size of the tube and bear skin was used to seal the annular space. To slow the vehicle down, doors were opened at each end of the vehicle. Vallance's system worked, but was not adopted commercially. Pinkus In 1835, Henry Pinkus patented a system with a square section tube with a low degree of vacuum, limiting leakage loss. He later changed to a small-bore vacuum tube. He proposed to seal the slot that enabled the piston to connect with the vehicle with a continuous rope; rollers on the vehicle lifted the rope in front of the piston connection and returned it afterwards. He built a demonstration line alongside the Kensington Canal, and issued a prospectus for his National Pneumatic Railway Association. He was unable to interest investors, and his system failed when the rope stretched. However, his concept, a small bore pipe with a resealable slot was the prototype for many successor systems. Samuda and Clegg Developing a practical scheme Jacob and Joseph Samuda were shipbuilders and engineers, and owned the Southwark Ironworks; they were both members of the Institution of Civil Engineers. Samuel Clegg was a gas engineer and they worked in collaboration on their atmospheric system. About 1835, they read Medhurst's writings, and developed a small bore vacuum pipe system. Clegg worked on a longitudinal flap valve, for sealing the slot in the pipe. In 1838, they took out a patent "for a new improvement in valves" and built a full-scale model at Southwark. In 1840, Jacob Samuda and Clegg leased half a mile of railway line on the West London Railway at Wormholt Scrubs (later renamed Wormwood Scrubs), where the railway had not yet been opened to the public. In that year Clegg left for Portugal, where he was pursuing his career in the gas industry. Samuda's system involved a continuous (jointed) cast iron pipe laid between the rails of a railway track; the pipe had a slot in the top. The leading vehicle in a train was a piston carriage, which carried a piston inserted in the tube. It was held by a bracket system that passed through the slot, and the actual piston was on a pole ahead of the point at which the bracket left the slot. The slot was sealed from the atmosphere by a continuous leather flap that was opened immediately in advance of the piston bracket and closed again immediately behind