THE Guthrie Lecture for this year of the Physical Society is being delivered at the Imperial College of Science and Technology, South Kensington, at 5 p.m. on May 15 by Prof. F. A. Lindemann, professor of experimental philosophy in the University of Oxford, whose subject is “Physical Ultimates”. Prof. Lindemann has carried out theoretical and experimental researches in various branches of physics. Before the Great War he was distinguished for his work on the specific heat of solids at low temperatures; the Nernst-Lindemann formula was a pioneer attempt to connect the specific heat of a substance with its characteristic frequencies. During the War he was attached to the Royal Air Force, and the apparatus which he evolved and the experiments he performed himself in actual flight on the causes and elimination of spin were recognised as of the highest importance. In 1919, at a very early age, Prof. Lindemann was appointed to the chair which he now occupies at Oxford. He has written papers on the origin and nature of magnetic storms, and his research work on meteors gave the first indication of the then unsuspected rise of temperature at heights of about 50 km. hi the upper atmosphere, which has since been verified in other ways. His development of photo-electric cells and the electrometer which bears his name have been of incalculable service, not only to the solution of the astronomical problems which interested him and his father, who had his own observatory at Sidmouth, but also to physicists in general. Recently he has turned his attention to the more philosophical aspects of physics, and in his book on the “Physical Significance of the Quantum Theory”, he has attempted to clear up certain difficulties connected therewith.