Light, photometry and illumination : a thoroughly rev. ed. of ''Electrical illuminating engineering'' (1912)
Barrows, William Edward, 1878-1960 · New York ; London : McGraw-Hill Book Co. · leaf 133
y interposing a systemof moving screens as shown in Fig. 55. These screens are offiber, supported on brass rods and have apertures of sufficientsize to permit the direct rays from the lamp to pass unobstructed.At the same time they are of sufficient size to intercept anylight reflected from the… … Fig. 55.—Plan of Sharp-Millar photometer. of the box. This scale is equipped with a shutter which may belowered or raised by means of an external knob, and which maybe used to exclude external light from the interior of the box.To facilitate taking readings in dark places, a slit is cut in theside…
Light · Photometry · Electric lighting
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