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Timekeeping: The tech story

It’s about time.

Once upon a time, there was a time when no one bothered about time. Sounds nice, doesn’t it? Just like a wise wizard once said, “A wizard is never late, nor is he early, he arrives precisely when he means to.” Something like that would only be possible before humankind decided that there’s a need to know exactly what time of the day it was. There were several reasons behind it – as human civilisation gradually came into existence over the years, complicated activities like farming, craftsmanship, transportation and more required people to keep track of time. And as it is with most inventions, this necessity led to the development and subsequent refinement of what we know today as timekeeping. To understand this evolution, there is a certain amount of time travel into historical records that is required, that will often encounter degrees of inaccuracy not too alien to the act of timekeeping itself.

Sunnyside up

One of the earliest indicators of time that humans observed was the most significant celestial body in the sky – the sun. While Sumerians are often credited to be the first civilisation to properly get into timekeeping using the sun, the accounts are mostly speculative as compared to the evidence-based idea that it was the Egyptians who started it all.

Obelisks were strategically located so
that the length of the shadow could indicate the time of the day

To broadly keep track of the passing of the day, the Egyptians around 3500 BC built tall vertical structures known as obelisks, placed at well thought out locations where the shadow could be suitably tracked. Initially, they were only good for keeping track of the noon, as indicated by the time when the shadow was the shortest. But eventually, it was also used to track the longest and shortest days of the year based on the longest and shortest shadows it created. Further subdivisions were also marked around it to identify smaller sections of the day. This is the idea that eventually gave rise to the sundial.

A Sundial in action

The sundial was designed to have an axis that pointed towards the celestial north pole, around which the sun appeared to rotate. As the understanding of shadow formation and light evolved, so did the sundial, which could eventually accommodate for seasonal changes in the sun’s patterns. But there was still a major problem – how to keep track of time at night?

Starlight, star bright

Even when it came to timekeeping in the dark, the Egyptians turned out to be the brightest of the lot. Developed around 600 BC, Merkhets were more accurate than sundials and could also be used at night. A pair of merkhets aligned with the pole star would be used to determine the north, and as specific stars would cross the meridian created by them, time could be measured at night, if there weren’t any clouds.

Watered down

Water clocks were the first timekeeping devices that did not depend on the movement of celestial bodies for its objective (technically they still depended on the gravitational force generated by earth’s rotation, but we’ll take the liberty of discounting that here).

Clepsydras (Greek for ‘water thief’) also had Egyptian origins, with one of the very first being found in the tomb of Egyptian King Amenhotep I, who was buried around 600 BC. The name came into use when the Greeks started using them around 325 BC. The idea was to keep track of time by tracking a near constant flow of water – either by tracking the rise or fall of the level of water in a vessel.

A simple water clock

One of the most interesting accounts of a water alarm clock also comes from Greece. At Plato’s academy, a vessel containing lead balls was gradually filled with water overnight at a steady rate, causing it to overflow near dawn. The balls would then crash into a copper platter resulting in a cacophony that would wake his students up.

Over the next 500 to 1500 years, water-based clocks were refined and used in several places around the world, including the Middle East and the Far East as well. Mechanisation and inclusion of gears and other clockwork components were done to increase the degree of accuracy. Similar clocks were also developed using incense sticks, candles, and perhaps the most popularised medium, thanks to its association with seafaring – sand.

A mechanical change

As improved water clocks hit a ceiling even with the use of mechanical components, the driving mechanism was replaced by weights that turned the gears and operated the automata within. During this time, the idea of a clock-face with dials indicating the hours and minutes also grew in popularity, whereas earlier mechanisation only involved bells striking the hour or smaller intervals.

This abandonment of liquid or other medium-based timekeeping for a purely mechanical process was truly brought about by the verge escapement mechanism in the now agreed time period of the 13th century.

The verge escapement mechanism – the ring turning in any particular direction would keep the verge oscillating

Without going into a detailed explanation, it can be said that the verge escapement works on the basis of a circular wheel with jagged teeth creating an oscillating motion in another rod, the verge, that has two plates being nudged by the wheel at regular intervals. Clocks including the verge escapement increased accuracy to about ten seconds per day.

But the quest to make more accurate, intricate and compact clocks had by then being associated with superior craftsmanship. As a result, newer escapement mechanisms were being tried out regardless of the actual need for greater accuracy. One such mechanism brought into practice during the 15th century was the spring mechanism. But the overall precision of timekeeping was taken to a whole new level, and held there for a long time, by pendulum clocks in the 17th century.

Although Galileo had the idea of using a swinging bob to regulate timekeeping devices earlier in the 17th century, it is Christian Huygens who is credited as the inventor as he determined the formula that related pendulum swing to length and had the actual pendulum clock made in 1656. It was with further improvements, that accounted for things like the changes in the pendulum’s length due to temperature variations, that the accuracy of the pendulum clock was brought to a hundredth of a second a day and led to it being widely accepted as the standard for timekeeping until the arrival of quartz clocks.

The new age

The first quartz clock was constructed in 1927 in Bell Laboratories. Based on the piezoelectric properties of the quartz crystal that made it vibrate consistently when electrified, early models of the quartz clock erred by less than a third of a second every year. While initially bulky and cumbersome, quartz crystals eventually showed up abundantly in wristwatches later in the 20th century.

NIST-7: The seventh generation of atomic clocks at the National Institute of Standards and Technology. It was unveiled on April 22, 1993, and keeps time to an accuracy of one second in one million years. When this clock was fully evaluated, approximately a year after its unveiling, it had an accuracy of one second in three million years and was the world’s most accurate clock.

When the first atomic clock was built in the 1950s, its accuracy was actually lower than quartz counterparts. Eventually, the first accurate atomic clock, based on a certain transition of the Caesium-133 atom, was built by Louis Essen in 1955 at the National Physical Laboratory in the UK. Atomic clocks are still widely regarded as the most accurate form of timekeeping.

Without going into the details of the atomic clocks improvement in the last 20 years, it suffices to say that they are capable of neither gaining nor losing a second in 20 million years! If that amazes you, consider this: the next challenger for the throne of the most accurate timekeeper, the optical clock, would only be a hundred seconds off if it were to be running for the entire existence of our universe. And with that, it is time to call it a day for this article.

Arnab Mukherjee

Arnab Mukherjee