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Galileo's Predecessors

Popular Galilean biographies portray Galileo as a lone star in a dark world. We are left to believe that he had no contemporaries or predecessors who were worthy of mention. This is not true. In the 1630's Galileo had devised a brilliant experiment to prove the law of free fall using an inclined plane. But what he had really done is prove a law that had been taught in Jesuit schools across Europe for over a half century, and one that Galileo had accepted as true for 30 years. A Roman Catholic priest, Domingo deSoto had actually described the correct law of free fall in a textbook published 75 years before Galileo's famous experiment. The popular textbook had gone through 8 printings before Galileo finished university in Pisa. Galileo's Battle for the Heavens oversimplified Galileo's inclined plane experiment by repeating an old myth that Galileo had 'discovered by experiment' the law of free fall. There was no mention in the program of any preceding work.

The companion site also leaves the impression that the world had to wait for Galileo to perform simple experiments like dropping balls off a tower. There were literally thousands of high towers throughout Europe that would have been perfect for these experiments. The picture below shows the view from the top of one of these towers, the Torre Asinelli in Bologna. For reference, the smaller tower seen in the picture is the Torre Garisenda, itself only a few meters short of the height of the Tower of Pisa.

Torre Asinelli-Torre Garisenda

Galileo was not the first to conduct experiments in free fall. Giuseppe Moletti, Galileo's immediate predecessor at the University of Padua, and the greatest names of 16th century physics, Simon Stevin and Girolamo Cardanus (see Classical Mechanics Timeline) all conducted free fall experiments. They had shown that light objects fall as fast as heavy objects. During Galileo's own lifetime, the Jesuits used a pendulum to time the fall of objects from the Torre Asinelli. This resulted in the first accurate estimate of the acceleration due to gravity. Galileo derived his own estimate from experiment, but his was about half the actual value [_1_] .



Copyright Joseph Sant (2017).
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1. I. Bernard Cohen, W. W. Norton and Company, 1985, The birth of a new physics, , 97
Cohen mentions that Galileo's estimate of the acceleration due to gravity has been calculated to be 467 cm/sec/sec versus the actual value of 980 cm/sec/sec. The estimate produced by the Jesuit experiment from the Torre Asinelli was 914 cm/sec/sec.
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