Generally speaking, they consist largely of iron, in the form of sulphuret or magnetic oxide; but this is not always the case, some having been found to contain 96 per cent. and others barely two. According to the analysis of the German chemist, Gustav Rose, the residuum which remained insoluble after the aërolite had been boiled in acid, consisted of a mixture of minerals similar to those found in the volcanic rocks of our earth. This view seems rather to corroborate their volcanic origin from the moon.
Another chemist, Berzelius, found no less than seventeen elements in his analysis, viz., iron, nickel, cobalt, manganese, chromium, arsenic, zinc, potassium, sodium, sulphur, phosphorus, carbon, silicum, magnesium, copper, tin, and calcium So that in fact an aërolite seems to be a condensation of all the principal materials that form the earth's crust. A curious fact was noticed by a German writer named Olbers, viz., that no meteoric stones have ever been found in the secondary and tertiary formations, from which he inferred that the falling of aërolites was a phenomenon connected with the present condition only of the earth. But the fact has been partially disproved by Humboldt, who relates the discovery of large masses of meteoric iron buried thirty feet in the ground in the gold-bearing drifts of northern Russia; and Mr. Binney found meteoric stones embedded in coal in Lancashire. These exceptions, however, do not prove the rule. The number of aërolites that fall annually is estimated at about 700, and many interesting records have been kept of the circumstances under which they have fallen. One case happened in France, in the Départment de l'Orne, which is described as the sudden breaking up of a small dark cloud at one o'clock p.m. with an explosion like a rattle of muskets, simultaneously with which there fell over a surface of six miles a number of meteoric stones, the largest weighing seventeen pounds. They were hot, smoking, and more easily broken during the first twenty-four hours than at any subsequent time. In 1768 one fell near Chartres, accompanied by a report like a cannon. This was 7½ lbs., and was so hot that it could not be touched.
In 1857, in Austria, an aërolite was seen to fall, which, when extracted from the ground, into which it had penetrated a considerable depth, was found to weigh 30 lbs.
In the British Museum may be seen, amongst many others, one weighing 56 lbs., which fell in the East Riding of Yorkshire; and the enormous mass of 270 lbs. that fell near Alsace, in 1492, just at the time when the Emperor Maximilian, king of the Romans, was on the point of engaging with the French army. Notwithstanding the many cases on record, and the large size of the meteorites, there is, I believe, only one in which a person is known to have been killed by the fall.
We can scarcely wonder at these phenomena causing the greatest consternation and fear wherever they appeared; for even in these days of enlightenment, when the common effects and results of natural philosophy are taught in almost every school, the fact of a thunderbolt falling or being supposed to have fallen is a fruitful theme for village talk.
Before we take leave of this portion of the subject, I should mention one feature respecting them, viz., the periodicity of the appearance of aërolites. Arago, writing in 1839, considered that "there existed a zone composed of millions of these small bodies, the orbits of which zone cut the plane of the ecliptic at about the point which our earth annually occupies between the 11th and the 13th of November." So that, according to him, aërolites may be looked for about that time. There is no reason to suppose, however, that there may not be other periods besides this, particularly as the cases which are on record have happened at different times of the year. These, however, are only a microscopical proportion of the vast number which must have come down to the earth.
Fossil lightning seems almost as great a misnomer as fossil thunder; though, perhaps, it is really more applicable, and is a term used by Professor Owen to the effect of lightning on rocks of past geological epoch, some of which effects are so clearly marked that even the varieties of forked lightning could be distinguished.
The supposed fossils originating from lightning have been named "fulgurites," and consist of conical tubes, hollow and tapering down towards their furthest end, which is almost always closed. They are of various lengths, depending, apparently, on the intensity of the flash which has in fact penetrated into the sand or rock for a certain depth, vitrifying with the heat of electricity the surrounding material. The localities where fulgurites are found, depend on the character of the soil upon which the lightning has acted; and in the two places where they are most common, viz., at La Plata, in South America, and Drigg, on the Cumberland Coast, the same kind of ground prevails, viz., sand formed of quartz and porphyry. Doubtless every flash of lightning that strikes the earth leaves its mark behind it; but owing to the siliceous or flinty character of these particular spots, the effects are more peculiar and durable. That these have been