Of the Rainbow.

Those things which affect the air in the superior places of it are of two sorts. Some have a real subsistence, such are rain and hail; others not. Those which enjoy not a proper subsistence are only in appearance; of this sort is the rainbow. Thus the continent to us that sail seems to be in motion.

Plato says, that men admiring it feigned that it took origination from one Thaumas, which word signifies admiration. Homer sings:—

Jove paints the rainbow with a purple dye,
Alluring man to cast his wandering eye.
(Iliad, xvii. 547.)

Others therefore fabled that the bow hath a head like a bull, by which it swallows up rivers.

But what is the cause of the rainbow? It is evident that what apparent things we see come to our eyes in right or in crooked lines, or by refraction: these are incorporeal and to sense obscure, but to reason they are obvious. Those which are seen in right lines are those which we see through the air or horn or transparent stones, for all the parts of these things are very fine and tenuous; but those which appear in crooked lines are in water, the thickness of the water presenting them bended to our sight. This is the reason that oars in themselves straight, when put into the sea, appear to us crooked. The third manner of our seeing is by refraction, and this is perspicuous in mirrors. After this third sort the rainbow is affected. We conceive it is a moist exhalation converted into a cloud, and in a short space it is dissolved into small and moist drops. The sun declining towards the west, it will necessarily foll............