Person: Dandelin, Germinal Pierre
Germinal Dandelin was a French mathematician best known for a method of approximating the roots of an algebraic equation.
Mathematical Profile (Excerpt):
- They lived in Ghent and, in 1807, Dandelin entered the lycée there.
- However, Dandelin volunteered for military service and joined the Escaut National Guard as a sergeant.
- Dandelin returned to the Lycée where he completed his school education being awarded First Prize in Mathematics in August 1813.
- In November 1813 Dandelin began his university studies at the École Polytechnique in Paris.
- When the allied armies arrived near Paris on 30 March 1814, Dandelin was in the opposing French army defending the walls of the city.
- During Napoleon's time back in control of France, Dandelin worked at the Ministry of the Interior under the command of Lazare Carnot who presented him with the Légion d'Honneur for his bravery in the defence of Paris in the previous year.
- After Napoleon was defeated at Waterloo, Dandelin returned to Belgium.
- Prince Bernhard, who had noticed how talented Dandelin was, also arranged for him to become second lieutenant in the military engineering corps on 16 April 1817.
- Back in Ghent, Dandelin renewed his friendship with Adolphe Quetelet whom he had become friendly with while studying at the Lycée in Ghent.
- They shared interests in mathematics, literature and music, with Dandelin being an excellent violinist.
- Dandelin continued his military career as an second lieutenant in the engineering corps.
- Quetelet was able to talk to the right people so that Dandelin might obtain a university post.
- However, Dandelin had always wanted to have a position in Brussels and made his wishes known to General Buzen who, at the time, was the Minister of War.
- However, Dandelin's health rapidly deteriorated and he suffered a painful end to his life at the age of only fifty-two.
- Dandelin, having lost out on his university education, received most of his early mathematical influence from Quetelet, who was two years younger than him, and his early interests were in geometry.
- Dandelin proved an important theorem on the intersection of a cone and its inscribed sphere with a plane.
- Dandelin's generalisation gives independent proofs of the theorems of Pascal and Brianchon.
- This 1826 paper is considered by most to be Dandelin's finest contribution.
- Dandelin also worked on stereographic projection of a sphere on a plane, publishing an important contribution in "Mémoire sur l'emploi des projections stéréographiques en géométrie" Ⓣ(Memoir on the use of stereographic projections in geometry) (1827).
- He gave a method of approximating the roots of an algebraic equation, now named the Dandelin-Gräffe method, and published this in "Recherches sur la résolution des équations numériques" Ⓣ(Researches on solving numerical equations) (1826).
- Dandelin then considers the possibility of accelerating both processes by applying them to the equation whose roots are the squares of those of the original.
- However, Dandelin had afterthoughts which he recorded in four appendices, and in the second of these he goes further into the matter of root squaring, making two important observations that are not always to be found in modern treatments.
- Among the honours which Dandelin received was election to the Royal Belgium Academy of Science in Brussels on 1 April 1822.
Born 12 April 1794, Le Bourget, near Paris, France. Died 15 February 1847, Brussels, Belgium.
View full biography at MacTutor
Thank you to the contributors under CC BY-SA 4.0! 
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- non-Github:
- @J-J-O'Connor
- @E-F-Robertson
References
Adapted from other CC BY-SA 4.0 Sources:
- O’Connor, John J; Robertson, Edmund F: MacTutor History of Mathematics Archive
