And smirch the serene vision of the world,
Stroking the air with motions. For oft are seen
The giants' faces flying far along
And trailing a spread of shadow; and at times
The mighty mountains and mountain-sundered rocks
Going before and crossing on the sun,
Whereafter a monstrous beast dragging amain
And leading in the other thunderheads.
Now [hear] how easy and how swift they be
Engendered, and perpetually flow off
From things and gliding pass away....
*****
For ever every outside streams away
From off all objects, since discharge they may;
And when this outside reaches other things,
As chiefly glass, it passes through; but where
It reaches the rough rocks or stuff of wood,
There 'tis so rent that it cannot give back
An image. But when gleaming objects dense,
As chiefly mirrors, have been set before it,
Nothing of this sort happens. For it can't
Go, as through glass, nor yet be rent--its safety,
By virtue of that smoothness, being sure.
'Tis therefore that from them the images
Stream back to us; and howso suddenly