Museo Galileo
Virtual Museum
Hourglasses, water clocks, and combustion clocks
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Hourglasses consist of two glass globes placed on top of each other. The powder or sand falls from the upper globe into the lower globe through a small aperture. To restart the cycle, the hourglass is turned upside down. Hourglasses can also be arranged in a series to measure longer lapses of time by summing the successive partial times taken to empty each globe.

Water clocks have the same structure and function in the same way, except that the substance flowing into the lower globe is water. Other water clocks, instead, are actuated by complex hydraulic mechanisms.

In oil clocks, which resemble oil lamps, time is measured by the consumption of oil through combustion.

Incense clocks, typically found in the East, marked time by means of burning incense sticks.

Fire clocks are usually composed of lit candles, marked with equidistant notches that define a conventional unit of time.



Inv. 138
Maker unknown, 17th cent.

Hourglass (sand)

Hourglass (sand)

Inv. 429
Maker unknown, Italian?, 17th cent.

Oil clock

Oil clock

Inv. 3570
Maker unknown, 18th cent.