The post office and its story an interesting account of the activities of a great government department

All the tubes are worked on the block system, and by an electrical contrivance the traffic is regulated. In long-distance tubes delay would arise if it were only possible for one carrier to be in the tube at one time, and to meet this intermediate automatic signallers are inserted at various distances in the tube, so that as soon as a carrier passes one section, it automatically notifies the sending section, enabling a second carrier to be inserted. Thus several carriers equidistant from each other may be passing through the one tube at the same time. The power by which these tubes are worked is derived from large compound pneumatic pumping engines fitted in the basement, but eventually the power station which has recently been established at Blackfriars will supply the power required. There are at present thirty-seven pneumatic tubes connecting the various branch offices with the Central Office, in addition to seven which connect the offices of the various cable companies with the cable room. Adjoining the central hall are the phonogram and the tube switch rooms. The former is set apart for telephone telegram business, and by its means telephone subscribers may speak direct into the head telegraph office. In this way they can dictate telegrams by telephone for subsequent transmission by telegraph. Telegrams are also sent in the opposite direction to certain subscribers who desire to receive their telegrams by telephone instead of by hand delivery from the nearest delivery office. The telephone circuits connecting the Post Office Savings Bank at West Kensington with St. Martin's le Grand, and used in connection with Savings Bank withdrawal telegrams, are also situated in this room.