Bartholomew says: "The rainbow is a phenomenon produced by a cloud which is hollow and dewy, and which is disposed toward rain in an infinite fall of droplets, shining as though in a mirror; it has a bow-shaped form, emitting various colors from the rays of the sun. Alternatively, it is produced by the moon, though the way it is caused by the rays of the moon, [occurs] but twice every fifty years, as Aristotle says. And so the bow in the sky is a watery cloud, penetrated through all of its parts by the rays of the sun, as [Marc. ??] says. It is called a “bow” from its similarity to a curved bow, since it extends into a kind of convexity in the very top of the clouds, and it bends and extends its tips back down to the earth, as Isidore says."

Original Latin