Reflecting systems for image inversion

The method of investigating systems of plane reflectors described in another paper* has been applied to determine how many optical surfaces are necessary in an inverting prism. Four surfaces involve oblique refraction into the prism whatever the number and order of the reflections. With five surfaces one form is possible with four reflections. All possible arrangements with six reflections at five surfaces are considered, and the application of the method to prisms with a greater number of reflections is illustrated.