In 1202 he was again in Italy and published his great work, Liber **abaci**, which probably procured him access to the learned and refined court of the emperor Frederick II.

Some years afterwards (perhaps in 1228) Leonardo dedicated to the well-known astrologer Michael Scott the second edition of his Liber **abaci**, which was printed with Leonardo's other works by Prince Bald.

All these treatises seem to have been written nearly at the same period, and certainly before the publication of the second edition of the Liber **abaci**, in which the Liber quadratorum is expressly mentioned.

In his Practica geometriae plain traces of the use of the Roman agrimensores are met with; in his Liber **abaci** old Egyptian problems reveal their origin by the reappearance of the very numbers in which the problem is given, though one cannot guess through what channel they came to Leonardo's knowledge.

The Liber **abaci**, which fills 459 printed pages, contains the most perfect methods of calculating with whole numbers and with fractions, practice, extraction of the square and cube roots, proportion, chain rule, finding of proportional parts, averages, progressions, even compound interest, just as in the completest mercantile arithmetics of our days.

Among the contents of this book we simply mention a trigonometrical chapter, in which the words sinus versus arcus occur, the approximate extraction of cube roots shown more at large than in the Liber **abaci**, and a very curious problem, which nobody would search for in a geometrical work, viz.

His travels and mercantile experience had led E t u eopre him to conclude that the Hindu methods of computing were in advance of those then in general use, and in 1202 he published his Liber **Abaci**, which treats of both algebra and arithmetic. In this work, which is of great historical interest, since it was published about two centuries before the art of printing was discovered, he adopts the Arabic notation for numbers, and solves many problems, both arithmetical and algebraical.