The Balance Wheel was made from magnetic material. When the
balance wheel rotates, a small nib on the balance axis moves
an electrical contact arm to complete the electric circuit,
thus switching on the electromagnets which attract the extended
horns of the balance wheel.
Further rotation of the balance wheel causes the nib to pass
the contact, the contact is disconnected, then the electromagnetic
After the balance wheel reaching its full amplitude, the
balance is returned by the force of the balance spring; however,this
time, the nib on the balance axis passes the contact without
When the balance returns, the process is repeated and the
electromagnets again attract the balance wheel, giving another
The following animated image explains the process.
The yellow represents the electromagnets are