Torque and gas lamp: what they have in common

1. Step 1. Torque — is used in — Geneva drive. It turns continuous rotation into intermittent motion.
2. Step 2. Geneva drive — is part of — Film projector. Intermittent advance of the film.
3. Step 3. Film projector — has part — Incandescent light bulb. The light source (formerly an arc).
4. Step 4. Incandescent light bulb — evolved from — Gas lamp. Electricity displaced gas lighting.

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