Bradley Jackson, age 11. Of Rockford, Ill., for his question:

Where is the troposphere?

Where, said the little fish, is the water? He was, of course, living in the water, just as we live in the troposphere. We live in an ocean of air that surrounds us on all sides. This air is the atmosphere that reaches hundreds of miles above our heads. The densest layer of the atmosphere is nearest the ground. It is the restless, cloudy air, which makes the weather.

The top of the troposphere blends with the stratosphere. The boundary between these two, layers of the atmosphere is highest over the equator. Here the troposphere reaches up about ii miles. At the poles, it reaches up about 5 miles.