Mark Kinsler's comments regarding automatic roll changers have prompted
me to reply.  Many mechanical music machines have roll changers.  The
designs are varied.  Large commercial orchestrions seem to have the
most reliable systems.  Home instruments such as reproducing pianos and
player pipe organs could be equipped with automatic roll changers, too.

Aeolian seemed to be the most successful in marketing their "Concertola"
ten-roll changer for Duo-Art pipe organ and Duo-Art reproducing piano.
The pipe organ version showed up first around 1925.  It cost $3,500,
so it sold in very limited numbers.

I own a Duo-Art Concertola for pipe organ.  It is fully restored.  From
an engineering standpoint it really is a marvelous device for the time
period.  Reliability is not too good, however.  Lacking proper feedback
on several key functions, the machine can fail.

As an example, the drum that holds ten rolls need not be fully loaded.
A sensor will detect any missing roll position and stop the loading
mechanism from "firing" on that empty position.  The problem is, the
storage drum will keep revolving forever, looking for the selected but
missing roll.

With dozens of adjustments, fragile rolls, and limited qualified field
technicians, the machine did not win widespread admiration from owners.
No one seems to know how many Concertola were made.  I have tried to
compile a list, but it is still too incomplete to draw conclusions.
The serial numbers seem to start at "200" for the pipe organ models.
The serial numbers are in the "300's" for the pianos and later
Aeolian-Skinner pipe organ roll changers.

Your lecture including these mechanisms is indeed made more meaningful
as we study the progress of automation.  Early efforts failed to include
proper feedback.  As automation evolved we soon learned that feedback
was necessary and thus "Fail-Safe" systems became known.  Of course
now, we have systems that are "Fail-Operational", where system redundancy
properly monitored leads to voting the failed component out of the loop.

Clearly, evolution of automation is an on-going process and mechanical
music systems were very important building blocks.

Bob Taylor