Lucretius, De Rerum Natura
William Ellery Leonard, Ed.

     Now come, and how
The rainy moisture thickens into being
In the lofty clouds, and how upon the lands
'Tis then discharged in down-pour of large showers,
I will unfold. And first triumphantly
Will I persuade thee that up-rise together,
With clouds themselves, full many seeds of water
From out all things, and that they both increase-
Both clouds and water which is in the clouds-
In like proportion, as our frames increase
In like proportion with our blood, as well
As sweat or any moisture in our members.
Besides, the clouds take in from time to time
Much moisture risen from the broad marine,-
Whilst the winds bear them o'er the mighty sea,
Like hanging fleeces of white wool. Thuswise,
Even from all rivers is there lifted up
Moisture into the clouds. And when therein
The seeds of water so many in many ways
Have come together, augmented from all sides,
The close-jammed clouds then struggle to discharge
Their rain-storms for a two-fold reason: lo,
The wind's force crowds them, and the very excess
Of storm-clouds (massed in a vaster throng)
Giveth an urge and pressure from above
And makes the rains out-pour. Besides when, too,
The clouds are winnowed by the winds, or scattered
Smitten on top by heat of sun, they send
Their rainy moisture, and distil their drops,
Even as the wax, by fiery warmth on top,
Wasteth and liquefies abundantly.
But comes the violence of the bigger rains
When violently the clouds are weighted down
Both by their cumulated mass and by
The onset of the wind. And rains are wont
To endure awhile and to abide for long,
When many seeds of waters are aroused,
And clouds on clouds and racks on racks outstream
In piled layers and are borne along
From every quarter, and when all the earth
Smoking exhales her moisture. At such a time
When sun with beams amid the tempest-murk
Hath shone against the showers of black rains,
Then in the swart clouds there emerges bright
The radiance of the bow.
     And as to things
Not mentioned here which of themselves do grow
Or of themselves are gendered, and all things
Which in the clouds condense to being- all,
Snow and the winds, hail and the hoar-frosts chill,
And freezing, mighty force- of lakes and pools
The mighty hardener, and mighty check
Which in the winter curbeth everywhere
The rivers as they go- 'tis easy still,
Soon to discover and with mind to see
How they all happen, whereby gendered,
When once thou well hast understood just what
Functions have been vouchsafed from of old
Unto the procreant atoms of the world.