Central heating and davy lamp: what they have in common

1. Step 1. Central heating — has part — Valve. Valves on the radiators set how much hot water flows into a room.
2. Step 2. Valve — is part of — Carbide lamp. It regulates the water supply.
3. Step 3. Carbide lamp — evolved from — Davy lamp. Miners’ lamps.

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