A system of natural philosophy, designed for the use of schools and academies (1845)
Moffat, J[ohn] M. [from old catalog] · Philadelphia, E. C. Biddle · leaf 373
d Hare named conjugatefoci, becausethe place of one depends on that of the other, and though everylens has only one principal focus, it may have an indefinite num-ber of conjugate foci, as rays may fall on it converging at innu-merable angles. The conjugate focal distance, C H, may befound by… … 118. When diverging rays, or those issuing from one point, asE A, and E B, fall on a convex lens A B, the principal focus ofwhich is at O, the refractive power of the lens will make themconverge to a focus at G, beyond 0. As the point whence therays diverge recedes from the lens, the focus G will…
Physics
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