=Intermediate Station Time-Lock.=—We have another time-lock attached to the sending apparatus that has been already referred to in describing the “block system” used at intermediate stations; a time-lock to prevent carriers being inserted into the tube at intermediate stations while another carrier is passing that station. This time-lock is shown in Fig. 27 at W´, and is shown in detail by a sectional drawing, Fig. 31. When a carrier closes an electric circuit in passing one of the boxes located in a manhole about three hundred feet from an intermediate station, it indicates its approach to the station by exciting the electro-magnet A, Fig. 31. This magnet pulls down its armature B and raises the small piston valve C, which admits compressed air to a small chamber, D. The air is supplied to this chamber from the main tube through the pipe E. In one end of this chamber is fitted a piston, F, held to one end of its stroke by a spring, G. When compressed air is admitted to the chamber D, this piston is moved to the left, and by such movement throws the controlling valve of the sending apparatus into its normal position (shown in Fig. 29) and holds it there. This forms a positive lock, and, no matter in what position the sending apparatus may be, it puts the tube B, Fig. 29, into line with the main tube so that the approaching carrier can pass through the apparatus. The piston-rod H, Fig. 31, is connected to the finger _d_, Fig. 29, and by rocking this finger moves the controlling valve, or prevents it being moved by the handle K. [Illustration: FIG. 31. INTERMEDIATE STATION TIME-LOCK.]