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Abstract

PROF. DE SITTER, who is to give a lecture at the Imperial College of Science and Technology on May 7, on “Problems of Fundamental Astronomy,” and will lecture also at Manchester on May 9, and at Edinburgh on May 18, was a pupil of Kapteyn's, who was invited by Gill in 1896 to work for a time at the Cape. He made determinations of the parallaxes of several southern stars with the heliometer. For his thesis for doctor of science at Groningen he presented a “Discussion of the Heliometer Observations of Jupiter's Satellites.” He has continued these researches and developed a new method for treating the mutual perturbations of the satellites, and is still engaged discussing photographs taken at the Cape and Greenwich for the determination of the necessary constants. After his return to Groningen Prof, de Sitter participated in a number of Kapteyn's investigations dealing with the dimensions and structure of the stellar universe. British men of science owe a debt to Prof, de Sitter for giving during the War, before Einstein's work reached England, three papers in the Monthly Notices of the Royal Astronomical Society which presented to English readers an account of the generalised theory of relativity. Prof, de Sitter has made important contributions to this subject and has examined the various cases where any astronomical verifications maybe obtained.