"Don't ask me. Ask the metal detector, it's supposed to work...”
Manny, from American crime drama series CSI
When U.S. President James Garfield was shot in an assassination attempt in 1881 the doctors called on Alexander Graham Bell (1847-1922) to find the bullet in his dying body. For this purpose Bell quickly threw together a makeshift instrument that could detect metal, but unfortunately the President was lying in a bed with a metal frame, unusual at the time, and this interfered with the instrument. Bell eventually realized why his detector was not functioning properly, but it was too late and President Garfield died shortly after.
Metal detectors rely on the relationship between electricity and magnetism. A current is run through a coil of wire, and this causes a magnetic field. If a metal object passes through the field, then an electric current will be generated on the object. This, in turn, causes an opposite signal in the coil and this change alerts the user to the presence of metal.
Bell's crude metal detector was eventually improved upon, and the modern detector dates from the 1930s. Metal detectors are commonly seen today in airports, where they are used to detect concealed weapons. They are also used to detect land mines on the battlefield and to check food for shards of metal in factories. Simple metal detectors are cheap to buy and easy to make, and some take up metal detecting as a hobby to look for coins and other metal items.
