Emily Dickinson Lexicon

LENS, n. [plur. Lenses. L. lens, a lentil.]

A transparent substance, usually glass, so formed that ray of light passing through it are made to change their direction, and to magnify or diminish objects at a certain distance. Lenses are double-convex, or convex on both sides; double-concave, or concave on both sides; plano-convex or plano-concave, that is, with one side plane, and the other convex or concave; or convex on one side and concave on the other; the latter is called a meniscus. – Encyc.