title: The prism-substrate: a new tool for determining an angle of incidence.
abstract: In addition to the ray externally reflected from the base of an isosceles prism, another ray leaves the base after refraction and two internal reflections. The angle of incidence is related to the angle between these two rays, to the vertex angle of the prism, andto the index of refraction of the prism. The relation provides a simple, convenient, and accurate procedure for measuring the angle of incidence when the reflecting surface is inaccessible, e.g., a freshly formed mirror enclosed in a vacuum chamber.
authors.forename: L B
authors.initials: LB
authors.lastname: Emmons
authors.forename: M P
authors.initials: MP
authors.lastname: Givens