. Lighthouse construction and illumination; . Elevation a is the mask in elevation, and h in plan, and d the fixedapparatus. Flashes of equal power may be produced, andthus made to show over the whole of the small arc, byusing opaque leaves, a, Fig. 102, arranged either verticallyor horizontally, like the Venetian blinds for house windows. DISTINCTIONS OF LIGHTS. 131 It is proposed to alter a sector of 79° at Dhii Heartach onthis principle, in order to mark by red colour the extensive. and dangerous reef called the Torrin Eocks, which lie tothe south of the Eoss of Mull. The superiority of thi
. Lighthouse construction and illumination; . Elevation a is the mask in elevation, and h in plan, and d the fixedapparatus. Flashes of equal power may be produced, andthus made to show over the whole of the small arc, byusing opaque leaves, a, Fig. 102, arranged either verticallyor horizontally, like the Venetian blinds for house windows. DISTINCTIONS OF LIGHTS. 131 It is proposed to alter a sector of 79° at Dhii Heartach onthis principle, in order to mark by red colour the extensive. and dangerous reef called the Torrin Eocks, which lie tothe south of the Eoss of Mull. The superiority of thismode of marking dangers, as compared with a fixed redsector, is about 4 to 1, for the full power of the light ispreserved, wliile a red shade causes a loss of about three-fourths, VI. and VII.—Alternating Red and White Lights.—The French alternating red and white light has an uppercupola of holophotal prisms, each of which parallelises 45°of light. The refractor and lower prisms give a fixed of the upper panel of prisms has a divergence ofabout 5°, and has a red shade placed in front. There alsorevolve, in front of the refractors and lower prisms, redshades, subtending an angle of 5°, being the same as theangle of divergence of the upper panels; and thus arcs of5° of red and 40° of white are simultaneously illuminated,and shown alternately when the apparatus revolves, produc-ing an alternation of red and white light of—say 40seconds white and 5 seconds re
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Keywords: ., bookcentury1800, bookdecade1880, bookpublisherlondo, bookyear1881
