Andrew Lind, age 9, of Arlington Heights, I11., for his question:

WHY DOES FOG FORM IN POCKETS?

Sometimes the fog forms a misty blanket over all the scenery, far and wide. Sometimes it only settles in patches, here and there. As a rule, the foggy patch gathers in a hollow, where the ground is damp. Sometimes it forms along a river or over a low lying swamp. Almost always a patch of fog forms over a spot of ground that happens to be damper than the ground around it.

This is because fog forms from moisture in the air ¬and the air is more likely to soak up moisture from patches of damp ground. In the warm sunshine this dried up moisture becomes water vapor. We do not see it because it is an invisible gas.     But when the air cools, some of the gaseous vapor turns into misty droplets  and we see a patch of fog over the old swamp.