Carvão ativado e optical telegraph: o que têm em comum

1. Passo 1. Carvão ativado — é um tipo de — Carbono. Porous carbon.
2. Passo 2. Carbono — é material para — Hearing aid. The first hearing aids used a carbon microphone.
3. Passo 3. Hearing aid — evoluiu de — Telephone. The first electric hearing aids were built from telephone components.
4. Passo 4. Telephone — evoluiu de — Electrical telegraph. The telephone grew out of attempts to send several signals over telegraph lines (the “harmonic telegraph”).
5. Passo 5. Electrical telegraph — evoluiu de — Optical telegraph. The electrical telegraph replaced semaphore lines.

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