=278. Typical Working of Auto-Controlled Manual System.=—The mode of employing these signals can be illustrated in a typical way by the diagrams, Figs, 11, 12, and 13, which exhibit in a skeleton manner Pattenall’s improved Sykes system which belongs to the Auto-Controlled Manual class. In these figures the end of block 1, the whole of blocks 2 and 3, and the beginning of block 4 are shown. Stations _A_, _B_, and _C_ indicate the extremities of blocks. The signals _S_, _Sʹ_, and _S″_ are the home signals, while _D_, _Dʹ_, and _D″_ indicate distant signals, and _A_, _Aʹ_, and _A″_ advance signals. As the diagrams indicate, the stretch of double-track road is represented with east- and west-bound tracks. In order to simplify the diagrams, signals and stations are shown for one track only; they would simply be duplicated for the other track. The signal cabin is supposed to be located at each station, and at that cabin are found the levers and other appliances for working the signals operated there, the signals themselves being exposed alongside the track. In each signal cabin there is an indicator, as shown at _I_, _Iʹ_, and _I″_. On the face of each indicator there are two slots, shown opposite the lines _E_ and _F_. In the upper of these slots appears either the word “Clear” or “Blocked.” In the lower slot appears either the word “Passed” or “On.” The significance of these words will appear presently. On this indicator face at _P_, _Pʹ_, and _P″_ are located electric push-buttons called plungers. The operation of the levers indicated at _L_, the counterweights _d_, and the locking detail _l_ are evident from an inspection of the figure, and need no special explanation. It is only necessary to state that the locking-device _l_ holds the bar _bc_ until it is released at the proper time, and that the counterweight may then return the lever from its extreme leftward position to that at the extreme right, at the same time placing the semaphore arm _S_ in the position of danger. It is particularly important to bear in mind this last observation. The counterweight is the feature of the system which always holds the semaphore arm in the position of danger, making that its normal position, except when it is put to safety for the passing of a train. [Illustration: FIG. 11.] [Illustration: FIG. 12.] [Illustration: FIG. 13.]