G'morning Paul

 PR> (Do you know what it is yet?  If you know your history of physics
 PR> that should be hint enough.  ;-)

Foucault's thingie ?

 PR> Have a friend take the barometer to the top of the building.
 PR> Attach, oh, let's say a spool of piano wire to the barometer,
 PR> and let it down till it nearly touches the ground.  Pull the
 PR> barometer aside and release it.  Time the period of its
 PR> swings.

Good one ... and incidently, I guess one could mark the swing path 
and track any rotation ?  Excellent....

:-)

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