![]() ![]() In mainland Britain, this was Greenwich Mean Time – a time that was chosen because time signals were available directly from the Royal Observatory at Greenwich via the electric telegraph. In order to make the timetable workable, instead of using local times, the railway companies introduced a single standard time across their network. When it was midday local time in Bristol for example, it was already ten past twelve in London some 100 miles to the east. Whilst local time had sufficed in the age of the horse drawn carriage, it was inappropriate for the railways. It was the emergence of new technologies, in particular the railways in the 1830s, that forced a wider reform of the time system, and with it the adoption of a single Prime Meridian. A similar change was made in America in 1848. The potential for confusion because of the similarity between astronomical and nautical days was much reduced when on 11 October 1805 the British Admiralty issued an order to end the use of the nautical day. The nautical day also began at noon, but started twelve hours earlier than the civil day. Until then, sailors had used the civil day along with the nautical day. The introduction of the Nautical Almanac in 1767 had required sailors to make use of astronomical time, where the day was reckoned from noon, beginning twelve hours after the start of the civil day. To rationalise one, would require the rationalisation of the other. But the problem was not one of geographical location alone it was also linked to the measurement of time. The start of the nineteenth saw calls for unification and the adoption of a single common meridian. Over the years, it has been measured from many different places, including national observatories, the island of Hierro in the Canaries and St Paul’s Cathedral in London – each country having chosen for itself where to measure from. ![]() The adoption of a Prime Meridian and the International Meridian Conference of 1884 In the beginningĪlthough latitude has always been measured from the Equator, there is no equivalent point from which to measure longitude. ![]()
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