[Illustration: ELECTRIC APPARATUS FOR A FIXED LIGHT.]
Both lighthouses are supplied with two lenticular apparatus, placed one above another in the same lantern. The regulators of the progress of the carbons were invented by M. Serrin, whose object has been to augment their sensibility, and, consequently, the regularity of the light; in which respect, now-a-days, little is left to be desired. The mean intensity of the light produced by a machine of six discs is computed as equal to 200 Carcel burners. The intensity of the cone of light emanating from the lenticular apparatus, when illuminated in this manner, rises to 5000 burners.
The electric light, as yet, is applied only to lighthouses with fixed lights, for a special arrangement would be necessary in the lenticular apparatus before it could be employed with the same advantage in the production of intermittent lights (_feux à éclipses_). Experiments, however, have been made in this direction, which promise good results. Yet, in the present state of its mechanical conditions, the system of electric illumination does not seem susceptible of any very great development upon our shores. It cannot be applied economically to lights which require no very great intensity,—and these lights are the most numerous; and, on the other hand, the intricate constructions which it necessitates, the chances of accident which it presents, and the quantity of coal which it consumes, are obstacles to its employment in lighthouses isolated at sea, whose communications with the mainland are liable to interruption, and where it is of importance to reduce as much as possible the dimensions of the edifice as well as the amount of transport. However this may be, the electric light would seem destined to render valuable services to navigation at every point where it can be employed, and like the two great inventions which the history of marine lightage signalizes—that of paraboloidal reflectors, and next, that of the lenticular apparatus—it constitutes a special and noteworthy progress, under the threefold aspect of intensity of light, diversity of character, and the value of luminous unity.
We may add that Mr. Wilde, of Manchester, has invented a powerful electro-magnetic apparatus for lighthouse illumination, which may probably prove valuable. Modifications of the lime light, resulting from the action of an oxy-hydrogen flame upon a surface of prepared lime, have also been suggested; and the least powerful of these surpasses in brilliancy the best oil-lamp, as that surpasses the open coal-fire. We may, therefore, expect that as the latter barbarous mode of illumination gave way to the catoptric, or _reflecting_ system, so will the dioptric, before many years have passed, succumb to some ingenious apparatus capable of utilizing either the lime or the electric light.