The Absorption of Fluorescing Sodium Vapour

Abstract

ACCORDING to Bohr's theory concerning the origin of spectral lines, electrons in the atoms of sodium vapour under the influence of exciting D radiation are displaced from their normal 1.5 S orbit to the 2p orbits. During the return of the electrons to their normal orbit the so-called “resonance” radiation, first observed by Wood (Phil. Mag., November, 1905, and “Researches in Physical Optics,” part 2, p. 166), is re-emitted as fluorescent light. It has been suggested, therefore, by more than one observer (Foote and Meggers, Phys. Rev., vol. 15, part 4, p. 323, and Phil. Mag., vol. 40, p. 80, 1920) that fluorescing sodium vapour should absorb lines of the first and second subordinate series 2p₂ â ms and 2p₂ â md. To test this point I have made use of the experimental arrangement outlined below. While a negative result was obtained, it seems worth while to record the trial, along with one or two suggestions for a more rigid test which I am not able to make at present.