Leonardo da Vinci designed a hygrometer to indicate changes in atmospheric moisture.
A hygrometer measures humidity, meaning the amount of water vapor in the air. Leonardo’s concept used materials whose weight or behavior could change as they absorbed moisture, allowing atmospheric dampness to be observed or compared.
The design reflects Leonardo’s interest in measuring natural phenomena with practical instruments. Humidity affects materials, weather, comfort, and the preservation of objects, so a device for detecting moisture had useful applications beyond pure scientific curiosity.
A hygrometer is different from a barometer, which measures air pressure, and from an anemometer, which measures wind speed. Leonardo’s humidity instrument should also not be confused with modern digital hygrometers, which use electronic sensors. His design was an early mechanical or material-based approach recorded in his notebooks.