n 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.

DIEMEN, ANTHONY VAN (1593-1645), Dutch admiral and governor-general of
the East Indian settlements, was born at Kuilenburg in 1593. He was
educated in commerce, and on entering the service of the East India
Company speedily attained high rank. In 1631 he led a Dutch fleet from
the Indies to Holland, and in 1636 he was raised to the
governor-generalship. He came into conflict with the Portuguese, and
took their possessions in Ceylon and Malacca from them. He greatly
extended the commercial relationships of the Dutch, opening up trade
with Tong-king, China and Japan. As an administrator also he showed
ability, and the foundation of a Latin school and several churches in
Batavia is to be ascribed to him. Exploring expeditions were sent to
Australia under his auspices in 1636 and 1642, and Abel Tasman named
after him (Van Diemen's Land) the island now called Tasmania. Va