Stilts and telephone: what they have in common

1. Step 1. Stilts — uses — Lever. An extended support.
2. Step 2. Lever — is used in — Optical telegraph. The arms were moved by a system of levers and rods.
3. Step 3. Optical telegraph — evolved into — Electrical telegraph. The electrical telegraph replaced semaphore lines.
4. Step 4. Electrical telegraph — evolved into — Telephone. The telephone grew out of attempts to send several signals over telegraph lines (the “harmonic telegraph”).

Open Evothings