432 Sir James N. Douglass [March 15, 



flat wick oil lamps, fixed at a yard arm, and here appears to have 

 occurred the first application of a distinctive character to beacon 

 lights, for the Dudgeon was fitted with two lights, one being placed 

 at each arm of the yard. The next light-vessel was placed at the 

 Newarp Shoal in 1790, and in 1795 one was placed at the north end 

 of the Goodwin Sands. The two latter vessels were provided with 

 three fixed lights, and the lanterns were larger and surrounded each 

 mast-head, as shown by the model before us. An improvement was 

 also eifected in these lights by providing each lamp with a silvered 

 reflector. 



In 1807 the late Mr. Eobert Stevenson, the engineer of the Bell 

 Eock lighthouse, to whom and his successor is due much valuable 

 engineering and optical work connected with coast lighting, designed 

 a larofer lantern to surround the mast, and capable of being lowered 

 to the deck for properly trimming the lamps. Soon after the adop- 

 tion of the system of catoptric illuminations in lighthouses, it was 

 extended to floating lights ; each lamp and reflector was hung in 

 gimballs, to ensure horizontal direction of the beams of light during 

 the pitching and rolling of the vessel. We have here one of these 

 apparatus. The intensity of the beam sent from it was 500 candle 

 units nearly. 



On the 1st January, 1837, the Trinity House installed the first 

 revolving floating light, at the Swin Middle, and, later in the same 

 year, another on board the Gull light-vessel. The lamps and 

 reflectors were carried on a roller frame surrounding the mast, and 

 rotated through light shafting, by clockwork placed between decks. 

 There w^ere nine lamps and reflectors arranged in three groups, of 

 three each, and thus the collective intensity of each flash was equal 

 to that of three fixed lights, or 1600 candle units nearly. In 1872 

 the Trinity House further increased the dimensions of the lanterns 

 and reflectors of their floating lights, the lanterns from six to eight 

 feet in diameter, with cylindrical instead of polygonal glazing, and 

 the reflectors from 12 inches to 21 inches diameter at the aperture. 

 These improvements, together with the adoption of improved burners, 

 have effected a considerable increase in the intensity of these lights ; 

 and, during the last two years, a further improvement has been 

 obtained, by the ado23tion of concentric wick burners with more con- 

 densed flames, and of higher illuminating power, by which the 

 intensity of the beam from each reflector has been raised to 5000 

 candle units ; being just ten times the intensity of the smaller appa- 

 ratus ; while, by the adoption of mineral oil in lieu of colza, the 

 annual cost for the illuminant has been reduced 51 per cent. 



Dioptric apparatus for light-vessels was proposed by M. 

 Letourneau in 1851, several small fixed light apparatus being in- 

 tended to be employed in each lantern, and arranged nearly in the 

 same way as the reflectors. This arrangement has been adopted in 

 some instances by Messrs. D. and T. Stevenson, engineers to the 

 Commissioners of Northern Lighthouses, and by the engineers of the 



