Leonardo da Vinci designed a hygrometer to indicate changes in humidity using a balance.
Leonardo’s device used a material that gained or lost weight as it absorbed or released moisture from the air. The changing weight affected a balance, providing an indication of atmospheric humidity. This was an early attempt to turn an invisible environmental condition into a measurable mechanical signal.
The instrument belongs to Leonardo’s studies of weather and natural processes. He was interested in how air, water, evaporation, and moisture affected the world around him. His hygrometer was an indicator rather than a modern precision instrument, and the surviving descriptions do not make it equivalent to electronic humidity sensors.
A hygrometer measures humidity, while an anemometer measures wind speed and a barometer measures atmospheric pressure. Leonardo’s design is therefore part of the early history of meteorological instruments, alongside his work on wind observation and water movement.