=The Sender.=—The sending apparatus is for the purpose of enabling the operator to place a carrier in the tube without allowing the air to escape. In other words, it is a means of despatching carriers. The apparatus for this purpose, already referred to, is simply a valve. A side view and section of it are shown in Fig. 12. Fig. 15 is a view of the apparatus in the main post-office. The sending apparatus is seen on the left. Fig. 13 is a view of the sub-post-office apparatus, and here a man may be seen in the act of despatching a carrier. Referring to the section, Fig. 12, it will be seen that the sending apparatus consists of a short section of tube supported on trunnions and enclosed in a circular box. Normally this short section of tube stands in line with the main tube, and the air-current passes directly through it. It is shown in this position in the figure. When a carrier is to be despatched, this short section of tube is rotated by a handle until one end comes into coincidence with an opening in the side of the box. In this position the air flows through the box around the movable tube. A carrier can then be placed in the short section of tube and be rotated by the handle into line with the main tube. The carrier will then be carried along with the current of air. A circular plate covers the opening in the box where the carrier is inserted when the sending apparatus is closed. At the sub-post-office this sending apparatus is placed in a horizontal position, but its operation is the same. [Illustration: FIG. 13. RECEIVING AND SENDING APPARATUS IN THE SUB-POST-OFFICE.] [Illustration: FIG. 14. _APPARATUS AT SUB-STATION—PHILA._] [Illustration: FIG. 15. TERMINALS OF THE TUBE IN THE MAIN POST-OFFICE.]