When brought near the dome of a generator, the whirl
spins rapidly in a direction that is away from the points.
The electrons escaping
from the dome to the spokes ionize the air at the sharp points.
Since the spokes are
continuously charged, the ionized air particles are repelled and the spinning results from
an equal and opposite force reaction.
Even if it is given an initial spin in the opposite direction, it will
stop and reverse.