Grandpa Doug,
I came up with this answer in respose to your contest question:

All mechanical rotary tremolo systems, including Leslie's, are based on the Doppler-effect. Discovered by Austrian mathematician and physicist Christian Doppler (1803-1853) in the early nineteenth century, the Doppler-effect is the apparent variation in pitch that a stationary listener hears from a moving sound source. In practice, the loudness of the sound also appears to vary and it is this combination of frequency (vibrato) and ampli-tude (tremolo) modulation that give Leslie Speakers their characteristic sound.

Do I win that trip to Hawaii ?
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Larry Hawk