Thunder and Lightning Part 18

The production of this ponderable matter has often been attributed to bolides, but direct observation proves beyond a doubt that the electricity carries various solid substances found on earth after a storm.

Lightning is truly the most venerable of gla.s.s-makers. Long before the most remote peoples of antiquity appeared, whose gla.s.swares encrusted with marvellous iridescent tones by the pa.s.sing of the centuries, are unearthed by scientific excavations, and displayed in national collections; long before man could have learnt to make use of the resources of nature, lightning, burrowing in the sand, there fashioned tubes of gla.s.s that hold the hues of the opal, and are called fulgurites.

The ancients seem to have known of these fulgurite tubes, but we owe the first precise description and the first specimen of these extraordinary vitrifactions to Hermann, a pastor at Ma.s.sel in Silesia.

His fulgurite, found in 1711, is in the Dresden Museum.

Since this discovery, fulgurites have often been sought for and found.

The tubes, contracted at one end, and ending in a point, are to be seen in sandy soils.

Their diameter varies from 1 to 90 millimetres, and the thickness of their sides from half to 24 millimetres. As to the length, it sometimes exceeds 6 metres. Vitrified inside, they are covered outside with grains of sand agglutinated and apparently rounded as if they had been subjected to a beginning of fusion. The colour depends on the nature of the sand in which they have been formed. Where the sand is ferruginous the fulgurite takes a yellowish hue, but if the sand is very clean, it is almost colourless or even white. As a rule, the fulgurites penetrate the ground vertically, Nevertheless, they have been found in an oblique position. At times, also, they are sinuous, twisted, or even zigzag if they have met with pebbles of considerable size.

It is not uncommon for the fulgurite tube to divide in two or three branches, each of which gives birth to little lateral branches of 2 or 3 centimetres long, and ending in points.

There are also solid fulgurites and foliated fulgurites. The former, no doubt, had a ca.n.a.l originally, which has been stopped up by matter in fusion. The latter, instead of being stretched out in cylindrical form, are composed of slender layers like the leaves of a book.

The scientific museum at the Observatory of Juvisy possesses a very curious fulgurite which was offered to me some years ago by M. Bernard d'Attanoux, and found by him in Sahara. It is not a tube ending in a point. The lightning penetrating the sand, vitrified it on its pa.s.sage, and branched irregularly in three princ.i.p.al directions. One might say it was slag formed by the juxtaposition, irregular and crumpled, of three blades of vitrified sand, which would be pressed together by leaving a narrow opening to their central vertical axis.

This fulgurite, which is extremely light, measures six centimetres in length. It was found in the sand of Grand-Erg, at a depth of several centimetres. It has been found possible to produce miniature fulgurites by means of our electrical machines. By adding ordinary salt to the sand, and directing a strong current into it, complete vitrification of a tube of several millimetres is obtained.

CHAPTER VIII

THE EFFECTS OF LIGHTNING ON METALS, OBJECTS, HOUSES, ETC.

When lightning strikes the earth, it makes straight for metals. Their perfect conducting powers place them in the first rank of conductors, and the innumerable cases of lightning with which they are a.s.sociated have gained them a certain celebrity in the annals of thunder.

We know, indeed, the preference of the spark for metals; we know it nurses a veritable pa.s.sion for nails, wire, bell-pulls, that it dotes on rain-spouts, leaden pipes, and telegraph wires, that it is very feminine in its adoration of jewels, which it sublimates sometimes with a truly fantastic dexterity.

Now and then lightning deviates from its path, and performs acrobatic feats, elfin capers to reach the objects it covets. On April 24, 1842, it struck the church of Brexton, springing on the cross of the steeple at first and running down the stem, but, arrived at the masonry which supported it, broke it into pieces; then with one bound it fell upon a second conductor, whose support was also broken. Finally, it struck a third conductor much lower down.

The fluid often searches for metals hidden beneath non-conductors, which it breaks or pierces. It avoids the mattress to pursue the iron of the bed, glances off the windows to glide over the curtain-rods, or the lead of the sash. It has been seen to penetrate thick walls to reach the iron safes hidden behind them.

We have already mentioned the case of the woman who, without having been killed, had her ear-ring split. Well, we have a certain number of similar examples to that.

On June 1, 1809, in a boarding-school for young ladies, at Bordeaux, a gold chain, worn by one of the young ladies, was melted by the lightning, which left a black indented line in its place, which, however, soon pa.s.sed off. The lady was struck, but recovered consciousness within a few hours, being none the worse. Her slender chain, worn in three rows round her neck, had been cut into five pieces. Some of the fragments showed signs of fusion, and had been carried to a distance.

Other examples, in which the consequences were more dramatic, will show ladies the dangers of a love of adornment.

On September 21, 1901, during a violent thunderstorm which burst over the region of Narbonne, a fireball fell in the domain of Castelou. A young girl of fourteen was fatally struck by the meteor. The gold chain which she wore round her throat was completely evaporated. There was not a trace of it to be found.

It is not unusual to see gold chains broken, melted, partially or completely, in the pocket which had held them.

Thus, lightning melted a watch and chain into a single lump in the pocket of a man killed on board a pa.s.senger boat.

Bracelets, hairpins, and even precious stones are sometimes very strangely altered.

As for watches, without speaking of the magnetization observed after a violent electrical discharge, it has been remarked that the movement became slower. In some cases they stopped short, and marked the exact instant when the lightning stopped them.

When the ship _Eagle_ was struck by lightning, none of the pa.s.sengers were injured, but all their watches stopped at the moment the shock took place.

At other times there are peculiarities in the works which are absolutely inexplicable. The following observation, related by Biot, is a curious case in point.

A young man was slightly struck by lightning in the street of Grenelle-Saint-Germain. His watch was in no wise hurt outside, but, although it was only a quarter-past eleven, the hands pointed to a quarter to five.

Convinced that it was in need of repair, the young man placed it on his table, intending to take it to the watchmaker; but next day, thinking he would wind it up to make sure of the extent of the damage, he saw, to his amazement, the hands moved and kept regular time.

In some instances the case of the watch is seriously injured, while the works are none the worse.

A man wore a watch with a double cap attached to a gold chain. The chain was broken, some of the links soldered together. The cap had been perforated, and the gold spilt in his pocket. The watch itself had not been altered.

But if lightning sometimes stops the works of watches, it also produces the contrary effect.

Beyer relates that a flash of lightning, having entered a room and broken the corner of a gla.s.s, set a watch going which had been stopped for a long time.

I find the following note amongst my papers: "M. Coulvier-Gravier, director of the meteoric observatory of the palace of Luxembourg, told me yesterday that on Sunday, April 8, at 9.35 in the evening, a watch (wound up), which had stopped a week previously, went on at the moment lightning struck the lightning conductor on the Luxembourg above these rooms."

Often enough the case is badly injured: the polish is rubbed off the metal, it is melted, bored through, and even dented, without any trace of fusion.

A case of the latter is rare. Here is an example, however.

In the month of June, 1853, a man from Aigremont having been killed by lightning, his silver watch was found in his watch-pocket completely smashed.

Indeed, one of the most common effects of lightning on watches is the magnetization to which the various pieces of steel are subjected. We have a considerable number of records concerning these magnetic properties. In one case the balance had its poles so well pointed that, when placed on a raft, it served as a compa.s.s.

We may observe, by the way, that clocks and chronometers are sometimes as much injured also by the spark. It often gives an energetic twist to the needles, or to the spring for regulating the strokes, or it even melts the wheel-works, either partially or completely.

It is difficult to form any idea of the various operations of lightning; here it hurls itself down like a fiery torrent, there it makes itself so tiny that it can pa.s.s through the smallest apertures.

Does it not even slip under women's corsets, melting the busks and the little k.n.o.bs which serve to hook them.

It even attacks the various metal articles which set off our garments, even to the shoe-buckles, b.u.t.tons, etc.

Keys are, as a rule, very ill-treated by the fire of heaven: they are twisted, flattened, melted or soldered to the ring from which they hang.

On May 12, 1890, a man living at Troyes returned to his house while a violent storm was raging. The moment he put his key into the lock, the white gleam of a dazzling flash of lightning surrounded him, the ring holding his keys was broken in his hand, and they were scattered on the threshold.

At times, too, scissors, needles, etc., are s.n.a.t.c.hed out of the hands of the workers, and carried some distance off when they are not reduced to vapour.

At Saint-Dizier (Haute-Marne) in July, 1886, lightning fell on the workshop of M. Penon, a chain-maker. Five or six workmen were finishing their work or getting ready to leave.

Entering by the window near which M. Penon--who was absent at the time--usually worked, the fluid grazed the bellows which were opposite, and caught up a piece of it, which one would have thought was cut off with a knife. Turning to the left, and pa.s.sing behind a chain-maker, who felt a violent shock, it pa.s.sed to a heap of chains which it did not damage much. All the links in a chain of about a metre long were, however, soldered together; the whole chain seemed to be galvanized, and the soldering was not easily broken by hand.

Pieces of iron which had been cut and prepared for the manufacture, were found twisted and soldered together in the same way. Finally the lightning s.n.a.t.c.hed the iron hoops from a tub, and, returning the same way, broke a piece of wood from a board, so as to go through the lower part of a part.i.tion, the masonry of which was carried away for a length of fifty centimetres.

Very often lightning rivals the most skilful cabinet-makers: iron or copper nails are pulled out of a piece of furniture with a most amazing skill, without doing any harm to the material they kept in place. Ordinarily they are thrown far away. Here are two examples of this curious phenomenon:--

On September 23, 1824, lightning penetrated a house at Campbeltown; the copper nails in the chairs were pulled out very precisely, without the stuff being spoiled. Some were conveyed to the corner of a box standing at the opposite end of the room, others were so solidly fixed in the part.i.tions, that it was only with great difficulty that they were pulled out (Howar). At another time, close to Ma.r.s.eilles, lightning slipped into a drawing-room, one might say, like a robber, one evening, and pilfered all the nails out of a couch covered with satin. Then it departed by the chimney through which it had entered.