Christoph Arnold, a German astronomer, born at Sommerfeld, near Leipsic, Dec. 17, 1G50, died April 15, 1695. He was a farmer, but devoted his leisure to astronomy, erected an observatory at his own house, and was the first to call attention to the comets of 1682 and 1686. He also acquired fame by his observation of the passage of Mercury across the sun's disk, Oct. 31, 1690. The town of Leipsic gave him a present of money and exempted him from all city taxation.