The drawing of the altarpiece was nearing completion. The monks were fascinated by the spectacle of the Adoration appearing before their eyes. The soft, umber outlines deepened with gray, the ochre highlighting the central figures charmed them and they sent another gift to Leonardo’s house—a cask of Tuscan red wine. As it turned out, Leonardo never finished this altarpiece. It is not known why. But the drawing for it can be seen today in the Uffizi Gallery in Florence just as Leonardo left it. It is certain, however, that Leonardo was far from idle during this time. He drew the design for eliminating the friction of a turning axle by mounting the axle in roller-bearings. He experimented with, and solved the problem of, transmitting motion to revolving machine parts by friction—the possible forerunner of our modern friction clutch. Another device, found in modern automobiles—the differential—was also drawn by Leonardo. This idea provided for the difference in speed between the two drive wheels when rounding a curve. Leonardo also drew the first known plans for a self-propelled vehicle—an “automobile.” It was designed to operate by a system of elastic springs wound by hand by the person on the vehicle; the “car” was then supposed to run the short distance allowed it by the unwinding of the springs. In addition, Leonardo continued designing machines for both offensive and defensive military action. One of these was a breech-loading cannon, together with the first known projectiles that took into consideration better penetration through the air and greater stability in their trajectory. Indeed, these very much resembled present-day aerial bombs, with pointed noses and stabilizing fins. As the months passed, however, Leonardo began to feel that his time and talents were being wasted in Florence. Although the monks and friends of the monastery were pleased with the work he was doing, other artists were being called to greater tasks in Rome. For example, Domenico di Tommaso del Ghirlandaio, Sandro Botticelli, and even Leonardo’s fellow student, Pietro Perugino, had left Florence to work in the chapel of Pope Sixtus IV in Rome—known to us as the Sistine Chapel. Now, too, it was becoming clear that Lorenzo and his court had no time for this solitary genius whose ideas stretched beyond his age. So Leonardo looked about him. He was thirty years old and the walls of Florence seemed to bind his spirit. To what city could he go where his talents would be put to fruitful use? Rome seemed to hold out no hope, for no one had offered him a position there.