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Standard time is the result of synchronizing clocks in different geographical locations within a time zone to the same time rather than using the local meridian as in local mean time or solar time. Historically, this helped in the process of weather forecasting and train travel. The concept became established in the late 19th century. The time so set has come to be defined in terms of offsets from Universal Time. Where daylight saving time is used, the term standard time typically refers to the time without the offset for daylight saving time.
The adoption of Standard Time, because of the inseparable correspondence between time and longitude, solidified the concepts of halving the globe into an eastern and western hemisphere, with one Prime Meridian (as well its opposite International Dateline) replacing the various Prime Meridians that were in use.
A standardized time system was first used by British railways on December 11, 1847, when they switched from local mean time, which varied from place to place, to Greenwich Mean Time (GMT). It was also given the name railway time reflecting the important role the railway companies played in bringing it about. The vast majority of Great Britain's public clocks were standardised to GMT by 1855.
Until 1883 United States railroads each chose their own time standards. Almost all railroads out of New York ran on New York time, but the Pennsylvania Railroad used Philadelphia time from Jersey City to Pittsburgh. Railroads west from Chicago mostly used Chicago time, but between Chicago and Pittsburgh/Buffalo the norm was Columbus time, even on railroads like the PFtW&C and LS&MS that didn't run through Columbus. The Santa Fe used Jefferson City (Missouri) time all the way to its west end at Deming, New Mexico, as did the east-west lines across Texas; Central Pacific and Southern Pacific used San Francisco time all the way to El Paso. The Northern Pacific had seven time zones between St Paul and the 1883 west end of the railroad at Wallula Jct, but Union Pacific had two between Omaha and Ogden.
In 1870 Charles F. Dowd had proposed four time zones based on the meridian through Washington, DC for North American railroads. In 1872, he recommended the Greenwich meridian. Sandford Fleming, a Canadian, proposed worldwide Standard Time at a meeting of the Royal Canadian Institute on February 8, 1879. Cleveland Abbe advocated standard time to better coordinate international weather observations and resultant weather forecasts, which had been coordinated using local solar time. He recommended four time zones across the contiguous United States, based upon Greenwich Mean Time, in 1879. The General Time Convention (renamed the American Railway Association in 1891), an organization of American railroads aimed at coordinating schedules and operating standards, became increasingly concerned that if the United States government adopted a standard time scheme it would work to the disadvantage of its member railroads. William F. Allen, the secretary of the General Time Convention, argued that North American railroads should adopt a five zone standard, similar to the one in use today, to avoid government action. On October 11, 1883, the heads of the major railroads met in Chicago at the former Grand Pacific Hotel and agreed to adopt Allen's proposed system. The members agreed that at noon on Sunday, November 18, 1883, all United States and Canadian railroads would readjust their clocks and watches to reflect the new five zone system. Although most railroads adopted the new system as scheduled, some did so early on October 7 and others late on December 2. The Intercolonial Railway serving the Canadian maritime provinces of New Brunswick and Nova Scotia just east of Maine decided not to adopt Intercolonial Time based on the 60th meridian west of Greenwich, instead adopting Eastern Time, so only four time zones were actually adopted by U.S./Canadian railroads in 1883. Major American observatories, including the United States Naval Observatory, the Harvard College Observatory, and the Yale University Observatory, agreed to provided telegraphic time signals at noon Eastern Time.
Standard time was not enacted into law until the 1918 Standard Time Act established standard time in time zones in U.S. law as well as daylight saving time (DST). The daylight savings time law was repealed in 1919 over a presidential veto, but reestablished nationally during World War II. In 2007 the United States enacted a federal law formalizing the use of Coordinated Universal Time as the basis of standard time, and the role of the Secretary of Commerce (effectively, the National Institute of Standards and Technology) and the Secretary of the Navy (effectively, the U.S. Naval Observatory) in interpreting standard time.