Lucretius, De Rerum Natura
William Ellery Leonard, Ed.

     Now let us sing what makes the stars to move.
In first place, if the mighty sphere of heaven
Revolveth round, then needs we must aver
That on the upper and the under pole
Presses a certain air, and from without
Confines them and encloseth at each end;
And that, moreover, another air above
Streams on athwart the top of the sphere and tends
In same direction as are rolled along
The glittering stars of the eternal world;
Or that another still streams on below
To whirl the sphere from under up and on
In opposite direction- as we see
The rivers turn the wheels and water-scoops.
It may be also that the heavens do all
Remain at rest, whilst yet are borne along
The lucid constellations; either because
Swift tides of ether are by sky enclosed,
And whirl around, seeking a passage out,
And everywhere make roll the starry fires
Through the Summanian regions of the sky;
Or else because some air, streaming along
From an eternal quarter off beyond,
Whileth the driven fires, or, then, because
The fires themselves have power to creep along,
Going wherever their food invites and calls,
And feeding their flaming bodies everywhere
Throughout the sky. Yet which of these is cause
In this our world 'tis hard to say for sure;
But what can be throughout the universe,
In divers worlds on divers plan create,
This only do I show, and follow on
To assign unto the motions of the stars
Even several causes which 'tis possible
Exist throughout the universal All;
Of which yet one must be the cause even here
Which maketh motion for our constellations.
Yet to decide which one of them it be
Is not the least the business of a man
Advancing step by cautious step, as I.