Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . ieces of glass9 and g. The Marten Photometer Head.—A photometrical arrangementsimilar in principle to the Lummer-Brodhun is shown in Fig. two sides of the screen S are viewed through the telescopictube, the prisms ab and the mirrors MM. A recent type of the Bechstein photometer^ is shown in Figs. 35and 36. This photometer can be used either as a contrast orequality of brightness instrument. It has a Ritchie wedge of » nium. Eng., Lond., Vol. 1, p. 498, 1908, THE PRINCIPLES OF PHOTOMETRY 9
Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . ieces of glass9 and g. The Marten Photometer Head.—A photometrical arrangementsimilar in principle to the Lummer-Brodhun is shown in Fig. two sides of the screen S are viewed through the telescopictube, the prisms ab and the mirrors MM. A recent type of the Bechstein photometer^ is shown in Figs. 35and 36. This photometer can be used either as a contrast orequality of brightness instrument. It has a Ritchie wedge of » nium. Eng., Lond., Vol. 1, p. 498, 1908, THE PRINCIPLES OF PHOTOMETRY 91 plaster-of-Paris G which receives the light from the two sourcesand which is viewed through the telescopic combination asshown. Two biprisms located at Z^ and Z^ at right angles toeach other present the illuminated fields in the shape of fourquadrants, alternate ones of which are illuminated by the samelamp. The angles of the prisms are so adjusted that the prismwith its dividing edge vertical, Z^, Fig. 36, divides the field intotwo equal portions, the left portion being illuminated by the.
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectlight, bookyear1912
