LENS, lax. A town of France. in the Depart ment of Pas-de-Calais. on the Souchez, 17 miles south-snuthwest of Lille. It is a place of great antiquity, and was once strongly fortified. It has iron and steel foundries and manufactures sugar, soap. etc. In the vicinity are highly pro ductive coal-mines. It is famous for the victory gained by the Prince of •on& Over Leopold William, Archduke of Austria, under its walls, in 1646. Population, in 1691, )3,Sti2; in lout, 24,370.
LENS (Neo-Lat., from Lat. lens, lentil; se called on account of the shape of the lens). A circular section of a transparent substance, hav ing its surfaces either both spherical, or one of them plane and the other spherical. Lenses are either convex (thickest in the middle) or con cave (thickest at the edges), and a ray of light in passing through a lens is brat toward its thickest part. The former class changes the direction of the rays by making them more convergent than before; the latter makes them more divergent. The point to which the rays converge, or from which they diverge, is called a focus—principal focus when the rays are paral lel. The focus for a convex lens is real, i.e. the rays actually pass through it, form a rent and inverted image smaller or larger than the object. according as the object is at a distance greater or less than twice the focal length; but if the object be within the principal focal length a virtual image is formed, erect and magnified.
For a concave lens the focus is virtual—the rays seem to come front it and form an erect image smaller than the object. See LIGHT, where a section is devoted to lenses and the various theo retical questions involved are discussed. For different forms of lenses as used in various op tical instruments, see PHOTOG RAPH Y TELESCOPE, etc. See, also. ABERRATION, SPIIERI CA I, ; and ABERRATION, CHROMATIC. Con sul t : Preston, Theory of Light (New York. 1895) : Glazebrook, Physical Optics (London and New York, 1898).
LENSTRoM, len'stri7m, emit Jutaus (1811 93). A Swedish poet and critic, born at Gelle. He studied philosophy and theology at Upsala, took orders in 1834. and taught literature at the University of Upsala from 1836 to 1843. During the next two years he taught philosophy at Gelle. In 1845 he was appointed rector at Ves ter-Loefsta. Ile wrote on philosophy, poetry, theology, and festheties, and his principal publi cations include a compendium of the Chureh his tory of his country, Ldrobok i allntlinna eels srenska. Kyrkohistorian ( 1842 ) contributions to the history of Swedish ;esthetics, Bidrag till den• srenska iisthetikens historia (1840); Fah(u jurelen (1838). a novel; Crow ( 1860), a poem; Gustaf II. Adolf (1860). poems, and some sketches. Dc fyra stdnden, tailor air svcnskt sedclif (1865).