2. Notice relative to the Polyzonal Lenses belonging to the Commissioners of the Northern Light-houses

Extract

These lenses, which were exhibited to the Society by Mr Stevenson, are three in number. One, a plano-convex lens, two feet six inches square, was made by M. Soleil at Paris, under the superintendence of the late M. Fresnel. Another is a double-convex circular lens of flint-glass, three feet in diameter, which was constructed by the Messrs Gilbert of London, at the suggestion of Sir David Brewster. The third is a circular plano-convex lens, two feet six inches in diameter, cast in one piece as originally proposed by Buffon. This lens has been executed for the first time by the Messrs Cookson, plateglass-makers, Newcastle.