Tallow and tunnelling shield: what they have in common

1. Step 1. Tallow — is used in — Oil lamp. The fuel was animal fat, later oil.
2. Step 2. Oil lamp — evolved into — Incandescent light bulb. The electric lamp replaced oil and gas lamps.
3. Step 3. Incandescent light bulb — evolved from — Gas lamp. Electricity displaced gas lighting.
4. Step 4. Gas lamp — evolved into — Street light. Gas lamps.
5. Step 5. Street light — is part of — Tunnel. Lighting.
6. Step 6. Tunnel — uses — Tunnelling shield. Shield tunnelling.

Open Evothings