Barrel organ and boyle’s air pump: what they have in common

1. Step 1. Barrel organ — has part — Bellows. Bellows feed air into the pipes.
2. Step 2. Bellows — has part — Check valve. An air intake valve.
3. Step 3. Check valve — is part of — Vacuum pump. Valves stop air from flowing back.
4. Step 4. Vacuum pump — evolved into — Boyle’s air pump. An improved version of Guericke’s pump.

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