Ewald was one of the founders of x-ray optics and structural crystallography. He came to Cambridge as a refugee from Nazi Germany in 1937, subsequently moving to Queen's University Belfast as lecturer and then professor. In 1949 he moved to the USA as head of the physics department at the Polytechnic Institute of Brooklyn, New York.

Hodgkin first corresponded with Ewald in 1934 about her paper on the interpretation of Weissenberg photographs (Bibliog. 12).