Spectral lines and electric fan: what they have in common

1. Step 1. Spectral lines — uses — Spectroscope. They are observed with a spectroscope.
2. Step 2. Spectroscope — is used in — Helium. Helium was discovered by spectroscopy in the solar spectrum.
3. Step 3. Helium — is used in — Airship. After the Hindenburg — helium.
4. Step 4. Airship — has part — Propeller. Air propellers.
5. Step 5. Propeller — is part of — Electric fan. The blades.

Open Evothings