What makes a pitcher of water sweat?
Sometimes the outside of a pitcher of ice water gathers a coating of beady sweat. This is caused by a trick of air and moisture. This very same trick operates outdoors on a grand scale. It causes clouds to form in the sky and dew to gather on the grass. When sweaty moisture gathers outside a pitcher, we might take it for granted that the water it contains is seeping through the sides. Then we recall that the pitcher I has sides of glass or same other material too solid to let through even a drop of moisture. We look for cracks and there are none. We check further and find that no one sprayed the beady droplets on the outside of the pitcher. At this point we know we have a mystery to cope with, and the time has come to ask a question. The answer explains a trick performed by the filmy air, its temperature and its content of water vapor. There is a certain amount of this gaseous water in the air, even above the driest deserts. This vapor is a gas made of separate water molecules. As a ga
