History of hygrometers

Perhaps it was Rianando---- a man born in Italy in the 15th century--- who was the first to come up with this instrument to measure the amount of water vapor in the air. He placed a piece of dried cotton on the side of a thump. Then he placed an object of exactly the same weight as cotton on the other side of the slam. As the dried cotton absorbs water vapor from the air, it becomes heavier and this side of the slam begins to land. The difference between the two weights is a measure of humidity.

Scientists measure relative humidity using an instrument called a "psychrometer." A "psychrometer" consists of two thermometers tied together. A thermometer bubble is encased in a material soaked in clean water. To begin measuring relative humidity, rotate the psychrometer until the wrapped thermometer maintains a stable temperature, which must be lower than the dry one. The temperature that the real air temperature is dried measures the degree. The difference between the two temperatures is called "wet-bulbdepression" and is the result of the evaporation of water from a substance. Scientists record the temperature and "wet-bulbdepression" of a low-dry thermometer and then make a graph to calculate the relative humidity. This is also how psychrometer works in a psychrometrophic bulb hygrometer.