Elementary natural philosophy : designed for high schools and academies (1881)
Griffin, La Roy F. (La Roy Freese), 1844-1916 · Philadelphia : Sower, Potts & Co. · leaf 212
202 HEAT. through the centre of the lens itself, called the Optical Centre. 704. Focus of Parallel Rays. The focus of parallel rays,called the Principal Focus, is found by drawing perpen-diculars to the surface, and tracing the direction of the rajsthrough the glass. Thus the ray L, Fig. 231, meets… … Fig. 231. perpendicular, and crosses to D. CD is the perpendicular to thatpoint, and the emergent ray is refracted from the perpendicular,and reaches the focus at F. If the lens is of crown glass, this pointcoincides with the centre of curvature. 705. Conjugate Foci. If the source of light be at…
Physics
Internet Archive · Library of Congress · Public Domain Mark 1.0. Free to use for anything.
