Elementary natural philosophy : designed for high schools and academies (1881)
Griffin, La Roy F. (La Roy Freese), 1844-1916 · Philadelphia : Sower, Potts & Co. · leaf 214
710. If the rays proceed fromany point, as L, Pig. 236, therefracted rays become more di-vergent, so that the focus is atI. This point is between the lensand the principal focus, and this Fig. 236. focus is also virtual, while the luminous point and thefocus are much nearer than before.
Physics
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