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At wavelengths outside the photographic range the determination of the optical constants of absorbing media involves the measurement of intensity changes on reflection at the surface of the medium. A review of previous methods for their determination is made and the experimental difficulties are indicated. A method is described which surmounts some of these difficulties by avoiding the direct measurement of reflection coefficients. The accuracy to be expected from the method and an example of its use are briefly discussed
David Avery (Sun,) studied this question.