. Lighthouse construction and illumination; . , until1852, that a committee of the American Board resolved—That the Fresnel or lens system, modified in specialcases by the Holophotal apparatus of Mr. Thomas Steven-son, be adopted as the illimiinating apparatus of the UnitedStates, to embrace all new lights now or hereafter authorised,and all lights requiring to be renovated either by reason ofdeficient power or defective apparatus. 21, Mr. Alan Stevensons Improvements.—When estab-lishing the new system in Scotland, Mr. Stevenson made thefollowing improvements:— 1. Refractor of a tridy Cylindri
. Lighthouse construction and illumination; . , until1852, that a committee of the American Board resolved—That the Fresnel or lens system, modified in specialcases by the Holophotal apparatus of Mr. Thomas Steven-son, be adopted as the illimiinating apparatus of the UnitedStates, to embrace all new lights now or hereafter authorised,and all lights requiring to be renovated either by reason ofdeficient power or defective apparatus. 21, Mr. Alan Stevensons Improvements.—When estab-lishing the new system in Scotland, Mr. Stevenson made thefollowing improvements:— 1. Refractor of a tridy Cylindric Form.—Owing todifficulties in construction Fresnel had to adopt a polygonalinstead of a cylindric form for his refractor. But for theIsle of May light, in 1836, Mr. Stevenson succeeded in get-ting Messrs. Cookson of Newcastle to construct a first-orderrefractor of a truly cylindric form. ^ Report of the American Lighthouse Board, 1852, p. 602. 74 LIGHTHOUSE ILLUMINATION. 2. Helical Glass Joints for Fixed Liyhts (Figs. 44, 45).— A. Section. Mr. Stevenson also introduced tlie valuable improvementof constructing the refractor in rhomboidal, instead of rec-tangular pieces. In this way the joints of the glass, A B C D (Fig. 44), in-stead of being upright, were helical,;^ and the loss of light at the joints wasbetter distributed, and prevented ob-scuration in any one direction. Theamount of light intercej^ted in anyazimuth is inversely j)roportional to thesine of the angle of inclination of thejoint. 3. Helical Metallic Framings.—The internal metalKc framings for sup-porting the upper cupola of prismswere also, in like manner, and for the same reason, made byhim of a helical form, as seen at the bottom of Fig. 45.
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Keywords: ., bookcentury1800, bookdecade1880, bookpublisherlondo, bookyear1881
