THE twenty-first annual exhibition of the Physical and Optical Societies was opened by Sir Arthur Eddington, president of the Physical Society, on Tuesday, Jan. 6. Sir Arthur commented on the growth of the exhibition since its inception in 1905, and spoke of the mutual debt of the scientific worker and the instrument maker, saying that progress is making them more and more interdependent. All types of apparatus for physical and optical work could be seen at the exhibition, and everyone should find something of particular interest to himself. Sir Frank Smith proposed a vote of thanks, and this was seconded by Mr. H. T. Tizard, Rector of the Imperial College, where the exhibition was housed.