go 



NA TURE 



\^May 23, 1 339 



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 

 •effected in these lights by providing each lamp with a silvered 

 reflector. 



In 1807 the late Mr. Robert Stevenson, the engineer of the 

 Bell Rock Lighthouse, to whom and his successors are due 

 much valuable engineering and optical work connected with 



• coast-lighting, designed a larger lantern to surround the mast, 

 and capable of being lowered to the deck for properly trimming the 

 lamps (Fig. 4). Soon after the adoption of the system of catoptric 

 illumination in lighthouses, it was extended to floating lights ; 

 each lamp and reflector was hung in gimbals, to insure hori- 

 zontal 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 January i, 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 shaftings by clockwork placed 

 between decks. There were 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 1500 

 candle units, nearly. In 1872 the Trinity House further 

 increased the dimensions of the lanterns and reflectors of their 

 floating lights — the lanterns from 6 to 8 feet in diameter, with 

 cylindrical instead of polygonal glazing, and the reflectors from 

 12 inches to 21 inches diameter at the aperture. These im- 

 provements, 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 adoption of concentric wick burners with 



xnore condensed 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 

 ~*he smaller apparatus ; while, by the adoption of mineral oil in 

 lieu of colza, the annual cost for the illuminant has been reduced 

 50 per cent. 



Dioptric apparatus was proposed for light-vessels by M. 

 Letourneau in 1851, several small fixed-light apparatus being 

 intended 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 French Lighthouse Service ; but, for 

 ■efficiency and adaptability to meet the rough duty to which 

 floating lights are occasionally subjected in stormy weather and 

 -collisions, this system has been found to be inferior for this 

 service to the catoptric. 



An intere ting experiment was recently made by the Mersey 

 Docks and Harbour Board with the electric arc light, on board 



one of their light-vessels, at the entrance of the Mersey ; but 

 unfortunately it did not prove successful. The present difficulties 

 experienced afloat with this powerful illuminant will doubtless be 

 overcome, and it will be found to be, as in lighthouses, by far the 

 most efficient illuminant for some special stations, where a higher 

 intensity than can be obtained with flame luminaries is demanded. 

 Experiments have been in progress during the past two years 

 at the Sunk light- vessel, off the coast of Essex, for maintaining 

 electrical telegraphic communication with the shore for reporting 

 wrecks and casualties in the locality. This vessel is connected 

 with the post office at Walton-on-Naze, through nine miles of 

 cable. The instruments adopted are the Wheatstone ABC 

 Morse, and the Gower Bell telephone, the telephone for the 

 first time for this purpose on board a vessel at sea, and its effi- 

 ciency has been found to be so perfect that it is preferred by the 

 operators to the telegraphic instruments. Many difficulties have 

 been experienced in maintaining trustworthy communication 

 during stormy weather, owing to consequent wear and tear of the 

 connections with the vessel, but the system, which was designed 



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