|"This valuable time chart shews at a glance the exact difference between Greenwich Mean Time and the local time at all principle towns around the world."|
This time chart was produced in the 19th century to quickly determine the time in various parts of the world. Until the latter part of the 18th century, time was normally determined in each town by a local sundial. Solar time is calculated with reference to the relative position of the sun. This provided only an approximation as to time due to variations in orbits and had become unsuitable for day-to-day purposes. It was replaced by local mean time, which eliminated the variation due to seasonal differences and anomalies. It also took account of the longitude of a location and enabled a precise time correction to be applied.
However, such new found precision did not overcome a different problem – differing times in neighbouring towns and cities. The time differences between parts of Great Britain were as much as 20 minutes from that of London. For example, Oxford time was 5 minutes behind Greenwich and Ipswich was 5 minutes in front! These differences could be as much as 60 minutes in larger countries.
This was problematic as rail travel grew more popular and necessary. Railway time was introduced to eliminate confusion caused by having different times in each town and station stop along a quickly expanding rail network. You can imagine how confusing it would be if you had to change your watch by a few minutes each time your train stopped at a new station. Charts like this one were published and placed in railway stations to allow stationmasters to set their clocks to London time. In turn, train guards set their chronometers against those clocks. So, in around 1840, railway companies started to standardise their schedules in accordance with London time, set by the Greenwich observatory, already widely known as Greenwich Mean Time.
|Exchange clock in Bristol showing two minute hands|
Railway companies were met with quite fierce resistance from local people when railway time was first introduced. People didn’t like the idea that London was telling them howto set their clocks. As a result of this, stations often had clocks with two minute hands; one showing the local time and one showing Greenwich Mean Time, the latter being the time to schedule your railway journeys by.