On the Luminescence of Atoms.

K. Försterling. Über das Leuchten der Atome. Zs. f. Ph., X, 6, p. 387, 1922.

Försterling’s work attempts to find experimental grounds for deciding the question of whether the connection between the emitting electron and the radiation breaks off instantaneously (Sommerfeld), or whether there exists between them a lasting connection of a differential character (Mie). First of all, there is no doubt that radiation issuing from a moving electron, even if Sommerfeld’s assumption is accepted, cannot be regarded as propagating as from a stationary center, from the point at which the electron was at the moment the connection was broken. For, owing to the duration of luminescence (Wien’s experiments and the older experiments of Lummer and Gehrcke on interference), an observer connected with the electron but facing it with his back would see light issuing from this center and overtaking the observer (since \(c > v\)). Thus, the possibility of “seeing” an electron located behind the observer’s back would serve as proof of the motion of the observer and the electron, i.e. in the sharpest form it would contradict the principle of relativity.

Having established the spatial proximity of the emitting electron and the center of the emitted wave, Försterling argues as follows. An electromagnetic field cannot act upon free radiation, but only upon the emitting electron. Therefore the influence of the field on the radiation of a moving electron can decide the question of whether the radiation exists independently of the electron or remains connected with it throughout the entire time of emission. In Stark’s arrangement the luminescence of canal rays began, at least in part, before they entered the region where a high electric field prevailed. The velocity of the canal rays (\(10^7\ \mathrm{cm/sec}\)), the duration of luminescence (\(10^{-8}\ \mathrm{sec}\)), and the length of the free path in the region described (about 3 mm) are such that the canal rays, during the time of luminescence, should not undergo collisions with other atoms. Thus, if the radiation that follows the atom into the region of the electric field has already lost its connection with the atom, it should not experience any action from the electric field, and alongside the lines that have undergone the Stark effect there should be lines that have not undergone splitting. However, Stark’s observations never revealed such unsplit lines. Consequently, it must be admitted that the connection between the radiation and the electron is preserved throughout the entire time of emission.

Tr. Landsberg.