The Decimal Point Is 150 Years Older Than We Thought, Emerging in Renaissance Italy

His­to­ri­ans have long thought that the dec­i­mal point first came into use in 1593, when the Ger­man math­e­mati­cian Christo­pher Clav­ius wrote an astron­o­my text called Astro­labi­um. It turns out, how­ev­er, that the his­to­ry of the dec­i­mal point stretch­es back anoth­er 150 years–to the work of the Venet­ian mer­chant Gio­van­ni Bian­chi­ni. In his text Tab­u­lae pri­mi mobilis, writ­ten dur­ing the 1440s, Bian­chi­ni used the dec­i­mal point to cal­cu­late the coor­di­nates of plan­ets. In so doing, he invent­ed a sys­tem of dec­i­mal frac­tions, which, in turn, made the cal­cu­la­tions under­pin­ning mod­ern sci­ence more effi­cient and less com­plex, notes Sci­en­tif­ic Amer­i­can.

Glen Van Brum­me­len, a his­to­ri­an of math­e­mat­ics, recent­ly recount­ed to NPR how he dis­cov­ered Bian­chini’s inno­va­tion:

I was work­ing on the man­u­script of this astronomer, Gio­van­ni Bian­chi­ni. I saw the dots inside of a table — in a numer­i­cal table. And when he explained his cal­cu­la­tions, it became clear that what he was doing was exact­ly the same thing as we do with the dec­i­mal point. And I’m afraid I got rather excit­ed at that point. I grabbed my com­put­er, ran up and down the dorm hall­way look­ing for col­leagues who still had­n’t gone to bed, say­ing, this per­son­’s work­ing with the dec­i­mal point in the 1440s. I think they prob­a­bly thought I was crazy.

In a new arti­cle appear­ing in the jour­nal His­to­ria Math­e­mat­i­ca, Van Brum­me­len explains the his­tor­i­cal sig­nif­i­cance of the dec­i­mal point, and what this dis­cov­ery means for the his­tor­i­cal devel­op­ment of math­e­mat­ics. You can read it online.

Relat­ed Con­tent 

Trigonom­e­try Dis­cov­ered on a 3700-Year-Old Ancient Baby­lon­ian Tablet

How the Ancient Greeks Shaped Mod­ern Math­e­mat­ics: A Short, Ani­mat­ed Intro­duc­tion

The Map of Math­e­mat­ics: An Ani­mat­ed Video Shows How All the Dif­fer­ent Fields in Math Fit Togeth­er

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