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disposed on five successive zones of four on alternating meridians, the zones corresponding to equator, tropics and circumpolar circles 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. Acanthometra, J. Müll. (fig. iv. 6, 7); Astrolonche, Haeck.; Amphilonche, Haeck. (fig. III. 18).

Fam. 3. SPHAEROPHRACTIDA: Spines equal, branching and often coalescing into a latticed shell, homaxonic.

Fam. 4. PRUNOPHRACTIDA: 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 (coneshaped), 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 beehivelike structure of monaxonic form, a tripod or calthrop, a sagittal ring, or a combination of these.

Fam. 1. NASSOIDEA, Haeck. Skeleton absent. Cystidium,
Haeck.

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Fam. 2.

PLECTIDA, Haeck. Skeleton formed of a single

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

Fam. 3. SPYROIDEA. Shell latticed around the sagittal ring("cephalis "), sometimes with a lower chamber added.

Fam. 4. BOTRIDEA, Haeck. Shell latticed, composed of several chambers agglomerated without definite order; a single central capsule. Genera: Botryocyrtis, Haeck.; Lithobotrys, Haeck.

Fam. 5. CYRTOIDEA, Haeck. Skeleton a monaxonic or triradiate shell, or continuous piece (beehiveshaped). Genera: Halicalyptra, Haeck.; Eucyrtidium, 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.; 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 of spicules, a network of hollow filaments, or a minutely alveolate 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.; Thalassoplancta, Haeck.

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Fam. 2. PHAEOSPHAERIDA. Spicules united into latticed shell. Genera: Aulosphaera, Haeck. (fig. IV. 9); Auloplegma, Haeck.; Cannacantha, Haeck.

Fam. 3. PHAEOGROMIDA, Haeck. Shell continuous,

traversed by fine canals or finely alveolate, provided with at least one pylome. Genera: Challengeria, Wyv., Thomson; Lithogromia, Haeck.

Fam. 4. PHAEOCONCHIDA. Shell as in Phaeosphaerida, but of two symmetrical halves (valves), which meet in the plane of the three oscules (" frontal of Haeckel, who terms the plane of symmetry through the shells "sagittal"). Genera: Conchidium, Haeck.; Coelodendrum, Haeck. (fig. IV. 4).

The following passages may be repeated here from Sir E. Ray Lankester's article "Protozoa " in the 9th edition of this Encyclopaedia;

"The important differences in the structure of the central capsule of different Radiolaria were first shown by Hertwig, who also discovered that the spines of the Acanthometridea consist not of silica but of an organic compound (but see above). In view of this latter fact and of the peculiar numerical and architectural features of the Acanthometrid skeleton, it seems proper to separate them altogether from the other Radiolaria. The Peripylaea may be regarded as the starting-point of the Radiolarian pedigree, and have given rise on the one hand to the Acanthometridea, which

FIG. III.-Radiolaria. 1. Central capsule of Thalassicolla nucleata, Huxley, in radial section. a, the large nucleus (Binnenbläschen); b, corpuscular structures of the intracapsular protoplasm containing concretions; c, wall of the capsule (membranous shell), showing the fine radial pore-canals; d, nucleolar fibres (chromatin substance) of the nucleus. 2. 3. Collozoum inerme, J. Müller, two different forms of colonies, of the natural size. 4. Central capsule from a colony of Collozoum inerme, showing the intracapsular protoplasm and nucleus, broken up into a number of spores, the germs of swarm-spores or flagellulac; each encloses a crystalline rod. c, yellow cells lying in the extracapsular protoplasm. 5. A small colony of Collozoum inerme, magnified 25 diameters. a, alveoli (vacuoles) of the extracapsular protoplasm; b, central capsules, each containing besides protoplasm a large oil-globule. 6-13. Yellow cells of various Radiolaria: 6, normal yellow cell; 7. 8, division with formation of transverse septum; 9, a modified condition according to Brandt; 10, division of a yellow cell into four; 11, amoeboid condition of a yellow cell from the body of a dead Sphaerozoon; 12, a similar cell in process of division; 13, a yellow cell the protoplasm of which is creeping out of its cellulose envelope. 14. Heliosphaera inermis, Haeck., living example; a, nucleus; b, central capsule; c, siliceous basket-work, skeleton. 15. Two swarm-spores (flagellulac) of Collozoum inerme, set free

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from such a central capsule as that drawn in 4; each contains a crystal b and a nucleus a. 16. Two swarm-spores of Collozoum inerme, of the second kind, viz. devoid of crystals, and of two sizes, a macrospore and a microspore. They have been set free from central capsules with contents of a different appearance from that drawn in 4. a, nucleus. 17. Actinomma asteracanthion, Haeck.; one of the Peripylaea. Entire animal in optical section. a, nucleus; b, wall of the central capsule; c, innermost siliceous shell enclosed in the nucleus; c, middle shell lying within the central capsule; c, outer shell lying in the extracapsular protoplasm. Four radial siliceous spines holding the three spherical shells together are seen. The radial fibrillation of the protoplasm and the fine extracapsular pseudopodia are to be noted. 18. Amphilonche messanensis, Haeck.; one of the Acanthometridea. Entire animal as seen living.

of the protoplasmic body. a, the tri-lobed nucleus; b, the siliceous shell; 6, oil-globules; d, the perforate area (pore-plate) of the central capsule. 4. Coelodendrum gracillimum, Haeck.; living animal, complete; one of the Tripylaea. a, the characteristic dark pigment (phacodium) surrounding the central capsule b. The peculiar branched siliceous skeleton, consisting of hollow fibres, and the expanded pseudopodia are seen. 5. Central capsule of one of the Tripylaea, isolated, showing a, the nucleus; b, c, the inner and the outer laminae of the capsule wall; d, the chief or polar aperture; e, e, the two secondary apertures. 6, 7. Acanthometra claparedei, Haeck. 7 shows the animal in optical section, so as to exhibit the characteristic meeting of the spines at the central point as in all Acanthometridea; 6 shows the transition from the uninuclear to the multinuclear condition by the breaking up of the large nucleus. a, small nuclei; b, large fragments of the single nucleus; c, wall of the central capsule; d, extracapsular jelly (not protoplasm); e, peculiar intracapsular yellow cells. 8. Spongosphaera streptacantha, Haeck.; one of the Peripylaea. Siliceous skeleton not quite completely drawn on the right side. a, the spherical extracapsular shell (compare fig. III. 17), supporting very large radial spines which are connected by a spongy network of siliceous fibres. sphaera elegantissima, Haeck.; one of the Phaeodaria. Half of the spherical siliceous skeleton.

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FIG. IV.-Radiolaria. 1. Lithocircus annularis, Hertwig; one of the Monopylaea. Whole animal in the living state (optical section); a, nucleus; b, wall of the central capsule; c, yellow cells; d, perforated area of the central capsule (Monopylaea). 2. Cystidium inerme, Hertwig; one of the Monopylaea. Living animal. An example of a Monopylacon destitute of skeleton. a, nucleus; b, capsule-wall; c, yellow cells in the extracapsular protoplasm. 3. Carpocanium diadema, Haeck.; optical section of the beehive-shaped shell to show the form and position

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.

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"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. differences inter se do not affect their essential structure. The variations in the chemical composition of the skeleton and in the perforation 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 characteristic of the group that it may be wanting altogether. It is not known how far the form-species and form-genera which have been distinguished in such profusion by Haeckel as the result of a study of the skeletons are permanent (.e. relatively permanent) physiological 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 Acanthometra and in the Polycyttaria and Thalassicollidae, and only in the two latter groups have any detailed observations been made. Two distinct processes of swarm-spore production have been observed by Cienkowski, confirmed by Hertwig,-distinguished by the character of the resulting spores, which are called crystalligerous and isospores (fig. III. 15) in the one case, and dimorphous or anisospores in the other (fig. 1. 16). In both processes the nucleated protoplasm within the central capsule breaks up by a more or less regular cell-division into small

pieces, the details of the process differing a little in the two cases. In those individuals which produce crystalligerous swarm-spores, each spore encloses a small crystal (fig. 111. 15). On the other hand, in those individuals which produce dimorphous swarm-spores, the contents of the capsule (which in both instances are set free by its natural rupture) are seen to consist of individuals of two sizes, megaspores' and microspores,' neither of which contain crystals (fig. 111. 16). The further development of the spores hast not been observed in either case. Both processes have been observed in the same species, and it is suggested that there is an alternation of sexual and asexual generations, the crystalligerous spores develop ing directly into adults, which in their turn produce in their central capsules dimorphous swarm-spores (megaspores and microspores), which in a manner analogous to that observed in the Volvocinean Flagellata copulate (permanently fuse) with one another (the larger with the smaller) before proceeding to develop. The adults resulting from this process would, it is suggested, produce in their turn crystalligerous swarm-spores. Unfortunately we have no observations to support this hypothetical scheme of a life-history. "Fusion or conjugation of adult Radiolaria, whether preliminary to swarm-spore-production or independently of it, has not been observed this affording a distinction between them and Heliozoa. Simple fission of the central capsule of adult individuals, preceded of course by nuclear fission, and subsequently of the whole protoplasmic mass, has been observed in several genera of Acantharia and Phaeodaria, and is probably a general method of reproduction in the group. In Spumellaria it gives rise to colonial forms when the extracapsular protoplasm does 'Polycyttarian not divide.

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"The siliceous shells of the Radiolaria are found abundantly in certain rocks from Palaeozoic times onwards. They furnish, together with Diatoms and Sponge spicules, the silica which has been segregated as flint in the Chalk formation. They are present in quantity (as much as 10%) in the Atlantic ooze, and in the celebrated Barbados earth' (a Tertiary deposit) are the chief components."

BIBLIOGRAPHY.-The most important systematic works are those of E. Haeckel, Die Radiolarien (1862-87), and the "Report" on the Radiolaria of the." Challenger" Expedition (vol. xviii., 1887), which contains full lists of the older literature. Among the most important recent studies we cite K. Brandt, "Die Koloniebildenden Radiolarien" in Fauna and Flora des Golfes von Neapel, xii. (1885); A. Borgert in Zeitschrift f. Wissenschaftliche Zoologie, li. (1891), and Zoologische Jahrbücher (Anatomie), xiii. (1900); F. Dreyer in Jenaischer Zeitschr., xix. (1892); V. Häcker in Zeitsch. f. Wiss. Zool., Ixxxiii. (1905). (M. HA.)

RADIOMETER. It had been remarked at various times, amongst others by Fresnel, that bodies delicately suspended within a partial vacuum are subject to apparent repulsion by radiation. The question was definitely investigated by Sir W. Crookes, who had found that some delicate weighings in vacuo were vitiated by this cause. It appeared that a surface blackened so as to absorb the radiant energy directed on it was repelled relatively to a polished surface. He constructed an apparatus in illustration, which he called a radiometer or lightmill, by pivoting a vertical axle carrying equidistant vertical vanes inside an exhausted glass bulb, one side of each vane being blackened and the other side bright, the blackened sides all pointing the same way round the axle. When the rays of the sun or a candle, or dark radiation from a warm body, are incident on the vanes, the dark side of each vane is repelled more than the bright side, and thus the vanes are set into rotation with accelerated speed, which becomes uniform when the forces produced by the radiation are balanced by the friction of the pivot and of the residual air in the globe. The name radiometer arose from an idea that the final steady speed of rotation might be utilized as a rough measure of the intensity of the exciting radiation.

The problem of the cause of these striking and novel phenomena at first produced considerable perplexity. A preliminary question was whether the mechanical impulsion was a direct effect of the light, or whether the radiation only set up internal stresses, acting in and through the residual air, between the vanes and the walls of the enclosure. The answer to this was found experimentally by Arthur Schuster, who suspended the whole instrument in delicate equilibrium, and observed the effect of introducing the radiation. If the light exerted direct impulsion on the vanes, their motion would gradually drag the case round after them, by reason of the friction of the residual air in the bulb and of the pivot On the other

hand, if the effects arose from balanced stresses set up inside the globe by the radiation, the effects on the vanes and on the case would be of the nature of action and reaction, so that the establishment of motion of the vanes in one direction would involve impulsion of the case in the opposite direction; but when the motion became steady there would no longer be any torque either on the vanes or on the case, and the latter would therefore come back to its previous position of equilibrium; finally, when the light was turned off, the decay of the motion of the vanes would involve impulsion of the case in the direction of their motion until the moment of the restoring torque arising from the suspension of the case had absorbed the angular momentum in the system. Experiment showed that the latter prediction was what happened. The important part played by the residual air in the globe had also been deduced by Osborne Reynolds from observing that on turning off the light, the vanes came to rest very much sooner than the friction of the pivot alone would account for; in fact, the rapid subsidence is an illustration of Maxwell's great theoretical discovery that viscosity in a gas (as also diffusion both of heat and of the gas itself) is sensibly independent of the density. had led Sir G. G. Stokes and Sir W. Crookes to the same general Some phenomena of retardation in the production of the effect conclusion.

The origin of these phenomena was recognized, among the first by O. Reynolds, and by P. G. Tait and J. Dewar, as a consequence of the kinetic theory of the constitution of gaseous media. The temperature of a gas is measured by the mean energy of translation of its molecules, which are independent of each other except during the brief intervals of collision; and collision of the separate molecules with the blackened surface of a vane, warmed by the radiation, imparts heat to them, so that they rebound from it with greater velocity than they approached. This increase of velocity implies an increase of the reaction on the surface, the black side of a vane being thus pressed with greater force than the bright side. In air of considerable density the mean free path of a molecule, between its collisions with other molecules, is exceedingly small, and any such increase of gaseous pressure in front of the black surface would be immediately neutralized by flow of the gas from places of high to places of low pressure. But at high exhaustions the free path becomes comparable with the dimensions of the glass bulb, and this equalization proceeds slowly. The general nature of the phenomena is thus easily understood; but it is at a maximum at pressures comparable with a millimetre of mercury, at which the free path is still small, the greater number of molecules operating in intensifying the result. The problem of the stresses in rarefied gaseous media arising from inequalities of temperature, which is thereby opened out, involves some of the most delicate considerations in molecular physics. It remains practically as it was left in 1879 by two memoirs communicated to the Phil. Trans. by Osborne Reynolds and by Clerk Maxwell. The method of the latter investigator was purely a priori. He assumed that the distribution of molecules and of their velocities, at each point, was slightly modified, from the exponential law belonging to a uniform condition, by the gradient of temperature in the gas (see DIFFUSION). The hypothesis that the state was steady, so that interchanges arising from convection and collisions of the molecules produced no aggregate result, enabled him to interpret the new constants involved in this law of distribution, in terms of the temperature and its spacial differential coefficients, and thence to express the components of the kinetic stress at each point in the medium in terms of these quantities. As far as the order to which he carried the approximationswhich, however, were based on a simplifying hypothesis that the molecules influenced each other through mutual repulsions inversely as the fifth power of their distance apart-the result was that the equations of motion of the gas, considered as subject to viscous and thermal stresses, could be satisfied by a state of equilibrium under a modified internal pressure equal 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 such as gravity are not considered, the gas would exert no resultant force on any body immersed in it. On this ground Maxwell inferred that the forces acting in the radiometer are connected with gliding of the gas along the unequally heated boundaries; and as the laws of this slipping, as well as the constitution of the adjacent layer, are uncertain, the problem becomes very intricate. Such slipping had shown itself at high exhaustions in the experiments of A. A. Kundt and E. G. Warburg in 1875 on the viscosity of gases; its effects would be corrected for, in general, by a slight effective addition to the thickness of the gaseous layer.

Reynolds, in his investigation, introducing no new form of law of distribution of velocities, uses a linear quantity, proportional to the mean free path of the gaseous molecules, which he takes to represent (somewhat roughly) the average distance from which molecules directly affect, by their convection, the state of the medium; the gas not being uniform on account of the gradient of temperature, the change going on at each point is calculated from the elements contributed by the parts at this particular distance in all directions. He lays stress on the dimensional relations of the problem, pointing out that the phenomena which occur with large vanes in highly rarefied gas could also occur with proportionally smaller vanes in gas at higher pressure. The results coincide with Maxwell's so far as above stated, though the numerical coefficients do not agree. According to Maxwell, priority in showing the necessity for slipping over the boundary rests with Reynolds, who also discovered the cognate fact of thermal transpiration, meaning thereby that gas travels up the gradient of temperature in a capillary tube, owing to surface-actions, until it establishes such a gradient of pressure (extremely minute) as will prevent further flow. In later memoirs Reynolds followed up this subject by proceeding to establish definitions of the velocity and the momentum and the energy at an element of volume of the molecular medium, with the precision necessary in order that the dynamical equations of the medium in bulk, based in the usual manner on these quantities alone, without directly considering thermal stresses, shall be strictly valid-a discussion in which the relation of ordinary molar mechanics to the more complete molecular theory is involved.

Of late years the peculiarities of the radiometer at higher gas-pressures have been very completely studied by E. F. Nichols and G. F. Hull, with the result that there is a certain pressure at which the molecular effect of the gas on a pair of nearly vertical vanes is balanced by that of convection currents in it. By thus controlling and partially eliminating the aggregate gas-effect, they succeeded in making a small radiometer, horizontally suspended, into a delicate and reliable measurer of the intensity of the radiation incident on it. With the experience thus gained in manipulating the vacuum, the achievement of thoroughly verifying the pressure of radiation on both opaque and transparent bodies, in accordance with Clerk Maxwell's formula, has been effected (Physical Review, 1901, and later papers) by E. F. Nichols and G. F. Hull; some months earlier Lebedew had published in the Annalen der Physik a verification for metallic vanes so thin as to avoid the gasaction, by preventing the production of sensible difference of temperature between the two faces by the incident radiation. (See RADIATION.)

More recently J. H. Poynting has separated the two effects experimentally on the principle that the radiometer pressure acts along the normal, while the radiation pressure acts along the ray which may be directed obliquely. (J. L.) RADISH, Raphanus sativus (nat. order Cruciferae), in botany, a fleshy-rooted annual, unknown in the wild state. Some varieties of the wild radish, R. Raphanistrum, however, met with on the Mediterranean coasts, come so near to it as to suggest that it may possibly be a cultivated race of the same species. It is very popular as a raw salad. There are

The radish succeeds in any well-worked not too heavy garden soil, but requires a warm, sheltered situation. The seed is generally sown broadcast, in beds 4 to 5 ft. wide, with alleys between, the beds requiring to be netted over to protect them from birds. The earliest crop may be sown about the middle of December, the seed-beds being at once covered with litter, which should not be removed till the plants come up, and then only in the daytime, and when there is no frost. If the crop succeeds, which depends on the state of the weather, it will be in use about the beginning of March. Another sowing may be made in January, a third early in February, if the season is a favourable one, and still another towards the end of February, from which time till October a small sowing should be made every fortnight or three weeks in spring, and rather more frequently during summer. About the end of October, and again in November, a late sowing may be made on a south border or bank, the plants being protected in severe weather with litter or mats. The winter radishes, which grow to a large size, should be sown in the beginning of July and in August, in drills from 6 to 9 in. apart, the plants being thinned out to 5 or 6 in. in the row. The roots become fit for use during the autumn. winter use they should be taken up before severe frost sets in, and stored in dry sand. Radishes, like other fleshy roots, are attacked by insects, the most dangerous being the larvae of several species of fly, especially the radish fly (Anthomyia radicum). The most effectual means of destroying these is by watering the plants with a dilute solution of carbolic acid, or much diluted gas-water; or gas-lime may be sprinkled along the rows.

For

Forcing.-To obtain early radishes a sowing in the British Isles should be made about the beginning of November, and continued fortnightly till the middle or end of February; the crop will gener 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 or in a pit with a temperature of from 55° to 65°. Gentle waterings must be given, and air admitted at every favourable opportunity; but the sashes must be protected at night and in frosty weather with straw mats or other materials. Some of these crops are often grown with forced potatoes. The best forcing sorts are Wood's carly frame, and the early rose globe, early dwarf-top scarlet turnip, and early dwarf-top white turnip.

Those best suited for general cultivation are the following:Spindle-rooted. Long scarlet, including the sub-varieties scarlet short-top, early frame scarlet, and Wood's early frame; long scarlet short-top, best for general crop.

Turnip-rooted.-Early rose globe-shaped, the earliest of all; early dwarf-top scarlet turnip, and early dwarf-top white turnip; earliest Erfurt scarlet, and early white short-leaved, both very early sorts; French breakfast, olive-shaped; red turnip and white turnip, for summer crops.

Winter sorts.-Black Spanish, white Chinese, Californian mammoth.

RADIUM (from Lat. radius, ray), a metallic chemical element obtained from pitchblende, a uranium mineral, by P. and Mme. Curie and G. Bémont in 1898; it was so named on account of the intensity of the radioactive emanations which it yielded. Its discovery was a sequel to H. Becquerel's observation in 1896 that certain uranium preparations emitted a radiation resembling the X rays observed by Röntgen in 1895. Like the X rays, the Becquerel rays are invisible; they both traverse thin sheets of glass or metal, and cannot be refracted; moreover, they both ionize gases, i.e. they discharge a charged electroscope, the latter, however, much more feebly than the former. Characteristic, also, is their action on a photographic plate, and the phosphorescence which they occasion when they impinge on zinc sulphide and some other salts. Notwithstanding these resemblances, these two sets of rays are not indentical. Curie, regarding radioactivity-i.e. the emission of rays like those just mentioned as a property of some undiscovered substance, submitted pitchblende to a most careful analysis, After removing the uranium, it was found that the bismuth separated with a very active substance-polonium; this element was afterwards isolated by Marckwald, and proved to be identical with his radiotellurium; that the barium could be

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separated with another active substance-radium; whilst a third fraction, composed mainly of the rare earths (thorium, &c.), yielded to Debierne another radioactive element-actinium, which proved to be identical with the emanium of Giesel. Another radioactive substance-ionium-was isolated from carnotite, a uranium mineral, by B. B. Boltwood in 1905. Radioactive properties have also been ascribed to other elements, e.g. thorium and lead. There is more radium than any other radioactive element, but its excessive rarity may be gauged by the facts that Mme. Curie obtained only a fraction of a gramme of the chloride and Giesel 2 to 3 gramme of the bromide from a ton of uranium residues.

There is a mass of evidence to show that radium is to be regarded as an element, and in general its properties resemble those of the metals of the alkaline earths, more particularly barium. To the bunsen flame a radium salt imparts an intense carmine-red colour (barium gives a green). The spectrum, also, is very characteristic. The atomic weight, 226-4, places the element in a vacant position in group II. of the periodic classification, along with the alkaline earth metals.

Generally speaking, the radiation is not simple. Radium itself emits three types of rays: (1) the a rays, which are regarded as positively charged helium atoms; these rays are stopped by a single sheet of paper; (2) the ẞ rays, which are identified with the cathode rays, i.e. as a single electron charged negatively; these rays can penetrate sheets of aluminium, glass, &c., several millimetres thick; and (3) the y rays-which are non-electrified radiations characterized by a high penetrating power, 1% surviving after traversing 7 cm. of lead or 150 cm. of water. In addition, radium evolves an “emanation" which is an extraordinarily inert gas, recalling the "inactive" gases of the atmosphere. We thus see that radium is continually losing matter and energy as electricity; it is also losing energy as heat, for, as was observed by Curie and Laborde, the temperature of a radium salt is always a degree or two above that of the atmosphere, and they estimated that a gramme of pure radium would emit about 100 gramme-calories per hour.

The Becquerel rays have a marked chemical action on certain substances. The Curies showed that oxygen was convertible into ozone, and Sudborough that yellow phosphorus gave the red modification when submitted to their influence. More interesting are the observations of D. Berthelot, F. Bordas, C. Doelter and others, that the rays induce important changes in the colours of many minerals. (See RADIOACTIVITY.)

The action of radium on human tissues was unknown until 1901, when, Professor Becquerel of Paris having incautiously carried a tube in his waistcoat pocket, there appeared on the skin within fourteen days a severe inflammation which was known as the famous. "Becquerel burn." Since that time active investigation into the action of radium on diseased tissues has been carried on, resulting in the establishment in Paris in 1906 of the "Laboratoire biologique du Radium." Similar centres for study have been inaugurated in other countries, notably one in London in 1909. The diseases to which the application has been hitherto confined are papillomata, lupus vulgaris, epithelial tumours, syphilitic ulcers, pigmentary naevi, angiomata, and pruritus and chronic itching of the skin; but the use of radium in therapeutics is still experimental. The different varieties of rays used are controlled by the intervention of screens or filtering substances, such as silver, lead or aluminium. Radium is analgesic and bactericidal in its action. See Radiumtherapie, by Wickham and Degràis (1909); Die therapeutische Wirkung der Radiumstrahlen, by O. Lassar, in Report of Radiology Congress, Brussels, 1906; E. Dorn, E. Baumann and S. Valentiner in Physische Zeitung (1905); Abbé in Medical Record (October 1907).

RADIUS, properly a straight rod, bar or staff, the original meaning of the Latin word, to which also many of the various meanings seen in English were attached; it was thus applied to the spokes of a wheel, to the semi-diameter of a circle or sphere and to a ray or beam of light, "ray" itself coming through the Fr. raie from radius. From this last sense comes

radiant," "radiation," and allied words. In mathematics, a radius is a straight line drawn from the centre to the circum ference of a circle or to the surface of a sphere; in anatomy the name is applied to the outer one of the two bones of the fore-arm in man or to the corresponding bone in the fore-leg of animals. It is also used in various other anatomical senses in botany, ichthyology, entomology, &c. A further application of the term is to an area the extent of which is marked by the length of the radius from the point which is taken as the centre; thus, in London, for the purpose of reckoning the fare of hackneycarriages, the radius is taken as extending four miles in any direction from Charing Cross.

RADNOR, EARLS OF. The 1st earl of Radnor was John Robartes (1606-1685), who succeeded his father, Richard Robartes, as 2nd baron Robartes of Truro in May 1634, the barony having been purchased under compulsion for £10,000 in 1625. The family had amassed great wealth by trading in tin and wool. Educated at Exeter College, Oxford, John Robartes fought on the side of the Parliament during the Civil War, being present at the battle of Edgehill and at the first battle of Newbury, and was a member of the committee of both kingdoms. He is said to have persuaded the earl of Essex to make his ill-fated march into Cornwall in 1644; he escaped with the earl from Lostwithiel and was afterwards governor of Plymouth. Between the execution of Charles I. and the restoration of Charles II. he took practically no part in public life, but after 1660 he became a prominent public man, owing his prominence partly to his influence among the Presbyterians, and ranged himself among Clarendon's enemies. He was lord deputy of Ireland in 1660-1661 and was lord lieutenant in 16691670; from 1661 to 1673 he was lord privy seal, and from 1679 to 1684 lord president of the council. In 1679 he was created viscount Bodmin and earl of Radnor, and he died at Chelsea on the 17th of July 1685. His eldest son, Robert, viscount Bodmin, who was British envoy to Denmark, having predeceased his father, the latter was succeeded as 2nd earl by his grandson, Charles Bodvile Robartes (1660-1723), who was a member of parliament under Charles II. and James II., and was lord lieutenant of Cornwall from 1696 to 1705 and again from 1714 to 1723. Henry, the 3rd earl (c. 1690-1741), was also a grandson of the 1st earl, and John, the 4th earl (c. 1686-1757), was another grandson. When John, whose father was Francis Robartes (c. 1650-1718), a member of parliament for over thirty years and a musician of some repute, died unmarried in July 1757, his titles became extinct.

Lanhydrock, near Bodmin, and the other estates of the Robartes family passed to the earl's nephews, Thomas and George Hunt. Thomas Hunt's grandson and heir, Thomas James Agar-Robartes (1808-1882), a grandson of an Irish peer, James Agar, 1st viscount Clifden (1734-1789), was created baron Robartes of Lanhydrock and of Truro in 1869, after having represented East Cornwall in seven parliaments. His son and successor, Thomas Charles Agar-Robartes, the 2nd baron (b. 1844), succeeded his kinsman as 6th viscount Clifden in 1899.

In 1765 William Bouverie, 2nd viscount Folkestone (17251776), son of Sir Jacob Bouverie, bart. (d. 1761), of Longford, Wiltshire, who was created viscount Folkestone in 1747, was made earl of Radnor. Descended from a Huguenot family, William Bouverie was a member of parliament from 1747 until he succeeded to the peerage in February 1761. He died on the 28th of January 1776. His son and successor, Jacob, the 2nd earl (1750-1828), who took the name of PleydellBouverie in accordance with the will of his maternal grandfather, Sir Mark Stuart Pleydell, bart. (d. 1768), was the father of William Pleydell-Bouverie, the 3rd earl (1779-1869), a politician of some note. In 1900 his great-grandson, Jacob Pleydell-Bouverie (b. 1868), became 6th earl of Radnor.

RADNORSHIRE (Sir Faesyfed), an inland county of Wales, bounded N. by Montgomery, N.E. by Shropshire, E. by Hereford, S. and S.W. by Brecknock and N.W. by Cardigan. This county, which is lozenge-shaped, contains 471 sq. m., and is

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