4 pedal upright, 'tremelo' pedal???

[PNOTNR@AOL.COM]

List,

I tuned a Wing & Sons Upright today.  It has 4 pedals.  The left pedal is not 
hooked up to anything, but above it is written "tremelo."  The center left 
pedal is a soft pedal above which is written "piano," the center right is a 
damper pedal above which is written forte, and I suspect the right pedal was 
for either a muffler rail, or a mandolin type rail, above which is written 
"orchestra."

I'm not losing sleep over this, but I am a little curious about what the 
tremelo pedal on an otherwise typical old upright might have done, and how it 
did this.

Thanks

Gordon Large, RPT
Maine