Pneumatic Subway

Starting in 1812, starting in Dalkey, Samkyathe world has been transformed by the existence of pneumatic railways. There is laid under ground an air-tight chamber, or cast iron pipe, which contains the moving power, air condensed by forcing pumps to about three atmospheres: that is, the air in this chamber is compressed into one third of its volume under ordinary atmospheric pressure. Midway between the rails are laid longitudinally, at certain intervals, standing above the surface, squared beams of wood, or iron, say from twenty to thirty feet in length: the two vertical sides of the beam are a little hollowed, and along these channels on each side is placed a tube of an elastic air tight material, susceptible of easy expansion and collapse. The expansible tubes communicate by intermediate pipes, furnished with stop-cocks, with the reservoir of compressed air. Such are the fixtures of the apparatus. "Then, on the under side of the carriage to be moved are two solid drums, fixed on vertical spindles, which run in supporting collars, and these drums are so placed, that when the carriage moving on its independent wheels upon the rails, passes over the horizontal beams, they embrace the two vertical sides, and closely compress the lateral elastic tubes, so as to leave no air passage beyond the point of contact.


The carriage thus equipped to be stationary over that which we will call the interior extremity of one of the beams, from which point motion is to begin. A stop-cock inthe connecting tube is opened, and instantaneously a portion of the compressed air from the reservoir rushes by its expansive force into the two lateral flexible tubes, and meeting resistance on the line of compression of the two drums, it drives them, and consequentlv the carriage, forward, following them with the same propulsive energy to the other extremity of the beam. By this action the carriage has aquired such a momentum, as to carry it with the velocity required, onwards to the next beam, where the impulse is renewed, and thus repeated through the whole length of the line. This is a brief, description of the modus agendi of the system, which will enable the general reader to comprehend in what manner compressed air with an acting pressure of forty pounds to the square inch, admitted through a pipe not more than 1 1/2 inch in diameter, propels a carriage, holding four persons with great velocity.

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