The nail violin (or nail harmonica) is one of the most unusual instruments in the string family. Invented by a German violinist named Johann Wilde in 1740, it consists of a wooden soundboard (often circular or semi-circular) with a series of iron or brass nails of varying lengths driven into the edge. The nails are tuned by how deep they are driven into the wood—the shorter the nail, the higher the pitch. To play it, the musician uses a standard violin bow to rub against the nails, causing them to vibrate and produce a sound similar to a glass armonica or a musical saw. Despite its name, it has no strings and is technically a friction idiophone. It enjoyed a brief period of popularity in European salons during the 18th century as a novelty instrument but fell into obscurity because it was difficult to tune and had a very limited dynamic range.