overtones // moving frets

The historical development of the partial idea: if you're talking just
about the knowlege that the octave and twelth are contained, in some sense,
in the sounding tone, this goes back earlier than Descartes and Mersenne.
Stringed-instrument players have always known that when a low tone is
played, strings tuned an 8ve or 12th higher resonate sympathetically.
There's a long process of turning that knowledge into physics, though.

Shaun,
I suggest the fishing line frets method of getting moveable frets because
it gives you a chance to experiment. It's hard to make it work on an
acoustic guitar. If you use an electric you don't need line that's too
thick and rigid. You still lose tone quality on the highest string though.
You also need one or two pairs of pliers and a good knot which holds the
line firmly to the neck. It's hard to explain the knot, but I can try if
you want me to.

jason