Current and voltage coils and optical telegraph: what they have in common

1. Step 1. Current and voltage coils — is part of — Electricity meter. They create fields proportional to current and voltage.
2. Step 2. Electricity meter — has part — Permanent magnet. A braking magnet.
3. Step 3. Permanent magnet — is part of — Pickup. A magnet magnetizes the string.
4. Step 4. Pickup — has part — Copper wire. A winding.
5. Step 5. Copper wire — is part of — Electrical telegraph. Communication lines.
6. Step 6. Electrical telegraph — evolved from — Optical telegraph. The electrical telegraph replaced semaphore lines.

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