. Lighthouse construction and illumination; . eamers Side Lights. The condensing principle is equally available for steamersside lights, for which purpose the apparatus is placed in asmall tower in front of the paddle boxes, so as to distributeall the rays with strict equality over 112° 30, which isthe arc prescribed by the Board of Trade regulations. Inorder to give a steady light, the apparatus and burner arehung on gymbals. This application of the condensingprinciple was first introduced into the Pharos, NorthernLights Tender, in 1866 (Plates XVII. and XVIII.) Two ofthe Anchor Line of Tran
. Lighthouse construction and illumination; . eamers Side Lights. The condensing principle is equally available for steamersside lights, for which purpose the apparatus is placed in asmall tower in front of the paddle boxes, so as to distributeall the rays with strict equality over 112° 30, which isthe arc prescribed by the Board of Trade regulations. Inorder to give a steady light, the apparatus and burner arehung on gymbals. This application of the condensingprinciple was first introduced into the Pharos, NorthernLights Tender, in 1866 (Plates XVII. and XVIII.) Two ofthe Anchor Line of Transatlantic steamers were also, in 118 LIGHTHOUSE ILLUMINATION. 1873, furnished with similar condensing apparatus placed iniron towers, large enough to admit a sailor to trim the lamp,and having means of entrance during bad weather, providedbelow the deck. 11. Eevolving or Inteemittent Lights, which condensethe light into one sectoe. In Fig. 92 a dioptric holophote throws its parallelisedlight on curved condensing prisms P P, which are so con-. Fig. 92. structed as to give the required amount of divergence, whilemasks M, turning horizontally on hinges, cut off the lighteither slowly or suddenly, as may be wanted for producinga revolving or intermittent light, both of which will thusbe made to condense the whole of the rays uniformly overthis one sector. CONDENSING EEVOLVING LIGHTS. 119 12. Eevolving Condensing Lights of Unequal Eange,which do not illuminate the whole hoeizon. Repeating Light.âFig. 93 shows an apparatus which Idesigned in 1860, inwhich plane mirrors Mrevolve on an endlesschain passing over roll-ers placed outside of themain apparatus, for alter-ing the direction of theflashes after they passinto the dark arc on thelandward side, so as tocause the lenses L L torepeat their flashes overthe seaward arc which re-quires strengthening. Theonly objection which was --^^c- / Â¥ \ y/ Nv / ^^^,<^/ â X ^ ^ ^^***l r**^ ^F^lâ :: /⢠â¢/.[{%iy\ /(s^^^i^ %^0^^
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