Stretch Vs.Temperament, (was Beat Rates)

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>The reason Dr. Sanderson gave was that two strings moved in opposition
> reducing the movement of the bridge. He was able to measure the drop in
> pitch with his accutuner. The class could also hear the change in the beat
> rates when shown by Virgil.

Greetings, 
   It has been shown that a flexible termination will allow that string to 
behave as though it is longer than it really is, and a very rigid termination 
will show the opposite, ie. two strings of equal diameter, length, and 
tension will show two different frequencies  if one has a rigid termination 
point and the other a more flexible one.  The reason for this is that the 
flexible terminus allows the string to effectively "end" farther away, while 
the rigid one requires that all of the energy rebound from a point that is, 
on a microscopic scale, not quite at the terminus,itself.  
   This effect is made manifest when two strings are operating simultaneously 
on a bridge; if they move together, the bridge moves more.  It is not the 
"Weinreich" effect, but shares some of the same physics.  The "Virgil" effect 
depends on very closely matched unisons, and if there is cause to "detune" 
one string to compensate for variables,  I don't think the flattening will 
show itself.  
Regards, 
Ed Foote RPT