Thunder and Lightning Part 3

A sailor tells us that once when he was out at sea, more than 100 kilometres from Lima, he saw a number of bright flashes, without any thunder, to the east and north-east of the horizon. The weather was perfect, and the sky absolutely serene. Now we know that storms, and the electric phenomena which they produce, are unknown upon that coast; but this immunity does not extend for more than 100 kilometres to the interior of this country, so that this lightning which was observed at sea, 100 kilometres from the sh.o.r.e, must have taken place more than 200 kilometres away.

One of our correspondents, M. Soleyre of Constantine, sent us word, in 1899, of an interesting case of lightning without thunder.

"In August," he says, "I noticed it in the valley of the Arve above Salambes; when I came back to Algiers I saw it again on September 16, and on October 19.

"It was not sheet lightning, but ordinary lightning concentrated in very thin lines. This lasted long, and was very near. Another thing, there was no hail. This is not very rare in Algiers."

On September 1, 1901, I happened to be in Geneva at about 6 p.m. The weather was heavy but very fine. I noticed a good deal of lightning on the south-west of the horizon. It went on almost without interruption above the Savoy Alps. Each flash illuminated at the same time the ridge of the mountains and the fringed edge of the great sombre clouds lying low on the horizon. This lightning was silent; the noise of the thunder did not reach Geneva. The next day I learnt that a terrible storm had devastated the neighbourhood of Chambery and Aix-les-Bains.

Moreover, apart from storms, there have been other records of this lighting up of the sky being observed at great distances.

Thus, in 1803, a service of luminous communications was established on Mount Brocken in the Hartz Mountains in order to determine the differences of longitude. The combustion of 180 to 200 grammes of powder, burnt in the open air, for each of the signals, produced a light which was observed by astronomers stationed on Mount Kenlenberg, although they were 240 kilometres from Brocken, which is itself invisible from Kenlenberg.

On certain fete-days, July 14, for example, when the princ.i.p.al monuments in Paris are illuminated, at a distance of 20 and 30 kilometres we can see a sort of luminous vapour which floats above the town and reflects the lights of the boulevards, although the lights themselves are invisible from the point of observation.

Here is another example which any Parisian can verify: the captive balloon of the Aerodrome at Porte-Maillot, which soars some hundreds of yards above Paris during the spring and summer, as seen from the dark paths of the Bois de Boulogne, appears against the azure of the sky like a magnificent globe bathed in light, resembling an enormous moon. Well, this gentle, pale light is only the reflection of the lights of Paris which are invisible from the Bois de Boulogne.

The earth and all the planets which are dark in themselves, shine in s.p.a.ce lighted up by the sun.

The silent lightning which flashes in the sky is only the reflection of a distant storm. Whether on account of the spherical shape of the earth or on account of the irregularities of the land, the clouds are invisible, but the effluvium which escapes from them can be seen at a great distance.

These poetic and ephemeral flames which glide through the sky, appeal to the imagination of the dreamer, and yet they are quite as terrible as the flashes which are accompanied by thunder. If the noise which accompanies these is not perceptible, it is because the sound of the thunder does not carry far, and has been lost in s.p.a.ce before reaching us.

It is the same with the silent lightning which gleams in a stormy sky.

This phenomenon is particularly frequent in the Antilles. Either the storm breaks too far from the observer, or the discharge has taken place between two beds of clouds, the lower of which intercepts the waves of sound without preventing the escape of the electric spark, and the thunder is not heard.

As a rule we imagine that lightning always descends, that it comes to us from the higher celestial regions to be lost in the common reservoir. But this is quite inaccurate. Lightning sometimes ascends.

Sometimes it descends and reascends. That is to say, after it reaches the ground, either there is no attraction there, or a stronger force draws it back to the aerial regions, and it flies back to the clouds whence it came.

As a rule we only fear the direct lightning. This is a great mistake.

There are many cases of lightning striking from a distance.

For example, at the end of May, 1866, an English coastguard was making his rounds on the coast of one of the Shetland Isles, when a flash of lightning pa.s.sed near him, striking a great rock. The unfortunate man was completely blinded, and plunged into darkness thus suddenly, he would inevitably have fallen down an abyss, if his companions, attracted by his cries, had not come to the rescue and taken him home.

Here is another case:--

On September 24, 1826, a terrible storm burst over Versailles, accompanied by a great deal of thunder and lightning. At the moment when the lightning struck Galli's farm, an old man who was in a street in Versailles, at a distance of two kilometres from the farm, suddenly felt a violent shock, accompanied by a feeling of oppression and giddiness and a semi-paralysis of the tongue and the whole of his left side. Next morning this had pa.s.sed away, but in the evening at the same time as the shock had occurred, he felt similar sensations of fainting, and it was the same to the end of the week. It would be well to remark here that at the moment of the accident, M. B---- happened to be near the wall of a house, not far from the metallic tube which conducted the rain-water into the level of the pavement.

The following phenomenon, to which we have already alluded, is no less curious:--

On July 22, 1868, at about 7 o'clock in the evening, at Gien-sur-Cure (Nievre), the thunder had been growling violently for some time, when all of a sudden the lightning struck a thatched house, which it set on fire. At the same time a woman who was in a house ten yards away, felt a shock, and saw the tiled floor rise beneath her. Her two sabots were broken on her feet, and a bottle of Holy Water with which she was blessing the house was broken in her hand, only the neck remained in her fingers. She herself suffered nothing but the shock. Nineteen of the tiles were flung in all directions.

Here is another very remarkable case of _ascending lightning_, published in the _Comptes Rendus_ of the Academie des Sciences:--

At Porto-Alegre, on June 9, 1870, at 2 a.m., during a violent storm, on the property of M. Laranja e Oliveira, at Brazil, a servant was entering the house; he was about ten yards away, when a flash of lightning illuminated it; at the same moment he felt a great tingling in the flesh of his feet, then in his legs, then all over his body, and finally in his head, on which the hair stood on end to such an extent that _he was obliged to hold his hat on_ in order to prevent its falling off. At the same time, a white flame burst from the ground about two yards in front of him, accompanied by a shower of sparks.

Terrified by such a phenomenon, which he attributed to souls from another world, he thought he was petrified to the spot; finally, he ran away. Anything metallic which he had about him at the time of this occurrence became magnetized. A key which was in his pocket remained magnetic for two days.

Thus, as well as the ordinary fulguration, in which the lightning (which we imagine descends from the clouds) acts directly on the body, and the lightning which strikes indirectly, there are other electric shocks which can be experienced by men and animals. Notable among these is the _striking from the earth_, commonly known as _choc de retour_, and which is in reality only an instance of the ascending current, or of lightning striking from a distance. We must also describe the striking _by a man who has been struck_.

The Abbe Richard, in his _Histoire de l'Air_, tells the following story:--

In the neighbourhood of the village of Rumigny, in Picardy, on August 20, 1769, at six o'clock in the morning, there was a sudden irruption of fulminating matter from the bosom of the earth in such quant.i.ties as to produce the most violent results. The sky was cloudy, and looked like a storm. A young farmer and his wife were following, at some distance, a vehicle drawn by four horses. Suddenly the driver of this, _without seeing the lightning or hearing the thunder_, was thrown to the earth. His four horses were stretched dead on the ground near the carriage. There was a _smoking hole_ in the ground, from which the effluvium came forth and killed the young man and his wife at ten paces off and separated from each other by twenty paces. The current also knocked down, at a hundred paces, the father of the young man in the same fashion as it had done the driver, but without injuring one or the other.

The bodies showed no signs of a wound, only a considerable swelling and a great deformity of the features. The woman, who was young and pretty, became hideous; the whole of her body as well as that of her husband was absolutely yellow. The four horses had their intestines drawn from their bodies. They were all thrown on the same side. The man's hat was pierced and his hair burnt, but he had no bruise on his head.

This account, in which we must not be surprised to find the ideas and language of the time (let us observe in pa.s.sing that the man who was struck did not hear the thunder, and had not even time to see the lightning of which he was the victim)--this account, I say, gives us an instance of ascending lightning. Here is another.

The traveller Brydone gives the following example, which he himself observed:--

On July 19, 1785, a storm burst near Coldstream between 12 and 1 a.m.

A woman who was cutting hay on the banks of the Tweed _fell backwards_. She at once called to her companions, and said she had just received a violent blow on her foot for which she could in no way account. At the time there was no thunder or lightning in the sky. The shepherd of a farm at Lennel Hill saw a sheep fall near him, which a few minutes before appeared to be in perfect health; he found it stone dead. The storm then appeared very far off. Two carts laden with coal, and each driven by a young driver seated on a small seat in front, crossed over the Tweed. They had just climbed a small hill near the banks of this river when they heard a great detonation round about, similar to that which would be produced by the discharge of several guns. At the same instant the driver of the second cart saw the first, with his companion and the two horses, fall to the ground. _The driver and horses were stone dead. The ground was pierced with three circular holes at the very spot where the wheels had touched it when the accident happened._ Half an hour after this event the holes emitted an odour which Brydone compared to that of ether. The two circular iron bands which covered the felloes of the wheels showed evident signs of fusion in the two spots which rested on the ground at the moment of the detonation, and in no other place. The skin of the horses had been burnt, particularly about the legs and under the stomach. The body of the driver had marks of burning here and there. His clothes, his shirt, and, above all, his hat, were reduced to shreds, and gave out a strong smell.

Orioli gives an example of two men who were surprised by a violent storm near the village of Benvenide. They lay down on the ground to let the meteor pa.s.s. Some moments later one of them got up feeling very tired, but the other was dead. The bones of the latter were so soft that it was easy to bend them; his whole body was of the consistency of paste. The tongue had been torn from the roots, and no one knew what had become of it.

Now, just as the earth can strike, so can the human body become fulminating and act like lightning. After having been struck, it can effectively acquire the power to strike in its turn.

For instance, on June 30, 1854, a man named Barri was killed by lightning near the Jardin des Plantes, in Paris, and his body lay for some time exposed to a beating rain. After the storm had pa.s.sed, two soldiers from the neighbouring guard-house tried to remove the body, and each received a violent blow when they touched it. They got off with a shock, perhaps because the body had been drenched with rain, which acted as a conductor to the electricity, and thus it had had time to lose a part of the fluid.

What a mysterious world is that of atmospheric electricity! It is truly the New World for the scientific mind--a mine, fruitful in unknown and even unsuspected marvels, which is perpetually disclosing its riches for our admiration.

One of our most valued collaborators in our researches on the nature of lightning is photography. Faithfully and unhesitatingly it registers an indestructible doc.u.ment of the fugitive lightning, which imprints itself on the sensitized plate, and the astronomer can afterwards examine the smallest details of the sudden apparition comfortably and at his leisure. We have already a considerable number of plates of the outline of the lightning in flight. An examination of these electric pictures is very interesting.

Who knows whether, later on, when phonography is brought to perfection, it will not also register the noisy accompaniment to the electric flash? Then, with the help of the cinematograph, we could have dramatic representations of sensational storms. While the photograph unrolls all the phases of the lightning, from its emerging from the cloud to its fall to earth, before the gaze of the spectators, the phonograph will repeat the sonorous accents of the terrorizing voice of thunder.

Thunder, as all the world knows, is the noise which accompanies lightning. It is produced when a change of electricity--a neutralization--takes place between two points more or less distant.

The causes which provoke it are still somewhat of a mystery.

The luminous rocket which flings itself precipitately from a cloud saturated with electricity, spreads itself like a trail of flames in the atmosphere where an infinity of invisible molecules are floating; these it repels. The pa.s.sage of this whirlwind of fire in a centre which is greatly compressed produces a momentary void into which the surrounding air at once rushes, and it is the same all the way along the route followed by lightning.

In all probability the equilibrium of the atmosphere, which is momentarily disturbed by the intrusion of the ignited matter, hastily re-establishes itself by a rush of the air which the lightning has ejected, and which is swallowed up with a crash in the opening which has been made. It is, on a large scale, a similar phenomenon to that which is produced by opening a case which has been hermetically sealed. The air rushing in makes a dull noise.

Pouillet objects to this very natural explanation on the ground that the flight of a cannon-ball ought to produce a similar noise. But this objection errs in its basis, because, as regards velocity, a cannon-ball is as a tortoise as compared with the arrow of lightning, and as regards size, who can compare a few grammes of powder to the torrents of fire launched into s.p.a.ce by the prodigious force of electricity?

The lightning discharge produces a violent concussion in the cloud, and very often a shower of rain immediately follows it. The electric conditions of the different clouds which make a storm being separately liable the one to the other, the discharge of one must lead to that of several others more or less distant. In all cases the noise is caused by the expansion of the air where a more or less partial void has been made. It is the same with firearms, _creve-vessie_, etc.

One of the chief characteristics of thunder is the rolling, which is often prolonged, and reverberates on the sides of steep mountains.

This voice, with its lugubrious tone, becomes grave and sometimes sinister in the revolution of s.p.a.ce--this voice, celestial and infernal, seems to momentarily dominate the world, while the clouds are enveloped with a thousand diabolical flames. Sometimes it rings in the air with fierce calls, at others it spreads itself in dull, languorous complaints.

Nevertheless, the intenseness of thunder undergoes a thousand fluctuations, and presents astonishing variations. Generally it strikes and frightens, but the curious thing is that, for the ear, in reality it is less strong than the crinkling noise of a piece of paper torn close to it.

Often, too, it may be compared to the discharge of firearms, a pistol or a cannon.

Thus, when the lightning penetrated Volney's apartments at Naples, the people present, among whom was Saussure, had the impression of a pistol-shot in the next room.

There is a case given of M. and Mme. Boddington, who were seated on the back seat of their coach in order to enjoy the view of the country, and had given the inside seats to two servants. Suddenly there was a flash of lightning, which struck M. and Mme. Boddington and flung the postillion to a great distance. The servants were untouched, and escaped with a fright. When they got over their terror, one of them said that a very brilliant flash of lightning had been immediately followed by a noise similar to that of a heavily charged musket. He thought some one had shot the horses. His fright had stunned him so that he hardly knew what had happened.

At other times thunder is accompanied by a whistling noise, but as a rule it is the rolling which predominates.

We ask ourselves to what it is due that this rolling lasts so long.