Jigsaw puzzle and optical telegraph: what they have in common

1. Step 1. Jigsaw puzzle — uses — Saw. Cut out with a fretsaw.
2. Step 2. Saw — is used in — Sawmill. The cutting tool is a saw.
3. Step 3. Sawmill — has part — Crank. A crank turns the wheel’s rotation into the stroke of the saw.
4. Step 4. Crank — is part of — Cinématographe. The film was advanced by turning a handle.
5. Step 5. Cinématographe — has part — Lens. A lens.
6. Step 6. Lens — is used in — Optical telegraph. Signals were read through telescopes.

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