CARDAN (Ital. CARDANO), GIROLAMO (GERONYMO or HIER0NIMO) (1501-1576), Italian mathematician, physician and astrologer, born at Pavia, was the illegitimate son of Facio Car dano (1444-1524), a learned jurist of Milan. He was educated at Pavia and at Padua, where he graduated in medicine. He was, however, excluded from the college of physicians at Milan on account of his illegitimate birth. In 1534 he became a public lec turer in geometry, on the foundation of one Thomas Plat, at Milan, and also (1535) physician to the Augustine Friars, whose prior he cured. A cure of the child of the Milanese senator Sfondrato led to his admission into the medical body, of which he actually became rector in 1541. In 1539 he published his Practica arithmeticae generalis, and he corresponded with Niccolo Tartaglia, who had discovered a solution of cubic equations. In the University of Pavia, driven by war to teach at Milan, offered Cardan its chair of medicine, and he accompanied the university on its return to Pavia in In his comprehensive treatise on Algebra (Artis magnae sive de regulis Algebrae liber onus, Nuremberg, 1545) Cardan published the cubic solution, which he had obtained from Tartaglia under pledge of secrecy. In he had published his celebrated treatise on astrology.
His works on algebra and astrology had procured for him a European renown, and flattering offers from Pope Paul III. and the king of Denmark, which he declined. In 1551 his reputation was crowned by the publication of his great work, De Subtilitate Rerum, which embodied both the soundest physical learning of his time and its most advanced spirit of speculation. It contains indications for a method of teaching the blind to read and write by the sense of touch, and elsewhere Cardan suggests the use of signs for teaching the deaf. De V arietate Rerum 0557), is a supplement to it. Cardan gives false explanations of common phenomena, but glimpses of principles not fully understood by him or acceptable to his age are of interest. Inorganic nature he asserts to be animated no less than the organic; all creation is development ; all animals were originally worms ; the inferior metals must be regarded as conatus naturae towards gold. The indefinite variability of species is implied in the remark that nature is seldom content with a single variation from a type. The oviparous habits of birds are explained, precisely in the manner of modern naturalists, by their value for the perpetuation of the species. Animals were not created for the use of man, but exist for their own sakes. The origin of life depends upon cosmic laws, which Cardan naturally connects with astrology. The physical divergencies of mankind arise from the effects of climate and circumstances.
In 1552 Cardan was summoned to Scotland to attend Arch bishop Hamilton of St. Andrews. The chief interest of his jour ney lies in his account of the disputes of the medical faculty at Paris over the new anatomical teaching of his friend Vesalius, and his favourable opinion, as an ecclesiastically unbiased ob server, of the character and ability of Edward VI. of England.
Cardan had now reached the height of his prosperity; but later his fortune turned. His son, Giovanni Battista, also a physician, had contracted an imprudent marriage with a girl named Bran donia Seroni, who proved unfaithful. The injured husband's revenge by poison was detected, and the exceptional severity of the punishment—execution—seems to justify Cardan in attribut ing it to the rancour of his medical rivals (156o). The blow all but crushed him. His reputation and his practice waned. He was banished from Milan on some accusation unspecified, and although the decree was rescinded he accepted a professorship at Bologna (1562). There he was arrested (157o), deprived of his profes sorship and removed to Rome, where he spent his remaining years in receipt of a pension from the pope, and wrote his com mentaries, De Vita Propria, which, with De Libris Propriis, is our principal authority for his biography.