Jet bridge and davy lamp: what they have in common

1. Step 1. Jet bridge — has part — Hydraulic cylinder. Raising the bridge.
2. Step 2. Hydraulic cylinder — has part — Piston. The piston is moved by liquid.
3. Step 3. Piston — is part of — Newcomen engine. Atmospheric pressure moves the piston.
4. Step 4. Newcomen engine — uses — Coal mine. Pumping water out of mines.
5. Step 5. Coal mine — uses — Davy lamp. Protection against methane explosions.

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