Earth inductor compass

The Earth inductor compass (or simply induction compass) is a compass that determines directions using the principle of electromagnetic induction, with the Earth's magnetic field acting as the induction field for an electric generator. The electrical output of the generator will vary depending on its orientation with respect to the Earth's magnetic field. This variation in the generated voltage is measured, allowing the Earth inductor compass to determine direction.

The earth inductor compass was first patented by Donald M. Bliss in 1912 and further refined in the 1920s by Paul R. Heyl and Lyman James Briggs of the United States National Bureau of Standards, and in 1924 by Morris Titterington at the Pioneer Instrument Company in Brooklyn, New York. Heyl and Briggs were awarded the Magellan Medal of the American Philosophical Society for this work in 1922. Designed to compensate for the weaknesses of the magnetic compass, the Earth inductor compass provided pilots with a more stable and reliable reference instrument. They were used in the Douglas World Cruisers in 1924 during the Around-the-World flight by the U.S. Army Air Corps.Charles Lindbergh used the compass on his transatlantic flight in the Spirit of St. Louis in 1927. Over the transatlantic leg of his voyage - a distance of about 2,000 miles (3,200 km) - he was able to navigate with a cumulative error of about 10 miles (16 km) in landfall, or less than one percent of the distance travelled, by computing his position at hourly intervals by dead reckoning with the induction compass.

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