We are indebted to Peter E Davies of www.carnforth-station.co.uk for permission to reproduce this article on Railway Time which explains the advent of Greenwich Mean time.
For many centuries, there was little need for time to be accurately measured. The transition from day to night, the movement of the moon and the changing of the seasons were enough to measure large units of time, and for most people, the passing of the sun through the sky was adequate to indicate sunrise, sunset and mid-day.
For those who needed to order their daily time more accurately, such as monks or scientists, they used a combination of crude measuring devices, such as sand timers or burning candles, or, if the sun was shining, the shadow of a sundial.
The mechanical devices in use to measure time were highly unreliable, a candle may burn erratically, depending on draughts, damp in the air, and its physical construction, sand timers were only slightly more accurate.
The Sun was the most accurate way of measuring time, but although the Greeks had discovered a way of calibrating a sundial to show equal hours, most sundials were of a simple type that only divided the day up into a unequal parts.
The Sun itself is not a very accurate way of measuring simple time. Because of the way the Earth circles the Sun, the apparent time of mid-day, when the Sun is at its highest in the sky, may vary up to 16 minutes early or late, from the real time, depending upon the time of year. This cyclic variation away from true time also means that the solar day is not exactly 24 hours long, but becomes longer, or shorter, by a small amount each day, depending where in the cycle the Earth is.
The Earth rotates once every 24 hours, and so places to the East start their day sooner, than places to the West. Mid-day in one place takes place at the same instant as sunrise, or sunset, at other places on the Earth. Across Britain there is a difference in time of approximately half an hour, from the Eastern to the Western extremities.
Until late into the 18th century watches and clocks were mostly for the rich, and their inaccuracy made the difference between clock and sundial less obvious.
From 1792, in England, it became normal to use local mean time, rather than apparent time from a sundial.
Whilst travel and communications were slow, these local time differences were of little importance, and most towns and cities in Britain used local time. By the 18th Century horse drawn coaches were taking mail and passengers across Britain, and the guards on these coaches carried timepieces, so that they could regulate the arrival and departure times. Because of the local time differences across Britain, these timepieces were adjusted to gain about 15 minutes in every 24 hours, when travelling west - east, to compensate for the local time differences. (and of course adjusted to lose 15 minutes in 24 hours when returning)
In the early part of the 19th century, communications started to be significantly improved, the railways started to be constructed, and "Galvanic Communication" (Telegraph by wires) started to become common.
To many aspects of life, accurate time was becoming more and more essential, and the usage of local time became a great inconvenience. A telegraph message wired from London, early Saturday morning, might arrive instantaneously in Dublin late Friday night. Two babies born at the same instant in time, but in different east / west parts of the country might be officially born on two different days, with possibly quite serious legal implications for inheritances
By the 1840's there were at least three organisations which suffered inconveniences because of the use of local times - The railways, the telegraph companies, and the Post Office.
In June 1836, John Henry Belville, who was employed at the Greenwich Observatory in London, started making a weekly visit to the principal chronometer makers in London , he took a pocket chronometer with him, set to Greenwich time.
In November 1840, the Great Western Railway ordered that London time should be used in all its timetables, and at all its stations.
In 1845 the Liverpool and Manchester Railway company unsuccessfully petitioned Parliament, to ask that a single uniform time be used for all ordinary and commercial purposes.
In January 1846, the North Western Railway introduced London time, to their station at Liverpool and Manchester.
On 22nd September 1847, the Railway Clearing House recommended that every railway company in Britain adopt Greenwich time at their stations, as soon as possible.
In 1st December 1847, the London and North Western, and the Caledonian Railway both adopted London time.
Bradshaws Railway Guide for January 1848 list the London and south western, London and North western, Midland, Chester and Birkenhead, Lancaster and Carlisle, East Lancashire and the York and North Midland railways as all keeping Greenwich time.
The Great Western, South Eastern and the Caledonian were also keeping Greenwich time.
On 17th February 1852, the installation of telegraph lines between the Greenwich Observatory, and Lewisham station was completed, by August time signals were sent on a regular basis from the Greenwich Observatory, to London Bridge station, and onwards from there through the railways telegraph system, and also through the Central Telegraph Station of the Electric Time Company in Lothbury, for further distribution all over the country.
On 30th October 1852 the following instruction was passed to the South Eastern Railway. (A similar order went to the Great Western, and probably to other railways as well.
From the start, some railway companies used "London" time, while others
used local time. Trains travelling east to west appeared to be travelling
slower than the return journey, west to east, which caused may problems
with timetabling. At stations of Railway Companies that used London time,
the Railway time could be quite different to local time, with all sorts of
problems of missed trains and connections, in some places, there were even
two minute hands on the public clocks, one showing local, the other
showing London time.
At last, a "standard" time was in use across the whole of Britain, and there was no more confusion caused by local time.