240 PHYSICS. 
about fifteen miles high, and 2500 feet in diameter; March 8, 1798, in 
Switzerland; October 28, 1805; &c. With respect to the one seen on the 
Main, June 4 and 5, 1737, its least distance from the earth was estimated 
at thirty-four miles, and its velocity at somewhat more than that of the 
earth. There is no year in which fire balls are not observed in some place 
or other. Among those from which masses of iron fell are to be reckoned 
the meteors of May 26, 1751, near Agram; December 14, 1807, in North 
America, of 500 feet in diameter; June 15, 1821, m France, about 
three P.M.; &c. 
The preceding remarks will suggest a connexion as existing between the 
fire balls and the meteoric stones, or aerolites, as we call those stones and 
mineral matters which fall after the splitting of the former. Aerolites do 
not, however, always fall from fire balls; sometimes they are cast from a 
small dark cloud, which suddenly forms in a clear sky, with a noise 
resembling that of single discharges of cannon. In much rarer instances 
the sky was clear, and there was no noise. Since the time of Chladni 
scientific men have been convinced of the quite frequent occurrence of falls 
of stones of greater or less dimensions from the atmosphere; the earlier 
accounts of this nature were generally considered as fabulous. On the 
16th of June, 1794, a shower of stones occurred at Sienna; on the 18th of 
December, 1795, a stone fell in England weighing fifty-six pounds; on 
December 13th, 1798, several stones fell from a great fire ball; and on the 
26th of April, 1803, a great shower of stones occurred near Aigle in France, 
r which was verified and investigated by Biot. In France ten such falls were 
observed in twenty-six years (1790 to 1815), from which it has been 
calculated that on an average 700 take place in the year, over the whole 
surface of the earth, or nearly two daily. In 1803 there fell at Aigle about 
2000 fragments of stones, weighing from two drachms to seventeen and a 
half pounds each, over a surface of two and a half French miles in length, 
and one mile in breadth; the masses examined immediately after their fall 
were hot, some still glowing, and many exhibited traces of impression or 
indentation. The depth to which these stones bury themselves in the 
earth is very various; the greatest known is that of the mass weighing 
seventy-one pounds, which fell at Agram on the 26th of May, 1751; its 
diameter amounted to eighteen feet. 
The shape of meteoric stones varies very much, in general it appears to 
be based on that of an inequilateral three or four-sided prism, or a distorted 
pyramid. The surfaces of the stones are rarely smooth, generally curved 
in such a manner that the convexity of one side corresponds to the ' 
concavity of the other; larger or smaller indentations are frequently seen 
on the outside. A characteristic of all meteoric stones is a peculiar thin, 
black rind, sometimes over a quarter of a line thick; they are occasionally 
of a pitchy lustre, and sometimes veined, frequently soft at first, discolored, 
or dusty. 
The internal structure of different meteoric stones exhibits some general 
resemblances, and at the same time great differences. Some are very © 
porous, absorbing water very readily; others are very compact. The 
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