Jerom, one of the most extraordinary geniuses of his age, was born at Pavia on the 24th of September 1501. As his mother was not married, she tried every method to procure an abortion, but without effect. She was three days in labour, and they were at last obliged to cut the child from her. He was born with his head covered with black curled hair. When he was four years old he was carried to Milan, his father being an advocate in that city. At the age of twenty he was sent to study at the university of that city; and two years afterwards he explained Euclid. In 1524 he went to Padua, and the same year he was admitted to the degree of master of arts. In the end of the following year he took the degree of doctor of physic. He married about the year 1531. During ten years before, his impotency had hindered him from having knowledge of a woman, which was a great mortification to him. He attributed it to the evil influences of the planet under which he was born. When he enumerates, as he frequently does, the greatest misfortunes of his life, this ten years impotency is always one. At the age of thirty-two he became professor of mathematics at Milan. In 1539 he was admitted as a member of the college of physicians at Milan; in 1543 he read public lectures on medicine in that city, and at Pavia the year following; but he discontinued them because he could not get payment of his salary, and returned to Milan. In 1552 he went into Scotland, having been sent for by the archbishop of St Andrews, who had in vain applied to the French king's physicians, and afterwards to those of the emperor of Germany. This prelate, then forty years old, had for ten years been afflicted with a shortness of breath, which had returned every eight days during the two preceding years. But he began to recover from the moment that Cardan prescribed for him. Cardan took his leave of him at the end of six weeks and three days, leaving him prescriptions which in two years wrought a complete cure.

Cardan's journey to Scotland gave him an opportunity of visiting several countries. He crossed France on his way thither, and returned through Germany and the Low Countries, along the banks of the Rhine. It was on this occasion that he went to London, and calculated King Edward's nativity. This tour occupied about four months; after which, returning to Milan, he continued there till the beginning of October 1552, and then went to Pavia, whence he was invited to Bologna in the year 1562. He taught in this last city till the year 1570, at which time he was thrown into prison; but some months afterwards he was sent home to his own house. He left Bologna in 1571, and went to Rome, where he lived for some time without any public employment. He was, however, admitted as a member of the college of physicians, and received a pension from the pope. He died at Rome, on the 21st of September 1575, according to Thuanaus. This account may be sufficient to show the reader that Cardan was of a very fickle temper; but he will have a much better idea of his singular and odd turn of mind by examining what he himself has written concerning his own good and bad qualities. He paid himself congratulatory compliments for not having a friend in this world; but that in requital he was attended by an aerial spirit, emanated partly from Saturn and partly from Mercury, who was the constant guide of his actions, and teacher of every duty to which he was bound. He declared, too, that his manner of walking the streets was so irregular, that it induced all beholders to point at him as a fool. Sometimes he walked very slowly, like a man absorbed in profound meditation; then all on a sudden quickened his steps, accompanying them with very absurd attitudes. In Bologna his delight was to be drawn about in a mean vehicle with three wheels. When nature did not visit him with any pain, he would procure to himself that disagreeable sensation by biting his lips so wantonly, or pulling his fingers to such a vehement degree, as sometimes to force the tears from his eyes; and the reason he assigned for so doing was to moderate certain impetuous sallies of the mind, the violence of which was to him far more insupportable than pain itself; and that the sure consequence of such a severe discipline was the enjoying the pleasure of health. He says elsewhere, that, in the greatest tortures of soul, he used to whip his legs with rods, and bite his left arm; that it was a great relief to him to weep, but that very often he could not; that nothing gave him more pleasure than to talk of things which made the whole company uneasy; that he spoke on all subjects, in season and out of season; and that he was so fond of games of chance as to spend whole days in them, to the great prejudice of his family and reputation, for he even staked his furniture and his wife's jewels.

Cardan makes no scruple of owning that he was revengeful, envious, treacherous, a dealer in the black art, a backbiter, a calumniator, and addicted to all the foul and detestable excesses that can be imagined; yet, notwithstanding, as one would think, so humbling a declaration, there was never perhaps a vainer mortal, or one who with less ceremony expressed the high opinion he had of himself, than Cardan, as will appear by the following proofs. "I have been admired by many nations; an infinite number of panegyrics, both in prose and verse, have been composed to celebrate my fame. I was born to release the world from the manifold errors under which it groaned. What I have found out could not be discovered either by my predecessors or my contemporaries; and that is the reason why those authors who write anything worthy of being remembered scruple not to own that they are indebted to me for it. I have composed a book on the dialectic art, in which there is neither one superfluous letter nor one deficient. I finished it in seven days, which seems a prodigy. Yet where is there a person to be found who can boast of his having become master of its doctrine in a year? And he who shall have comprehended it in that time must appear to have been instructed by a familiar demon."

The same capriciousness observable in his outward conduct is observable in the composition of his works. We have a multitude of his treatises, in which the reader is stopped almost every moment by the obscurity of his text, or his digressions from the point in hand. In his arithmetical performances there are several discourses on the motions of the planets, on the creation, and on the tower of Babel. In his dialectic work we find his judgment on the historians and the writers of epistles. The only apology which he makes for the frequency of his digressions is, that they were purposely done for the sooner filling up of his sheet, his bargain with the bookseller being at so much per sheet; and that he worked as much for his daily support as for the acquisition of glory. The Lyons edition of his works, printed in 1663, consists of ten volumes in folio.