Cast iron and voltaic pile: what they have in common

1. Step 1. Cast iron — is material for — Gas lamp. The posts are cast iron.
2. Step 2. Gas lamp — evolved into — Incandescent light bulb. Electricity displaced gas lighting.
3. Step 3. Incandescent light bulb — is part of — Torch (flashlight). A bulb (today an LED).
4. Step 4. Torch (flashlight) — has part — Dry cell. Batteries.
5. Step 5. Dry cell — evolved from — Voltaic pile. A convenient form of the galvanic cell.

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