Pantograph and optical telegraph: what they have in common

1. Step 1. Pantograph — is part of — High-speed train. A current collector.
2. Step 2. High-speed train — works like — Maglev. The same task without contact between wheel and rail.
3. Step 3. Maglev — uses — Electromagnetism. Electromagnets hold and move the train.
4. Step 4. Electromagnetism — is used in — Electrical telegraph. A telegraph receiver is an electromagnet that attracts an armature.
5. Step 5. Electrical telegraph — evolved from — Optical telegraph. The electrical telegraph replaced semaphore lines.

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