Use the words in the list to complete the texts: • ancient • flow • mechanics • precise • predetermined • principles • seconds • structures •track •vertical

The sundial was one of the first timekeeping devices created, and dates back to 1)Roman and Greek societies . It used a central 2)rod, cal a gnomon, and the sun's light to cast a shadow onto a platform which was marked to show the hours of the day.

The first clepsydra or water-clock was created around 500 600BC. It was widely used in Egypt. Greece and the Arab world. The concept was quite simple and used the naturally consistent movement of water to 3)time. This was done by allowing water to 4)either in orout of a marked container.

By far the most modern device on this list, the atomic clock was developed in 1949. It is accurate to a couple of 5)over several million years making it by far the most 6)timekeeping device to date The atomic clock is incredibly advanced. Amazingyit uses the rotation of subatomic particles to measure the passing of time!

Commonty seen even today, the hourglass uses similiar 7)to that of a clepsydra. It uses two glass bulbs, one above the other, with a small opening in between. The sand inside gradualy falls from top to bottom, indicating that a(n) 8)amount of time has passed. It is believed that it was first created in the 8th century, although it only truly became popular around the 1300s.

Obelisks were the next logical step from the sundial, and used the same basic 9)They were towering pointed 10)which cast a shadow across a large public area, similar to how a gnomon did. They made timekeeping easier for wider communities. There are still many famous obelisks around the world today, such as the Washington monument in the USA.

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