| Year | 1923 |
| Date | 16-Aug |
| Volume | 49 |
| Issue | 1,164 |
| Page | 181 |
| Category | Railway |
| Part | 1 |
| Title | Some Notes on the Development of Railway Signalling |
| Author | E.H.Ellingham |
| Notes | Historical Outline. G.W.R. ball signal, disc signal, for use at junctions, square board, method of illumination of modern square signal, continental square board signal |