the same patent. This meant that if any one improvement were found to have infringed a copyright, the whole patent would be invalidated. Despite the manoeuvrings of Boulton and Watt, the firm of Fenton, Murray and Wood became serious rivals to them, attracting many orders. Middleton Railway In 1812 the firm supplied John Blenkinsop, manager of Brandling's Middleton Colliery, near Leeds, with the first twin-cylinder steam locomotive (Salamanca). This was the first commercially successful steam locomotive. The double cylinder was Murray's invention, he paid Richard Trevithick a royalty for the use of his patented high pressure steam system, but improved upon it, using two cylinders rather than one to give a smoother drive. Because only a lightweight locomotive could work on cast iron rails without breaking them, the total load they were capable of hauling was very much limited. In 1811, John Blenkinsop patented a toothed wheel and rack rail system. The toothed wheel was driven by connecting rods, and meshed with a toothed rail at one side of the track. This was the first rack railway, and had a gauge of 4 ft 1½ ins. Once a system had been devised for making malleable iron rails, around 1819, the rack and pinion motion became unnecessary, apart from later use on mountain railways. However, until that time it enabled a small and lightweight locomotive to haul loads totalling at least 20 times its own weight. Salamanca was so successful that Murray made three more models. One of these was known as Lord Wellington, and the others are said to have been named Prince Regent and Marquis Wellington, though there is no known contemporary mention of those two names. The third locomotive intended for Middleton was sent, at Blenkinsop's request, to the Kenton and Coxlodge Colliery waggonway near Newcastle upon Tyne, where it appears to have been known as Willington. There it was seen by George Stephenson, who modelled his own locomotive Blücher on it, minus the rack drive, and therefore much less effective. After two of the locomotives exploded, killing their drivers, and the remaining two were increasingly unreliable after at least 20 years hard labour, the Middleton colliery eventually reverted to horse haulage in 1835. Rumour has it that one remaining locomotive was preserved for some years at the colliery, but was eventually scrapped. Marine engines In 1811 the firm made a Trevithick-pattern high-pressure steam engine for John Wright,