Dante's Purgatorio Canto XV

At the beginning of Canto XV there Dante encounters a “light far brighter” than any he has encountered so far.  He tells us that his “mind was stunned by what it did not know” (XV.12).  To explain the intensity of the light, Dante uses the image of a ray of light reflecting from a surface.

 

A ray leaps from water or from glass,
Reflecting back the other other way as it
Ascends in the same way it first came down,

Forming an angle with the plummet line
Exactly equal to the incidence –
As theory and experiment both show (16-21)

 Dante’s physics are correct, though Mark Musa comments (p 167) that how this description serves to explain Dante’s experience “is none too clear”.  The description does however remind me of a similar description in Virgil’s Aeneid.  In comparing Aeneas with Turnus, Virgil also uses an image of reflecting light.  Unfortunately I have misplaced my Aeneid in the mounds of books which create a second wall of insulation in my basement.  I’ll find it and update the post later.  The gist of the comparison is this:  it is about the source of power and motivation for the two men.  The light which guides Aeneas is reflected from above – it is a divine thing.  Here perhaps Dante is alluding to that passage in (book 8, if I recall) the Aeneid where Virgil introduces this idea.  The image used of Turnus is that of a boiling cauldron – which fits one for the next cornice:  the wrathful.  Be all that as it may, and we’ll patch it up as needed.  The question is this:  does one’s direction come from above (reflecting the Divine), or from below?