Bonita Rhiniu, age 13, of Lancaster, Penna., for her question:

How do clouds stay up in the sky?

Clouds are made from vapor and vapor is a gas like the other gases of the air. When water evaporates, its molecules separate into separate molecules of gas and join the gases of the air. On sunny days, the lowest layer of air is warmed by the ground and the surface of the sea. And warm air tends to rise.

As the warm air rises, the vapor mixed with the air rises also. Once aloft, the air cools and the vapor becomes fine droplets of moisture. This is the misty stuff from which the clouds are made. It is light enough to float in the air for a while. The cloudy puffs of mist are wafted along by the breezes and, maybe warm rising air helps keep then aloft. But sooner or later, they sink and return to the earth as rain.