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The evolution of United States standard time zone boundaries from 1919 to 2024 in five-year increments. Plaque in Chicago marking the creation of the four time zones of the continental US in 1883 Colorized 1913 time zone map of the United States, showing boundaries very different from today Map of U.S. time zones during between April 2, 2006, and March 11, 2007.
The borders of all zones were lines of longitude. In 1872, he modified his proposal so that the first zone was centered on the 75th meridian west of Greenwich, with the others 90°, 105°, and 120° west of Greenwich. Now all had geographic borders, such as the Appalachian Mountains for a portion of the border between the first and second zones ...
Time zones were therefore a compromise, relaxing the complex geographic dependence while still allowing local time to be approximate with mean solar time. Railroad managers tried to address the problem by establishing 100 railroad time zones, but this was only a partial solution to the problem. [2]
In 1870, Charles F. Dowd published a pamphlet titled A System of national time and its application advocating three time zones across the country based on the Washington meridian, modifying this to four zones based on the Greenwich meridian in 1872.
The Standard Time Act of 1918, also known as the Calder Act, was the first United States federal law implementing Standard time and Daylight saving time in the United States. [2] It defined five time zones for the continental United States and authorized the Interstate Commerce Commission to define the limits of each time zone.
Time zones of the world. A time zone is an area which observes a uniform standard time for legal, commercial and social purposes. Time zones tend to follow the boundaries between countries and their subdivisions instead of strictly following longitude, because it is convenient for areas in frequent communication to keep the same time.
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So for example cosmopolitan time G:45 would map to local time 14:45 in one zone and 15:45 in the next. [15] [17] In two papers "Time reckoning" and "Longitude and Time Reckoning" presented at a meeting of the Canadian Institute in Toronto on February 8, 1879, Fleming revised his system to link with the anti-meridian of Greenwich (the 180th ...