Helmholz, 1877 - Helmholz motion
Observed pattern: Triangle rotating on parabolic curve.
Triangular displacement function.
Two distinct velocities at any point x of the string.
Helmholz’s theory: the sound quality increases with the wave-form approaching the ideal (sharp) Helmholz pattern.
eyepiece on a tuning fork creating Lissajous figures as in x-y mode on a scope.