Il terzo fonte par ch'al sol s'indori
Come suol ne le nubi arco dipinto,
E dispiega sue forme e suoi colori
Onde fe' Delia la corona e 'l cinto;
E verghe e spegli in luminosi horrori,
Da cui lo stil d'Apelle anchora è vinto;
Né formerìa l'algente et humida ombra
Ch'a' rai s'alluma, e 'l lume in lei s'adombra.
The third spring shines golden in the sun
Like a rainbow painted amid the clouds,
And unfolds its own shapes and colors
As Delia, the moon, does with her corona;
And stripes and mirrors in luminous
Darkness, that would defeat Apelles.
It would not cast any cold, wet shadow
Made by sunbeams and darkening them.
The third river seems to symbolize the light effects in the atmosphere, 'lightier' than the effects of sun and shadows on earth (see lines 7-8), basically like water-colors. If our hypothesis holds, Tasso is developing a "Metaphysics of Water" in parallel to the Medieval Metaphysics of Light (see Robert Grosseteste, Dante). After the "divine waters" symbolized by the first spring, and the "spiritual waters," e.g. divine grace and/or angels, of the second spring, now the emanation starts to reach down towards the Earth. Air as a thinner version of water proper (well, both are made of hydrogen and oxygen, we could volunteer). The next two rivers will apparently confirm this conjecture.