Leonardo da Vinci designed a hygrometer to record changes in atmospheric humidity. A hygrometer measures moisture in the air, and Leonardo’s interest in the subject formed part of his broader investigations into weather, water, and the physical environment.
Historical descriptions of his device associate changes in moisture with a material that responds by gaining weight or changing condition. The instrument was not a modern electronic sensor, and surviving accounts do not establish that Leonardo produced a widely used working model. It is best understood as an early attempt to make humidity measurable.
Humidity is often confused with temperature or air pressure. A thermometer measures temperature, a barometer measures pressure, and an anemometer measures wind speed. Leonardo studied all kinds of natural phenomena through drawings and experiments, but his scientific instruments were frequently prototypes or concepts rather than standardized tools used by later meteorologists.