Haidinger, Wilhelm Karl von (1795–1871),
Austrian mineralogist. Haidinger is known for his pioneering studies in crystallography, in particular the absorption of light in crystals. In 1848 he designed an instrument with which he made observations of pleochroic minerals, with both transmitted and reflected light. His observations on the connection between absorption and the direction of polarization of transmitted and reflected light led him to develop the theory that a greater absorption (of the whole spectrum of visible light) corresponds to a higher index of refraction. He also discovered the phenomenon which enables the detection of polarized light without instruments.