Leonardo da Vinci designed a hygrometer to estimate the moisture in air.
His proposed instrument used the changing weight of an absorbent material to indicate humidity. As the material took in moisture, its weight changed; comparing that change with a reference could provide an indication of atmospheric dampness. The idea reflects Leonardo’s broader interest in measuring natural phenomena rather than merely observing them.
A hygrometer measures humidity, while an anemometer measures wind speed and a barometer measures air pressure. Leonardo’s device was an early conceptual instrument, not a modern calibrated electronic hygrometer. Humidity measurement later developed through hair hygrometers, wet-and-dry-bulb psychrometers, and electronic sensors. The historical importance of Leonardo’s design lies in connecting a physical material change with a measurable atmospheric property.