But to Leonardo the eclipse was a moment of great scientific importance. At this time in history, the Ptolemaic, or geocentric theory of the universe was the popular belief. This theory taught that the earth is fixed and the sun and moon revolve around it. Leonardo himself had believed this theory for a long time. As he grew older, however, he read and heard discussions of the heliocentric theory. This theory proposed that the sun is fixed and the earth and stars move around it. Now, as he watched the eclipse, his doubts of the Ptolemaic concept were renewed and he resolved to make experiments of his own. The new theory was so daring for his times, however, that it would be many years before he became convinced of its truth. Later that night, deep in thought over the experience of the day, he noted down his observations of the eclipse and his doubts of the medieval concept of the heavens. The Church believed the earth was the fixed center of the universe. Scholars and scientists supported the belief of Aristotle in the four elements, earth, water, air, and fire—but something was wrong. What were the planets—what was the moon? He picked up his pen and on a clean sheet of paper he wrote, “Make glasses in order to see the moon large.” 6 _The Monument_ During this time, Leonardo had been struggling with the design for the bronze equestrian statue. Drawing after drawing lay scattered on his studio floor. Lately, however, a daring plan for this statue had come to him. It was to be a huge bronze warrior, Francesco Sforza, mounted on a rearing horse. Weighing perhaps a hundred thousand pounds, it was to be cast in sections in five furnaces—a fitting monument to the power of the Sforza family. But there still remained a big problem to be solved: how could he balance the plunging horse and man on just the two rear legs of the horse? Meanwhile, Leonardo had another problem to work on—a wooden model of the Milan cathedral. He had entered his name with the cathedral authorities as a competitor in the design and construction of the cathedral’s dome. Many architects had been brought in and had failed, partly because of the antagonism of the Milanese workmen to foreign craftsmen, and partly because the committee found it difficult to decide what designs it liked. Leonardo had sent them a letter outlining his own recommendations and had drawn many pages of possible plans. He put forward his knowledge of various building materials, his understanding of classical architecture, and his wish to keep his own ideas in harmony with the Gothic tradition of the cathedral itself. Often he would make a point of walking about the city, observing the different constructions under way and drawing up plans to shorten the labor by mechanical means.