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disposed on five successive zones of four on alternating meridians, the zones corresponding to equator, tropics and circumpolar circles

1 on the globe; pores of central capsule in scattered groups. Fam. 1. ACTINELIDA. Spines numerous,

more than
twenty, irregularly grouped. Litholophus,

Haeck.; Xiphacantha, Haeck.
Fam. 2. ACANTHONIDA. Spines twenty, simple, usually

equal. Acanthometro, J. Müll. (fig. iv. 6, 7);
Astrolonche, Haeck.;' Amphilonche, Haeck.

(fig. I. 18).
Fam. 3. SPHAEROPHRACTIDA: Spines equal, branching

and often coalescing into a latticed shell,

homaxonic. Fam. 4. PRUNOPHRACȚIDA: Branching spines coalescing

into a latticed shell which is elongated and

elliptical in at least one plane.
C. Nassellaria, Haeck. (Monopylaea, Hertw.). Silico-skeletal
Radiolaria in which the central capsule is typically monaxonic (cone.
shaped), with a single perforate area (pore-plate) placed on the basal
face of the cone; the membrane of the capsule, the nucleus single;
the skeleton is extracapsular, and forms a scaffold-like or beehive.
like structure of monaxonic form, a tripod or calthrop, a sagittal
ring, or a combination of these.
Fam. 1. NASSOIDEA, Haeck. Skeleton absent. Cyslidium,

Haeck.
Fam. 2. PLECTIDA, Haeck. Skeleton formed of a single

branching spicule, a tripod or usually a 4.
radiate calthrop, its branches sometimes
reticulate. Genera: Plagiocantho, Haeck.;

Plegmatium, Haeck.
Fam. 3. SPYROIDEA. Shell latticed around the sagittal

ring ("cephalis "), sometimes with a lower

chamber added.
Fam. 4. BOT RIDEA, Haeck. Shell latticed, composed of

14
several chambers agglomerated without definite
order;

a single central capsule. Genera:
Botryocyrtis, Haeck.; Lithobotrys, Haeck.

12 Fam. 5. CYRTOIDEA, Haeck. Skeleton a monaxonic or

triradiate shell, or continuous piece (beehive.
shaped) Genera: Halicalyptra, Haeck.;
Eucyrlidium, Haeck. (fig. 11.); Carpocanium,

Haeck. (fig. IV. 3).
Fam. 6. STEPHOIDEA, Haeck. Skeleton a sagittal ring

continuous with the branched spicule, and
sometimes growing out into other rings or
branches. Genera: Acanthodesmia, Haeck.;

16
Zygostephanus, Haeck.; Lithocircus, Haeck.

(fig. iv. 1). D. Phaeodaria, Haeck. (Tripylaea, Hertw.). Radiolaria of cruciate symmetry, prolonged into tubular processes with three oscula to the central capsule, one inferior, the principal, and two symmetrically placed on either side of the opposite pole; skeleton 17 of spicules, a network of hollow filaments, or a minutely alveolate

c? shell, of a combination of silica with organic substance; extracapsular protoplasm containing in front of the large oscule an agglomeration of dusky purplish or greenish pigment (“phaeodium "). Fam. 1. PHAEOCYSTIDA, Haeck. Siliceous skeleton absent

or of separate needles. Genera: Aulacantha,

Haeck.;' Thalassoplancto, Haeck.
Fam. 2. PHAEOSPHAERIDA. Spicules united into

latticed shell. Genera: Aulosphaera, Haeck.
(fig. iv. 9); Auloplegma, Haeck. ; Canna-

18
cantha, Haeck.
Fam. 3. PHAEOGROMIDA, Haeck. Shell continuous,

traversed by fine canals or finely alveolate. Fig. III.-Radiolaria. 1. Central capsule of Thalassicolls provided with at least one pylome. Genera:

nucleata, Huxley, in radial section. a, the large nucleus (BinnenChallengeria, Wyv., Thomson; Lilhogromia,

bläschen); b. corpuscular structures of the intracapsular protoHaeck.

plasm containing concretions; &, wall of the capsule (membranous Fam. 4. PHAEOCONCHIDA. Shell as in Phaeosphaerida,

shell), showing the fine radial pore-canals; d, nucleolar fibres but of two symmetrical halves (valves), which

(chromatin substance) of the nucleus. 2, 3. Collozoum meet in the plane of the three oscules (" frontal inerme, J. Müller, two different forms of colonies, of the natural of Haeckel, who terms the plane of symmetry

size. 4. Central capsule from a colony of Collozoum inerme, through the shells " sagittal"). Genera: Conchidium,

showing the intracapsular protoplasm and nucleus, broken up Haeck.; Coelodendrum, Haeck.

into a number of spores, the germs of swarm-spores or flagellulae; (fig. Iv. 4).

each encloses a crystalline rod. c, yellow cells lying in the extra. The following passages may be repeated here from Sir E. Ray capsular protoplasm. 5. A small colony of Collosoum inerme, Lankester's article “ Protozoa" in the 9th edition of this

magnified 25 diameters. a, alveoli (vacuoles) of the extra. Encyclopaedia:

capsular protoplasm; b. central capsules, each containing besides

protoplasm a large oil-globule. 6-13. Yellow cells of various " The important differences in the structure of the central capsule Radiolaria: 6, normal yellow cell; 7. 8. division with formation of different Radiolaria were first shown by Hertwig, who also dis- of transverse septum:

9. a modified condition according to covered that the spines of the Acanthometridea consist not of Brandt;. 10, division of a yellow cell into four;. 11, amoeboid silica but of an organic compound (but see above). In view of condition of a yellow cell from the body of a dead Sphaerozoon; this latter fact and of the peculiar numerical and architectural 12, a similar cell in process of division; 13. a yellow cell the features of the Acanthometrid skeleton, it seems proper to separate protoplasm of which is creeping out of its cellulose envelope. them altogether from the other Radiolaria. The Peripylaea may 14. Heliosphaera inermis, Haeck., living example; e, nucleus; be regarded as the starting-point of the Radiolarian pedigree, and b, central capsule; ¢, siliceous basket-work skeleton. have given rise on the one hand to the Acanthometridea, which Two swarm-spores (flagellulae) of Collozoum inerme, set free

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15.

from such a central capsule as that drawn in 4; each contains of the protoplasmic body. Q. the tri-lobed nucleus; 6, the a crystal b and a nucleus a. 16. Two swarm-spores of Collo- siliceous shell; 6, oil-globules; d, the perforate area (pore-plate) zoum inerme, of the second kind, viz. devoid of crystals, and of of the central capsule. 4. Coelodendrum gracillimum, Haeck. ; two sizes, a macrospore and a microspore. They have been set living animal, complete; one of the Tripylaea. Q, the character free from central capsules with contents of a different appearance istic dark pigment (phacodium) surrounding the central capsule b. from that drawn in 4.

Q, nucleus. 17. Actinomma astera. The peculiar branched siliceous skeleton, consisting of hollow canthion, Haeck.; one of the Peripylaea. Entire animal in fibres, and the expanded pseudopodia are seen. 5. Central optical section. a, nucleus; 6, wall of the central capsule: capsule of one of the Tripylaea, isolated, showing a, the nucleus; c, innermost siliceous shell enclosed in the nucleus; c, middle b, c, the inner and the outer laminae of the capsule wall; d, the shell lying within the central capsule; c', outer shell lying in the chief or polar aperture; e, e, the two secondary apertures. extracapsular protoplasm. Four radial siliceous spines holding 6, 7. Acanthometra claparedei, Haeck. 7 shows the animal in the three spherical shells together are seen. The radial fibrilla- optical section, so as to exhibit the characteristic meeting of the tion of the protoplasm and the fine extracapsular pseudopodia are spines at the central point as in all Acanthométridea; 6 shows the to be noted.

18. Amphilonche messanensis; Haeck.; one of the transition from the uninuclear to the multinuclear condition by Acanthometridea. Entire animal as seen living.

the breaking up of the large nucleus. 2, small nuclei; 6, large

fragments of the single nucleus; s, wall of the central capsule; 2

ted, extracapsular jelly (not protoplasm); e, peculiar intracapsular

yellow cells. 8. Spongosphaera Streptocantha, Haeck.; one of the Peripylaea. Siliceous skeleton not quite completely drawe. on the right side. e, the spherical extracapsular shell (compare fig. n. 17), supporting very large radial spines which are connected by a spongy network of siliceous fibres.

9. Aulo. sphaera elegantissima, Haeck.; one of the Phaeodaria. "Half of

the spherical siliceous skeleton. retain the archaic structure of the central capsule whilst developing a peculiar skeleton, and on the other hand to the Monopylaea and Phacodaria, which have modified the capsule but retained the siliceous skeleton.

Phacodaria. Monopylaca. Acanthometridca.

[graphic]

Peripylaca.

Silico-skeleta.

Acanthino-skeleta.

Archi-peripylaea.

RADIOLARIA. "The occasional total absence of any siliceous or acanthinous skeleton does not appear to be a matter of classificatory importance, since skeletal elements occur in close allies of those very few forms which are totally devoid of skeleton. Similarly it does not appear to be a matter of great significance that some forms (Polycyttaria) form colonies, instead of the central capsules separating from one another after fission has occurred.

"It is important to note that the skeleton of silex or acanthin does not correspond to the shell of other Sarcodina, which appears rather to be represented by the membranous central capsule. The skeleton does, however, appear to correspond to the spicules of Heliozoa, and there is an undeniable affinity between such a form as Clathrulina and the Sphaerid Peripylaca (such as Heliosphaera, fig. III. 14). The Radiolaria are, however, a very strongly marked group, definitely separated from all other Sarcodina by the membranous central capsule sunk in their protoplasm. Their differences inter se do not affect their essential structure. The varia. tions in the chemical composition of the skeleton and in the perforațion of the capsule do not appear superficially. The most obvious features in which they differ from one another relate to the form and complexity of the skeleton, a part of the organism so little character. istic of the group that it may be wanting altogether. It is not

known how far the form-species and form-genera which have been 8

distinguished in such profusion by Haeckel as the result of a study of the skeletons are permanent (i.e. relatively, permanent), physio. logical species. There is no doubt that very many are local and conditional varieties, or even merely stages of growth, of a single Protean species. The same remark applies to the species discriminated among the shell-bearing Reticularia. It must not be supposed, however, that less importance is to be attached to the distinguishing and recording of such forms because we are not able to assert that they are permanent species.

The streaming of the granules of the protoplasm has been observed in the pseudopodia of Radiolaria as in those of Heliozoa and Reticularia; it has also been seen in the deeper protoplasm; and granules have been definitely seen to pass through the pores of the central capsule from the intracapsular to the extracapsular protoplasm. A feeble vibrating movement of the pseudopodia has been occasionally noticed.

* The production of swarm-spores has been observed only in FIG. IV.- Radiolaria. 1. Lithocircus annularis, Hertwig; one Acanthometra and the Polycyttaria and Thalass llidae, and

of the Monopylaea. Whole animal in the living state (optical only in the two latter groups have any detailed observations been section); a, nucleus; b, wall of the central capsule; c, yellow made. Two distinct processes of swarm-spore production have cells; d, perforated area of the central capsule (Monopylaea). been observed by Cienkowski, confirmed by Hertwig,-dis2. Cystidium inerme, Hertwig; one of the Monopylaea. Living tinguished by the character of the resulting spores, which are animal. An example of a Monopylaeon destitute of skeleton. called 'crystalligerous' and isospores' (fig. 111. 15) in the one 6, nucleus; 6, capsule-wall; c, yellow cells in the extracapsular case, and dimorphous' or 'anisospores' in the other (fig. 1. protoplasm. 3: Carpocanium diadema, Haeck.;, optical 16). In both processes the nucleated protoplasm within the central section of the beehive-shaped shell to show the form and position 1 capsule breaks up by a more or less regular cell-division into small

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pieces, the details of the process differing a little in the two cases. I hand, if the effects arose from balanced stresses set up inside In those individuals which produce crystalligerous swarm-spores,

the globe by the radiation, the effects on the vanes and on the each spore encloses a small crystal (fig. 111. 15). On the other hand, in those individuals which produce dimorphous swarm-spores, the

case would be of the nature of action and reaction, so that the contents of the capsule (which in both instances are set free by its establishment of motion of the vanes in one direction would natural rupture) are seen to consist of individuals of two sizes, involve impulsion of the case in the opposite direction; but megaspores

and
microspores,' neither of which contain

when the motion became steady there would no longer be any crystals (fig. III. 16). The further development of the spores has not been observed in either case. Both processes have been observed torque either on the vanes or on the case, and the latter would in the same species, and it is suggested that there is an alternation therefore come back to its previous position of equilibrium; of sexual and a sexual generations, the crystalligerous spores develop; finally, when the light was turned off, the decay of the motion ing directly into adults, which in their turn produce in their central capsules dimorphous swarm-spores (megaspores and microspores), of their motion until the moment of the restoring torque arising

of the vanes would involve impulsion of the case in the direction which in a manner analogous to that observed in the Volvocinean Flagellata copulate (permanently fuse) with one another (the larger from the suspension of the case had absorbed the angular with the smaller) before proceeding to develop. The adults resulting momentum in the system. Experiment showed that the latter from this process would, it is suggested, produce in their turn prediction was what happened. The important part played crystalligerous swarm-spores. Unfortunately we have no observa- by the residual air in the globe had also been deduced by tions to support this hypothetical scheme of a life-history.

" Fusion or conjugation of adult Radiolaria, whether preliminary Osborne Reynolds from observing that on turning off the to swarm-spore-production or independently of it, has not been light, the vanes came to rest very much sooner than the friction observed this affording a distinction between them and Heliozoa.

of the pivot alone would account for; in fact, the rapid sub" Simple fission of the central capsule of adult individuals, preceded of course by nuclear fission, and subsequently of the whole sidence is an illustration of Maxwell's great theoretical disprotoplasmic mass, has been observed in several genera of Acan-covery that viscosity in a gas (as also diffusion both of heat tharia and Phacodaria, and is probably a general method of repro, and of the gas itself) is sensibly independent of the density. duction in the group. Polycyttarian ' °forms when the extracapsular protoplasin does had led Sir G. G. Stokes and Sir W. Crookes to the same general

In Spumellaria it gives rise to colonial Some phenomena of retardation in the production of the effect not divide.

"The siliceous shells of the Radiolaria are found abundantly in conclusion. certain rocks from Palaeozoic times onwards. They furnish, The origin of these phenomena was recognized, among together with Diatoms and Sponge spicules, the silica which has the first by O. Reynolds, and by P. G. Tait and J. Dewar, as a been segregated as flint in the Chalk formation. They are present in quantity (as much as 10%) in the Atlantic ooze, and in the consequence of the kinetic theory of the constitution of gaseous celebrated Barbados carth • °(a Tertiary deposit) are the chief media. The temperature of a gas is measured by the mean components."

energy of translation of its molecules, which are independent BIBLIOGRAPHY.—The most important systematic works are

of each other except during the brief intervals of collision; those of E. Haeckel, Die Radiolarien (1862-87), and the “ Report on the Radiolaria of the." Challenger " Expedition (vol. xviii., 1887), and collision of the separate molecules with the blackened which contains full lists of the older literature. Among the most

surface of a vane, warmed by the radiation, imparts heat to important recent studies we cite K. Brandt, “ Die Koloniebildenden | them, so that they rebound from it with greater velocity than Radiolarien" in Fauna and Flora des Golfes von Neapel, xii. (1885); they approached. This increase of velocity implies an increase A. Borgert in Zeitschrift f: Wissenschaftliche Zoologie, li. (1891), and Zoologische Jahrbücher (Anatomie), xiii. (1900); F. Dreyer in

of the reaction on the surface, the black side of a vane being Jendischer Zeitschr., xix. (1892); V. Häcker in Zeitsch. S. Wiss.

thus pressed with greater force than the bright side. Ia air Zool., Ixxxiii. (1905).

(M. Ha.)

of considerable density the mean free path of a molecule,

between its collisions with other molecules, is exceedingly RADIOMETER. It had been remarked at various times, small, and any such increase of gaseous pressure in front of the amongst others by Fresnel, that bodies delicately suspended black surface would be immediately neutralized by flow of the within a partial vacuum are subject to apparent repulsion by gas from places of high to places of low pressure. But at high radiation. The question was definitely investigated by Sir W. exhaustions the free path becomes comparable with the dimenCrookes, who had found that some delicate weighings in cacuo sions of the glass bulb, and this equalization proceeds slowly. were vitiated by this cause. It appeared that a sursace black. The general nature of the phenomena is thus easily understood; ened so as to absorb the radiant energy directed on it was but it is at a maximum at pressures comparable with a millirepelled relatively to a polished surface. He constructed an metre of mercury, at which the free path is still small, the apparatus in illustration, which he called a radiomeler or light-greater number of molecules operating in intensifying the mill, by pivoting a vertical axle carrying equidistant vertical result. The problem of the stresses in rarefied gaseous media vanes inside an exhausted glass bulb, one side of each vane arising from inequalities of temperature, which is thereby being blackened and the other side bright, the blackened sides opened out, involves some of the most delicate considerations all pointing the same way round the axle. When the rays in molecular physics. It remains practically as it was left of the sun or a candle, or dark radiation from a warm body, in 1879 by two memoirs communicated to the Phil. Trans. are incident on the vanes, the dark side of each vane is repelled by Osborne Reynolds and by Clerk Maxwell. The method of more than the bright side, and thus the vanes are set into the latter investigator was purely a priori. He assumed that rotation with accelerated speed, which becomes uniform when the distribution of molecules and of their velocities, at each the forces produced by the radiation are balanced by the point, was slightly modified, from the exponential law belonging friction of the pivot and of the residual air in the globe. The to a uniform condition, by the gradient of temperature in the name radiometer arose from an idea that the final steady speed gas (see DIFFUSION). The hypothesis that the state was steady, of rotation might be utilized as a rough measure of the intensity so that interchanges arising from convection and collisions of of the exciting radiation.

the molecules produced no aggregate result, enabled him to The problem of the cause of these striking and novel pheno- interpret the new constants involved in this law of distribution, mena at first produced considerable perplexity. A preliminary in terms of the temperature and its spacial differential coquestion was whether the mechanical impulsion was a direct efficients, and thence to express the components of the kinetic effect of the light, or whether the radiation only set up internal stress at each point in the medium in terms of these quantities. stresses, acting in and through the residual air, between the As far as the order to which he carried the approximationsvanes and the walls of the enclosure. The answer to this was which, however, were based on a simplifying hypotbesis that sound experimentally by Arthur Schuster, who suspended the molecules influenced each other through mutual repulsions the whole instrument in delicate equilibrium, and observed inversely as the fifth power of their distance apart-the result the effect of introducing the radiation. If the light exerted was that the equations of motion of the gas, considered as direct impulsion on the vanes, their motion would gradually subject to viscous and thermal stresses, could be satisfied by drag the case round after them, by reason of the friction of a state of equilibrium under a modified internal pressure equal the residual air in the bulb and of the piunto On the other l in all directions. If, therefore, the walls of the enclosure held the gas that is directly in contact with them, this equilibrium two principal forms, the spindle-rooted and the turnipwould be the actual state of affairs; and it would follow rooted. from the principle of Archimedes that, when extraneous forces The radish succeeds in any well-worked not too heavy garden such as gravity are not considered, the gas would exert no soil, but requires a warm, sheltered situation. The seed is resultant force on any body immersed in it. On this ground generally sown broadcast, in beds 4 to 5 ft. wide, with alleys Maxwell inferred that the forces acting in the radiometer are between, the beds requiring to be netted over to protect them connected with gliding of the gas along the unequally heated from birds. The earliest crop may be sown about the middle boundaries; and as the laws of this slipping, as well as the of December, the seed-beds being åt once covered with litter, constitution of the adjacent layer, are uncertain, the problem which should not be removed till the plants come up, and then becomes very intricate. Such slipping had shown itself at only in the daytime, and when there is no frost. If the crop high exhaustions in the experiments of A. A. Kundt and E. G. succeeds, which depends on the state of the weather, it will be Warburg in 1875 on the viscosity of gases; its effects would be in use about the beginning of March. Another sowing may be corrected for, in general, by a slight effective addition to the made in January, a third early in February, if the season is a thickness of the gaseous layer.

favourable one, and still another towards the end of February, Reynolds, in his investigation, introducing no new form from which time till October a small sowing should be made of law of distribution of velocitics, uses a linear quantity, every fortnight or three weeks in spring, and rather more proportional to the mean free path of the gaseous molecules, frequently during summer. About the end of October, and which he takes to represent (somewhat roughly) the average again in November, a late sowing may be made on a south border distance from which molecules directly affect, by their con- or bank, the plants being protected in severe weather with litter vection, the state of the medium; the gas not being uniform or mats. The winter radishes, which grow to a large size, should on account of the gradient of temperature, the change going be sown in the beginning of July and in August, in drills from on at each point is calculated from the elements contributed 6 to 9 in. apart, the plants being thinned out to 5 or 6 in. in by the parts at this particular distance in all directions. He the row. The roots become fit for use during the autumn. For lays stress on the dimensional relations of the problem, pointing winter use they should be taken up before severe frost sets in, out that the phenomena which occur with large vanes in highly and stored in dry sand. Radishes, like other fleshy roots, are rarefied

gas could also occur with proportionally smaller vanes attacked by insects, the most dangerous being the larvae of in gas at higher pressure. The results coincide with Maxwell's several species of fly, especially the radish fly (Anthomyia so far as above stated, though the numerical coefficients do not radicum). The most effectual means of destroying these is by agree. According to Maxwell, priority in showing the necessity watering the plants with a dilute solution of carbolic acid, or for slipping over the boundary rests with Reynolds, who also much diluted gas-water; or gas-lime may be sprinkled along discovered the cognate fact of thermal transpiration, meaning the rows. thereby that gas travels up the gradient of temperature in a Forcing.–To obtain early radishes a sowing in the British Isles capillary tube, owing to surface-actions, until it establishes such should be made about the beginning of November, and continued a gradient of pressure (extremely minute) as will prevent further fortnightly till the middle or end of February; the crop will generflow. In later memoirs Reynolds followed up this subject by be sown in light rich soil, 8 or 9 in. thick, on a moderate hotbed,

ally be fit for use about six weeks after sowing. The seed should proceeding to establish definitions of the velocity and the

or in a pit with a temperature of from 55° to 65°, Gentle waterings momentum and the energy at an element of volume of the must be given, and air admitted at every favourable opportunity: molecular medium, with the precision necessary in order that

but the sashes must be protected at night and in srosty weather

with straw mats or other materials. Some of these crops are often the dynamical equations of the medium in bulk, based in the

grown with forced potatoes. The best forcing sorts are Wood's usual manner on these quantities alone, without directly con-arly frame, and the early rose globe, early dwari-top scarlet turnip, sidering thermal stresses, shall be strictly valid-a discussion and early dwarf-top white turnip. in which the relation of ordinary molar mechanics to the more

Those best suited for general cultivation are the following: complete molecular theory is involved.

Spindle-rooted.-Long scarlet, including the sub-varieties scarlet Of late years the peculiarities of the radiometer at higher short-top: carly frame scarlet, and Wood's early frame; long scarlet gas-pressures have been very completely studied by E. F. Turnip-rooted.-Early rose globe-shaped, the earliest of all; Nichols and G. F. Hull, with the result that there is a certain early dwarf-top scarlet turnip, and early dwarf-top white turnip; pressure at which the molecular effect of the gas on a pair of early sorts; French 'breakfast,“ olive-shaped; red turnip and

earliest Erfurt_scarlet, and early, white short-leaved, both very nearly vertical vanes is balanced by that of convection currents in white turnip, for summer crops. it. By thus controlling and partially eliminating the aggregate Winter sorls.- Black Spanish, white Chinese, Californian gas-effect, they succeeded in making a small radiometer, hori. mammoth. zontally suspended, into a delicate and reliable measurer of RADIUM (from Lat. radius, ray), a metallic chemical element the intensity of the radiation incident on it. With the ex- obtained from pitchblende, a uranium mineral, by P. and Mme, perience thus gained in manipulating the vacuum, the achieve- Curie and G. Bémont in 1898; it was so named on account of ment of thoroughly verifying the pressure of radiation on both the intensity of the radioactive emanations which it yielded. opaque and transparent bodies, in accordance with Clerk Its discovery was a sequel to H. Becquerel's observation in 1896 Maxwell's formula, has been effected (Physical Review, 1901, that certain uranium preparations emitted a radiation resemand later papers) by E. F. Nichols and G. F. Hull; some months bling the X rays observed by Röntgen in 1895. Like the X earlier Lebédew had published in the Annalen der Physik a rays, the Becquerel rays are invisible; they both traverse thin verification for metallic vanes so thin as to avoid the gas- sheets of glass or metal, and cannot be refracted; moreover, action, by preventing the production of sensible difference of they both ionize gases, i.e. they discharge a charged electroscope, temperature between the two faces by the incident radiation. the latter, however, much more feebly than the former. Char(See RADIATION.)

acteristic, also, is their action on a photographic plate, and the More recently J. H. Poynting has separated the two effects phosphorescence which they occasion when they impinge on experimentally on the principle that the radiometer pressure zinc sulphide and some other salts. Notwithstanding these acts along the normal, while the radiation pressure acts along resemblances, these two sets of rays are not indentical. Mme. the ray which may be directed obliquely.

(J. L.*) Curie, regarding radioactivity i.e. the emission of rays like RADISH, Raphanus sativus (nat, order Cruciferae), in botany, those just mentioned-as a property of some undiscovered a fleshy-rooted annual, unknown in the wild state. Some substance, submitted pitchblende to a most careful analysis. varieties of the wild radish, R. Raphanistrum, however, met After removing the uranium, it was found that the bismuth with on the Mediterranean coasts, come so near to it as separated with a very active substance-polonium; this element to suggest that it may possibly be a cultivated race of the was afterwards isolated by Marckwald, and proved to be idensame species. It is very popular as a raw salad. There are l tical with his radiotellurium; that the barium could be separated with another active substance-radium; whilst a third " radiant,” “radiation," and allied words. In mathematics, a fraction, composed mainly of the rare earths (thorium, &c.), radius is a straight line drawn from the centre to the circum. yielded to Debierne another radioactive element-actinium, ference of a circle or to the surface of a sphere; in anatomy which proved to be identical with the emanium of Giesel. the name is applied to the outer one of the two bones of the Another radioactive substance-ionium-was isolated from car- fore-arm in man or to the corresponding bone in the fore-leg of notite, a uranium mineral, by B. B. Boltwood in 1905. Radio- animals. It is also used in various other anatomical senses in active properties have also been ascribed to other elements, e.g. botany, ichthyology, entomology, &c. A further application of thorium and lead. There is more radium than any other radio- the term is to an area the extent of which is marked by the active element, but its excessive rarity may be gauged by the length of the radius from the point which is taken as the centre; facts that Mme. Curie obtained only a fraction of a gramme of thus, in London, for the purpose of reckoning the fare of hackneythe chloride and Giesel -2 to •3 gramme of the bromide from a carriages, the radius is taken as extending four miles in any ton of uranium residues.

direction from Charing Cross. There is a mass of evidence to show that radium is to be RADNOR, EARLS OF. The ist earl of Radnor was John regarded as an element, and in general its properties resemble Robartes (1606-1685), who succeeded his father, Richard those of the metals of the alkaline earths, more particularly Robartes, as 2nd baron Robartes of Truro in May 1634, the barium. To the bunsen flame a radium salt imparts an intense barony having been purchased under compulsion for £10,000 in carmine-red colour (barium gives a green). The spectrum, 1625. The family had amassed great wealth by trading in tin also, is very characteristic. The atomic weight, 226-4, places and wool. Educated at Exeter College, Oxford, John Robartes the element in a vacant position in group II. of the periodic fought on the side of the Parliament during the Civil War, classification, along with the alkaline earth metals.

being present at the battle of Edgehill and at the first lattle Generally speaking, the radiation is not simple. Radium of Newbury, and was a member of the committee of both itself emits three types of rays: (1) the a rays, which are kingdoms. He is said to have persuaded the earl of Esser regarded as positively charged helium atoms; these rays are to make his ill-fated march into Cornwall in 1644; he escaped stopped by a single sheet of paper; (2) the B rays, which are with the earl from Lostwithiel and was afterwards governor identified with the cathode rays, i.e. as a single electron charged of Plymouth. Between the execution of Charles I. and the negatively; these rays can penetrate sheets of aluminium, glass, restoration of Charles II. he took practically no part in public &c., several millimetres thick; and (3) the y rays—which are life, but after 1660 he became a prominent public man, owing non-electrified radiations characterized by a high penetrating his prominence partly to his influence among the Presbyterians, power, 1% surviving after traversing 7 cm. of lead or 150 cm. and ranged himself among Clarendon's enemies. He was lord of water. In addition, radium evolves an “emanation ” which deputy of Ireland in 1660-1661 and was lord lieutenant in 1669is an extraordinarily inert gas, recalling the “ inactive” gases 1670; from 1661 to 1673 he was lord privy seal, and from 1679 10 of the atmosphere. We thus see that radium is continually 1684 lord president of the council. In 1679 he was created vislosing matter and energy as electricity; it is also losing energy count Bodmin and earl of Radnor, and he died at Chelsea on as heat, for, as was observed by Curie and Laborde, the tem- the 17th of July 1685. His eldest son, Robert, viscount Bodmin, perature of a radium salt is always a degree or two above that who was British envoy to Denmark, having predeceased his of the atmosphere, and they estimated that a gramme of pure father, the latter was succeeded as and earl by his grandson, radium would emit about 100 gramme-calories per hour.

Charles Bodvile Robartes (1660-1723), who was a member of The Becquerel rays have a marked chemical action on certain parliament under Charles II. and James II., and was lord substances. The Curies showed that oxygen was convertible lieutenant of Cornwall from 1696 to 1705 and again from 1714 into ozone, and Sudborough that yellow phosphorus gave the to 1723. Henry, the 3rd earl (c. 1690-1741), was also a grandred modification when submitted to their inf}uence. More son of the ist earl, and John, the 4th earl (c. 1686–1757), was interesting are the observations of D. Berthelot, F. Bordas, another grandson. When John, whose father was Francis C. Doelter and others, that the rays induce important changes Robartes (c. 1650–1718), a member of parliament for over in the colours of many minerals. (See RADIOACTIVITY.) thirty years and a musician of some repute, died unmarried in

The action of radium on human tissues was unknown until July 1757, his titles became extinct. 1901, when, Professor Becquerel of Paris having incautiously Lanhydrock, near Bodmin, and the other estates of the carried a tube in his waistcoat pocket, there appeared on the Robartes family passed to the earl's nephews, Thomas and skin within fourteen days a severe inflammation which was George Hunt. Thomas Hunt's grandson and heir, Thomas known as the famous , “ Becquerel burn." Since that time James Agar-Robartes (1808–1882), a grandson of an Irish peer, active investigation into the action of radium on diseased tissues James Agar, ist viscount Clifden (1734-1789), was created baron has been carried on, resulting in the establishment in Paris in Robartes of Lanhydrock and of Truro in 1869, after having 1906 of the “ Laboratoire biologique du Radium.” Similar represented East Cornwall in seven parliaments. His son and centres for study have been inaugurated in other countries, successor, Thomas Charles Agar-Robartes, the 2nd baron notably one in London in 1909. The diseases to which the (b. 1844), succeeded his kinsman as 6th viscount Clifden in application has been hitherto confined are papillomata, lupus 1899. vulgaris, epithelial tumours, syphilitic ulcers, pigmentary naevi, In 1765 William Bouverie, and viscount Folkestone (1725angiomata, and pruritus and chronic itching of the skin; but 1776), son of Sir Jacob Bouverie, bart. (d. 1761), of Longford, the use of radium in therapeutics is still experimental. The Wiltshire, who was created viscount Folkestone in 1747, was different varieties of rays used are controlled by the inter- made earl of Radnor. Descended from a Huguenot family, vention of screens or filtering substances, such as silver, lead William Bouverie was a member of parliament from 1747 until or aluminium. Radium is analgesic and bactericidal in its action. he succeeded to the peerage in February 1761. He died on

See Radiumtherapie, by Wickham and Degrais (1909); Die the 28th of January 1776. His son and successor, Jacob, therapeutische Wirkung der Radiumstrahlen, by o. Lassar, in Report the end carl (1750-1828), who took the name of Pleydellof Radiology Congress, Brussels, 1906; E. Dorn, E. Baumann and Bouverie in accordance with the will of his maternal grandS. Valentiner in Physische Zeitung (1905); Abbé in Medical Record father, Sir Mark Stuart Pleydell, bart. (d. 1768), was the father (October 1907).

of William Pleydell-Bouverie, the 3rd earl (1779-1869), a RADIUS, properly a straight rod, bar or staff, the original politician of some note. In 1900 his great-grandson, Jacob meaning of the Latin word, to which also many of the various Pleydell-Bouverie (b. 1868), became 6th earl of Radnor. meanings seen in English were attached; it was thus applied RADNORSHIRE (Sir Faesyfed), an inland county of Wales, to the spokes of a wheel, to the semi-diameter of a circle or bounded N. by Montgomery, N.E. by Shropshire, E. by Here sphere and to a ray or beam of light, “ray” itself coming ford, S. and S.W. by Brecknock and N.W. by Cardigan. This through the Fr. raie from radius. From this last sense comes 1 county, which is lozenge-shaped, contains 471 sq. m., and is

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