Leonardo da Vinci developed a hygrometer concept for measuring humidity through changes in material weight.
A hygrometer measures the amount of water vapor in the air. Leonardo’s design used an absorbent material, such as cotton or wool, whose weight would change as it took up moisture. Comparing the material before and after exposure could indicate how damp the air was.
This principle is different from an anemometer, which measures wind speed. It is also different from a barometer, which measures air pressure. Modern hygrometers may use electrical sensors, chilled mirrors, or materials whose dimensions change with humidity.
Leonardo’s hygrometer belongs to his broader work on natural measurement. He often converted observations into mechanical demonstrations, making invisible or changing conditions easier to record. The design should be understood as an early humidity-measuring concept, not as a modern calibrated digital instrument.