The Benjamin Franklin glass harmonica
Kathleen J. Allen · The Journal of the Acoustical Society of America · 1991
The instrument described is from a design by Benjamin Franklin, of modern manufacture by Gerhard Finkenbeiner of Waltham, Mass., played by Vera Meyer of Cambridge, Mass., and encompasses three octaves. Two notes from each octave were investigated at varying amplitudes of excitation and different speeds of rotation. Data will be presented to show that harmonic richness is a function of octave, and is relatively unaffected by amplitude of excitation; also that the rotation of the disks splits the degeneracy of the normal modes. An analysis will be presented of the splitting by decomposition into traveling waves around the circumference of the disk, which relates rotation speed and the shear velocity of sound in the glass medium.