In 1582, Italian scientist Galileo, then a teenager, had noticed the swaying chandeliers in a cathedral. It seemed to him that the movement back and forth was always the same whether the swing was a large one or a small one. He timed the swaying with his pulse and then began experimented with swinging weights. He found that the "pendulum" was a way of marking off small intervals of time accurately.

 

Once Galileo had made the discovery, the regular beat of the pendulum became the most accurate source used to regulate the movement of the wheels and gears of a clock.

 

It wasn't a perfect system, though, as a pendulum swings through the arc of a circle, and when that is so, the time of the swing varies slightly with its size. To make the pendulum keep truly accurate time, it must be made to swing through a curve known as a "cycloid."