AFTER fifty years devoted to teaching and research, Prof. Charles Fabry is retiring from the chair he has held in the Sorbonne, Paris. In his scientific career, Prof. Ch. Fabry has been pre-eminent for his work in optics. His interferometric work, with his determination (with Pérot and Benoit) of the length of the standard metre in wave-lengths of the monochromatic radiation of cadmium, has long been classical. His studies on the spectrum of the iron arc, his pioneer work on the mercury arc lamp, and on the application of interferometry to spectroscopic research must also be recalled. To a somewhat later period belong his researches in photometry and astrophysics. The microphotometer he designed with Prof. H. Buisson, and his studies on photographic density also represent pioneer work in a field which has since seen a wide development along the lines he predicted. During recent years, Prof. Fabry's interest has turned towards meteorological optics. Under his direction, researches on the composition of the upper atmosphere and its ozone content are being carried on by a group of his pupils. Soon after the Great War, Prof. Fabry founded in Paris the Institut d'Optique, of which he is still director. The activity of this institution has been devoted to industrial optics as well as to scientific investigation, to teaching and to the designing of optical parts as well as to research. The Revue d'Optique, also founded by Prof. Fabry, is published by the Institut d'Optique.