. Lighthouse construction and illumination; . 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 red, or any other periods inthese proportions. But these proportions cannot be altered;and as the light in the axis of the red arc is stronger at the 132 LIGHTHOUSE ILLUMINATION. sides, tlic time during which the red will be visible mustvary with the distance and state of the atmosphere. Condensing Intermittent Light of changing colour.—Theapparatus descr
. Lighthouse construction and illumination; . 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 red, or any other periods inthese proportions. But these proportions cannot be altered;and as the light in the axis of the red arc is stronger at the 132 LIGHTHOUSE ILLUMINATION. sides, tlic time during which the red will be visible mustvary with the distance and state of the atmosphere. Condensing Intermittent Light of changing colour.—Theapparatus described at p. 124 are obviously very differentfrom, and far more powerful than those last described, andare, besides, independent of the divergence of the flame. VIII. Tlie Intermittent Light.—The Catoptric intermit-tent light was introduced by Mr. E. Stevenson in 18 3 0 atthe Mull of Galloway. The occultations are effected bythe sudden closing and opening of two intercepting opaquedrums, Tigs. 103 and 104, which inclose the i^ v y V VI Fig. 103.
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Keywords: ., bookcentury1800, bookdecade1880, bookpublisherlondo, bookyear1881
