A text book of physics, for the use of students of science and engineering (1918)
Duncan, John, d. 1941, Starling, Sydney George, 1873- · London Macmillan · leaf 571
and P2 are theilluminating powers of the sources, and f/x and d2 their distancesLfromthe screen when they produce equal illuminations, then c^ a? or dld/ There are many devices for carrying out the required adjustment,but they nearly all depend upon illuminating one part of the screen byone source,… … FIG. 494.—Shadow photometer. Rumfords shadow photometer.—Two sources, such as a lamp anda candle, are placed upon an optical bench, as shown in Fig. I.H. anda vertical rod A is placed in front of a white screen, so that two sharpshadows are cast, one of which is illuminated only by the lamp andthe…
Physics
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