n the southern coast of Italy lies the little village of Amalfi. Apart from its picturesque setting and the view it offers of the Tyrrhenian Sea, Amalfi's principal claim to fame is symbolized by a tall bronze statue of its most famous son, Flavio Gioia, reverently honored as the inventor of the magnetic compass. But if the sculptor was somewhat noncommittal as to Flavio's facial features, it is only because no one knows what he looked like or, indeed, if he ever actually existed.

In The Riddle of the Compass, best-selling science writer Amir Aczel visits Amalfi to investigate the mysterious life of Gioia and to explore the innovation that occurred in the village between 1295 and 1302, when the magnetic compass was perfected, transformed from a needle floating in water or supported in air into the device we know today a round instrument containing a magnetic needle and a compass card divided into 360 degrees. It was a modification that revolutionized maritime navigation. Aczel uses Gioia as a starting point for a fascinating exploration of navigation techniques. Aczel's own firsthand experiences at sea are also included in the book. As a child he lived on a passenger ship which his father captained and by the age of 10 was an apprentice at the helm, learning the finer points of negotiating the Mediterranean. Personal and poetic, his memories of sailing give the book extra texture.

In his exploration of the theories of ancient navigation, Aczel spurns the idea that mariners piloted by "hugging the coastline," which, he says, would have meant courting the greatest of dangers that of running aground. It was precisely this risk, he says, that led to the development of the sounding line, which was knotted at intervals and weighted with lead.

Tracing the roots of the modern-day device to ancient China, The Riddle of the Compass is full of delightful digressions. Although Aczel himself follows a winding course in the narrative, he moves methodically toward his destination and with the aplomb of Hercule Poirot carefully flicking a speck of lint off his coat sleeve, gracefully explains the final difficulties of the riddle of the compass.

H.

V. Cordry is a former professor, now writing from his home in Kansas.

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