Qanat and optical telegraph: what they have in common

1. Step 1. Qanat — is made of — Clay. Weak sections of a qanat were reinforced with clay rings.
2. Step 2. Clay — is material for — Oil lamp. Later — clay ones.
3. Step 3. Oil lamp — is used in — Magic lantern. The light source is an oil lamp.
4. Step 4. Magic lantern — has part — Lens. Lenses.
5. Step 5. Lens — is used in — Optical telegraph. Signals were read through telescopes.

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