Of spherical lenses, there are six varieties, as shown in section in the figures herewith given: viz., a plano-concave; b double-concave; c plano-convex; d double-convex; e converging concavo-convex, or converging meniscus; f diverging concavo-convex, or diverging meniscus.
(Opt.), a double-convex lens with one radius equal to six times the other. --
(Anat.) See Eye. --
(Opt.), a compound lens formed by placing around a central convex lens rings of glass so curved as to have the same focus; used, especially in lighthouses, for concentrating light in a particular direction; -- so called from the inventor. --
(Opt.), a lens one side of which is plane and the other convex, but made up of a number of plane faces inclined to one another, each of which presents a separate image of the object viewed through it, so that the object is, as it were, multiplied. --
Polyzonal lens. See Polyzonal.
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