The description in the 1922 catalogue of the W. M. Welch Scientific Company of Chicago notes that "by means of this instrument the foot candles of illumination of any surface can be read directly. It operates on the same principle as the Bunsen Photometer. A light inside and the illumination outside shine on opposite sides of a strip with transparent circles on it and the position of disappearance of grease spot is compared to a scale on the front of the instrument. The case contains a battery, rheostat and small voltmeter for regulating illumination and giving it greater range." No price is given, but the 1929 catalogue of the Chicago Apparatus Company lists it at $35.00.
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