The design and construction of an apparatus for domain observation and for the measurement of magneto-optic rotation and coercivity of thin magnetic films, by means of the Faraday effect, are described. A spatial resolution of 5 μ is achieved, allowing scanning of magneto-optic properties across the film. Gas flow cooling and heating of the samples result in a temperature range of -120 to +200°C. A special sampling detector allows continuous recording of magneto-optic rotation and coercivity as a function of temperature and wavelength. © 1970 The American Institute of Physics.