During
World War II, he supervised numerous government contracts for work on aluminium and magnesium alloys. After the war he returned to Oxford "
to carry on research in intermetallic compounds and problems on the borderland of metallography and chemistry" and remained there for the rest of his working life. In 1938 he was appointed lecturer in metallurgical chemistry. In his research, he concluded that the microstructure of an alloy depends on the sizes of the component atoms, as well as the valency electron concentration, and electrochemical differences. This led to the definition of the
Hume-Rothery rules. In the 1950s he founded the
Department of Metallurgy (which is now the Department of Materials) at the
University of Oxford, and was a fellow of
St Edmund Hall, Oxford. He was also involved in founding the
Journal of the Less-Common Metals, which developed out of an international symposium on metals and alloys above 1200 °C that he organised at Oxford University on 17–18 September 1958. The papers presented at the symposium "The study of metals and alloys above 1200°C" were published as Volume 1 of the
Journal of the Less-Common Metals. He was a member of the Oxford Philatelic Society. == Selected publications ==