TLDR
AX. I.
The Angles of Reflexion and Refraction, lie in one and the same Plane with the Angle of Incidence.
AX. II.
The Angle of Reflexion is equal to the Angle of Incidence.
AX. III.
If the refracted Ray be returned directly back to the Point of Incidence, it shall be refracted into the Line before described by the incident Ray.
AX. IV.
Refraction out of the rarer Medium into the denser, is made towards the Perpendicular; that is, so that the Angle of Refraction be less than the Angle of Incidence.
AX. V.
The Sine of Incidence is either accurately or very nearly in a given Ratio to the Sine of Refraction.
Whence if that Proportion be known in any one Inclination of the incident Ray, 'tis known in all the Inclinations, and thereby the Refraction in all cases of Incidence on the same refracting Body may be determined. Thus if the Refraction be made out of Air into Water, the Sine of Incidence of the red Light is to the Sine of its Refraction as 4 to 3. If out of Air into Glass, the Sines are as 17 to 11. In Light of other Colours the Sines have other Proportions: but the difference is so little that it need seldom be considered.via the TL;DR App
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