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Measuring Humidity

Some people describe humid weather as muggy. The maximum amount of vapor that can be in the air depends on the air temperature. Warmer air can hold more water vapor within it. That’s why the muggiest days usually happen at the height of summer heat. But as the temperature goes down, the air can hold less vapor and some of it turns into liquid water.

In the pictures below, Dewdrop has a box that is one cubic meter in size. The air in the box is very humid when it is warm. Notice that as the temperature decreases, there is more liquid water at the bottom of Dewdrop’s box. That’s because the water vapor must come out of the air as it cools.

The amount of water coming out of the air is exaggerated in the picture above. In fact, the total amount of water in the warmest air, 1.85 grams, would only fill a measuring cup about 1/8 full.