empress of the east, celebrated for her valour, wit, and beauty; but detestable for her cruelty, having sacrificed her own son to the ambition of reigning alone. She died in 803.

IRIS, in Physiology, the rainbow. The word is Greek, supposed by some to be derived from ἰάω, 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.