Perhaps the surprising thing is that this was developed and used in a watch before being adopted for clocks.

The basis of operation is that a tuning fork is electrically maintained and will vibrate at its natural frequency. One tine of the fork carries a small magnet and this is in close proximity to a mumetal wheel with many arms. The clock is not self starting, but if the wheel is spun up manually to synchronous speed the wheel and fork interact, without physical contact, to keep the wheel turning in syncronism with the fork. The wheel is then geared to the motion work and hands.

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