. American telephone practice . ck framework, where it ends in a suitable clip, to which thewire may be soldered. The other contacts of the jack are mountedin the rear strip only, each of them being provided with clips pro-jecting rearwardly from this strip for the purpose of soldering theconnecting wires. Such a strip of jacks is provided with means forfastening it rigidly in the iron framework of the switch-board. Thisconstruction has many advantages over the individually mountedjack, the principal ones being that of greater rigidity and economyof space. The spacing of the jacks in this stri
. American telephone practice . ck framework, where it ends in a suitable clip, to which thewire may be soldered. The other contacts of the jack are mountedin the rear strip only, each of them being provided with clips pro-jecting rearwardly from this strip for the purpose of soldering theconnecting wires. Such a strip of jacks is provided with means forfastening it rigidly in the iron framework of the switch-board. Thisconstruction has many advantages over the individually mountedjack, the principal ones being that of greater rigidity and economyof space. The spacing of the jacks in this strip is the same as thaton the drops shown in Fig. 169, and therefore these jacks may be .90 AMERICAN TELEPHONE PRACTICE. used in connection with the drops, being mounted directly above orbelow them in the same switch-board cabinet. The ringing and listening keys, by which the operators generatoror telephone may be connected with the circuit of any line through acord circuit, have assumed a great variety of forms, only a few types. FIG. 171.—RINGING AND LISTENING KEY. of which have survived. One of the most common types is shownin Fig. 171, in which is represented the under side of the key handle by which the key is operated projects through theshelf, and is shown at the top of the cut. This handle is pivotedwithin the shelf, and operates a ball cam in a manner to cause it toslide between one or the other pairs of springs, between which it nor-mally rests. This is called a combined ringing and listening key,the act of ringing being accomplished by pressing the handle to theleft, causing the ball to move to the right, while the action of listen-ing is caused by a reverse movement of the handle, causing the camto move between the left-hand set of springs. The circuit connec-tions of such a key are shown in Fig. 172, where P and P are re-spectively the answering and calling plugs. The tip and sleevestrands of the answering cord are respectively connected to the
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