Mechanical pencil and optical telegraph: what they have in common

1. Step 1. Mechanical pencil — is made of — Silver. Early mechanical pencils were silver.
2. Step 2. Silver — uses — Electrical conduction. The best conductor.
3. Step 3. Electrical conduction — is used in — Copper wire. Copper conducts current well.
4. Step 4. Copper wire — is part of — Electrical telegraph. Communication lines.
5. Step 5. Electrical telegraph — evolved from — Optical telegraph. The electrical telegraph replaced semaphore lines.

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