| Name. | Diameter in miles. |
|---|---|
| Jupiter | 90,000 |
| Uranus | 35,000 |
| The Earth | 7,926 |
| Mercury | 3,000 |
| The Moon | 2,160 |
| Rhea, Saturn's 5th satellite | 1,200 |
| Dione Saturn's 4th satellite | 500 |
| Vesta[10] | 260 |
| Juno | 104 |
| Melpomene | 52 |
| Polyhymnia | 35 |
| Isis | 25 |
| Atalanta | 20 |
| Hestia | 15 |
The diminution doubtless continues indefinitely below the present limit of optical power. If, however, the orbits have small eccentricity, such asteroids could not become known to us unless their mean distances were nearly the same with that of the earth. But from the following table it will be seen that the variety is no less distinctly marked in the forms of the orbits:
| Name. | Eccentricity. |
|---|---|
| Venus | 0·00683 |
| The Earth | 0·01677 |
| Jupiter | 0·04824 |
| Metis | 0·12410 |
| Mercury | 0·20562 |
| Pallas | 0·24000 |
| Polyhymnia | 0·33820 |
| Faye's comet | 0·55660 |
| D'Arrest's comet | 0·66090 |
| Biela's comet | 0·75580 |
| Encke's comet | 0·84670 |
| Halley's comet | 0·96740 |
| Fourth comet of 1857 | 0·98140 |
| Fifth comet of 1858 (Donati's) | 0·99620 |
| Third comet of 1827 | 0·99927 |
Were the eccentricities of the nearest asteroids equal to that of Faye's comet, they would in perihelion intersect the earth's orbit. Now, in the case of both asteroids and comets, the smallest are the most numerous; and as this doubtless continues below the limit of telescopic discovery, the earth ought to encounter such bodies in its annual motion. It actually does so. The number of cometoids thus encountered in the form of meteoric stones, fire-balls, and shooting-stars in the course of a single year amounts to many millions. The extremely minute, and such as consist of matter in the gaseous form, are consumed or dissipated in the upper regions of the atmosphere. No deposit from ordinary shooting-stars has ever been known to reach the earth's surface. But there is probably great variety in the physical constitution of the bodies encountered; and though comparatively few contain a sufficient amount of matter in the solid form to reach the surface of our planet, scarcely a year passes without the fall of meteoric stones in some part of the earth, either singly or in clusters. Now, when we consider how small a proportion of the whole number are probably observed, it is obvious that the actual occurrence of the phenomenon can be by no means rare.[11]
Although numerous instances of the fall of aerolites had been recorded, some of them apparently well authenticated, the occurrence long appeared too marvelous and improbable to gain credence with scientific men. Such a shower of rocky fragments occurred, however, on the 26th of April, 1803, at L'Aigle, in France, as forever to dissipate all doubt on the subject. At one o'clock P.M., the heavens being almost cloudless, a tremendous noise, like that of thunder, was heard, and at the same time an immense fire-ball was seen moving with great rapidity through the atmosphere. This was followed by a violent explosion which lasted several minutes, and which was heard not only at L'Aigle, but in every direction around it to the distance of seventy miles. Immediately after a great number of meteoric stones fell to the earth, generally penetrating to some distance beneath the surface. The largest of these fragments weighed 17½ pounds. This occurrence very naturally excited great attention. M. Biot, under the authority of the government, repaired to L'Aigle, collected the various facts in regard to the phenomenon, took the depositions of witnesses, etc., and finally embraced the results of his investigations in an elaborate memoir.
It would not comport with the design of the present treatise to give an extended list of these phenomena. The following account, however, includes the most important instances of the fall of aerolites, and also of the displays of meteoric fire-balls.
1. According to Livy a number of meteoric stones fell on the Alban Hill, near Rome, about the year 654 B.C. This is the most ancient fall of aerolites on record.
2. 468 B.C., about the year in which Socrates was born. A mass of rock, described as "of the size of two millstones," fell at Ægos Potamos, in Thrace. An attempt to rediscover this meteoric mass, so celebrated in antiquity, was recently made, but without success. Notwithstanding this failure, Humboldt expressed the hope that, as such a body would be difficult to destroy, it may yet be found, "since the region in which it fell is now become so easy of access to European travelers."
3. 921 A.D. An immense aerolite fell into the river (a branch of the Tiber) at Narni, in Italy. It projected three or four feet above the surface of the water.
4. 1492, November 7th. An aerolite, weighing two hundred and seventy-six pounds, fell at Ensisheim, in Alsace, penetrating the earth to the depth of three feet. This stone, or the greater portion of it, may still be seen at Ensisheim.