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met on fire by some unknowu 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
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. 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 tbe vast ocean of space ; combined and inflamed by causes unkuowu 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. Curr. vij. 148, as also Phil. Mag. xv. 289.) and has siuce 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
Account of several extraordinary Meteors, or Lights in the
By Dr. Edmund Halley, F.R.S. Tee 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; fur, supposing the sanje 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. Sapt. 1676) from Dr. Wallis, which was seen in very distant counties almost over all the south part of England. Of which, thongh 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, beineen vine 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 pro. nounce concerning its height with more certainty; yet, as it is, we may securely conclude, that it was not many nriles 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 alti. tude 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 thau tifty degrees; and the like may be concluded from the aliitude 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 dies
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 inight 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 eartli, 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 Montavari, as may be seen in his Italian treatise about it, soon after published at Bononia. He observes that at Bononia, its greatest altitude iu 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 Rimiui and Savigniano on the one side, and to Leghorn on the other : that ils perpendicular altitude was at least thirty-eight mies : that in all places near this course, it was heard to make a laissing uoise 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 beard to give a very loud report like a great cannon; inimediately 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 Bono. nia, at above fifty miles distance, that it could not be less swift, than 160 miles in a micute 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. tude, which appeared at Bononia larger than the moon in one dia. meter, and above half as large again in the other; which with the given distance of the eye, makes its real less diameter above half a mile, and the other in proportion. This supposed, it cannot be wondered that so great a body moving with such an amazing velo. city through the air, though so much rarefied as it is in its upper regions, should occasion so loud a hissing noise, as to be heard at such a distance as it seems this was. But it will be inuch harder to conceive, how such an impetus could be impressed on this body, wbich far exceeds that of any cannon ball; and how this impetus should be determined in a direction so nearly parallel to the horizon; and what sort of substance it must be, that could be so im. pelled and ignited at the same time: there being no volcano, or other spiraculum of subterraneous fire, in the N. E. parts of the world, that we ever yet heard of, from whence it might be projected.
I have much considered this appearance, and think it one of the hardest things to account for, that I bave yet met with in the phæ. noniena of meteors; and am induced to think that it must be some collection of matter formed in the æther, as it were by some for. tuitous concourse of atoms, and that the earth met with it as it passed along in its orb, then but newly formed, and before it had conceived any impetus of descent towards the sun. For its direc. tion was exactly opposite to that of the earth, which made an angle with the meridian at that time (the sup being in about eleven degrees of Aries) of 67o; that is, its course was from W. S. W. to E.N. E. so that the meteor seemed to move the contrary way. And besides, falling into the power of the earth's gravity, and losing its motion from the opposition of the medium, it seems that it descended towards the earth, and was extinguished in the Tyrrhene Sea, to the W. S.W. of Leghorn. The great report being heard on its first inmersiou into the water; and the rattling, like the driving a cart over stones, being what succeeded on its quenching; some. thing like which is always observed on quenching a very hot iron in water. These facts being past dispute, I would be glad to have the opinion of the learned on them, and what objection can be reasonably made against the abovesaid hypothesis, wbich I bumbly submit to their censure.
P. S. Since this was written, there has fallen into my bands an account of nearly such another appearance, seen in Germany, in the year 1686, at Leipsie, by the late Mr. Gottfried Kirch, who was for many years a very diligent observer of the heavens, and was perfectly well instructed in astronomical matters. In an Appendix to his Ephemerides for the year 1688, he gives this reinarkable account of it. “On the 9th of July, 0. S. at half an hour past one in the morning, a fire ball with a tail was observed, in 84 degrees of Aquarius, and 4° north, which continued immoveable for half a quarter of an hour, having a diameter nearly equal to half the moon's diameter. At first, its light was so great that we could see to read by it: after which, it gradually vanished in its place. This phenomenon was observed at the same time in several other places ; especially at Schlaitza, a town distant from Dantzic eleven German miles towards the south, its altitude being about 6° above the southern horizon."
At the time of this appearance the sun was in 261° of Cancer, and by the given place of the meteor, it is plain, it was seen about
of an hour past the meridian, or ip S. by W. and by its declination it could not be above 24° high at Leipsic, though the same, at Schlaize was about 60° high: the angle therefore at the meteor was about 36°. Whence, by an easy calculus, it will be found, that the same was not less than sixteen German miles distant in a right line from Leipsic, and above 6 ! such miles perpendicular above the horizon, that is at least thirty English miles high in the air. Aud though the observer says of it, immotus perstitit per semi-quadrantem hors, it is not to be understood that it keeps its place like a fixed star, all the time of its appearzuce; but that it had no very remarkable progressive motion. For he himself has, at the end of the said Ephemerides given a figure of it, which he has marked fig. D, whence it appears that it darted downwards obliquely to the right-hand, and where it ended, left two globules or nodes, not visible but by an optic tube (a telescope.)
The same Mr. Gottfried Kirch, in the beginning of a German trea. tise of his, concerning the great comet which appeared in the year 1680, entitled Newe Himinels Zeitung, printed at Nurenburg, anno 1681, gives an account of such another luminous meteor, seen like. wise at Leipsic, on the 22d of May, 1680, 0. S. about three in the