The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 264
ther line if one is engaged. The markingsgreatly assist the operators in their work. Automatic Night Lighting,—In order to economise theelectric-light current at night an arrangement known as theBelfast system is used in the more important exchanges. Anextra relay, a (Fig. 255), is included in the… … Fig. 255 bar switch, D.B., is to the left. The armature of E.M. whenattracted closes the lighting switch, L.S., which lights a lampover the section on which the call is made. When the night operator inserts his instrument plug intothe instrument-]ack of the section, the relay b is brought intoplay,…
Telephone
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