  We study theoretically and experimentally the transmission intensity of
polarized light through the air-spaced Glan-type polarizing prsims. It is found
that the variation of the transmitted intensity with the rotation angle
deviates from Malus Law, exhibiting a cyclic fluctuation with the rotation
angle. The occurrence of the disturbance is explained by the use of an argument
based on the interference effect produced from the air-gap in the prisms. The
theoretcal results are well agreed with the experimental ones. By selecting the
proper cut angle of prism and reducing the thickness of air-gap in prism, the
disturbance may be minimized.
