. American telephone practice . etip and the sleeve strand. A point in the operators telephone cir- MAGNETO MULTIPLE SWITCH-BOARD. 229 cuit between the receiver and the secondary winding of the induc-tion coil is grounded so as to make the receiver available for test-ing. The test is made when the key, K, is depressed, the test cir-cuit then being from the tip of the plug, P, through the tip strandto the right-hand spring of the key, and through its anvil and thereceiver coil to the ground. The condenser, C, is for the purposeof preventing disturbances in the line with which the plug, P, is co
. American telephone practice . etip and the sleeve strand. A point in the operators telephone cir- MAGNETO MULTIPLE SWITCH-BOARD. 229 cuit between the receiver and the secondary winding of the induc-tion coil is grounded so as to make the receiver available for test-ing. The test is made when the key, K, is depressed, the test cir-cuit then being from the tip of the plug, P, through the tip strandto the right-hand spring of the key, and through its anvil and thereceiver coil to the ground. The condenser, C, is for the purposeof preventing disturbances in the line with which the plug, P, is con-nected from giving a false busy test. The line circuit and cord circuit shown in Figs. 204 and 205 wereat one time standard with the American Bell Telephone companies,the most notable case of their use being in the old Cortlandt Streetexchange in New York. This was at the time the largest multipleswitch-board in existence. While the old switch-board has been tornout to be substituted by one of modern construction, it formed a. FIG. 205.—CORD CIRCUIT FOR METALLIC CIRCUIT SERIES-ULTIPLE BOARD. landmark in switch-board development, and therefore the actual cir-cuits employed in it may be of interest. There were both groundedand metallic circuit lines used in this exchange, the wiring of eachline, as well as that of the cord circuit, being shown in Fief; 206,in which the line at the left of the figure is a metallic circuit, andthat on the right a grounded circuit. There were in all 44 sectionsto this switch-board, the jacks in all of which, except the 44th. woreprovided with a tip spring normally resting against a contact point,the circuit being broken on the insertion oi the plug. This jack isdiagrammatically shown in detail, a, of Fig. 206. The jacks at the44th section were provided with a double break—that is. they wereadapted to break both sides of the line instead of onlv one. The ar- 230 AMERICAN TELEPHONE PRACTICE. rangement of springs in the jacks at this section is s
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