Lucretius, De Rerum Natura
William Ellery Leonard, Ed.

     Now come, and why beyond a looking-glass
An image may be seen, perceive. For seen
It soothly is, removed far within.
'Tis the same sort as objects peered upon
Outside in their true shape, whene'er a door
Yields through itself an open peering-place,
And lets us see so many things outside
Beyond the house. Also that sight is made
By a twofold twin air: for first is seen
The air inside the door-posts; next the doors,
The twain to left and right; and afterwards
A light beyond comes brushing through our eyes,
Then other air, then objects peered upon
Outside in their true shape. And thus, when first
The image of the glass projects itself,
As to our gaze it comes, it shoves ahead
And drives along the air that's in the space
Betwixt it and our eyes, and brings to pass
That we perceive the air ere yet the glass.
But when we've also seen the glass itself,
Forthwith that image which from us is borne
Reaches the glass, and there thrown back again
Comes back unto our eyes, and driving rolls
Ahead of itself another air, that then
'Tis this we see before itself, and thus
It looks so far removed behind the glass.
Wherefore again, again, there's naught for wonder
     . . . . . .
In those which render from the mirror's plane
A vision back, since each thing comes to pass
By means of the two airs. Now, in the glass
The right part of our members is observed
Upon the left, because, when comes the image
Hitting against the level of the glass,
'Tis not returned unshifted; but forced off
Backwards in line direct and not oblique,-
Exactly as whoso his plaster-mask
Should dash, before 'twere dry, on post or beam,
And it should straightway keep, at clinging there,
Its shape, reversed, facing him who threw,
And so remould the features it gives back:
It comes that now the right eye is the left,
The left the right.