Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/230

212 R A D R A D into relations with the democratic leaders. It was in fact at this time the mainstay of the house of Hapsburg, while everything around the central government tottered ; and, when the restoration of authority began, and the young emperor Francis Joseph ascended the throne that had been vacated by his imbecile predecessor, Radetzky gave to the new monarch the prestige of a crushing victory over his Italian enemies. The armistice was denounced by Charles Albert on the 12th of March 1849. On the 20th Radetzky crossed the Ticino at Pa via, and on the 23d he annihilated the Italian army at Novara. Peace followed this brief and decisive campaign, and for the next eight years Radetzky governed upper Italy. He retired from service in 1857, and died at the age of ninety-two in the following year. Radetzky was idolized by the Austrian army, but his reputation as a general has not survived him. RADHANPUR, a petty state of India, within the group of states under the supervision of the political superintend- ent of Palanpur ; it is situated in the north-western corner of Gujarat, close to the Runn of Cutch, Bombay presidency, and lies between 23 26' and 23 58' N. lat. and between 71 28' and 72 3' E. long. The country is an open plain without hills and with few trees, square in shape, and about 35 miles across. Including the pergunnahs of Munjpur and Sami, it contains an area of 1150 square miles with a popu- lation (1881) of 98,129 (males 50,903, females 47,226), the majority being Hindus. Though subject to very great extremes of heat and cold, the climate is healthy. The estimated yearly revenue of the state is from 50,000 to 60,000. Its chief products are cotton, wheat, and all the common varieties of grain ; the only manufacture of any importance is the preparation of a fine description of salt- petre. Radhanpur came under British protection in 1819, when the nawab applied for aid to check the raids of mar- auders. No tribute is exacted and its domestic relations are left entirely free. RADHANPUR, chief town of the state and the seat of the nawab, had a population of 14,722 in 1881. The nearest railway station is at Kharagoda, 40 miles distant. RADIATA. This term was introduced by Cuvier in 1812 to denote the lowest of his four great animal groups or " embranchements." He defined them as possessing radial instead of bilateral symmetry, and as apparently destitute of nervous system and sense organs, as having the circulatory system rudimentary or absent, and the respira- tory organs on or coextensive with the surface of the body; he included under this title and definition five classes, Echinodermata, Acalepha, Entozoa, Polypi, and Infusoria. Lamarck (Hist. nat. d. Anim. s. Vertebres) also used the term, as when he spoke of the Medusae as radiata medusaria et anomala ; but he preferred the term Radiaria, under which he included Echinodermata and Medusae. Cuvier's term in its wide extension, how- ever, passed into general use ; but, as the anatomy of the different forms became more fully known, the difficulty of including them under the common designation made itself increasingly obvious. Milne -Ed wards removed the Poly- zoa; the group was soon further thinned by the exclu- sion of the Protozoa on the one hand and the Entozoa on the other; while in 1848 Leuckart and Frey clearly distinguished the Ccelenterata from the Echinodermata as a separate sub -kingdom, thus condemning the usage by which the term still continued to be applied to these two groups at least. In 1855, however, Owen included under Lamarck's term Radiaria the Echinodermata, Anthozoa, Acalepha, and Hydrozoa, while Agassiz also clung to the term Radiata as including Echinodermata, Acalepha, and Polypi, regarding their separation into Coelenterata and Echinodermata as "an exaggeration of their anatomical differences" (Essay on Classification, London, 1859). These attempts, however, to perpetuate the usage were finally discredited by Huxley's important Lectures on Com- parative Anatomy (1864), in which the term was finally abolished, and the "radiate mob " finally distributed amonLr the Echinodermata, Polyzoa, Venues (Platyhelminthes), Coelenterata, and Protozoa. On radiate symmetry, see MORPHOLOGY. Compare also CUVIER, ANIMAL KINGDOM, ECHINODERMATA, CORALS, &c. RADIATION AND CONVECTION. 1. When a red- hot cannon ball is taken out of a furnace and suspended in the air it is observed to cool, i.e., to part with heat, and it continues to do so at a gradually diminishing rate till it finally reaches the temperature of the room. But the pro- cess by which this effect is produced is a very complex one. If the hand be held at a distance of a few inches from the hot ball on either side of it or below it, the feeling of warmth experienced is considerable; but it becomes intolerable when the hand is held at the same distance above the ball. Even this rude form of experiment is sufficient to show that two processes of cooling are simul- taneously at work, one which apparently leads to the loss of heat in all directions indifferently, another which leads to a special loss in a vertical direction upwards. If the ex- periment is made in a dark room, into which a ray of sun- light is admitted so as to throw a shadow of the ball on a screen, we see that the column of air above the ball also casts a distinct shadow. It is, in fact, a column of air very irregularly heated by contact with the ball, and rising, in obedience to hydrostatic laws, in the colder and denser air around it. This conveyance of heat by the motion of the heated body itself is called convection ; the process by which heat is lost indifferently in all directions is called radiation. These two processes are entirely different in their nature, laws, and mechanism ; but we have to treat of both in the present article. 2. To illustrate how the third method by which heat can be transferred, viz., conduction (see HEAT, vol. xi. p. 577), is involved in this process, let the cannon ball (which for this purpose should be a large one) be again heated and at once immersed in water until it just ceases to be luminous in the dark, and then be immediately hung up in the air. After a short period it again becomes red-hot all over, and the phenomenon then proceeds precisely as before, except that the surface of the ball does not become so hot as it was before being plunged in the water. This form of experiment, which requires that the interior shall be very considerably cooled before the surface ceases to be self- luminous, does not succeed nearly so well with a copper ball as with an iron one, on account of the comparatively high conductivity of copper. In fact, even when its surface is covered with lamp-black, to make the loss by radia- tion as great as possible, the difference of temperature between the centre and the surface of a very hot copper ball which is only an inch or two in diameter is in- considerable. 3. In conduction there is passage of heat from hotter to colder parts of the same body; in convection an irregularly heated fluid becomes hydrostatically unstable, and each part carries its heat with it to its new position. In both processes heat is conveyed from place to place. But it quite otherwise with radiation. That a body cools in co sequence of radiation is certain ; that other bodies whi absorb the radiation are thereby heated is also certain ; but it does not at all follow that what passes in the radiant form is heat. To return for a moment to the red-hot cannon ball. If, while the hand is held below it, a thick but dry plate of rock-salt is interposed between the to and the hand there is no perceptible diminution of warmth, and the temperature of the salt is not perceptibly raised by the radiation which passes through it. When a piece