An Adaptation of Major Grant's Graphical Method of Predicting Occultations to the Elements Now Given in the Nautical Almanac by CROMMELIN - LONGITUDE AT SEA - 1902

London: William Cloves, 1902. 8vo. 6 pages, plus 2 large folding diagrams. A rare separate offprint printed for the Royal Geographical Society. Publisher's blue titled wrappers, string-tied and bearing the society's crest. Some light foxing, otherwise in very good and original condition. The author, a respected astronomer and well-known authority on comets, renders praise to the primary research and calculations of Major S.C.N. Grant in 1896, which forms the basis for his dissertation. With meticulous and detailed instruction Crommelin presents a simplified method to predict and decipher the instantaneous and momentary occultation of stars which greatly simplifies the detremination of Longitude at Sea. He further introduces the application to the Solar Eclipse phenomenon. Exceedingly rare dissertation by an important nineteenth century astronomer. Six years prior to Crommelin's study, Grant published a six page report and illustration, titled "Diagram for Determining the Parallaxes in Declination and Right Ascension of a Heavenly Body, and its Application to the Prediction of Occultations." Crommelin was famed for his computations of cometary orbits. He took part in expeditions to observe total solar eclipses in 1896, 1900, 1905, 1912, and 1927. In 1919 he participated in the solar eclipse expedition to Brazil which aimed to determine the amount of the deflection of light caused by the gravitational field of the Sun. The results from these observations were crucial in providing confirmation of the General Theory of Relativity, which Albert Einstein had proposed in 1916..