Elementary natural philosophy : designed for high schools and academies (1881)
Griffin, La Roy F. (La Roy Freese), 1844-1916 · Philadelphia : Sower, Potts & Co. · leaf 202
Fig. 215Fig. 215 shows how the principal focus is determined, The parallel rays meet the mirror M at the points a, b, c, d, etc. Eadii … 192 OPTICS. drawn to these points give the angles of incidence, and the raysare then reflected, making the angles of reflection equal to theangles of incidence. They then meet at F the principal focus. Thisis half way between C and E. This discwssion shows that the principal focus is uponthe…
Physics
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