Leonardo da Vinci designed a hygrometer to measure humidity using a balance.
His apparatus compared the weight or moisture response of materials affected by damp air with a reference material. A balance could reveal changes caused by atmospheric moisture, allowing an observer to estimate whether conditions were becoming wetter or drier.
Leonardo’s design belongs to the early history of hygrometry, the measurement of humidity. It was a qualitative or comparative instrument rather than a modern electronic sensor, and its accuracy depended on the materials and calibration used.
The hygrometer is sometimes confused with Leonardo’s anemometer, which addressed wind. It is also different from a barometer, which measures air pressure. Leonardo’s interest in humidity connected practical weather observation with his broader studies of air, water, and mechanical measurement.