allowed to enter his section. In this way a section of line with a full complement of signals is always interposed between any two trains.
THE WORKING OF SINGLE LINES.
We have dealt with the signalling arrangements pertaining to double lines of railway, showing that a system of signals is necessary to prevent a train running into the back of its predecessor. Where trains in both directions pass over a single line, not only has this element of danger to be dealt with, but also the possibility of a train being allowed to enter a section of line from each end at the same time. This is effected in several ways, the essence of each being that the engine-driver shall have in his possession visible evidence of the permission accorded him by the signalman to enter a section of single line.
A SINGLE TRAIN STAFF.
The simplest form of working is to allocate to the length of line a "train staff"—a piece of wood about 14 inches long, bearing the names of the stations at either end. This is adopted where only one engine is used for working a section, such as a short branch line. In a case like this there is obviously no danger of two trains meeting, and the train staff is merely the authority to the driver to start a journey. No telegraphic communication is necessary with such a system, and signals are placed only at the ends of the line.
TRAIN STAFF AND TICKET.
On long lengths of single line where more than one train has to be considered, the line is divided into blocks in the way already described for double lines, and a staff is assigned to each, the staffs for the various blocks differing from each other in