the.com/hygrometer
The instrument that knows the air is sweating before you do.
means A device that measures the amount of water vapor, or humidity, present in the air.
from From Greek hygros, meaning wet or moist, plus metron, a measure — literally a wetness-counter, coined in the 1600s when scientists realized air itself held secret water.
Hair-poweredEarly models used human hair, which stretches when damp.
Da VinciLeonardo sketched one around 1480 using wool and a scale.
Not a thermometerMeasures moisture, not heat — common confusion, different beast.