. Lighthouse construction and illumination; . substituted liis totally reflecting prisms for Marcets re-flectors, so as to spread the light uniformly over the horizonsolely by dioptric agents. This was not only the first appli-cation of total reflection to lighthouses, but was the first optical- combination, which, for the purpose required, was both geo-metrically and physically perfect (excepting of course theinevitable loss due to the divergence of the exfocal rays ofthe flame), leaving in fact no room for improvement; and,accordingly, this beautifvil instrument continues till now inuniversa
. Lighthouse construction and illumination; . substituted liis totally reflecting prisms for Marcets re-flectors, so as to spread the light uniformly over the horizonsolely by dioptric agents. This was not only the first appli-cation of total reflection to lighthouses, but was the first optical- combination, which, for the purpose required, was both geo-metrically and physically perfect (excepting of course theinevitable loss due to the divergence of the exfocal rays ofthe flame), leaving in fact no room for improvement; and,accordingly, this beautifvil instrument continues till now inuniversal use. In Figs. 37, 38, E E represent the cylindric refractor,/ the focus, and p p the totally reflecting prisms placed attop and bottom. 17. Fresncls Revolving Light, 1822.—In Figs. 39 and 40,which showFresnels form of revolving light, the central burnerB is surrounded by annular lenses L, and a compoundarrangement of inclined trapezoidal lenses 1 and plane silveredmirrors ]\I. The inclined lenses fit closely to each other,forminga pjrram
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Keywords: ., bookcentury1800, bookdecade1880, bookpublisherlondo, bookyear1881
