Thunder and Lightning

by Camille Flammarion

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.