December 2, 2001

The earliest humans used the position of the sun in the sky to approximate the time of day. If the sun was on the horizon, it meant that either the day was starting or ending. If the sun was high in the sky, it was about midday. However, this system had obvious flaws: you couldn’t tell the exact time, you couldn’t see the sun at night, and the sun could be hard to see if there was heavy cloud cover.

Then, in around 3500 B.C., the Egyptians began to construct huge obelisks which served as primitive sundials. These huge pillars told time by casting shadows on the ground, which changed position depending on the time of day. This was a large improvement over simply looking at the sun, because it was much easier to tell the time by looking at a shadow on the ground than by hurting your eyes looking at the sun. By 1500 B.C., smaller, more refined sundials begin to appear, although, like previous sundials, they had limitations: they did not work at night or on cloudy days, and were not very accurate.

The next great advance in timekeeping occurred in about 3450 B.C. when a primitive hourglass was invented. This device was basically a bowl with a hole in the bottom. Water dripped through the hole slowly as the day wore on, and grooves cut into the side of the bowl measured the passage of time. They had many advantages over sundials, because they would work on cloudy days and at night. However, this device required careful calibration, because the water poured out faster when the bowl was full since the water pressure was greater. Also, these devices would not work in freezing weather.

More than 2000 years later, in the 700’s, glass hourglasses, which used sand pouring through a small hole in a glass tube to measure time, began to appear. Although, like the water bowls, they worked under clouds and at night, they had a drawback. Due to the heavy weight of sand, they were mainly used for measuring small amounts of time.

A huge advance occurred in the 1300’s when mechanical clocks, which used weights or springs, began to appear. At first, they had no faces, and no hour or minute hands; rather, they struck a bell every hour. Later, clocks with hour, and then minute hands began to appear. These early mechanical clocks worked by using an escapement, a lever that pivoted and meshed with a toothed wheel at certain intervals. This controlled the movement, or "escape" of either the weights or the springs that were powering the clock, in order to regulate the speed at which the gears and wheels which measured the time turned.

In the 1400’s, another important discovery in timekeeping was made: it was learned that coiled springs, which used small coiled springs unwinding at a speed controlled by an escapement, were able to move the hands on a clock as well as weights or springs of previous, larger clocks. This discovery made smaller clocks, and later watches, possible.

Then, in 1656, Christiaan Huygens invented the pendulum clock, which used weights and a swinging pendulum. These clocks were much more accurate than previous clocks, off by less than a minute a day, compared to the 15 minutes a day of earlier clocks. The bigger the pendulum, the more accurate the clock was.

In 1714, the British Parliament offered a cash reward to anyone who could invent a clock accurate enough for use in navigation at sea. Thousands of sailors died because they were unable to find their exact position, because the exact time was needed to find longitude, and pendulum clocks would not work at sea. For every minute lost by a clock, it meant that there would be a navigational error of 15 miles, and sailors died because they were lost or smashed against rocks because they were unable to figure out their exact position. Then, in 1761, after 4 attempts, John Harrison finally succeeded at inventing a small clock accurate enough to use for navigation at sea. This tiny pocket watch lost only 5 seconds in 6 and ½ weeks.

In the early 1800’s, one of the most important events in clock making occurred. Eli Terry developed machines, patterns, and techniques that produced clock parts that were exactly alike, so they could be mass-produced and interchanged from one clock to another. This drove the price of clocks way down, and allowed common people to own at least one, if not many, timekeeping devices.

During the mid to late 1800’s, many countries saw the need to create standard time zones so that everyone could agree on the time and nations could work more efficiently. In 1852, Great Britain implemented a telegraph network that transmitted "Greenwich Mean Time", so the whole country would be running on exactly the same time. Then, in 1882, the United States created 4 standard time zones, still in use today. In 1884, delegates from 25 countries met and agreed on worldwide time zones.

At the dawn of the 20^th century, only women wore wristwatches. No self-respecting "real man" would wear one. However, in the first World War, soldiers wore wristwatches because taking out a pocket watch to check the time was difficult or impossible in battle. After the war was over, it was considered "socially acceptable" to wear wrist watches, and they became popular. Half a century later, digital watches, which used electrical currents running through quartz crystals to cause vibration and tell the time very accurately, began to appear.

Throughout the last 5,000 years, many advances have been made in the field of timekeeping. Timekeeping techniques have continuously evolved, and will keep evolving in the future. Perhaps one day, humans will invent a clock that accomplishes that long sought after, seemingly unreachable goal: a timekeeping device which is 100% accurate and never gains or loses a second, not even in billions of years. Also, as time progresses, everyday clock will gain more features, such as the ability to automatically adjust for daylight savings time, and the ability to synchronize with atomic clocks through radio waves. Watches will gain new features as well, such as integrated radios and displays that show altitude, temperature, and heart rate. Aside from that, who knows what the future will bring?

See a timeline of the history of clocks

If you are interested in reading more about the history of clocks, I highly recommend the book "Time's Pendulum". Click here to buy it from amazon.com