THE Guthrie lecture of the Physical Society is being delivered this year at the Imperial College of Science and Technology, South Kensington, on February 1, by Prof. Arthur H. Compton, of the University of Chicago. Prof. Compton, who is at present Eastman visiting professor at the University of Oxford, is perhaps best known for his discoveries of the laws of interaction between radiation and free electrons, and for the associated effect, called after him, which results in a modification in the quality of a beam of monochromatic radiation such as X-rays on passing through matter. It was for these discoveries that he was awarded the Nobel Prize for physics in 1927. He is also one of the leading authorities on X-rays and the author of one of the finest books on this subject. In recent years, Prof. Compton has turned his attention mainly to the investigation of the cosmic rays, those mysterious and exceedingly penetrating radiations which come into the earth's atmosphere from outside. In this connexion he has organised twelve expeditions, with the collaboration of about a hundred physicists, which have made a cosmic ray survey of the globe. He also initiated, and was scientific director of, the balloon flight of Settle and Fordney in November 1933 for investigating conditions in the upper atmosphere, which achieved what still remains the official world's record altitude of 11·8 miles.