This exhibit has
a counter, a vibrating steel strap, and an electromagnet. Contacts on
either side of the metal strap either turn on the electromagnet (attracting
the steel strap) or cause the counter to increment by one. By carefully
adjusting the spacing of the electrical contacts near the steel strap,
an oscillation can be created as the strap alternately makes and breaks
its electromagnet contact. A sliding weight can be attached to the steel
strap that will change the frequency of vibration.