"When this work, which neither the countryman nor Ser Piero any longer inquired for, was completed, Leonardo went to his father and told him that he might send for the shield at his earliest convenience, since, so far as he was concerned, the work was finished; Ser Piero went accordingly one morning to the room for the shield, and, having knocked at the door, Leonardo opened it to him, telling him nevertheless to wait a little without, and, having returned into the room, he placed the shield on the easel, and, shading the window so that the light falling on the painting was somewhat dimmed, he made Ser Piero step within to look at it. But the latter, not expecting any such thing, drew back, startled at the first glance, not supposing that to be the shield, or believing the monster he beheld to be a painting; he therefore turned to rush out, but Leonardo withheld him, saying,--'The shield will serve the purpose for which it has been executed; take it, therefore, and carry it away, for this is the effect it was designed to produce.' "The work seemed something more than wonderful to Ser Piero, and he highly commended the fanciful idea of Leonardo; but he afterwards silently bought from a merchant another shield, whereon there was painted a heart transfixed with an arrow, and this he gave to the countryman, who considered himself obliged to him for it to the end of his life. Some time after, Ser Piero secretly sold the shield painted by Leonardo to certain merchants for one hundred ducats, and it subsequently fell into the hands of the Duke of Milan, sold to him by the same merchants for three hundred ducats." Leonardo painted also the "Head of Medusa," in the Uffizi Gallery, twined about with green, hissing serpents. For the King of Portugal he painted a cartoon for a tapestry curtain,--"Adam and Eve in the Garden of Eden." Of the flowers and fruits in this picture, Vasari says, "For careful execution and fidelity to nature, they are such that there is no genius in the world, however godlike, which could produce similar results with equal truth." This cartoon is lost. The "Madonna della Caraffa," celebrated for the exquisite beauty of the flowers with dew upon them, which stood in a vase by the Virgin, and was highly prized by Clement VII., has also disappeared. The "Adoration of the Magi" and a "Neptune in his Chariot drawn by Sea-horses" were among Da Vinci's works at this time. He was also studying military engineering, completed a book of designs for mills and other apparatus working by water, invented machines for dredging seaports and channels, and urged the making of a canal from Pisa to Florence, by changing the course of the Arno, a thing accomplished two hundred years later.