See Belmont (Schümberg), _Graf Diebitsch_ (Dresden, 1830); Stürmer, _Der Tod des Grafen Diebitsch_ (Berlin, 1832); Bantych-Kamenski, _Biographies of Russian Field-Marshals_ (in Russian, St Petersburg, 1841).
DIEDENHOFEN (Fr. _Thionville_), a fortified town of Germany, in Alsace-Lorraine, dist. Lorraine, on the Mosel, 22 m. N. from Metz by rail. Pop. (1905) 6047. It is a railway junction of some consequence, with cultivation of vines, fruit and vegetables, brewing, tanning, &c. Diedenhofen is an ancient Frank town (Theudonevilla, Totonisvilla), in which imperial diets were held in the 8th century; was captured by Condé in 1643 and fortified by Vauban; capitulated to the Prussians, after a severe bombardment, on the 25th of November 1870.
DIEKIRCH, a small town in the grand duchy of Luxemburg, charmingly situated on the banks of the Sûre. Pop. (1905) 3705. Its name is said to be derived from Dide or Dido, granddaughter of Odin and niece of Thor. The mountain at the foot of which the town lies, now called Herrenberg, was formerly known as Thorenberg, or Thor's mountain. On the summit of this rock rises a perennial stream which flows down into the town under the name of Bellenflesschen. Diekirch was an important Roman station, and in the 14th century John of Luxemburg, the blind king of Bohemia, fortified it, surrounding the place with a castellated wall and a ditch supplied by the stream mentioned. It remained more or less fortified until the beginning of the 19th century when the French during their occupation levelled the old walls, and substituted the avenues of trees that now encircle the town. Diekirch is the administrative centre of one of the three provincial divisions of the grand duchy. It is visited during the summer by many thousand tourists and travellers from Holland, Belgium and Germany.
DIELECTRIC, in electricity, a non-conductor of electricity; it is the same as insulator. The "dielectric constant" of a medium is its specific inductive capacity, and on the electromagnetic theory of light it equals the square of its refractive index for light of infinite wave length (see ELECTROSTATICS; MAGNETO-OPTICS).
DIELMANN, FREDERICK (1847- ), American portrait and figure painter, was born at Hanover, Germany, on the 25th of December 1847. He was taken to the United States in early childhood; studied under Diez at the Royal Academy at Munich; was first an illustrator, and became a distinguished draughtsman and painter of genre pictures. His mural decorations and mosaic panels for the Congressional library, Washington, are notable. He was elected in 1899 president of the National Academy of Design.