Keith Devlin, The Man of Numbers (2011)

themanofnumbers_keithdevlin_2011 Keith Devlin, The Man of Numbers (2011) is a largely historical biography about Leonardo Bigollo (~1170 – ~1250 CE), better known in his own time as Leonardo Pisano or in our time as Leonardo Fibonacci.

Fibonacci is best known for the sequence of Fibonacci numbers (1,2,3,5,8,13,21… etc), whose limit of ratios we know as the Divino Proportion coined by Luca Pacioli (1445-1517), the Golden Ratio coined by Martin Ohm (1792-1811), or as it is called in Euclid’s Elements, the extreme and mean ratio. Fibonacci numbers are only one of several mathematical puzzles posed in his Liber Abaci (1202), the Book of Calculation, a teaching book for mercantile administration, in which Leonardo describes the basics of the Hindu-Arab counting system, at the time largely unknown in Europe, where the Roman and medieval systems were still dominant. Devlin argues that the Liber Abaci caused a mathematical revolution that facilitated the mercantile boom of the Renaissance.

The book by Devlin is a little light on facts and mathematics, though none are absent, maybe because there are only few historic facts known about Leonardo, and because most of the math in our time sounds like very basic modern mathematics described in very cryptically described textual puzzles. If you really want to know everything about Fibonacci’s influence, you should read the translation of the Liber Abacci. If you really want to know everything about the mercantile revolution, you should read perhaps about Cosimo de’ Medici (1389-1464), or about the scientific revolution, you should read perhaps about Galileo Galilei (1564-1642).


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