Leonardo da Vinci designed a hygrometer to measure humidity using a balance and absorbent material.
A hygrometer measures moisture in the air. Leonardo is credited with an early design that used a balance: an absorbent substance, such as cotton or wool, would gain weight as it took up moisture from the atmosphere. A counterweight or scale could then indicate the change.
The instrument belongs to Leonardo’s broader interest in measuring natural phenomena rather than merely describing them. It was conceptually different from a thermometer, which measures temperature, and from a barometer, which measures atmospheric pressure. An anemometer, another instrument associated with his studies, measures wind.
Leonardo’s hygrometer was an early scientific concept, not a modern electronic humidity sensor. Historical sources sometimes describe the exact material or arrangement differently, because Leonardo’s notebooks contain preliminary sketches and notes rather than a single standardized manufactured instrument. The central principle remains the same: humidity can be inferred from a material’s change in mass.