Leonardo da Vinci is credited with designing an early hygrometer to measure atmospheric humidity. His concept used the changing weight of an absorbent material to indicate moisture in the air.
A hygrometer measures water vapor in the atmosphere. In Leonardo’s design, a material such as wool could gain weight as it absorbed moisture, creating a measurable difference between drier and more humid conditions.
The instrument was an early example of turning a natural physical change into a measurement. It did not provide the precise digital readings or calibrated relative-humidity percentages produced by modern sensors.
The hygrometer is often confused with related weather instruments. A thermometer measures temperature, a barometer measures air pressure, and an anemometer measures wind speed. Leonardo’s design addressed moisture instead.