Calendar hanging clip and optical telegraph: what they have in common

1. Step 1. Calendar hanging clip — is part of — Wall calendar. A spring or a clip.
2. Step 2. Wall calendar — is made of — Paper. Calendars were printed on paper.
3. Step 3. Paper — is material for — Loudspeaker. The cone is paper.
4. Step 4. Loudspeaker — is part of — Telephone. The earpiece reproduces the other person’s voice.
5. Step 5. Telephone — evolved from — Electrical telegraph. The telephone grew out of attempts to send several signals over telegraph lines (the “harmonic telegraph”).
6. Step 6. Electrical telegraph — evolved from — Optical telegraph. The electrical telegraph replaced semaphore lines.

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