Part 18 (1/2)

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 fas.h.i.+oned 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 s.h.i.+p _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.