Interferometer arm vacuum tubes and plough: what they have in common

1. Step 1. Interferometer arm vacuum tubes — is part of — LIGO. Two 4 km vacuum tubes.
2. Step 2. LIGO — is a kind of — Interferometer. An interferometer.
3. Step 3. Interferometer — is made of — Stone. Michelson’s instrument stood on a stone slab.
4. Step 4. Stone — is material for — Hoe. The working part was of stone or antler.
5. Step 5. Hoe — evolved into — Plough. The plough mechanized loosening the soil with a hoe.

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