Brewster's Law

In 1811 Sir D. Brewster made a series of experiments with a view to determining the polarizing angle for light in relation to different media, and connecting them by a general law. The result was that "the index of refraction of a substance is the tangent of the angle of polarization." If a denote the polarizing angle, and a ray of light be incident IMG:content-0614.jpg:[blocks in formation] the angle of refraction; therefore sin v = cos a , and v + a = 90°. Now the angle of reflection is also a , and therefore the reflected ray and the refracted ray are at right angles; which is another form of this law.