Willem Hendrik ("Wim" amongst his family) van den Bos, astronomer, was a son of Willem Hendrik van den Bos, a teacher, and his wife Antonia Johanna Rijken, also a teacher and a musician. He studied astronomy under Professor Willem de Sitter* at the University of Leiden and was awarded his doctorate (Dr. Math. and Phys.) in 1925 with a thesis on double stars. Meanwhile he worked at the Leiden Observatory as an assistant from 1921 and as an observer from 1923. While still a student he met Cornelia Johanna Francisca ("Corrie") Manders, with whom he shared his love of music. They were married in August 1923 and during the next eight years had a son and two daughters. Meanwhile Professor de Sitter had made arrangements with R. T. A. Innes*, Director of the Union Observatory in Johannesburg, which enabled van den Bos to spend three years at the observatory as the Leiden astronomer to assist Innes in his work on double stars with the observatory's new 673 mm refractor. He arrived in Johannesburg in August 1925 and at the end of his contract period applied for and was granted an extension of the loan of his services to the Union Observatory for a further two years. This enabled him to meet the five year residence requirement to become a naturalized South African citizen, which allowed him to obtain a permanent appointment at the observatory. He was appointed chief assistant to the new director, H. E. Wood*, in October 1930. The whole family returned to Europe in 1935 so that van den Bos could attend the congress of the International Astronomical Union (IAU) in Paris. At the invitation of Dr Voûte, director of the Indonesian Observatory at Lembang, he and his wife visited Indonesia to consider the possibility of becoming Voûte's successor, but eventually they decided against it. They then extended their trip into a world tour which included a lengthy stay in the United States where van den Bos visited several observatories, as well as visits to Java, Hawaii, Japan and China.
Early in 1941 van den Bos succeeded Wood as Union Astronomer, with W. S. Finsen as his chief assistant. He retained this post until his retirement in 1956. During his term in office the observatory improved its time service with the installation of modern quartz clocks. However, he is remembered mainly for his life-long dedication to the study of visual double stars, which earned him enduring fame. With exceptional skill and keen eyesight he discovered 2895 new double stars during his lifetime. In the process he, with Innes and Finsen, investigated all the stars south of declination -19° with a brightness down to the ninth magnitude in search of double stars. His work required over 70 000 observations, which Finsen (1974) claimed was a world record. He also compiled a comprehensive catalogue of previous observations of southern double stars and these were incorporated in the Index catalogue of visual double and multiple stars, covering the whole sky, published in 1963 in collaboration with H. M. Jeffers and F. M. Greeby of the Lick Observatory. In addition he computed and published the orbits of almost 100 binaries, using methods that he developed himself but that came to be accepted by other astronomers as standard procedures. He came to be recognized as a world authority in double star astronomy and served as president of the Double Star Commission of the IAU for an unusual and unbroken period of 14 years. In addition to his work on double stars he discovered about a hundred new minor planets. He published numerous papers during the nineteen-twenties to nineteen-sixties, dealing mainly with his double star observation and the calculation of orbits.
After his retirement van den Bos and his wife left South Africa early in 1957 on an extended tour during which he worked at several leading observatories in the United States, including Mount Palomar. Upon his return, from 1959 to 1961, he continued working at the Union Observatory as a guest astronomer on a research grant from the Council for Scientific and Industrial Research. He then spent two years as an assistant professor at the University of California and made observations at the university's Lick Observatory. His observational work finally came to an end in 1966 as a result of severe illness.
In recognition of his work van den Bos was awarded the gold medal of the Royal Danish Academy and the Gill Medal of the Astronomical Society of Southern Africa. He served as president of the society in 1943 and 1955. In 1969 the Double-star Colloquium of the IAU, held in Nice, France, was dedicated to him as a mark of the esteem in which he was held. He was a man with a charming personality and in his dealings with a young astronomer (Hirst, 1974) was meticulous in answering questions and treated his protégé as a colleague rather than a student.
Van den Bos and his wife both developed their musical talents over the years. Both were competent pianists but Willem's strength was the flute while Corrie was a singer. They helped to organize several concerts and Willem later became first flautist of the Johannesburg Symphony Orchestra.
