XXXI. The photo-electric theory of vision
The London Edinburgh and Dublin Philosophical Magazine and Journal of Science
The Photo-Electric Theory of" Vision. 347 Obliquely Inddent Light.--When the fihn is tilted relatively to the direegi.n of the incident rays, the rings seen on the fihn contract and move inwards. As in the case of normal incidence, perfectly black rings may be seen on the fihn, if it be viewed in monochromatic tight very nearly in the direction of the transmitted rays, and the appearance of these rings alters with the obliquity of observation in much the same way. It should be remarked,
... e remarked, however, that in the present ease the effects observed vary not only with the anglo between the transmitted pencil and the directio~l of observation, but also with the particular phme in which the latter direction lies. The maximum permissitde angle ~f observation varies ~ith this plane. In the plane of incidence it is 7r/2--a and ,r/2 + a respectively on the two sides of the tc.ansmitted pencil, where a is the ang]e of incidence. If a is considerable, the rings continue to be visible when the film is viewed nearly along the surface of the plate on one side of the transmitted l,encil, while ou the other side the rings move out and disappear from the film ata moderate obliquity, so that in white light the film appears achromatic over a wide range of angles of observation.