RADIOACTIVITY. 643 BADIOMETER. X; but an emanation from it has not yet been discovered. Both kinds of radiation, the a and j3, are not present to the same extent in all the transformations which occur in these various cases; and in some only the o radia- tions have been detected and in others only the j3 radiations. It seems probable, however, that the production of the a radiations goes on quite independently of the j3 radiations,' which is a secondary phenomenon, the a radia- tions playing by far the most important part in the changes which take place in radioactive matter. One of the most important questions con- nected with radioactivity is that of the origin of the energj' which is manifested by the ex- (julsion of these rapidly moving particles. The amounts of this energy have been measured ap- pro.ximately, and various theories have been advanced based upon obvious assumptions in regard to the nature of the atom and the mo- tion in it of its parts, which are to a certain degree satisfaetor}'. The atom is thought to consist of a definite space within which are moving many thousand particles negatively charged, and which are icTentical with the ^ radiations. If the atom is unstable, it is not difficult to see that some of these particles might be from time to time thrown off, and a consistent theory of matter along these lines has been devised by Professor J. J. Thomson. One of the most interesting evidences of the intense energy furnished by these radioactive bodies is the fact that M. Curie has shown that in certain experiments radium sets free in a con- tinuous manner energy in such a form as to main- tain itself at a temperature higher than that of the surrounding bodies, and of such an amount that one gram of radium would raise the tempera- ture of one hundred grams of water one degree Centigrade in an hour. A noteworthy fact is that the radioactive substances uranium, thorium, and radium are of very high atomic weights, standing at the end of their groups of elements in the Periodic Table ; and that there- fore they may mark a condition in which mat- ter is on the verge of instability under present conditions of pressure and temperature. For the more detailed statements in regard to the properties of radioactive bodies, refer- ence should be made to articles by Rutherford in the Philosophical Maga:::ine, and to a popular article, "Some Recent Advances in Radio- activity," by Professor Soddy, in the Contem- porary Review, May, 1903. RA'DIOLA'RIA (Neo-Lat. nom. pi., from Lat. radlolus, diminutive of radius, ray). A group of minute marine animals forming an order of rhizopodous Protozoa (q.v.). About 85 families, including many thousand species, are known, most of them microscopic. They live in the surface water of the ocean and their shells, after death, sink to the bottom and form siliceous deposits, known as radiolarian ooze. (See Ooze.) They are distinguished from all other Protozoa by their complex and generally very beautiful shells, which are composed of silicon, except in a few cases where either the material is a horny substance called 'acanthin,' or the shell is entire- ly wanting. The radiolarians are further distin- guished by the presence of a peculiar, mem- branous, inner capsule. This is either spherical and perforated by numerous small openings or it is ovoid with a single large opening. Within it is some clear transparent cj'toplasm and the nucleus, while outside is a layer of protoplasm which is covered by a gelatinous envelope, known as the calymna. The skeleton or shell consists of one or more fenestrated spheres ; when more than one are present thej' are concentric. They are con- nected with each other by radiating rods and spi- cules which are usually continued outside the outermost sphere as projecting spines, and may be continued inwardly to meet within the centre of the capsule. The variety of form and arrange- ment is very great and is the cause of the beauty of these animals under the miscroscope. The pseudopodia are usually very flexible and anasto- mose freely, but in some cases they are stiff and not inclined to fuse. Contractile vacuoles are not present, but in most radiolarians are very small yellowish spheres, supposed to be parasitic algae; it is possible that these are concerned with the process of excretion. Reproduction takes place either by fission or by spore formation. In the latter case both maerospores and miscrospores are formed, and it is .supposed that one of each must fuse together to give rise to a new individual. Radiolarians play an important part in the economy of the ocean, furnishing food for count- less hosts of minute crustaceans and other ani- mals, which in turn supply the fishes. All re- cent investigations into the biology of the ocean give an important place to this order. Fossil Fobms. Radiolaria are abundant in a fossil state ; they have been found in rocks of most of the geological sj-stems, and in many cases they have formed siliceous rocks of con- siderable thickness. These latter, described from Brittany, England, and New South Wales, recall the radiolarian ooze of the modern ocean bottom. They are among the oldest known organisms, for they are found in quartzites interbedded with Pre-Cambrian gneiss in Brittany. They occur in abundance in phosphate nodules in the lower Cambrian of New Brunswick, Canada, and in Cambrian rocks of other regions. Cherts and jaspers of Ordovician, Silurian, Devonian, and Carboniferous age in Europe, Asia, and Aus- tralia have been found to contain them, often in abundance. The ilesozoic and Tertiary flint- bearing deposits, like the chalk of Europe and America, yield them, and the polishing earths known as 'Barbadoes earth' and 'tripoli' owe their abrasive powers to them. Consult: Haeckel, Die Radiolarien (Berlin, 1862-88) : id., Rejjm-t cm the Radiolaria (Chal- lenger Reports, London, 1887); Von Zittel and Eastman, Text-book of Palwontologi/, col. i. (New York and London, 1900) ; Rust, "Beitrage zur Kenntnis der Fossilen Radiolarien," in Paloe- ontographica, vols, xxxi., xxxiv., xxxviii. (Jena, 1885-94). RADIOLITES, ra'dl-S-li'tez (Neo-Lat. nom. pi., from Lat. radioUis, little ray). A very pecu- liar fossil pelecypod of Cretaceous age, allied to Rudistes. See Rudist.e. RADIOMETER (from Lat. radius, ray -f Gk. fiirpov. metron, measure). An instrument invented by Crookes and improved by Pringsheim and E. F. Nichols. It consists essentially of a framework carrying one or more mica vanes supported and free to turn around an axis in an inclosed space from which prac-
