Dr. Gregory's Elements of catoptrics and dioptrics / Translated from the Latin original, with a large supplement, by William Browne.

Gregory, David, 1659-1708. Catoptricae et dioptricae sphaericae elementa. English

Date:: 1735

Credit: Dr. Gregory's Elements of catoptrics and dioptrics / Translated from the Latin original, with a large supplement, by William Browne. Source: Wellcome Collection.

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$If the Ray E D be near enough to the right Line EB (for we fpeak here only of thofe Rays that fall near the Axis, lince thefe only do, after Refraction, affeCt the Eye placed, by Suppolition, in the Axis of Radiation produced ] thofe that fall more obliquely palling by the Pupil of'the Eye, and conducing nothing at all towards dis¬ cerning the Point E, as we have before obferved in Catoptrics) ED will be nearly equal to E B, and C D to C B. Where¬ fore CD is to ED, as I to R : But C D . is to E D, as the Sine of the Angle BED, or its equal EDA, to the Sine of the An¬ gle BCD, or its equal ODF : Therefore the Sine of the Angle E D A is to the Sine of the Angle QDF, as I to R. But the Angle EDA is the Angle of Incidence of the Ray E D: Therefore O D F is the refpeCtive Angle of Refraction * that is, DF is the refraCted Ray of the Incident ED. And the fame may be fhewn of any other Ray diverging from E ; whence C is the Focus required. 0, E. L C o r o l. 1. From hence, and from Corel, r. Frop* XI. it follows, that the fame Things be¬ ing fuppofed as before, Rays in the Me¬ dium BDO converging towards C, will, after RefraCtion, converge towards E. I And$