The decimal point was invented around 150 years earlier than previously thought, according to an analysis of astronomical tables compiled by the Italian merchant and mathematician Giovanni Bianchini in the 1440s. Historians say that this discovery rewrites the origins of one of the most fundamental mathematical conventions, and suggests that Bianchini — whose economic training contrasted starkly with those of his astronomer peers — might have played a more notable part in the history of maths than previously realized. The results are published in Historia Mathematica.
“It’s a very nice discovery,” says José Chabás, a historian of astronomy at the Pompeu Fabra University in Barcelona, Spain. The decimal point was “a step forward for humanity,” he says, enabling the ease and efficiency of calculations that underpin modern science and technology. Previously, its earliest-known appearance was generally said to be in an astronomical table written by the German mathematician Christopher Clavius in 1593. But now it’s clear that “the inspiration was taken from Bianchini,” Chabás says.
Bianchini worked as a Venetian merchant before becoming an administrator of the estate of the powerful d’Este family, who ruled the Duchy of Ferrara at the time. As well as managing assets and guiding investments, Bianchini was responsible for casting horoscopes, which meant that he had to master astronomy. He published several works on topics ranging from planetary motions to predicting eclipses.
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Glen Van Brummelen, a historian of mathematics at Trinity Western University in Langley, Canada, had hoped that Bianchini’s work might help to reveal how and when Islamic astronomical knowledge reached…
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