Clock and Watch | Research & Encyclopedia Articles

About 5 pages (1,509 words)

Clock Summary

Clock and Watch

In the early days of humanity, only three divisions of time existed: days (the interval between successive sunrises), months (the interval between complete lunar orbits), and years (the interval between the start of one planting season and the start of the next). The first artificial division of time was the hour, probably established by the Egyptians during the fourth millennium b.c. Beginning at dawn and dusk, twelve hours each were given to night and day. Unfortunately, since the changing seasons cause the length of night and day to vary by several hours, the Egyptian hour was not really a fixed unit. In winter, for example, because nights are longer than days, twelve night "hours" would last longer than twelve day "hours." What was needed was a device that could measure time in regular, unvarying amounts. Toward this end, early scientists began the evolution of the modern clock. Ancient observers noticed that as the sun traveled across the sky, shadows on the ground would move and vary in size. This led to the invention of the sundial, most likely beginning as a simple stick in the ground and eventually leading to the construction of large obelisks. Ancient writers credit the Greek scientist Anaximander of Miletus (610-c. 547 b.c. ) with the invention of the sundial during the sixth century b.c., but it is presently considered almost certain that it appeared in the Chinese and Egyptians civilizations many years earlier. When properly read, sundials served as a fairly accurate method for marking the passage of time; however, they proved to be difficult for many to interpret. In addition, the markings for each sundial had to be adjusted according to its latitude, and the readings differed as the seasons progressed. The first mechanical timekeeping device was a water clock called a clepsydra. It operated by pouring a steady stream of water into a vessel; after a certain period the vessel would fill, then tip itself empty, and be ready for refilling. The amount of time this took could be regulated by changing the size of the vessel. Later versions of the clepsydra began with a filled vessel, which would release the water over time. Such clepsydras were first used from about 1500 b.c. through the Middle Ages. During this time some rather elaborate water clocks were constructed. One built for the Emperor Charlemagne in 800 a.d. dropped a metal ball into a bowl to mark the arrival of a new hour, while others, which were used by astronomers, regulated astrolabes and other equipment. There were many problems with water clocks. Depending upon the climate, the water in the clock would often evaporate, causing the device to lose time, or freeze solid, stopping the machine entirely. Even under optimal temperatures the continual flow of water through an aperture would cause the opening to erode and widen, thus making the clock increasingly inaccurate. It became evident to clockmakers of the time that a completely mechanical clock was necessary. During the Middle Ages the two professionals most skilled in the construction of clocks were astronomers, who used the devices to plot the motions of the heavens, and monks, who needed them to determine when to toll the monastery bell. A monk probably invented the first completely mechanical clock around a.d. 1275. This first clock, which was driven by the slow pull of a falling weight that had to be reset to its starting position after several hours, was much more accurate than the water clocks of the past. The clocks in monasteries were also among the first alarm clocks; fitted with a striking mechanism, the clock could be set to sound when the monastery's great bell needed to be rung. As the accuracy of timepieces increased, society came to certain realizations about the nature of the world. First, it became readily apparent that days (that is, daylight hours) varied in length throughout the year. Second, it was found that the sun did not rise at the same time all over the world. This latter phenomenon was not addressed until 1884, when the world adopted Greenwich Mean Time, giving us time zones. The next step in the evolution of the clock was the development of improved escapements, which are mechanical devices that ensure regular motion within the clock. Often pictured as a tiny hammer falling into the teeth of a gear, the escapement allows the minute hand to move once each minute. The first escapement was designed around a.d. 1300 and was fitted into a weight-driven clock.

Called the verge-and-foliot escapement, it used a rotating bar with foliots to alternately halt and release the teeth of a ratchet wheel. Improvements in escapement design allowed the Italian Giovanni dé Dondi to build an elaborate astronomical clock over a span of sixteen years in the 1300s. Near the beginning of the fifteenth century, engineers were using coiled springs in door locks and handguns. Borrowing from this technology, clockmakers developed the first spring-driven clocks around 1430. By replacing the heavy, long-corded weights, horologists were able to build timepieces small enough to be carried on one's person. The main drawback of coiled springs was that they unwound quickly at first and then more slowly. Clockmakers soon added the fusee , a trumpet-shaped pulley that increased mechanical leverage as a spring wound down, allowing the watch to run at a constant rate. First suggested by Leonardo da Vinci in 1407, the fusee is so efficient that it is often used in many of today's clocks. Even with the addition of springs, clocks before the mid-1600s were notoriously inaccurate. About that time, history tells us, Galileo was in the Tower of Pisa during an earthquake. As the ground shook, Galileo watched the motion of swinging chandeliers with fascination; by timing their swing against his own pulse, Galileo found that the amount of time it took a chandelier to swing from one side to another was constant, no matter what the distance. This supposedly was the inspiration for his swinging pendulum, an invention he designed but never actually built. The first working pendulum clock was constructed in 1656 by the brilliant Dutch scientist Christiaan Huygens. With the pendulum imparting a steady motion and the addition in 1675 of the anchor escapement by William Clement, the weight-driven pendulum clock became the most precise yet. During this same time scientists became occupied with a new puzzle--inventing a timekeeping device that could be used aboard sailing ships for navigation. Because of the turbulence at sea, both weight-driven and pendulum clocks were unsuitable. In 1674 Huygens introduced a watch that featured a balance spring as a regulator, acting in place of a pendulum. Besides sparking a tremendous controversy with the English scientist Robert Hooke, who claimed that Huygens had stolen his idea, the introduction of the balance spring made an immediate impact upon the world of clockmakers. However, it was not until 1761 that an English inventor, John Harrison, joined a balance spring with a mainspring-driven clock to produce a precise and completely portable watch, suitable for ships as well as a person's wrist. Harrison's design forms the basis for most modern spring-driven clocks. The common wristwatch is among the most precise mechanical instruments. If a watch loses 20 seconds every day it is still operating at an error rate of only 0.023 percent--all the more remarkable since it is expected to run 24 hours a day, 365 days a year, a task required of no other measuring device. Still, clockmakers at the turn of the twentieth century were not yet satisfied. Clocks powered by electricity had been in existence since the late 1800s, but most required large and ungainly machinery in order to function. These early battery clocks used tiny motors to wind the mainspring when it ran down. The real revolution in battery operated timepieces came during the 1950s when the Swiss put a tiny electric tuning fork inside a watch. When the battery applies a small charge to the tuning fork, it will vibrate continuously at a very specific rate, and that vibration can be used in place of a clock's slowly unwinding mainspring. Since the invention of the Swiss-movement watch, most tuning forks have been replaced with tiny pieces of quartz crystal, a natural substance which can vibrate with much greater precision than any man-made tuning fork. Even the most affordable quartz clock is accurate to within one minute per year. Currently the apogee of human efforts to monitor time is the atomic clock. Technically not a timepiece since it does not indicate time, the atomic clock is used as a reference standard for absolute time. First constructed in 1948, the atomic clock measures the unvarying frequencies at which molecules vibrate. By knowing how many times a molecule will vibrate within a unit of time, the atomic clock can be used to regulate the accuracy of other clocks. Such absolute precision is essential for navigation, particularly in space, as well as research on the atomic level. Chronographs regulated by atomic clocks will lose less than one second every one thousand years.

This is the complete article, containing 1,509 words (approx. 5 pages at 300 words per page).

Clock and Watch article