Published
Worcester, Mass. ; New York : Carnegie Endowment for International Peace, Division of Intercourse and Education, [1931]
Notes
A reprint of two addresses, the first delivered in Johannesburg on July 31, 1929, and published in the Report of the British Association for the Advancement of Science, 1929; the second delivered in London on Jan. 29, 1930, as the Trueman Wood lecture, and published in the Journal of the Royal Society of Arts, vol. LXXVIII, Feb. 14, 1930.