[18] To be more exact than have been the majority of authors who have written on lighthouses, we must add that a small revolving apparatus, with three reverberators (probably with spherical shells), had been planted at the mouth of the port of Marstrand, in Sweden, prior to 1783. The French engineer, however, had thought out the invention for himself, in ignorance that it had been elsewhere realized, and his was the merit of imagining a system so complete and so rational in all its parts, that nothing has since been added to or taken from his conception. M. Leonel Reynard informs us that we are likewise wrong in attributing to Argand the idea of a lamp with a double current of air. It is to Teulère that it should, in the main, be attributed. However, this engineer, who has asserted the priority of his claim to the invention of the reflectors, and the system of eclipses, has not insisted upon that of the lamp. He limits himself to saying that Argand entertained the same idea as himself, and derived great profit from it. * * * * * This method of lightage was obviously a great improvement, and all the maritime powers hastened to adopt it. As the _Catoptric System_, it was, until within the last few years, exclusively employed on the coast of England. Though less esteemed in France, its use has not been entirely abandoned; and the French still employ catoptric apparatus for “the illumination of narrow channels, or for harbour-lights; to strengthen in a given direction a light whose range is sufficient for the maritime horizon generally; to illuminate lightships; and for service as provisional appliances.” [Illustration: CATOTROPIC APPARATUS.] In the accompanying design we represent a plan and elevation of a catoptric apparatus, which is composed, as will be seen, of nine reflectors arranged in groups of threes. A small rotatory machine sets the system in motion, and eclipses at greater or shorter intervals are obtained by the varying speed with which it is worked. The range of the apparatus depends partly on its power, and partly on its position. The reflectors, as used in the best lighthouses, are made, says Mr. Stevenson,[19] of sheet copper, plated in the proportion of six ounces of silver to sixteen ounces of copper. They are moulded to a paraboloidal form by a delicate and laborious process of beating with mallets and hammers of various forms and materials, and are frequently tested during the operation by the application of a mould carefully formed. After being brought to the curve, they are stiffened round the edge by means of a strong bizzle, and a strap of brass which is attached to it for the purpose of preventing any accidental alteration of the figure of the reflector. Polishing powders are then applied, and the instrument receives its latest finish. [19] Stevenson, “On Lighthouses,” pp. 92, 93.