=Three- to Eight-Station Line.=—Thus far we have described only two-station lines. In Fig. 26 we have a diagram of three stations connected together by a double line of tubes, and the arrangement would be similar if it were extended to four, five, six, seven, or eight stations. The stations are called A, B, and H. Station A is arranged exactly the same as stations A in Figs. 24 and 25, therefore, needs no description. Station B, being an intermediate station, is quite differently arranged from any of the preceding. From station A the air flows through the tube _f_ to station B, where it enters the automatic receiving and transferring apparatus, _s_. From this it flows through the tube _f_{´}_ to the sending apparatus _r_, and thence through the tube _f_{´´}_ to the next station, which may be another intermediate station, C, or the terminal station H. Station H is arranged like station B, Fig. 25. The air from the tube _f_{´´}_ enters the receiver _p_, and is then returned, through the pipe _l_, to the sending apparatus _n_. From the sending apparatus _n_ it continues on its return journey through the tube _g_ to the intermediate station B, where it enters the receiver and transfer apparatus _t_, then passes to the sending apparatus _q_, and through the tube _g_{´´}_ back to the receiver _b_ at station A. Thus we have followed the air-current out through one tube and back through the other. The current is kept circulating by the compressor located at station A. The pressure is at a maximum in the tank _d_, and falls gradually as the air flows along the tube until it returns to the tank _e_, when the pressure has fallen to atmospheric. A carrier is despatched from station A, and after passing through the tube _f_ arrives at station B, where it stops momentarily in the automatic receiver and transfer apparatus _s_. If the carrier is intended for station B, and was properly adjusted when it was despatched at A, it will be discharged from the apparatus _s_ on to the table _u_. But if it were intended for some other station and were so adjusted, after the delay of two or three seconds in the apparatus _s_, it will be automatically transferred to the tube _f_{´},_ pass through the sending apparatus _r_, and go on its journey through tube _f_{´´}_ to the next station. If it is not discharged from the tube at any of the intermediate stations, it will finally arrive at the terminal station H and there stop. Just how the carriers are adjusted and the details of the receiving and transfer apparatus will be described hereafter. Carriers arrive at station B from H, or other stations on the line, through tube _g_, in the apparatus _t_, which either discharges them on to the table _u_ or sends them on through the tube _g_{´}_ and _g_{´´}_ to station A. Carriers are despatched from station B to station A by means of the sending apparatus _q_, and from station B to other stations along the line, C, D, E, F, G, and H, by means of the sending apparatus _r_.