Henderson, C. Hanford (Charles Hanford), 1861-1941, Woodhull, John F. (John Francis), 1857-1941 · New York, D. Appleton and company · leaf 356
cause rays of light to diverge (Fig. 231).Far-sightedness, on the contrary, results from too littlecurvature of the lens, so that images form back of the ret-ina. It must be remedied by glasses which cause rays oflight to converge (Fig. 232). It is a universal defect of oldage. Astigmatism means an… … Fig. 232.—Double-convex glass for far-sightedness. cal surfaces. Few people have eyes that are perfectly adapt-ed for parallel vision. The muscular eifect necessary tobring them to parallel is a most frequent cause of headaches.320. The Spectrum.—We have seen that the index ofrefraction is in…
Physics
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