Dear Pavel Sigizmundovich,
I'm sending you a brief note regarding the question about the possible
shape of the universe more general than the cylindrical world of
Einstein, and the spherical world of De Sitter; aside from these two cases
there appears also a world, the space of which possesses a curvature
radius _varying_ with time; it seemed to me that a question of
this sort may interest you or De Sitter. In the near future I will
send you a German translation of this note, if you find the question
considered in it interesting, then please be so kind to have it
placed in some journal. Send my regards to Tatyana Alekseevna.
Please be so kind, due to mail malfunction, to confirm
the receipt of this letter.
3 June 1922,
Sincerely yours,
A. Friedmann
P.S. Please be so kind to ask De Sitter to send me an offprint of his
work "On Einsteins theory etc"; Monthly Notices R. Acad. Soc. 1917. It
can be found in Pulkovo, but getting the journal from there is almost
impossible, and walking over there is very hard.
Petrograd, Main Physics Observatory, to Friedmann.