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560 BC: Sundials: Anaximander of Miletus, Greek philosopher, is believed to have introduced sundials into Greece.
3rd century BC: Escapement mechanism - Philo of Byzantium, Greek engineer, described the first liquid-driven escapement (a mechanical device that transfers energy to the timekeeping element of a clock in small portion in order to enable time counting; escapements are also used for other applications) for a washstand water pouring automaton, possibly used also in ancient water clocks.
45 BC: Julian calendar - introduced by Julius Caesar after consultation with the astronomer Sosigenes of Alexandria. The Julian calendar was faulty because it was inconsistent with the solar year - 11 minutes difference per year.
2nd scentur AD: Water clock - Zhang Heng, Chinese astronomer and mathematician, introduced an inflow water clock by adding another water tank into which the first one drips for time measurement. This configuration is more accurate than the simple outflow model.
725 AD: Water clock : Yi Xing, Chinese monk and mathematician, is believed to have introduced the first known hydraulic clock with an escapement design.
9th century AD: Candle clock - most commonly attributed to King Alfred the Great - King of Wessex.
996: Weight-Driven Clock - maybe the first weight-driven clock was built by Gerbert, French monk and the future Pope Sylvester II, for the German town of Magdeburg.
11th century AD: Incense clock - a Chinese timekeeping device that appeared during the Song Dynasty (960-1279) and spread to neighboring countries such as Japan. The clock consists of incense sticks that have been manufactured to a known rate of combustion, used to measure minutes, hours, or days.
11th century AD: Astronomical clock, water-driven: Su Song, Chinese astronomer, horologist and mechanical engineer, created during the Song Dynasty a water-driven astronomical clock for his clock tower of Kaifeng City.
1330: Mechanical clock - Richard of Wallingford, English mathematician and abbot of St. Alban's abbey, built a mechanical clock as an astronomical orrery (a mechanical device that illustrates the relative positions and motions of the planets and moons in the Solar System).
1386: Salisbury cathedral clock - the oldest working clock in the world, still with most of its original parts.
1462: Pocket watch - an early reference to a pocket watch is made in a letter from the Italian clockmaker Bartholomew Manfredi to the Marchese di Mantova Federico Gonzaga, where he offers him a "pocket clock" better than that belonging to the Duke of Modena..
1522: Hourglass (sand clock) - Ferdinand Magellan, Portuguese navigator and explorer, used 18 hourglasses on each ship during his circumnavigation of the globe.
1556: Clock, weight-driven - the Ottoman engineer Taqi al-Din described in his book a weight-driven clock with a verge-and-foliot escapement, gears, an alarm, and a representation of the moon's phases.
1579: Clock that marked seconds - Jost Bürgi, Swiss clockmaker and mathematician, built a clock for William of Hesse that marked seconds. In 1581, Tycho Brahe, Danish astronomer, redesigned clocks that displayed minutes at his observatory so they also displayed seconds.
1582: Gregorian calendar - Pope Gregory XIII, after whom the calendar was named. The motivation for the Gregorian calendar was to correct errors created by the Julian calendar (see above).
1638: Water clock, use in physics: in his Two New Sciences, Galileo Galilei, Italian physicist, mathematician and astronomer, used a water clock to measure the time taken for a bronze ball to roll a known distance down an inclined plan.
1657: Pendulum clock - invented by Christiaan Huygens, Dutch mathematician and astronomer.
1675: Greenwich Mean Time (GMT) - was established by King Charles II when the Royal Observatory was built as an aid to English mariners to determine longitude at sea, providing a needed reference time because at those times each city in England kept a different local time.
1687: Absolute time - Sir Isaac Newton, English physicist, mathematician and astronomer: in his Principia, absolute time and space are independent aspects of objective reality, a concept which provides a theoretical foundation that facilitates Newtonian mechanics.
1767: Marine chronometer - invented by John Harrison, English carpenter and clockmaker. His device was instrumental in solving the problem of establishing the longitude of a ship at sea, thus revolutionizing and extending the possibility of safe long distance sea travel.
1781: Subjective time - Immanuel Kant, German philosopher and Gottfried Leibniz, German mathematician and philosopher: maintained an opposing view to Newton's (see above) - that time does not refer to any kind of materially real or objective entity but that it is instead a part of a fundamental intellectual structure (together with space and number) of the mind within which humans sequence and compare events. Or in other words, reality is subjective, relative and mentally constructed.
1859: Big Ben begins ticking - The designers were the English lawyer and amateur horologist Edmund Beckett Denison, and George Airy, the Astronomer Royal. Construction was entrusted to clockmaker Edward John Dent and after his death in 1853 his stepson Frederick Dent completed the work.
1868: Wristwatch - invented by Patek Philippe (a Swiss luxury watch manufacturer), but only as a lady’s bracelet watch, intended as jewelry. It is also believed that Girard-Perregaux (a high-end Swiss watch manufacture) equipped the German Imperial Navy in a similar fashion as early as the 1880s - the wristwatches were used while synchronizing naval attacks and firing artillery.
1879: Atomic clock - Lord Kelvin, British physicist and engineer, was the first to suggest the idea of using atomic transitions (when electrons in a molecule are excited from one energy level to a higher energy level) to measure time.
1895: The Time Machine - a science fiction novella by H. G. Wells, English science fiction author. The story is generally credited with the popularisation of the concept of time travel using a vehicle that allows an operator to travel back in time. Wells also coined the term "time machine".
1905: Special relativity - in his theory, Albert Einstein challenged the notion of absolute time and suggests length contraction and time dilation.
1908: Spacetime - a mathematical model that combines space and time into a single continuum - it was first explicitly proposed mathematically by Hermann Minkowski, German mathematician, building on and extending Einstein's work. His concept (Minkowski space) is the earliest treatment of space and time as two aspects of a unified whole, the essence of special relativity.
1911: Twin paradox - Paul Langevin, French physicist, spread the theory of relativity in France and created what is now called the twin paradox
1916: General theory of relativity - suggested by Albert Einstein. General relativity generalises special relativity and Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or spacetime.
1924-27: Quantum mechanics - developed by Niels Bohr,Danish physicist, Werner Heisenberg, German theoretical physicist and others. According to quantum theory a quantum particle can be present in two different states (wave–particle duality) at the same time, but not observed simultaneously. The Copenhagen interpretation (one of the earliest and most commonly taught interpretations of quantum mechanics) states that the wave-particle duality does not mean that a photon or any other subatomic particle is both a wave and particle simultaneously, but that it could manifest either a wave or a particle aspect depending on circumstances.
1927: Quartz clock - the first quartz clock was built by Warren Marrison, Canadian telecommunications engineer and J. W. Horton at Bell Telephone Laboratories in Canada.
1927: Arrow of time - a term coined by the British astronomer Arthur Eddington to describe the "one-way direction" or "asymmetry" of time.
1955: Atomic clock - Louis Essen, English physicist, built the first accurate atomic clock, based on a certain transition of the caesium-133 atom, at the National Physical Laboratory in the UK.
1994: GPS: - developed by the U.S. Department of Defense (DOD). The Global Positioning System in coordination with the Network Time Protocol can be used to synchronize timekeeping systems across the globe.
General Time Resources Mathematical Models of Water Clocks
The Christian calendar: Easter - webexhibits.org
Leap years: National Maritime Museum (NMM)
Introduction to Chinese Calendar - chinapage.com
Daylight Saving Time - California Energy Commission
Time Exhibits - time.gov
Time Traveler - PBS A Walk Through Time - NIST
It's about Time - Why Files
Atomic Clocks - Science Museum
Huygens' Clocks - Science Museum
Time Travel - PBS
Science Fair Projects and Experiments
Time Science Fair Projects
A Simple Escapement Mechanism
Time Timeline - Why Files
A Walk Through Time - NIST
Time on Stamps
Instruments & Measurements - Buffalo University