Complex sentence: He served as professor of chemistry at William and Mary (1869-1878) and in 1871 helped reorganize a volunteer militia for the city of Williamsburg and James City County, Virginia, which he commanded.
Split into simpler sentences: He served as a professor of chemistry at William and Mary (1869-1878). In 1871 he helped reorganize a volunteer militia for the city of Williamsburg and James City County, Virginia, which he commanded.