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urved surfaces are usually spherical, though rarely cylindrical, or of some other figure. Lenses

The act or the state of declining; declination; descent; slope. The declension of the land from that place to the sea. T. Burnet.

Belonging to declension. Declensional and syntactical forms. M. Arnold.

To strip the blubber or skin from, as from a whale, seal, etc. the flensed carcass of a fur seal. U. S. Census (1880).

See under Lens.

The half of a lens divided along a plane passing through its axis.

The convergence to different foci, by a lens or mirror, of rays of light emanating from one and the same point, or the deviation of such rays from a single focus; called spherical aberration, when due to the spherical form of the lens or mirror, such form giving different foci for central and marginal rays; and chromat…

Uncolored; not absorbing color from a fluid; -- said of tissue. Achromatic lens (Opt.), a lens composed usually of two separate lenses, a convex and concave, of substances having different refractive and dispersive powers, as crown and flint glass, with the curvatures so adjusted that the chromatic aberration produced…

The state or quality of being achromatic; as, the achromatism of a lens; achromaticity. Nichol.

An instrument for viewing pictures by means of a lens, so as to present them in their natural proportions and relations.

An arrangement of lenses and mirrors which enables a person to see an object in spite of intervening objects.

Uniting the chemical rays of light into one focus, as a certain kind of lens; amacratic.

Not astigmatic; --said esp. of a lens system which consists of a converging lens and a diverging lens of equal and opposite astigmatism but different focal lengths, and sensibly free from astigmatism.

An anomalous state of refraction caused by the absence of the crystalline lens, as after operations for cataract. The remedy is the use of powerful convex lenses. Dunglison.

arts of different curvatures, so combined as to remove spherical aberration; -- said of a lens. Aplanatic focus of a lens (Opt.), the point or focus from which rays diverging pass the lens without spherical aberration. In certain forms of lenses there are two such foci; and it is by taking advantage of this fact that t…

Free from chromatic and spherical aberration; -- said esp. of a lens in which rays of three or more colors are brought to the same focus, the degree of achromatism thus obtained being more complete than where two rays only are thus focused, as in the ordinary achromatic objective. --Ap`o*chro"ma*tism (#), n.…

), one the humors of the eye; a limpid fluid, occupying the space between the crystalline lens and the cornea. (See Eye.) -- Aqueous rocks (Geol.), those which are deposited from water and lie in strata, as opposed to volcanic rocks, which are of igneous origin; -- called also sedimentary rocks.

taining to, astigmatism; as, astigmatic eyes; also, remedying astigmatism; as, astigmatic lenses.

A defect of the eye or of a lens, in consequence of which the rays derived from one point are not brought to a single focal point, thus causing imperfect images or indistictness of vision.

An instrument for measuring the magnifying power of a lens or system of lenses.