Longitude - Page 1
Longitude - Page 3
If the guard set their watch to the correct time in London, and they then set off to Bristol, 122 miles to the west, they would find that the further west they went, the more their watch would be 'wrong'. By the time they got to Bristol, 16 hours later, their watch would still be telling them 'London time', while the clocks in Bristol would be showing 'Bristol time'. The difference is 11 minutes. So if the mail coach was to leave Bristol at 11 o'clock for the return journey, should it leave at 11 o'clock Bristol time, or 11 o'clock London time? The Post Office solved this problem by working to local time, and the special guards watch had a lever on the back. If the coach was travelling west, you moved the lever so that the watch ran slow. In fact it would lose 15 minutes in 24 hours. And when the coach turned around to head back east again, the lever was moved the other way, and now the watch would gain 15 minutes every 24 hours.
The system worked well for around 50 years. But then a new arrival swept aside the mail coaches, and also started a process that would also sweep aside the concept of 'local time' on this small scale.
The coming of the Railways…
In 1841, the new Great Western Railway started running the first trains between London and Bristol. They were faster than the mail coaches, and working with local time was not practical. The Great Western issued an order - on all its trains, and in all its stations, London time, or railway time as it was often known, was the standard they would work to.
This was fine for the railway. But what about the passengers? If you wanted to catch the 8 o'clock train from Bristol to London, you needed to remember that it would leave at 8 o'clock London time, which is 11 minutes to 8 in local time. No wonder people sometimes missed their train! In order to help, a public clock was put up in Bristol on the Corn Exchange with 2 minute hands. One showed London time. The other minute hand, painted red, and showing a time 11 minutes earlier, was Bristol time.
As the railways spread around the country, they took the idea of London time with them, and with the coming of the electric telegraph there was now an easy way of transmitting time around the country. And in 1880, London time, or Greenwich Mean Time, became the official time throughout the country. But for the 40 years or so when both time systems were in operation there was a clever little trick that a few people must have noticed.
Let us suppose you were travelling from London to Bristol on the Great Western Railway in 1860 or thereabouts, and you had fallen asleep as you left London, and had now woken up and wanted to know how far you had gone. You look out of the window and see that the local church clock says 3 o'clock. However when you consult your watch, which tells London time, it says 7 minutes past 3. So we know we are not yet in Bristol, where the difference would be 11 minutes. In fact we have travelled about two thirds of the way, about 77 miles.