A gambling doctor wrote the first serious study of probability
Gerolamo Cardano was always short of money, so he gambled and played chess to stay solvent. Out of that habit came a book on dice that holds the first systematic treatment of probability, plus a section on how to cheat. The same restless mind gave cars a key joint.
Born illegitimate in Pavia in 1501, Cardano was the son of Fazio Cardano, a mathematically gifted lawyer and friend of Leonardo da Vinci. His father wanted him to study law; he chose medicine, taking a doctorate at Padua in 1525. His combative manner and illegitimate birth kept Milan's College of Physicians from admitting him for years, so he practised without a licence in the small town of Piove di Sacco, where he married and later called those years the happiest of his life.
Once licensed, he grew into a physician much of Milan's elite wanted at their bedside, and he claimed to have rejected invitations from the French and Danish monarchs and from Scotland's queen. His Book on Games of Chance, written around 1564 but published only in 1663, used dice to define odds as favourable against unfavourable outcomes and hinted at the rule for multiplying independent events, though he was unsure what to multiply.
In algebra, his 1545 Ars Magna was the first European work to use negative numbers systematically, and it acknowledged imaginary numbers even though he did not grasp their properties. It published solutions to cubic and quartic equations, crediting Scipione del Ferro and his own student Lodovico Ferrari. Niccolò Tartaglia, who had sent Cardano a cubic solution disguised as a poem in 1539, claimed Cardano had sworn secrecy, and a decade-long feud followed; del Ferro's solution, however, came first.
His name survives in machinery. The Cardan shaft with universal joints transmits rotation at an angle and is still used in vehicles, and he described the gimbal, three nested rings that let a compass swing freely, as well as an early combination lock. His studies of rolling circles later helped build fast printing presses, and his notes on steam condensation creating a vacuum are seen as a milestone on the road to the steam engine. He also invented a cryptographic grille, wrote on music, and produced more than 200 scientific works.
Source: Gerolamo Cardano
