Johnson's natural philosophy and key to philosophical charts : illustrated with 500 cuts; being reduced photographic copies of all the diagrams contained in the author's philosophical series of indestructible school charts ; for the use of schools and families (1878)
ses must have focal lengths directly proportional tothe dispersive powers of the media of which they are respectivelycomposed. If the combination is made of crown and flint glass, the focus ofthe croion should be to that of the flint as 2 to 3, or rather, in ordi-nary cases as to 3 to 4 ; since… … Figure 4.—Recomposition of light by means of reversedprisms. For an explanation of this diagram, see 431. 252 OPTICS. VISION. ^o9.—Figure 5.—The camera obscura.—The camera ob-scura as the name implies, is a dark chamber, and, in a portable form, Fig. 5.
Physics · Astronomy
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