French mathematician known for his contributions to algebraic and projective geometry. Chasles wrote an important historical reference, still in use today, on the development of methods used in geometry. He also developed the theory of cross ratios independently of the famous mathematician August Möbius. Chasles also won unfortunate distinction as the victim of a fraud; he paid over $30,000 for forged letters from famous scientists. He was elected to the Royal Society and awarded the Copley Medal for his scientific contributions.