Here is an example of instrument design that came from the Csound Anthology. There are some brief animations that illustrate the auditory illusion. Csound orchestra and score files are also included, as well as some brief sound examples.
Sound files are AIFF and animations are quicktime.
Here are pair of quicktime movies showing how the partials cycle. Your WWW client will need to support the viewing of Quicktime movies. In these two the frequency is linear on the x-axis. Each partial is one octave higher that the one previous, so the frequency of any partial is 2 times the one previous. With the partials all displayed the same color and the animation set to loop, the endless illusion can be easily seen.