Origines de la statique, 1905) thought that Jordanus also introduces infinitesimal considerations into statics in his discussion of "virtual" displacements (this being another interpretation of Duhem) of objects in equilibrium. He proves the law of the lever by means of the principle of work. 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. The Elementa super demonstrationem ponderum seems to be the one work which can definitely be ascribed to Jordanus; and the first of the series. 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. An early commentary on this (which also contains a necessary correction to Proposition 9) is the “Corpus Christi Commentary”. The Liber de ponderibus fuses the seven axioms and nine propositions of the Elementa to the four propositions of the De canonio. There are at least two commentary traditions to the Liber de ponderibus which improve some of the demonstrations and better integrate the two sources. The De ratione ponderis is a skillfully corrected and expanded version (45 propositions) of the Elementa. This is usually ascribed to Jordanus, but more likely it is the work of an unidentified mathematician because the citations by Jordanus of his other works are deleted. Related to these treatises is an anonymous set of comments, each of which begins with the words “Aliud commentum” (and thus known as the “Aliud commentum” version). This commentary surpasses all others, especially the commentary on Proposition 1. Algorismi treatises 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 believed that the Communis et consuetus was certainly by Jordanus. The later Demonstratio de algorismo contains 21 definitions and 34 propositions. This is probably a later version of the Communis et consuetus, made either by Jordanus himself or by some