| Year | 1939 |
| Date | 09-Feb |
| Volume | 80 |
| Issue | 1,970 |
| Page | 164 |
| Category | Electrical |
| Part | |
| Title | An Electric Switching Problem |
| Author | J.Gordon Hall |
| Notes | Controlling a single lamp by means of two two-way switches, an unsuccessful attempt to introduce a third switch into the circuit, a suitable intermediate switch |