Several makers have explored this technique for string harmonics, most prominently Hans Reichel and Glenn Branca. The idea is that a center bridge divides the strings into two segments. A magnetic pickup is placed on one side, but the strings are played primarily on the other side, usually with a slide. When a frequency sounding on the played side matches any of the harmonics of the same string on the unplayed side, it sets up a sympathetic vibration in the unplayed segment. That’s the sound that comes through the pickup. The tone is dreamy and ethereal, with a floating, swelling presence.
In the audio clip, the Harmonic Zither is joined by the Elastic Zither, a rubber-band instrument. In the photos appearing here, two different versions of Handsome Glenn can be seen. In the video linked below, Handsome Glenn is the second of several instruments described.