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 107
Fig. 38 b. Fig. 37.—Contrasting elements. Figs. 38 a and 33 b.—Balanced and unbalanced condition. construct a practical instrument have failed to yield satisfactoryresults. The disturbing influences are mainly the moisture andheat of the air and a gradual alteration in the condition of theselenium… … Fig. 39.—Diagram of the Selenium photometer. The most successful selenium photometer is of German make.It consists of a device for exposing the cell alternately to thelight from the standard and the source to be measured. Thearrangement is shown in Fig. 39, wdiere S is the selenium cellwhich is…
Light · Photometry · Electric lighting
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