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The figure 60 was probably taken from the ancient Babylonian counting system which used 60 in much the same way as we use 10. However, the earlier mechanical clocks did not bother about marking smaller divisions for minutes on their dials, or using a minute hand. This was just as well, considering that they were not very accurate anyway! Some of these early clocks still exist. The oldest surviving clock in England is at the Salisbury Cathedral, and is over 500 years old. It has an ornate dial, with 24 hours marked on its face in two lots of 12 hours each.

If, on the other hand, the egg keeps boiling after the sandglass has run through, you will have to chew a very hard-boiled egg indeed! Some popular indoor games too use sandglasses to set a time limit. A watch would, no doubt, be more accurate, but a sandglass 50 is an easy and interesting way of keeping track of the minutes. The Chinese adopted a rather peculiar and laborious way of telling time. They knotted a rope at equal distances. This rope was wetted and set alight at one end. The time taken by the fire to reach from one knot to the next marked a unit of time!

It consists of a stick raised above the ground, and a circular dial with markings for hours around it. As the sun changed its position in the sky, the length and position of the stick's shadow falling on the dial would change as well. The Egyptians divided the day between sunrise and sunset into twelve periods of time, which were marked on their sundials. They divided the night too into twelve time periods, corresponding to the rising of twelve stars. Why did they have twelve divisions and not eight or ten?

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