PL
W. de Sitter, „On the relativity of inertia. Remarks concerning Einstein’s latest hypothesis”, Proceedings of the Section of Sciences. Koninklijke Akademie van Wetenschappen te Amsterdam, Vol. XIX, No. 9 i 10, Johannes Müller, Amsterdam, September 1917, pp. 1217–1225 (section: „Mechanics”). Translated to Polish by Robert Janusz.