IRIS, in Physiology, the rainbow. The word is Greek, iris, supposed by some to be derived from uēw, I speak, I tell; as being a meteor that is supposed to foretell, or rather to declare rain.
Iris is also applied to those changeable colours which sometimes appear in the glasses of telescopes, microscopes, and such like instruments, and is so called from their similitude to a rainbow. The same appellation is also given to that coloured spectrum, which a triangular prismatic glass will project on a wall, when placed at a due angle in the sunbeams.