Historic and Modern Timing Devices
In today's world, time is all around us and we're constantly reminded of how much we're driven by and rely on it - clocks are everywhere. The ease of manufacturing digital clocks in recent decades has led to their appearance on countless fixtures and appliances: Microwaves, ovens, dishwashers, coffee makers, stereos, cars and public signs are inundated with time pieces but they even appear on some blenders, recliners, fans, pens and toilets' but it wasn't always this way.
The desire to divide the day into hours came about probably just as early as the interest in dividing the year into months and days. The very first devices for dividing the day used the same logic that was used to divide the year; the movement of celestial bodies. Sumerian and Egyptian cultures used the movement of shadows created by the sun to track the progression of time.
As early as 3500 B.C. the Egyptians created slender monuments known as obelisks. Markings around the base of the monument marked noon and also showed the longest and shortest days of the year. By 1500 B.C. the Egyptians had created a portable shadow clock consisting of an upright crossbar and a long, divided base that was situated with the upright crossbar facing the East in the morning and the West after noon ' as the crossbar shadow passed the markings on the base the day was further divided into segments.
By 600 B.C. the Egyptians created the merkhet. A North-South line could be established by aligning two merkhets with the Pole Star and time could be tracked as stars crossed over the meridian.
The natural properties of elements and other natural phenomena were first used to create crude time measuring apparatuses. Gravity was utilized with sand filled hour glasses and many types of water clocks used the buoyant properties of water coupled with gravity to measure time: Bowls with a small hole in the bottom and markings on the inner walls could be placed in a larger body of water to measure time as they sunk while similar bowls filled with water could measure time as the water leaked out of them ' of course, these methods didn't produce a constant rate for measuring time. The burning process was used in many ways as well: Candles were given vertical markings, oil lamp reservoirs were notched and mazes were filled with incense that burned at a constant pace.
By the late 13th century the first mechanical clocks were devised. These clocks were driven by weight and used a verge-and-foliot mechanism. The verge escapement would drive the oscillation of the horizontal foliot ' a primitive balance wheel. This type of mechanism was used in many cathedral clocks throughout 14th century Europe. By the 15th century clockmakers began experimenting with spring driven clocks and by the early 16th century clocks began changing into portable timepieces.
In the middle of the 17th century, the first pendulum clock was invented that kept time with less than 1 minute of error a day. Within years the error in clocks was reduced to mere seconds a day and the error in watches was reduced to 10 minutes a day. Over the next century improvements to balance wheel escapement would reduce error in watches to 1/5th a second a day and by the late 19th century refinements in freeing the pendulum would allow clocks to attain accuracy to one hundredth of a second a day.
By the 1930's quartz clocks replaced pendulum and balance-wheel escapements. This technology is based on the piezoelectric property of quartz crystals. When an electric field is applied to the crystal it changes shape and when squeezed it generates an electric field. By creating an electronic circuit a highly constant frequency can be generated that can be used to operate an electronic clock.
But, due to the fact that no two crystals are perfectly similar, they all have slightly varying vibrations and frequency. Thus, modern science has reached into the resonances of single atoms as atoms are stable over time and space. The first atomic clock was built in 1949 and was based on microwave resonances in the ammonia molecule, but was quickly replaced by the cesium atomic clock in 1957. The cesium atom's natural frequency is 9,192,631,770 oscillations per second, and today's atomic clocks keep time to one millionth of a second per year' well within the natural adjustment of earth's slowing day.
Stopwatch and Timer Essentials