open enough to pass; the elasticity of the tube would close it again behind the piston carriage. Joseph Shuttleworth; suggested a hydraulic tube; water pressure rather than a partial atmospheric vacuum, would propel the train. In mountainous areas where plentiful water was available, a pumping station would be unnecessary: the water would be used directly. Instead of the flap to seal the slot in the tube, a continuous shaped sealing rope, made of cloth impregnated with india-rubber would be within the pipe. Guides on the piston would lift it into position and the water pressure would hold it in place behind the train. Use of a positive pressure enabled a greater pressure differential than a vacuum system. However, the water in the pipe would have to be drained manually by staff along the pipe after every train. Samuda's treatise In 1841, Joseph Samuda published A Treatise on the Adaptation of Atmospheric Pressure to the Purposes of Locomotion on Railways. It ran to 50 pages, and Samuda described his system; first the traction pipe: The moving power is communicated to the train through a continuous pipe or main, laid between the rails, which is exhausted by air pumps worked by stationary steam engines, fixed on the road side, the distance between them varying from one to three miles, according to the nature and traffic of the road. A piston, which is introduced into this pipe, is attached to the leading carriage in each train, through a lateral opening, and is made to travel forward by means of the exhaustion created in front of it. The continuous pipe is fixed between the rails and bolted to the sleepers which carry them; the inside of the tube is unbored, but lined or coated with tallow 1/10th of an inch thick, to equalize the surface and prevent any unnecessary friction from the passage of the travelling piston through it. The operation of the closure valve was to be critical: Along the upper surface of the pipe is a continuous slit or groove about two inches wide. This groove is covered by a valve, extending the whole length of the railway, formed of a strip of leather riveted between iron plates, the top plates being wider than the groove and serving to prevent the external air forcing the leather into the pipe when the vacuum is formed within it; and the lower plates fitting into