Knife-edge pivot and submarine: what they have in common

1. Step 1. Knife-edge pivot — is part of — Balance scale. A low-friction pivot for the beam.
2. Step 2. Balance scale — is made of — Stone. Weights were hewn from stone.
3. Step 3. Stone — is material for — Interferometer. Michelson’s instrument stood on a stone slab.
4. Step 4. Interferometer — has part — Mirror. Mirrors.
5. Step 5. Mirror — is part of — Periscope. Mirrors or prisms.
6. Step 6. Periscope — is part of — Submarine. A periscope.

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