Immanuel Bonfils

Immanuel ben Jacob Bonfils (c. 1300 – 1377) was a French-Jewish mathematician and astronomer in medieval times who flourished from 1340 to 1377, a rabbi who was a pioneer of exponential calculus and is credited with inventing the system of decimal fractions. He taught astronomy and mathematics in Orange and later lived in Tarascon, both towns in the Holy Roman Empire that are now part of modern-day France. Bonfils studied the works of Gersonides (Levi ben Gershom), the father of modern trigonometry, and Al-Battani and even taught at the academy founded by Gersonides in Orange.

Bonfils preceded any attempt at a European decimal system by 150 years, publishing the treatise Method of Division by Rabbi Immanuel and Other Topics on the general theory of decimal fractions around 1350. This was a forerunner to Simon Stevin, the first to widely distribute publications on this topic, and employed decimal notation for integers, fractions, and both positive and negative exponents.

While living in Tarascon in 1365, Bonfils published the work for which he would become best known, Sepher Shesh Kenaphayim (Book of Six Wings) , a manuscript on eclipses that featured astronomical tables predicting future solar and lunar positions (divided into six parts). The book included data for every important date on the Jewish calendar and even correction factors necessary for those who lived as far away as Constantinople. Bonfils, Immanuel (c. 1350), Method of Division by Rabbi Immanuel and Other Topics, , a course of decimal arithmetics, including decimal fractions.