Editing Georg Mohr

{{Short description|Danish mathematician}}
{{For|the chess player|Georg Mohr (chess player)}}
[[File:Georg_Mohr.png|thumb]]
{{Use dmy dates|date=February 2025}}
'''Jørgen Mohr''' (Latinised ''Georg(ius) Mohr''; 1 April 1640 – 26 January 1697)<ref name="mactutor"/> was a [[Denmark|Danish]] [[mathematician]], known for being the first to prove the [[Mohr–Mascheroni theorem]], which states that any geometric construction which can be done with [[compass and straightedge]] can also be done with compasses alone.

==Biography==
Mohr was born in [[Copenhagen]], the son of a tradesman named David Mohrendal.<ref name="mactutor">{{MacTutor Biography|id=Mohr}}</ref> Beginning in 1662 he traveled to the [[Netherlands]], to study mathematics with [[Christiaan Huygens]].<ref name="mactutor"/><ref name="impression">{{citation|title=An Impression of Mathematics in Denmark in the Period 1600–1800|first=Kirsti|last=Andersen|doi=10.1111/j.1600-0498.1980.tb00381.x|journal=Centaurus|volume=24|issue=1|year=1980|pages=316–334|bibcode=1980Cent...24..316A}}.</ref> In 1672 he published his first book, ''[[Euclides Danicus]]'', simultaneously in Copenhagen and Amsterdam, in Danish and Dutch respectively. This book, proving the Mohr–Mascheroni theorem 125 years earlier than [[Lorenzo Mascheroni]], would languish in obscurity until its rediscovery in 1928.<ref name="gla">{{citation
 | last = Alexanderson | first = Gerald L. | author-link = Gerald L. Alexanderson
 | date = July 2014
 | doi = 10.1090/S0273-0979-2014-01458-2
 | issue = 3
 | journal = Bulletin of the American Mathematical Society
 | pages = 463–467
 | title = About the cover: Two theorems on geometric constructions
 | volume = 51| doi-access = free
 }}.</ref> Mohr served in [[Franco-Dutch War]] in 1672–1673, and was taken prisoner by the French.<ref name="mactutor"/><ref name="impression"/> By 1673, he had published his second book, ''Compendium Euclidis Curiosi''.<ref name="impression"/> A third book was later mentioned by Mohr's son; for many years this was believed to be the ''Gegenübung auf Compendium Euclidis Curiosi'' but {{harvtxt|Andersen|Meyer|1985}} argue that it must be a different book, and that the ''Gegenübung'' has a different author.<ref name="mactutor"/><ref name="am85">{{citation
 | last1 = Andersen | first1 = Kirsti
 | last2 = Meyer | first2 = Henrik
 | doi = 10.1111/j.1600-0498.1985.tb00833.x
 | issue = 2
 | journal = Centaurus
 | mr = 825846
 | pages = 139–144
 | title = Georg Mohr's three books and the ''Gegenübung auf Compendium Euclidis Curiosi''
 | volume = 28
 | year = 1985| bibcode = 1985Cent...28..139A
 }}.</ref> As well as his work on geometry, Mohr contributed to the theory of [[nested radical]]s, with the aim of simplifying [[Cardano's formula]] for the roots of a [[cubic function|cubic polynomial]].<ref name="am85"/>

While in the Netherlands, Mohr became a friend of [[Ehrenfried Walther von Tschirnhaus]]. The two visited [[Gottfried Wilhelm Leibniz]] in France and [[John Collins (mathematician)|John Collins]] in England together. Mohr returned to Denmark in 1681; he had dedicated ''Euclides Danicus'' to [[Christian V]] and hoped for a position in exchange, but was offered only a position as a shipyard supervisor, which he declined. He married Elizabeth von der Linde of Copenhagen on 19 July 1687, and soon after returned to Holland; their son, Peter Georg Mohrenthal, eventually settled in [[Dresden]] as a bookseller and publisher.<ref name="impression"/><ref>{{citation|title=''Euclides danicus'', Amsterdam 1672 by Georg Mohr; Johannes Hjelmslev; ''Beiträge zur Lebensbeschreibung von Georg Mohr'' (1640–1697) by Johannes Hjelmslev|first=George|last=Sarton|author-link=George Sarton|journal=[[Isis (journal)|Isis]]|volume=26|issue=1|year=1936|pages=167–170|jstor= 225067|doi=10.1086/347140}}.</ref> In 1695 he took a job with Tschirnhaus,<ref name="impression"/> and spent his last few years as a guest in Tschirnhaus's house. He died in [[Sławnikowice, Lower Silesian Voivodeship|Kieslingswalde]] near [[Görlitz]], Germany.<ref name="mactutor"/>

The [[Georg Mohr competition]], which is used to select Danish participants to the [[International Mathematical Olympiad]], is named after Mohr.<ref>Official website for the [http://www.georgmohr.dk/ Georg Mohr-Competition] (in Danish), retrieved 27 June 2014.</ref>

==References==
{{reflist}}

==Further reading==
*{{citation|title=Mohr, Georg|series=The Galileo Project|url=http://galileo.rice.edu/Catalog/NewFiles/mohr.html|first=Richard S.|last=Westfall|year=1995}}
*{{citation|contribution=Mohr, Georg|title=Complete Dictionary of Scientific Biography|year=2008}}.

{{Authority control}}

{{DEFAULTSORT:Mohr, Georg}}
[[Category:1640 births]]
[[Category:1697 deaths]]
[[Category:17th-century Danish mathematicians]]