The Ptolemaic Helicon (Eight-Stringed)

It was an ingenious stringed instrument used to study musical concords and the mathematical relations that define them. It consisted of a square wooden soundbox with an extended arm, (eight parallel strings equal in length and thickness and two tailpieces that formed a perfect square) and a rotating bridge around one point of the arm. The pivoting point lay at the extension of the square base at a distance equal to the side of the square. The strings abstained from each other distances in proposition to the musical intervals of the octave. The rotating bridge, at whichever position, determined the string length corresponding to the musical intervals of the octave. Thus, it produced a complete octave at any tonality.