Chimney Sweeps. [Studio portrait of two young chimney sweeps.]

Robert Dennis's stereographs collection includes more than 72,000 stereoscopic views organized primarily by geography. The collection bears the name of the native New Yorker who assembled it over a period of more than six decades, Robert N. Dennis (1900-1983).
Stereographs consist of two nearly identical photographs or photomechanical prints, paired to produce the illusion of a single three-dimensional image, usually when viewed through a stereoscope. Stereographs were produced from the 1850s to the 1940s, with the bulk between 1870 and 1920.