Magic Staircase by Gary Cuba (803)776-5295 -- developed
    1/31/86. All copyrights waived, but mention the author!
  
Will the tones ever stop ascending?
   
 This is a musical illusion based upon perceptual circularity
    of widely space tones whose volumes are defined as a
    sinesoidal relationship TO their frequency.
There are 4 tones spaced an octave apart. each tone advances
    in frequency by one half-note until it is within 1/2
    note of the NEXT octave. at this POINT it starts over
    again at its beginning frequency. 
Each tone's volume is set according to its position along a
    sinewave. 
See Roger N. Shepard, 'Circularity in Judgements of Relative
    Pitch', The Journal of the Acoustical Society of America,
    (December 1964).