Oil-lamp clocks are

clock A clock or chronometer is a device that measures and displays time. The clock is one of the oldest Invention, human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month, a ...

s consisting of a graduated glass reservoir to hold oil - usually

whale oil Whale oil is oil obtained from the blubber of whales. Oil from the bowhead whale was sometimes known as train-oil, which comes from the Dutch word ''traan'' ("tear drop"). Sperm oil, a special kind of oil used in the cavities of sperm whales, ...

, which burned cleanly and evenly - supplying the fuel for a built-in lamp. As the level in the reservoir dropped, it provided a rough measure of the passage of time. The principle behind such a time-keeping device is that it measures a quantity that either decreases or increases at a constant rate. Lamps or candles, burning fuel at a steady pace, fit this category, and as a bonus produce useful light. Hourglasses depend on the steady draining of fine sand through a small aperture.

Water clocks A water clock, or clepsydra (; ; ), is a timepiece by which time is measured by the regulated flow of liquid into (inflow type) or out from (outflow type) a vessel, and where the amount of liquid can then be measured. Water clocks are some of t ...

or clepsydra measure a gain or loss of water by using drops of uniform size and frequency. The Persian fenjaan made use of the constant time it took for the sinking of a floating bowl with a hole in its underside. It is unknown when or where the oil-lamp clock was first introduced. This clock was mainly used during the mid-18th century.

References

Clocks {{time-stub

See also

References