| Answer | Crossword Clue |
|---|---|
| ARGON | Gas in a vacuum tube |
| ARGON | Vacuum-tube gas |
| ARGON | Vacuum tube gas |
| NEON | Light in a vacuum tube. |
| NEON | It glows red in a vacuum tube. |
| ANODE | ... dark space (region in a vacuum tube) |
| ELEMENT | One of the electrodes in a vacuum tube. |
| NEON | Gas in a tube |
| ANODE | ... ray (stream of positive ions in a gas-discharge tube) |
