Bent wire hairpin and optical telegraph: what they have in common

1. Step 1. Bent wire hairpin — is part of — Hairpin. An elastic U-shaped wire.
2. Step 2. Hairpin — is made of — Bone. Ancient hairpins were bone.
3. Step 3. Bone — is material for — Spectacle frame. The first frames were made of bone and horn.
4. Step 4. Spectacle frame — is part of — Glasses. A frame.
5. Step 5. Glasses — evolved into — Telescope. The first telescopes were assembled by spectacle makers.
6. Step 6. Telescope — is used in — Optical telegraph. Signals were read through a telescope.

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