On Talbot's bands and the theory of the Lummer-Gehrcke interferometer

New Simple Method of Observing Talbot's Bands.-If a thin strip of cover glass is immersed in a dispersive medium, such as a suitable mixture of CS2 and benzene, with a refractive index such that the group velocity in it is less than in the plate, and if a vertical slit illuminated with white light is observed through the glass strip held in a vertical plane very oblique to the plane of the incident light, two out of the four spectra formed by the edges of the plate exhibit Talbot's bands. The theory of the formation of the bands in this way is closely similar to that of the Lummer-Gehrcke plate, and as in the latter, the maxima are narrow and the minima crossed by secondary maxima when the number of internal reflections is small. The appearance, too, is not affected by opening the slit wide. Interference Bands Analogous to Those given by a Fabry-Perot etalon were also observed with the same simple arrangement. The appearance and behavior of these bands are described and explained