Prior to the adoption of universally accepted time zones, the vast majority of settlements around the world observed local mean solar time. Because of variations in geographical longitude, this meant that different towns and cities had slightly differing time standards. Although Greenwich Mean Time had been established in 1675 to help mariners navigate at sea, no law existed to mandate its use for local time.
The arrival of the railways in the mid-19th Century increased the need for a standardised time across the network, since local time would differ in all the towns the train visited. In Great Britain, Greenwich Mean Time was first adopted by the Great Western Railway and it is estimated that by 1855 up to 98% of all public clocks in the country displayed Greenwich Mean Time.
The use of a standard time in Britain was, however, not mandated by law. It was the New Zealand government that first introduced such legislation in order to allow the easier synchronisation of railways, steam ships, and the electric telegraph. Having consulted with Scottish-born scientist and explorer James Hector, the government adopted his recommendation of a time zone based on New Zealand’s mean longitude 172° 30′ east of Greenwich. Originally established at 11½ hours ahead of Greenwich Mean Time, New Zealand Mean Time was adopted on 2 November 1868.
Britain eventually implemented a standardised national time in 1880, while the U.S. Congress passed the Standard Time Act on 19 March 1918.