greater part of tlie time he remained in it was stationed in the fortress of 

 Thorn. He quitted the Prussian service in March 18 IG, and in the follow- 

 ing July became assistant to von Lindenau in the Observatory of Seeberg. 



He was appointed Vice-Director of the Observatory in 1820, and Director 

 on the retirement of von Lindenau in July 1822. His works on the 

 transits of Venus of 1761 and 17G9 were pubhshed in 1822 and 1824 

 respectively. A supplement to the latter, rendered necessary by the dis- 

 covery made by von Littrow, that Hell had tampered with the original ob- 

 servations made by himself at "Wardhus, appeared in the Transactions of 

 the Berlin Academy for 1835. In 1819 he published his identification of 

 the comets observed by Mechain and Messier on the. 1 7th of January, 1 786, 

 by Miss Herschel on the 17th November, 1795, by Pons on the 20th of 

 October, 1805, and again by Pons on the 26th of November, 1818. This 

 comet, to which Encke's name has been given, having a periodic time of 

 about 1207 days, was observed on the 3rd of June, 1822, at Paramatta by 

 Eiimker. The discussion of all the observations led Encke to the conclu- 

 sion that the only way of reconciling them was by the supposition of a 

 resisting medium by which the times of its revolutions are successively 

 lessened. One of the Royal Medals of the Society for the year 1 828 was 

 awarded to him for this investigation. He had already (in 1825) been 

 elected a Foreign Member. 



In 1825 he was called to Berlin as Professor of Astronomy in the Uni- 

 versity and Director of the Observatory. In his hands the Berlin Ephemeris 

 received many improvements, of which he gave an account in the Trans- 

 actions of the Berlin Academy for 1827. He superintended the publication 

 of this work from the volume for 1830 to that for 1852, when he was 

 assisted by Professor Wolfers till the publication of the volume for 1863, 

 after which the latter became sole editor. The volumes contain numerous 

 supplements by Encke on the perturbations of planets, the method of least 

 squares, mechanical quadratures, the solution of numerical equations, the 

 form and dimensions of the earth, and many papers on the correction of 

 the errors of astronomical instruments. 



The Observatory, a tower dating from 1711, being unsuitable for the 

 reception of fixed instruments, and in a bad situation, at von Humboldt's 

 suggestion a new Observatory was erected on a plan approved of by Encke ; 

 and on the 11th of October, 1835, he observed the position of Halley's 

 comet with the large equatoreal mounted in its place in the new Observatory. 

 The observations made here were published in four quarto volumes between 

 the years*! 840 and 1857. He is the author of upwards of one hundred 

 separate works and memoirs dating from 1812 to 1860. The latter are 

 contained chiefly in the ' Zeitschrift' of von Lindenau and Bohnenberger, 

 von Zach's ' Correspondance Astronomique,' Bode's and Encke's ' Jahr- 

 biicher,' the * Astronomische Nachrichten,' and the * Sitzungsberichte ' 

 and ' Abhandlungen ' of the Berlin Academy. 



In 1859 he suffered from an apoplectic attack, brought on, it is supposed. 



