Leonardo da Vinci proposed a hygrometer, a device for measuring atmospheric moisture.
His design used a moisture-sensitive material, traditionally described as wool, whose weight would change as it absorbed water from the air. By comparing the material’s weight under different conditions, an observer could estimate humidity. This made the concept an early attempt to turn an invisible atmospheric property into a measurable quantity.
A hygrometer measures humidity, not wind speed or air pressure. That distinction matters because Leonardo also studied anemometers and other instruments connected with weather and flight. His work belongs to the broader Renaissance effort to quantify natural phenomena through observation and mechanical devices.
Leonardo’s hygrometer was a proposal rather than a modern calibrated sensor. Later instruments used materials such as hair, which lengthens as humidity changes, and eventually electronic sensors. The modern term covers instruments that report relative humidity, absolute humidity, or related measures of water vapor.