Movable type and barrel: what they have in common

1. Step 1. Movable type — is made of — Clay. Bi Sheng’s type was made of fired clay.
2. Step 2. Clay — is material for — Qanat. Weak sections of a qanat were reinforced with clay rings.
3. Step 3. Qanat — works like — Aqueduct. An underground channel instead of an overground one.
4. Step 4. Aqueduct — has part — Arch. Roman aqueducts rested on arcades.
5. Step 5. Arch — works like — Barrel. Staves squeezed by hoops hold their shape by the same compression as the stones of an arch.

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