delegates returned to Philadelphia on learning of the British retreat and by July 7, 1778, acquired a quorum, and thus were able to re-convene Congress on Penn's College of Philadelphia campus (briefly establishing Penn as site of capital of the United States). Such status as capital of the United States is evidenced by letter sent on July 13, 1778, from Josiah Bartlett (a signatory to the Articles of Confederation and the Declaration of Independence) to John Langdon (who was Bartlett's fellow New Hampshire "Founding Father" as Langdon later became a signatory of the United States Constitution): 9th Street campus In 1802, the university moved to the unused Presidential Mansion at ninth and Market Streets, a building that both George Washington and John Adams had declined to occupy while Philadelphia was the temporary national capital. Among the classes given in 1807 at this building were those offered by Benjamin Rush, a professor of chemistry, medical theory, and clinical practice who was also a signer of the United States Declaration of Independence, member of the Continental Congress, and surgeon general of the Continental Army. Classes were held in the mansion until 1829 when it was demolished. Architect William Strickland designed twin buildings on the same site, College Hall and Medical Hall (both 1829–1830), which formed the core of the Ninth Street Campus until Penn's move to West Philadelphia in the 1870s. West Philadelphia campus After being located in downtown Philadelphia for more than a century, the campus was moved across the Schuylkill River to property purchased from the Blockley Almshouse in West Philadelphia in 1872, where it has since remained in an area now known as University City. Residential university In the 1750s, roughly 40 percent of Penn students needed lodging as they came from areas too far to commute including other colonies in the South or the West Indies. Before the completion of the construction of the first dormitory in 1765, out of town students were typically placed with "guardians" in the homes of faculty or in suitable boarding houses (such as the one run by widow Rachel Marks Graydon, mother of Penn College Class of 1775 (who did not graduate) alumnus Alexander Graydon). In 1765, the campus was expanded by the opening of the newly completed dormitory run by Ben Franklin's collaborator on the study of electricity using electrostatic machines and related technology and Penn Professor and "chief master" Ebenezer