There needs must be a limit, beyond which
Its contrary prevents the further passing,

And thence the foreign radiance is reflected,
Even as a colour cometh back from glass,
The which behind itself concealeth lead.

Now thou wilt say the sunbeam shows itself
More dimly there than in the other parts,
By being there reflected farther back.

From this reply experiment will free thee
If e'er thou try it, which is wont to be
The fountain to the rivers of your arts.

Three mirrors shalt thou take, and two remove
Alike from thee, the other more remote
Between the former two shall meet thine eyes.

Turned towards these, cause that behind thy back
Be placed a light, illuming the three mirrors
And coming back to thee by all reflected.

Though in its quantity be not so ample
The image most remote, there shalt thou see
How it perforce is equally resplendent.

Now, as beneath the touches of warm rays
Naked the subject of the snow remains
Both of its former colour and its cold,