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Rh 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 α rays, which are regarded as positively charged helium atoms; these rays are stopped by a single sheet of paper; (2) the β 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 γ 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 .)

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.

 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 circumference 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 hackney carriages, 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 1669–1670; 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 (1725–1776), 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 Pleydell-Bouverie 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 