As the earth rotates on its axis from west to east, night and day arrive at different parts of the earth at different times. Until the late 1800s, every town, county, or isolated group of islands observed its own time and set clocks according to the local sunrise and sunset. Time differences between locations were practically unnoticeable, however, because it took days, weeks, or months to travel, and instant modes of communication did not exist.

Demand for a unified time system evolved as a result of two technological advances: the telegraph and the locomotive. In the 1830s, the telegraph made possible instantaneous communication between distant points, and the first locomotives developed in England and America made rapid travel possible. With the development of telegraph and railroad networks on a continental scale in North America, Europe, and elsewhere, local times came into conflict for it was nearly...