The United States Senate is the upper chamber of the United States Congress, which, along with the United States House of Representatives—the lower chamber—comprises the legislature of the United States. The Senate chamber is located in the north wing of the Capitol Building, in Washington, D.C. The composition and powers of the Senate are established by Article One of the United States Constitution. The Senate is composed of senators, each of whom represents a single state in its entirety. Each state, regardless of its population size, is equally represented by two senators who serve staggered terms of six years. There being at present 50 states in the Union, there are currently 100 senators. From 1789 to 1913, senators were appointed by legislatures of the states they represented; they are now elected by popular vote, following the ratification of the Seventeenth Amendment in 1913. As the upper chamber of Congress, the Senate has several powers of advice and consent which are unique to it. These include the approval of treaties, and the confirmation of Cabinet secretaries, Supreme Court justices, federal judges, flag officers, regulatory officials, ambassadors, other federal executive officials and other federal uniformed officers. In addition to these, in cases wherein no candidate receives a majority of electors for vice president, the duty falls to the Senate to elect one of the top two recipients of electors for that office. Furthermore, the Senate has the responsibility of conducting the trials of those impeached by the House. The Senate is widely considered both a more deliberative and more prestigious body than the House of Representatives due to its longer terms, smaller size, and statewide constituencies, which historically led to a more collegial and less partisan atmosphere. The presiding officer of the Senate is the vice president of the United States, who is president of the Senate. In the vice president's absence, the president pro tempore, who is customarily the senior member of the party holding a majority of seats, presides over the Senate. In the early 20th century, the practice of majority and minority parties electing their floor leaders began, although they are not constitutional officers.