Leonardo da Vinci designed a hygrometer to estimate humidity in the air.
Leonardo’s hygrometer concept used the changing weight of a moisture-sensitive material. As the material absorbed water from humid air, its weight changed; comparing that change with a dry reference could provide an indication of atmospheric moisture. The design reflects Leonardo’s interest in making invisible environmental conditions measurable.
A hygrometer measures humidity, especially the amount of water vapor in air. This is different from a barometer, which measures atmospheric pressure, and an anemometer, which measures wind. Leonardo’s instrument was an early humidity-measuring idea, not a modern electronic sensor or a precise calibrated weather station.
The design also illustrates a recurring feature of Leonardo’s engineering work: he often proposed practical mechanisms before the materials and scientific standards existed to make them highly accurate. Later hygrometers used materials such as hair, whose length changes with humidity, while modern instruments commonly use electronic sensors.