by John Vardalas, BHP Guest Expert
Industry Associate Professor, College of Arts & Letters
Stevens Institute of Technology
New Jersey, USA

 This article originally appeared in The Institute and is also available as a secondary source document on the IEEE REACH website,

Note from the BHP Team: What can everyday objects teach us about history? This month’s Big Question to look at familiar objects in new ways. We’ve kicked off the conversation with a deep dive into the history of one such object – the magnetic compass. What conditions led to its development? How did the handy navigational tool shift the balance of global power and politics? What later innovations did it inspire? Use the following article to supplement Unit 8 of your BHP course as you dig into themes of global expansion and interconnection. Or – if it’s Little Big History season at your school – treat it as a source of inspiration for uncovering the layers of history of other everyday objects.

 (For more ideas on how teachers are using this new Big Question article in class, check out this blog post and this conversation in the BHP Online Community!)

Eager to make this article and the concepts in it come alive? Don’t miss a chance to chat with the author, John Vardalas, March 4-6, for a BHP Yammer Exchange.

 This navigational instrument led to advances in trade, military might, and science.

Inhospitable as it can be, the sea has played an essential role in human history, and so did that indispensable navigation tool, the magnetic compass. The sea provided the cheapest way to move goods over great distances, generating wealth through trade. Navigating the oceans successfully also played a pivotal role for many countries in gaining political and military power. Along the way, the compass contributed to innovations in physics and electrical engineering.

Far from the sight of land, the sea is a seemingly endless, undifferentiated expanse. For most of history, getting lost at sea was a very real danger, often with disastrous consequences. Even when close to land, seafarers can become disoriented in bad weather. For ancient Greek and Roman sailors, weather conditions even limited visibility enough to shorten the sailing season in the Mediterranean Sea. The Roman military writer Publius Flavius Vegetius wrote in the fourth century that travel from June to mid-September was safe, but that sailing any other time was risky. He called the period between mid-November and mid-March mare clausum, or the time when “the seas are closed.”

Seafarers adhered to these guidelines until the early 14th century, when the magnetic compass made its first appearance in the Mediterranean. No longer completely dependent on landmarks, the mariner could now find his position relative to Earth’s magnetic field. With the Mediterranean now “open” for most of the year, trade increased substantially, which contributed to the rise of the Italian city-states.

Victoria, the sole ship of Magellan’s fleet to complete the circumnavigation. Detail from a map by Ortelius, 1590. Public domain.


Though the behavior of lodestone, a naturally magnetized piece of the mineral magnetite, was observed by the ancient Greek philosophers Thales of Miletus and Socrates, the evidence is clear that the idea for using it in a compass first appeared in China. There are allusions in the manuscript Wu Ching Tsung Yao, written in 1040, to “an iron fish” suspended in water that pointed to the south. And the earliest reference to a magnetic direction-finding device for land navigation is recorded in a Song Dynasty book dated to 1040-44.

In 1088, Song Dynasty scholar Shen Kuo wrote that when “magicians rub the point of a needle with lodestone, then it is able to point to the south…It may be made to float on the surface of water, but it is then rather unsteady…It is best to suspend it by a single cocoon fiber of new silk attached to the center of the needle by a piece of wax. Then, hanging in a windless place, it will always point to the south.”

In Europe, the magnetic compass first appeared in Amalfi, Italy, around the turn of the 14th century. But it is not known if the magnetic compass was also invented in the West or if it migrated to Europe along trade routes from China. However, it is clear that because sea trade and military advantage were of far more strategic importance to Western nations, they pushed the technology of the magnetic compass far more intensely than did the Chinese. With the successive rise of the Portuguese, Spanish, Dutch, and English empires, development of the compass shifted to the European nations facing the Atlantic Ocean.

Model of a Han Dynasty (206 BC–220 AD) south-indicating ladle or sinan, CC BY-SA 3.0.
Detail from Table of Geography, Hydrography, and Navigation, from the 1728 Cyclopaedia, public domain.

The biggest challenge raised by the compass was what we now call magnetic variation: the angular difference between geographic or “true” north and the magnetic north, or the direction in which a magnetized needle points. Under clear skies, one could find the geographic north-south axis for comparison with where the compass pointed by either referring to the polestar or looking at the sun at noon.

Across the Mediterranean, the difference between geographic north and magnetic north was relatively small. However, in the Atlantic, particularly in the northern latitudes, the difference was considerable. If this difference had been constant, there would be no problem, but it varied greatly as one traveled east to west. During his first voyage to North America from Spain in 1492, Christopher Columbus observed this mysterious behavior, but he kept it from his crew, fearing it would spook them.


Beginning in 1698, with the support of England’s Royal Society and the Admiralty, Edmund Halley, who would later be named the country’s Astronomer Royal, set out on several long expeditions to measure Earth’s magnetic variations across the northern and southern regions of the Atlantic Ocean. This data offered great advantage to the English Navy. In 1701, Halley produced the world’s first isogonic chart, which shows how the angle between magnetic north and true north varies at different points in the Atlantic Ocean.

Edmond Halley’s New and Correct Chart Shewing the Variations of the Compass (1701), the first chart to show lines of equal magnetic variation. Public domain.

The study of magnetism set the stage for work in electrostatics. And the compass also served as a scientific instrument. With it, Danish physicist Hans Christian Ørsted observed in 1820 that an electric current from a battery flowing through a wire produced a magnetic field. This important discovery in electromagnetism paved the way for telegraphy.

In 1831, English scientist Michael Faraday showed that moving a conductor in a magnetic field produced an electric current, leading to advances in electric power generation. James Maxwell combined the electric and magnetic phenomena in a set of elegant field equations. Heinrich Hertz’s discovery of radio waves, a type of electromagnetic radiation, set the stage for wireless telecommunications. This great chain of discoveries and inventions was set in motion by the seafarer’s compass, the tool that made it possible to voyage across Earth’s inhospitable seas.

One of Faraday’s 1831 experiments demonstrating induction. The liquid battery (right) sends an electric current through the small coil (A). When it is moved in or out of the large coil (B), its magnetic field induces a momentary voltage in the coil, which is detected by the galvanometer (G). Public domain.

About the author: Until his retirement from IEEE, in July 2016, Dr. John Vardalas was the senior historian at the IEEE History Center. He is still an industry associate professor in the College of Arts & Letters at Stevens Institute of Technology. He has written numerous articles on the history of technology in society. His current historical interests center on the interrelationships between “command of the sea,” trade, geopolitics, and the development of science and technology over the millennia. He is an avid sailor.

The IEEE History Center (, which contributed this article, is funded by donations to the IEEE Foundation (

Header image: An ancient Chinese nautical compass ©NYPL/Science Source/Getty.

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