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

  • Newton, Isaac, 1642-1727.
Date:
1704
Catalogue details

Licence: Public Domain Mark

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. Source: Wellcome Collection.

    66/406 (page 56)
    C0] its Reftilincar Sides, did when produced pafs exadly through the middle of that white round Image S. And when the Refradion of the fecond Prifm was equal to the Refradion of the firft, the refradling Angles of them both being about 6o degrees, the Axis of the Spedlrum if made by that Refra(^ion, did when produced pafs alfo through the mid¬ dle of the fame white round Image S. But when the Re- fradtion of the fecond Prifm was lefs than that of the firft, the produced Axes of the Spe6trums tp or it if made by that Refraction did cut the produced Axis of the Spe- xStrum TP in the Points m and w, a little beyond the Cen¬ ter of that white round Image S.. Whence the Proportion of the Line ^ ^ T to the Line 3 p P was a little greater than the Proportion of 2 rT to 2 pP, and this Proportion a little greater than that of tT to pP. Now when the Light of the Spc6lrumP T falls perpendicularly upon the Wall, thofe Lines 3 ^T, 3p P, and 2f T, 2p P and tT,pP,are the Tan¬ gents of the Refractions 3 and therefore by this Experiment the Proportions of the Tangents of the RefraClions are ob¬ tained, from whence the Proportions of the Sines being deriv¬ ed, they come out equal, fo far as by viewing the SpeClrums and ufing fome Mathematical reafoning I could Eftimate. For I did not make an Accurate Computation. So then the Propofition holds true in every Ray apart, fo far as ap¬ pears by Experiment. And that it is accurately true may be demonftrated upon this Suppofition, That bodies refrah Light by aHing upon its ^ys in Lines Perpendicular to their Surfaces, But in order to this Demonftration, I muft di- ftinguilh the Motion of every Ray into two Motions, the one Perpendicular to the refraCting Surface, the other Pa¬ rallel to it, and concerning the Perpendicular Motion lay down the following Propofition. If