Greenhouse frame and optical telegraph: what they have in common

1. Step 1. Greenhouse frame — is part of — Greenhouse. A metal or wooden frame.
2. Step 2. Greenhouse — has part — Window glass. It lets light in and holds heat.
3. Step 3. Window glass — is part of — Solar panel. Tempered cover glass.
4. Step 4. Solar panel — is part of — Space telescope. Solar panels.
5. Step 5. Space telescope — is a kind of — Telescope. A space telescope is a telescope above the atmosphere, so air does not blur the view.
6. Step 6. Telescope — is used in — Optical telegraph. Signals were read through a telescope.

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