Sommerfeld recommended Bethe for a Rockefeller Foundation Travelling Scholarship in 1929. This provided $150 a month (about $3,000 in 2023 dollars) to study abroad. In 1930, Bethe chose to do postdoctoral work at the Cavendish Laboratory at the University of Cambridge in England, where he worked under the supervision of Ralph Fowler. At the request of Patrick Blackett, who was working with cloud chambers, Bethe created a relativistic version of the Bethe formula.