Laura Brown, age 11, of Doraville, Ga., for her question:     

WHAT IS A LODESTONE?

The first people who put a lodestone to work were the Chinese. They learned that a bit of magnetic iron can perform a fabulous trick. When allowed to turn freely, it points to the north. So they floated a sliver of magnet on a little raft in a bowl of water. It turned around to point north  and became the world's first magnetic compass. In the 1200s, Marco Polo returned from his visit to China with many tales of fabulous inventions. For one thing, he described how a lodestone  or leading stone  is used as a compass to point to the north. Actually these remarkable stones were discovered long before, though nobody in Europe thought they could be useful.

The Roman writer Pliny reported that certain magic stones were found by a shepherd boy of ancient Greece. This boy, named Magnus, wore tips of iron on his sandals and on his shepherd's crook. As he wandered the slopes of Mount Ida, he noticed that certain stones tended to cling to his bits of iron. They were, of course, natural magnets  perhaps an iron oxide called magnatite. Or perhaps they were bits of a metallic meteorite that became magnetized as it plummeted down to the ground.

The story of Magnus may or may not be true. But we do know the wise men of ancient Greece knew a lot about their so¬called magnet stones, though they did not figure out how to use them as lodestones to create the magnetic compass.

This discovery was made by those clever Chinese. During the Crusades, all sorts of Eastern ideas were borrowed and toted westward across Europe. One such idea was the magnetic compass, based on a suspended lodestone. Later observers noted that the magnets, alias lodestones, have opposite poles that either attract or repel each other.

In the 1500s, Dr. William Gilbert of England figured out that the compass works because the earth itself is a giant magnet. Its North Pole pulls the opposite pole on each little compass magnet.

This sounds confusing because we assume that the north pole of a magnet swings around to face the North Pole of the earth. Actually, it is more accurate to say that the north¬ seeking pole of the magnetic lodestone points to the North Pole. The opposite end of the little magnet is its south seeking pole   which naturally swings around to point to the South Pole.