. Lighthouse construction and illumination; . i^ v y V VI Fig. Fig. 104. and are moved vertically in opposite directions by means ofmacliinery. IX. Intermittent Light of Unequal Periods. 1. Professor Bcdtbages Mode, 1851.—The method pro-posed by Babbage for producing occultations was by suc-cessive descents and ascents of an oj^aque shade over theflame, instead of Mr. Stevensons system of drums movingoutside of the apparatus. The inequalities m the periods DISTINCTIONS OF LIGHTS. 133 were not introduced for producing optical distinctions, butin order to sliow the differences of numbers,
. Lighthouse construction and illumination; . i^ v y V VI Fig. Fig. 104. and are moved vertically in opposite directions by means ofmacliinery. IX. Intermittent Light of Unequal Periods. 1. Professor Bcdtbages Mode, 1851.—The method pro-posed by Babbage for producing occultations was by suc-cessive descents and ascents of an oj^aque shade over theflame, instead of Mr. Stevensons system of drums movingoutside of the apparatus. The inequalities m the periods DISTINCTIONS OF LIGHTS. 133 were not introduced for producing optical distinctions, butin order to sliow the differences of numbers, as, for example,to indicate by a larger interval that three succeeding occult-ations meant 300, and not 30 or 3. A great practical objec-tion to Babbages proposal is the obstruction which it opposesto the access of the keeper to the burners for trimming theflames. 2. Mr. B. L. Stevensons Strengthened Intermittent Light
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Keywords: ., bookcentury1800, bookdecade1880, bookpublisherlondo, bookyear1881
