Pneumatic

3765

Pocahontas

position is governed by the auxiliary arc valve
which is thrown by the piston. The upper
end of the piston is rifled, and engages a coarse
screw or rifle bar on a ratchet to give the
piston and bit the small constant rotation nec-
essary to prevent the drill from sticking. The
long screw and handle underneath advances
the drill on its support as the rock is pene-
trated.

Air-driven Channeling Machines, now ex-
tensively used in quarrying, are engine-driven
carnages traveling back and forth on short
tracks, and carrying a cutter which makes a
deep groove or channel in the quarry floor—
a first step in separating the stone blocks from
the vein or ledge. Coal Punchers and Cutters
are also important. The former are essentially
percussion air drills mounted on low trucks or
wedged columns, and used to cut into the
coal vein preparatory to throwing down part
of the face. The cutters are usually low trucks
with a motor driving a bar, disc, or endless
chain, equipped with bits and mounted on an
outstanding arm. Electric motors are steadily
supplanting air engines for coal cutters. There
are a variety of rotary air drills, etc., embody-
ing some sort of a small rotary engine and tool
chuck. In most of these devices, however, the
motor has reciprocating pistons that impart
a rotary motion to the drilling spindle by the
usual crank.

Pneumatic Trough, a round, rectangular
or other suitable vessel used for the collection
of gases over a liquid—usuaHy water. It was
invented by Priestly, and for use is filled with
the liquid; the jars or cylinders destined to
hold the gas are filled and inverted in the li-
quid, and supported on a shelf or perforated
tray called a 'beehive/ through which the gas
is bubbled up into the jar, displacing the liquid.

Pneumogastric Nerve, the roth cranial
nerve which, from its wide distribution, is
often called the Vagus (or wanderer).

Pneumonia, an acute, febrile disease char-
acterized by inflammatory reactions in the
lungs or bronchi. It is generally described
as of three varieties: lobar or croupous pneu-
monia; lobular, catarrhal, or broncho-pneu-
monia ; chronic interstitial pneumonia. It oc-
curs at all ages, but is rare in the first year of
life* It frequently follows other acute infec-
tions and is often seen post-operatively. In
1941 the extensive use of sulphonomide drugs
helped to reduce the death rate from pneu-
monia from 33% to 10%. Since then the
death rate has dropped even lower.

Pneuraonoconiosis or Pneumonokonio-
sis, a disease of the lungs due to the inhala-

tion of dusts, especially those encountered
in the metallic industries, characterized b>
fibrosis of the lung tissue,

Pnom-Penh, capital of Cambodia, French
Indo-China, at the confluence of the Mekong
with an arm of the Tale (or Tonle) Sap;
130 m. n.w. of Saigon. It exports rice, pep-
per, fish, cotton, tobacco, cardamoms, gam-
boge, sugar cane, indigo, maize, silk, betel
tortoise shells, and skins. Since 1894 Pnom-
Penh has been transformed into a place of
European appearance; p.83,000.

Po (ancient Endanus and Padus], the larg-
gest river of Italy, rises in the Cottian Alps,
at the northern foot of Monte Viso» at an
altitude of 6400 ft., close to the French fron-
tier. The Po discharges principally by the
branch known as the Po della Maestra. The
total length is 355 m., while its basin covers
some 29,000 sq. m. The Po is navigable from
above Turin. From Piacenza to the sea it is
protected by embankments on both sides.
It has always been difficult to cross, owing
to its width and the great volume of its
waters.

Poa, or Meadow Grass, a large genus of
grasses widely distributed in temperate and
cold countries, having six colored spikelets
arranged in open panicles. The June Grass
or Kentucky Blue Grass (P. pratensis) found
in fields and meadows throughout the United
States and in British Columbia is one of the
best-known species.

Poaching-, though originally a popular ra-
ther than a legal term, has come to be gen-
erally used to denote the offense of entering
on the lands of another in pursuit of game
without permission from the proprietor, deer
stealing, and also of fishing under like cir-
cumstances in waters belonging to another.
See GAME LAWS.

Pobiedonostzeff, Constantine (1827-
1907), procurator of the Holy Synod of
Russia, was born in Moscow. He was strong-
ly opposed to liberal reforms, and especially
to religious tolerance, and thereby stirred up
bitter hostility, which culminated in an at-
tempt on his life in July, 1905. His chief
work is Reflections of a Russian Statesman
(1898).

Pocahontas, (c. 1595-1617), daughter of
an Indian chief, Powhattan, famous espe-
cially for her reported rescue of Captaic
John Smith from death at the hands of the
Indians. Pocahontas was brought a prisoner
to Jamestown by Captain Argall in 1613,
was converted to Christianity, and in 1614
married an Englishman. John Rolfe, with