Leonardo da Vinci designed an early hygrometer to help measure humidity.
A hygrometer measures the amount of water vapour in air. Leonardo’s proposed device used a material that would change weight as it absorbed moisture, with a balance indicating the difference. The design belongs to his wider study of atmospheric conditions and the physical properties of materials.
Leonardo’s instrument was not a modern electronic humidity sensor. Early hygrometers often relied on organic materials, whose moisture content changes with the surrounding air. Such instruments could indicate relative dampness, but they were less precise and less standardized than later scientific instruments.
The device is sometimes confused with an anemometer, which measures wind speed, or a barometer, which measures atmospheric pressure. Leonardo’s contribution was an early attempt to make humidity observable through a controlled mechanical comparison. As with many of his inventions, the surviving evidence primarily consists of drawings and notes rather than a confirmed working prototype.