Leonardo da Vinci designed a hygrometer, an instrument for measuring humidity by comparing changes in the weight of moisture-sensitive material.
His concept used a balance: a material capable of absorbing moisture was placed on one side, and the change in balance indicated how much water vapor had been taken from the air. This made the device an early attempt to quantify atmospheric humidity rather than merely observe wetness.
Leonardo’s instrument was not a modern electronic humidity sensor, and the numerical accuracy of a reconstructed version would depend on its materials and calibration. Nevertheless, the design shows his interest in turning observations of weather into measurable physical quantities.
A hygrometer measures humidity, while an anemometer measures wind speed and a barometer measures air pressure. Leonardo also studied anemometers, but those are separate instruments.