Lectures and Addresses The lectures and writings deal with such topics as economic aid, world poverty, population growth, and the disparity between 'rich' and 'poor' countires. Blackett described the latter as the 'Gap', a term which he used and adapted in various ways as the title of several of his published works on the subject. See G.60, G.72, G.120, and also H.57-73, H.146-153. The material is presented chronologically. 1953-1970