Until the middle of the nineteenth century, time was a local affair: every town set noon by the sun passing overhead, so London and Bristol, Istanbul and Edirne, differed by minutes. Until the coming of the railway, this hardly troubled anyone. But once trains began running to intercity timetables in the 1840s, stations each keeping their own clock produced a dangerous muddle; two trains on the same line could no longer agree whose noon to obey. The telegraph then magnified the problem at the speed of an electric pulse: a message could cross a continent in seconds while the clocks at its ends ran on different planes.

The answer came from the Canadian engineer Sir Sandford Fleming. After missing a train in Ireland in the mid-1870s, Fleming proposed dividing the world into 24 zones, all referenced to a single prime meridian, each separated from its neighbours by exactly one hour. Because the maritime charts of the British Empire already used Greenwich, that meridian was the most practical candidate in terms of existing infrastructure. At President Chester A. Arthur's invitation, delegates from 25 nations gathered at the Diplomatic Hall in Washington for the International Meridian Conference on 1 October 1884. After three weeks of debate — with France defending the Paris meridian and finally abstaining — Greenwich was declared the prime meridian on 22 October, and the universal day was set to begin at midnight at Greenwich.

The conference's resolutions were recommendations rather than a binding treaty; implementation took years and varied from country to country. North American railway companies had already adopted their own zones in 1883; the British Empire moved quickly. Germany followed in 1893, Japan in 1888. The Ottoman Empire kept its classical "ezani" hour, set to sunset, into the twentieth century; the Republic would formally adopt the international system in 1925. France, out of national pride, did not officially accept Greenwich until 1911 — until then French clocks were described, by law, as keeping "Paris mean time retarded by 9 minutes 21 seconds" — a Greenwich in all but name.

The significance reaches far beyond calendar housekeeping. Standard time is the infrastructure of a global economy: stock exchanges, shipping schedules, telegraph charges, then telephony, radio broadcasting, air traffic, the internet — all run on the grid drawn in 1884. It is also an unequal globalism: the world's time is read from the observatory of the empire with the largest navy. Today's global finance still speaks the same meridian logic — "London close," "New York open." The Washington conference of 1884 was, alongside the partition of colonial empires that same year, one of the quiet but lasting steps in the synchronisation of the modern world.