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B.4.1
Historical Background |
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Because the Earth is a sphere, different points on its surface are in different positions relative to the Sun at any given moment. Thus, if the Sun is directly overhead at one point on the Earth, it is not directly overhead at another point to the East or the West. To be at a different longitude implies being at a different time. |
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Historically, cities in most of the world have kept their own time, using an astrolabe or other instrument to observe the sun's zenith at noon. The responsibility for maintaining correct time was considered a local matter. By the late medieval period in Europe, most towns of any size had a large clock in the public square indicating the correct local time. A town twenty miles to the east literally had a different time. |
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This system is correct, in terms of both astronomy and calendar record keeping. That it is not in use today is due to a set of historical circumstances peculiar to the late nineteenth century. |
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As the Industrial Revolution proceeded, the speed and scope of the transportation networks increased, although the means of processing information were still rudimentary. This particular set of circumstances led to a problem. Increased speed meant that people could move fast enough to pass through many towns in one day, and the enlarged scope of the rail network meant that they actually did so. The result of increased physical complexity was a need to process a much larger amount of information, and the manual methods of the day were completely inadequate to the task. From a practical standpoint, the transportation industries of the late nineteenth century were simply unable to cope with the complexity of the existing situation and responded with a characteristically Second Wave solution standardization and drastic simplification. |
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For the purposes of navigation, the local time in Greenwich, England, had been considered to be the official time for years, but it was the defining industry of the Industrial Revolution, the railroad, which faced the problem in its most difficult form. And it was in Canada and the United States, with the greatest distances, and soon, the largest networks, that the problem of coordinating local times became an economic burden. |
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Under prodding by the railroad companies, the United States was divided into four time zones on 18 November 1883, and jurisdiction for the zones was given to the Interstate Commerce Commission. Within each zone, all places keep the same time, which is the local mean solar time of a standard meridian which runs through the approximate center of each zone. In the United States, the zones were intended to represent the mean times of four different meridians: |
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