'inches square and six inches deep, and as truly regular as if cut out by art.' In other instances, lightning drills small holes, which are not less surprising for their perfect circularity of form. It bores them as cleverly as if it were a human artisan working with gimlets or augers. Window-panes have been frequently pierced in this fashion, without cracking or affecting the rest of the glass. Some years ago, a gentleman at Poole was writing at a desk before a window, when a flash of lightning passed 'before him, accompanied at the same moment by a loud clap of 'thunder. The lightning cut out from one of the frames a perfectly circular disc of glass, which fell upon the paper on 'which the observer was writing.'*

All juvenile electricians are in the habit of making holes in cards by passing discharges through them; and if philosophically disposed, the operators request you to observe that a burr or projection is left on both sides of the aperture. This double protrusion, they tell you, with the look of sages, is supposed to prove the existence of two electrical fluids, because a single agent passing through the card need only drive the resisting material before it in one direction. And whatever may be said in favour of the one-fluid theory, and though some electricians are willing to ascribe the effect in question to the expansive or disrupting force of which we have already spoken, yet this explanation may be checked by the fact, that a single discharge sometimes produces two holes in the card, each puncture appearing to be distinguished by a single burr, one on the upper, and the other on the under side of the card, as if the positive fluid had travelled one way and the negative the other. Jupiter makes burrs also. In 1821, he launched a shaft from Vulcan's smithy against the church of Saint Gervais, at Geneva, and, amongst other perforations, produced two neighbouring holes in a sheet of tin upon the roof. They were nearly circular in shape, and about an inch in diameter, but in the one the edges of the metal were turned outwards, and in the other inwards; and this so distinctly, that no one could mistake the opposite set of the projections. In some instances, the results are such as to suggest that a flash may be slit up into several fiery filaments before it strikes an object. From the top of a church at Cremona, the angry god hurled a weathercock of tinned copper, in the year 1777. This meteorological implement was found to be pierced with eighteen holes; in nine of them the burr was conspicuous on one side, and in nine it was equally prominent on the other; in all, the slope or inclination of the protruded matter

*The Thunder-storm, p. 198, (from information communicated by Thomas Bell, Esq., F.R.S.)

Lightning-scabbards.

49

was nearly identical. There was no evidence that these openings had been made by several lightning strokes; and to suppose that they had been thus produced, Arago thinks would involve us in a venturesome assumption that the flashes-hunting in couples, as the two-fluid theory requires-had alighted in pairs on different occasions upon the same piece of metal with the same inclination, though coming in opposite directions. Or, if adopting the single-fluid hypothesis, we should hold that not nine but eighteen discharges were necessary to riddle this mysterious weathercock, then we must be prepared to believe that a small object, placed equidistant between Sebastopol and the late besieging lines, would be found with nine Russian holes, all piercing it in parallel routes, and with exactly nine contrary burrs, exhibiting a corresponding inclination, but equitably produced by the allied balls. Such compound coincidences are scarcely to be presumed, though, as will be afterwards seen, lightning does sometimes repeat its strokes in a singular manner, as if bent upon copying its previous performances to the very letter. We would not wish to speak disrespectfully of the skill of the Thundering Jove, but we humbly doubt whether, practised as he is in this flaming archery, he could have hit the weathercock of Cremona eighteen times running, under conditions such as the circumstances seem to prescribe.

If the apertures thus made in bodies may be said to indicate the breadth of the lightning when it strikes-to afford a kind of cross section of the meteor-there are occasions when it stamps its form in the soil, so as to leave longitudinal evidence (if we may so speak) of its transit. Fulgurites are tubes which the lightning constructs when it falls upon a siliceous spot by fusing the sand. They show us how the electric fluid comports itself when it reaches the ground. They may be called casts of thunder-bolts. Some of the finest samples were discovered in hillocks of sand, near Drigg, in Cumberland. They consist of hollow tubes, with a diameter varying from of an inch to upwards of two inches, and frequently tapering as they descend, until their extremities are reduced to a mere point. At first there may be a single tube only; but at some little depth beneath the surface this will, perhaps, separate into two or three branches, and these, again, sometimes throw off twigs a few inches in length, so that, taken as a whole, the thunder-sheath appears something like the skeleton of an inverted tree. The entire extent of the tubes may amount to as much as thirty feet, but usually they break up into short pieces of less than six inches in length. Internally, they are lined with glass, as smooth and perfect as if it had been manufactured in a glass-house. Outwardly, they are composed of grains of

quartz or sand, exhibiting decided traces of fusion, and glued together so as to form a rind or crust, which has been compared to the bark on the stump of an old birch tree. The appearance of the tube, however, will be determined by the nature of the soil in which it is formed, being nearly white where the sand is extremely pure.

When these singular productions were first examined they afforded fine themes for speculation to ingenious minds. Some supposed them to be stalactites; others the stony sheaths of roots which had decayed; and others again imagined that they might be the cells of ancient worms; but the modern, and still more the moveable nature of the hillocks in which fulgurites were discovered dispelled these conjectures, and most people now treat them as the scabbards of spent thunder-bolts. Nature, indeed, as Arago intimates, has been caught in the act of fabricating them. In 1823, the electric fluid struck a birch tree near the village of Rauschen, on the shores of the Baltic. Two holes were immediately observed, one of which, notwithstanding the falling rain, was still hot. They were examined by Professor Hagen, and found to be true fulgurites. Further, these interesting creations have been mimicked in the laboratory by means of artificial electricity. Sand has been operated upon in such a way as to show that it is capable of answering the appearances presented by the genuine lightning tube, and bolts discharged from ordinary batteries have moulded powdered glass into imitative fulgurites.

From what has already been stated, the power of fusing substances another prominent property of lightning-will be readily inferred. Rocks have been scathed, and their surfaces vitrified by this terrible meteor. Metals have been reduced to fluids when its furious march was interrupted by refractory objects. An American packet, the New York, was attacked by a storm on her passage to England, in April, 1827. Several links of an iron chain were melted, and, descending in glowing drops upon the deck, set fire to everything they touched: part of the chain is even said to have burnt like a taper. Connected with this power of fusion there is one circumstance which has excited much curiosity. If certain narratives are to be implicitly received, it would seem that lightning can develop sufficient heat to liquefy metallic bodies, without damaging or even singeing the more fragile materials with which they may happen to be associated. Aristotle says that copper has been melted off a shield without the wood being injured. Seneca affirms that money has been fused in a purse without burning the latter; and that a scabbard may be left unhurt though the implement of valour within is reduced to a fluid by the lightning flash. To explain this incon

gruous behaviour, Franklin temporarily adopted a supposition which was just as incongruous in itself. He concluded that electricity might sever the particles of metals in such a way as to render them liquid, without producing any sensible manifestations of heat. Hence the process was designated cold fusion. This was certainly blowing hot and cold with a vengeance; but then the difficulties of the case might well have excused a wilder surmise than that of the American Prometheus. Lightning is unquestionably a most capricious meteor, and the pranks it plays are sometimes perfectly inexplicable. A man in Cornwall was once struck by a bolt, which burnt the sleeve of his shirt, and also of his coat to tinder, without frizzling or even damaging the outside of the coat at all. Balls of electrical matter, capable of firing combustible objects, or melting metals like wax, have been seen to issue from the sea, or to drop into sheets of water, without producing any hissing sound, or occasioning any symptoms of ebullition. So, artificially, sparks which will ignite inflammable substances may be drawn from an icicle. But it is clear that when lightning fuses metals, it does so by augmenting their temperature, for where bell-wires, as frequently happens, have been destroyed by the electric fluid, the wall is found blackened by the process, and the floor is sometimes dimpled with the globules which have burnt themselves into the wood. We saw it rain fire in the room,' said a servant who had seen a wire thus dissipated by a lightning stroke in a house at Southwark. Instead, therefore, of resorting to so enigmatical an explanation as the cold fusion of Franklin, it may be more natural to assume, that where liquefaction takes place without injuring susceptible substances in the immediate vicinity, the melting of the metal must be extremely superficial. Done in an instant, and limited to a thin layer of the body, the heat produced by the stroke will be discharged before any further act of incendiarism can be performed.

These are a few scanty examples of the mechanical effects of lightning. It works chemically as well. It has the power of developing a peculiar odour, which some have compared to that of phosphorus, others to nitrous gas, but most observers to the fumes of burning sulphur. Even in the open air this emanation has sometimes proved almost intolerable. Wafer mentions a storm on the Isthmus of Darien, which diffused such a sulphureous stench throughout the atmosphere that he and his marauding companions could scarcely draw their breath, particularly when the party plunged into the woods. And on another occasion, when, to use his expressive language, it seemed as if 'heaven and earth were coming together,' and every minute was marked by a terrible clap of thunder, the perfume attained such diabolical pun

gency that the men expected to be suffocated. In the year 1749, the British ship Montague was struck by globular lightning, which left such a Satanic savour behind it that the vessel seemed nothing but sulphur.' This odour has been known to cling to a place for several hours together. 'Both kitchen and chamber,' says the reporter of a Norwich storm about a century old, smelt as strong of sulphur for some hours after as if fumigated with brimstone matches.' Persons struck by lightning have been said to retain a strong taste of sulphur in their mouths and throats for several days after the assault. Nor does the electric fluid on these occasions always play on the olfactories alone; it sometimes raises a thick vapour, which appeals just as inconveniently to the eye as its fragrance does to the nose. Stricken ships have been filled with an exhalation of such opacity that it was impossible to perceive any object through it. And in 1819, a church at Châteauneuf les Moustiers (Basses Alpes), after receiving a bolt, was pervaded by a dense smoke, through which the people groped their way as if enveloped in Egyptian night.

Various causes have been assigned for this unsavoury phenomenon. Schönbein ascribed it to the formation of ozone by the electrical decomposition of the air. Faraday has attributed it to the production of nitrous acid. De la Rive, with many more, are of opinion that the lightning sweeps along with it various particles which may be floating in the atmosphere, and heats or affects them, so as to produce impressions of smell. Others have referred in triumph to a real ball, nearly an inch in diameter, and consisting principally of sulphur, which was deposited in a meadow in the Isle of Wight (1733), after a night of almost incessant thunder and lightning. The sources, however, of this peculiar odour, are still too subtle to admit of any positive explanation; but the lingering scent which a bolt sometimes leaves behind it shows that its aroma, whatever it may be, is widely and pertinaciously diffused.

That lightning may produce chemical modifications in the atmosphere Cavendish's well-known experiment has sufficiently shown. By transmitting electric sparks through a quantity of air confined in a glass globe this old philosopher developed the red fumes of nitrous acid gas. But what is the discharge of a puny battery to the fierce flashes which are ploughing their way continually through the atmosphere in a storm? Have these no chemical operation? We are aware that Liebig's analyses have been modified by subsequent researches; but it is a striking circumstance that, having collected seventy-seven samples of rain water, seventeen which had fallen during thunder-storms were