Glass light bulb envelope and hollerith tabulator: what they have in common

1. Step 1. Glass light bulb envelope — is part of — Incandescent light bulb. A glass bulb with a vacuum or inert gas.
2. Step 2. Incandescent light bulb — evolved from — Gas lamp. Electricity displaced gas lighting.
3. Step 3. Gas lamp — uses — Coal gas. Coal gas.
4. Step 4. Coal gas — is used in — Traffic light. A gas lamp lit the signal.
5. Step 5. Traffic light — has part — Relay. Relay controllers.
6. Step 6. Relay — is part of — Hollerith tabulator. Relays controlled the sorting box.

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