Ophthalmoscope and archimedes’ screw: what they have in common

1. Step 1. Ophthalmoscope — has part — Mirror. A mirror.
2. Step 2. Mirror — is part of — Periscope. Mirrors or prisms.
3. Step 3. Periscope — is part of — Submarine. A periscope.
4. Step 4. Submarine — has part — Propeller. A propeller.
5. Step 5. Propeller — evolved from — Archimedes’ screw. The first propellers by Smith and Ericsson were a variation on the Archimedes’ screw.

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