What Do Sundials And The Industrial Revolution Have To Do With International Time Zones?

Until the Industrial Revolution, there was no pressing need for a system of world time zones. Indeed, most places set their local time by observing the town's sundial. Even in the UK, this practice created significant time differences. For example, at noon in Greenwich, which is zero degrees, the sundial in Norwich will indicate the time is 12.05 and in Torquay to the west, the sundial will say it is only 11.46.

As the Earth rotates on its axis the Sun appears to us to move from east to west. At any given moment in time, the shadows cast on sundials will point to different times in different locations at a rate of around four minutes for each degree east or west.

Before the age of railways, steam ship and the telegraph, these small but significant differences in time were neither here nor there. With the advent of timetables, travel and instant telegraph communications, getting everyone working on the same time became a vital issue.

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