The bodies to which I allude are called aeroliths, or air stones, having received this denomination from the circumstance of their falling from, or through our atmosphere, and frequently penetrating a considerable depth into the earth; being commonly preceded by a luminous appearance which indicates their motion in the heavens.

Meteors, or fire-balls, have, in all ages and climates, been observed, at times, to traverse the higher regions of the air; and many of them have been described by eye-witnesses. A remarkable phenomenon of this kind was observed in 1783, when a meteor exceedingly large and brilliant passed over England and a considerable portion of the continent of Europe, illuminating every place over which it passed with an awful grandeur that astonished every beholder; its inotion was amazingly rapid; and from observations made upon it in different places, it is computed that its diameter was little less than three quarters of a mile, and its altitude above the terrestrial surface, at least sixty miles.

The motion of meteors in general is accompanied with a hissing noise, resembling that of a shell in the air when projected from a piece of ordnance; and at their disappearance an explosion takes place resembling that of a clap of thunder; which is usually attended by the fall of several stones of different magnitudes, that bury themselves in the earth; many of them continuing luminous till they reach the surface; being then still warm, and bearing evident marks of recentfusion. These stones

are frequently mentioned by ancient authors, but the truth of their reports was much doubted, and supposed to have had no other foundation than in the chimerical ideas of fanciful philosophers. But since, of late years, the truth of the fact has been positively ascertained, considerable attention has been paid to this curious subject; many recent falls of a similar kind have been well attested; and the bodies themselves submitted to a chemical analysis. From this latter process one of the strongest characteristics of aeroliths has been deduced; which is, that they bear an exact resemblance to each other, at the same time that they are totally different from any known terrestrial body.

I shall not, of course, enter here into a minute description of their component parts, as that subject belongs properly to chemistry; but shall barely observe, that they are composed of a mixture of earths and metals, in certain proportions, which have been found to obtain in all those that have hitherto been examined, on whatever part of the globe they may have fallen; their specific gravity being also nearly the same. This striking resemblance in their composition seems to indicate that they have a common origin; while their dissimilarity to all terrestrial substances, denotes it to be foreign to our globe; but what it is, or the cause to which it may be attributed, has, at present, eluded the researches of every philosophical enquiry which has been instituted, in order to elucidate this interesting question. But though no physical explanation of the origin or

formation of these bodies has been yet found, various hypotheses have been advanced on one hand, and refuted on the other. Some have attributed them to terrestrial volcanoes, and others to those of the moon; and on submitting the latter supposition to computation, it has been ascertained, that a velocity of about four times that commonly given to a cannon ball, would be sufficient to bring them within the sphere of the earth's attraction; after which they would fall towards its centre from the established laws of gravity. And as the existence of such volcanoes has been discovered from observations on the lunar disc, and those of the earth being known to possess a much greater power than is required in the present case, this hypothesis is not so extravagant as it may on the first view of it be imagined.

Other philosophers have supposed them to be small planets, which coming within the attractive power of the earth, are drawn towards it, and take fire from the resistance and friction which they experience in passing through our atmosphere; to which hypothesis, the discovery of the planets Ceres, Juno, &c. is considered by some, as giving a considerable degree of probability. But the most general opinion of modern chemists is, that they are concretions, formed in the atmosphere itself; although at present we are without the support of sufficient experiments to countenance this supposition. Various objections, indeed, might be made against every hypothesis that has yet been advanced, to account for the origin of these sin

gular substances; which are found of different magnitudes, weighing from two or three pounds, to several hundred weight. All that is known with certainty on the subject is, that they are the fragments of meteors, or fire-balls, that have exploded in the atmosphere; but whence they derive their origin, and to what cause it may be attributed, are questions which at present are involved in the greatest mystery, and will probably continue for ages to baffle all the attempts of philosophers to explain them.()

() The following are some of the most interesting and best authenticated facts, that have been hitherto related, respecting the falls of aeroliths.

LETTER XXIII.

OF THE ECLIPSES OF THE SUN AND MOON.

Of all the phænomena of the heavens, there are none that engage the attention of mankind more than eclipses of the sun and moon; and to those who are unacquainted with astronomical principles, nothing appears more extraordinary than the accuracy with which they can be predicted. In the early ages of antiquity, ere religion and science had enlightened the world, appearances of this kind were generally regarded as alarming deviations from the established laws of nature, and but few, even among philosophers themselves, were able to account for them. At length, when men began to apply themselves to observations, and the celestial motions were better understood, these phænomena were found to depend upon a regular cause, and to admit of a natural and easy solution.

It is to be observed, however, that most of the ancient calculations of eclipses must have been extremely defective; for as astronomy, in those times, was but imperfectly understood, all its dependent parts must have been subject to great inaccuracies. It is only since Newton has unfolded the theory of gravitation; and the science of mechanics has been brought in to give its assistance to philosophy, that we have had a just idea of the construction of the universe; and though eclipses might have been computed independently of this