penal method based on the principle that solitary confinement fosters penitence and encourages reformation. The idea was advocated by the Philadelphia Society for Alleviating the Miseries of Public Prisons, whose most active members were Quakers. In 1829 the Eastern State Penitentiary, on Cherry Hill in Philadelphia, applied this so-called separate philosophy. Prisoners were kept in solitary confinement in cells 16 feet high, nearly 12 feet long, and 7.5 feet wide (4.9 by 3.7 by 2.3 m). An exercise yard, completely enclosed to prevent contact among prisoners, was attached to each cell. Prisoners saw no one except institution officers and an occasional visitor. Solitary penitence, however, was soon modified to include the performance of work such as shoemaking or weaving. The Pennsylvania system spread until it predominated in European prisons. Critics in the United States argued that it was too costly and had deleterious effects on the minds of the prisoners. The Pennsylvania system was superseded in the United States by the Auburn system.