Time keeping device

For thousands of years, devices have been used to measure and keep track of time. The current sexagesimal system of time measurement dates to approximately 2000 BC. The earliest devices relied on shadows cast by the sun, and hence were not useful in cloudy weather or at night and required recalibration as the seasons changed, so they had to invent a clock! Here we summarize the 10 most memorable early firsts in making of clocks.

10. Sundials and Obelisks

Sundials have their origin in shadow clocks, which were the first devices used for measuring the parts of a day.The oldest known shadow clock is from Egypt, and was made from green schist Ancient Egyptian obelisks, constructed about 3500 BC, are also among the earliest shadow clocks. Egyptian shadow clocks divided daytime into 10 parts, with an additional four “twilight hours”—two in the morning, and two in the evening. One type of shadow clock consisted of a long stem with five variable marks and an elevated crossbar which cast a shadow over those marks. It was positioned eastward in the morning, and was turned west at noon. Obelisks functioned in much the same manner: the shadow cast on the markers around it allowed the Egyptians to calculate the time. The obelisk also indicated whether it was morning or afternoon, as well as the summer and winter solstices.

9. Hourglass

An hourglass ( sandglass, sand timer, sand clock, egg timer ) measures the passage of a few minutes or an hour of time. It has two connected vertical glass bulbs allowing a regulated trickle of material from the top to the bottom. Once the top bulb is empty, it can be inverted to begin timing again. The name hourglass comes from historically common hour timing. Factors affecting the time measured include the amount of sand, the bulb size, the neck width, and the sand quality. Alternatives to sand are powdered eggshell and powdered marble. (Sources disagree on the best material.) Modernly, hourglasses are ornamental or used when an approximate measure suffices, as in egg timers for cooking or for board games. The earliest hourglass appears in the 1338 fresco Allegory of Good Government by Ambrogio Lorenzetti