Many thanks to John Wolff (Australia) for his answer to my request,
with the fine description and the details he gave yesterday about
playing and tuning a Triola mechanical zither, and his list of music
rolls.

I am very puzzled by a sentence in his description:  "With his third
hand, the operator works a lever to control the depth of the plucking
mechanism, to act as a volume control."

What do you mean exactly by "With his third hand..." ?

Best regards,

Philippe Rouille (Paris, France)
http://www.cnam.fr/museum/musica_mecanica/

 [ That's the extra arm and hand one needs to operate all the controls.
 [ The illusionist also has a third hand, but you never see it!  ;)
 [ -- Robbie