itself downwards. As one may suppose that an immense quantity of fire being accumulated in the clouds dilates, violently bursting the substance which envelops it, because the resistance of the centre hinders it from proceeding further. This effect is especially produced in the neighbourhood of high mountains; and, accordingly, they are very frequently struck with the thunderbolts. In short, one may give a number of explanations of the thunderbolt; but we ought, above all things, to be on our guard against fables, and this one will easily be, if one follows faithfully the sensible phænomena in the explanation of these things, which are not perceived, except indirectly.
“Hurricanes (πρηστῆρες) may be caused either by the presence of a cloud, which a violent wind sets in motion and precipitates with a spiral movement towards the lower regions, or by a violent gust which bears a cloud into the neighbourhood of some other current, or else by the mere agitation of the wind by itself, when air is brought together from the higher regions and compressed without being able to escape on either side, in consequence of the resistance of the air which surrounds it; when the hurricane descends towards the earth, then there result whirlwinds in proportion to the rapidity of the wind that has produced them; and this phænomenon extends over the sea also.
“Earthquakes may arise from the wind penetrating into the interior of the earth, or from the earth itself receiving incessantly the addition of exterior particles, and being in incessant motion as to its constituent atoms, being in consequence disposed to a general vibration. That which permits the wind to penetrate is the fact that falls take place in the interior, or that the air being impressed by the winds insinuates itself into the subterraneous caverns. The movement which numberless falls and the re-action of the earth communicate to the earth, when this motion meets bodies of greater resistance and solidity, is sufficient to explain the earthquakes. One might, however, give an account of them in several other ways.