A couple of years back, Ron Tyroler, the demo manager at UC Berkeley,
showed me a mechanical model of polarization which illustrates circular
polarization. It is operated by turning a crank which operates a camshaft
that moves rods up and down and back and forth. It was an old apparatus
and I do not know where it came from. I haven't found it in current
manuals. There are little white balls on the tips of the rods which are
meant to move the way the electric (or magnetic) field does.