Whistle e optical telegraph: o que têm em comum

1. Passo 1. Whistle — utiliza — Sound wave. The sound of a flow.
2. Passo 2. Sound wave — é utilizado em — Phonograph. It records sound vibrations as a groove.
3. Passo 3. Phonograph — foi inspirado por — Electrical telegraph. Edison came to the phonograph while working on recording telegraph and telephone signals.
4. Passo 4. Electrical telegraph — evoluiu de — Optical telegraph. The electrical telegraph replaced semaphore lines.

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