Leonardo da Vinci designed an early hygrometer, an instrument for measuring humidity.
His concept used the changing weight of moisture-sensitive material to indicate how damp the air was. The principle was qualitative or approximate by modern standards, but it reflects Leonardo’s effort to turn observations of the natural world into measurable quantities.
Humidity is the amount of water vapor in the air. Modern hygrometers may use electronic sensors, hair, or other materials whose physical properties change with moisture. Leonardo’s design predates these later instruments and belongs to the experimental tradition of Renaissance science.
The device is easily confused with an anemometer, which measures wind, and a barometer, which measures air pressure. Leonardo investigated all three areas because weather and atmospheric conditions also affected his studies of flight and engineering.