Applicability of the Electric Light to Lighthouses. 327 



rate pieces, in 1811 ; and thus what was carried into practice 

 eleven years after by Fresnel, and has been considered his 

 invention, is merely the application of the polyzonal lens of Sir 

 David Brewster. These improvements, and the substitution of 

 totally reflecting prisms by Alan Stephenson, for reflectors 

 previously employed with the new dioptric apparatus, seem to 

 leave nothing more to be desired in this department of light- 

 house construction. But, like other valuable discoveries and 

 inventions, that of Sir David Brewster, notwithstanding all its 

 advantages, came but slowly into use. France was the first to 

 avail itself of so important a contrivance. In 1822 Fresnel 

 built up a lens, and, as suggested long before by Sir David, 

 used it in conjunction with mirrors in the lighthouse of the 

 Tour de Cordouan. In 1834, in consequence of the recom- 

 mendation of the House of Commons, a revolving light, on the 

 same principle, was placed on Inchkeith, and a fixed light on the 

 Isle of May. 



The attention of scientific men, as far as lighthouses are 

 concerned, is now almost confined to the discovery of the best 

 mode of producing the light. That in ordinary use leaves little 

 to be desired, when the weather is tolerably clear : since a first- 

 class oil light, at the height at which it is usually elevated, is 

 visible from the masthead when the vessel comes above the 

 horizon of the lighthouse — the nature of our climate would not 

 allow a greater elevation to be given to the lights. It is, 

 therefore, in hazy weather that a more intense light becomes 

 desirable. Science furnishes more than one such fight. Among* 

 these is the Drummond Light, which possesses both advan- 

 tages and disadvantages when applied to lighthouses — the 

 preponderance of the one over the other not being, however, 

 very decided • and the electric light, which may in time super- 

 sede all others on the mainland, especially if some of the 

 inconveniences by which it is accompanied are removed, or 

 even lessened. The necessity for a steam-engine, when it is 

 employed, renders it inapplicable on rock stations, such as the 

 Eddy stone Lighthouse, and the Bell Eock. 



In the employment of the electric light, two very important 

 matters are to be considered : the production of the electricity, 

 and its transformation into light. The most obvious mode of 

 effecting the former would be the use of the galvanic battery : 

 and, accordingly, numerous experiments have been made with 

 that object. Among others, a most important series, in the 

 central workshops of the Administration of Lighthouses in 

 France from 1818 to 1857. So far as the mere production of 

 an intense light was concerned, the success of these experi- 

 ments was complete. But the expense of the battery was very 

 great, and the irregularity of the results obtained was very 



