String instrument strings, or play them by rolling the bell of a brass instrument such as a trombone on the array of strings. However, these are relatively rarely used special techniques. Other keyed string instruments, small enough for a strolling musician to play, include the plucked autoharp, the bowed nyckelharpa, and the hurdy-gurdy, which is played by cranking a rosined wheel. Steel-stringed instruments (such as the guitar, bass, violin, etc.) can be played using a magnetic field. An E-Bow is a small hand-held battery-powered device that magnetically excites the strings of an electric string instrument to provide a sustained, singing tone reminiscent
Hurdy-gurdy Is Made), known through a much later copy, but its authenticity is very doubtful. Another 10th-century treatise thought to have mentioned an instrument like a hurdy-gurdy is an Arabic musical compendium written by Al Zirikli. One of the earliest visual depictions of the organistrum is from the twelfth-century "Pórtico da Gloria" (Portal of Glory) on the cathedral at Santiago de Compostela, Galicia, Spain: it has a carving of two musicians playing an organistrum. Later on, the "organistrum" was made smaller to let a single player both turn the crank and work the keys. The "solo organistrum" was known from Spain