The 33-1/3 RPM phonograph disc was initiated by the Vitaphone company.
The sound tracks for their early talkies were on 16-inch discs, played
at 33-1/3 RPM with a 2.5 mil stylus.  The 33-1/3 RPM figure came from
a power take-off in the mechanism that moved the film through the
projector.

This information was given to me by a close friend, former
projectionist and _serious_ record collector Bill John of Victoria, BC.
I am sorry to say that Bill died recently at the age of 75, taking an
immense store of knowledge with him.  Others may be able to add to or
correct my recollection of Bill's explanation of the origin of 33-1/3
disc.

Cheers

Doug Rhodes