I awoke one day last week to discover, just outside my bedroom window, the Leaning Tower of Pisa. It was no illusion or delusion; the Piazza del Miracoli lay below me, tastefully adorned with Pisa's cathedral and its tilted campanile.
The tower in person, so to speak, leans even more than you would imagine from its photographs. Its belfry, 190ft above the ground, is 13ft off-centre at its highest point, and the tilt increases at four hundredths of an inch a year. It was begun in 1173, but building was suspended several times because of subsidence, and it was not completed until 1372. Now, its inclination seems gravity-defying.
The Piazza is infused with the genius of Galileo. As a mere stripling he demonstrated to a gathering of university professors, by dropping a variety of objects from the tilting tower, his theory that falling bodies, whatever their size and weight, took the same amount of time to reach the ground. And when you go inside the cathedral, a large bronze lamp can be seen hanging from the vault of the impressive nave. It is known as Galileo's lamp.
The story goes that Galileo, when he was 17, gazed at this massive lamp and noticed, by timing its rhythmic movement with his pulse, that that no matter how narrow or wide might be its arc of swing, the time per oscillation was the same. He had discovered the delightfully elegant secret of the simple pendulum. Many years later, just before he died, Galileo thought out a methodology for using the movement of a pendulum to regulate a clock, and shortly afterwards Christopher Huygens, using this principle, was able to build timepieces that gained or lost no more than 10 seconds every day - a quite revolutionary development for that era.
There was still a problem, of course. The accuracy of a pendulum clock depended crucially on the pendulum's length, and that in turn depended on the temperature. In winter, the rod contracted and the clock went fast. In summer the rod expanded and, with a longer pendulum, the clock lost time. But this difficulty was solved around 1725 by John Harrison's so-called "grid-iron" pendulum, and by the early 1900s pendulum clocks were capable of keeping accurate time to within one hundredth of a second in a day.
But the story has a disappointing twist. It seems the bronze lamp currently hanging in Pisa cathedral was placed there in 1587. This means that either Galileo, born in 1564, was much older than 17 when he made his great discovery, or else this lamp was not the lamp he watched. Or perhaps the truth is something else entirely?