A clock usually consists of a face with three hands. One counts seconds, one counts minutes and one counts hours. There are 60 seconds in a minute, 60 minutes in an hour and 24 hours in a
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Clocks need energy to make their cogs and hands turn and their bells ring. In the earliest clocks the energy came from a slowly falling weight, although this prevented them from being used when in motion or placed on certain surfaces. The first mechanical clocks were built in monasteries and cathedrals during the 13th century. They were big and heavy, with metal cogs and a bell. They also contained a mechanism called an 'escapement' that controlled the rate at which the cogs turned. They had no face or hands and told the time by ringing a bell every hour which alerted the sacristan to toll a bell calling the monks to prayer. In the late 15th century clockmakers realised that they could use the energy stored in a coiled spring to drive some clocks, enabling them to be moved around and positioned anywhere, although they still had no glass or minute hand. In the mid 17th century the accuracy of clocks improved with the introduction of the pendulum.
Modern clocks have three parts: a power source, a pace regulator and something that shows the time. The latest invention to indicate time and by far the most accurate is the atomic clock, which can be accurate to within 1 second in many thousands or even millions of years.