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Pieces of glass or other transparent materials used for magnification or increased visual acuity.

A piece of glass or other transparent substance, so shaped that rays of light passing through it are made to change their direction, and to magnify or diminish objects at a certain distance; the crystalline humour of the eye.

In optical instruments, a piece of glass of a convex, concave, or other shape, for changing the direction of rays of light, and thus magnifying or diminishing objects.