Sleeping car and optical telegraph: what they have in common

1. Step 1. Sleeping car — has part — Bogie. Bogies.
2. Step 2. Bogie — is part of — Diesel locomotive. Bogies with wheelsets.
3. Step 3. Diesel locomotive — has part — Electric generator. The generator powers the traction motors.
4. Step 4. Electric generator — has part — Copper wire. Windings.
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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