Lucretius, De Rerum Natura
William Ellery Leonard, Ed.

     In following wise
The clouds suffuse with leaping light the lands,
And the storm flashes with tremulous elan:
When the wind hath invaded a cloud, and, whirling there,
Hath wrought (as I have shown above) the cloud
Into a hollow with a thickened crust,
It becomes hot of own velocity:
Just as thou seest how motion will o'erheat
And set ablaze all objects,- verily
A leaden ball, hurtling through length of space,
Even melts. Therefore, when this same wind a-fire
Hath split black cloud, it scatters the fire-seeds,
Which, so to say, have been pressed out by force
Of sudden from the cloud;- and these do make
The pulsing flashes of flame; thence followeth
The detonation which attacks our ears
More tardily than aught which comes along
Unto the sight of eyeballs. This takes place-
As know thou mayst- at times when clouds are dense
And one upon the other piled aloft
With wonderful upheavings- nor be thou
Deceived because we see how broad their base
From underneath, and not how high they tower.
For make thine observations at a time
When winds shall bear athwart the horizon's blue
Clouds like to mountain-ranges moving on,
Or when about the sides of mighty peaks
Thou seest them one upon the other massed
And burdening downward, anchored in high repose,
With the winds sepulchred on all sides round:
Then canst thou know their mighty masses, then
Canst view their caverns, as if builded there
Of beetling crags; which, when the hurricanes
In gathered storm have filled utterly,
Then, prisoned in clouds, they rave around
With mighty roarings, and within those dens
Bluster like savage beasts, and now from here,
And now from there, send growlings through the clouds,
And seeking an outlet, whirl themselves about,
And roll from 'mid the clouds the seeds of fire,
And heap them multitudinously there,
And in the hollow furnaces within
Wheel flame around, until from bursted cloud
In forky flashes they have gleamed forth.