A ‘clock’ is an instrument used to specify, record, and manage time. The word ‘clock’ comes from the French word “cloche” meaning bell, came into use when timekeepers were kept in bell towers in the Middle Ages. Historians do not who or when mankind “invented” a time-keeping device or a “clock”. Probably thousands of years ago when someone stuck a stick in the ground and saw a shadow of the sun move across the ground, known as the sundial. (Cummings, 1997-2012).
After the Samarian culture left little knowledge behind, the Egyptians were next to divide their day in two parts. A vertical stick, or obelisk that is used to cast a shadow is known as a sundial. They were used as early as 3500 B.C.. Another shadow clock or sundial, possibly the first portable timepiece, came into use around 1500 B.C. to measure the passage of hours. As the sun moves from east to west, the shadows predict the time of the day. They also showed the year’s longest and shortest days when the shadow at noon was the shortest or longest of the year. The Greeks used a sundial called “pelekinon”. These sundials are marked to predict time accurately throughout the year. They built a more accurate sundial based on their knowledge of geometry. An ancient Egyptian sundial from the 8th century and a Greek sundial are still in existence today.
Water clocks along with sundials are known to be the oldest time-measurements devices. The bowl-shaped outflow is the simplest form of a water clock and is known to have existed in Babylon and in Egypt around the 16th century BC. Other regions of the world, including India and China, also have early evidence of water clocks, but the earliest dates are less certain. Some authors, however, claim that water clocks appeared in China as early as 4000 BC. (Cowan, 1958) Ctesibius or Ktesibios or Tesibius (Greek: Κτησίβιος) (fl. 285–222 BC) was a Greek inventor and mathematician in Alexandria, Ptolemaic Egypt. (As of 2008, 1768–2010)
He improved the clepsydra in the 3rd century by B.C. by which water that dripped into the container raised a float that carried a cursor to mark the hours. He attached a toothed rack with a float switch that when raised would turn a wheel where he installed mechanical signing birds and bells to signify certain hours of the day such as noon or midnight. In the 16th century A.D. clepsydras were used by Galileo to time his experimental falling objects.
A candle-timepiece is also of ancient origin. No one knows exactly when it originated. It was used to measure the transitory of time by marking intervals along the span of the candle. Ancient Egyptians used tallow, an animal substances to make candles. The Romans were the first to use a wick inside of a candle. Beeswax was used to make candles during the middle ages, however it was very expensive. It was said that the Romans and the Chinese would use candle-timepieces as alarm clocks. They would stick a nail in a certain point of the candle depending on the desired time. Whenever the candle wax melted down to the nail, the nail would then fall onto a tin pan and make a noise.
An hourglass or sand clock was a commonly used time device. Its consist of two glass compartments connected by a narrow neck containing an certain amount of sand that slowly trickles from the bottom chamber to the lower in a set amount of time, often one hour or so. Hourglasses were very popular on board ships, as they were the most dependable measurement of time while at sea. Unlike the clepsydra, the motion of the ship while sailing did not affect the hourglass. The fact that the hourglass also used granular materials instead of liquids gave it more accurate measurements, as the clepsydra was prone to get condensation inside it during temperature changes. (Balmer, (Oct., 1978)). In the early-to-mid -14th century A.D., large mechanical clocks begin to appear in towers of several large Italian cities.
These clocks were weight driven and very inaccurate. One of the first clocks to strike the hour was in Milan in around 1335 A.D. These clocks only had one hand, the hour hand. In 1510, a man by the name of Peter Henlein, a locksmith and clock maker of Nuremburg, Germany, invented the spring driven clock. He is often considered the inventor of the watch. (Dohrn-van Rossum & Dunlap, 1996). In 1557, the minute hand was invented. However, it wasn’t until the invention of the pendulum in the late 1600’s that the minute hand became useful.
As electricity was introduced, clocks began to use an electrical impulse to operate the dials of a master clock. The electrical current replaced the spring and weight as a power source. The piezoelectric effect given by the quartz crystals was discovered by the Curie brothers, Pierre and Paul-Jacques Curie in 1880, but wasn’t applied into a clock until 1929. This effect exhibited by certain crystals generating a voltage when subject to an electric field, induced an electric potential to nearby conductors, therefore powering the clock. These clocks can have an accuracy of one second every 10 years.
Along with these inventions, Charles Dowd introduces the idea of time zones in 1870 dividing the United States by meridians one hour, and 15 degrees apart using Greenwich, England as zero meridian. In 1883 the railroads adopt the four time zones for the continental United States. And in 1918 the United States Congress passes the ‘Standard Time Act’, authorizing The Interstate Commerce Commission to establish standard time zones within the United States, and establishing daylight saving times. Finally, In 1949 The National Institute of Standards and Technology built the first atomic clock, using ammonia. A second is formally defined as 9,192,631,770 vibrations of the cesium atom. Atomic clock NIST-7 has been the main atomic time standard for the United States, and is among the best time standards in the world.
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