Christian Sophus Juel (25 January 1855,

Randers Randers () is a city in Randers Municipality, Central Denmark Region on the Jutland peninsula. It is List of cities and towns in Denmark, Denmark's sixth-largest city, with a population of 64,511 ().Copenhagen Copenhagen ( ) is the capital and most populous city of Denmark, with a population of 1.4 million in the Urban area of Copenhagen, urban area. The city is situated on the islands of Zealand and Amager, separated from Malmö, Sweden, by the ...

) was a Danish mathematician, specializing in geometry.

Education and career

Juel went to school in

Svendborg Svendborg () is a town on the island of Funen in south-central Denmark, and the seat of Svendborg Municipality. With a population of 27,616 (1 January 2025), Svendborg is Funen's second largest city.Technical University of Denmark The Technical University of Denmark (), often simply referred to as DTU, is a polytechnic university and school of engineering. It was founded in 1829 at the initiative of Hans Christian Ørsted as Denmark's first polytechnic, and it is today ran ...

. From 1876 he studied mathematics at the

University of Copenhagen The University of Copenhagen (, KU) is a public university, public research university in Copenhagen, Copenhagen, Denmark. Founded in 1479, the University of Copenhagen is the second-oldest university in Scandinavia, after Uppsala University. ...

; there he received In 1879 his undergraduate degree in mathematics and in 1885 his Ph.D. (promotion) with thesis ''Inledning i de imaginaer linies og den imaginaer plans geometrie''. From 1894 he was a docent at the Technical University of Denmark, where he became in 1897 a full professor; during this time he also sometimes lectured at the University of Copenhagen. Juel did research on

projective geometry In mathematics, projective geometry is the study of geometric properties that are invariant with respect to projective transformations. This means that, compared to elementary Euclidean geometry, projective geometry has a different setting (''p ...

, algebraic curves, polyhedra, and surfaces of revolution from ovals. In projective geometry, he generalized results of

Karl von Staudt Karl Georg Christian von Staudt (24 January 1798 – 1 June 1867) was a German mathematician who used synthetic geometry to provide a foundation for arithmetic. Life and influence Karl was born in the Free Imperial City of Rothenburg, which is n ...

and independently obtained results similar to those of

Corrado Segre Corrado Segre (20 August 1863 – 18 May 1924) was an Italian mathematician who is remembered today as a major contributor to the early development of algebraic geometry. Early life Corrado's parents were Abramo Segre and Estella De Ben ...

. In addition to a monograph on projective geometry, Juel wrote textbooks dealing with stereometry, rational mechanics, and introductory mathematics for chemists. From 1889 to 1915 he was an editor of ''Matematisk Tidsskrift''. In 1922 he was made a member of the Finnish Academy of Sciences. In 1925 he was made a member of the Norwegian Academy of Sciences and an honorary member of the Danish Mathematical Association. In 1928 he was an

invited speaker at the International Congress of Mathematicians An invitation system is a method of encouraging people to join an organization, such as a Club (organization), club or a website. In regular society, it refers to any system whereby new members are chosen; they cannot simply apply. In relation to w ...

at Bologna and gave a talk ''Beispiele von Elementarkurven und Elementarflächen''. His wife's father was the mathematician and astronomer Thorvald Nicolai Thiele. Juel was awarded in 1913 a rank of Knight (''Ridder'') in 1913 and in 1921 a rank of the Cross of Honour (''Dannebrogordenens hæderstegn'') of the

Order of Dannebrog The Order of the Dannebrog () is a Danish order of chivalry instituted in 1671 by Christian V. Until 1808, membership in the Order was limited to fifty members of noble or royal rank, who formed a single class known as ''White Knights'' t ...

Selected works

*''Vorlesungen über Projektive Geometrie mit besonderer Berücksichtigung der von Staudtschen Imaginärtheorie'', Grundlehren der mathematischen Wissenschaften, Springer Verlag 1934
Online
*''Vorlesungen über Mathematik für Chemiker'', Kopenhagen 1890 *''Elementar stereometri'', Kopenhagen, 1896 *''Analytisk stereometri'', Kopenhagen, 1897 *''Ren og anvendt aritmetik'', Kopenhagen 1902; 153 pages
''Forlaesinger over rationel mekanik''
Kopenhagen 1913, 2nd edition 1920
''Grundgebilde der projectiven Geometrie''
Acta Mathematica, vol. 14, 1890, 1–30 *''Über die Parameterbestimmung von Punkten auf Curven zweiter und dritter Ordnung. Eine geometrische Einleitung in die Theorie der logarithmischen und elliptischen Functionen'', Mathematische Annalen, vol. 47, 1896, 72-10
Online
*

Sources

*Herbert Oettel in

Dictionary of Scientific Biography The ''Dictionary of Scientific Biography'' is a scholarly reference work that was published from 1970 through 1980 by publisher Charles Scribner's Sons, with main editor the science historian Charles Coulston Gillispie, Charles Gillispie, from Pri ...

References

{{DEFAULTSORT:Juel, Christian 1855 births 1935 deaths 19th-century Danish mathematicians 20th-century Danish mathematicians People from Randers University of Copenhagen alumni Academic staff of the Technical University of Denmark Danish knights