Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . Fig. 49.—The Wild flicker photometer. Fig. 50.—The Bechsteinflicker photometer. illuminated by rays from the left-hand source, and the outerring by means of rays from the right-hand source. If the pris-matic arrangement Kk is kept stationary, we can employ thephotometer on the equality of brightness principle, andobtain a balance by judging when ring and center appear equallyilluminated. In order to obtain the flicker, the prismatic disk,Kk, is rotated about a horizontal axis by means of a band
Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . Fig. 49.—The Wild flicker photometer. Fig. 50.—The Bechsteinflicker photometer. illuminated by rays from the left-hand source, and the outerring by means of rays from the right-hand source. If the pris-matic arrangement Kk is kept stationary, we can employ thephotometer on the equality of brightness principle, andobtain a balance by judging when ring and center appear equallyilluminated. In order to obtain the flicker, the prismatic disk,Kk, is rotated about a horizontal axis by means of a band froma small motor passing over the pulley R. It is obvious thatwhen the disk has rotated through 180 degrees, the rays of light THE PRINCIPLES OF PHOTOMETRY 105 which formerly illuminated the center now illuminate the ring,and vice versa. Hence, when the disk is rotated at a suitable speed, both ringand center will appear alternately dark and bright, and a flickerwill be seen which disappears only .vhen the center and ring areequally bright. One model of this instrument is so constructedtha
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectlight, bookyear1912
