Spectral lines and gas lamp: 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 — evolved from — Hot air balloon. A steerable balloon.
5. Step 5. Hot air balloon — has part — Gas burner. It heats the air in the envelope with a propane flame.
6. Step 6. Gas burner — is part of — Gas lamp. A coal-gas burner.

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