Ultraviolet and electrical telegraph: what they have in common

1. Step 1. Ultraviolet — is used in — Sunglasses. A UV filter.
2. Step 2. Sunglasses — evolved from — Glasses. Glasses with dark lenses.
3. Step 3. Glasses — evolved into — Telescope. The first telescopes were assembled by spectacle makers.
4. Step 4. Telescope — is used in — Optical telegraph. Signals were read through a telescope.
5. Step 5. Optical telegraph — evolved into — Electrical telegraph. The electrical telegraph replaced semaphore lines.

Open Evothings