David Gone Hurst, age 10, of Shreveport, La., for his question:

What is dew?

Some people say that the dew rises and some say that it falls. Neither of these theories is correct, though we have to rise early in order to see what actually happens. The dew is a weather event which occurs during the night or before sun‑up. It covers the grass, small plants and objects near the ground with pearly drops and films of moisture, All of it disappears as the sun takes his first few strides up the sky.

The first few sunbeams send the dew scuttling back to where it came from. We cannot see it because it has turned back into water vapor which is an invisible gas in the air.

There is always some vapor, even in the driest air. This is why we sometimes have a dewy morning in the desert. There is vapor even in your warm dry living room and you can use this warm dry air to show how the dew forms outdoors.

Put a few chunks of ice into a glass and fill it up with water. Set it on a table and wait a while. Soon the outside of the glass will be covered with a misty film of water. Did this moisture seep out from the ice water inside the glass? Not at all. It is moisture taken from the air in your warm dry wing room.

Air is always thirsty and it contains moisture whether it is warm or cool. But warm air can hold more vapor than cool air. When warm air becomes chilled it usually has to give up some of its water vapor. Some of the gaseous vapor is turned back again into liquid water,

The warm air of your living room touched the cold outside of the glass of icewater. This warm air was made chilly and gave up some of its vapor, The vapor collected in a misty haze on the outside of the glass, during: the day, the outside air is warmed as it touches the warm earth,

During the night, the earth cools, for these are no sunbeams falling upon it to  keep it warm.  As the night progresses, the earth loses more and more heat until it is cooler than the air above it. The air near the ground  is now like the air around the cold glass of ice water. It chills as it touches the cooler ground, the small plants and the grass.

Now it has more than its quota of water vapor. This surplus gas must be turned back into liquid moisture. It becomes dew. The blades of grass are hung with pearly necklaces, the spider webs are clothed in silvery sleeves of moisture and the pansies get their pretty faces washed,

The morning sun warms the earth again and the earth in turn warms the air above it. The thirsty air can now take back the moisture it had to give up. The dewy moisture is turned back again into water vapor, an invisible gas hidden among the other gases of the air.