On the nature of things (books 4 - 6)   

That from one single fountain-head may stream
This heat and light. And seest thou not, indeed,
How widely one small water-spring may wet
The meadow-lands at times and flood the fields?
'Tis even possible, besides, that heat
From forth the sun's own fire, albeit that fire
Be not a great, may permeate the air
With the fierce hot- if but, perchance, the air
Be of condition and so tempered then
As to be kindled, even when beat upon
Only by little particles of heat-
Just as we sometimes see the standing grain
Or stubble straw in conflagration all
From one lone spark. And possibly the sun,
Agleam on high with rosy lampion,
Possesses about him with invisible heats
A plenteous fire, by no effulgence marked,
So that he maketh, he, the Fraught-with-fire,
Increase to such degree the force of rays.

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,