Thunder and Lightning

John Stuart Mill · en
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.