Radiometer

red phosphorus; they make glass and tin*

3909

Raeburu

halides of pola'-Miim

sodium become

colored, etc. Tlie\ id>o al'feet photographic
plates in their neighborhood: and bihm about
luim'nesre'ire ot stilHaiu'et, Mich as barium
Nunide and vine blende. Added to

this, their present P has worked physiological
effects de.stro\in« tissues when the radia-
tions act ujioii them too long or too intensive-
ly. Fortunately, the radiations also destroy
disease cells of certain types, as well as nor-
mal tissue. Thi> is notably the ease in ma-
lignant tumors (see (\\NruO and in certain
superficial tumors as red lupus. Consult
Millikan's The Klcilrtw In) 17); Soddy's The
Intt'rprrltitnni of RittUitM (iu:o).

Radiography. Through this process, by
the use of portable million-vull X-ray equip-
ment, radiographs weie being made in fac-
tories daily in ni,j.>. These X ra\s detect

buried Haws through eight inches of steel.
More powerful equipment i.s being developed.

Radiometer, a device invented by Sir Wil-
liam Crookcs to exhibit the motion caused
by the action of light. The instrument con-
sists of a light hori/ontal vane, formed of
four metal discs, supported by cross arms at
right angU'S on an easily moving pivot in a
highly exhausted glass globe. The discs are
brightly polished, and blackened on alternate
sides, and when exposed to light rotate round
the vertical axis at a rate that depends on
the brightness of the light. This behavior is
probably dm to the gas left in the globe un-
der the heating effect of the rays, Thus the
black sides of the discs become hotter, so that
the gas molecules left in the bulb acquire a
greater velocity when they lly off after strik-
ing the black sides than the bright, This dif-
ference in velocity of the molecules causes a
corresponding difference in the reaction on
the vanes, so that rotation occurs.

Radiophotography. Sec Telephotog-
raphy.

Radiotelegraphy, and Radiotelephony.
Sec Radio; Wirclc**.

Radifth (Ra film nun sat fan*), a garden vege-
table belonging to the family Crudjcra1, cul-
tivated for the sake of its thickened edible
root, which is eaten raw. In order to attain
the host quality, the plant should be grown
quickly in a rich, light> loose soil

Radium, Ra (atomic weight, 526), a high-
ly radio-active dement discovered by M. and
Mme, Curie, in i8c)X, Although it is widely
distributed in very minute quantities, its prin
cipal source was originally the pitchblende of
Joachimsthal, in North Bohemia, which yields

about i part in 3 million. At the present
time, however, almost the whole of the
world's supply comes from the carnotite,
sands of Colorado and adjacent regions of
the United States, which contain about 2 per
cent, of uranium nitrate. Though radium is
always obtained in practice in the form of a
bromide or a chloride, the element itself was
successfully isolated in 1911, by Mme. Curio
? nd Debierne, who subjected the amalgam to
distillation in an atmosphere of pure hydro-
gen. After all the mercury has been expelled,
a brilliant white metal—practically pure ra-
dium—was obtained. Metallic radium alters
very rapidly in contact with air, decomposes
water energetically, and is considerably more
volatile than barium. Direct tests showed
that the increase of activity occurs in accord-
ance with the law of the production of em-
anation, the limit of radio-activity of the
metal being about normal. The primary uses
of radium are in producing self-luminous
paints for watch dials, etc., and in the treat-
ment of certain types of diseases, as cancel
and skin affections. In radium hospitals it is
the first disintegration product of radium,
namely, the so-called radium emanation,
which is brought into proximity to the dis-
eased part rather than the radium itself. A
machine for the artificial production of ra-
dium from such common substances as table
?alt and phosphorus has been developed. The
artificial radium differs from true radium in
its brief life time, which is 15 hours instead
of 1700 years. Doctors hope that, because of
its low price, it may be used more extensively
in medical practice. See RADIO-AcrrviTY,

Radius. See Circle.

Radius, in anatomy, the smaller of the two
bones of the forearm. It forms the smaller
part of the elbow joint and the greater part
of the wrist.

Radom, town, Poland, 60 m. s. of War-
saw. Js of much commercial importance;
manufactures leather products and machinery.
It suffered greatly in the Swedish war of
1701-7, and figured prominently in the
maneuvers of the Russian and German
armies during the World war; p, 65,000,

Raeburn, Sir Henry (1756-182.0, Scot-
tish portrait painter, sometimes called the
Scottish Reynolds, was born in Stockbridge,
near Edinburgh. He was elected president of
the Society of Scottish Artists and an asso-
ciate of the Royal Academy in 1813, and be*
came a Royal Academician in r8t«j. Among
his sitters were Sir Walter Scott and Christo-
pher North.