Public address system e telescope: o que têm em comum

1. Passo 1. Public address system — tem como parte — Loudspeaker. Loudspeakers.
2. Passo 2. Loudspeaker — faz parte de — Telephone. The earpiece reproduces the other person’s voice.
3. Passo 3. Telephone — evoluiu de — Electrical telegraph. The telephone grew out of attempts to send several signals over telegraph lines (the “harmonic telegraph”).
4. Passo 4. Electrical telegraph — evoluiu de — Optical telegraph. The electrical telegraph replaced semaphore lines.
5. Passo 5. Optical telegraph — utiliza — Telescope. Signals were read through a telescope.

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