ENCKE, JOHANN FRANZ (1791-1865.) A Ger man astronomer, born in Ilambnrg. where his father was a clergyman. After studying at G6t tingen, tinder Gauss, he took part in the cam paign of 1813-14, and in 1815 SCrved in the Prus sian Army as lieutenant of artillery. On the establishment of peace, he left, the service and became assistant and afterwards principal as tronomer in the Observatory of Seeberg, near Gotha. In 1825, chiefly at the instance of Bessel, he was called to Berlin to become secretary of the Academy of Sciences and director of the observatory. While at Gotha, the astronomical prize offered by C'otta was awarded to Eneke by the judges. Gauss and (fibers. for his de termination of the orbit of the comet of 1680. This led him to investigate another problem—viz. the determination of the distance of the sun from the earth. Encke's results, based upon the two transits of Venus, in 1761 and 1769, were pub lished in two separate tracts. entitled Die Entfer
ung der Bonne (1822-24). His best-known work, however, is his discussion of the orbit of the comet discovered by Pons, November 20, 1819, which has a short period of about 1200 days, and which has since gone by the name of Encke's comet and has appeared regularly. (See COMET.) Encke's researches on this subject are contained in the transactions of the Berlin Academy. He endeavored to explain a remarkably regular change in the comets period of revolution as the result of some resisting substance in the space traversed by the comet. 'There is, however, much doubt among astronomers as to the correctness of this hypothesis. In 1830 he undertook to edit the Berlin Astronomiselies Jahrbuch, in which he published a number of astronomical papers. He issued four volumes of Astronomische Brolatch tungen oaf der Sterntearte zit Berlin (1840-56).