Girolamo Cardano, born in Pavia in 1501, was an Italian physician, mathematician and astrologer. He is remembered for his frank memoir, written while under house arrest for heresy, and the offending work, On subtlety. In this chapter, along with methods to encode letters, write in invisible ink and send secret signals by fire, Cardano describes his system for recording large numbers as a single character. He wrongly attributes the system to Agrippa, but in fact these are Basingstoke ciphers, used by English Cistercian monks in the thirteenth century for marking pagination in manuscripts. Cardano’s method becomes unreliable once it enters five figures, but can be used to illustrate numbers into the billions.
(One of two pages)
Author: Girolamo Cardano
Title: De subtilitate libri XXI [On subtlety] (Basel, 1582)
Shelfmark: H.18.14 (catalogue record)