Potentilla

3807

Potter

supposed to be placed at the point. Once the
function is known, we obtain the force in any
direction at the point of calculating the rate
of change of the potential in that direction.
Thus we arrive at the conception of what are
called equipotcntial surfaces, which are at
every point perpendicular to the force at the
point. The general mathematical conception
of a potential function h that I1.13 a function
whose rates of change alone any three chosen
perpendicular directions give the components
in those directions of an important directed
quantity, such as a force in attractions or a
velocity in fluid motion.

Potentilla, a genus of mostly perennial
herb? and shrubs belonging to the order Ros-
accae. They usually bear corymbose cymes of
white or yellow flowers with a ten-cleft calyx

' Virginia and Virginia on the s. and w., and
empties into Chesapeake Bay. The scenery
of the upper Potomac is picturesque, but is
marred by the yellow color of the water. It
is about 400 m. long and its chief tributaries
are the Shenandoah, the largest, the Cacapon,
the Monocacy, and Bull Run.

Potosi, town, Bolivia, on the flank of Cerro
de Potosi (15,724 ft.); 50 m. s.w. of Sucre.
The leading industry is mining but the once
famous silver mines have greatly decreased in
output, though still profitable.

Potsdam, city, Prussia, capital of Bran-
denburg province; 16 m. s.w. of Berlin. It is
beautifully situated on an island in the Havel
River which here expand? into a series of
lakes. It is chiefly celebrated for the royal
palace erected and adorned by Frederick the

Potsdam, Germany: Orangerie at Sans Souci.

in two rows, five petals, and numerous stam-
ens. Among the species are the common P.
canadensis, the cinquefoil, a trailing, early-
flowered plant.

Potenza, town, Italy, capital of Potenza
orovince; 93 m. n.w. of Taranto. It has a
cathedral and a small museum. In 1857 nearly
the entire town was destroyed by an earth-
quake; p. 23,738.

Pot-holes, circular depressions in the chan-
nel of rivers where they flow rapidly over
bare rock. They may be a few inches or several
feet across, and at the bottom there are usu-
ally a few pebbles.

Potidaea, ancient Greek city, founded by
a colony from Corinth about 600 B.C., on the
isthmus of Pallene, s. of Macedonia. At the end
of the 4th century B.C. Cassander built a new
city on the site, called Cassandria, which be-
came the most prosperous city in Macedonia.

Potomac River, an important river in the
United States which forms the boundary be-
tween Maryland on the n. and e. and West

Great; the Babelsberg palace in English Goth-
ic style, erected in 1843-9, where Emperor
William i. spent his summers; p. 65,795.

Potsdam Beds, The, comprise the Upper
Cambrian rocks of North America, and in-
clude the Olenus fauna. They are developed
about Lake Champlain, in the Adirondacks,
and in the St. Lawrence valley.

Potsdam Conference. See U. S. United
Nations Conferences.

Pottawatamies, a tribe of North Ameri-
can Indians, a western branch of the Algon-
quian stock, who formerly ranged round the
southern shore of Lake Michigan.

Potter, Edward Clark (1857-1923), Amer-
ican sculptor, was born in New London, Conn.
He collaborated with D. C, French in sculpture
for the Chicago Exposition, and executed stat-
ues of General Grant, Washington, Hooker,
De Soto and others. Other works include
groups at the'Buffalo Exposition and in the
Morgan Library, New York City.

Potter, CoraUrquhart (1859-1936), Am-