Astronomer and mathematician, born in Salem, Massachusetts, USA. Self-taught after age 10, he worked in a ship's chandlery, and by 15 had compiled an astronomical almanac. He went to sea (1795--1803), serving as master on his last voyage. He began by correcting errors in the writings of others, especially John Hamilton Moore's Practical Navigator; his contributions were so extensive that by 1802 the book became the New American Practical Navigator and was credited to him; it has remained to this day the "seaman's bible'. He chose to pursue research on his own, while working as an insurance actuary. His publications include a translation of four volumes of Laplace's Mécanique céleste, which appeared with his commentary and updating as Celestial Mechanics, (1829--39). He was also president of the American Academy of Arts and Sciences (1829--38).