A simple electroscope using plastic straws, tape, and
plastic film cans with some clay in the bottom.
When the tape gets an unbalanced charge on it, you
can see it repel the other piece of tape.
In the replica of Hess' electroscope, the tape is replaced
by very fine hairs, shielded from breezes, and equipped wirth
a microscope and a ruler to measure very fine changes in the deflection.
The
Exploratorium has a page of activities with this electroscope.
Hess' balloon experiment involved charging his electroscope,
and then observing the rate at which the "leaves" (the
pieces of tape) lost charge and returned to normal. You could
do the same with a cheap electroscope.
