In 1954, the material contained in this pamphlet waspublished, in commemoration of the 50th Anniversary of our Company, to help signalmen get a better understanding of signaling systems, of their principles of operation and how these principles are applied.

These principles still apply today and, for this reason, the material contained in the original publication (Handbook 50) is reproduced herein to provide a valuable reference for thosepersons new to the signaling field.