什麼是鍾

一種計算和記錄時間的機械或電子裝置。機械鐘包含一種相等時距內作有規律運動的裝置及與之相聯動的將運動次數記錄下來的計數機件的機器。第一座時鐘可能是由修道院發明使用的。歐洲第一座公用打點的時鐘是在米蘭建造的（1335）。現存最古老的時鐘儲存在英格蘭（1386）和法國（1389）。最早的家庭時鐘出現在14世紀後期。約1500年德國鎖匠亨萊恩（P. Henlein, 1480～1542）開始製造由彈簧控制、第一次可攜帶的小時鐘。惠更斯在1656年發明鐘擺。1859年在威斯敏斯特安裝了大班鍾，該鐘成為所有精確塔鐘之標準。最準確的機械計時器（每天誤差在千分之幾秒以內）是短鐘擺（擺長約為99公分）的時鐘。1929年石英晶體首先應用於計時，天文臺石英鐘最大誤差每天不過萬分之幾秒。1951年第一座原子鐘開始運作，這是一種利用原子的某種共振頻率使時間保持特殊精準度的計時器，其準確度每天只超出十億分之一秒，成為目前最精準的時鐘。

clock

Machine or electronic device that measures and records time. A mechanical clock consists of a device that performs regular movements in equal intervals of time, and is linked to a counting mechanism that records the number of movements. The first clocks may have been invented for use in monasteries. The first European public clock that struck the hours was erected in Milan in 1335. The oldest surviving clocks are in England (1386) and France (1389). The first domestic clocks appeared late in the 14th century. About 1500 Peter Henlein, a German locksmith (1480-1542), began to make the first portable timepieces, small clocks driven by a spring. Christiaan Huygens invented pendulum clocks in 1656. Big Ben, the great clock at Westminster in London, was installed in 1859 and is the standard for all accurate tower pendulum clocks. The most accurate mechanical timekeepers (within a few thousandths of a second per day) are clocks with short pendulums (about 39 in., or 990 mm). In 1929 the vibration of a quartz crystal was first applied to timekeeping; the maximum error of an observatory quartz-crystal clock is only a few ten-thousandths of a second per day. The first atomic clock went into operation in 1951. Atomic clocks, regulated by the natural periodic behavior of a system of atoms (such as vibrations or emission of radiation), can have accuracies exceeding one billionth of a second per day, making them the most accurate clocks yet invented.