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Evening Post, Volume CXXI, Issue 4, 6 January 1936, Page 6

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A GALILEO MYTH

THE PISA EXPERIMENT

HOW DID IT ARISE ?

One of the best stories in the history of science is that of Galileo's dropping a couple of balls of unequal weight from the famous Leaning Tower of Pisa and proving to a large crowd at the bottom that they reached the ground at the same time (writes Professor A. S. Russell in "The Listener"). Aristotle had declared that bodies fell equal distances from heights in times inversely proportional to their weights? thus, a ball of ten pounds reaches the ground when one of a single pound, starting at the same time, has gone a tenth of the way only. Almost literally in one fell swoop, in a place that no one afterwards would have difficulty in remembering, the "little dark Italian," by doing something instead of trusting to deduction or imagination, dramatically demolished an assertion that had been, unchallenged since ancient Greece. The event is supposed to have occurred about the year 1590 and to mark a turningpoint in the history of science; "epochmaking" has described it. With different embellishments the gist of the story is found in most of the books and even in the critical histories. As there are, many descriptions to choose from it may not be unfair to take the latest. Here is Bertrand Russell's breezy account in his book, "The Scientific Outlook," "Galileo, it must be confessed, was something of a gamin. When still very young he became Prolessor of Mathematics at Pisa, but as the salary was only 7£d a day, he does not seem to have thought that a very dignified bearing could be expected of him. . . .He would amuse himself by arranging occasions which would make his colleagues look silly. They asserted, for example, on the basis of Aristotle's Physics, that a body weighing ten pounds would fall through a given distance in one-tenth of the time that would be taken by a body weighing one pound. So he went up to the top of the Leaning Tower of Pisa one morning with a tenpound shot and a one-pound shot, and just as the professors were proceeding with leisured dignity to their respective lecture-rooms in the presence of their pupils, he attracted their attention and dropped the two weights from the top of the tower at their feet. The two weights arrived practically simultaneously. The professors, however, maintained that their eyes must have deceived them, since it was impossible that Aristotle could be in error." MUCH-REPEATED TALE. Other writers say substantially the same. The story is given in the "Encyclopaedia Britannica," by Whewell in his "History of the Inductive Sciences," by Fahie (Galileo's most reputable biographer in this country), and by modern writers like Dr. Charles Singer, Mr. Ivor Hart, Sir Richard Gregory, and Sir William Dampier. Often the verisimilitude of the detail, as in the example given, is worthy of Defoe. It will come, therefore, as a complete surprise to most readers that this story, like so many other good stories in the history books, has, alas! got to go. It cannot certainly be shown to be false, but that is the most that can be said for it; there is no evidence whatever for its truth. In addition, even if the Leaning Tower experiment was carried out by Galileo it certainly cannot be claimed to be epoch-making. It wasn't even done for the first time by him; others before had quite certainly shown what in the story Galileo was said to have shown. Further, it is not necessarily true that Aristotle ever said anything—to us—so silly about the respective rates of fall of bodies of different weight as is always quoted about him. Nor, finally, is it right to say that the event, if it occurred, marks the turning-point between the older traditional and the new experimental philosophies. What was believed to be Aristotle's view of the matter had been challenged before. Aristotle has had, in fact, a succession of critics stretching back from Galileo's time to the sixth century A.D. A DESTRUCTIVE ATTACK. Most of the credit'for demolishing this excellent story so effectively must go to the Professor of English at Cornell, Dr. Lane Cooper. There was no published article or book in English where amateurs like himself could study the evidence for this story of Aristotle, Galileo, and the Leaning Tower, and no publication at all where specialists with but limited access to foreign or ancient books could do so. In consequence Dr. Lane Cooper, although no professional scientist, undertook the task of making a critical study of the field and finding out from the written word what actually occurred. He has taken immense trouble in collecting the evidence and weighing it fairly, and given in his book, "Aristotle, Galileo, and the Tower of Pisa," all the relevant quotations, with translations where necessary. He has built up a remarkable and apparently strong case; at the same time, he has got some fun out of many historians of science for taking things unscientifically on tradition, and even for embellishing tradition, instead of getting to the sources themselves for the facts. He shows that in none of Galileo's extant writing is there any reference to the Leaning Tower or to his experimenting from it.-There is no reference in contemporary literature to an event that must have been an- important public occasion if it occurred. For example, Mazzoni discussed Galileo's work on motion in a book that came out in 1597; seven years after the great day. He was pro-Galileo and antiAristotle, but he said nothing of the Pisa experiments. In 1612 Coresio, who was anti-Mazzoni, described some work he had done from the Cathedral tower. In testing the supposed statement of Aristotle about the heavier body falling far faster than the lighter, lie found in contradiction to Mazzoni, that Aristotle was right! But in the dispute between them was no mention of Galileo's similar work. Further, Renieri, Galileo's successor in the Pisa Chair of Mathematics, did indeed experiment from the Leaning Tower in 1641. and wrote to Galileo about his results, but there is no hint from either correspondent in the letters that passed that similar experiments had been done in the same place fifty years before. It is hardly conceivable, Dr. Cooper concludes, that if the younger man knew of the older man's work he would have failed to allude to it. WHAT REALLY HAPPENED. Galileo was a very great man. (There is no denial of this in Dr. Cooper's book.) He was the first to make the correct interpretation of the results of the experiments which now we are told there is no proof that he ever did. Surely, you will say, he must have done the experiments somewhere, somehow. No doubt, but what is in issue is the Leaning Tower story. Actually there was no need at that lime to "expose" Aristotle. The facts which, in the story, were derived from Galileo's experiment were fairly well known "in his day. He was bora in 1564, but Bendetti in 1554, Taisnior in 1562, Cardan in 1570, and especially Stevin of Bruges, all seem to have criticised Aristotle's doctrine on (his point before Galileo's time. And why not? It is ridiculous to say, as so often has been done, that everybody.; was

paralysed by the Aristotelian learning into refusing to experiment. All you had to do was to heave a couple of different heavy weights from a bridge, or out of a high window, and the matter was settled. How, then, did the yam get going? A man called Viviani. started it a dozen years after Galileo's death and sixty-four years after the event. Cardan had.shown by 1570 that two different balls, falling in air, arrive at a plane at the same instant, and had illustrated the point with a very nice diagram in which one ball looks ten times the other; Galileo at the supposed time was at Pisa; in Pisa is a Leaning Tower; Galileo once went up a tower —that of St. Mark's in Venice in 1609 —to demonstrate, however, not the fall of bodies but his telescopes; lastly, if the experiment had been done, it was bound to have worked as reported. It was easy for the enthusiastic Viviani to telescope facts like these into one nice, effective, gripping, not necessarily untrue story, which would do honour to an undoubtedly great man, Somehow began the story' then; so ends, I am afraid, the story now. I do not see how one is going to controvert Dr. Cboper's evidence.