# Jordanus de Nemore

Jordanus Nemorarius (also Jordanus de Nemore ) was a mathematician and mechanic of the early 13th century.

## Life

His life data are not recorded, but can be inferred from the mention of his writings in other dated works that he had in the first half of the 13th century. In the catalog Biblionomia of Richard de Fournival from Amiens from the period 1246 to 1260 twelve of his works are listed. Some historians assume an identity with the Dominican Jordan of Saxony, but this is not conclusive to prove. Commonly reported survival data are those of Jordan of Saxony. Besides this identification with Jordan of Saxony have no contemporary list of clerics found references to him, so that he may have been no clergyman.

In a manuscript, there is a handwritten addition which suggests a teaching at the University of Toulouse, but the attribution to Jordanus was doubted.

The origin of the name of the additive de Nemore is unclear. A place of this name as Nemus can be determined by Edward Grant (Dictionary of Scientific Biography ) do not identify with certainty (eg Nemi ( Lazio ) ), according to Moritz Cantor, he refers to Latin Nemus (forest ) and is used by him to support his identification with Jordan used of Saxony, in the sense of coming from a wooded area. The name could also originate to his employment with arithmetic ( Corrupted by de numero de or numeri ).

## Works

He wrote numerous books on arithmetic, algebra, geometry and astronomy. The transcript of his works was probably by his students. Until the 17th century, his works were often in use. In his major work, the Liber de numeri Datis, he explains, among other things, the solution of quadratic equations using a method similar to that of al - Khwarizmi, however, in general terms, since for the first time letter symbols replace concrete figures.

Of particular importance, it is also for the history of mechanics. The first correct description of the statics of weights derived on an inclined plane from him. According to Pierre Duhem found in Jordanus also the first use of the principle of virtual work in its description of the lever.

A total of six drives are mapped Jordanus Nemorarius with certainty:

- Communis et consuetus ( Opus numerorum ). After Gustav connected Eneström a shorter, older version of Demonstrationes de algorismo (see below) .. The work ( and the below-mentioned longer version Demonstrationes de algorismo ) is a short treatise Tractatus minutiarum (after Eneström ) about fractions.
- De elementis arismetice artis - first medieval book on number theory. It was in 1496 ( and in several editions until 1514) printed in Paris with his own additions, comments and evidence of Jacques Lefèvre d'Etaples.
- Expositions de plana spera (via stereographic projection). It is based on the treatment of Claudius Ptolemy in his treatise Planisphaerium. In it is generally shown for the first time that doing circles are mapped to circles. It was printed in 1536 in Basel ( Planispherium ) and in Venice in 1558 by Federico Commandino.
- Elementa super demonstrationem ponderum (or Elementa de ponderibus ) on mechanics
- Liber de numeri Datis ( 4 volumes, university textbook on algebra, linear and quadratic equations and systems of equations ).
- Liber de philotegni triangulis ( on geometry )

Other works are also attributed Jordanus Nemorarius, in which case the association is not backed up:

- De isoperimetris ( about Isoperimetric Figures)
- De proportionibus
- De ratione ponderis (via weights )
- Demonstrationes de algorismo ( explanation of the Arabic number system )

He had such a prominent position in the teaching of arithmetic and static in the Middle Ages, that much appeared under his name, which came from the hands of others and later printed as a book, for example, algorithm demo stratus Jordani (Nuremberg, 1534) after an anonymous manuscript that is found in the estate of Regiomontanus.

Excerpts of his writings mechanical (or Jordanus ascribed writings ) published in the 16th century, for example, by Peter Apian (Nuremberg, 1533) and Nicolo Tartaglia ( Quesiti et INVENTIONI diverse, first Venice 1546). From manuscripts in the estate of Tartagalia ( De ratione ponderis ) published Curtius Trojanus 1565 ponderositate in Venice Jordani Opusculum de.