where he remained until 1610. In Padua, Galileo invented a calculating "the compass" for the practical solution of mathematical problems. This instrument was a sophisticated and versatile calculating device that rendered several possible geometrical and arithmetical operations by comparing the sides of similar triangles. He later changed his focus from speculative physics to using careful measurements. He discovered the law of falling bodies, outlined in his book On Motion. Even during his earliest studies and experiments, for example, his class experiment on the Leaning Tower, Galileo realized that the speed of a falling body is independent of its weight. His argument was as follows: suppose, as Aristotle did, that the speed at which a body falls does depend on its weight or other characteristics such as its earthly character. If this were true, for example, a two pound rock should fall faster than a one pound rock. However, if we take a two-pound rock, split it in half and join the halves by a light string then, on the one hand, this contraption should fall as fast as a two-pound rock, but on the other hand, it should fall as fast as a one-pound rock. Since any object should have a definite speed as it falls, this argument shows that Aristotle's assumption that the speed of falling bodies is determined by their weight is simply wrong. Two bodies released from a given height will reach the ground at different times not because they have different earthly characteristics, but simply because they a
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