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25 Jan 1855 
Randers, Denmark 
24 Jan 1935 
Copenhagen, Denmark 
Christian Juel's father was a judge but Christian never knew him for he died before Christian was one year old. He was brought up in the country and attended the Realschule in Svendborg, a coastal town in southern Funen Island, Denmark. When he was fifteen years old he went to Copenhagen and, in the following year, he entered the Technical University of Copenhagen. He studied at the Technical University from 1871 until 1875, then he decided that technical studies were not to his liking and that he would prefer to study pure science in general and pure mathematics in particular. In January 1876 Juel took the entrance examinations for the University of Copenhagen and completed his first degree there in 1879. Continuing with his doctoral studies at the University of Copenhagen he received his doctorate in 1885 for a dissertation on geometry. Juel had spent sixteen years completing his university education and so, despite starting young, was 30 years old before he received his doctorate. Juel taught at the Polytechnic Institute in Copenhagen from 1894, being promoted to a full professorship three years later. He also sometimes lecturer at the University of Copenhagen. Juel married a daughter of the professor of mathematics in Copenhagen, Thorvald N Thiele . He made substantial contributions to projective geometry and wrote an important book on the topic. His approach is similar to that of von Staudt but goes beyond von Staudt 's in places. Although he was not alone in making these improvements, since Corrado Segre also proved similar results, but there is no doubt that Juel's results were obtained independently of Corrado Segre . Juel also worked on the theory of finite equal polyhedra and on oval surfaces. In 1914 he introduced the concept of an elementary curve : ... which is in the projective plane without straightline segments and has the topological image of a circle and a tangent at every point. Outside these points a convex arc can be described on each side. Thus an elementary curve consists of an infinite number of convex arcs passing smoothly one into another.
Although these ideas are clever, Juel did not treat them with care and his writings on this topic, although interesting, are less than precise and leave something to be desired. Juel served mathematics in other important ways. He was an editor of Matematisk Tidsskrift for over 25 years from 1889 until 1915. He also wrote textbooks for school level mathematics as well as for university level mathematics courses. Among the honours which he received was being elected to honorary membership of the Mathematical Association in 1925, then receiving an honorary degree from the University of Oslo four years later.
Source:School of Mathematics and Statistics University of St Andrews, Scotland
