Electrical engineer's pocket-book: a hand-book of useful data for electricians and electrical engineers (1901)
Foster, Horatio A. (Horatio Alvah), 1858-1913 · New York, D. Van Nostrand co.; London, E.& F.N. Spon, ltd. · leaf 405
e the surfaces of the opaque gypsum screen. Dif-fused light from these white surfaces reaches two parallel mirrors (inside)at an angle of 45°, and is reflected to rigbt angled prisms which have theouter portions of their hypothenuse surfaces cut away and coated with as-phalt varnish to secui-e… … Fig. 4. Lummer-Brodhun Photometer Carriage. 393 from one side of the gypsum screen surrounded by an annular ring of lightfrom the other side, the boundary line between the two being sharply defined.The sensibility of this instrument as proved both theoretically and prac-tically, is between three…
Electrical engineering
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