Webster 1913 Edition
lensa lentil. So named from the resemblance in shape of a double convex lens to the seed of a lentil. Cf.
A piece of glass, or other transparent substance, ground with two opposite regular surfaces, either both curved, or one curved and the other plane, and commonly used, either singly or combined, in optical instruments, for changing the direction of rays of light, and thus magnifying objects, or otherwise modifying vision. In practice, the curved surfaces are usually spherical, though rarely cylindrical, or of some other figure.
☞ Of spherical lenses, there are six varieties, as shown in section in the figures herewith given: viz.,
econverging concavo-convex, or converging meniscus;
fdiverging concavo-convex, or diverging meniscus.
a double-convex lens with one radius equal to six times the other.–
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.–
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.–
Webster 1828 Edition