Exhalation valve and electrical telegraph: what they have in common

1. Step 1. Exhalation valve — is part of — Respirator. It makes exhaling easier.
2. Step 2. Respirator — is made of — Activated carbon. The filter is activated carbon.
3. Step 3. Activated carbon — is a kind of — Carbon. Porous carbon.
4. Step 4. Carbon — is material for — Carbon microphone. Carbon granules.
5. Step 5. Carbon microphone — is part of — Telephone. For a century, telephone microphones were carbon microphones.
6. Step 6. Telephone — evolved from — Electrical telegraph. The telephone grew out of attempts to send several signals over telegraph lines (the “harmonic telegraph”).

Open Evothings