‎"LUMMER, O. (+) E GEHRCKE.‎
‎Über die Anwendung der Interferenzen an planparallelen Platten zur Analyse feinster Spektrallinien. - [THE LUMMER-GEHRCKE INTERFEROMETER]‎

‎(Leipzig, Johann Ambrosius Barth, 1903). 8vo. No wrappers. Extracted from ""Annalen der Physik"" Vierte Folge. Bd. 10. Entire issue no. 3 offered. Pp. 457-477. [Entire issue: Pp.‎

Reference : 50377

‎First appearance of this important paper in which the ""Lummer-Gehrcke interferometer"" was presented for the first time. ""Since Lummer fringes are the result of differences in path length of many wavelengths, Lummer arrived at the idea, in 1901, of developing the plane parallel plates into a spectroscope of the highest resolution. This device had the advantage of possessing greater resolving power than the interferometer produced in 1897 by Fabry and Perot. The considerable drawback of low luminous intensity, caused by the glancing incidence of the light, was eliminated in 1902 by Gehrcke, who cemented a prism to the plate with Canada balsam. The new apparatus, for which Lummerproposed the name Lummer-Gehrcke interference spectroscope, proved to be an excellent tool for spectroscopy and superior to the simple line grating."" (DSB)Lummer-Gehrcke interferometer is a multiple-beam interferometer similar to the Fabry-Perot etalon, but using light at a steep angle of incidence. The interferometer consists of a long plate of glass or quartz, with faces that are polished accurately flat and parallel. Light bounces back and forth inside the plate, striking the faces at an angle just below the critical angle as it propagates along. Because of the steep angle of incidence, nearly all of the light is reflected, but a tiny fraction leaks out on each bounce.‎