From bankers to scientists

Within a longer New York Review of Books article about a recent banking exhibition in Florence, there is a concise accounting of the rise of Hindu-Arabic numerals in 13th century Italy and the impact that grew from that transition. It's a longish excerpt, but I couldn't help myself!

The earliest medieval merchants wrote down their sums in Roman numerals and made their calculations with the help of an abacus. This is how Pietro Bernardone dei Moriconi, a merchant of Assisi, must have made the small fortune that allowed him to spoil his handsome son Francis, at least until the day that Francis fell seriously ill and decided to reject his family’s materialistic way of life... 

By the time Saint Francis stripped off his peacock garments and exchanged them for a homespun robe in 1206, Italian trading networks had already spread throughout the Mediterranean; a vast web of agents traded Chinese silk for English wool or wove the two together in the fabric called damask, after the city of Damascus, an important stop on the Silk Road. At about the same time that Francis was preaching to the birds, a merchant of Pisa named Leonardo Fibonacci, from a base in Bugia on the Algerian coast, threw over family tradition as egregiously as Francis, although in an entirely different realm: he abandoned the old European way of reckoning for the numbering system of his Arab colleagues, who claimed to have gotten it from the Indians. In 1202, Fibonacci presented these “nine numbers of the Indians” for his fellow Italians in a book called Liber Abaci. In the business world abaco, “abacus,” was a synonym for “commercial arithmetic.” He wrote in Latin so that he could be understood throughout the Italian peninsula, and beyond. And he was understood, so well that he changed the way that Italian merchants did business.

It was somewhat easier to calculate with Hindu-Arabic numbers than it was with Roman numerals, but the abacus and the slide rule were still useful tools until the advent of small electronic calculators. It was easier to read a ledger when the columns of numbers denoted consistent orders of magnitude. But the real advantage presented by the “nine numbers of the Indians” and especially a tenth cipher, zero, was their relationship to an Arab discipline called algebra; with these numbers it was possible to write equations.

Quadratic equations were already in use by Fibonacci’s time, and the ability to make quick calculations would eventually have a decisive impact on the discipline not yet called science...