Kathleen McCarry, age 13, of Spokane, Wash., for her question:

What causes magnetism?

It is thought that magnetism is present in tiny atoms and molecules. Each atom, we think, has its own miniature north and south magnetic pole. In an iron poker, the little atoms are arranged with their magnetic poles all mixed up. Some pull in one direction and some in another. In a magnet, most of the atoms are arranged to pull in the same direction.

The biggest magnet in the world is the earth itself. Its mighty magic pulls at all the little magnets and lines them up, pointing to the north and south magnetic poles. It is thought that the earths magnetism is in the metallic core where most of the atoms are arranged to exert their pull in a north south direction.