Railway switch e telephone: o que têm em comum

1. Passo 1. Railway switch — faz parte de — Railway track. Switches.
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 para — Telephone. The telephone grew out of attempts to send several signals over telegraph lines (the “harmonic telegraph”).

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