A recent discovery of documents dating back to the 15th century in Italy sheds new light on the history of the decimal point, revealing that this key element of mathematics was used much earlier than previously thought.
Who would have believed that the decimal point, this modest mark that greatly facilitates calculations by separating whole numbers from their fractions, goes back to the era of a flourishing medieval Italy? Far from being an invention of the late Renaissance, as suggested by the systematic use of decimals by the German mathematician Christopher Clavius in 1593, new research highlights the work of a Venetian merchant in the 15th century, Giovanni Bianchini, who was already using the decimal point between 1441 and 1450.
The document now featuring the oldest known decimal point
This revelation is the result of the hard work of Glen Van Brummelen, a historian of mathematics at Trinity Western University in Canada. It was during a mathematics camp for middle school students that Van Brummelen discovered the use of the decimal point in one of Bianchini's treatises, a discovery that prompted him to share his find with enthusiasm.
The idea of breaking down whole numbers into smaller parts is not new and dates back well before the Middle Ages. However, the method used by astronomers at the time, based on a decimal system of base 60, significantly differs from our current base 10 decimal system, which is taught from elementary school today. Despite the existence of notations that evoke our current decimal system, these innovations did not persist over time.
Van Brummelen's study, published in the journal
Historia Mathematica, highlights the difficulty in attributing the invention of the decimal point to a single historical figure, as practices and systems have varied over time. Nevertheless, it is easier to trace the history of the decimal point notation, a symbol that endures to this day, which made its first documented appearance in Bianchini's "Tabulae primi mobilis B". This merchant, who became an administrator in the service of the ruling family of Venice, the d'Estes, used the decimal point in the calculation of stellar coordinates for astrological purposes.
Although the adoption of this notation was slow, Clavius, informed of Bianchini's work, along with other mathematicians inspired by his works, eventually embraced and popularized the decimal point. It was ultimately the Scottish mathematician John Napier, the inventor of logarithms, who firmly anchored the decimal point in the mathematical landscape at the beginning of the 17th century.