What is dew?

   On sunshiny summer mornings the grass is often wet with dew. It may be so wet that it is hard to believe that there has not been a shower. There may be drops of dew on flowers and bushes and spider-webs, too. The drops of dew sparkle like jewels when the sun shines on them.
   Drops of dew look like drops of rain. But they do not fall from clouds as rain-drops do. They are formed where they are found. They are formed from the water vapor in the air when moist air strikes something cold. Cold air cannot hold as much moisture as warm air.
   Drops of water form on the outside of glasses of cold water or lemonade on hot summer days. They form when the warm, moist air strikes the cold glass. They are like drops of dew.
   Dew is formed much oftener in fair weather than in cloudy weather. On clear nights things near the ground cool off much faster than on cloudy nights. Clouds act as a kind of blanket. Unless flowers and leaves and spiderwebs are cooler than the air, dew will not form on them.
   Wind also keeps dew from forming. On a windy night the air is constantly moving about. None of it stays near the cool ground long enough to be cooled off and to lose some of its moisture.
   Dew does not stay on very long after the sun comes up. The grass and other things on which the dew has formed soon get warm. Then the dew changes again to water vapor. This same water vapor may become dew again the next night if the weather is calm and fair.