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Once a Week (magazine)/Series 1/Volume 10/Fossil thunder and lightning

FOSSIL THUNDER AND LIGHTNING.

 

 

I can fancy my readers, especially those who have an incipient interest in geology, taken rather aback by the heading of my paper, and imagining that geology must be a more extensive science than they thought for, since it embraces not only things but sounds. Everybody knows what a fossil shell is—it is something palpable and tangible; but fossil thunder and lightning must be a joke on a par with that of the sailor who swore that he once caught a gale of wind and tied it in a knot. I will first take the thunder, which, I may as well confess at once, is a sad misnomer, given in the days when popular science was not. I remember, as a lad, seeing in my father's study a large oval ball, of a dark metallic colour, and covered all over with little bumps, that I always used to call a thunderbolt; and it is with a chat about these that I may, perhaps, interest my reader for a few minutes. What are popularly called thunderbolts are known to chemists and geologists as aërolites, or meteorites—the latter term being given from their supposed connection with meteors and shooting stars. From all ages of the world these aërolites have been invested with a great amount of fascination and mystery, and have been the subject of philosophic speculations from the earliest times; for in the Chinese annals mention is made of upwards of sixteen falls between the seventh century before Christ up to 333 years after Christ. Subsequently the Greek and Roman savans propounded their views on the phenomena, the sage Anaxagoras being of opinion that the stars were masses torn away from the earth by the violence of the rotation, and that the whole heavens were composed of stones. He even suggested that these dark masses of stones, getting between the earth and the moon, produced an eclipse. The general view which has been arrived at by the philosophers of the present day, including that tower of strength Baron Humboldt, is that aërolites are in reality heavenly bodies, which, moving in the space or "cosmos" above, have come within the earth's attraction, been deviated from their course, and arrived in these regions in a high state of temperature. Some have supposed that they are the results of eruptions of the volcanoes in the moon, projected with incredible force so as to pierce the atmosphere of this earth, and thus to be drawn within its attraction.

In both cases the result arrived at appears to be nearly the same, viz., that an aërolite is a foreign body, which has lost its way and come to the earth, though, whether from the moon, or, as an independent heavenly body, doctors differ. The high temperature appears to be a constant accompaniment, and was noticed by Anaxagoras, who observed that the stony bodies were made to glow by the fiery ether, so that they reflected the light communicated to them by the ether. The temperature may be owing to the extreme velocity of the fall of the aërolite, but may also arise from the circumstances under which it is ejected. However that may be, it is one of the most wonderful facts that these bodies, emerging from the heavenly spaces above, can be touched, weighed, and analysed by the creatures of this earth; and still more wonderful to find that they consist of substances identical with substances which we find in the mineral structure of the earth, making it probable, according to the conjecture of Sir Isaac Newton, that the materials which belonged to one group of cosmical bodies are, for the most part, the same. It seems as though analysing a meteorite was like questioning a messenger from the stars, and throws a glow of light on the probable structure of the sister world. When broken, their appearance inside is grey, earthy, or metallic; but the outside is invariably covered by a dark metallic shining crust, produced, perhaps, by a fusion of the constituent elements.

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 caused by lightning is borne out by the fact that artificial fulgurites have been made by French and English experimenters by transmitting a powerful electric shock through powdered sand and quartz.

The discovery of these curious effects has been limited to sandy localities, which, from their open position facing the sea, and from their not being protected by vegetation, appear to be peculiarly liable to the electric discharge. They have, however, also been found in the chalk cliffs of Dover and in the Isle of Wight by Dr. Bigsby. In some cases the fulgurite occurs as a solid and not a hollow tube; and Dr. Gibb calls attention to the presence of fossil fulgurites in the heart of London, viz., on a flagstone on the east side of Tottenham Court Road; also on the eastern side of Russell Square, close to Guilford Street. How little do the tens of thousands who daily hurry over the pavement know of the history of the stone on which their feet are treading. Little do they think that even if there are no remains of extinct forms embedded in the flag, it exhibits on its surface the atmospheric effects of rain, sunshine, storm and wind, of myriads of ages past, forming a subtle link between the busy world of to-day and the scarcely revealed world of eras so far back that they defy calculation or even imagination. There is deep matter for reflection even in a London pavement.

G. P. Bevan.