Clock

• 1. Introduction

  ›

  In 1820, according to a lasting legend, a clock inside the House of Lords stopped at nearly the hour King George III died, and people later told similar stories about a clock at Balmoral Castle stopping when Queen Victoria died, and about clocks once linked to William IV and Elizabeth I. A clock, at its simplest, is any device built to measure and display time, and it ranks among the oldest human inventions. What people needed first was a way to divide a day into pieces smaller than a day, a month, or a year. The earliest answers to that problem did not tick. They used a moving shadow, a dripping trickle of water, or a burning candle. How did that basic need push people toward gears, pendulums, quartz crystals, and eventually the vibration of atoms themselves? And how did a tool built for a practical job end up wrapped in superstition, wired into empires, and staked to the survival of sailors lost at sea?

• 2. Marking Time Before Machines

  ›

  A sundial tells time by tracking the position of a shadow cast onto a flat, marked surface, and it saw wide use across the ancient world. With a known latitude, a well-built sundial could measure local solar time to within a minute or two, and people kept using sundials to check mechanical clocks against the sun as late as the 1830s, when telegraph lines and railway schedules began to standardize time between cities.

  Duration timers such as candle clocks and incense clocks measured elapsed time instead of the position of the sun, relying on a steady, predictable rate of consumption. An hourglass worked on a related principle: fine sand poured through a narrow opening at a constant rate, and unlike a candle or a stick of incense, the sand was never used up. It could simply be flipped and reused.

  Water clocks, the oldest true timekeeping devices apart from the day-counting tally stick, are hard to date precisely, since evidence for them stretches back further than for almost any other timekeeping tool. The simplest form, a bowl that slowly filled or emptied through a hole, is known to have existed in Babylon and Egypt by around the 16th century BC, and early water clocks have also turned up in India and China, though their dates are less certain; some writers have argued they existed in those regions as far back as 4000 BC. In the societies that built them, water clocks were mostly used for astrological purposes rather than to regulate daily labor, and they were typically calibrated against a sundial.

• 3. Water Clocks Around the World

  ›

  In Athens in the 1st century BC, the astronomer Andronicus of Cyrrhus supervised construction of the Tower of the Winds, a structure that housed a large clepsydra alongside several prominent sundials on its exterior, functioning as an early clocktower. Greek and Roman engineers steadily improved water clock design, and their advances passed through Byzantine and Islamic hands before eventually returning to Europe. In China, independently developed water clocks existed by 725 AD, and Chinese timekeeping knowledge later spread to Korea and Japan.

  Islamic engineers pushed water clock accuracy further still. In 797, or possibly 801, the Abbasid caliph of Baghdad, Harun al-Rashid, sent Charlemagne a gift that included an elaborate water clock, delivered alongside an Asian elephant named Abul-Abbas. Around 1000 AD, Pope Sylvester II introduced clocks to northern and western Europe. Centuries later, in 12th century Mesopotamia, the engineer Al-Jazari, who worked for the Artuqid king Nasir al-Din in Diyar-Bakr, built numerous elaborate clocks, including an elephant clock, a scribe clock, and a castle clock, several of which have since been reconstructed; beyond telling time, they served as displays of the Artuqid state's wealth and status.

• 4. China's Astronomical Towers

  ›

  In 723, or possibly 725, the Tang dynasty Buddhist monk Yi Xing worked with the government official Liang Lingzan to build an escapement for a water-powered armillary sphere, creating what is considered the world's first clockwork escapement. The astronomer Zhang Sixun built on that work in 976 AD, using liquid mercury instead of water to drive his own astronomical clock tower.

  The Song dynasty polymath Su Song, who lived from 1020 to 1101, incorporated this escapement into a far larger project: an astronomical clock tower built in Kaifeng and completed in 1088, sometimes called the Cosmic Engine. Water turned the mechanism in spring, summer and autumn, while liquid mercury took over during the freezing temperatures of winter. The tower's great driving wheel measured 11 feet across and carried 36 scoops, fed at a steady rate from a constant-level tank, and the whole structure stood roughly ten metres, or about 30 feet, tall. Su Song wrote that the design worked because water, like the heavens, moves without ceasing, so pouring it evenly kept the machine's motion matched to the sky's. A full-scale working replica, about 12 metres tall, now stands in the National Museum of Natural Science in Taichung, Taiwan, built from Su Song's original drawings and descriptions. The escapement technology built into his tower eventually spread west and shaped the mechanisms Western clockmakers would later develop.

• 5. Bells, Towers and Church Records

  ›

  In 1176, records show that Sens Cathedral in France installed an 'horologe', though the mechanism it used is unknown, and the word itself, drawn from the Greek for 'hour' and 'to tell', concealed as much about early clocks as it revealed. In 1198, monks at the abbey of St Edmundsbury, now Bury St Edmunds, ran to fetch water from their clock to fight a fire, according to the chronicler Jocelyn de Brakelond, which suggests their water clock held a large reservoir. The word 'clock' itself, from the Latin clocca meaning bell, gradually replaced 'horologe' as bells came to define the mechanical clocks appearing across 13th century Europe.

  Between 1280 and 1320, church records across Europe show a surge in references to clocks and horologes, evidence that a new kind of mechanism, the verge escapement, had emerged. It let a mechanical clock take its power from falling weights instead of flowing water or mercury. In 1283, a large clock went up at Dunstable Priory in Bedfordshire, positioned above the rood screen rather than near a water source. Canterbury Cathedral installed a 'great horloge' in 1292, and in 1322 Norwich replaced an earlier 1273 clock with a new one carrying a 2 metre astronomical dial, automata and bells, a job that kept two clockkeepers employed full-time for two years. These early mechanical clocks served two main purposes: signalling the canonical hours of prayer, which varied in length as sunrise and sunset shifted through the year, and modeling the solar system for astronomers and astrologers, a job that drew naturally on the existing astrolabe and its rotating plate. Simple notification clocks installed in towers did not always need a face or hands at all, since their job was just to sound a bell at the right hour.

  The most elaborate result of this era was the Astrarium, built in Padua between 1348 and 1364 by the physician and clockmaker Giovanni Dondi dell'Orologio. It stood about 1 metre tall on seven decorative paw-shaped feet, with seven faces and 107 moving gears tracking the sun, the moon, the five known planets and the church's religious feast days. A contemporary, Richard of Wallingford, built a comparably ambitious clock at St Albans by 1336, complete with a wheel of fortune and a tide indicator for London Bridge. Neither original survives, though detailed descriptions let later builders reconstruct both. The Salisbury Cathedral clock, built in 1386, is considered the world's oldest surviving mechanical clock that strikes the hours.

• 6. The Race for Precision

  ›

  Spring-driven clocks first appeared in the 15th century, despite a popular but mistaken belief that the Nuremberg watchmaker Peter Henlein invented them around 1511. The earliest surviving spring-driven clock is a chamber clock made for Philip the Good, Duke of Burgundy, around 1430, now held in the Germanisches Nationalmuseum. Springs solved one problem and created another: clockmakers now had to keep a mechanism running at a steady rate as its spring wound down, which led to inventions like the stackfreed and the fusee, and eventually the modern going barrel in 1760.

  A 1475 manuscript by Paulus Almanus illustrated a clock dial that indicated minutes, and some 15th century German clocks marked both minutes and seconds. A clock in the Fremersdorf collection carries one of the earliest known seconds hands, dating to about 1560. Clockmaking flourished during the 15th and 16th centuries in the metalworking towns of Nuremberg and Augsburg, and in Blois, France. In 1584, the clockmaker Jost Burgi invented the cross-beat escapement and also developed the remontoire; his clocks kept time accurate to within a minute a day, precise enough to help the astronomer Tycho Brahe track celestial events with new confidence.

  The real leap in accuracy came after 1656 with the pendulum clock. Christiaan Huygens is usually credited as its inventor, though Galileo had earlier proposed using a swinging bob to regulate a timekeeping device. Huygens worked out the formula linking pendulum length to time, roughly 99.4 centimetres for a one-second swing, and had the first pendulum clock built in the Hague in 1657. The English clockmaker William Clement built the longcase clock, also called the grandfather clock, to house the pendulum in 1670 or 1671, introduced the anchor escapement as an improvement on Huygens' crown escapement, and added a pendulum suspension spring in 1671. In 1675, Huygens and Robert Hooke invented the spiral balance spring, or hairspring, which finally made accurate pocket watches practical; the clockmaker Thomas Tompion was among the first to use it successfully, and he later adopted the minute hand design that eventually became standard. Daniel Quare, a London clockmaker, added a concentric minute hand and helped introduce the second hand around the same period. The rack and snail striking mechanism, introduced in the 17th century, improved on the older 'countwheel' system used in striking clocks; a repeating clock that chimed out the hour on demand was invented by either Quare or the inventor Edward Barlow in 1676, though a 20th century misconception credited Barlow alone with rack and snail striking, when his actual invention was a related repeating mechanism. George Graham invented the deadbeat escapement for clocks in 1720.

• 7. The Longitude Prize

  ›

  A ship's navigator could fix its position at sea with reasonable accuracy only if their clock lost or gained less than about 10 seconds a day, and a pendulum, which needs stillness, was useless on a rocking deck. In 1714, the British government offered a reward worth 20,000 pounds to anyone who could solve the problem of measuring longitude accurately at sea. John Harrison spent his life pursuing that prize. He built his first marine chronometer in 1735 and spent the next thirty years refining it, adding bearings to cut friction, weighted balances to counter a ship's pitch and roll, and two different metals to offset the effects of heat. When his son tested the clock in 1761, it had drifted by less than 5 seconds after ten weeks at sea. The Noon gun in Cape Town still fires a daily signal accurate enough for ships to check their chronometers against, a tradition that echoes the large dropping balls once mounted on towers near major ports for the same purpose. Satellite navigation systems such as GPS have since removed the need for that entirely, since ships now draw their timing from equipment carried on the satellites rather than from an onboard clock.

• 8. Electric, Quartz and Atomic Time

  ›

  In 1816, the Connecticut clockmaker Eli Terry, working with other local clockmakers, developed a way to mass-produce clocks using interchangeable parts, decades before Britain's own attempt at industrializing clock manufacture with the British Watch Company in 1843. Aaron Lufkin Dennison opened a Massachusetts factory using the same interchangeable-parts approach in 1851, and by 1861 it had grown into the Waltham Watch Company.

  Electricity arrived early. In 1815, the English scientist Francis Ronalds published a design for the first electric clock, powered by dry pile batteries, and in 1840 the Scottish clockmaker Alexander Bain patented his own electric clock, later patenting the electromagnetic pendulum in 1841.

  Quartz timekeeping traced back to 1880, when Jacques and Pierre Curie discovered the piezoelectric properties of crystalline quartz. Alexander M. Nicolson built the first crystal oscillator in 1917, Walter G. Cady built the first quartz crystal oscillator in 1921, and in 1927 Warren Marrison and J.W. Horton built the first quartz clock at Bell Telephone Laboratories in Canada. The United States based its official time standard on quartz clocks from late 1929 until the 1960s. In 1969, Seiko released the Astron, the world's first quartz wristwatch.

  Atomic clocks reach further still. Lord Kelvin first theorized them in 1879, and a prototype ammonia maser was built at the U.S. National Bureau of Standards in 1949, though it proved less accurate than existing quartz clocks. Louis Essen built the first genuinely accurate atomic clock in 1955 at Britain's National Physical Laboratory, based on a transition inside the caesium-133 atom. As of 2013, the most stable atomic clocks used ytterbium, stable to within less than two parts in one quintillion.