Photometric recording of the variation in intensity of light transmission by the analyser of a petrological microscope whilst the polarizer is rotating at a rate sufficient to eliminate the periodic output from the photocell as the polars cross and uncross, and a thin section of a crystal aggregate is slowly rotated upon its stage, is found to yield information on the direction and degree of development of any preferred optical orientation that may be present in the section. The theory of the method is considered and an equation derived for the representation of any preferred optical orientation in terms of a direct percentage of areal extent. The direction of the preferred orientation is found to be parallel to the plane of polarization of the stationary analyser when the section is rotated to a position of minimum intensity of light transmission. It is suggested that the method has potential applications in the study of any fabric which is displayed in terms of an optical orientation.

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