Upper water reservoir and electric motor: what they have in common

1. Step 1. Upper water reservoir — is part of — Carbide lamp. Water drips onto the carbide.
2. Step 2. Carbide lamp — evolved from — Davy lamp. Miners’ lamps.
3. Step 3. Davy lamp — is used in — Coal mine. Protection against methane explosions.
4. Step 4. Coal mine — uses — Mine ventilation. Airing the workings.
5. Step 5. Mine ventilation — has part — Electric fan. Fans.
6. Step 6. Electric fan — has part — Electric motor. A motor.

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