The clock was so named about the late 13th century. It was called the horologium or hour-teller before then. Like the calendar, it originated from the desire of ancient humans to functionally and accurately calibrate the periodicity of the movement of the astronomical bodies they observed. The calendar in a broad sense is a type of clock. However, the clock is essentially the device used to calibrate the smallest unit of the calendar, the day.
The day is generally considered to be the period required for one rotation of an astronomical body (for humans, earth is the astronomical body) about its axis. This period depends on the star used as the reference point. For example, the sidereal day (one rotation of earth about its axis relative to a star that is not the sun) is about 4 minutes shorter than the mean solar day. The solar day is the interval between meridian passages of the sun. The meridian is the imaginary line on the earth's surface drawn from pole to pole. It is midday at a specific place on earth when the sun's direct rays are over the meridian of the place. The solar day varies in length because the earth's speed varies as it moves in its orbit. The mean solar day is the average derived from the solar days measured over a period of one year. The mean solar day is divided into 24hrs and it is used for all civil and many astronomical activities. Our modern civil day begins at midnight, local time. However, this was not generally the case in ancient times. For ancient Babylonians, the day began at sunrise. For ancient Athenians and Jews, the day began at sunset. The sunrise-sunset and sunset-sunrise days are still vey much alive in ecclesiastical settings. No matter the interval chosen, the desire for precise calibration of the day has been a common interest.
The shadow clock or gnomon (a vertical stick or obelisk),and the sundial were perhaps ancient humans' first attempts to calibrate the day. There other ancient clocks such as the hour glass, the water clock (aslo called the clepsydra), and the Chinese knotted rope. These clocks respectively used the flow of sand, the flow of water and the flow of fire (the chinese burned knotted rope in order to determine the time required to burn successive knots of the rope), to calibrated the day. as the search for better clocks progressed, some of these ancient clocks were improved on while others became obsolete. For example, a weight falling under gravity replaced water flow in time devices. This development anticipated the mechanical clock.
Mechanical clocks appeared in Europe at about the end of the first decade of the 14th century. They were heavy, bulky and generally not very accurate. Their dials had only one hand which indicated the nearest quarter hour. About 1360 A.D., Charles V, monarch of France, authorized Henry De Vick of Wuttenberg to make a tower clock for his Paris Royal Palace (now Palais de Justice). The project took eight years. The clock had a dial with only one hand, it was heavy and it kept time within a range of two hours a day. It was regulated by shifting the weight from each end of a balance and powered by falling weights: a 500 lb (227 kg) weight with a descent of 32 feet (9.8 m). A 1500 lb weight was used to strike the bell. The De Vick clock is generally considered the first mechanical clock. However, some clock historians believe that various crude forms of the mechanical clock were in Europe before the De Vick clock.
Several inventions in the 17th and 18th centuries made further development of the mechanical clock possible. In the late 16th century, the great physicist and astronomer Galileo Galilei discovered that the period of the swing (back-and-forth oscillation) of the pendulum is a constant. This property of the pendulum is known as isochronism. While it is generally true, there are a few instances when the period of the swing varies. If the amplitude (maximum height) of the swing is to large, the period will depend on the amplitude. Also elevation influences the swing of the pendulum because of the role of gravity. The period of the swing is greater on a mountain than at sea level. In 1657, physicist Christiaan Huygens demonstrated how the pendulum could be used to regulate a clock. In 1667, physicist Robert Hooke invented an escapement (the part of a time device that connects the power source to the pendulum) that made it possible for a pendulum with a small swing to be used in a clock. George Graham improved the escapement and John Harrison developed a method that compensated for the variations in the length of a pendulum due to changes in temperature.
The desire for watches (small clocks that owners can carry along) was realized when coiled springs were introduced as the power source in clocks. About 1500 A. D., Peter Henlein of Numberg produced portable watches known as the Numberg eggs. The popularity of watches spurred increased activities in their production and development. Jacob Zech of Prague invented the spiral pulley (fusee) to equalize the uneven pull of the spring. Robert Hooke invented a spiral hairspring for the balance wheel, and Thomas Mudge devised a lever escapement. Later, minute and second hands, crystals to protect the dial and hands, and jewel bearings to reduce friction and improve durability, were introduced. These developments brought about elevated craftsmanship. Clockmaker guilds such as the Paris Guild of Clockmakers (1544), Clockmakers Company in London (1630), and others in the Netherlands, Switzerland, Germany, and Italy, were formed to oversee the art of clockmaking and its apprenticeship. The Guilds in these countries and in countries outside Europe such as China and Japan produced distinguished artisans who made beautiful and highly accurate decorative mechanical watches. Eventually, the art of clockmaking gradually diminished with the availability of machine-made parts.
The transition from mechanical clocks to electric clocks occurred in America. European immigrants had brought their clockmaking skills with them to the new world. So as early as 1650 A.D., there was a clock in Boston, Massachusetts' church tower. In 1716, the city hall at Nassau and Wall streets in New York City, had a public clock, and by 1753 a clock was in place in Independence Hall, Philadelphia, Pennsylvania. At about 1800, Thomas Harland of Norwich, Connecticut established a clock factory that produced a significant volume of watches. In the early 1800s, Simon Willard of Roxbury, Massachusetts, patented the popular banjo clock, and Eli Terry of Connecticut introduced the pillar-and-scroll clock a shelf clock that required winding once a day. At Plymouth Hollow (now Thomaston), Connecticut, Seth Thomas founded the Seth Thomas Clock Company, which became one of the largest clock factories in the world by the mid-20th century. In 1836, the Pitkin brothers of East Hartford, Connecticut, produced the first American-designed watch. It also contained the first machine-made part. These innovations and others such as the rolled-brass clock movement devised by Chauncey Jerome of Bristol, Connecticut, and the invention of automatic production machinery in Massachusetts by Aaron Dennison and Edward Howard, together with the economies of mass production, significantly lowered the prices of well designed watches. For example, it became possible to price the first Waterbury, a famous American pocket watch, at $4. Later watches like the Ingersol and the Ingraham were called the dollar watches. By the early 1900s, Henry E. Warren had invented the electric clock.
The accuracy provided by the electric clock was improved on when in 1921 W.H. Shortt invented the Shortt Free Pendulum which was first installed in the Edinburgh Observatory. In 1929, the accuracy of Shortt Free Pendulum was improved on when the quartz clock was introduced in the United States. In 1955, the cesium atomic clock was developed in England and it became the most accurate clock at that time. Several other developments, especially in the direction of design, followed. In 1957, the electric wristwatch appeared on the market. A couple of years later, the electronic watch which had a battery-powered transistorized oscillating circuit, and a small tuning fork as escapement, followed. In the 1960s, LED (Light Emitting Diode) watches appeared. Their illuminated digital time displays were made possible by the light-producing property of certain semiconductors and the oscillations from quartz crystals were reduced to compute the digital time. In the 1970s, LCD watches which use liquid crystals (substances with optical properties akin to liquids and solid crystals) appeared. Developments in various fields like metallurgy, solid state physics, and molecular chemistry continue to influence horological developments. Modern mechanical watches now have their mainsprings made from rust-proof and break-proof metals. Precious stones in jewel bearings can now be replaced with synthetics. Cases that seal out dust and moisture and calendar watches (watches that display day month and year) are everywhere. Sources of power such as sunlight, body heat, and atomic energy have tapped for horological uses and research continues in these fields. Highly accurate technique for studing atomic energy oscillations which was invented by physicists Paul Wolfgang, Norman Forster Ramsey, and Georg Dehmelt became the basis for modern atomic clocks. Atomic clocks are precise and are used to keep worldwide time, the universally accepted time.
Atomic clocks measure time by measuring the frequency of the radiation emitted by an atom when its energy state changes. The energy state of an atom changes when it moves from one energy level to another. If the movement is to a higher energy level, it absorbs an amount of energy (or quanta), if the movement is to a lower energy level, it emits an amount of energy. The amount of energy absorbed or emitted is dependent on the difference between the energy levels. The emitted energy is in the form of electromagnetic radiation (energy waves with specific wavelengths and frequencies). The frequency of the radiation can be determined either by: (1) Inducing a group of atoms in an elevated energy state to a lower energy state and then measuring the emitted radiation, or (2) Exposing a group of atoms in a lower energy state to electromagnetic radiation with variable frequency. The frequency at which the majority of the atoms jump to the next energy level is the correct frequency. Active atomic clocks are based on process (1) while passive atomic clocks are based on process (2). Most modern atomic clocks are passive cesium clocks. The United States National Institute of Standards and Technology (NIST) established the second as the time required to complete 9,192,631,770 cycles at the frequency emitted by cesium atoms making the transition from one energy state to another. Cesium clocks are so accurate that their error rate is estimated to be only a second off, per 300 million operational years.
The development of atomic clocks made several innovations in time and distance measurement possible. Statellite navigation, positioning systems like the Global Positioning System (GPS), and measurement of the cycles of astronomical objects such as the millisecond pulsars, rely on atomic clocks. Atomic clocks are the clocks used in space projects by the various space agencies of countries with advanced space programs.
From the primitive shadow clocks and sundials to the sophistication and precision of atomic clocks... What a journey! How has this impressive journey influenced our perception of time? Evidently it has heightened our awareness of periodicity and the numerous benefits from its measurement (or disbenefits, as some eastern sages would say). But has the journey put to rest our desire for a whole understanding of Time? Is the question: What Is Time? wholly answered as a result of humanity's mastery of the measurement of periodicity? Read on!.
Peter Oye Sagay