  A geometric visualization is presented for the Brewster angle for a plane
wave reflecting from an interface. The surface is assumed isotropic but it is
allowed to display both dielectric and magnetic susceptibility, and hence the
Brewster (polarizing) angle can attain any value between 0 and 90 degrees, and
can exist for both parallel and perpendicular polarizations. The geometric
construction (a tetrahedron) is spanned by the basic material parameters of the
surface. The Brewster angle appears in one of the faces of the tetrahedron.
