Complex sentence: From 1787 he and his father founded the company Arnold & Son, which, after his father's death in 1799, John Roger continued the business taking into partnership John Dent between 1830 and 1840.
Split into simpler sentences: From 1787 he and his father founded the company Arnold & Son. After his father's death in 1799, John Roger continued the business, taking into partnership John Dent between 1830 and 1840.