the exhausting machines is equal to six absolute atmospheres. He described the valve: Throughout the entire length of the tube, a section is made in the top, leaving an open space of about five inches. In each cut edge of the section there is an offset, to catch the edges of a valve which fits down upon it. The valve is made of a piece of sole leather half an inch thick, having plates of iron attached to it on both the upper and corresponding under side to give it strength ... which are perhaps one-fourth of an inch in thickness ... The plates are about nine inches long, and their ends, above and below, are placed three quarters of an inch apart, forming joints, so as to give the leather valve pliability, and at the same time firmness. Clayton records the name of the engineer, Mallet, who had been Inspector general of Public Works, and gives a slightly different account: Clayton says that Mallet used a plaited rope to seal the slot. He also says that vacuum was created by condensing steam in a vacuum chamber between runs, but that may have been a misunderstanding of the pressure accumulators. London and Croydon Railway A steam railway at first The London and Croydon Railway (L&CR) obtained its authorising Act of Parliament in 1835, to build its line from a junction with the London and Greenwich Railway (L&GR) to Croydon. At that time the L&GR line was under construction, and Parliament resisted the building of two railway termini in the same quarter of London, so that the L&CR would have to share the L&GR's London Bridge station. The line was built for ordinary locomotive operation. A third company, the London and Brighton Railway (L&BR) was promoted and it too had to share the route into London by running over the L&CR. When the lines opened in 1839, it was found that congestion arose due to the frequent stopping services on the local Croydon line; this was particularly a problem on the 1 in 100 ascent from New Cross to Dartmouth Arms. The L&CR engineer, William Cubitt proposed a solution to the problem: a third track would be laid on the east side of the existing double track main line, and all the local trains in both directions would use it. The faster Brighton trains would be freed of the delay following