. American telephone practice . n this case the ringing would cause the 406 AMERICAN TELEPHONE PRACTICE. operation of the trunk drop at the private branch switch-board. • Theprivate branch attendant, seeing this signal, would plug in with theanswering plug and answer in the name or number of the firm towhich the private branch exchange belonged. The calling sub-scriber then would tell her the nature of his business, or, perhaps,the person to whom he wished to speak, whereupon the attendantwould complete the connection with the proper private branch line,using her calling plug, and by the opera
. American telephone practice . n this case the ringing would cause the 406 AMERICAN TELEPHONE PRACTICE. operation of the trunk drop at the private branch switch-board. • Theprivate branch attendant, seeing this signal, would plug in with theanswering plug and answer in the name or number of the firm towhich the private branch exchange belonged. The calling sub-scriber then would tell her the nature of his business, or, perhaps,the person to whom he wished to speak, whereupon the attendantwould complete the connection with the proper private branch line,using her calling plug, and by the operation of her ringing key wouldcall the subscriber on that line. The operation of the relays A andB would remove the private branch battery from the cord circuit,and, therefore, when the private branch subscriber responded, threesupervisory signals would be operated. In the operation of this cir-cuit, when the call is originated by the main office subscriber, theanswering of the private branch attendant actuates the supervisory. FIG. EXCHANGE LINE CIRCUIT OF CHICAGOTELEPHONE COMPANY. circuits upon the calling plug at the main office to show the mainoffice operator that the call has been responded to, and that no fur-ther action at the main office is required. The main office operator performs exactly the same function inconnecting with the private branch trunk line as she does in con-necting with a regular subscribers line. It might be said that the compelling of the private branch opera-tor to restore manually the trunk line drop is a disadvantage, butthis is hardly a valid objection, as the private branch attendant hasvery much more to do in the way of talking and listening than shehas with her hands. In Fig. 308 is shown a line circuit of the latest private branchexchanges used by the Chicago Telephone Company. This em-ploys a jack which cuts off both sides of the line, and also has threeadditional spring contacts used entirely for modifying the opera- PR
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