CLOCKS AND CALENDARS

A SCALE MODEL OF SU SONG'S 
ASTRONOMICAL CLOCK TOWER 
BUILT IN KAIFENG, CHINA, IN
THE11TH CENTURY.  IT WAS
DRIVEN BY A LARGE
WATERWHEEL, CHAIN DRIVE
AND ESCAPEMENT MECHANISM.

The medieval monks relied on the bells to call them to their prayers or mass. This was not only in the day but also nights. They surely could have done with an alarm clock where they could sleep soundly and be awoken by the alarm.

The Egyptian had a clepsydras in 1450 BC which was a clock measuring time by flow of water through a hole. These were perfect timekeepers but need to be constantly seen to.

The sundials were around for centuries and the big sundials were very accurate. Another method was candles with notches to measure time indoors.

The first clocks were made at the end of the 13th century. The invention had a 'verge escapement' which was a mechanism releasing the driving power of weights at a steady speed.

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The portable clocks and watches with a spring were made at the end of the 15th century. The accuracy came with the pendulum which was developed from Galileo's observation.

The words 'clocks' and 'watches' came from the watches aboard of a ship and the bells were rang which the French word is 'cloches'.

However, you couldn't use pendulum clocks at sea. The correct time had to be measured with longitude and local time, the Sun and stars with Greenwich Time on the zero line of longitude. In 1762 John Harris developed the first chronometer which proofed perfect.

Calendar

To ordinary people the calendar was more important. They divided the year by the season to make sure the right time for sowing and harvesting.

The Egyptian had three seasons. The time the Nile flooded; the time for sowing; the time for harvesting.

It became a problem to establish an exact month. The phases of the moon did not match-up with the length of the year. The time Earth orbiting the Sun.

Many theories were put forward but the best was from Julius Caesar. He established that the year was 365 1/4 days. He put an extra day in every four years, the so-called leap year. Even this proved not to be exact and there was by 11 minutes out every year.

In 1582 they realized that it built up ten days. Since 10 days were lost Pope Gregory XIII requested to change the calendar to 97 leap years in 400 years. A lot of countries refused the Gregorian calendar because it came from Rome and therefore it was only accepted in Britain in 17 century