Brian Anderson, age 14, of Searboro, Ont., Canada, for his question:

Who invented the compass?

Before the dawn of history, wonderers took their bearings from the Sky and perhaps from landmarks such as rivers and mountains. The Greeks found natural magnets more than 2000 years ago, but they regarded them as amusing toys. Perhaps they never hung a sliver of magnet on a string and learned that its two ends point to the earth's North and South poles.

The Chinese made this discovery perhaps 1100 years ago. Marco Polo found them using the magnetic compass when he journyed to far Cathay. At about the same time, the people of the Mediterranean at last hit upon the same idea. They made magnetic compasses to guide their trading ships.