English: Photograph shows Nancy Maria Donaldon Johnson (1794-1890). Johnson and her sister Mary Donaldson, were active in the American Missionary Association. Additionally, in 1862, both women volunteered to teach freed slaves at Port Royal, South Carolina as part of the Port Royal Experiment. In addition to teaching and missionary work Nancy was an inventor. She patented the first hand-crank mechanism for ice cream freezers in 1843. Her husband, Walter Rogers Johnson (1794-1852), was a scientist, serving as the first Secretary of the American Association for the Advancement of Science in 1848. The couple married in 1823 at Medfield, Massachusetts, eventually establishing residence in Washington, D.C. They adopted two children, Walter W. Johnson (1836-1879) and Mary Maria Stroud (1834-1921). The family is buried at Oak Hill Cemetery, Washington, D.C.