THE TOWER at Pisa is famous for at least two things - it leans over so far it must eventually topple if things continue as they have; and Galileo is said to have proved Aristotle wrong when Galileo was supposed to have dropped cannonballs from the tower of Pisa to show that balls of different weights reach the ground at the same time (more or less) when dropped from a great height. The Galileo story is almost certainly apocryphal as Galileo already knew that Aristotle was wrong.
Aristotle had stated that heavy objects fell to the ground faster than lighter objects. For nearly 2,000 years nobody challenged his authority, the one recorded exception being Philoponus in the 6th century, who apparently did drop weights and showed that they did fall at the same rate.
But Galileo could show Aristotle to be wrong without climbing the tower. Consider, he wrote, that Aristotle is correct and then let us climb the tower and drop two weights, one 10 times as heavy as the other. According to Aristotle the heavy one will reach the ground before the light one.
So now repeat the experiment but bind the two weights together - we should now expect that the heavy one will be slowed down and the light one speeded up and so the combined weights should fall at some intermediate speed. But together they weigh more than the heavy one and so the combined mass should fall faster than either ball when dropped alone. There is an obvious logical contradiction in this, so Aristotle must be wrong.
For those who think science is a natural mode of thought, let them explain why it took nearly 2,000 years for someone to point out Aristotle's error. It is not easily done. And will the Leaning Tower of Pisa topple? Not if Professor John Burland of Imperial College, London is correct. When Professor Burland was called in to help in 1990 he also had to deal with not only the soil beneath the tower - he is a soil mechanic - but a minefield of politics and scaremongering; the tower at Pavia had just collapsed and Pisa's tower was closed to the public.
The tower at Pisa was leaning south at an angle of six degrees from the vertical. Under Professor Burland's direction, the tower has been pulled back from the brink of collapse to the tilt it was in 1969, reversing a …