Steam locomotive and optical telegraph: what they have in common

1. Step 1. Steam locomotive — uses — Railway track. It runs on rails.
2. Step 2. Railway track — inspired — Time zones. Introduced because of railway timetables.
3. Step 3. Time zones — uses — Electrical telegraph. Synchronizing time by telegraph.
4. Step 4. Electrical telegraph — evolved from — Optical telegraph. The electrical telegraph replaced semaphore lines.

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