Leonardo da Vinci designed an early hygrometer to measure humidity by comparing the weight of two materials.
A hygrometer measures the amount of moisture in air. Leonardo’s proposed device used a moisture-sensitive material, such as wool or cotton, alongside a material less affected by humidity. Changes in the damp material’s weight could be compared with a fixed reference to indicate whether the air was becoming wetter or drier.
The design belongs to Leonardo’s wider investigations of weather, water, and physical change. It was not a modern electronic humidity sensor and did not provide a digital percentage reading. Instead, it used a balance-based comparison, making the result relative rather than highly precise.
Leonardo did not invent the scientific study of atmospheric moisture, and later hygrometers used more sensitive materials and calibrated scales. His proposal is important because it shows an early attempt to turn an invisible environmental condition into a measurable mechanical effect.