Scythe and pneumatic tube: what they have in common

1. Step 1. Scythe — evolved from — Sickle. Mowing while standing, with a long snath.
2. Step 2. Sickle — evolved into — Combine harvester. The machine replaced reaping by hand.
3. Step 3. Combine harvester — has part — Belt drive. Belt drives.
4. Step 4. Belt drive — is part of — Supercharger. Belt-driven from the crankshaft.
5. Step 5. Supercharger — uses — Compressed air. It forces air into the cylinders.
6. Step 6. Compressed air — is used in — Pneumatic tube. Air pressure.

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