At the time when
Viviani asserts that the experiment took place, Galileo had not yet formulated the final version of his
law of falling bodies. He had, however, formulated an earlier version which predicted that bodies of the same material falling through the same medium would fall at the same speed. While this story has been retold in popular accounts, there is no account by Galileo himself of such an experiment, and many historians believe that it was a
thought experiment. An exception is
Stillman Drake, who argues that it took place, more or less as Viviani described it, as a demonstration for students. He writes: His argument is that if we assume heavier objects do indeed fall faster than lighter ones (and conversely, lighter objects fall slower), the string will soon pull taut as the lighter object retards the fall of the heavier object. But the system considered as a whole is
heavier than the heavy object alone, and therefore should fall
faster. This contradiction leads one to conclude the assumption is false. ==Later performances==