Pittsburgh stands at the point where the Allegheny and Monongahela rivers come together to become the Ohio River. It is the second most populous city in Pennsylvania, after Philadelphia, and the metropolis of the western part of the state. George Washington visited the Pittsburgh area in 1753 on an expedition dispatched by the governor of Virginia. He reported that the site was well suited for a fort. The French thought so as well, and built Fort Duquesne there in 1754. Towards the end of their conflict with the British, the French abandoned and burned the fort in the face of an advance by General John Forbes. The British then built their own fort, which they called Fort Pitt in honor of their prime minister. The first community of settlers was established in 1764 and took the name Pittsburgh. A town was laid out in 1784. That year, Pittsburgh received a charter as a borough and became a city in 1816. Possession of Pittsburgh was disputed between Virginia and Pennsylvania, but the dispute was resolved in Pennsylvania's favor by a joint commission in 1785. Discontent in Western Pennsylvania came to a boil in the Whiskey Rebellion of 1794. The uprising was supported throughout the area and the citizens of Pittsburgh were particularly active in it. In 1877, the first great American railroad strike took place. In Pittsburgh, the state militia refused to fire on strikers, so the governor ordered the National Guard fromPhiladelphia to restore order. Those soldiers were willing to fire on the crowd, which they did with a loss of more than 20 lives, including women and children. A strike in 1892 at the Carnegie plant at Homestead, a few miles outside Pittsburgh, resulted in battles between the company-employed Pinkerton detectives and strikers. Eventually, martial law was declared. Pennsylvania law has made it easy for municipalities to be formed and difficult to merge them. In general, a majority in favor from both municipalities has been required. In 1905, the legislature was persuaded to pass a law allowing a one-time exemption to this rule, in order to combine Pittsburgh with its northern neighbor Allegheny. Under that law, only a majority of the combined voters was required. The following year, voters in Pittsburgh and Allegheny voted on consolidation, with Pittsburgh favoring it and Allegheny opposing. However, Pittsburgh's numerical superiority meant that a majority was in favor. In 1907, the U.S. Supreme Court ruled that the law was valid and Allegheny was annexed on December 9 of that year. Allegheny now constitutes the north side of Pittsburgh. The many steel mills and other industrial concerns in Pittsburgh once produced so much smoke and soot that the city earned the title "Smoky City." Efforts to clean up the air began in 1941 and stringent regulations on air pollution, combined with a decline in the industries that produced it, has resulted in Pittsburgh now having air that is clean and healthful. The Allegheny Observatory is a University of Pittsburgh research facility. The Carnegie Science Center boasts an interactive planetarium and a World War II submarine. Fallingwater, Frank Lloyd Wright's masterpiece, offers tours to visitors. Hartwood Mansion, a 629-acre estate park, contains a 16th-century Tudor-style mansion with an original collection of English and American antiques, and a farm and stable complex. The Houdini Museum commemorates the great escape artist's life with memorabilia and a daily show. Pittsburgh's first teaching hospital was Allegheny General Hospital, still in service. Chatham College enjoys a $50-million-dollar endowment, one of the largest per student in the nation. Other higher-education institutions in Pittsburgh include Point Park College and the University of Pittsburgh.