Jordanus Nemorarius

d. c. 1260

European Mathematician

Jordanus Nemorarius was the first mathematician to correctly formulate the law of the inclined plane. His writings on geometry were important for explorers who relied on the astrolabe for navigation. Furthermore, Jordanus used letters in place of numbers in his books on mathematics, and was able to articulate general algebraic theorems in this manner. However, his system of algebraic notation was only a distant antecedent to the algebra that is used today. Thus, while Jordanus's work was influential, his system of notation was unused by later mathematicians.

The inspired, but rudimentary, forms expressed in Jordanus's writings are significant because of later developments they anticipated. For instance, since Jordanus substituted letters for numbers, he may be considered to have anticipated algebra as it was subsequently perfected by figures such as René Descartes (1596-1650) in the seventeenth century. However, Jordanus's work did not combine these letters with operational symbols.

Likewise, in a manner characteristic of medieval mathematicians and scientists, Jordanus maintained strong connections between algebra and geometry. To this extent, algebraic equations and formulas were derived from the interpretation of geometric formulas or phenomena. For example, Jordanus's significance as the first to correctly formulate the law of the inclined plane hints at the connections between geometry and algebra in his work. Furthermore, his use of letters to denote the magnitudes of stars in works on mathematical astronomy, such as Tractatus de Sphaera and Planisphaerium, suggest that his observation of the natural world influenced his speculations into mathematics.

However, for medieval scientists and explorers, these connections were of essential importance. Jordanus's work with the inclined plane was particularly significant for exploration. The astrolabe was the most important astronomical instrument of the era and was used to solve complex problems of spherical trigonometry. Jordanus's work with stereographic projections and his articulation of the relations that exist between circles and inclined planes aided explorers and mathematicians in refining and understanding the measurements taken by the astrolabe.

Though Jordanus's texts were of vital importance for medieval science, almost nothing is known of his life. Along with Leonardo Fibonacci (1170?-1240?), Jordanus is regarded as one of the dominant scientific figures of the medieval era. However, his identity itself remains a mystery.

In Latin, the phrase de Nemore (from which Nemorarius is derived) means "of the forest" or may even be used to refer to a forester. However, the same phrase could also refer to someone who comes from a specific area. In the thirteenth century there were many towns and villages named Nemoris or Nemus. Such place-names could be found all across Europe in countries such as Italy, Spain, Belgium, Germany, and France. Evidence based on manuscripts of Jordanus's work suggests to some investigators that he was Italian. Others have argued that Jordanus was German, and identify Jordanus de Nemore with Jordanus de Saxony, an important Dominican friar who was active in the early thirteenth century.

The main problem with this association results from the amount of work produced by both Jordanus de Nemore and Jordanus de Saxony. It seems impossible for one man to have produced the work of two fundamentally different men. Likewise, people did not live very long in the medieval era. Jordanus de Saxony, for example, died while in his fifties. Such facts make the connection between these two men less likely.

Futhermore, the life of Jordanus de Saxony is relatively well documented and does not support the view that he was Jordanus de Nemore. Jordanus de Saxony was German, studied theology in Paris, and became a successful leader of the Dominican order. His training suggests an aptitude in theology and the liberal arts, but does not indicate that he could have exhibited the mastery of mathematics and science found in the works attributed to Jordanus de Nemore.

DEAN SWINFORD