History of Thermohygrometers
A hygrometer is an instrument that measures the humidity of the surrounding gas. Humidity represents the water vapor content in the gas, divided into absolute humidity and relative humidity. Absolute humidity refers to the net content of water vapor in a gas, measured in grams per cubic meter. Relative humidity refers to the ratio of the water vapor content in the gas to the water vapor content when the water vapor in the gas reaches a saturated state under the same state, expressed as RH (%).
The "Historical Records" records a scale device with soil and charcoal placed on both sides of the scale. The book "Huainanzi" describes this device: when the weather is dry. When the charcoal is light, the balance tilts toward the soil; when the weather is humid, the charcoal becomes heavier, and the balance tilts toward the charcoal. This is the earliest measurement of air humidity.
The first hygrometers in Europe appeared in the 15th century, when an Italian invented a method of measuring humidity. This method is the same as the principle of using a balance device in China. Put a ball of dry cotton on one end of the balance, and then put a weight of the same weight on the other end. When the cotton absorbs the water vapor in the air, it will sink, and the balance will tilt toward the cotton. The amount of water vapor in the air can be determined based on how much water vapor the cotton absorbs.
The hygrometers used include hair hygrometers, wet and dry bulb hygrometers, lithium chloride hygrometers, etc. The principles are different, but they all measure relative humidity.
Mini LCD Digital Air Temperature Humidity Meter Thermometer Hygrometer Gauge Tester
