Leonardo da Vinci designed an early hygrometer to record changes in air humidity.
A hygrometer measures moisture in the atmosphere. Leonardo’s version used a balance principle: materials that absorbed moisture, such as wool, changed weight, and that change could be compared with a reference material. The device translated invisible atmospheric moisture into a measurable physical effect.
The design belongs to Leonardo’s wider interest in weather, water, and natural processes. He studied how air and moisture behaved and sought mechanical ways to observe changes that could not be seen directly. His instrument was an early contribution to scientific measurement rather than a finished modern laboratory device.
A hygrometer is often confused with a barometer or thermometer. A barometer measures air pressure, while a thermometer measures temperature. Leonardo also studied wind measurement, but wind speed and direction belong to anemometry, not hygrometry.