International Meridian Conference

The International Meridian Conference was a conference held in October 1884 in Washington, D.C., in the United States, to determine a prime meridian for international use. The conference was held at the request of U.S. President Chester A. Arthur. The subject to discuss was the choice of "a meridian to be employed as a common zero of longitude and standard of time reckoning throughout the world". It resulted in selection of the Greenwich Meridian as an international standard for zero degrees longitude.

By the 1870s there was pressure both to establish a prime meridian for worldwide navigation purposes and to unify local times for railway timetables. The first International Geographical Congress, held in Antwerp in 1871, passed a motion in favour of the use of the Greenwich Meridian for (smaller scale) passage charts, suggesting that it should become mandatory within 15 years.

In Britain, the Great Western Railway had standardised time by 1840 and in 1847 the Railway Clearing Union decreed that "GMT be adopted at all stations as soon as the General Post Office permitted it". The Post Office was by this time transmitting time signals from Greenwich by telegraph to most parts of the country to set the clocks. By January 1848, Bradshaw's railway guide showed the unified times and met with general approval, although legal disputes meant that it was not until 1890 that GMT was formally established across the UK.

In the United States, the problems were much more severe, with one table showing over 100 local times varying by more than 3 hours. 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.

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