Mute violins, known to have existed since the eighteenth century and mentioned by Leopold Mozart in his Versuch einer gründlichen Violinschule (1756), are built to allow violinists to practice technique without actually generating a sound -- and therefore without disturbing their neighbors. They may have an outer frame with the shape of the violin, or an even more minimal anchor-shaped frame to allow for a comfortable hold and for shifting hand positions. Some mute violins were constructed from the remnants of earlier functioning violins. Today's violinists have the option of practicing on an electric "silent violin," the successor to these eighteenth- and nineteenth-century instruments.