Stephen Timoshenko’s letters to Paul Ehrenfest, recently discovered at the museum Boerhaave, Leiden, The Netherlands

This article presents and discusses the letters sent by Stephen Timoshenko (1878-1972) to Paul Ehrenfest (1880-1933). The first three postcards were sent during a trip abroad to St. Petersburg, where Ehrenfest then lived, while the fourth letter was sent from St. Petersburg to Leiden in 1913 when Ehrenfest was working at Leiden University. The last letter mentions a refined theory for beams, which considers the effect of rotational inertia and shear deformation. The letters were found in the Ehrenfest archive at the Boerhaave Museum in Leiden. It seems that these letters have a certain historical interest and allow us to better understand the interaction between the two outstanding scientists. We take the liberty of providing both the Russian transliterations of these letters as well as their translations into English, so both the Russian (the language these letters were written in) and English readers would have full access to their contents.