Leonardo da Vinci designed a hygrometer to measure the amount of water vapor in the air.
His hygrometer concept used a material that gained weight when it absorbed moisture. By comparing the material’s weight before and after exposure, an observer could estimate atmospheric humidity. This was an early attempt to turn a weather observation into a measurable quantity.
Leonardo’s design was not the modern electronic hygrometer. Later instruments used hair, animal membranes, chemical substances, and other materials whose dimensions or weight changed with humidity.
Humidity is often confused with temperature or rain. A hygrometer measures moisture in the air, while a thermometer measures temperature and a rain gauge measures precipitation. Leonardo’s interest in the subject also connected with his broader studies of weather, water, and materials.