Speed of light and zip: what they have in common

1. Step 1. Speed of light — uses — Telescope. Observations of Jupiter’s moons.
2. Step 2. Telescope — evolved from — Glasses. The first telescopes were assembled by spectacle makers.
3. Step 3. Glasses — has part — Spectacle frame. A frame.
4. Step 4. Spectacle frame — is made of — Bone. The first frames were made of bone and horn.
5. Step 5. Bone — is material for — Button. Ancient buttons were carved from bone and shell.
6. Step 6. Button — works like — Zip. An alternative way of fastening.

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