THE EFFECTS OF LIGHTNING ON TREES AND PLANTS
Nearly two thousand years ago, Pliny wrote, "As regards products of
the earth, lightning never strikes the bay tree." And this is why the
Roman emperors, in fear always of the fire of heaven, crowned
themselves with laurels. This belief was almost universal in ancient
times, and survived for many centuries.
But every new century has proclaimed the immunity from lightning of
some one member of the vegetable world, though impartial research has
now established the fact that there is no such absolute privilege. If
certain trees are rarely struck, that is, perhaps, due less to its
species than to its size, its hygrometrical condition, and to other
influences which it is still difficult to specify; for lightning, as
we have seen, has capricious habits which we have not yet succeeded in
explaining.
Thus the bay tree has lost its proud position in this respect, and has
had to take its place amongst the ordinary run of trees, subject to
the unjust anger of Jupiter. Many bay trees of some size have been
seen to fall victims to the electric fluid.
The fig tree, the mulberry tree, and the peach tree have also been
reputed to enjoy safety, but this also is not the case. There is an
instance on record of a fig tree being struck by lightning and
completely withered, and another of a mulberry-tree, eighty years old,
being partly destroyed.
In our own days, the beech is believed to go uninjured. In the State
of Tennessee, in the United States, the opinion is so deeply rooted
that beech tree plantations are often resorted to as a refuge in times
of storm. But it would be a mistake to place too much trust in them.
There are records of beech trees being struck by lightning and
destroyed, just like bay trees, fig trees, and the rest.
In 1835, an old beech tree was struck in the forest of
Villers-Cotterets. This venerable patriarch was more than three
hundred years old. Of its upper branches, which were wide and strong,
four of the finest were destroyed; a fifth, stripped of its bark to a
great extent, was not torn off the trunk. The trunk was split where
the other four branches were torn from it. The interior of it was
blackened and slightly carbonized.
On July 15, 1868, at Chéfresne, canton de Percy (Manche), an oak and
an ash were struck by lightning within five minutes of each other.
On August 10, 1886, at Haute-Croix, in Brabant, an ash was struck and
destroyed. On August 23, in the same year, an ash was struck also at
Namur.
The box tree and the Virginian creeper used to be regarded as
safeguards against lightning. The same virtue was attributed to the
house-leek, a thick herbaceous plant, which grows usually upon walls
and roofs, and which the Germans call Donnerblatt or Donnerbarb,
Thunder-leaf or Thunder-beard.
According to some authors, again, lightning never strikes resinous
trees, such as pines or firs. But this also is disproved by the facts,
especially in regard to firs.
Among the many particulars I have collected of recent years, is the
following list of sixty-five different kinds of trees, with the record
of the number of times each species has been struck by lightning
within a given period:--
54 oaks.
24 poplars.
14 elms.
11 walnut trees.
10 firs.
7 willows.
6 pine trees.
6 ash trees.
6 beech trees.
4 pear trees.
4 cherry trees.
4 chestnut trees.
3 catalpas.
2 lime trees.
2 apple trees.
1 mountain ash.
1 mulberry tree.
1 alder.
1 laburnum.
1 acacia.
1 pseudo-acacia.
1 fig tree.
1 orange tree
1 olive tree.
0 birch.
0 maple.
Height obviously accounts for a good deal. It is incontestable that,
in the case of a clump of trees standing in the middle of a plain,
lightning will in most cases pick out the tallest. But this is not an
absolute rule. The isolation of trees, their qualities as conductors,
the degree of moisture in the soil in which they are rooted, their
distance from the storm clouds, the character of their foliage and of
their roots--all these things are important factors.
Numerous experiments have been made with a view to ascertaining the
amount of resistance offered to the electric spark by different kinds
of wood. Similar pieces of beech and oak have been exposed lengthwise
to the electric spark given out by one of Holtz's machines, with the
result that the oak wood was pierced by the electric fluid after one
or two revolutions of the machine, whereas for the beech wood a dozen
or twenty were needed. Black poplar wood and willow offer a moderate
resistance: a few revolutions suffice to penetrate them.
In all instances the susceptibility of the wood depends on the sap. It
has been proved by analysis that the woods which contain starch with
but little oil, such as the oak, poplar, willow, maple, elm, and ash,
offer much less resistance to the electric current than those trees
which are richer in fatty matter, as the beech tree, walnut tree, lime
tree, birch tree, and so on.
These conclusions are corroborated by the case of the pine tree, the
wood of which has a great quantity of oil in winter, but in summer
lacks it as much as those trees which contain more starch.
Experiments have proved that in summer this wood is quite as likely to
serve as a conductor as the oak; while in winter its resistance to the
electric spark equals that of the beech and other trees which are
rarely struck by lightning. Decayed trees are excellent conductors of
electricity; those in full vigour being much more rarely struck.
In any case, it has been proved that the effects of lightning are
particularly severe in the vegetable world. It has been pointed out
elsewhere in this little book to what dangers those persons are
exposed who take shelter beneath the trees during a thunderstorm;
there are innumerable examples of the imprudence of taking refuge from
the rain under thick foliage, people having been killed by a
fireball--for lightning does not always take the trouble to make a
selection, sparing neither the protector nor the protected.
We shall give some more instances, chosen from a considerable number
of similar observations.
In 1888, ten reapers, surprised by drops of rain and distant rumbling
of thunder, left their work and took refuge beneath a big walnut tree.
But one of them having questioned the security of this retreat, all
immediately fled in the direction of a neighbouring wood, except one
young girl of fourteen years. Several who returned to advise her to
follow them, saw her smilingly throw her arms round the trunk of the
tree, and almost at once fall backwards, her arms extended. She was
dead.
On the 22nd of August in the same year, four labourers, returning from
work, were overtaken by a thunderstorm. Three of them stopped under an
elm, the fourth prudently continued on his way. Well it was for him.
Several minutes later, the lightning struck the tree, killing two of
the labourers outright, and grievously wounding the third. The latter
was found almost completely naked; his garments, burnt and tattered,
were scattered round him. When he came to himself, he was in such a
violent delirium that it was necessary for several men to bring the
unfortunate victim to his home, where he died shortly afterwards in
the most horrible agony.
About six o'clock, on the 23rd of June, seven men employed on the farm
of Puy-Crouel, were working in a field of beet-root. Overcome with the
heat, they went into the shade of a walnut tree. All at once, a flash
of lightning illumined the sky; the seven workmen were thrown down,
one of them being hurled several yards away. Three of them were able
to get up and go to the farm, the others were severely burnt, and half
asphyxiated. One of the victims had his back skinned the whole length
of the vertebral column; the other had his face scratched, as if torn
by fingernails. All had lost their memory. The walnut tree under which
they had sheltered was cleft from top to bottom.
Here is another example no less terrible--
Seven children, belonging to Ahrens, were caught in a thunderstorm as
they were coming home from the fields, and took shelter under a tree.
The lightning killed the seven little people.
Another time, four young men taking refuge under an oak, were struck
and thrown down. One of them was killed instantly, his companions were
cruelly injured.
On the 10th of July, in Belgium, a woman gathering cherries was killed
on a tree which attracted the fluid. A young man standing beneath it
was paralyzed.
We might multiply these tragic tales; each year a number of similar
cases happen. The imprudence of human beings is truly incorrigible!
Everybody, however feeble his instinct of self-preservation, should
flee the vicinity of trees during a thunderstorm, and allow himself
to be drenched on the road, rather than offer his life as a too
generous burnt-offering to the lightning, for the oak's robust trunk,
or that of the poplar, elegantly plumed with its graceful foliage, may
be the altar on which the sacrifices in honour of Jupiter are made.
The wood of trees is not so good a conductor of electricity as the
human body. For this reason, a person leaning against a tree receives
the full discharge; at times the tree is splintered, because it did
not serve as a perfect conductor.
Yet the conductive power of certain species is so remarkable, that the
neighbourhood of particular trees may be regarded as a protection
against lightning (this, however, without coming in contact with
them!).
The tips of the branches pointing towards the clouds, and the moisture
they receive, undoubtedly influence the electricity of the atmosphere;
and, moreover, by means of these graceful branches, an inaudible but
continual exchange is effected between the electricity of the earth
and sky, thus holding the balance between two opposite charges.
Colladon asserts that poplars planted near houses may, in favourable
conditions, act as lightning conductors, on account of their height
and powers of conducting. He adds that it is necessary to take other
circumstances regarding the situation of the dwelling into account,
which are not always easy to define. Their protection of the
neighbourhood is not constantly the same. For it to be effectual, the
foliage should be very low, and they should be at least two metres
distant from the roof and walls. Their roots, too, should be in a damp
soil, and metal should not enter largely into the construction of the
neighbouring houses. In these conditions, poplars may fulfil the
useful functions of lightning conductors.
At times, during a storm, several trees are struck by the same flash.
For instance, on May 23, 1886, in Belgium, three poplars were blasted
by a single thunderbolt.
On the other hand, trees planted in lines are sometimes struck
alternately. A case occurred where the lightning seemed to have taken
aim and touched all the odd numbers in a row without striking the
others.
Certain plantations act on the fluid with an extraordinary intensity.
At Lovenjoul, in Belgium, a wood of undergrowth and big trees, planted
in marshy ground, seems to possess this singular privilege, and the
agriculturists of the country declare that no storm ever passes their
way without lightning falling there. In the middle of this wood one
can count seven oaks, near to one another, struck by it. Not far off,
a huge ash, and a little farther away two poplars, likewise blasted.
All the trees have not been struck in the same way; some are scorched
or stripped of their leaves; the others have their trunks perforated,
or split in different parts. Usually trees are cleft from top to
bottom; in some cases the furrow is horizontal or perpendicular in the
direction of the branches.
Pieces of bark or of wood are sometimes torn off lengthwise, and only
adhere to the trunk in strips here and there. But that does not prove
conclusively that the lightning struck upwards from the ground; it may
have rebounded (?) after striking from above.
Certain effects, however, can only be explained by an ascending
movement of the fluid. The following cases for example:--
"During the summer of 1787, two men were sheltering under a tree at
Tancon, Beaujolais, when they were struck by lightning. One of them
was killed on the spot, the other felt no ill effects other than
momentary suffocation. Their horses were caught up to the top of the
tree. An iron ring which bound the wooden shoe belonging to one of the
men, was found hanging from a high branch of the same tree. Now, at a
little distance, there was a tree which had also suffered greatly by
the passage of the electric fluid. In the soil at its base a round
hole was to be seen, shaped like a funnel. Directly above it the bark
had been loosened and slit into slender thongs. As for the tree
beneath which the men had sheltered, it also had half its bark off,
and long splinters were to be seen hanging only by the upper parts. On
one side of the tree the leaves were withered, on the other they were
still quite green."
In this most remarkable instance the lightning had come out of the
ground.
In the cleft of a willow tree blasted by lightning its roots were
found.
Besides, the soil is often undulating, and thrown up around trees
which have been struck.
Vegetables do not always succumb, any more than men, to these attacks.
They may be lightly struck in a vital part, in which case they recover
from their wounds. Very often they are merely stripped of their
natural garments, in other words, of their bark and foliage. This is
one of those superficial injuries to which they are most subject.
The following is an example of this kind of fulguration:--
On July 16, 1708, two oaks were struck at Brampton. The larger
measured about ten feet around the base. They were both split asunder,
and the bark peeled off from the summit to the soil, a length of
twenty-eight feet. Completely detached from the trunk, it hung in long
strips from the top.
Boussingault witnessed the destruction by lightning of a wild pear
tree at Lamperlasch, near Beekelleronn. At the moment of the explosion
an enormous column of vapour arose, like smoke coming out of a chimney
when fresh coal has been put on the fire. The lightning flashed in all
directions, great branches gave way, and when the vapour cleared off,
there stood the pear tree, its trunk a dazzling white: the lightning
had taken the bark completely off. Sometimes the bark is only
partially stripped off one side, or left on, in more or less regular
bands, either on the trunk or on the branches.
During a violent storm at Juvisy, on May 18, 1897, an elm five hundred
metres distant from the Observatory was struck by lightning, which
took the bark off lengthwise in a strip, four centimetres wide and
five centimetres deep. This band of bark was cut clean off. There was
no trace of burning.
Sometimes only the mosses and lichens are whisked off the sides of the
trees, which escape with light scratches. Two great oaks which had
been struck by fireballs, only bore traces of two punctures which
might have been made by small shot.
Moreover, it is not uncommon to see the bark riddled with a multitude
of little holes, like those made by worms.
Two men were struck by lightning near Casal Maggiore on August 15,
1791, beneath an elm tree. One of them had his elbow on the tree at
the moment, and amongst other injuries were a number of little holes
in the arm. There was a twist in the tree at the part where the elbow
rested, and a hole penetrated the centre of it to the core of the
wood. The surrounding bark looked as if it had been mite-eaten.
Several scars started from this point and ascended almost
perpendicularly towards the top of the trunk. There was no damage done
to the branches.
Lightning cut through a chestnut tree, five metres high, on the
roadside at Foulain (Haute-Marne), burning several leaves, then struck
some water-pipes at a depth of a metre and a half, and finally passed
into the dike through two holes a metre deep by a decimetre in
diameter.
The bark is often reduced to thin splinters scattered on the soil, or
hanging from the neighbouring trees, or even thrown to a considerable
distance.
On June 25, a fireball fell near Jare (Landes) on a pine tree, which
it shivered into a myriad slender strips, about 2 metres long, many of
which were caught on the branches of pines within a distance of 15
metres. Only a stump, 2-1/2 metres in height, remained standing. At
the same time three other pines, which stood 18 and 25 metres away
from the first, were destroyed. The bark had been stripped off each,
but only as far as the incision made for extracting the resin.
Furrows, of varying width, and running in different directions, may at
times be seen on trees, some short, others reaching to the top of the
tree, and occasionally to the roots. These marks show the passing of
the lightning.
Sir John Clark has seen a huge oak in Cumberland, at least 60 feet
high and 4 feet in diameter, from which the lightning had stripped a
piece of bark, about 10 centimetres wide and 5 centimetres thick, the
whole length of the trunk in a straight line.
The furrow is not always single, it may be double, and either stretch
in two parallel lines or diverge.
The Chevalier de Louville observed in the park of the castle at
Nevers, a tree struck at the top of the trunk by lightning which,
dividing in three shafts, hollowed three furrows that might have been
made by three rifle shots fired towards the roots. These three furrows
followed the irregularities of the trunk, always slipping, gliding
between the wood and the bark, and curiously enough the former was not
burnt.
But these bands are not invariably straight either; in the above
example they followed the caprices of the vegetable body. They are to
be found oblique in certain cases, but more often they surround the
trunk in long spirals of varying width, showing that the lightning
clasped the tree in the form of a serpent of fire.
Here is an example:--
During a violent storm on July 17, 1895, a poplar was blasted on the
road through the forest of Moladier, 160 metres north-west of the
castle of Valliere. The tree was 25 metres high, and in full leaf from
base to summit; it was struck halfway up by the discharge, and a
spiral furrow 10 centimetres wide twisted round the trunk to the
ground.
I noted a similar case, August 25, 1901.
Lightning struck one of the highest trees in the park at Juvisy, a
magnificent ash, stripping off and destroying the bark where the
electric fluid curved round and round down the full length of the
trunk, which was shattered by the meteor a few metres above the roots.
Enormous fragments lay all round the trunk, some hurled to such a
distance that it was obvious the explosive force of the phenomenon
must have been of extraordinary violence.
I was able to trace the course of the lightning to the foot of the
tree, along its roots to a great depth, by a black furrow.
The tree is not dead. The ivy which clung to it is dead.
The vast and splendid forest of Saint Germain often witnesses the
presence of the lightning, and the magnificent trees which adorn and
beautify this charming and celebrated place are, unfortunately, too
often the victims of these inopportune visitations.
Lightning has no respect for old memories. It demolished with a single
flash a superb giant whose long branches, laden with perfumed leaves,
had given shade to many generations. The splendid tree, which had
survived the severity of several centuries, fell beneath the arrow of
the pernicious fluid. Such was the fate of an oak near l'Etoile du
Grand-Veneur. Struck on the top, its upper branches were violently
torn off.... A spiral furrow beginning at the top ended within a metre
of the ground. But, wonderful to relate, the whole mass of the tree
appeared to have been twisted mightily by a force which worked with so
much power that the tree could never regain its original position. The
fibre, instead of growing vertically, followed the furrow made by the
lightning, and became twisted like a corkscrew. There exist certain
singular trees, the fibre of which grows in spiral fashion, and is
called twisted wood by carpenters and cabinet-makers. Pines and firs
in mountainous countries are fairly often affected in this curious
fashion. One can no more account for it than one can define the cause
of the curved form of some flashes of lightning. One does not know
exactly if they should be attributed to their following the direction
taken by the fibre, or whether, on the contrary, the tree had been
struck in its infancy by a spiral flash, and, submitting to that
influence, continued to grow up corkscrew fashion.
It is most probable that the fall of the thunder-ball on the trees in
this manner is governed by the laws of electricity. We may even note
casually that traces of similar spirals have been remarked on objects
as well as on the dead bodies of those struck by lightning, thus
preserving the ceraunic likeness of the mortal blow.
Other observers, besides, have declared that they saw distinctly the
spiral lightning flash through the atmosphere. But these observations
would need to be confirmed by photographs of indisputable accuracy. In
these circumstances, as in many others, the dark room is worth a
hundred human eyes!
In some cases the curved furrow turns several times. For instance, in
May, 1850, Grebel saw an alder nearly twenty metres high struck by
lightning on the right bank of the Elster below Zeitz. On the lower
part of its trunk were two spiral bands which had carried away bark
and sap-wood, leaving no trace of combustion.
The depth and width of the twist are very variable; at times the
furrow is deeper in the veined parts than at the edges; again it
reaches the core.
Two oaks were struck in June, 1742, in the park at Thornden. One was
marked with a spiral for a length of forty feet to within a little
distance of the ground. The band was five inches wide, but became
narrower as it descended, and was finally no more than two inches
wide. The wood was incised and even torn in places, but the branches
were not hurt. The rest of the bark seemed to have been riddled by
small shot.
All the injuries of which we have spoken (excoriation, stripping off
the bark, furrows), are not necessarily mortal. But there are other
more serious wounds from which the tree rarely recovers. We allude to
deep fissures and breaks produced by lightning. When the fracture
touches only a portion of the topmost part of the tree, the result of
the accident is not necessarily fatal. But this is not always so.
On May 14, 1865, a poplar was split in two by lightning at
Montigny-sur-Loing. One half to the full height continued standing.
The other half was chopped up in small fragments and thrown to a
distance of a hundred metres. These pieces, which were brought to me
by M. Fouché, are so dried up and fibrous that they might be taken for
hemp instead of wood.
In the majority of these cases the tree is split from top to bottom.
On July 5, 1884, in Belgium, a poplar, the biggest of a group of trees
of the same species, was struck and split down its full length.
In the month of August, 1853, on the side of the road from
Ville-d'Avray to Versailles, a poplar of about twenty years old was
cleft from the topmost bough to its roots; one half remained in its
place, the other fell on the road. A black line, about a millimetre
wide, ran down the centre of the tree.
Sometimes the tree is divided into several parts by vertical fissures.
For example, in 1827, near Vicence, a pear tree, three feet in
diameter, was split into four parts, from the top down.
How often one has remarked great tree trunks in the forests, decayed
and desolate, standing sadly, like poor headless bodies? Very often
lightning has been the executioner of these trees.
In the month of May, 1867, in the forest of Fontainebleau, a
magnificent oak, about two metres in circumference, was completely
decapitated by lightning; its branches fell on the ground. The part of
the trunk left standing was barked to the roots and splintered into
fragments of varying sizes. They were scattered on the ground or hung
from the branches of the surrounding trees. Several pieces of
considerable size were hurled more than thirty metres away, much to
the injury of the bark of the trees which they struck.
In numerous cases, the tree struck by lightning is broken in several
places, and fragments of it thrown far and wide.
On July 2, 1871, at the farm of Etiefs, near Rouvres, canton of
Auberive (Haute-Marne), lightning struck an Italian poplar, sixty
years old, thirty metres high, and three metres round at a height of
one metre from the ground, splintering off enough wood to make a heap
sixty-five centimetres round, and fifty centimetres high.
An ash was struck by lightning on July 17, 1895, on the road to
Clermont. This tree, ten metres high, was broken at a point 3-1/5
metres from the ground, and the crown, still hanging by a shred from
the trunk, lay on the embankment. The violence of the explosion threw
pieces thirty centimetres wide and 3-1/2 metres in length, into a
field from twenty-five to thirty metres off.
On July 4, 1884, in Belgium, a willow was reduced to a heap of atoms
on the ground. In March, 1818, at Plymouth, a fir more than a hundred
feet high and forty feet in circumference, the admiration of the
countryside, disappeared, literally shattered into bits. Some
fragments were thrown two hundred and fifty metres away.
One of the most curious effects of lightning is to divide the interior
of the tree into concentric layers, fitting them perfectly one into
the other, but at the same time separating them with extraordinary
precision.
_Arbres roulés_ (thus are the trees called which are victims of this
odd phenomenon), as a rule, do not show any injury on the outside. But
the body, dissected by the electric fluid, soon succumbs.
An oak, twenty-five metres high, having been struck on August 25,
1818, was opened to be examined carefully, and it was stated that the
concentric layers were as detached from one another as the tubes of an
opera-glass.
The fireball sometimes hollows a canal through the centre of the trees
from the top to the bottom, the sides of which are burnt black. The
following is a curious example:--
In June, 1823, at Moisselles, lightning fell upon a great elm, and
striking against an enormous knob, rebounded on to a neighbouring elm
half its own height, pierced it through and through, shivering it to
tatters; the trunk was burst open to the roots, it looked as if it had
been bored through from one end to the other by a red-hot bullet that
blackened and charred it.
Does it not seem as if the lightning plays with the lives of the trees
as with man? It threatens, changes, apparently spares, returns to the
charge and finally annihilates. And this sport is accompanied, at
times, by inconceivable effects.
But records are still more eloquent than reflections: Nature, in her
own mute speech, tells us of a thousand marvels.
Is not the following phenomenon enough to make lightning more
mysterious in its fantastic and varied mode of action?
On the 19th of April, lightning struck an oak in the forest of Vibraye
(Sarthe), cut this tree, measuring a metre and a half in
circumference, at two-thirds of its height, pulverized the lower
parts, strewed the shreds over a circuit of fifty metres, and planted
the upper part exactly on the spot from which the trunk had been
snatched, with all the rapidity of a flash.
Moreover, the annual concentric circles were separated by the sudden
drying up of the sap so effectually, that, the strips only remained
welded together where the knots made too great an obstacle to their
separation.
How was the lightning able to plant in the earth, with such
inconceivable rapidity, the top of the tree where the roots had been?
This is something which no one can explain. It alone is capable of
creating such situations.
But it has done better still! Two years later, in 1868, it took the
opportunity of playing a good trick on two trees of different species,
an English oak and a forest pine, which, without race jealousy,
fraternized in the forest of Pont-de-Bussière (Haute-Vienne). These
two trees were about ten yards apart, and were simultaneously hit by
the explosive matter, and in the twinkling of an eye, their leaves
were changed. The pine needles found themselves on the oak, and the
leaves of the oak went to brighten the austerity of the pine with
their delicate verdure. There was nothing commonplace about the
metamorphosis. Accordingly all the inhabitants went in crowds to the
scene of this miracle to contemplate the unusual spectacle of a
pine-oak and an oak-pine.
And the unexpected happened: both trees appeared to thrive very well
in these new conditions: the pine continued to be agreeably adorned
with its festival foliage, whilst the oak agreed perfectly with the
sombre needles of the pine.
After such marvels, my readers will not be surprised to learn that
lightning sometimes shatters the living wood, or decayed wood, into a
thousand morsels without setting it on fire.
For instance, a bundle of faggots lying on the hearth has been reduced
to atoms by lightning, without any trace of combustion being visible.
A fireball fell on a sheaf of barley in the open field without setting
it on fire, and buried itself in the ground without doing other
further damage.
In certain cases the electric fluid chars wood at varying depths: the
blackened layer is often very slight; sometimes, on the contrary,
combustion is complete.
As for the leaves, they are unhurt as a rule. When they are attacked
they shrivel up; an autumnal shade takes the place of their charming
green tints; they turn brown and dry up quickly.
One of the trees in the Champs-Élysées having been struck, it was
proved that all round it the ground was full of little holes. In two
or three places the bark was raised from beneath; the leaves were
yellow and shrivelled up as parchment would be by the fire; the upper
part remained green. Everything seemed to prove that the lightning
came out of the ground.
At other times the same effect may be observed on the leaves, when the
trunk and roots are apparently uninjured. It is not unusual to see the
tree instantly stripped of its leaves as if by some mysterious power.
The lightning acts also on the roots, as we have seen in the preceding
examples. They have been seen uncovered where the ground was much
disturbed, torn in strips, or cleft in more or less regular pieces.
We see that lightning does not make more ado about exhaling its
baleful breath on the life of plants, than on animals and men. And
moreover, that it often strikes these latter with sudden death without
leaving a trace of its passing, just as sometimes it strikes the trees
without leaving any exterior injury. Now and then life is not
completely extinguished, and little by little the tree recovers its
health. Often the vitality is not changed, one sees the tree which was
struck bear fruit as before the catastrophe.
Has it not been asserted that lightning may exert a benign influence
on vegetation?
This was the opinion of the ancients.
_A propos_ of this, Pliny said, "That thunder is rarely heard in
winter, and that the great fertility of the soil is due to the
frequency of thunder and rain in spring; for the countries where it
rains often and in good earnest during the spring, as in the island of
Sicily, produce many and excellent fruits."
It has been proved in our times that the ancients were right in
extolling rainwater as nourishment for the products of the earth, and
science has discovered the cause to be the presence of great
quantities of nitrogen and ammonia in the thunder-rain and in hail.
Perhaps electricity has a similar effect.
In the neighbourhood of Castres, on April 13, 1781, an old poplar was
stripped of its bark in several places. Now, shortly afterwards it
burst into leaf, although the neighbouring poplars were much later
than it.
The ravages caused in the fields by the electric meteor to forage and
vegetables are sometimes considerable. This is especially so with
grass when cut, to haycocks, ricks of straw, barley, etc. We have a
collection of records of men or animals who, when leaning against
haystacks, were struck.
As a rule the haystack is burnt; sometimes, however, the grass is
simply scattered and thrown to a distance.
In 1888, a very curious occurrence was observed at Vayres
(Haute-Vienne).
The lightning struck a field of potatoes at the village of
Puytreuillard; some of the stalks were burnt to cinders; but most
remarkable of all, _the potatoes were done to a turn_, just as if they
had been cooked beneath hot ashes.
A belief which was very general in ancient times and derived without
doubt from a recollection of the circumstances which were said to
accompany the birth of Bacchus, gave the vine the privilege of
protecting the neighbourhood from the fatal effects of lightning. But
this again is only a legend. The following observation proves it:--
On July 10, 1884, at Chanvres (Yonne), fifty vine-stocks were frizzled
up by lightning.
It used to be supposed, too, that the electric fluid held the lily in
particular respect. But here is a note which shows us that the white
flower is visited by the burning flashes. During a violent
thunderstorm on June 25, 1881, at Montmorin (Haute-Garonne)----But let
M. Larroque, who witnessed the curious phenomenon, describe it: "In a
clump of lilies in my garden," says he, "I see the highest of them
surrounded by a violet glimmer, which formed an aureola round the
corolla. This glimmer lasted for eight or ten seconds. As soon as it
disappeared, I went close to the lily, which, to my great surprise, I
found had been deprived of its pollen, while the surrounding flowers
were laden with it. So the electric fluid must have scattered or
carried off the pollen."
When Jupiter thunders, he still seems to dominate our world, as in the
days when the graceful legends of mythology flourished.
And not only does he work above ground, but, contrary to the belief of
the ancients, his influence extends beneath the soil.
A great number of men were working in the mines at Himmelsfurth on
July 5, 1755. They were, as often happens, working at various points
along the vein of metal, and never dreaming of the events which might
take place on the surface of the ground. All at once they were
conscious of several very violent shocks, given in the oddest and most
extravagant fashion. Some felt the shock in their backs, while their
neighbours received them on their arms or legs. They might have been
shaken by a mysterious invisible hand, stretching now up from below,
now from above, now from the sides of the galleries. One of the
miners found himself hurled against the wall, two others, whose backs
were turned, almost came to blows, each believing that his mate had
thumped him.
The real culprit was the thunder, of whom they might well demand an
explanation of these strange proceedings.
Here is another example which bears out the foregoing:--
On the 25th of May, the watchman on guard at the pit mouth of one of
the principal mines at Freyberg, perceived an electric glimmer run
along the wire rope going to the bottom of the mines, and used by the
miners to exchange signals with the men employed in working the lifts.
Suddenly all the pits were brilliantly lit up. At the same moment the
watchman saw a clear vivid flame shoot out at the other end of the
chain. On this occasion the lightning behaved with due discretion, and
shone through the mine without giving any one the slightest shock.
In vain the monster Tiberius, and the infamous Caligula, sought a
subterranean refuge from lightning. Their impure consciences, laden
with crimes, dreaded the chastisement of heaven. By fleeing from the
lightning flash, they believed themselves saved from death. Lightning
dogs our footsteps, and works even when the criminals believe
themselves in safety. It is conceivable that the ancients should have
dreaded it as an instrument of celestial justice.
Usually lightning strikes the ground with a vertical stroke, but at
times obliquely, when it traces long, horizontal lines. Often the
ground may be seen turned up at the foot of trees which have been
struck, the sod is torn, and stones thrown to a great distance.
Sometimes, too, an excavation may be seen in the ground near the
object struck, of varying breadth and height. This opening may be like
a funnel or hemispherical.
In a case observed on June 6, 1883, at Côte (Haute-Saône), a circular
hole, having a depth of 1·20 metres, has been seen in a dyke on the
declivity of the road, below a coach which was not struck.
Occasionally the hole is but the beginning of a canal, hollowed rather
deeply and perpendicularly in the ground, the sides of which serve as
a sheath to the fulgurite. But before treating of fulgurite tubes,
which constitute the most curious phenomena in the world connected
with lightning, we shall discuss certain remarkable effects observed
on the surface of the ground.
Falling on solid rocks, the electric spark can break them, cut them,
or pierce them in one or more places. Often instead of spoiling or
cutting off pieces of the stone, it covers the surface instantaneously
with a vitreous coat, having blisters of various colours. This
vitrification is often to be seen on mountains.
De Saussure found rocks of schistous amphiboles covered with vitreous
bubbles, like those seen on tiles where struck by lightning. Humboldt
made similar observations on porphyritic rocks at Névada de Toluca, in
Mexico, and Ramond, at the Sanadoire rock in Puy-de-Dôme.
In these cases, the spark, on reaching the surface, melts it more or
less completely over a varying extent, and this fusion, worked upon by
an extraordinary heat, produces a coat having a peculiar appearance,
but in which microscopical analysis finds the elements of the body it
covers.
Thus the vitreous layer deposited over chalk is of chalky origin; that
covering granite is of the nature of granite, etc.
This does not apply to certain deposits found on rocks, and even on
trees, which have been struck by lightning, and which are of very
different origin.
Whilst the former is only the stone in a fused or vitrified condition,
the latter is caused by the presence of foreign bodies, some fragments
of which have been detached by the ray and travel with it. This
transport of solid substances by lightning has often been observed.
Here are two examples of this strange phenomenon:--
On July 28, 1885, at Luchon, on the Bigorre road a passer-by saw
lightning fall twenty yards away from him. Recovered from the shock,
he went out of curiosity to look at the result, and saw the wall at
the edge of the road, the schistous and chalky rocks, even the trees
themselves, coated over with layers of brown. It was certainly a case
of the lightning having effected a deposit. This latter was very
curious. Lines could be traced on it with the finger-nail, it fell to
powder under slight pressure, became soft with gentle rubbing, caught
fire from a candle, and then gave off a resinous odour with much
smoke. What is this resinous matter? That is what no one yet can say.
In the month of July, 1885, on the day following a violent
thunderstorm which had struck the telegraph-office in the station of
Savigny-sur-Orge, I myself picked up a little black powder off the
telegraph poles, which had been left by the lightning, and which had a
sulphurous smell.
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 glass-makers. Long before the
most remote peoples of antiquity appeared, whose glasswares encrusted
with marvellous iridescent tones by the passing 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 glass 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 Massel 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 canal 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
passage, and branched irregularly in three principal 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.