fall through the air on the earth. And if in this comparison a striking coincidence or resemblance shall always or mostly be found, it will be difficult for the human mind to resist the persuasion, that the assumed cause involves a degree of probability but little short of certainty itself. Now the chief phænomena attending these blazing meteors, or burning stones, are these: 1. That they appear or blaze out suddenly. 2. That they move with a surprising rapid motion, nearly horizontal, but a little inclined downwards. 3. That they move in several different directions, with respect to the points of the compass. 4. That in their flight they yield a loud whizzing sound. 5. That they commonly burst with a violent explosion and report. 6. That they fall on the earth with great force, in a sloping direction. 7. That they are very hot at first; remain hot a considerable time; and exhibit visible tokens of fusion on their surface. 8. That the fallen stony masses have all the same external appearance and contexture, as well as internally the same nature and composition. 9. That they are totally different from all our terrestrial bodies, both natural and artificial.

Now these phænomena will naturally compare with the circumstances of a substance projected by a lunar volcano, and in the order in which they are here enumerated. And first with respect to the leading circumstance, that of a sudden blazing meteoric appearance, which is not that of a small bright spark, first seen at an immense distance, and then gradually increasing with the diminu. tion of its distance. And this circumstance appears very naturally to result from the assumed cause. For, the body being projected from a lunar volcano, may well be supposed in an ignited state, like inflamed matter thrown up by our terrestrial volcanoes; which, passing through the comparatively vacuum, in the space between the moon and the earth's sensible atmosphere, it will probably enter the superior parts of this atmosphere with but little diminu. tion of its original heat; from which circumstance, united with that of its violent motion, this being ten or twelve times that of a cannon ball, and through a part of the atmosphere probably consisting chiefly of the inflammable gas, rising from the earth to the top of the atmosphere, the body may well be supposed to become suddenly inflamed, as the natural effect of these circumstances;

From whence it ap

indeed it would be surprising if it did not. pears, that the sudden inflammation of the body, on entering the earth's atmosphere, is exactly what might be expected to happen.

2. Secondly, to trace the body through the earth's atmosphere; we are to observe, that it enters the top of it with the great velocity acquired by descending from the point of equal attraction, which is such as would carry the body to the earth's surface, in a very few additional seconds of time, if it met with no obstruction. But as it enters deeper in the atmosphere, it meets with still more and more resistance, from the increasing density of the atmo sphere; by which the great velocity of six miles per second must soon be greatly reduced to one that will be uniform, and only a small part of its former great velocity. This remaining part of its motion will be various in different bodies, being more or less as the body is larger or smaller, and as it is more or less specifically heavy: but, for a particular instance, if the body were a globe of twelve inches diameter, and of the same gravity as the atmospheric stones, the motion would decrease so as to be little more than a quarter of a mile per second of perpendicular descent. Now while the body is thus descending, the earth itself is affected by a two-fold motion, both the diurnal and the annual one, with both of which the descent of the body is to be compounded. The earth's motion of rotation, at the equator, is about seventeen miles in a minute, or two-sevenths of a mile in a second: but in the middle latitudes of Europe little more than the half of that, or little above half a quarter of a mile in a second and if we com. pound this motion with that of the descending body, as in mechanics, this may cause the body to appear to descend obliquely, though but a little, the motion being nearer the perpendicular than the horizontal direction. But the other motion of the earth, or that in its annual course, is about twenty miles in a second, which is eighty times greater than the perpendicular descent in the in. stance above-mentioned: so that, if this motion be compounded with the descending one of the body, it must necessarily give it the appearance of a very rapid motion, in a direction nearly parallel to the horizon, but a little declining downwards., A circumstance which exactly agrees with the usual appearances of these meteoric bodies, as stated in the second article of the enumerated phæ

nomena.

3. Again, with regard to the apparent direction of the body, this will evidently be various, being that compounded of the body's descent, and the direction of the earth's annual motion at the time of the fall, which is itself various in the different seasons of the year, according to the direction of the several points of the ecliptic to the earth's meridian or axis. Usually, however, from the great excess of the earth's motion, above that of the falling body, the direction of this must appear to be nearly opposite to that of the former. And in fact this exactly agrees with a remark made by Dr. Halley, in his account of the meteors in his paper above given, where he says that the direction of the meteor's motion was exactly opposite to that of the earth in her orbit. And if this shall gene. rally be found to be the case, it will prove a powerful confirmation of this theory of the lunar substances. Unfortunately, however, the observations on this point are very few, and mostly inaccurate: the angle or direction of the fallen stones has not been recorded; and that of the flying meteor commonly mistaken, all the various observers giving it a different course, some even directly the re. verse of others. In future, it will be very advisable that the observers of fallen stones, observe and record the direction or bearing of the perforation, made by the body in the earth, which will give us perhaps the course of the path nearer than any other observation.

4. In the flight of these meteoric stones, it is commonly observ. ed that they yield a loud whizzing sound. Indeed it would be surprising if they did not. For if the like sound be given by the smooth and regularly formed cannon ball, and heard at a consider. able distance, how exceedingly great must be that of a body so much larger, which is of an irregular form and surface too, and striking the air with 50 or 100 times the velocity.

5. That they commonly burst and fly in pieces in their rapid flight, is a circumstance exceedingly like to happen, both from the violent state of fusion on their surface, and from the extreme rapidity of their motion through the air. If a grinding-stone, from its quick rotation, be sometimes burst, and fly in pieces; and if the same thing happen to cannon-balls, when made of stone, and discharged with considerable velocity, merely by the friction and resistance of the air; how much more is the same to be expected to happen to the atmospheric stones, moving with more

than fifty times the velocity, and when their surface may well be supposed to be partly loosened or dissolved by the extremity of the heat there.

6. That the stones strike the ground with a great force, and penetrate to a considerable depth, as is usually observed, is a circumstance only to be expected, from the extreme rapidity of their motion, and their great weight, when we consider that a cannon ball, or a mortar shell, will often bury itself many inches, or even some feet, in the earth.

7. That these stones, when soon sought after and found, are hot, and exhibit the marks of recent fusion, are also the natural consequences of the extreme degree of inflammation in which their surface had been put during their flight through the air.

8. That these stony masses have all the same external appear. ance and contexture, as well as internally the same nature and composition, are circumstances that strongly point out an identity of origin, whatever may be the cause to which they owe so gene. rally uniform a conformation. And when it is considered, 9thly, that in those respects they differ totally from all terrestrial compo. sitions hitherto known or discovered; they lead the mind strongly to ascribe them to some other origin than the earth we inhabit; and none so likely as coming from our neighbouring planet.

Upon the whole then it appears highly probable, that the flaming meteors, and the burning stones that fall on the earth, are one and the same thing. It also appears impossible, or in the extremest degree improbable, to ascribe these, either to a formation in the superior parts of the atmosphere, or to the eruptions of terres. trial volcanoes, or to the generation by lightning striking the earth. But, on the other hand, that it is possible for such masses to be projected from the moon so as to reach the earth: and that all the phænomena of these meteors, or falling stones, have a surprising conformity with the circumstances of masses that may be expelled from the moon by natural causes, unite in forming a body of strong evidence, that this is in all probability and actually the

case.

[Phil. Trans. Abr. Vol. 6, p. 100.

SECTION X.

Falling or Shooting Stars.

We have already observed, that there is much doubt as to the origin of this elegant meteor, common as it is to all countries and seasons. The learned writer of the article in the preceding section seems to ascribe them to the same source as the largest and most concrete meteors of the heavens, and consequently to refer them to a lunar source. And, generally speaking, whatever has been the hypothesis entertained concerning the one class, it has been equally applied to explain the other.

"I am unwilling to assert," says Mr. Cavallo, "though I have no particular reason to deny, that the large meteors, and those which are commonly called shooting stars, have a common origin, or are of the same nature, and differ only in size; our utter igno rance of their nature, and the want of accurate observations, do not enable us to form any other distinction. It appears then, that the number of meteors is immense; for the shooting stars, or the meteors of the smallest size, are to be seen in plenty every clear night. Some of them are so small as to be accidentally seen only through telescopes; others are visible to the naked eye, that happens to be directed to that part of the sky; whilst others, by casting more or less light, excite attention and are remarked. The apparent size of these meteors is various; but their apparent motions, when they happen to direct their course nearly at right angles to the spectator, seem not to differ much: whence we may conclude, that they are nearly at equal distances from the earth; and of course they must actually differ in size. This point, how. ever, is much in want of confirmation; and it might be wished, that three or four observers, in a pleasant autumnal evening, were situated at certain distances (for instance ten or twenty miles) from each other, and would endeavour to mark the altitudes of all the shooting stars they saw, together with the time of their appearance. The altitude may be easily ascertained by observing the stars over or near which the meteor passes, and by referring it to a common celestial globe, rectified for the latitude of the place and time of the apparition*.”

* Elem. of Philos. vol. iv. p. 365.