shadow-photometern. a kind of photometer invented by Rumford, in which light is measured by means of two shadows cast by a vertical rod upon a white screen.
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1905 G. F. Goodchild & C. F. TweneyTechnol. & Sci. Dict. s.v. Photometers A simpler arrangement, which possesses the advantage that it may be used in a room which is not quite dark, is Rumford's Shadow Photometer.