Lucretius, De Rerum Natura
William Ellery Leonard, Ed.

     Nor is there one sure cause revealed to men
How the sun journeys from his summer haunts
On to the mid-most winter turning-points
In Capricorn, the thence reverting veers
Back to solstitial goals of Cancer; nor
How 'tis the moon is seen each month to cross
That very distance which in traversing
The sun consumes the measure of a year.
I say, no one clear reason hath been given
For these affairs. Yet chief in likelihood
Seemeth the doctrine which the holy thought
Of great Democritus lays down: that ever
The nearer the constellations be to earth
The less can they by whirling of the sky
Be borne along, because those skiey powers
Of speed aloft do vanish and decrease
In under-regions, and the sun is thus
Left by degrees behind amongst those signs
That follow after, since the sun he lies
Far down below the starry signs that blaze;
And the moon lags even tardier than the sun:
In just so far as is her course removed
From upper heaven and nigh unto the lands,
In just so far she fails to keep the pace
With starry signs above; for just so far
As feebler is the whirl that bears her on,
(Being, indeed, still lower than the sun),
In just so far do all the starry signs,
Circling around, o'ertake her and o'erpass.
Therefore it happens that the moon appears
More swiftly to return to any sign
Along the Zodiac, than doth the sun,
Because those signs do visit her again
More swiftly than they visit the great sun.
It can be also that two streams of air
Alternately at fixed periods
Blow out from transverse regions of the world,
Of which the one may thrust the sun away
From summer-signs to mid-most winter goals
And rigors of the cold, and the other then
May cast him back from icy shades of chill
Even to the heat-fraught regions and the signs
That blaze along the Zodiac. So, too,
We must suppose the moon and all the stars,
Which through the mighty and sidereal years
Roll round in mighty orbits, may be sped
By streams of air from regions alternate.
Seest thou not also how the clouds be sped
By contrary winds to regions contrary,
The lower clouds diversely from the upper?
Then, why may yonder stars in ether there
Along their mighty orbits not be borne
By currents opposite the one to other?