[East front of the U.S. Capitol, with airship (drawn?) above, Washington, D.C.]

The main types of airship are non-rigid, semi-rigid, and rigid. Non-rigid airships, often called "blimps", rely on internal pressure to maintain the shape of the airship. Semi-rigid airships maintain the envelope shape by internal pressure but have a supporting structure. Rigid airships have an outer structural framework which maintains the shape and carries all structural loads, while the lifting gas is contained in internal gas bags or cells. Rigid airships were first flown by Count Zeppelin and the vast majority of rigid airships built were manufactured by the firm he founded. As a result, all rigid airships are sometimes called zeppelins. In early dirigibles, the lifting gas used was hydrogen, due to its high lifting capacity and ready availability. Helium gas has almost the same lifting capacity and is not flammable, unlike hydrogen, but is rare and relatively expensive. Airships were most commonly used before the 1940s, but their use decreased over time as their capabilities were surpassed by those of aeroplanes.

United States Capitol Free Sock Photos. Public Domain, Royalty Free Images. The United States Capitol, often called the Capitol Building or Capitol Hill, is the home of the United States Congress, and the seat of the legislative branch of the U.S. federal government. President George Washington in 1791 selected the area that is now the District of Columbia from land ceded by Maryland. French engineer Pierre Charles L'Enfant who planned the new city of Washington located the Capitol at the elevated east end of the Mall, on the brow of what was then called Jenkins' Hill. The site was, in L'Enfant's words, "a pedestal waiting for a monument." President Washington laid the cornerstone of the U.S. Capitol in the building's southeast corner on September 18, 1793, with Masonic ceremonies. Construction was a time-consuming process: the sandstone used for the building had to be ferried on boats from the quarries at Aquia, Virginia and workers had to be induced to leave their homes to come to the relative wilderness of Capitol Hill. Some third-floor rooms were still unfinished when the Congress, the Supreme Court, the Library of Congress, and the courts of the District of Columbia occupied the U.S. Capitol in late 1800.