Scattering in the Case of Regular Reflection from a Transparent Grating: an Analogy to the Reflection of X-Rays from Crystals

Abstract

1. The Phenomenon.—No doubt the following phenomenon has been noticed before, but I have seen no description of it. If a vertical sheet of white light L from a collimator is reflected from the two faces of a plateglass grating, having about 10,000 or more lines to the inch, g being the ruled face, the two beams b and y going to the opaque mirror N are respectively vividly blue and brownish-yellow. In other words, more blue light is regularly reflected from the ruled surface than is transmitted, and more reddish light transmitted than is reflected. Singe the plate grating is not quite plane parallel, two of the four rays, b¹ and y¹, are seen in the same colours in the telescope. This is a great convenience in adjusting the displacement interferometer, where the spectra from b alone are wanted, and the y ray may be screened off at N, while the other y¹ has no spectrum.