For most of human history, time was something read from the sky. The sun told people when to rise, when to eat and when to stop work, and the seasons told them when to plant and when to harvest. Such time was elastic. An hour in June was not the same length as an hour in December, because the daylight was simply divided into twelve parts whatever the season, and nobody found this strange.
The device that broke this arrangement appeared in Europe towards the end of the thirteenth century. Its central component was a mechanism called the verge escapement, which took the steady pull of a falling weight and released it in tiny, regular steps. Nobody knows who invented it, and no drawing of the first one survives.
These early clocks would disappoint anyone expecting to read the time from them. Many had no face and no hands at all. Their purpose was to strike a bell, calling monks to prayer at the proper hours. Nor were they accurate. A large tower clock of this period could gain or lose fifteen minutes in a single day, which meant it had to be corrected constantly against a sundial.
