Laurence, Lionel · London, School of Optics · leaf 235
o besimilarly divergent or convergent after refraction, provided the pencil oflight is small, and the axial ray suffers minimum deviation. Also the prismitself must be of comparatively small angle. Large Light Pencils.—In Fig. 233, which is purposely exaggerated for thesake of clearness, let a wide… … These rays suffer unequal deviation towards M, 0 and N respectively, and ifL E is at minimum deviation, the others cannot be so and are deviatedrelatively more than L E, which is travelling in the direction OO. Both, whenproduced backwards, cut OO nearer than 0, but L F, being more deviatedcuts it…
Optics
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