Leonardo da Vinci is sometimes credited with designing an early hygrometer, an instrument for measuring humidity.
A hygrometer measures the amount of water vapor in air. Leonardo’s proposed device used a material whose weight changes with moisture, such as wool or another absorbent substance, and a balance arrangement to indicate the change. The concept reflects his habit of turning observations of natural materials into measurable experiments.
The attribution requires care. Leonardo’s notebooks contain an early humidity-measuring design, but the history of hygrometers includes later instruments and competing claims about priority. The word hygrometer applies to the scientific function, not necessarily to a single standardized device made by Leonardo.
This instrument is easy to confuse with other weather devices. A thermometer measures temperature, a barometer measures atmospheric pressure, and an anemometer measures wind speed. Humidity can be reported in several ways today, including relative humidity expressed as a percentage, but Leonardo’s proposed mechanism predates modern electronic sensors and calibrated digital displays.