THE early years of the twentieth century saw a recrudescence of the movement towards international intercourse in science. The natural philosophers of previous centuries, so far as they were free to carry on their studies, enjoyed a peculiar individual licence to visit and maintain communication with their brethren in other lands. With the growth of science itself, those associated with it began to band themselves together for the more frequent discussion of the many topics in which they were interested, and it was natural that such groups, at first local, should with the improvement of communications become national in scope. The national bodies continued to maintain a limited amount of intercourse by the exchange of publications and by the election of distinguished men of science as foreign members, but this in turn became inadequate to meet the needs of the rising tempo of scientific discovery and its applications. Thus were born the international associations, with regular meetings held at intervals of a year or more, attended by individuals and delegate bodies, and with international secretariats to transact their business during the intervals between successive meetings.