Vol. 1. Lat. & Eng.
C.XXIII.
Fig. 1-9
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CHAPTER XXIV.
OF REFRACTION AND REFLECTION.
[1.] Definitions.—[2.] In perpendicular motion there is no refraction.—[3.] Things thrown out of a thinner into a thicker medium are so refracted that the angle refracted is greater than the angle of inclination.—[4.] Endeavour, which from one point tendeth every way, will be so refracted, as that the sine of the angle refracted will be to the sine of the angle of inclination, as the density of the first medium is to the density of the second medium, reciprocally taken.—[5.] The sine of the refracted angle in one inclination is to the sine of the refracted angle in another inclination, as the sine of the angle of that inclination is to the sine of the angle of this inclination.—[6.] If two lines of incidence, having equal inclination, be the one in a thinner, the other in a thicker medium, the sine of the angle of inclination will be a mean proportional between the two sines of the refracted angles.—[7.] If the angle of inclination be semirect, and the line of inclination be in the thicker medium, and the proportion of their densities be the same with that of the diagonal to the side of a square, and the separating superficies be plane, the refracted line will be in the separating superficies.—[8.] If a body be carried in a strait line upon another body, and do not penetrate the same, but be reflected from it, the angle of reflection will be equal to the angle of incidence.—[9.] The same happens in the generation of motion in the line of incidence.
Definitions.
I. Refraction is the breaking of that strait line, in which a body is moved or its action would proceed in one and the same medium, into two strait lines, by reason of the different natures of the two mediums.