Crookes's Radiometer. 
radiometer 
2. An instrument which serves to transform 
radiant energy into mechanical work, it con- 
sists of four crossed 
arms of very fine glass, 
supported in thecenter 
by a needle-point, and 
having at the extreme 
ends thin vertical disks 
or squares of pith, 
blackened on one side. 
When placed in a 
glass vessel nearly ex- 
hausted of air, and ex- 
posed to rays of light 
or heat, the blackened 
surfaces absorb the ra- 
diant energy and be- 
come heated, the mole- 
cules of the air remain- 
ing in the vessel strik- 
ing against them gain 
from them greater ve- 
locity, and there results 
an increased pressure, 
causing a more or less 
rapid revolution of the 
arms By varying the 
conditions as to degree 
of exhaustion, size of 
bulb, etc., a number 
of experiments are performed with the radiometer which 
serve to illustrate the mechanical effects of the rapidly 
moving molecules of a gas. 
radiometric (ra"di-o-met'rik), a. Pertaining to 
the radiometer, or to the experiments performed 
radiomicrometer (ra"di-o-mi-krom'e-ter), . 
[< L. radius, ray, + E. micrometer.'] An in- 
strument serving as a very delicate means of 
measuring small amounts of heat, it consists 
essentially of an antimony-bismuth thermo-electric cou- 
ple of very small dimensions, with the ends joined by a 
hoop of copper wire, and suspended by a slender thread in 
a powerful magnetic field. It is claimed for it that it can 
be made even more sensitive than Langley's bolometer. 
radioimiKCular (ra"di-6-mus'ku-lar), a. [< L. 
radius, radius, + musculus, muscle: see muscle 1 , 
muscular."] In anat., pertaining to the radius 
and to muscles: specifically noting muscular 
branches of the radial artery and of the radial 
nerve. Cones. 
radiophone (ra'di-o-fon), . [< L. radius, ray, 
+ Gr. <j>avf/, voice, sound: seephone 1 ."] An in- 
strument in which a sound is produced by the 
successive expansions and contractions of a 
body under the action of an intermittent beam 
of radiant heat thrown upon and absorbed by it. 
radipphonic (ra/di-o-fon'ik), a. [< radiophone 
+ -ifl.] Pertaining to radiophony, or the pro- 
duction of sound by the action of a beam of 
light and heat ; relating to the radiophone, or 
produced by it. 
radiophonics (ra/di-o-fon'iks),. [PI. otradio- 
phonic (see -ics)."] Same as radiophony. 
radiophony (ra'di-o-fo-ni), . [< L. radius, ray, 
+ Gr. <fiuvrt, voice, sound : seephone 1 .] The pro- 
duction of sound by the action of an intermit- 
tent beam of radiant heat ; that branch of acous- 
tics which considers sound so produced. For ex- 
ample, if the beam from a lime-light is thrown upon a 
rotating disk perforated with a series of holes, and, after 
thus being rendered intermittent, is made to fall upon a 
confined mass of a liquid or gas capable of absorbing 
radiant heat, a musical note is obtained from the latter 
whose pitch depends upon the rapidity of the rotation. 
Similar results are obtained with a plate of an appropriate 
solid, as hard rubber. Radiophony also includes the more 
complex case where an intermittent beam of light, falling 
upon a substance like selenium (also in a less degree sul- 
phur), serves to vary its electrical resistance, and hence the 
strength of current passing through it, so as to produce a 
corresponding sound in a telephone-receiver placed in the 
circuit. This is illustrated in the photophone. 
radio-ulnar (ra"di-6-ul'nar), . [< L. radius, 
radius, + ulna, ulna : see ulna, vlnar."] Of or be- 
longing to the radius and the ulna : as, the radio- 
ulnar articulation Radio-ulnar flbrocartilage. 
See fibrocartilage. 
radious (ra'di-us), a. [< ME. radinus, radyous, 
radius, < OF. "radios, F. radieux = Sp. Pg. It. ra- 
dioso, < L. radiosus, radiant, beaming, < radius, 
a ray: see radius."] If. Consisting of rays, as 
light. Berkeley. 2f. Radiating; radiant. 
His radious head with shameful thorns they tear. 
G. Fletcher, Christ's Triumph over Death, st. 35. 
3. In hot., same as radiant. [Rare.] 
radish (rad'ish), n. [Formerly also raddish 
(also dial, redisli, reddish, appar. simulating 
reddish, of a red color); early mod. E. radice, 
radyce ; < ME. radish = D. radijs = LG. rady.i 
= G. radics = Dan. radis = Sw. radisa, radix, 
radisa, < OF. radix, F. radix, a radish, < Pr. ra- 
ditz, a root, a radish, = OF. mi's, rmz (also ra- 
dice), a root, = It. radice, a root, radish, = AS. 
rtedie, redic, erroneously hrsedie, ME. radik = 
MLG. redik, redek, redich = OHG. rdtilt, rdtich, 
'"G. rsetic.li. riilich, rcticli, G. rcttirh, re/tit/ = 
4935 
Dan. raddikr = Sw. riittiktt, a radish, < L. radix 
(radic-), a root, in particular an edible root, esp. 
a radish: see radix.'] 1. A plant, Rafilianus 
sativus, cultivated forits edible root ; also other 
species of the same genus. (See phrases below. ) 
The radish of cultivation is unknown in a wild state, but 
is thought by many to be derived from the wild radish, A'. 
Jtaphanistrum. It has been highly prized from the days 
of ancient Egypt for its crisp ileshy root, which is little 
nutritious, but pleasantly pungent and antiscorbutic, and 
is mostly eaten raw as a relish or in salads. The radish 
commonly must be young and fresh, but some varieties 
are grown for winter use. The root varies greatly In size 
(but is ordinarily eaten when small), in form (being long 
and tapering, turnip-shaped, olive-shaped, etc.), and also 
in color (being white, scarlet, pink, reddish-purple, yel- 
lowish, or brown). The leaves were formerly boiled and 
eaten, and the green pods make a pickle somewhat re- 
sembling capers. 
2. A root of this plant. 
When a' was naked, he was, for all the world, like a 
forked radish, with a head fantastically carved upon it 
with a knife. Shalt., 2 Hen. IV., til. 2. 834. 
3. Same as water-radish __ Horse radish. See 
horse radish. Rat-tall radish, a species (Ilaphanux cau- 
datus) or perhaps a variety of the common radish, a cu- 
riosity from the East Indies, with narrow pods a foot or 
more long, which are boiled or pickled for the table. Sea- 
radish, or seaside radish, a variety of the wild radish, 
sometimes regarded as a species (Raphanwt maritimus) 
found on European coasts __ Wild radish, :i noxious field- 
weed, Raphanus Raphanistrum, resembling charlock, but 
haying necklace-formed pods, and hence sometimes called 
fainted charlock. It has rough lyrate leaves, and yellow- 
ish petals turning whitish or purplish. It is adventive in 
the eastern United States. 
radish-fly (rad'ish-fli), n. An American dip- 
terous insect, Anthomyia raphani, injurious to 
the radish. 
radius (ra'di-us), n.; pi. radii(-l). [< L. radius, 
a staff, rod, spoke of a wheel, a measuring-rod, 
a semidiameter of a circle (as it were a spoke 
of the wheel), a shuttle, spur of a bird, sting of 
a fish, the radius of the arm; by transfer, a 
beam of light, a ray. Cf. rayi (a doublet of 
radius) and the derived radiant, radiate, irra- 
diate, etc.] 1. In math., one of a number of 
lines proceeding from a center; 
a ray; especially, a line drawn 
from the center to the periphery 
of a circle or sphere; also, the 
measure of the semidiameter. 
2. In anat. and :ool., the outer 
one of the two bones of the fore- 
arm, or corresponding part of 
the fore leg; the bone on the thumb side of 
the forearm, extending from the humerus to 
the carpus, and bearing upon its distal end 
the manus or hand : so called from its re- 
volving, somewhat like a spoke, about the 
ulna, as in man and other mammals whose 
fore limb exhibits the motions called pronation 
and supination. In most animals, however, the radius 
is motionless, being fixed in a state of pronation, when it 
appears as the inner rather than the outer of the two 
bones, or as by far the larger bone, of the forearm, the 
ulna being often much reduced. In man the radius 
is as long as the ulna without the olecranon, and some- 
what stouter, especially in its distal parts. It presents a 
small, circular, cupped and button-like head, for articu- 
lation with the capitulum of the humerus and lesser 
sigmoid cavity of the ulna, following which is a constric- 
tion termed the neck, and next to this a tubercle for the 
insertion of the biceps muscle. The shaft enlarges from 
above downward, and is of somewhat prismatic form, with 
the sharpest edge of the prism presenting toward the 
ulna. The lower end has two large articular facets for 
articulation with the scaphoid and lunar bones (forming 
the radiocarpal articulation, or wrist-joint), a lateral facet 
for the radio-ulnar articulation, and a stout projection 
called the styloid process, for the insertion of the supinator 
longus muscle. The radius is pronated by the pronator 
radii teres and pronator quadratus, and supinated by the 
supinator longus and supinator brevis, assisted by the 
biceps. Quite a similar form and disposition of the radius 
characterize various mammals which use their fore paws 
like hands, as monkeys, mice, squirrels, opossums, etc. 
The radius of others, as the horse and ox, is more differ- 
ent, and associated with a much reduced and ankylosed 
ulna. In birds the radius is so peculiarly articulated with 
the humerus that it slides lengthwise back and forth upon 
the ulna in the opening and closing of the wing, prona- 
tion and supination being absent in this class of animals. 
See pronation and supination, and cuts under carpus, Ca- 
tarrhina, Eqwi.se, forearm, ox, pinion, Plesiosaurus, and 
solidunffulate. 
3. In ichth., a bone of the pectoral arch, wrong- 
ly identified by some naturalists with the ra- 
dius of higher vertebrates. The one so called 
by Cuvier is the hypercoracoid, and that of 
Owen is the hypocoracoid. 4. In en torn., a vein 
of the wing of some insects, extending from 
the pterostigma to the tip of the wing. 5. 
[<y<p.] In conch., a genus of Omtlidee. B. volra 
is the shuttle-shell or weaver-shell. 6. pi. In 
ornitn., the barbs of the main shaft of a feather ; 
the rays of the first order of the rachis. 7. In 
araclintiloii!/, one of the radiating lines of a geo- 
metrical spider's web, which are connected by 
radix 
a single spiral line. 8. In echinoderms, one 
of the five radial pieces of the dentary apparatus 
of a sea-urchin, being an arched rod-like piece 
articulated at its base with the inner extremity 
of each rotula, running more or less nearly par- 
allel with the rotiila, and ending in a free bi- 
furcated extremity. Also called the conijittsx 
of the lantern of Aristotle (which see, under /tin- 
tern). See also cut B under lantern. 9. pi. 
Specifically, in Cirripedia, the lateral parts of 
the shell, as distinguished from the paries, when 
they overlap: when overlapped by others, they 
are called alee. 10. In bot., a ray, as of a 
composite flower, etc. 11. The movable limb 
or arm of a sextant; also, a similar feature in 
any other instrument for measuring angles. 
12. In fort., a line drawn from the center of 
the polygon to the end of the outer side Au- 
ricular radii See auricular. Geometrical radius of 
a cog-wheel, the radius of the pitch-circle of the wheel, 
in contradistinction to its real radius, which is that of the 
circle formed by the crests of the teeth. Oblique line 
of the radius. See oblique. Pronator radii quadra- 
tus. See pronator quadratus, under pronatftr. Pronator 
radii teres. See pronator. Proportional radii, in a 
system of gears, or in a set of gears of the same pitch, 
radii proportioned in length to the number of teeth in 
the respective wheels. The proportional radii of any two 
geared wheels, when taken together, are equal to the line 
connecting the centers of the wheels, which line is the 
basis of computation in determining them. Also called 
primitive radii. Radii 
CA, CD, CB, CE, 
Radii of Circle. 
accessor!!, the barbs of 
the aftershaft or hypora- 
chis of a feather. Ra- 
dius astronomicus. 
Same as radiometer, 1. 
Radius of concavity. 
Same as radius of curva- 
ture. Radius of curva- 
ture, the radius of the 
circle of curvature that 
is, of the osculating circle 
at any point of a curve. 
In the cut, AHBC is the 
primitive curve (in this 
case an ellipse); KHJ, the 
circle of curvature, oscu- 
lating the primitive curve 
at H ; T, the center of cur- 
vature; TH, the radius of 
curvature; GFTED, the 
locus of centers of curva- 
ture, or the evolute. The 
radius of curvature wrap- 
ping itself upon the evo- 
luti 
II 
Radius of Curvature. 
ite gives the primitive 
curve. Radius of dissipation. See dissipation. Ra- 
dius of explosion. See mine?, 2 (6). Radius of gyra- 
tion, in mech., the distance from the axis to a point such 
that, if the whole mass of a body were concentrated into 
it, the moment of inertia would remain uncharged. If 
the axis is a principal axis, this radius becomes a prin- 
cipal radius of gyration. Radius of rupture. See 
min2, 2 (6). Radius of the evolute. Same as ra- 
dius of curvature. Radius of torsion, the element 
of the arc of a curve divided by the angle of torsion. 
Radius vector (pi. radii ixctores\ the length of the 
line joining a variable point to a fixed origin : in as- 
tronomy the origin is taken at the sun or other cen- 
tral body. See vector. Real radius. See geometrical 
radiwt. 
radius-bar (ra'di-us-bar), n. In a steam-engine, 
one of a pair of rods pivoted at one end and 
connected at the other with some concentri- 
cally moving part which it is necessary to keep 
at a definite distance from the pivot or center. 
Also called radius-rod and bridle-rod. See cuts 
under grasshopper-beam and paddlc-u-lieel. 
radius-saw (ra'di-us-sa), n. A circular saw 
journaled at the end of a swinging frame or 
radial shaft, used in cross-cutting timber. 
radix (ra'diks), .; pi. radices (ra-di'sez). [< 
L. radix (radic-), a root, = Gr. pdihf, a branch, 
rod. Hence ult. E. race* and radinh (doublets 
of radix), radical, radiccl, radicle, radicule, rad- 
icate, eradicate, arace 1 , etc.] 1. The root of 
a plant : used chiefly with reference to the roots 
of medicinal plants or preparations from them. 
Hence 2. The primary source or origin ; that 
from which anything springs, or in which it 
originates. [Rare.] 
Her wit Is all spirit, that spirit flre, that fire flies from 
her tongue, able to hurne the radix of the best invention ; 
in this element she is the abstract and briefe of all the 
eloquence since the incarnation of Tully. 
Heywood, Fair Maid of the Exchange (Works, 1874, II. 54). 
Judaism is the radix of Christianity Christianity the 
integration of Judaism. De Quincey r Essenes, iii. 
3. In e tym ., a primitive word or form from which 
spring other words; a radical ; a root. 4. In 
math., a root, (a) Any number which is arbitrarily 
made the fundamental number or base of any system of 
numbers, to be raised to different powers. Thus, 10 is the 
radix of the decimal system of numeration (Briggg's). In 
the common system of logarithms, the radix is also 10 ; in 
the Napierian it is 2.7182818284 ; every other number is 
considered as some power of the radix, the exponent of 
which power constitutes the logarithm of that number. 
(&) The root of a finite expression from which a series is 
derived. 
