A prime meridian, based at the Royal Observatory, Greenwich, was established by Sir George Airy in 1851. By 1884, over two-thirds of all ships and tonnage used it as the reference meridian on their charts and maps. In October of that year, at the behest of U.S. President Chester A. Arthur, 41 delegates from 25 nations met in Washington, D.C., United States, for the International Meridian Conference. This conference selected the meridian passing through Greenwich as the official prime meridian.
