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…
Light · Photometry · Electric lighting
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