Who Invented the Compass?

Crediting an invention to any particular individual has its pitfalls. Most, if not all inventions are based to some extent on work already done by somebody else. Then there is the question of what is truly a new idea, and what is only an improvement of something that is already known to exist. When it comes to assigning ancient inventions there is the additional difficulty of determining just when something was first put to use. We have access only to a tiny fraction of the books and records that were ever written and often it is a casual mention or perhaps an old painting or woodcut that produces evidence for an items existence. So it is with the magnetic compass.

In the Italian port of Amalfi, about twenty-five miles southeast of Naples, there stands a monument to a Flavio Gioia who in the year 1302 invented the compass. At least that is what it says on his statue, and never mind that historians found no evidence that such a person ever existed. Never mind also that a century earlier an English Augustinian monk by the name of Alexander Neckam (1157-1217) wrote a book he called De naturis rerum, in which he mentioned that mariners used the magnetic needle to guide them at sea.

Perhaps the problem is one of definition. How complicated does the gadget in question have to be before one can call it a compass. Is a horizontally balanced magnetic needle hanging on a silken thread a compass? Or does it have to be encased in a box? Does it have to be balanced on a pin above a graduated piece of cardboard? How about the custom of mariners to insert a magnetized iron pin into a piece of straw in order to float it in a bowl filled with water, where it was free to align itself with the earths magnetic field?

A compass is really a marriage of two separate items that existed side by side for centuries without getting into each others way, the magnetic needle and the wind rose. For well over a millennium mariners and geographers used the winds as symbols of direction, referring from where the winds blew. Already in the 5th century B.C. the sky was divided into four quarters. In the Bible we read: And upon Elam will I bring down the four winds from the four quarters of heaven [Jeremiah 49:36]. Aristotle divided each wind into three parts, creating a set of twelve directions, each with a distinctive name. In later times wind roses developed into 32-point stars and became prominent and highly decorative additions to maps. Perhaps the celebrated navigator of Amalfi was first to glue such a wind rose into the bottom of a box, into the center of which he installed a pivoted magnetic needle.

Not that Italys claim to fame has gone unchallenged. The Chinese, the Greeks, the Arabs, the Vikings, the Finns, and others have claimed to have been first to use a compass. It is possible that different peoples in different parts of the world have invented it independently. At an international conference on magnetism held in Beijing in July 1992, participants were given a replica of a magnetic south-pointing device (in China south is the reference direction), used by Chinese as early as 200 B.C. It consisted of a polished, deep-bowled spoon, carved out of magnetite (the Chinese referred to it as loving-stone). When placed on a polished bronze plate, where it was free to rotate in response to the earths magnetic field, the handle of the spoon would seek south, while the shape of the spoon itself was believed to represent the constellation of the Big Dipper. The magnetic spoon seems to have been used only as a charm or as a divining tool, as there is no evidence that the Chinese used it for navigation. In the 1950s a scholar at Columbia University by the name of Li Shu-Hua said he had found a Chinese text dated AD 1040 that described the construction of a magnetized iron turtle balanced on a pin.

The magnetic properties of a black iron oxide called magnetite (lodestone) were known already in antiquity. Sailors yarn had it that if they sailed too close to a magnetic mountain that was believed to exist somewhere, all the iron nails would be pulled out of the ship and the planks would come apart. This is what supposedly happened to a careless crew of Arabs in Scheherazades Tales of the Arabian Nights. A prudent shipwright put his boats together with wooden pegs, just in case.

Iron needles had coercivities (a term that describes how permanent a magnet is) so low that they had to be frequently remagnetized; carrying a lodestone therefore was as necessary as the compass itself. To the medieval mind the magnetic attraction seemed magical, and superstitious sailors (which included just about all of them) were careful not to have onions or garlic on their breath, the fumes of which were believed to destroy the magnetic power, rendering the compass useless. A London physician and scientist named Gilbert wrote in 1600 that he had tested that garlic claim by belching garlic fumes into a compass, even rubbing the needle with garlic juice; it did nothing to alter the needles properties.

It took considerably longer to discover that the magnetized needle did not point to true north. Although the first book listing compass variations was printed in 1701, as late as 1757 a Spanish scholar wrote about magnetic variation which sailors have not believed and do not now believe. The reason for declination was not understood and often explained to be due to poor quality of a particular compass. The log of Columbus for September 17, 1492 reads: Last night the pilots took a reading on the North Star and found that the compasses declined to the NW a full point (11 degrees). This perceived irregularity so alarmed the crew, that Columbus ordered the north to be fixed again just before sunrise, after which he explained that it was Polaris and not the compass that had moved (in 1492 Polaris was 3 degrees 27 minutes from the pole).

That magnetism arose from the earth itself may have been discovered during the 1570s by English instrument maker Robert Norman. Norman had always carefully balanced his compass needles prior to magnetizing them and soon noticed that subsequent magnetization would throw the needle off balance. To confirm his suspicion he built a dip-needle that was suspended on a horizontal axis and thereby free to point down, showing the terrestrial source of magnetism (or, more to the point, the vertical components of it).

There exists on earth a magnetic equator, an irregular, ever-changing line, where the vertical component of the magnetic field is zero. In my never-ending quest to ferret-out nonsense in learned books I remember reading a book about the explorations of Alexander von Humboldt, in which the author claimed that in crossing that line Humboldt watched his compass needle spin from north to south. Poppycock; why should it? If a compass needle is balanced at the magnetic equator, its north end will dip below the horizontal when traveling north, and the south end will do likewise when traveling south.

Even in our age of global positioning systems the magnetic compass has retained its usefulness. Though as a surveying tool it is on its way out, it remains popular with hunters and hikers. In Europe, some hotels give small, complimentary compasses to their Arabian guests, helping them to find the direction of Mecca for their daily prayers. Like almost everybody else, these folks dont know that a compass does not point to any single point, but only aligns itself with the horizontal component of the local magnetic field.

For an excellent, encyclopedic in scope, yet witty and entertaining treatment of magnets and magnetism I refer the reader to Driving Force by James D. Livingston (Harvard University Press, 1996, paperback 311 pp). Mr. Livingston is a lecturer at MIT and also has written about New Mexicos surveyor general William Pelham, to whom he has a family connection.

About the Author

Fred Roeder, LS

Fred Roeder lives in Tularosa, New Mexico. He emigrated to the United States from Germany in 1957 and spent most of his surveying career in the Southwest, working for the U.S. Forest Service. Now retired, he started writing a regular column for the New Mexico Professional Surveyors Newsletter in 1988. In 1994, NMPS produced Antepasados, a book of his columns. Many surveyors are good writers, especially about technical or legal matters. However, it's not often that we find a surveyor/story-teller who can present historical facts in a manner that makes them fun to read. Fred Roeder is such a writer and we are pleased to present more than 80 of his stories here. Bibliography is a list of the books Fred used in his writings, and includes a numbered index of the articles. Index is a list of all the articles Fred has written and when. Editor's pick: The King Who Had No Title
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