Railway switch et telephone : ce qu'ils ont en commun

1. Étape 1. Railway switch — fait partie de — Railway track. Switches.
2. Étape 2. Railway track — a inspiré — Time zones. Introduced because of railway timetables.
3. Étape 3. Time zones — utilise — Electrical telegraph. Synchronizing time by telegraph.
4. Étape 4. Electrical telegraph — a évolué en — Telephone. The telephone grew out of attempts to send several signals over telegraph lines (the “harmonic telegraph”).

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