Autograph letters and postcards from European physicists and mathematicians to Korn. There are brief as well as long and technical letters, some sent to Korn as editor of PHYSIKALISCHE BERICHTE, some on the presentation of papers at French and German academies, some discussing theories of mathematical physics, and some of a personal nature. Among the correspondents are Albert Einstein, Emile Picard, Max Planck, and Wilhelm Roentgen.