Keeping Time

Some people are really good at tapping their foot to keep time. Other folks can get within a second or two if you ask them to estimate when they think a minute has gone by.

Even the very best of us, though, makes mistakes. Seconds add up to minutes, and these missing minutes made a difference even in the ancient world.

The Sun provides a simple, reliable way to track the time. For millennia, humans could simply look at the Sun’s position in the sky to guess what time it was in the day. This was important at first because daylight could determine survival, but it became increasingly important to be accurate as our population grew.

Someone had the idea of observing the shadow the Sun cast instead of tracking its position in the sky. Eventually, someone else had the idea to put marks on the ground around a stick. Discrete markers of the day were now possible.

This led to the creation of the sundial, a standalone device for just this purpose. 3500 years ago, they were making these in Ancient Egypt.

Sundials remained the most accurate way to keep time for a thousand years or so, and they remained the most reliable way to tell time for even longer.

Water clocks were being developed in Egypt around the same time, but they weren’t as accurate—just very useful if there was no sunlight. It took a famous Greek polymath named Ctesibius to create a much more accurate water clock, although both Egypt and Babylon had these clepsydras for at least a thousand years first.

Water flowed from one vessel into another, and there were little marks on the side, so you could see how much water had come out—and, thus, how much time had passed. This was great for shorter times, but as the water got near the bottom, the pressure changed, and so did the rate of flow.

Ctesibius invented something much, much better. First, he added a second “overflow tank” that was constantly overflowing. This meant that pressure would remain constant, no matter how long you ran the clock. Meanwhile, a siphon and a float valve kept the water level stable in the upper tank.

If this sounds anything like a modern toilet, that is not a coincidence. Ctesibius’s accurate clock would set the stage for automatically refilling toilets centuries later. The next time you flush, remember Ctesibius.

For 18 centuries, the water clock remained the most accurate way to tell time. Finally, around the turn of the 17th century, Galileo noticed that a swinging chandelier kept incredible time. It didn’t matter how wide or short the swing was, either—remember that problem with those early water clocks, where they got worse as time went on?

Christiaan Huygens, a brilliant inventor and physicist in his own right, put Galileo’s observation into practice, finally making something more accurate than Ctesibius’s water clock. Pendulum clocks were only usurped by quartz clocks in the early 20th century, and those clocks were overtaken by today’s paradigm, the atomic clock.

Pendulum clocks brought us into an era where the 20th century world could function. People could meet at precisely the same time (give or take a second), and events could be coordinated to be virtually simultaneous, even in different locations.

The precision of atomic clocks brought us into the 21st century, where we rely on GPS devices and computers that rely on insane accuracy in order to work at all.

What’s the earliest timekeeping device you can remember from your own life? Have clocks or watches changed much within your own lifetime?