Nuclear fusion and optical telegraph: what they have in common

1. Step 1. Nuclear fusion — is used in — Tokamak. The goal is controlled fusion.
2. Step 2. Tokamak — uses — Electromagnetism. Magnetic fields confine the plasma.
3. Step 3. Electromagnetism — is used in — Electrical telegraph. A telegraph receiver is an electromagnet that attracts an armature.
4. Step 4. Electrical telegraph — evolved from — Optical telegraph. The electrical telegraph replaced semaphore lines.

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