374 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



ever, laid upon the ground, and the carriages passed over it, a longitudinal 

 or continuous valve openiiig at the top, along which a rod connecting the 

 piston with the carriages passed, tlie valve closing as the rod moved for- 

 ward. The area of" this tube was necessarily small, and the pressure 

 required to be exerted was proportionate. All the attempts to prevent the 

 Avaste of power by leakage were useless, and the attempt has been univer- 

 sally abandoned on account of the great expense of working such lines of 

 railway. 



In the case of the pneumatic railwaj^, the carriages themselves, and not 

 the small piston, travel througli the tiibe. The area upon \vhi(;h the atmos- 

 phere has to act is at least lifty times greater than tliat offered by tiie 

 smaller tube, and leakage or waste of power is {)ractically altogetiier 

 obviated. Tlie tunnel is large enough to admit the broad-gauge carriages 

 of the Great Western Railway. The carriage, which is like an elongated 

 omnibus, ha:s at one end a framework of the %iune form and nearly the same 

 dimensions as the sectional area of the tunned. On the outer edge of this 

 frame a fringe of bristles forming a thick brush is placed, and as the car- 

 riage passes on its way through the tunnel the brushes come nearly into 

 contact with the brickvv'ork and prevent, though of course not entirely, the 

 passage of the air. The carriage, with its collar of bristles, forms in fact 

 a loosely-fitting piston. 



The power which propels the piston carriage proceeds from a rotary 

 machine, or "ejector," concave in surface, and 22 feet in diameter. This 

 is made to I'evolve by a small steam engine at such velocity as may be 

 required, the pressure of air increasing, according, to the greater or less 

 A^elocity. Nothing can be more simple than this mode of accumulating 

 power. To the engineer, accustomed to the complicated movements of a 

 steam engine necessary to applj' mechanical power to any given object, it 

 appears almost ludicrously simple to see an enormous disc moving at high 

 velocity on its axis, and producing all the force that is necessary to carry 

 a heavy carriage, Avith some 30 or 40 passengers, up an incline more steep 

 than that upon any railway in the kingdom. The "ejector" revolves iu 

 an iron case something like that of a huge paddle wheel above the ground, 

 but there is no crank, or axle, or shaft to which it gives motion. 



When driving the air into the tunnel there rise fresh breezes to the sur- 

 face of the disc to supply the partial vacuum caused by the air sent below; 

 on the other hand, when exhausting the tunnel and when tlie escape valvea 

 are opened the air rushes out in a gale, or a hurricane, according to the 

 rate at which the disc is moving. When at full speed the gale of wind 

 makes the branches of the trees near the engine house sway to and fro 

 violently, and many an earnest searcher after scientific truth will see his 

 hat spinning round in the whirlwind, and feel some difficulty in standing 

 quietly upon his legs in the gale which suddenly springs up. A small 

 amount of force is sufficient to set the disc in motion, and, when once 

 moving, it rapidly accumulates power, so much so that its own unaided 

 revolutions are sufficient to bring the carriage through a large portion of 

 the tunnel. 



The power thus obtained is applied in a very simple manner. The down 

 train, the carriage from the higher to the lower station, is " blown " through 



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