The paper presented here was written as early as sometime between 1939 and 1944 by the eminent mathematician Aleksandr Yakovlevich Khinchin, who is well known for his contributions to the theory of probability, statistical physics, theory of numbers, and theory of functions. For reasons unknown to me, it remained unpublished, although I remember that Khinchin had submitted it to the periodical Uspekhi matematicheskikh nauk. After he died, while I was putting in order the scientific and literary heritage of Khinchin, I remembered this work and began looking for it. Regrettably, I was unable to find any copies of a final version and the editorial office of Uspekhi did not have any record of the article. So I decided to make use of a copy that had been retyped in 1946 by my students, E. L. Rvacheva and D. G. Meyzler, even though it had some lacunae. I am convinced that even in this state, Khinchin's work is of considerable interest.