### A MINUTE HISTORY OF TIMEKEEPING

In fact, minutes were not considered by the general public until the end of the seventeenth century. Although some clocks built in the fifteenth century already indicated minutes and seconds, such elaborate instruments were very rare, and their accuracy was poor. Most clocks from that time only had an hour hand. In 1656, the Dutch mathematician and physicist Christiaan Huygens (1629–1695) invented the pendulum clock, a crucial step in the history of timekeeping devices. He was able to build clocks that erred by less than one minute per day. The accuracy of pendulum clocks was further improved by the invention of the anchor escapement, probably by the British physicist Robert Hooke (1635–1703). An escapement is a mechanism that turns the clock's wheels by a fixed angle with each swing of the pendulum, thereby moving the clock's hands forward. The anchor escapement reduced the required amplitude of the swing of the pendulum from about 100° to only 5°, thus allowing for pendulums to be much longer and to swing at a slower rate. With the resulting improvement in accuracy, around 1680–1690 the minute hand became standard in pendulum clocks. Finally, the invention of the balance spring, attributed to both Christiaan Huygens and Robert Hooke, made it possible to build reasonably accurate and slim clocks, enabling the production of pocket watches displaying minutes, and eventually also seconds.

But why is an hour divided into 60 minutes and not, as might be expected, 10 or 100 minutes, using numbers of our base-10 system? Although the historical origin of a division into 60 parts could never be fully clarified, it most probably derives from the sexagesimal system, a numeral system based on the number 60 that was developed in Mesopotamia (modern Iraq) around 2000 BCE.