Electroscope and optical telegraph: what they have in common

1. Step 1. Electroscope — uses — Static electricity. The leaves repel each other.
2. Step 2. Static electricity — is used in — Xerography. Toner sticks to a charged drum.
3. Step 3. Xerography — is used in — Photocopier. A photocopy.
4. Step 4. Photocopier — has part — Lens. Optics.
5. Step 5. Lens — is used in — Optical telegraph. Signals were read through telescopes.

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