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 147
examination is then given on the scales by the positions ofthe indicators. For measuring the brightness of objects of greater intensitythan 1 foot-candle on the screen C, slides of smoked glass areprovided which may be placed between the object being meas-ured and the opening D. These slides are… … Fig. 70.—Martens polarization photometer. of the right candle-power be chosen it can be so placed that theinstrument will be direct reading. This position can be deter-mined or the instrument may be calibrated by illuminating anauxiliary screen, which comes with the apparatus and is presum-ably of…
Light · Photometry · Electric lighting
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