Dutch amateur astronomer Cornelis Easton studied French and obtained qualifications to teach that language in secondary schools, but in the end he became a journalist and newspaper editor. As a teenager he became interested in astronomy, inspired by the writings of Camille Flammarion. During most of his career he was active as an amateur astronomer and contributed important papers in international, professional astronomical journals on aspects of the Milky Way. Much material in this paper is based on a hand-written Notebook, which is an autobiographical account of his astronomical work. This concerned three areas. The first of these derived from his enthusiasm as a youth for mapping the Milky Way. Mapping the Milky Way was induced by Friedrich Argelander’s book (translated into Dutch by the son of Frederik Kaiser, founder of the new Leiden Observatory), who recommended it as an observational project for astronomers without a telescope. The resulting book, La Voie Lactée dans l’Hémisphère Borèal, which Easton published in 1893, made some impression. In addition to drawings of the surface brightness of the Milky Way, it also contained extensive descriptions and discussions of features in the structure, and a comprehensive, essentially complete, listing and discussion on everything that had ever been published on the Milky Way, so this stood out as by far the most impressive book on this subject. Later Easton produced an isophotal chart and used photographs to improve the map. Comparison with Pannekoek’s similar work showed excellent agreement. While observing the Milky Way for many hours, Easton had been struck by the idea that what he saw was actually a spiral nebula, of which he had seen illustrations in books, but then seen edge-on. He proposed a form for the spiral in the Milky Way System that resembled these nebulae with the center in the direction of the constellation Cygnus. His publications on this ‘Theory of the Milky Way’ in the Astrophysical Journal in 1900 and 1913 drew much attention, although many astronomers, including Jacobus Kapteyn, had some reservations. The third area concerned correlations between surface densities of stars and surface brightness of the Milky Way. Easton maintained that there was such a correlation for relatively bright stars, in particular for stars of magnitude nine in the Bonner Durchmusterung. This would mean that the Milky Way clouds would have to be rather close by. This contradicted Pannekoek’s work, who maintained that such a correlation only started around apparent magnitude 14 or so, and pointed at a much larger Galactic system. There is a publication Easton failed to discuss in his Notebook, in his list of his publications, and that is an 1894 short paper that appeared in Nature. He noted that the elliptical companion NGC205 of the Andromeda Nebula between pictures in 1874 and 1889 had rotated by 15°. This observation in fact was correct; the later photograph goes to fainter surface brightnesses and the now known isophote twists are responsible for the apparent rotation. In 1903 Kapteyn and the University of Groningen bestowed an honorary doctorate upon Easton. This special honor was granted on the occasion of Kapteyn’s 25th anniversary of becoming a Professor at the University. For Easton it meant an important recognition of his work by the professional astronomical community. During the visit of Harlow Shapley and his wife to the Netherlands in 1922, after the first General Assembly of the International Astronomical Union in Rome, and a discussion session held in Leiden, Easton turned out to be the only one to oppose Shapley’s view of a large Galactic system by defending his correlation studies. After the 1900 publication of his spiral nebula theory, Easton directed an increasing fraction of his attention to climate studies. Contributing, he felt, to observational astronomy was no longer possible without professional equipment. For a number of years he chaired the board of the amateur astronomers and meteorologists society and the editorial board of its magazine Hemel & Dampkring, saving it from bankruptcy and giving it a healthy financial basis. In reaction to the request of one of the referees of this paper I provide in an End Note translations into English of titles that originally were in Dutch, French, German, etc.
Pieter C. Van der Kruit (Mon,) studied this question.