Opticks: or, a treatise of the reflexions, refractions, inflexions and colours of light. Also two treatises of the species and magnitude of curvilinear figures / By Sir Isaac Newton, Knt.

Isaac Newton

Date:: 1721

Credit: Opticks: or, a treatise of the reflexions, refractions, inflexions and colours of light. Also two treatises of the species and magnitude of curvilinear figures / By Sir Isaac Newton, Knt. Source: Wellcome Collection.

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$E74 Circumference in FE, and joyning CE, this Line C FE, fhall be the Line of the refratted Ray. For if EF be let fall perpendicularly on the Line P Q, this Line EF fhall be the Sine of Re- fraction of the Ray CE, the Angle of Refraction being FE CQ; and this Sine FE. F is equal toD H, and confequently in Proportion to the Sine of Incidence A D as 3 to 4. In like manner, if there be a Prifm of Glafs (that is a Glafs bounded with two Equal and Parallel Triangular ends, and three plain and well polifhed Sides, which meet in three Parallel Lines running from the three Angles of one end to the three Angles of the other end) and if the Refradtion of the Light in pafling crofs this Prifm be defired: Let ACB [in /zg. 2.] reprefent a Plane cutting this Prifm tranverily to its three Parallel lines or edges there where the Light paffeth through it, and let D FE; be the Ray inci- dent upon the firft fide of the Prifm AC where the Light goes into the Glafs; and by putting the Proportion of the Sine of Incidence to the Sine of Refraction as 17 to 11 find EF. F the firft refracted Ray. ‘Then taking this Ray for the Incident Ray upon the fecond fide of the Glafs BC where the Light goes out, find the next — refracted Ray FG by putting the Proportion of the Sine of Incidence to the Sine of Re- fraction as 1: to 17. For if the Sine of Iaci- dence out of Air into Glafs be to the Sine of RefraGtion as 17 to 11, the Sine of Incidence out of Glafs into Air muft on the contrary be to the Sine of Refraction as 11 to 17, by the third Axiom. B 4 Much$