In a note published in 1934 as well as in the subsequent publications the present author reported his discovery of feeble visible radiation emitted by pure liquids under the action of fast electrons (-particles of radioactive elements or Compton electrons liberated in liquids in the process of scattering of -rays). This radiation was a novel phenomenon, which could not be identified with any of the kinds of luminescence
then known, as the theory of luminescence failed to account for a number of unusual properties (insensitiveness to the action of quenching agents, anomalous polarization, marked spacial asymmetry, etc.) exhibited by the radiation in question. In 1934 the earliest results obtained in the experiments with -rays led S. I. Vavilov to interpret the radiation observed as a result of the retardation of the Compton electrons liberated in liquids by -rays.
A comprehensive quantitative theory subsequently advanced by I. M. Frank and I. E. Tamm afforded an exhaustive interpretation of all the peculiarities of the new phenomenon, including its most remarkable characteristic - the asymmetry. According to their theory, an electron moving in a medium- of refractive index n with a velocity exceeding that of light in the same medium ( > 1/n) is liable to emit light which must be propagated in a direction
forming an angle with the path of the electron, this angle being determined by the equation: cos = 1/ n (1) where is the ratio of the electron velocity to that of light in vacuum. A successful experimental verification of formula (1) was only performed with water for which, at the moment of publication of the above theory, data
were already available which had been obtained by visual observations by the method of quenching. We recently performed additional experiments in which the intensity of radiation was recorded photographically, the records being taken simultaneously for all the angles lying in a plane passing through the primary electron beam. All the results obtained are in good agreement with I. M. Frank and I. E. Tamm's theory of the coherent radiation of electrons
moving in a medium. (Extracted from the introductory part of the paper.).
Related references See also P. A. Cerenkov, Doklady Akad. Nauk SSSR 2 (1934) 451;
P. A. Cerenkov, Doklady Akad. Nauk SSSR 12 (1936) 413;
P. A. Cerenkov, Doklady Akad. Nauk SSSR 14 (1937) 102;
E. Brumberg and S. I. Vavilov, Doklady Akad. Nauk SSSR 3 (1934) 405;
P. A. Cerenkov, Bull. of Ac. of Sci. USSR Phys. Ser. 7 (1933) 919;
S. I. Vavilov, Doklady Akad. Nauk SSSR 2 (1934) 457;
I. M. Frank and I. E. Tamm, Doklady Akad. Nauk SSSR 14 (1937) 109;
P. A. Cerenkov, Doklady Akad. Nauk SSSR 14 (1937) 105;
Confirmation of the Frank-Tamm theory of the Vavilov- Cerenkov effect.