Henderson, C. Hanford (Charles Hanford), 1861-1941, Woodhull, John F. (John Francis), 1857-1941 · New York, D. Appleton and company · leaf 349
blackboard erasers ordusty clothing near it, the rays of light are easily tracedby means of these reflecting particles, and they are seen tomeet and cross, forming two cones of light as representedin Fig. 226. The points where the apices of the conesmeet is the principal focus, and its distance… … Fig. 226.—Principal focus. screen is placed halfway between the lens and the focus,the circle of light has about half the diameter of the lens; REFRACTION OF LIGHT 327 its area is therefore one quarter as great as in the first posi-tion, and the intensity of its light four times as great.When it is…
Physics
Internet Archive · Library of Congress · Public Domain Mark 1.0. Free to use for anything.
