Jacob’s staff and tank: what they have in common

1. Step 1. Jacob’s staff — evolved into — Davis quadrant. Davis spared the navigator from looking at the Sun.
2. Step 2. Davis quadrant — evolved into — Octant. Reflecting angle gauges.
3. Step 3. Octant — has part — Mirror. Two mirrors.
4. Step 4. Mirror — is part of — Periscope. Mirrors or prisms.
5. Step 5. Periscope — is part of — Tank. Observation devices.

Open Evothings