Steam locomotive e optical telegraph: o que têm em comum

1. Passo 1. Steam locomotive — utiliza — Railway track. It runs on rails.
2. Passo 2. Railway track — inspirou — Time zones. Introduced because of railway timetables.
3. Passo 3. Time zones — utiliza — Electrical telegraph. Synchronizing time by telegraph.
4. Passo 4. Electrical telegraph — evoluiu de — Optical telegraph. The electrical telegraph replaced semaphore lines.

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