Time is one of the world’s deepest mysteries. No one can say exactly what it is. Yet, the ability to measure time makes our ways in life possible. Most human activities involve groups of people acting together at the same place and time. People could not do this if they did not measure time in the same way (History of American Heritage NP).
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One way to think about time is to imagine a world without it. A timeless world would be at a standstill. But if some kind of change took place, that timeless would be different now than it has ever been. No matter how brief, the period between before and now indicate that time must have passed. Thus, time and change are related because the passing of time depends on changes taking place. In the real world, change is that which is kept constant (History of American Heritage NP, Time – for – time.com NP).
The sundial was one of the earliest devices for measuring time. But it can work only in a cloudless daylight. Early peoples also used ropes with knots tied at regular intervals or candles marked with regularly spaced lines. When burned, such devices measured time. An hourglass or sandglass tells time by means of sand trickling through a narrow opening. By allowing water to drip slowly coming from one marked container into the other, time is measured by a clepsydra or water clock. By the 1700s, peoples have developed clocks and watches that told time to the minute (Masato 367).
The minute is a unit used to measure time. In time, 60 minutes is equivalent to 1 hour. Each minute is divided into 60 seconds. The minute in time is an exact measurement, which means exactly so much time (Boardman NP).
Second is a unit in the metric system which is used to measure time. In measuring time, 60 seconds is equivalent to 1 minute. There are sixty minutes in an hour, and twenty – four hours in a day (Boardman NP).
A second of time equals an exact fraction of a day. But days are not equal in length because the earth does not travel in a perfect circle around the sun. Therefore, measurements of time based on the day are not constant and cannot be used for scientific work (Boardman NP).
The Romans called the first division of the degree the partes minutae primae, or “first small parts.” The second division they called the partes minutae secundae, or “second small parts.” These terms were finally shortened to minute and second (Boardman NP).
Hour is defined as the interval of time. It consists of 60 minutes. A day, from midnight to midnight has 24 hours. Every nation regulates its activities according to the hour. But people did not begin to use hours to mark uniform periods of day until the 1300s, when the mechanical clock was invented (Masato 367; Time – for – time.com NP; Boardman NP, Museum of American Heritage NP).
The ancient Romans used the hour to note a point of time, such as sunrise and sunset. They later added the hour of noon. At the beginning of the Christian era, the Romans divided the hours of daylight into five periods, which they marked on their sundials (Masato 367; Time – for – time.com NP; Museum of American Heritage NP).
Clock is an instrument that shows the time. They not only measure and tell time they also serve as decorations in homes and other buildings (Time – for – time.com NP; Kuhn NP; Museum of American Heritage NP).
A watch is a small portable clock. People use them to tell time and also to wear or carry them as personal accessories. Portable clocks were first used during the 1500s by town watchmen in Europe. As the watchmen made their rounds, they carried the portable clock on straps around their necks. As other people began carrying timepieces, the name was shortened to watch (Masato 367; Time – for – time.com NP; Kuhn NP; Museum of American Heritage NP).
Peter Henlein, a German locksmith, traditionally has been credited with making the first watch. In the early 1500’s Henlein invented a mainspring to power clocks. Until then, clocks had been driven by falling weights and had to remain stationary and stand upright for the weights to operate. Mainsprings enabled clockmakers to produce small, portable clocks. Watchmaking soon spread to England, France, and Switzerland (Time – for – time.com NP; Kuhn NP; Museum of American Heritage NP).
In A.D. 605, the Christian church named the seven canonical hours or hours of prayer. They were the matins or morning and lauds or praise; prime or first; tierce or third; sext or sixth; nones or ninth; vespers or evening; and complin or complete. These hours marked only periods of daylight, beginning at 6 a.m. The nights were sometimes divided into watches, which marked the times when guards reported for duty or were changed. The length f the hour varied with the season. The winter hours were shorter than the summer hours, because there was less daylight during the winter (Masato 367; Time – for – time.com NP; Museum of American Heritage NP).
By the 1500s, many churches and palaces in Europe had installed mechanical clocks with 12 – hour dials. These clocks did not keep good time, and had to be set every sunshiny day at noon, when the sun was at its highest point, or on the meridian. From this we get the letters a.m., meaning ante or before meridiem, or before noon, p.m. means post or after meridiem, or after noon. When people first began to tell time by the clock, they substituted the word o’clock, meaning by the clock, for the word hour (Kuhn NP; Boardman NP).
Confusion can result if the letters a.m. and p.m. are not used. European railroads and airplane timetables use a single 24 – hour system. To avoid confusion, four figures are used. Thus, 1:00 a.m. is written as 01:00 and 1:00 p.m. is written as 13:00, and 12:00 midnight is 24:00. The United States armed force also use this system, but without the colon. In conversation, all four figure are used, such as “0 one hundred” for 1:00 a.m., “twelve hundred” for 12:00 noon, and “twenty – four hundred” for 12:00 midnight (Kuhn NP; Boardman NP).
The earliest watches were heavy and inaccurate. They weighed so much that they had to be suspended from a cord or chain and worn around the neck or hanging from a belt. Early watches had only an hour hand, and their cases were spherical or drum-shaped. Unusual shapes, including skulls and crosses, became popular during the mid-1600’s (Time – for – time.com NP; Kuhn NP; Museum of American Heritage NP).
Many watches had a minute hand by the late 1600’s, but a hand for the seconds did not become common until the 1900’s. The balance spring and escape lever mechanisms had been developed by the late 1700’s (Masato 367; Time – for – time.com NP; Kuhn NP; Boardman NP; Museum of American Heritage NP).
During the late 1600’s, watches became small and light enough to fit into a pocket or a jacket or vest. These pocket watches were the most popular style of watch for more than 200 years (Masato 367; Time – for – time.com NP; Kuhn NP; Museum of American Heritage NP).
Mechanical watches are powered by a coiled spring called a mainspring. Some have to be wound at various intervals. Some have to be wound everyday, but others can run for seven or eight days without rewinding. There are two main kinds of mechanical clocks, weight driven and spring driven clocks. Almost all of them are dial clocks (Masato 367; Time – for – time.com NP; Kuhn NP; Museum of American Heritage NP).
Weight – driven clocks are powered by a heavy weight that hangs from a cord or chain. When the clock is wound, the cord or chain gets wrapped around a drum and draws the weight up near the drum. As gravity pulls the weight down, the cord or chain slowly unwinds and turns the drum. The hands of the clock are attached to individual wheels in the train. Each of these wheels turns at a specific speed. A pendulum and an escapement prevent the weight from being lowered too fast. They also regulate the clock’s speed (Masato 367).
Spring – driven clocks contain a coiled spring called the mainspring. This spring gets wound up when the clock is wound. Then the mainspring unwinds slowly, turning the wheels in the train. The escapement in a spring – driven clock resembles that of the weight – driven clock. However, most spring – driven clocks have a balance wheel replacing the pendulum. It coils and uncoils and makes the balance wheel swing back and forth at a fixed rate. The pallets alternately catch and release the escape wheel and regulate the speed of the train (Masato 367).
In many watches, the mainspring is wound by turning a knob, or crown, that is connected to a shaft inside the case. Other watches, called self-winding watches, contain a weight mechanism that winds the mainspring automatically when the watch is moved about. As the watch runs, the mainspring unwinds. The power supplied by the unwinding mainspring turns several tiny gear wheels that are connected in a series called the train. A watch’s hands are attached to individual gear wheels that turn at specific speeds. The speed of the wheels is partially determined by a mechanism called the escapement (Masato 367).
The escapement includes an escape wheel, a balance spring, and a pallet lever. The escape wheel is connected to the train and turns when the watch runs. It also transmits energy to the balance wheel, which is the time base, or timekeeping device of the watch. The balance spring, also called the hairspring, makes the balance wheel oscillate or spring back and forth at a specific frequency. Most balance wheels oscillate five or six times a second. The pallet lever has two pallets or hooks one at either end that catch on the escape wheel. Each oscillation of the balance wheel causes the pallet lever to swing, thus enabling the escape wheel briefly to escape the grip of the pallets. The escape wheel then turns slightly before the pallets again catch on it. This catching action stops the movement of the escape wheel and also produces the characteristic ticking sound of a mechanical watch. Each slight movement of the escape wheel is transmitted through the other wheels of the train to the hands of the watch. Because the oscillations of the balance wheel regulate the speed of the escape wheel, they are responsible for the accuracy of the timepiece (Masato 367).
Many mechanical watches have more than one hundred parts. The most expensive watches, some parts are finished by hand to ensure accuracy and durability. In addition, the pallets and various other parts of such watches are made from tiny, hard jewels such as natural or synthetic rubies to reduce wear. Such timepieces contain fifteen or more jewels (Masato 367).
The first mechanical clock was probably invented in China in the late 1000’s. However, this invention was never developed further, and later Chinese clocks were based on European models (Masato 367; Time – for – time.com NP; Kuhn NP; Museum of American Heritage NP).
Historians believe the first mechanical clocks in Western civilization were developed by a number of inventions during the late 1200s. These clocks were weight driven, but they had no pendulum or hands. They had a bell that rang to indicate the hour. By the mid – 1300s, the dial and hour hand had been added. The first spring – driven clocks were probably developed in Italy during the late 1940s (Masato 367; Time – for – time.com NP; Kuhn NP; Museum of American Heritage NP).
Most early clocks ran unevenly and inaccurately. The pendulum and the balance spring, which were developed in the mid – 1960s, greatly improved timekeeping accuracy. Minute and second hands became common (Masato 367; Time – for – time.com NP; Kuhn NP; Museum of American Heritage NP).
A device called an escapement is fastened to the clock’s mechanism. It gives small but regular pushes to the pendulum, and keeps it swinging. The escapement lets one tooth of a toothed – wheel turn past it each time the pendulum swings aside. This action gives the clocks its tick – tack sound (Masato 367; Time – for – time.com NP, Kuhn NP; Museum of American Heritage NP).
The rod in a clock pendulum tends to expand when it is warm and to shorten when it is cold. This would make a clock run slower in warm weather than in cold. Clocks known as regulators come with so called – gridiron pendulums. These consist of several brass and steel rods so attached that some expand upward and some downward. This keeps the total length of the pendulum constant. In another device, the length is kept constant by the expansion and contraction of mercury in a cup which swings at the end of the rod (Masato 367; Time – for – time.com NP; Kuhn NP; Museum of American Heritage NP).
Any change that takes place again and again stands out from other changes. The rising and setting of the sun are examples of such change. The first people to keep time probably counted such natural repeating events and used them to keep track of events that did not repeat. Later, people made clocks to imitate the regularity of natural events. When people began to count repeating events, they began to measure time (Time – for – time.com NP).
Boardman, Pete. 24 Hour Clocks and Watches because there are 24 hours in a day. (2007). MAC.com. Retrieved March 11, 2008, from http://homepage.mac.com/pete.boardman/24hourclock/history/index.html.
It’s About Time. (3 November 2004). Museum of American Heritage. Retrieved March 11, 2008, from http://www.moah.org/exhibits/archives/time/index.html.
Kuhn, Marcus. (19 December 2004). A Summary of the International Standard Date and Time Notation. Retrieved March 11, 2008, from http://www.cl.cam.ac.uk/~mgk25/iso-time.html.
Masato, Takenaka. “History of Measuring Time.” Journal of the Japan Society of Mechanical Engineers 104 (2001): 366 – 7.
“History of Telling Time.” 2003. Time – for – time.com. Retrieved March 11, 2008, from http://www.time-for-time.com/timeline.htm.