The first thing to make clear is that scientists, freely making their own choice of problems and pursuing them in the light of their own personal judgment, are in fact co-operating as members of a closely knit organization.

An outstanding teacher; two of his pupils won Nobel Prizes. He emigrated to Germany working at the Kaiser Wilhelm Institute and then to England working at the University of Manchester. He pioneered the theory of fiber diffraction analysis in 1921 and the dislocation theory of plastic deformation of ductile metals and other materials in 1934.