Part 6 (2/2)

Photograph taken June 3, 1902, at 9.20 p.m., by M. G. Loppe. Published in the _Bulletin de la Societe Astronomique de France_ (May, 1905)]

We see that it is not absolutely inimical to points, nor to metals, but it prefers its independence, and he must get up early who would catch it in a snare.

It is an anarchist--it acknowledges no rule.

But we must confess that if spheroidal lightning seems particularly capricious, it is because we are still ignorant of the laws which guide it. Our ignorance alone is the cause of the mystery.

We try to discover the enigma in the silence of the laboratories, where physicians question science without ceasing; we try to reproduce fireb.a.l.l.s artificially, but the problem is complicated, and its solution presents enormous difficulties.

Hypotheses are not wanting. Some years ago, M. Stephane Leduc recorded an interesting experiment, producing a moving globular spark.

When two very fine and highly polished metallic points, each in affinity with one of the poles of an electro-static machine, rest perpendicularly on the sensitive face of a gelatine bromide of silver photographic plate, which is placed on a metallic leaf, the two points being 5 to 10 centimetres the one from the other, an effluvium is produced round the positive point, while at the negative point a luminous globule is formed.

When this globule has reached a sufficient size, you can see it detach itself from the point, which ceases to be luminous, begin to move forward slowly on the plate, make a few curves, and then set off for the positive point; when it reaches this, the effluvium is extinguished, all luminous phenomenon ceases, and the machine acts as if its two poles were united by a conductor.

The speed with which the luminous globe moves is very slight. It takes from one to four minutes to cover a distance of 5 to 6 centimetres.

Sometimes, before reaching the positive point, the globe bursts into two or more luminous globules, which individually continue their journey towards the positive point.

On developing the plate, you will find traced on it the route followed by the globule, the point of explosion, the routes resulting from the division, the effluvium round the positive point. Also, if you stop the experiment before the arrival of the globule at the positive point, the photograph will only give the route to that point.

The globule makes its course the conductor. If during its journey you were to throw powder on the plate--sulphur, for example--the course it followed will be marked by a line of little aigrettes, looking like a luminous rosary.

Of all the known electric phenomena, this is the most a.n.a.logous with globular lightning.

[Ill.u.s.tration: PHOTOGRAPH OF THE POSITIVE POLE OF AN ELECTRIC SPARK.]

[Ill.u.s.tration: PHOTOGRAPH OF THE NEGATIVE POLE OF AN ELECTRIC SPARK.]

But the really complicated part of the question is when ball lightning loses part of its fluidity and becomes a semi-solid body, as in the following instance:--

On April 24, 1887, a storm burst over Mortree (Orne), and the lightning literally chopped the telegraph wire on the route to Argentan for a distance of 150 yards. The pieces were so calcinated that they might have been under the fire of a forge; some of the longer ones were bent and their sections welded together. The lightning entered by the door of a stable in the form of a fireball, and came near a person who was preparing to milk a cow; then it _pa.s.sed between the legs of the animal_, and disappeared without causing any damage. The terrified cow raised itself on its hind legs with frantic bellowing, and its master ran away, frightened out of his wits, but there was no harm done.

The inexplicable phenomenon was that at the precise moment when the lightning crossed the stable, a great quant.i.ty of incandescent stones fell before a neighbouring house. ”Some of these fragments, of the size of nuts,” wrote the Minister of Post and Telegraphs at the Academy, ”are of a not very thick material, of a greyish-white, and easily broken by the fingers, giving forth a characteristic odour of sulphur. The others, which are smaller, are exactly like c.o.ke.

”It would perhaps be useful to say here, that during this storm the thunderclaps were not preceded by the ordinary muttering, they burst quickly like the discharge of musketry, and succeeded one another at short intervals. Hail fell in abundance, and the temperature was very low.”

It is only by a semblance of disbelief that one can get the peasants to tell us the stories of what they pretend to have seen of the fall of aeroliths during storms. They have christened the uranoliths ”thunder-stones.”

These substances have evidently no relation to uranoliths, but they prove none the less that ponderable matter may accompany the fall of lightning.

Here are two more examples--

In the month of August, 1885, a storm burst over Sotteville (Seine-Inferieure); lightning furrowed the sky, the thunder muttered, and the rain fell in torrents. Suddenly, in the Rue Pierre Corneille, several small b.a.l.l.s, about the size of a common pea, were seen to fall; these burned on touching the ground, sending out a little violet flame. People counted more than twenty, and one of the spectators, on putting her foot on one of them, produced a fresh flame. They left no trace on the ground.

On August 25, 1880, in Paris, during a rather violent storm, in broad daylight, M. A. Trecul, of the Inst.i.tute, saw a very brilliant voluminous body, yellowish-white, and rather long in shape, being apparently 35 to 40 centimetres in length, by about 25 in width, with slightly conical ends.

This body was only visible for a few seconds; it seemed to disappear and re-enter a cloud, but in departing--and this is the chief point--it dropped a little substance, which fell vertically like a heavy body under the sole influence of gravity. It left a trail of light behind it, at the edges of which could be seen sparks, or rather red globules, because their light did not flash. Near the falling substance the luminous trail was almost vertical, while in the further part it was sinuous. The small substance divided in falling, and the light went out soon after, when it was on the point of reaching the tops of the houses. When it was disappearing, and at the moment of the division, no noise was heard, although the cloud was not far away.

<script>