Io, in the Greek mythology a daughter of Inachos (q.v.), beloved by Zeus, whom Hera out of jealousy changed into a heifer and set the hundred-eyed Argus to watch, but when Zeus had by Hermes slain the watcher, Hera sent a gadfly to goad over the world, over which she ranged distractedly till she reached Egypt, where Osiris married her, and was in connection with him worshipped as Isis.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Invisible, The * Iodine