Decimal numbers, i.e. those non-integer numbers in which the decimal part is separated with a comma, are at least 150 years older than previously thought: their use was found in an ancient manuscript dating back to 1440 circa by Giovanni Bianchini, a Venetian merchant.
Bianchini is therefore a century and a half ahead of the first known use of the decimal point, which until now was attributed to Cristoforo Clavio, a German Jesuit, mathematician and astronomer, known above all for his contribution to the definition of the Gregorian calendar: Clavio used the decimals in a work published in 1593. The discovery is due to Glen Van Brummelen of the Canadian Trinity Western University, who published his study in the journal Historia Mathematica.
The invention of the decimal comma (in the United States the period is used instead) led to the development of the so-called decimal system, which made it much easier to calculate non-integer numbers, i.e. fractions.
The young Giovanni Bianchini, as a merchant, undoubtedly received the necessary training in subjects such as arithmetic and algebra, essential for his profession, and put his mathematical skills to good use by also working as an administrator of the powerful family's assets d'Este of Ferrara.
Almost all of his known works, written between 1440 and 1460, deal with themes related to astronomy, from the movement of the planets to the prediction of eclipses.
The new discovery suggests, therefore, that Bianchini played a more important role in the development of the foundations of mathematics than he believed.
According to Van Brummelen, the Venetian merchant certainly had the opportunity to travel a lot, even visiting places in the Islamic world where, at the time, various mathematical concepts were being developed.
These travels, therefore, may have influenced Bianchini and his way of representing non-integer numbers.
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