Gage, Alfred P. (Alfred Payson), 1836-1903, Fessenden, C · Toronto : W.J. Gage · leaf 376
TMAGES FORMED. 353 beyond the principal focus, the rays are rendered convergent.A concave lens causes parallel incident rays to diverge as ifthey came from a point, as F (Fig. 26G). This point is there-fore its principal focus. It is, of course, a virtual focus. § 299. Conjugate foci. — When a…
Physics
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