celebrated mathematician of Alexandria, reputed to be the inventor of algebra. It is not certain when Diophantus lived; some have placed him before Christ, and some after, in the reigns of Nero and the Antonines, but all with equal uncertainty. It seems he is the same Diophantus who wrote the Canon Astronomicus, which, Suidas says, was commented on by the celebrated Hypatia, daughter of Theon of Alexandria. His reputation must have been very high among the ancients, since they ranked him with Pythagoras and Euclid in mathematical learning. Bachet, in his notes upon the fifth book De Arithmetica, has collected, from Diophantus's epitaph in the Anthologia, the following circumstances of his life, namely, that he was married when he was thirty-three years old, and had a son born five years thereafter; that this son died when he was forty-two years of age, and that his father did not survive him above four years. From Diophantus this it appears that Diophantus was eighty-four years old when he died.

Diopase of Haïs; the rhombohedral emerald malachite of Mohs. This is a very rare mineral; it occurs in crystals of small dimensions, of a brilliant emerald green colour, disposed in limestone, and is only found in the Kirghese steppes, Siberia. See Mineralogy, Index.