Semaphore signal arms and submarine: what they have in common

1. Step 1. Semaphore signal arms — is part of — Optical telegraph. The positions of the arms encode characters.
2. Step 2. Optical telegraph — uses — Telescope. Signals were read through a telescope.
3. Step 3. Telescope — includes — Reflecting telescope. A telescope.
4. Step 4. Reflecting telescope — has part — Mirror. The primary mirror.
5. Step 5. Mirror — is part of — Periscope. Mirrors or prisms.
6. Step 6. Periscope — is part of — Submarine. A periscope.

Open Evothings