Jordanus de Nemore
[2] A fourteenth-century chronicle of the Order of Preachers by the Englishman Nicholas Trivet (or Triveth, 1258–1328) suggested that the second master-general of the Dominican Order, Jordanus of Saxony (d. 1237) wrote two mathematical texts with titles similar to two by Jordanus de Nemore, but this late suggestion is more likely a confusion on the part of Trivet, rather than any proof of identity.
Jordanus of Saxony never uses the name “de Nemore” and is nowhere else credited with mathematical writings – in fact he had lectured in theology at the University of Paris.
The De ratione ponderis also proves the conditions of equilibrium of unequal weights on planes inclined at different angles – long before it was re-established by Simon Stevin (with his clootcrans -- "wreath of spheres" experiment) and later by Galileo.
Jordanus took what Joseph Brown has called the "Logician’s Abstract of On the Karaston" (a skillful compression of the conclusions of Thābit ibn Qurra’s Liber karastonis) and created a new treatise (7 axioms and 9 propositions) in order to establish a mathematical basis for the four propositions on the Roman balance called the Liber de canonio.
There are 5 algorismi treatises in this category, examined by Gustaf Eneström early in the twentieth century, dealing with practical arithmetic.
The Communis et consuetus (its opening words) appears to be the earliest form of the work, closely related to the much expanded Demonstratio de algorismo.
Eneström thought it highly unlikely, however, that this version was the work of Jordanus since no manuscript ascribes it to him (if they give an author, it is generally a Magister Gernarus, or Gerhardus or Gernandus).
Definitions, axioms and postulates lead to propositions with proofs which are somewhat sketchy at times, leaving the reader to complete the argument.
Here also Jordanus uses letters to represent numbers, but numerical examples, of the type found in the De numeris datis, are not given.
[5] The editor of this treatise on algebra, Barnabas Hughes, has found two sets of manuscripts for this text, one containing 95 propositions, the other, 113.
Jordanus used a system similar to that of Viète (although couched on non-symbolic terms) of formulating the equation (setting out the problem in terms of what is known and of what is to be found), of transforming the initial given equation into a solution, and the introduction of specific numbers that fulfil the conditions set by the problem.
Again there are two versions of this text: the shorter and presumably first edition (the Liber philotegni Iordani de Nemore) and a longer version (Liber de triangulis Iordani) which divides the text into books, re-arranges and expands book 2, and adds propositions 4-12 to 4-28.
The De proportionibus (on ratios), the Isoperimetra (on figures with equal perimeters),[6] the Demonstrationes pro astrolapsu (on astrolabe engraving), and the Pre-exercitamina (“a short introductory exercise”?)
[7] The book "Eresia Pura", by Adriano Petta is a fiction, in italian, based on historical research, around the life of Jordanus de Nemore.
Mechanics: The three main treatises and the “Aliud commentum” version (Latin and English) are published in The Medieval Science of Weights, ed.
The Algorismi treatises: The articles by Gustaf Eneström, which contain the Latin text of the introductions, definitions and propositions, but only some of the proofs, were published in Biblioteca Mathematica, ser 3, vol.
Geometry: "De triangulis" was first published by M.Curtze in "Mittheilungen des Copernicusvereins für Wissenschaft und Kunst" Heft VI - Thorn, 1887.
Stereographic projection: The text of version 3 of the Demonstratio de plana spera and the introduction were published in the sixteenth century – Basel, 1536 and Venice, 1558.
