THE PNEUMATIC DESPATCH. 
465 
perfectly open despatch-tube. This waste of steam-power is 
prevented by a trigger at m, which shuts off the steam and 
closes the open valves. Our carriage has now before it, at 
this end of the despatch-tube, a similar cushion of air to that 
which resisted its progress at the other end. As the effect of 
the exhaust upon it ceased at the open grating G, it has only 
its own momentum against the increasing resistance of the 
more and more compressed “ buffer ” of air in the extremity 
of the tube (G V), and as its speed becomes nearly entirely 
slackened, it passes the trigger x } the valve Y opens, and it 
quietly finishes its journey on the open rails. 
It will certainly occur to those who are acquainted with the 
resistive properties of air, that the effects of these terminal 
cushions of air will be directly proportional to the weight of 
the train received by them ; and that while a cushion of one 
extent would bring up a single carriage, it would not arrest 
a light train, and be still less efficacious against a heavy one. 
This, too, is very simply provided for. Everything about the 
Pneumatic Despatch is supremely simple. A length of air- 
cushion is taken, sufficient to stop the heaviest train. A 
special atmospheric pressure-gauge is connected with this 
portion of the tube containing it, as is also a cylinder and piston 
(P). Take the near end F, for example. While the exhaust 
is going on, the piston (p) is drawn towards the tube (t), and 
the valve it works closed. As soon, however, as the pellet- 
carriage has passed the grating, and the compression of air 
in the residual length of the despatch-tube commences, the 
increased pressure of air will lift higher and higher the piston- 
valve, and find escape. The engineer, therefore, screws down 
this piston-valve to a certain pressure of his pressure-gauge, 
and until this pressure is exceeded by the compression of the 
cushion or buffer of air, no escape will take place ; but as 
soon as the compression of air does exceed the amount of 
air-pressure thus fixed by the judgment and experience of the 
engineer as necessary to properly stop his train, the surplus 
air above that blows freely off* through the piston-valve. The 
skill attained by the engineer at the Euston Pneumatic station 
is very remarkable ; and he not only knows accurately what 
pressure is wanted for a train of one, two, three, or more car- 
riages, but he can judge exactly the differences between even 
individual carriages. Such niceties would never be necessary 
in working the pneumatic system on a grand scale. The time 
will come, we sincerely believe, when the projectors of this 
pneumatic method will be almost as highly regarded as 
those of our locomotives ; and while we properly acknowledge 
their higher merits of design, we may well spare a line to 
record the deserved praise of the humbler individual who has 
