Chronometry, has become a centuries-old race to develop better and more accurate ways of answering the question, What time is it?
Clocks regulate modern existence. Our days are packed with activities and obligations that require us to be in a particular place at a certain time. As a result, chronometry, or the science of timekeeping, has become a centuries-old race to develop better and more accurate ways of answering the question, “What time is it?”
Early agriculturalists during the Neolithic era developed season-oriented calendars to guide crop planting. These timekeeping structures tended to be megalithic and were used to track days, solar years, and lunar activity.
It has been speculated that Stonehenge is one such calendar, as the sunrise solstice can be seen between its two most eastern pillars on June 21 (the longest day of the year). On December 21, the shortest day, the sunset solstice is visible from between the opposite set of stones.
In 2013 a Mesolithic arrangement of an arc and twelve pits was discovered in Aberdeenshire, Scotland. It dates to approximately 10,000 years ago and is believed to have been a type of lunar calendar. Archaeologists believe that it is the world’s oldest known calendar.
When complex human societies evolved, with hierarchical governments and long-distance trade, keeping records became important. As a result, time needed to be broken down into smaller units.
People in Central America, Egypt, Mesopotamia, India, and China started numbering the years, transforming chronometry from nature-based cycles into a linear phenomenon. When the Hebrews introduced seven-day weeks and the Babylonians and Chinese divided days into hours, any remaining links between timekeeping and nature were broken. An alternate form of measurement appeared in the form of clocks.
The earliest clocks used natural elements such as sunlight, water, and sand to log the hours. As technology progressed, springs, gears, quartz, and even electromagnetic waves associated with the internal workings of atom powered clocks and improved their accuracy.
The ancient Egyptians were the first to divide their days into something resembling hours. Around 3500 BC, they built four-sided monuments called obelisks, whose sun-directed shadows allowed people to divide the day into two parts (before and after noon). Later obelisks had markers around their base, measuring time in more precise increments.
Building upon the success of the obelisks, the Egyptians developed the more accurate sundial, or ‘shadow clock’, circa 1500 BC. These devices were divided into 10 daylight sections, with allowance for two twilight hours. Because they only kept time for half a day, they had to be turned 180 degrees at midday to chart the afternoon hours.
Clepsydras, or water clocks, appeared in Egypt around 1400 BC. Devised as a cloudy-day timekeeping solution, they worked by allowing water to flow along a tube from a higher container into a lower one, which was marked by with rings. Each time the water level reached a new ring, it meant that another hour had passed.
Also known as hourglasses, sand clocks came into vogue during the 14th century, when Europeans began sailing to all four corners of the earth. Rocking ships made the water clocks inaccurate, so mariners embraced this sand-driven timekeeper.
Sand clocks consisted of two connected glass bulbs, positioned so that the top’s contents could trickle down to the bottom. When the top bulb was empty, it meant that a certain amount of time had passed. Sand clocks could be designed to measure various lengths of time, although few ran for more than an hour.
The future pope, Sylvester II, invented the first completely mechanical clock in 996, but it wasn’t until centuries later that the technology was widely embraced. Mechanical clocks remained the exclusive property of the church for so long because they were seen as essential to maintaining the strict work and prayer schedules that religious institutions followed.
These clocks had intricate (and, for the era, ingenious) gear and wheel arrangements that were turned by attached weights. A pointer attached to the wheels marked the hours. They were eventually engineered to strike the hour and even chime the quarter-hour.
The next breakthrough in the science of timekeeping took place in 1656, when Christian Huygens, a Dutch astronomer, acted on the Galileo’s theory that a swinging pendulum could power a clock. He devised a wood-encased clock with a short pendulum that beat several times per second.
This new invention had an error of less than one minute per day, which was a big improvement over earlier mechanical clocks. In 1670, British clockmaker William Clement created the grandfather clock by using a longer pendulum and added a minute hand, as time could now be measured by the second.
The Guinness Book of Records states that the first wrist watch was designed in 1868 for the Countess Koscowicz of Hungary. The concept didn’t really catch on, because these ‘bracelet watches’ were seen as women’s jewelry.
When WWI arrived, however, soldiers were equipped with wrist watches to synchronize their movements during maneuvers. These ‘campaign watches,’ now heralded as appropriately masculine, have been worn ever since.
During the 1920s, Warren Marrison and J.W. Horton at Bell Telephone Laboratories discovered that quartz crystal generates a consistent frequency. Inspired, they built in the first quartz clock in 1927. Today, quartz is used to power clocks, watches, computers, and other appliances that have an integral timekeeper.
The first atomic clock, which used atom frequencies to keep time, was invented in 1949 at the National Bureau of Standards (now the National Institute of Standards and Technology). It was so accurate compared to other timekeeping solutions that more research was devoted to atomic clock development.
In 2014, a new strontium atomic clock was unveiled at JILA, a joint institute of the University of Colorado Boulder and NIST. Its performance is so precise that it can allegedly keep perfect time for 5 billion years. This clock presently serves as the time and frequency standard for the United States.