Commentary Purg XV 16-24

This simile introduces a 'second sun' to Dante's dazzled glance, now the reflected radiance of the angel, as seems clear from the context and despite some early commentators who believe this is the direct beam of the light of God or of the sun itself.  It seems to be neither, nor indeed the direct beam of brightness from the angel of this second terrace.  As the elaborate simile and the sequential description of the light make plain enough, the light bounces down, like Pele's most famous goal, in a World Cup final some years ago, and then up, under Dante's protective hand, so that the angle of incidence is the same as the angle of reflection, notions established, for Dante, by such authorities as Euclid and Albertus Magnus.  For Dante's knowledge of the phenomenon see Conv.II.iii.vi (where he refers to the science of perspective, or optics) and [Par I 49-50].  Poletto (DDP Poletto.Purg.XV.16-24) reviews the debate over whether the light comes straight from God to the angel to Dante or bounces from the angel off the ground and back up; he strongly supports this second view.  And Dante's two evasive actions (shading his eyes with his hand as the angel approaches; turning away when the reflected ray bounces under that hand) come close to guaranteeing this reading.  Carroll (DDP Carroll.Purg.XV.10-24) adds a moral dimension to this interpretation: where the light shining from the Angel of Humility ([Purg XII 89-90]) was relatively demure, the light of this angel, countering the meanness of Envy even when reflected off the livid stone floor of this terrace, is brilliant with the loving mercy of God.

      The notion that these lines themselves reflect a source in Virgil (Aen. VIII.22-25) was perhaps first suggested by Poletto and enjoys some currency.