For centuries people believed that Aristotle was right when he said that the heavier an object, the faster it would fall to earth. Aristotle was regarded as the greatest thinker of all time, and surely he would not be wrong. Anyone, of course, could have taken two objects, one heavy and one light, and dropped them from a great height to see whether or not the heavier object landed first. But no one did until nearly 2,000 years after Aristotle's death. In 1589 Galileo summoned learned professors to the base of the Leaning Tower of Pisa. Then he went to the top and pushed off a ten- pound and a one-pound weight. Both landed at the same instant. The power of belief was so strong, however, that the professors denied their eyesight. They continued to say Aristotle was right.