Primitive clocks
The Egyptians made a tiny hole in the bottom of a stone bowl, which they filled with water. The inside of the bowl was marked to show the hours. As the water ran out through the hole, they could tell the time by looking at the top of water left in the bowl.
Sand was sometimes used instead of water. There is a sand-glass or hour-glass above. The sand ran through a narrow hole from the top glass bulb to the bottom. When the top was empty the hour-glass was turned upside down. The sand ran through again. Hour-glasses were later used in churches to time the length of sermons. Small ones can be bought today as egg-timers.