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A goniophotometer for determining to an accuracy of about 1% the reflecting properties of surfaces of low and medium gloss is described. The instrument is particularly suitable for the measurement of papers and boards, and works off the ordinary electric light mains. Arrangement is made for the inclusion of Polaroid and coloured filters when desired. The specimen holder may be rotated about two axes, perpendicular to and parallel to, the plane of incidence, and the specimen itself may be rotated in its own plane through 360°. The photometer consists of a barrier layer type photocell connected to a Tinsley galvanometer. Two specimen polar curves obtained with the instrument are reproduced.
V G W Harrison (Wed,) studied this question.