The Medieval Rabbi Who Invented the Decimal Fractions System


As you likely learned, the decimal system is the numerical system with a base of ten–the most widely used form in the world. But you were probably never taught that a rabbi named Immanuel ben Jacob Bonfils invented it.

The French Jewish rabbi (not to mention astronomer and mathematician) published his revolutionary treatise on metric decimals in 1350 under the catchy title “The Invention of the Decimal Fractions and the Application of the Exponential Calculus.”

But what may be more interesting–and certainly more intriguing–was Rabbi Immanuel’s Book of Six Wings, which he published in 1365 while living in Tarascon, France. The wondrously titled manuscript held extensive information on eclipses, future solar and lunar positions, and even data on important dates on the Jewish calendar. Rabbi Immanuel was considerate: he even included corrections for those who lived as far away as Constantinople. His calculations were so good that sailors and explorers used them for hundreds of years.

And if you’re wondering what was up with the titular six wings: the astronomical data were broken into six tables as an allusion to the six wings of the seraphim, thus earning Rabbi Immanuel his nickname: “Master of the Wings.”

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