Enjoyed Craig Brougher's article and Robbie's information about
the mercury trough switching.  As described, as a strictly on-off
switching system, this would have been entirely possible. I suspect a
bit of advertising "fluffing" if they claimed the system could measure
the "exact force and every subtlety of the pianist's expression".  We
can only hope the participants were in a well ventilated room.  It
might be interesting if some medical history was found showing that
some of the Welte technicians later suffered from overexposure to
mercury fumes. That would surely give more force to the story's
veracity.

I suppose if instead of a simple carbon prong, the system employed
something like resistance wire wrapped around or running the length of
a non-conducting prong, it would be possible to get variable resistance
readings throughout the keystroke.  But, would they have had the
electrical wherewithal at that time to transfer and utilize that
subtle electrical information?  Then there's the problem of the surface
tension of mercury that might now allow just any configuration of prong
to glide evenly into the pool.  This would be fascinating if all of the
claims are actually true and someone can explain how it functioned.

Tom Lear