The sun declining towards the west, it will necessarily follow that the whole bow is seen opposite to the sun; for the eye being directed to those drops receives a refraction, and by this means the bow is formed.

The eye doth not consider the figure and form, but the color of these drops; the first of which colors is a shining red, the second a purple, the third is blue and green.

Let us consider whether the reason of this red shining color be the splendor of the sun falling upon these small drops, the whole body of light being refracted, by which this bright red color is produced; the second part being troubled and the light languishing in the drops, the color becomes purple (for the purple is the faint red); but the third part, being more and more troubled, is changed into the green color.

And this is proved by other effects of Nature; if any one shall put water in his mouth and spit it out so opposite to the sun, that its rays may be refracted on the drops, he shall see the resemblance of a rainbow; the same appears to men that are blear-eyed, when they fix their watery eyes upon a candle.
Anaximenes thinks the bow is thus formed; the sun casting its splendor upon a thick, black, and gross cloud, and the rays not being in a capacity to penetrate beyond the superficies.

Anaxagoras, that, the solar rays being reflected from a condensed cloud, the sun being placed directly opposite to it forms the bow after the mode of the repercussion of a mirror; after the same manner he assigns the natural cause of the Parhelia or mock-suns, which are often seen in Pontus.