Pyrometer

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joys a feeling of relief and satisfaction when
watching the flames.

Pyrometer, an instrument for measuring
temperatures which go beyond the range of
the mercurial thermometer.

Pyrope, or Bohemian Garnet, is a dark,
blood-red stone found in rounded, corroded
grains in basic rocks of the serpentine and
peridotite groups and in the soils and sands
which result from their disintegration. It is
used in the manufacture of cheap jewelry un-
der such names as Bohemian ruby, garnet, etc.

Pyrosis, in medicine, the vomiting or eruc-
tation of a thin watery fluid, sometimes taste-
less, often bitter. It is preceded by pain or
discomfort about the stomach; but the pre-
cise cause is unknown. The terms pyrosis and
waterbrash are used as synonymous; but py-
rosis is used particularly for acid eructations.

Pyrosoma, the phosphorescent fire-flame,
a free-swimming, pelagic tunicate, remarkable
for its luminosity. It is a compound form and
is sac-shaped, the very numerous individuals
being embedded in the wall of the sac.

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Pyrotechnics.

Pyrotechnics, the art of making fireworks,
which are almost exclusively used for the pur-
poses of display, though to a small extent also
in warfare, life-saving at sea, and drain-test-

ing. The principle on which fireworks are
made is simple—by urging the combustion of
a material like charcoal and sulphur, by mix-
ing it with highly oxygenated compounds such
as nitrates or chlorates, so that the action be-
comes brilliant or noisy. The mixtures em-
ployed do not differ fundamentally from gun-
powder, though the proportions are varied to
alter the rapidity of combustion; the flame is
often colored by the addition of compounds
like those of strontium, barium, and copper,
which have well-marked lines in their flame
spectra, or is made to scintillate brilliantly by
the addition of filings of magnesium or iron.

Pyroxene. The pyroxenes are silicates with
the general formula Ca(Mg)SiOj, but may
contain also isomorphous admixtures of iron
oxide, alumina, chromium, oxide, etc. They
ran^e in color from white to dark green and
black.

Pyroxylic, or Wood Spirit, is the crude
spirit obtained by distilling the volatile prod-
uct of the dry distillation of wood, from which
the tar has been separated and the acetic acid
neutralized by lime. It is used as a solvent for
making varnishes, and also to mix with ordi-
nary alcohol to 'denature' it.

Pyroxylin, or Collodion Cotton, is a ni-
trated cellulose in which the nitration has not
been carried so far as in gun-cotton. It is used
for the preparation of collodion, celluloid, and
some kinds of smokeless powders.

Pyrrha, in Greek mythology, the wife of
Deucalion.

Pyrrhic Dance, the war-dance of the an*
cient Greeks, especially of the Lacedaemonians.

Pyrrho, the leader of the school of sceptical
philosophy in ancient Greece called Pyrrhon-
ism. He was a native of Elis, and a contem-
porary of Alexander the Great. .The Sceptic
philosophy admitted the reality of nothing but
sensations; as to the manner and cause of sen-
sation, it remained in a state of doubt or sus-
pense; and so, too, with regard to all judg-
ments of right or wrong, and noble or base,

Pyrrhus (318 to 272 B.C.), king of Epirus,
and one of the greatest generals of the ancient
world. He became master of a .large part of
Macedonian territory in return for aiding the
king Alexander.

Pyrrol, CJBUNB, a compound of 'ring*
structure, consisting of four CH groups con-
nected by an NH group, that occurs in coal
tar and bone oil, from the latter of which it
can be separated.

Pyms, a well-known genus of Rosaceae,
with about 40 species, from northern temper-
ate regions, including the pear, apple, and.