From a note on a page of designs for supplying and heating a bath we know that Leonardo continued his quiet life, only vaguely disturbed by the political upheaval taking place around him. His note reads, “On the first day of August 1499 I wrote here of movement and weight.” He had made many experiments and calculations concerning the movement and weight of objects. He had drawn, for example, the flight of an arrow to describe motion through air and although he wrote no specific formula, he marked the three stages of its trajectory—the initial push, the slowing and the steeper downward path as the arrow’s momentum was overcome by the resistance of the air. He also defined the law of movement on an inclined plane and he arrived at the root principle of Newton’s law of gravitation when he wrote, “every weight tends to fall toward the center by the shortest way.”
A diagram of this period is probably the first scientific graph. Leonardo had experimented with two balls dropped from a height. First he dropped them together and then one after the other. In attempting to solve the mathematical problems presented by these falling bodies he drew a graph of vertical and horizontal lines. The times it took for the balls to fall were marked on the horizontal lines and the distances on the vertical lines—thus, he could trace their relationship.
But this peaceful time of productive work was running out for Leonardo. Ludovico’s commander, Galeazzo, had yielded the fortress of Alessandria to the French at the first battle. Ludovico himself had sent his sons and his treasure to his brother, Cardinal Ascanio, in Germany. When he saw that his cause was lost, he turned the Sforza castle over to Bernardino da Corte, a trusted commander, making certain that it was fully supplied with arms and food. Then in sorrow, Ludovico Sforza, Duke of Milan, left his city for the last time as ruler of Lombardy. The gates of Milan were opened to the French in October of 1499, and Bernardino da Corte surrendered the Sforza castle.
French soldiers now occupied Milan as conquerors and the people of the city were in a state of confusion. Those who could made their peace with the French; but others, who had been supporters of Ludovico, fled to avoid arrest. Leonardo, who would be suspect to the French, packed up his few possessions—although he did manage to retain his estate—and left, together with Pacioli and an apprentice, for Mantua.
Leonardo had to flee Milan.
9
Cesare Borgia
Leonardo, Pacioli, and Salai, the apprentice, arrived in Mantua in February of the year 1500. They were given refuge in the castle of Isabella d’Este, who was the sister of Beatrice, and the wife of Francesco Gonzaga, governor of Mantua. Isabella was one of the eminent women of her time and attracted to her court the intellectual life of Italy. In Leonardo she recognized the man of genius; indeed, she treated him as an equal, putting her castle at his disposal. She persuaded him to paint her portrait and Leonardo commenced a preparatory drawing.
In the evenings at the castle there were discussions and music and here Leonardo again met his pupil and companion on the trip from Florence so many years ago—Atalante Migliorotti who had left Milan in 1490 to assume the post of court musician to Isabella.