I just spent a thoroughly enjoyable time reading about the Glass Armonica
on http://www.glassarmonica.com (the project of a local Seattle Musician
W. Zeitler). A scientific glassblower built him a copy of Franklin's
original instrument in fused quartz.
Wetfinger-wineglass trivia: should not a vibrating wineglass act as
four coherent sources, and so project a four-lobed interference pattern
into surrounding space?
So, if we make a wineglass "speak" by slowly rotating a finger along the
edge, should not the interference pattern rotate with the finger? If we
could see sound, a singing wineglass would appear to be surrounded with a
rotating "flower" of interference patterns, sending out a searchlight-
pattern of nodes and antinodes. I think it does do this, since wineglass
music has a 'wow-wow-wow' sound to it if our ears are near the plane
coincident with the rim of the glass. I wonder if there's a zone of
silence on axis with the glass.
The glass Armonica would NOT do this, since the fingers remain still and
the glass bowls are rotated mechanically.
For those who can afford to jump into their learjets, there's an Armonica
performance in Seattle April 4, 6pm, Henry Gallery, and April 5 3pm 'Hokum
Hall'. Be sure and bring your "Magic Schoolbus sound-visualization
goggles." :)