| Clue | Source | Date |
|---|---|---|
| In the wireless telegraphy era, a glass tube inside which iron filings clinging together indicated a radio signal | The Times Specialist Sunday | 28 Mar 2021 |
| Device used to detect radio waves | New York Times | 05 Nov 2016 |
| Device used to detect radio waves | ||
| Primitive radio receiver | ||
| One in agreement |