Originally Posted by ade_mcc
If it helps, Physics for Entertainment was originally published in 1913 (according to wikipedia) and Yakov Perelman died in 1942.
Given that I am based in the UK, are there other places that I can safely upload?
It is public domain in the US (it was published before 1923), it is public domain in Canada (its author died more than 50 years ago), but it is not
public domain in the UK (its author died less than 70 years ago). So, MobileRead can legally host it, but you cannot legally upload it from the UK; whether or not you care about that, that's a different matter
Note, however, that the above refers to the original Russian text (assuming the original was in Russian, which I don't know). For any translation, one would have to consider the date of publication of the translation
and the date of death of the translator