Great Exhibition of 1851, the American locksmith Alfred Charles Hobbs was able to open the lock and, following some argument about the circumstances under which he had opened it, was awarded the prize. Hobbs' attempt required some 51 hours, spread over 16 days. The Challenge Lock is in the Science Museum in London. An examination of the lock shows that it has been rebuilt since Hobbs picked it. Originally it had 18 iron slides and 1 central spring; it now has 13 steel slides, each with its own spring. Bramah received a second patent for a lock design in 1798. Machine tools Partly due to the precision requirements of his locks, Bramah spent much time developing machine tools to assist manufacturing processes. He relied heavily on the expertise of Henry Maudslay whom he employed in his workshop from the age of 18. Between them they created a number of innovative machines that made the production of Bramah's locks more efficient, and were applicable to other fields of manufacture. Just before Bramah died, his workshops also employed Joseph Clement who among other things made several contributions in the field of lathe design. Hydraulic press Bramah's most important invention was the hydraulic press. The hydraulic press depends on Pascal's principle, that pressure change throughout a closed system is constant. The press had two cylinders and pistons of different cross-sectional areas. If a force was exerted on the smaller piston, this would be translated into a larger force on the larger piston. The difference in the two forces would be proportional to the difference in area of the two pistons. In effect the cylinders act in a similar way that a lever is used to increase the force exerted. Bramah was granted a patent for his hydraulic press in 1795. Bramah's hydraulic press had many industrial applications and still does today. At the time Bramah was bringing his concepts to fruition, the field of hydraulic engineering was an almost unknown science. Bramah and William Armstrong, 1st Baron Armstrong were the two pioneers in the field. The hydraulic press is still known as the Bramah Press after its inventor. Other inventions Bramah was a very prolific inventor, though not all of his inventions were as important as his hydraulic press. They included: a beer engine (1797), a planing machine (1802), a paper-making machine (1805), a machine for automatically printing bank notes with sequential serial