Reported in Scientific American, this Week in World War I: November 13, 1915
The first two months of World War I saw intense, desperate fighting between French and German armies in Alsace-Lorraine. After the battle of Grand Couronée ended in September 1914, the fighting in the northeast corner of France eventually moved on to the pivotal town of Verdun. The French Department of Meurthe-et-Moselle, to the south of Verdun, never became a quiet sector, but the front lines there stabilized, and for the rest of the war, changed little. The farmers moved back to reclaim fields that were now sown with unexploded shells left over from ferocious artillery bombardments: between a quarter and a third of all the shells fired in World War I were duds.
In 1915 the French authorities turned to technology that had initially been developed to solve the result of violence that took place in 1881. An assassin had shot U.S. President James A. Garfield shortly after he took office in 1881. The bullet remained lodged in Garfield’s torso, and Alexander Graham Bell had constructed a simple metal detector to try and find it (and unfortunately, failed). That same technology was now employed in France:
When the erstwhile battlefields of Europe are reclaimed for the peaceful purposes of agriculture, there is an ever-present risk of death or serious injury to both the farmers and their horses as the result of plowshares coming in contact with buried shells that have failed to explode when fired. The instrument that has been devised by the French for the detection of buried shells is an adaptation of the Hughes induction balance. The original instrument was made by Professor C. Gutton at the request of the prefect of the Department of Meurthe-et-Moselle, and with it the constructor was able to detect the presence of a small caliber shell at a depth of about 40 centimeters (nearly 16 inches).
Those same fields are still littered with live ordnance: hundreds of tons of shells, bombs and grenades are still cleared by farmers every year—the “iron harvest”—from former battlefields in France and Belgium.
Our full archive of the war, called Scientific American Chronicles: World War I, has many articles from 1914–1918 the technology of the First World War. It is available for purchase at www.scientificamerican.com/products/world-war-i/