Prompted to post this squib, extracted from my book Science: A History, by seeing it yet again stated that Galileo dropped things from the leaning tower. All together now, in best panto style: Oh no he didn’t!
Another of the Galileo legends introduced by his disciple Viviani refers to Galileo’s time as Professor of Mathematics in Pisa, but is, once again, almost certainly not true. This is the famous story of how Galileo dropped different weights from the leaning tower to show that they would arrive at the ground below together. There is no evidence that he ever did any such thing, although in 1586 a Flemish engineer, Simon Stevin (1548-1620; also known as Stevinus), really did carry out such experiments, using lead weights dropped from a tower about 10 metres high. The results of these experiments had been published, and may have been known to Galileo. The connection between Galileo and weights being dropped from the leaning tower, which Viviani has confused with Galileo’s time as Professor of Mathematics in Pisa, actually dates from 1612, when one of the professors of the old Aristotelian school tried to refute Galileo’s claim that different weights fall at the same speed, by carrying out the famous experiment. The weights hit the ground at very nearly the same moment, but not exactly at the same time, which the peripatetics seized on as evidence that Galileo was wrong. He was withering in his response: Aristotle says that a hundred-pound ball falling from a height of one hundred cubits hits the ground before a one-pound ball has fallen one cubit. I say they arrive at the same time. You find, on making the test, that the larger ball beats the smaller one by two inches. Now, behind those two inches you want to hide Aristotle’s ninety-nine cubits and, speaking only of my tiny error, remain silent about his enormous mistake. The true version of the story tells us two things. First, it highlights the power of the experimental method – even though the peripatetics wanted the weights to fall at different speeds and prove Aristotle was right, the experiment they carried out proved that Aristotle was wrong. Honest experiments always tell the truth. Secondly, the quotation above gives a true flavour of Galileo’s style and personality. It is impossible to believe that if he really had carried out the famous experiment himself then there would be no mention of this triumph anywhere in his writings. For sure, he never did it.