PROF. WILLIAM WILSON, who has recently retired from the Hildred Carlile chair of physics at Bedford College, University of London, spent his student days at the Universities of London and Leipzig, and he found much to admire in the freedom of the German university system of those days and in the men who sustained it. In his early years as a physicist, he carried out much pioneer experimental work on photo-electric emission and developed a quantum theory of thermionic emission, which was published in 1912. By 1915 he had discovered the quantum relation ∫p.dq = n.h, and by introducing two quantum numbers, he found an expression for the eccentricities of the elliptic orbits of electrons; thus he opened up a large field of progress in the study of atomic structure. In 1921 he introduced the concept of generalized momentum into the theory of the electromagnetic field, and has since become much interested in Kaluza's five-dimensional theory of relativity. He was elected a fellow of the Royal Society in 1923.