2 to move the segment 3, yet they do not permit the rocker arm 2 to move so far to the left as to close even the talking circuit.  The exception is the deep notch, or selective notch, which is of such depth as to permit the pawl 6 to fall so far into the segment as to allow the rocker arm 2 to close both the talking and the ringing circuits.  Besides the moving pawl 6 there is a detent pawl 7.  This always holds the segment 3 in the position to which it has been last moved by the moving pawl 6.

The actuating magnet 1, as has been stated, is polarized and when energized by currents in one direction, the rocker arm moves the pawl 6 so as to step the segment one notch.  When this relay is energized by current in the opposite direction, the operation is such that both the moving pawl 6 and the detent pawl 7 will be pulled away from the segment, thus allowing the segment to return to its normal position by gravity.  This is accomplished by the following mechanism:  An armature stop is pivoted upon the face of the rocker arm so as to swing in a plane parallel to the pole faces of the relay, and is adapted, when the relay is actuated by selective impulses of one polarity, to be pulled towards one of the pole faces where it acts, through impact with a plate attached to the pole face of the relay, as a limiting means for the motion of the rocker arm when the rocker arm is actuated by the magnet.  When, however, the relay is energized by current in the opposite direction, as on a releasing impulse, the armature stop swings upon its pivot towards the opposite pole face, in which position the lug on the end of the armature stop registers with a hole in the plate on the relay, thus allowing the full motion of the rocker arm when it is attracted by the magnet.  This motion of the rocker arm withdraws the detent pawl from engagement with the segment as well as the moving pawl, and thereby permits the segment to return to its normal position.  As will be seen from Fig. 189, each of the relay magnets 1 is permanently bridged across the two limbs of the line.

Each station is provided with a push button, not shown, by means of which the subscriber who makes a call may prevent the rocker arm of his instrument from being actuated while selective impulses are being sent over the line.  The purpose of this is to enable one party to make a call for another on the same line, depressing his push button while the operator is selecting and ringing the called party.  The segment at his own station, therefore, remains in its normal position, in which position, as we have already seen, his talking circuit is closed; all of the other segments are, however, stepped up until the ringing and talking circuits of the desired station are in proper position, at which time ringing current is sent over the line.  The segments in Fig. 189, except at Station C, are shown as having been stepped up to the sixth position, which corresponds to the ringing position of the fourth station, or Station D. The condition shown in this figure corresponds to that in which the subscriber at Station C originated the call and pressed his button, thus retaining his own segment in its normal position so that the talking circuits would be established with Station D.