Message #168453

[Bathos]

Part 9

Let us go on to explain lightning and thunder, and further whirlwind,
fire-wind, and thunderbolts: for the cause of them all is the same.

As we have said, there are two kinds of exhalation, moist and dry,
and the atmosphere contains them both potentially. It, as we have
said before, condenses into cloud, and the density of the clouds is
highest at their upper limit. (For they must be denser and colder
on the side where the heat escapes to the upper region and leaves
them. This explains why hurricanes and thunderbolts and all analogous
phenomena move downwards in spite of the fact that everything hot
has a natural tendency upwards. Just as the pips that we squeeze between
our fingers are heavy but often jump upwards: so these things are
necessarily squeezed out away from the densest part of the cloud.)
Now the heat that escapes disperses to the up region. But if any of
the dry exhalation is caught in the process as the air cools, it is
squeezed out as the clouds contract, and collides in its rapid course
with the neighbouring clouds, and the sound of this collision is what
we call thunder. This collision is analogous, to compare small with
great, to the sound we hear in a flame which men call the laughter
or the threat of Hephaestus or of Hestia. This occurs when the wood
dries and cracks and the exhalation rushes on the flame in a body.
So in the clouds, the exhalation is projected and its impact on dense
clouds causes thunder: the variety of the sound is due to the irregularity
of the clouds and the hollows that intervene where their density is
interrupted. This then, is thunder, and this its cause.

It usually happens that the exhalation that is ejected is inflamed
and burns with a thin and faint fire: this is what we call lightning,
where we see as it were the exhalation coloured in the act of its
ejection. It comes into existence after the collision and the thunder,
though we see it earlier because sight is quicker than hearing. The
rowing of triremes illustrates this: the oars are going back again
before the sound of their striking the water reaches us.

However, there are some who maintain that there is actually fire in
the clouds. Empedocles says that it consists of some of the sun's
rays which are intercepted: Anaxagoras that it is part of the upper
ether (which he calls fire) which has descended from above. Lightning,
then, is the gleam of this fire, and thunder the hissing noise of
its extinction in the cloud.