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A Chronicle of Timekeeping
A
According to archaeological evidence, at least 5, 000 years ago, and long before the advent of the Roman Empire, the Babylonians began to measure time， introducing calendars to co-ordinate communal activities, to plan the shipment of goods and, in particular, to regulate planting and harvesting. They based their calendars on three natural cycles: the solar day, marked by the successive periods of light and darkness as the earth rotates on its axis; the lunar month, following the phases of the moon as it orbits the earth; and the solar year, defined by the changing seasons that accompany our planet's revolution around the sun.
B
Before the invention of artificial light, the moon had greater social impact. And， for those living near the equator in particular, its waxing and waning was more conspicuous than the passing of the seasons. Hence, the calendars that were developed at the lower latitudes were influenced more by the lunar cycle than by the solar year. In more northern climes, however, where seasonal agriculture was practiced, the solar year became more crucial. As the Roman Empire expanded northward, it organised its activity chart for the most part around the solar year.
C
Centuries before the Roman Empire, the Egyptians had formulated a municipal calendar having 12 months of 30 days, with five days added to approximate the solar year. Each period of ten days was marked by the appearance of special groups of stars called decans. At the rise of the star Sirius just before sunrise, which occurred around the all-important annual flooding of the Nile, 12 decans could be seen spanning the heavens. The cosmic significance the Egyptians placed in the 12 decans led them to develop a system in which each interval of darkness (and later， each interval of daylight) was divided into a dozen equal parts. These periods became known as temporal hours because their duration varied according to the changing length of days and nights with the passing of the seasons. Summer hours were long, winter ones short; only at the spring and autumn equinoxes were the hours of daylight and darkness equal. Temporal hours, which were first adopted by the Greeks and then the Romans, who disseminated them through Europe, remained in use for more than 2, 500 years.
D
In order to track temporal hours during the day, inventors created sundials， which indicate time by the length or direction of the sun's shadow. The sundial's counterpart, the water clock, was designed to measure temporal hours at night. One of the first water clocks was a basin with a small hole near the bottom through which the water dripped out. The falling water level denoted the passing hour as it dipped below hour lines inscribed on the inner surface. Although these devices performed satisfactorily around the Mediterranean, they could not always be depended on in the cloudy and often freezing weather of northern Europe.
E
The advent of the mechanical clock meant that although it could be adjusted to maintain temporal hours, it was naturally suited to keeping equal ones. With these， however, arose the question of when to begin counting, and so, in the early 14th century, a number of systems evolved. The schemes that divided the day into 24 equal parts varied according to the start of the count: Italian hours began at sunset， Babylonian hours at sunrise, astronomical hours at midday and 'great clock' hours， used for some large public clocks in Germany, at midnight. Eventually these were superseded by 'small clock', or French, hours, which split the day into two 12-hour periods commencing at midnight.
F
The earliest recorded weight-driven mechanical clock was built in 1283 in Bedfordshire in England. The revolutionary aspect of this new timekeeper was neither the descending weight that provided its motive force nor the gear wheels (which had been around for at least 1, 300 years) that transferred the power; it was the part called the escapement. In the early 1400s came the invention of the coiled spring or fuses which maintained constant force to the gear wheels of the timekeeper despite the changing tension of its mainspring. By the 16th century, a pendulum clock had been devised, but the pendulum swung in a large arc and thus was not very efficient.
G
To address this, a variation on the original escapement was invented in 1670， in England. It was called the anchor escapement, which was a lever-based device shaped like a ship's anchor. The motion of a pendulum rocks this device so that it catches and then releases each tooth of the escape wheel, in turn allowing it to turn a precise amount. Unlike the original form used in early pendulum clocks， the anchor escapement permitted the pendulum to travel in a very small arc. Moreover, this invention allowed the use of a long pendulum which could beat once a second and thus led to the development of a new floor-standing case design, which became known as the grandfather clock.
H
Today, highly accurate timekeeping instruments set the beat for most electronic devices. Nearly all computers contain a quartz-crystal clock to regulate their operation. Moreover, not only do time signals beamed down from Global Positioning System satellites calibrate the functions of precision navigation equipment, they do so as well for mobile phones, instant stock-trading systems and nationwide power-distribution grids. So integral have these time-based technologies become to day-to-day existence that our dependency on them is recognized only when they fail to work.
真题解析：
长难句练习：
1. They based their calendars on three natural cycles: the solar day, marked by the successive periods of light and darkness; the lunar month, following the phases of the moon; and the solar year, defined by the changing seasons.
参考译文：古巴比伦人的历法是根据三个自然循环建立的：太阳日(根据白天和黑夜接替的周期而来)、太阴月(由月月相变化而来)，以及太阳年(根据四季变化来界定)。
知识点：
主从复合句
含有两套或更多的主谓结构，其中有一个是主要的主谓结构，其他主谓结构从属于它并且担任起句子成分。
①They believe that the computer will finally take the place of human beings.
②He asked me where he could get such medicine.
2. Temporal hours, which were first adopted by the Greeks and then the Romans, who disseminated them through Europe, remained in use for more than 2,500 years.
参考译文：日光时先是被希腊人采用，后来被将它们传播到整个欧洲的罗马人采用，在超过2,500年的时间里，它一直被人们使用着。
知识点：此句包含两个定语从句：which引导的从句修饰temporal hours，who引导的从句修饰the romans。句子的主干是temporal hours remained in use for more than 2,500 years.
3. The revolutionary aspect of this new timekeeper was neither the descending weight that provided its motive force nor the gear wheels (which had been around for at least 1,300 years) that transferred the power; it was the part called the escapement.
参考译文：这种新型计时器所具有的革命意义既不在于依靠向下的重力提供起动力，也不在于依靠齿轮(至少有1300年的使用历史)传递动力，而在于它使用了一个叫做擒纵机构棘轮装置的部件。
知识点：这句话的主干是主系表结构，不过有两个并列的表语。主语是The revolutionary aspect，系动词是was，表语是neither the descending weight nor the gear wheels。第一个that引导定语从句修饰weight，括号里的句子做插入语，是对gear wheels的补充说明，that引导定语从句修饰gear wheels，分号后面是一个简单的句子。
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