Al Rhetta Hart, age 9 of Boise, Idaho, for his question:

Why is it cooler at the top of mountains?

Surely the mountain tops are nearer the sun than is the seashore. Since this is so, we would expect them to get more heat. After all, the closer we stand to a fire, the more heat we feel from it. But this rule does not apply to the earth and the sun's heat.

This is because sunlight does not give up its heat to the air. On the way down to us it passes through several hundred miles of atmosphere. But littler if any, of its heat is lost. This heat is saved for the solid earth and the sea.

The air gets its heat from the warmed land and oceans. The bottom layer of air is heated only when it touches warm land and sea. This warm air may rise but, as it does so, it expands and cools. Hence the higher we go, the cooler the air becomes.

Warm air from below cannot rise to the top of the tall mountains. Up there it is always cool. Even at the equator there are mountain tops cool enough to wear snow the year round.