624 



PNEUMATIC DISPATCH. 



PNEUMATIC DISPATCH. This work is 

 between the terminus of the Northwestern 

 Railway and one of the District Post-Offices in 

 London. The great principle may be briefly 

 explained as follows : A small cast-iron tunnel 

 or tube, arched above, but nearly flat below, 

 about 2 feet 9 inches high, and having nearly 

 Fig. 1. 



Fig. 3, supported on a short horizontal axis, to 

 which a small high-pressure engine is directly 

 geared. This disk is enclosed in a rectangular, 

 round-topped casing or box, of boiler-plate, 

 22^ feet wide by 4 feet thick. Connected 

 with its lower portion at one side is a large 

 tube or continuation of the tunnel, while 

 another similar tube, leaving the tunnel at 

 a point more distant from its terminus (see 

 Fig. 2), forms a connection with the interior 

 of the hollow disk, by means of the air-trunk, 

 which is seen in Fig. 3 to surround the lower 

 Fig. 3. 



the same width at its broadest part, provided 

 with a pair of rails, runs from one station to 

 the other. On these rails run four-wheeled 

 wagons, of which Fig. 1 shows an end view 

 and half cross-section. The general outline of 

 the wagon conforms, as the drawing shows, to 

 the section of the tunnel, but there is an abso- 

 lute clearance all around, of more than an inch. 

 The tubes composing the tunnel are cast in 

 ordinary lengths, and are put together with 

 leaded joints, like the ordinary water or gas 

 mains. They are laid with gradients, varying 

 from 1 in 100 to 1 in 80, and with three curves, 

 two of 110 feet radius and one of 40 feet. This 

 last curve is very short, but works well, and 

 proves the admirable flexibility of the system. 

 The apparatus for giving motion to these car- 

 riages is situated entirely at one end of the 

 line, of which Fig. 2 is the ground plan with 

 the boiler, engine, and tunnel, and Fig. 3 shows 

 on larger scale a vertical section of this ap- 

 paratus, which is known as the Pneumatic 

 Ejector. This consists of a hollow circular disk 

 of sheet iron, shown edgewise in the middle of 

 Fte. 2. 



half of the rectangular casing. This air-trunk 

 may, however, by appropriate valves, be shut 

 off from the tunnel and opened to the outer air, 

 as also may the rectangular casing mentioned 

 before. 



The action of this instrument, in a general 

 way, may be easily described. The hollow 

 disk being rotated by the engine, draws in air 

 at its centre from the air-trunk, and expels it 

 into the rectangular case. If the former is con- 

 nected with the tunnel, and the latter with the 

 outer air, a partial vacuum is produced, and 

 cars are sucked through from the further sta- 

 tion. But when the casing is con- 

 nected with the tunnel, and the 

 air-trunk with the atmosphere, 

 air is forced into the tube, and 

 drives a carriage from the nearer 

 to the further station. The hol- 

 low disk already mentioned is 

 about 21 feet in diameter, formed 

 of two thin sheets of iron, which 

 are but two inches apart at the 

 outer edge, but separating as they 

 approach the axis, so as to form 

 such surfaces of revolution as 

 would be generated by curves, 



