Giordano Vitale orVitale Giordano (bornBitonto, October 15, 1633 – November 3, 1711) was anItalian mathematician. He is best known for his theorem onSaccheri quadrilaterals. He may also be referred to asVitale Giordani,Vitale Giordano da Bitonto, and simplyGiordano.
Giordano was born inBitonto, in southeasternItaly, probably on October 15, 1633. As an adolescent he left (or was forced to leave) his city and, after an adventurous youth (that included killing his brother-in-law for calling him lazy) he became a soldier in the Pontifical army. During these adventures he read his first book of mathematics, theAritmetica prattica byClavius. At twenty-eight, living in Rome, he decided to devote himself to mathematics. The most important book he studied wasEuclid'sElements in the Italian translation byCommandino.
In Rome he made acquaintance with the renowned mathematiciansGiovanni Borelli andMichelangelo Ricci, who became his friends. He was employed for a year as a mathematician by ex-QueenChristina of Sweden during her final stay in Rome. In 1667, a year after its foundation byLouis XIV, he became a lecturer in mathematics at theFrench Academy in Rome, and in 1685 he gained the chair of mathematics at the prestigiousSapienza University of Rome. Friend ofVincenzo Viviani, Giordano metLeibniz in Rome when Leibniz stayed there during his journey through Italy in the years 1689–90. He gave Leibniz a copy of the second edition of his bookEuclide restituto. Giordano died on November 3, 1711, and was buried in theSan Lorenzo in Damaso basilica church in Rome.
Giordano is most noted nowadays for a theorem onSaccheri quadrilaterals that he proved in his 1668 bookEuclide restituto (named afterBorelli'sEuclides Restitutus of 1658).
In examining Borelli's proof of theparallel postulate, Giordano noted that it depended upon the assumption that a line everywhere equidistant from a straight line is itself straight. This in turn is due toClavius, whose proof of the assumption in his 1574Commentary on Euclid is faulty.[1][2] So using a figure he found in Clavius, now called a Saccheri quadrilateral, Giordano tried to come up with his own proof of the assumption, in the course of which he proved:
The interesting bit is the second part (the first part had already been proved byOmar Khayyám in the 11th century), which can be restated as:
Which is the first real advance in understanding theparallel postulate in 600 years.[3][4]
Giordano's published work includes:
Media related toGiordano Vitale (mathematician) at Wikimedia Commons