Original: He discovered or co-discovered several comets, including 23P/Brorsen-Metcalf and 97P/Metcalf-Brewington; he also discovered a number of asteroids.
Simplified: He found or co-found many comets, such as 23P/Brorsen-Metcalf and 97P/Metcalf-Brewington; he also found many asteroids.