Daniel Christian Ludolph Lehmus (July 3, 1780 in
Soest – January 18, 1863 in
Berlin
Berlin ( ; ) is the Capital of Germany, capital and largest city of Germany, by both area and List of cities in Germany by population, population. With 3.7 million inhabitants, it has the List of cities in the European Union by population withi ...
) was a
German
German(s) may refer to:
* Germany, the country of the Germans and German things
**Germania (Roman era)
* Germans, citizens of Germany, people of German ancestry, or native speakers of the German language
** For citizenship in Germany, see also Ge ...
mathematician
A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, mathematical structure, structure, space, Mathematica ...
, who today is best remembered for the
Steiner–Lehmus theorem
The Steiner–Lehmus theorem, a theorem in elementary geometry, was formulated by C. L. Lehmus and subsequently mathematical proof, proved by Jakob Steiner. It states:
: ''Every triangle with two angle bisectors of equal lengths is isosceles''.
...
, that was named after him.
Lehmus was the grandson of the German poet
Johann Adam Lehmus (1707-1788) and the Berlin-based physician
Emilie Lehmus (1841-1932) was his grandniece. His father Christian Balthasar Lehmus was a science teacher and director of a
gymnasium in Soest, as such he took it upon himself to school his son. From 1799 to 1802 Lehmus studied at universities of
Erlangen
Erlangen (; , ) is a Middle Franconian city in Bavaria, Germany. It is the seat of the administrative district Erlangen-Höchstadt (former administrative district Erlangen), and with 119,810 inhabitants (as of 30 September 2024), it is the smalle ...
and
Jena
Jena (; ) is a List of cities and towns in Germany, city in Germany and the second largest city in Thuringia. Together with the nearby cities of Erfurt and Weimar, it forms the central metropolitan area of Thuringia with approximately 500,000 in ...
. In 1803 he went to Berlin, where he was giving private lectures in mathematics and pursued further studies at the university, which awarded him a
PhD
A Doctor of Philosophy (PhD, DPhil; or ) is a terminal degree that usually denotes the highest level of academic achievement in a given discipline and is awarded following a course of graduate study and original research. The name of the deg ...
in 1811. From December 18, 1813 to Easter 1815 Lehmus was employed as a lecturer (
Privatdozent
''Privatdozent'' (for men) or ''Privatdozentin'' (for women), abbreviated PD, P.D. or Priv.-Doz., is an academic title conferred at some European universities, especially in German-speaking countries, to someone who holds certain formal qualifi ...
) by the university, but in 1814 he became a teacher for math and science at the ''Hauptbergwerks-Eleven-Institut'' (
mining school) in Berlin as well. In 1826 he also assumed a teaching position at the '' Königlichen Artillerie- und Ingenieurschule'' (military engineering school) and was granted the title of a professor at that school in 1827. In 1836 he was awarded the
Order of the Red Eagle
The Order of the Red Eagle () was an order of chivalry of the Kingdom of Prussia. It was awarded to both military personnel and civilians, to recognize valor in combat, excellence in military leadership, long and faithful service to the kingdom, o ...
(4th class). In addition to his two teaching positions Lehmus was giving lectures at the university until 1837 as well.
[Wilhelm Koner: ''Gelehrtes Berlin im Jahre 1845''. T. Scherk 1846, p. 209 () (German)]Siegmund Günther
Adam Wilhelm Siegmund Günther (6 February 1848 – 3 February 1923) was a German geographer, mathematician, historian of mathematics and natural scientist.
Early life
Born in 1848 to a German businessman, Günther would go on to attend several G ...
''Lehmus, Daniel Christian Ludolph.''
In: Allgemeine Deutsche Biographie
(ADB; ) is one of the most important and comprehensive biographical reference works in the German language.
It was published by the Historical Commission of the Bavarian Academy of Sciences between 1875 and 1912 in 56 volumes, printed in Lei ...
(ADB). Volume 18, Duncker & Humblot, Leipzig 1883, p. 147 (German)
Lehmus wrote a number of math and science textbooks, best known was probably his ''Lehrbuch der Geometrie'', which saw several editions. He published articles in various math journals, in particular he was a regular contributor to
Crelle's Journal
''Crelle's Journal'', or just ''Crelle'', is the common name for a mathematics journal, the ''Journal für die reine und angewandte Mathematik'' (in English: ''Journal for Pure and Applied Mathematics'').
History
The journal was founded by A ...
and provided an article for its very first edition in 1826. He published an elegant trigonometric solution of
Malfatti's problem in the French math journal ''Nouvelles Annales de Mathématiques'', but due to a copy error the author's name was given as ''Lechmütz''.
In 1840 Lehmus wrote a letter to the French mathematician
C. Sturm asking him for an elementary geometric proof of the theorem that is now named after him. Sturm passed the problem on to other mathematicians and
Jakob Steiner
Jakob Steiner (18 March 1796 – 1 April 1863) was a Swiss mathematician who worked primarily in geometry.
Life
Steiner was born in the village of Utzenstorf, Canton of Bern. At 18, he became a pupil of Heinrich Pestalozzi and afterwards st ...
was one of the first who provided a proof. In 1850 Lehmus came up with a different proof on his own. The theorem itself proved to be a rather popular topic in elementary geometry being a subject of somewhat regular publications for over 160 years.
[Diane and Roy Dowling]
''The Lasting Legacy of Ludolph Lehmus''
. Manitoba Math Links – Volume II – Issue 3, Spring 2002
Works
*''Aufgaben aus der Körperlehre''. Berlin/Halle 1811
*''Lehrbuch der Zahlen-Arithmetik, Buchstaben-Rechenkunst und Algebra''. Leipzig 1816
*''Lehrbuch der angewandten Mathematik''. Volume I-III, Berlin 1818, 1822 ()
*''Theorie des Krummzapfens''. Berlin 1818
*''Die ersten einfachsten Grundbegriffe und Lehren der höheren Analysis und Curvenlehre''. Berlin 1819
*''Uebungsaufgaben zur Lehre vom Größten und Kleinsten''. Berlin 1823 ()
*''Lehrbuch der Geometrie''. Berlin 1826
*''Sammlug von aufgelösten Aufgaben aus dem Gebiet der angewandten Mathematik''. Berlin 1828
*''Grundlehren der höheren Mathematik und der mechanischen Wissenschaften''. Berlin 1831
*''Anwendung des höheren Calculs auf geometrische und mechanische, besonders ballistische Aufgaben''. Leipzig 1836
*''Kurzer Leitfaden für den Vortrag der höheren Analysis, höheren Geometrie und analytischen Mechanik''. Duncker und Humblot 1842 ()
*''Algebraische Aufgaben aus dem ganzen Gebiet der reinen Mathematik mit Angabe der Resultate''. Duncker und Humblot 1846 ()
*''Grenz-Bestimmungen bei Vergleichungen von Kreisen, welche von demselben Dreieck abhängig sind, sowohl unter sich als auch mit dem Dreieck selbst''. C. Geibel 1851 ()
References
External links
Lecturers in mathematics at the University of Berlin 1810-1945
{{DEFAULTSORT:Lehmus, C. L.
1780 births
1863 deaths
19th-century German mathematicians
Mathematicians from the Kingdom of Prussia