Canadian-American astronomer James Craig Watson is credited with discovering twenty-two asteroids in his lifetime. While watching the 1874 transit of Venus in China, he discovered the asteroid 139 Juewa, which is an extremely large, main-belt asteroid, and he discovered 121 Hermione in Ann Arbor, Michigan. He published many articles and wrote A Popular Treatise on Comets (1861) and Theoretical Astronomy (1868). He established the James Craig Watson Medal, which is awarded by the National Academy of Sciences for contributions in astronomy.