Lucretius, De Rerum Natura
William Ellery Leonard, Ed.

Besides, since shape examined by our hands
Within the dark is known to be the same
As that by eyes perceived within the light
And lustrous day, both touch and sight must be
By one like cause aroused. So, if we test
A square and get its stimulus on us
Within the dark, within the light what square
Can fall upon our sight, except a square
That images the things? Wherefore it seems
The source of seeing is in images,
Nor without these can anything be viewed.
     Now these same films I name are borne about
And tossed and scattered into regions all.
But since we do perceive alone through eyes,
It follows hence that whitherso we turn
Our sight, all things do strike against it there
With form and hue. And just how far from us
Each thing may be away, the image yields
To us the power to see and chance to tell:
For when 'tis sent, at once it shoves ahead
And drives along the air that's in the space
Betwixt it and our eyes. And thus this air
All glides athrough our eyeballs, and, as 'twere,
Brushes athrough our pupils and thuswise
Passes across. Therefore it comes we see
How far from us each thing may be away,
And the more air there be that's driven before,
And too the longer be the brushing breeze
Against our eyes, the farther off removed
Each thing is seen to be: forsooth, this work
With mightily swift order all goes on,
So that upon one instant we may see
What kind the object and how far away.
     Nor over-marvellous must this be deemed
In these affairs that, though the films which strike
Upon the eyes cannot be singly seen,
The things themselves may be perceived. For thus
When the wind beats upon us stroke by stroke
And when the sharp cold streams, 'tis not our wont
To feel each private particle of wind
Or of that cold, but rather all at once;
And so we see how blows affect our body,
As if one thing were beating on the same
And giving us the feel of its own body
Outside of us. Again, whene'er we thump
With finger-tip upon a stone, we touch
But the rock's surface and the outer hue,
Nor feel that hue by contact- rather feel
The very hardness deep within the rock.