sun set, which happened to be observed, and was well considered, by the famous professor of mathematics in Bononia, Geminian Montanari, as may be seen in his Italian treatise about it, soon after published at Bononia. He observes that at Bononia, its greatest altitude in the S. S. E. was thirty-eight degrees, and at Siena, fifty-eight to the N.N.W.; that its course, by the concurrence of all the observers, was from E. N. E. to W.S.W. that it came over the Adriatic Sea as from Dalmatia: that it crossed over all Italy, being nearly vertical to Rimini and Savigniano on the one side, and to Leghorn on the other that its perpendicular altitude was at least thirty-eight mdes: that in all places near this course, it was heard to make a hissing noise as it passed, like that of artificial fire-works: that having passed over Leghorn, it went off to sea towards Corsica; and lastly, that at Leghorn it was heard to give a very loud report like a great cannon; immediately after which, another sort of sound was heard, like the rattling of a great cart running over stones, which continued about the time of a credo.

He concludes, from the apparent velocity it went with at Bononia, at above fifty miles distance, that it could not be less swift, than 160 miles in a minute of time, which is above ten times as swift as the diurnal rotation of the earth under the equinoctial, and not many times less than that with which the annual motion of the earth about the sun is performed. To this he adds, its magni.