| Year | 1923 |
| Date | 01-Nov |
| Volume | 49 |
| Issue | 1,175 |
| Page | 490 |
| Category | Railway |
| Part | 11 |
| Title | Some Notes on the Development of Railway Signalling |
| Author | E.H.Ellingham |
| Notes | Three-Position Signalling. On the Great Western Railway, electro-pneumatic locking frame, automatic train stop |