Abstract
Magneto-optic interaction of diluted magnetite colloid was inspected in the wave-guide capillary cells under an 1.1T magnetic field. The transmittances of the lights polarized parallel and perpendicular to the magnetic field decrease and increase by applying the magnetic field, respectively. Magnitude of this effect is proportional to the concentration of magnetite and the length of the capillary. This phenomenon also depends on the wavelength of the source light.