Brewster, David, Sir, 1781-1868, Bache, A. D. (Alexander Dallas), 1806-1867 · Philadelphia : Lea and Blanchard · leaf 65
increase, the cusp f of the imaginarycaustic will approach A, and its tangent Af, will diminish;and when the radiant point arrives at the circumference at A,the cusp f will also arrive at A, and the imaginary causticwill disappear. At the same time, the cusp / of the realcaustic will be a little to… … R A, a remarkable double caustic will be formed. Thiscaustic will consist of two short ones of the common kind, CHAP. VI. CAUSTIC CURVES. 61 ar, b r, having their common cusp at r, and of two longbranches, af, bf, which meet in a focus at f. When R C isgreater than R A, the curved branches that…
Optics
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