792 REPORT — 1886. 



These results led the Trinity House to adopt this explosive as a fog signal for 

 isolated stations on rocks or shoals where previously, from want of space, nothing 

 better than a bell could he applied. It is also applied with success to light-vessels. 

 But, wherever the siren can he installed, it is found to be the most efficient fog 

 signal yet known, chiefly in consequence of the prolongation that can he given to its 

 blasts, and the ease with which it can be applied, with any amount of motive power 

 available, to the production of any desired combination of high and low notes for dis- 

 tinctions corresponding with those of white and red, or short and long, flashes of 

 light, and thus affording the required individuality of each station. The experience, 

 however, with the most ^Dowerful fog signal is not at present to be considered 

 altogether satisfactory. With siren blasts absorbing about 150 H.P. or nearly 

 5 millions of foot-pounds per minute during the time they are sounding, the signal 

 is occasionally not heard, under some conditions of fog and wind, beyond one mile, 

 while at other times it is distinctly heard above ten mUes. 



For marking shoals, channel fairways, and landfalls, in positions where it is 

 found to be impossible to erect a permanent structure, important service is 

 rendered to the mariner by light-vessels. The first of these aids to navigation was 

 moored at the Nore in 1732. ller illuminating apparatus consisted of a small 

 lantern provided with flat wick oil lamps, the latter unaided by optical 

 apparatus of any kind. In 1807 the late Mr. Robert Stevenson, the eminent 

 engineer of the Bell Rock Lighthouse, designed a larger lantern to surround the 

 mast of the vessel, capable of being lowered down to the deck for trimming the 

 light, and raised when required to be exhibited. With the introduction of the 

 catoptric system of illimiination on shore, these lights were improved by the intro- 

 duction of Argand burners, aided by paraboloidal silvered reflectors, each reflector 

 and lamp being properly gimbaUed to insure the horizontal direction of the beam 

 during the pitching and rolling of the vessel. 



In 1872 the Trinity House increased the dimensions of their lanterns and reflec- 

 tors for floating lights, the lanterns from 6 feet to 8 feet in diameter, with cylindrical 

 instead of polygonal glazing, and the reflectors from 12 inches to 21 inches aperture, 

 which improvements effected a tenfold increase in the intensity of these lights. 

 The present 8-foot cylindrical lanterns are just large enough to admit of the lamp- 

 lighter entering them to manipidate the lamps. Further improvements have lately 

 been made in the lamps, and some of these lights have an intensity in the beam of 

 about 20,000 candles. In 1875 the first group flashing floating light, showing three 

 successive flashes at periods of one minute, was exhibited from a new vessel 

 moored at the Royal Sovereign Shoal, oft" Hastings. Since the above date this 

 class of floating lights, showing two or more flashes in a group, has been consider- 

 ablv extended with advantage. In connection with this class of distinctive lights, 

 I V70uld here remark that, in the following year, a 1st Order Dioptric Double Flash- 

 ing Light Apparatus, designed by Dr. John llopkinson, F.R.S., for the Trinity 

 House, and intended for the Little Basses Lighthouse, Ceylon, was exhibited at 

 the Special Loan Exhibition of Scientific Apparatus at South Kensington. In a 

 few cases the dioptric sj'stem has been adopted for light-vessels ; but, so far, the 

 catoptric system has been found to be most efficient for the special cu'cumstances 

 of a floating light. Up to the present, neither electricity nor gas has been tried as 

 an illuminant for light- vessels, but an interesting experiment is now being made by 

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

 the light-vessels at the entrance to the Mersey. 



The difficulties attending the maintenance of an efficient floating light in some 

 of the most exposed positions are great, and at times the service is a very arduous 

 one to the men on board, yet any failure whatever is of very rare occurrence, and 

 there is no instance on record of a British light-vessel having ever been deserted 

 by her crew during a storm. Collisions, which unfortunately are of frequent 

 occurrence, are probably the greatest source of danger to these vessels and their 

 crews. 



As it is a necessity that light-vessels remain at their stations with safety and 

 efficiency as long as possible, usually seven years, they are generally built of wood, 

 or are of composite construction, fastened and sheathed with Muntz metal. A few 



