Bar screens and LIGO: what they have in common

1. Step 1. Bar screens — is part of — Sewage treatment plant. They catch large debris.
2. Step 2. Sewage treatment plant — is part of — Sewerage. Treatment plants.
3. Step 3. Sewerage — uses — Gravity flow. Waste water flows down a gradient.
4. Step 4. Gravity flow — is used in — Water filter. Water seeps through by gravity.
5. Step 5. Water filter — is made of — Silica (sand). Slow filters are layers of sand and gravel.
6. Step 6. Silica (sand) — is material for — LIGO. The mirrors are fused silica.

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