Vll 



since been reestablished by Wolf, who, after prolonged attention to the 

 subject, proved the spot-period to be a little over 11 years. In 1837 the 

 Trigonometrical and Topographical Survey of Norway was commenced, 

 and Hansteen was placed at the head. 



In 1856, when he had completed his 50th year as a teacher of Science, 

 his jubilee was celebrated, and a medal struck in commemoration of it. 



In the year 1861 he retired from active work. His great work was 

 translated into German soon after its publication ; and he also made 

 various contributions in that language to Schweigger's ' Journal,' to Pog- 

 gendorfPs ' Annalen,' and to the ' Astronomischen Nachrichten.' 



He published some valuable contributions to Meteorology and Astro- 

 nomy. 



He was a member of the American Academy of Arts and Sciences, 

 of the Academies of Paris, Berlin, and St. Petersburg, and a foreign mem- 

 ber of the Eoyal Society. 



His death took place on the 11th of April, 1873. 



Charles Eugene Delaunay was born at Lusigny, in the Department of 

 the Aube, in the year 1816. He studied at the Ecole Polytechnique, of 

 which school he became a distinguished pupil. In the year 1836 he 

 joined the Ecole des Mines. "While there he wrote several reports on 

 the Coal-seams of the Valley of St. Etienne and Creusot, as well as on 

 the principal iron and steel works of France, which were remarkable 

 for clearness of thought and skill in theoretical speculations ; and he 

 was still a pupil in the School when a proposal was made by his 

 former masters at the Ecole Polytechnique that he should be appointed 

 as Teacher of Geodesy in their school. There were difficulties in the 

 way of this ; but the anxiety to obtain the benefit of the talents of young 

 Delaunay was so great that the- Council of the school, at the head of which 

 was M. Cordier, gave their sanction to the arrangement, and Delaunay 

 was appointed. He subsequently became a Professor in the Ecole Poly- 

 technique, and later on also in the Ecole des Mines. Erom the year 

 1845 to 1850, Delaunay held a Professorship in that section of the Ecole 

 des Mines which was specially devoted to the instruction of Engineers, 

 whether attached to the Corps des Mines or those connected with the 

 mining industry of Erance. He had classes for descriptive Geometry, 

 Stereotomy, Machine drawing, Analytical Mechanics, and Elementary 

 Physics, and his teaching is said to have been most successful. In 1850 

 Delaunay attached himself exclusively to the Ecole des Mines. He was 

 appointed to successive grades in the Corps des Mines, and became 

 Engineer in Chief in 1858. In 1867 he was raised to the first class of 

 his rank. 



His first memoir, " Sur la Distinction des Maxima et des Minima 

 dans les questions qui dependent de la Methode des Variations," was 

 published in 1841. Other important works followed it, on the Theory of 



