time of descent was independent of their mass. This was contrary to what Aristotle had taught: that heavy objects fall faster than lighter ones, in direct proportion to weight. While this story has been retold in popular accounts, there is no account by Galileo himself of such an experiment, and it is generally accepted by historians that it was at most a thought experiment which did not actually take place. An exception is Stillman Drake, who argues that the experiment did take place, more or less as Viviani described it. The experiment described was actually performed by Simon Stevin (commonly known as Stevinus) and Jan Cornets de Groot, although the building used was actually the church tower in Delft in 1586. However, most of his experiments with falling bodies were carried out using inclined planes where both the issues of timing and air resistance were much reduced. In any case, observations that similarly sized objects of different weights fell at the same speed is documented in works as early as those of John Philoponus in the sixth century and which Galileo was aware of. In his 1638 Discorsi, Galileo's character Salviati, widely regarded as Galileo's spokesman, held that all unequal weights would fall with the same finite speed in a vacuum. But this had previously been proposed by Lucretius and Simon Stevin. Cristiano Banti's Salviati also held it could be experimentally demonstrated by the comparison of pendulum motions in air with bobs of lead and of cork which had different weight but which were otherwise similar. Galileo proposed that a falling body would fall with a uniform acceleration, as long as the resistance of the medium through which it was falling remained negligible, or in the limiting case of its falling through a vacuum. He also derived the correct kinematical law for the distance traveled during a uniform acceleration starting from rest—namely, that it is proportional to the square of the elapsed time (d∝t2). Prior to Galileo, Nicole Oresme, in the 14th century, had derived the times-squared law for uniformly accelerated change, and Domingo de Soto had suggested in the 16th century that bodies falling through a homogeneous medium would be uniformly accelerated. Soto, however, did not anticipate many of the qualifications and refinements contained in Galileo's theory of falling bodies. He did not, for instance, recognise, as Galileo did, that a body would fall with a strictly uniform acceleration