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and his unbroken friendship for Boileau are the sole points of his life which are entirely creditable to him. His conduct to Molière and to Nicole cannot be excused; his attitude towards his critics and his rivals was querulous and spiteful; his relation to Corneille contrasts strikingly with the graceful position which young men of letters, sometimes by no means his inferiors, have often taken up towards the surviving glories of a past generation; his "conversion," though there is no just cause for branding it as hypocritical, appears to have been a singularly accommodating one, enabling him to tolerate adultery, to libel his friends in secret, and to flatter greatness unhesitatingly. None of these things perhaps are very heinous crimes, but they are all of the class of misdoing which, fairly or unfairly, mankind are apt to regard with greater dislike than positive misdeeds of a more glaring but less unheroic character.

The personality of an author is, however, by all the laws of the saner criticism, entirely independent of the rank to be assigned to his work, and, as in other cases, the strongest dislike for the character of Racine as a man is compatible with the most unbounded admiration of his powers as a writer. But here again his injudicious admirers have interposed a difficulty. There is a theory common in France, and sometimes adopted out of it, that only a Frenchman, and not every Frenchman, can properly appreciate Racine. The charm of his verse and of his dramatic presentation is so esoteric and delicate that foreigners cannot hope to taste it. This is of course absurd, and if it were true it would be fatal to Racine's claims as a poet of the highest rank. Such poets, such writers, are not parochial or provincial, and even the greatest nations are but provinces or parishes in the realm of literature. Homer, Shakespeare, Dante, even Molière, Rabelais, Goethe, are not afraid to challenge the approval of the whole world, and the whole world is not found incompetent or unwilling to give it. Nor need Racine in reality avail himself of this unwise pretension. Judged by the common tests of literature he is a consummate artist, but he is scarcely a great poet, for his art, though unsurpassed in its kind, is narrow in range and his poetry is neither of the highest nor of the most genuine.

He may be considered from two very different points of view,(1) as a playwright and poetical artificer, and (2) as a dramatist and a poet. From the first point of view there is hardly any praise too high for him. He did not invent the form he practised, and those who, from want of attention to the historical facts, assume that he did are unskilful as well as ignorant. When he came upon the scene the form of French plays was settled, partly by the energetic efforts of the Pléiade and their successors, partly by the reluctant acquiescence of Corneille. It is barely possible that the latter might, if he had chosen, have altered the course of French tragedy; it is nearly certain that Racine could not. But Corneille, though he was himself more responsible than any one else for the acceptance of the single-situation tragedy, never frankly gave himself up to it, and the inequality of his work is due to this. His heart was, though not to his knowledge, elsewhere, and with Shakespeare. Racine, in whom the craftsman dominated the man of genius, worked with a will and without any misgivings. Every advantage which the Senecan tragedy adapted to modern times was capable of he gave it. He perfected its versification; he subordinated its scheme entirely to the ono motive which could have free play in it, the display of a conventionally intense passion; he set himself to produce in verse a kind of Ciceronian correctness. The grammar criticisms of Vaugelas and the taste criticisms of Boileau produced in him no feeling of revolt, but only a determination to play the game according to these new rules with triumphant accuracy. And he did so play it. He had supremely the same faculty which enabled the rhétoriqueurs of the 15th century to execute apparently impossible tours de force in ballades couronnées, and similar tricks. He had besides a real and saving vein of truth to naturo, which preserved him from tricks pure and simple. He would be and he was as much a poet as prevalent taste would let him be. The result is that such plays as Phèdre and Andromaque are supreme in their own way. If the critic will only abstain from thrusting in tierce, when according to the particular rules he ought to thrust in quart, Racine is sure to beat him.

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however, he deliberately cut himself off. Of the whole world which is subject to the poet he took only a narrow artificial and conventional fraction. Within these narrow bounds he did work which no admirer of literary craftsmanship can regard without admiration. But at the same time no one speaking with competence can deny that the bounds are narrow. It would be unnecessary to contrast his performances with his limitations so sharply if those limitations had not been denied. But they have been and are still denied by persons whose sentence carries weight, and therefore it is still necessary to point out the fact of their existence.

Nearly all Racine's works are mentioned in the above notice. There is here no room for a bibliographical account of their separate appearances. The first collected edition was in 1675-76, and contained the nine tragedies which had then appeared. The last and most complete which appeared in the poet's lifetime (1697) was revised by him, and contains the dramas and a few miscellaneous works. Like the editio princeps, it is in 2 vols. 12mo. The posthumous editions are innumerable and gradually became more and more complete. The most noteworthy are the Amsterdam edition of 1722; that by Abbé d'Olivet, also at Amsterdam, 1743; the Paris quarto of 1760; the edition of Luneau de Boisjermain, Paris and London, 1768; the magnificent illustrated folios of 1805 (Paris); the edition of Germain Garnier with La Harpe's commentary, 1807; Geoffroy's of the next year; Aimé Martin's of 1820; and lastly, the grands écrivains edition of Paul Mesnard (Paris, 1865-73). This last contains almost all that is necessary for the study of the poet, and has been chiefly used in preparing the above notice. Louis Racine's Life was first published in 1747. Translations and imitations of Racine are innumerable. In English the Distressed Mother of Philips and the Phædra and Hippolytus of Smith, both composed more or less under Addison's influence, are the most noteworthy. (G. SA.)

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RACKETS. Like tennis, this game of ball is of French origin, and its name is derived from "raquette," the French term for the bat used in the pastime. In the United Kingdom it is not so universally pursued as cricket and football, and is essentially an indoor game, which is played only in prepared and covered courts. Such buildings have been erected at many of the large public schools, at the universities, and in garrison towns, where will be found the chief exponents of rackets, a game which requires active running powers, quick eyesight, and dexterity of hand. The old " open" courts, which merely consisted of a plain wall without any side walls, are now almost obsolete and need not be further mentioned. The usual dimensions of a close " court are 80 feet by 40 feet for fourhanded matches, whilst 60 feet by 30 feet are sufficient for a single match. Sometimes courts are built of an intermediate size so as to be available for either single or double matches. The front wall of a court should be 40 feet high, the back one 14 feet, the space over the latter being utilized by a gallery for spectators, umpire, and marker. The side walls are 40 feet throughout, in

But there is a higher game of criticism than this, and this game Racine does not attempt to play. He does not even attempt the highest poetry at all. His greatest achievements in pure passion-high the foiled desires of Hermione and the jealous frenzy of Phèdre -are cold, not merely beside the crossed love of Ophelia and the remorse of Lady Macbeth, but beside the sincerer if less perfectly expressed passion of Corneille's Cléopâtre and Camille. parts he fails still more completely. As the decency of his stage would not allow him to make his heroes frankly heroic, so it would not allow him to make them utterly passionate. He had, moreover, cut away from himself by the adoption of the Senecan model all the opportunities which would have been offered to his remarkably varied talent on a freer stage. It is indeed tolerably certain that he never could have achieved the purely poetical comedy of As You Like or the Vida es Sueno, but the admirable success of Les Plaideurs makes it at least probable that he might have done something in a lower and a more conventional style. From all this,

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order to support the roof. This must be well lit with skylights carried on light iron girders and protected inside with wire-work in order to ward off damage from the balls. Bricks make the best walls, which must be plastered inside with Roman cement or plaster of Paris, set to a perfectly level surface in order that the balls may rebound evenly. In the military officers' courts in India this plaster is painted white for the sake of XX.

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coolness, and black balls are in vogue. In England black | paint and white balls are used. In cool climates asphalt makes the best flooring. In the tropics stone paving, perfectly evenly set, or some similar material, must be used. Gutta-percha soles to the shoes of the players are indispensable, to prevent slipping and to preserve the evenness of the flooring. The narrow entrance door, made of very hard wood, is situated in the centre of the back wall and must be perfectly flush with the same on the inside. The bottom of the front wall is covered with hollow deal sounding boarding up to a height of 2 feet 2 inches, where is the "line." The sound betrays a ball striking the boarding below the line, which throws it out of play. At 7 feet 9 inches above the level of the floor comes another white line across the front wall, termed the "cut line," because the in-player, when serving, must first make the ball rebound from the front wall above this line. Across the floor, varying in position according to the length of the court, is the "short line," so called because an out-player is not bound to take any ball served which falls between it and the front wall. The space between here and the back wall is divided into two equal-sized parallelograms by a line drawn down to the doorway. As the front wall is faced, these are called "right" and "left" courts. An in-player serving from one side must make the ball fall in the other court after rebounding from the front wall. The "service spaces," in which an in-player stands when serving, are 8 feet 6 inches deep from the short line and 6 feet 6 inches wide from each side wall.

The game is played with no other implements but bats and balls. The striking portion of the former is ovalshaped and strung tightly across with catgut. The handle is of pliant ash covered with leather in order to give the hand a tight grip. The balls are about 1 inches in diameter, and very hard in order to rebound evenly and quickly.

2. The going in first, whether odds be given or not, to be decided by lot; but one hand only then is to be taken.

3. The ball to be served alternately from right and left, beginning whichever side the server pleases.

4. In serving, the server must have one foot in the space marked off for that purpose. The out-player to whom he serves may stand where he pleases, but his partner and the server's partner must both stand behind the server till the ball is served.

5. The ball must be served above, and not touching the line on the front wall, and it must strike the floor, before it bounds, within and not touching the lines enclosing the court on the side opposite to that in which the server stands.

6. A ball served below the line, or to the wrong side, is a fault, but it may be taken, and then the ace must be played out, and counts.

7. In serving, if the ball strikes anywhere before it reaches the front wall, it is a hand out.

8. In serving, if a ball touches the server or his partner before it has bounded twice it is a hand out, whether it was properly served or not.

In a four-handed game we will suppose A and B to be playing against C and D and that the former couple have won the choice of first innings. A accordingly commences serving from the right service space into the left court, that being the most difficult one to return the ball from. B stands behind A to return any balls for his side in the back portion of the court. C stands where he likes ready to take the ball about to be served by A, whilst C's partner, D, places himself between A and B to take the fore court play for his side. For A's service to be good his ball must first strike the front wall above the cut line, and secondly rebound from the floor of the left-hand court, though whether it strike the side or back walls or not after rebounding from the front wall is immaterial. If these rules are complied with, C is bound to return the ball, at its first bound off the floor, on to the front wall above the soundingboard. If he does not succeed A and B score one ace in their favour. If C achieves his purpose the game is continued by one of either side returning the ball alternately, till a player either strikes the sounding board, skies it into the roof or gallery, or strikes it later than the first bound off the floor. If A or B makes the first failure A is out. If it is C or D, the in-side scores an ace, and A continues serving alternately from each service space. The out-player may take a faulty service at his own option. If he does, the ace is played out in the usual way. When A is put out C goes in, then D, and lastly A's partner B, and so on in the same rotation. B is not allowed to follow A's first hand, as the latter has the advantage of possibly scoring the first ace. The player who gains the last ace of a game continues serving for the next. The mode of procedure in a single-handed match is precisely the same, each player going in alternately, but having no partner to aid him. It often happens that both sides go in and out several times running without scoring. The most difficult kind of services to take are the sharp "cut," which strikes the front wall just above the cut line and rebounds with great velocity, and the "nick" into the back corner of the court served into. Other strokes are the "drop," which places the ball only just above the wooden board, making it fall almost dead; the "volley," in which the ball is struck in the full before touching the floor; and lastly, the "cut," by which the ball acquires a twisting or rotatory spin as well as a forward motion caused by a descending diagonal stroke with the bat. The following are the rules of rackets as drawn up and used at Prince's Club, London, the leading racket club of the United Kingdom.

9. It is a fault

a. If the server is not in his proper place.

b. If the ball is not served over the line.

c. If it does not fall in the proper court.

d. If it touches the roof.

e. If it touches the gallery-netting, posts, or cushions.

The out-player may take a fault if he pleases, but if he fails in putting the ball up it counts against him.

1. The game to be 15 up. At 13 all, the out-players may set it to 5, and at 14 all, to 3, provided this be done before another ball is struck.

10. Two consecutive faults put a hand out.

11. An out-player may not take a ball served to his partner.

12. The out-players may change their courts once only in each game.

13. If a player designedly stops a ball before the second bound it counts against him.

14. If a ball hits the striker's adversary above or on the knee, it is a let; if below the knee, or if it hits the striker's partner or himself, it counts against the striker.

15. Till a ball has been touched, or has bounded twice, the player or his partner may strike it as often as they please.

16. Every player should get out of the way as much as possible. If he cannot, the marker is to decide whether it is a let or not.

17. After the service, a ball going out of the court or hitting the roof is an ace; a ball hitting the gallery-netting, posts, or cushions, in returning from the front wall, is a let; but if it hits the roof before reaching the front wall it counts against the striker.

18. The marker's decision is final. If he has any doubt, he should ask advice; and, if he cannot decide positively, the ace is to be played over again. (H. F. W.) RADAUTZ, a town in the Austrian duchy of Bukowina, is situated on the Suczava, about 15 miles from the frontier of Moldavia. It was formerly the seat of a Greek bishopric, removed to Czernowitz in 1786, and possesses a cathedral with the tombs of several Moldavian princes. It contains a Government stud, and manufactures paper, glass, machinery, beer, and brandy. In 1880 Radautz had 11,162 inhabitants.

RADBERTUS, head of the Benedictine abbey of Corbie, near Amiens, from 844 to 851, and one of the most prominent theological writers of his age, was born at or near Soissons towards the close of the 8th century, and became a monk of Corbie in 814, when he assumed the cloister name of PASCHASIUS. He soon gained recognition as a learned and successful teacher, and Adalhard, St Anskar the apostle of Sweden, Odo bishop of Beauvais, and Warinus abbot of Corvey in Saxony may be mentioned among the more distinguished of his pupils. In 844 he was chosen abbot, but as a disciplinarian he was more energetic than successful, and in 867 he resigned the office. In his official capacity he took part in the synod of Chiersy which condemned Gottschalk. Of the closing period of his life nothing is known, except that it was one of great literary activity.

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His works include an Expositio in Matthæum, in twelve books, favourable specimen of the exegesis of that period, and the Liber de Corpore et Sanguine Christi, a pious and popularly written treatise, designed to prove that the elements in the sacrament are completely changed. The latter work, originally composed in 831, elicited a reply by Ratramnus, a brother monk of Corbie, who maintained that the body and blood of Christ were present in the Eucharist only spiritualiter et secundum potentiam. The De Partu Virginis of Radbertus (845) was also taken exception to by Ratramnus for its Docetic teaching as to the manner of Christ's

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RADCLIFFE, a town of Lancashire, is situated on the river Irwell, crossed by a bridge of two arches, and on the Lancashire and Yorkshire Railway, 7 miles north-west of Manchester and 2 south-west of Bury. The church of St Bartholomew dates from the time of Henry IV. ; some of the Norman portions of the building still remain. The tower was rebuilt in 1665, the north transept added in 1846, and the whole building restored in 1870-73. It possesses some good windows and several ancient monu

ments. Radcliffe Tower, dating from the 13th century, and formerly an extensive manorial residence, is now a complete ruin. Cotton-weaving, calico-printing, and bleaching are the principal industries, and there are extensive collieries in the neighbourhood. The town is governed by a local board of health established in 1866. The area of the urban sanitary district is 2453 acres, with a population in 1871 of 11,446, and in 1881 of 16,267. Radcliffe is so called from a cliff of red rock on the south side of the Irwell opposite the town. The manor was held by Edward the Confessor, and was conferred on Roger de Poictou, but was forfeited by him soon after the Domesday survey. In the reign of Stephen it was granted to Ranulph de Gernons, earl of Chester. RADCLIFFE, ANN WARD (1764-1823), novelist, was born in London on 9th July 1764. She was the author of three novels unsurpassed of their kind in English literature, The Romance of the Forest (1791), The Mysteries of Udolpho (1794), The Italian (1797). The interval of three years between the successive publications is noticeable; works so elaborate, intricate, and closely interwoven could not be written in a hurry. The second of the three novels is the one commonly associated with Mrs Radcliffe's name, but the preference is probably due to the title; each is an improvement on its predecessor, and the last is considerably the best on the whole in style as well as in plot and character. She wrote two other novels before any of these, the Castles of Athlin and Dunbayne (1789) and the Sicilian Romance (1790), but they attracted no special attention and deserve none, although in them she works with the same romantic materials-dreadful castles, wild adventures, terrible characters. One other was written after the famous three, but not published till 1826, three years after her death-Gaston de Blondeville, interesting as an elaborate study of costume and scenery, and valuable as a monument of her accurate archæological learning, but comparatively tedious as a story, though not without passages in her best style. The circumstances that turned Mrs Radcliffe to literature are not recorded in the meagre memoir published under her husband's direction. Her maiden name was Ward, and her parents, who are described as persons of great respectability, though engaged in trade," in London, had literary relations. Her husband was an Oxford graduate and proprietor and editor of the English Chronicle. After The Italian she gave up writing for publication, and was reported to have been driven mad by the horrors of her own creations. This was purely mythical. It appears that she never saw the Italian scenery which she depicts with such minuteness, and never left England but once, in the summer of 1794, after the completion of her Udolpho. A record of the tour was published in the following year, along with descriptions of a visit to the English Lakes, the beauties of which she was one of the first to celebrate. Of scenery, as might be judged from her novels, where the descriptions are often felt as a tedious impediment, Mrs Radcliffe was an enthusiastic amateur, and made driving tours with her husband every other summer through the English counties. She died in February 1823.

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As a novelist Mrs Radcliffe deserves a much higher place than is accorded to her in general estimation. Critics familiar with her. works, from Sir Walter Scott downwards, have shown themselves fully alive to the difference; but the general public confound her with puerile and extravagant imitators, who have vulgarized her favourite "properties" of rambling and ruinous old castles, dark, desperate, and cadaverous villains, secret passages, vaults, trapdoors, evidences of deeds of monstrous crime, sights and sounds of mysterious horror. She deserves at least the credit of originality, but apart from this there are three respects in which none of her numerous imitators approach her, ingenuity of plot, fertility of incident, and skill in devising apparently supernatural occurrences capable of explanation by human agency and natural coincidence. Except in her last and posthumously published work she never introduces the really supernatural, and, whether or not we agree with Sir Walter Scott that this limitation was a mistake in art, it must at least be acknowledged to impose a heavier burden on the author's

ingenuity. Her imitators found it easier to follow Horace Walpole in this point. Some of the tragic situations in The Italian are worked out with a vivid power of imagination which it would be hard to parallel in English literature outside the range of the Elizabethan drama, with the minor celebrities of which Mrs Radcliffe may fairly challenge comparison.

RADETZKY, JOHANN J. W. A. F. C., Count of RADETZ (1766-1858), field-marshal of Austria, was born at Trzebnitz in Bohemia in 1766, to the nobility of which province his family belonged. He entered a cavalry regiment in 1784 and served under Joseph II. and Laudon against the Turks in 1788 and 1789. In 1793 his regiment was sent to the lower Rhine, and from this time onwards Radetzky was engaged in the wars which were continued (with intermission) between Austria and France for the next twenty years. In 1796 he was adjutant to General Beaulieu, over whom Bonaparte won his first victories in Italy. In 1799, when the Austrians with Suwaroff's help reconquered Northern Italy, he distinguished himself at the battles of Novi and the Trebbia, displaying, according to the despatches of General Mélas, great presence of mind in the midst of extreme danger. After the defeat of Marengo he was removed from Italy to Germany, and there took part in the still more disastrous engagement of Hohenlinden. In 1805 Radetzky, now major-general, was back in Italy, serving under the archduke Charles in the successful campaign of Caldiero, the fruits of which were lost by Mack's capitulation at Ulm and the fall of Vienna. In 1809 he fought at Wagram. In 1813, when all the great powers of Europe combined against Napoleon, Radetzky was chief of the staff under Schwarzenberg, the Austrian commander-in-chief of the allied forces, and he now gained a reputation outside his own country. The plan of the battle of Leipsic is said to have been in great part Radetzky's work, and in this engagement he was wounded. He entered Paris with the allied sovereigns in March 1814, and returned with them to the congress of Vienna, where he appears to have acted as an intermediary between Metternich and the czar Alexander, when these great personages were not on speaking terms. During the succeeding years of peace he disappeared from the public view and narrowly escaped being pensioned off in 1829. The insurrection of the Papal Legations in 1831 brought him, however, into active service again; and on the retirement of General Frimont he was placed in command of all the Austrian forces in Italy, receiving in 1836 the dignity of field-marshal. Radetzky was now seventy years old, but twelve more years were to pass before the really historical part of his career opened. When he was eighty-two the revolution of 1848 broke out. Milan rose in insurrection against its Austrian rulers, and after a struggle of five days Radetzky was forced to evacuate the city. Unable to retain any hold on Lombardy, he concentrated his troops at Verona, the fortifications of which were to a great extent his own creation. Charles Albert, king of Sardinia, now declared war upon Austria, occupied Milan, and laid siege to Peschiera. Radetzky, after the arrival of reinforcements, moved southwards to Mantua, and attempted from that point to turn the Sardinian flank; he was, however, defeated on the Mincio, and Peschiera fell into the enemy's hands. Radetzky, nevertheless, was secure in the possession of Verona and Mantua; and, after being still further reinforced, he resumed the offensive in July, defeated the Sardinians at Custozza and in several other encounters, and advanced victoriously upon Milan, where, on 6th August, an armistice was concluded, the Sardinian army retiring behind the Ticino. During the succeeding months, while Vienna and the central provinces of the Austrian empire appeared likely to fall into anarchy, Radetzky's army remained firm in its loyalty to the old order of things, and declined to enter

into relations with the democratic leaders. It was in fact | These attempts, however, to perpetuate the usage were

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 Pavia, 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 superintendent 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 population (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 saltpetre. Radhanpur came under British protection in 1819, when the nawab applied for aid to check the raids of marauders. 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.

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finally discredited by Huxley's important Lectures on Comparative Anatomy (1864), in which the term was finally abolished, and the "radiate mob" finally distributed among the Echinodermata, Polyzoa, Vermes (Platyhelminthes), Coelenterata, and Protozoa. On radiate symmetry, see MORPHOLOGY. Compare also CUVIER, ANIMAL KINGDOM, ECHINODERMATA, CORALS, &c.

RADIATION AND CONVECTION. 1. When a redhot 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 process 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 simultaneously 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 experiment is made in a dark room, into which a ray of sunlight 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 RADIATA. This term was introduced by Cuvier in once immersed in water until it just ceases to be luminous 1812 to denote the lowest of his four great animal groups in the dark, and then be immediately hung up in the air. "embranchements." He defined them as possessing After a short period it again becomes red-hot all over, and radial instead of bilateral symmetry, and as apparently the phenomenon then proceeds precisely as before, except destitute of nervous system and sense organs, as having the that the surface of the ball does not become so hot as it circulatory system rudimentary or absent, and the respira- was before being plunged in the water. This form of tory organs on or coextensive with the surface of the experiment, which requires that the interior shall be very body; he included under this title and definition five considerably cooled before the surface ceases to be selfclasses,-Echinodermata, Acalepha, Entozoa, Polypi, and luminous, does not succeed nearly so well with a copper Infusoria. Lamarck (Hist. nat. d. Anim. s. Vertèbres) ball as with an iron one, on account of the comparatively also used the term, as when he spoke of the Medusa as high conductivity of copper. In fact, even when its surface radiata medusaria et anomala; but he preferred the is covered with lamp-black, to make the loss by radiaterm Radiaria, under which he included Echinodermata tion as great as possible, the difference of temperature and Medusa. Cuvier's term in its wide extension, how-between the centre and the surface of a very hot copper ever, passed into general use; but, as the anatomy of the ball-which is only an inch or two in diameter—is indifferent forms became more fully known, the difficulty of considerable. including them under the common designation made itself 3. In conduction there is passage of heat from hotter to increasingly obvious. Milne-Edwards removed the Poly-colder parts of the same body; in convection an irregularly zoa; the group was soon further thinned by the exclu-heated fluid becomes hydrostatically unstable, and each sion of the Protozoa on the one hand and the Entozoa part carries its heat with it to its new position. In both on the other; while in 1848 Leuckart and Frey clearly processes heat is conveyed from place to place. But it is distinguished the Colenterata from the Echinodermata as quite otherwise with radiation. That a body cools in cona separate sub-kingdom, thus condemning the usage by sequence of radiation is certain; that other bodies which which the term still continued to be applied to these two absorb the radiation are thereby heated is also certain; groups at least. In 1855, however, Owen included under but it does not at all follow that what passes in the radiant Lamarck's term Radiaria the Echinodermata, Anthozoa, form is heat. To return for a moment to the red-hot Acalepha, and Hydrozoa, while Agassiz also clung to the cannon ball. If, while the hand is held below it, a thick term Radiata as including Echinodermata, Acalepha, and but dry plate of rock-salt is interposed between the ball Polypi, regarding their separation into Coelenterata and and the hand there is no perceptible diminution of warmth, Echinodermata as an exaggeration of their anatomical and the temperature of the salt is not perceptibly raised differences" (Essay on Classification, London, 1859). by the radiation which passes through it. When a piece

of clear ice is cut into the form of a large burning-glass it | evidence, are not heard by any one; when perceived at can be employed to inflame tinder by concentrating the all they are felt. sun's rays, and the lens does the work nearly as rapidly as if it had been made of glass. It is certainly not what we ordinarily call "heat" which can be transmitted under conditions like these. Radiation is undoubtedly a transference of energy, which was in the form commonly called heat in the radiating body, and becomes heat in a body which absorbs it; but it is transformed as it leaves the first body, and retransformed when it is absorbed by the second. Until the comparatively recent full recognition of the conservation and transformation of energy it was almost impossible to form precise ideas on matters like this; and, consequently, we find in the writings even of men like Prévost and Sir J. Leslie notions of the wildest character as to the mechanism of radiation. Leslie, strangely, regarded it as a species of "pulsation" in the air, in some respects analogous to sound, and propagated with the same speed as sound. Prévost, on the other hand, says, "Le calorique est un fluide discret; chaque élément de calorique suit constamment la même ligne droite, tant qu'aucun obstacle ne l'arrête. Dans un espace chaud, chaque point est traversé sans cesse en tout sens par des filets de calorique."

4. The more intensely the cannon ball is heated the more luminous does it become, and also the more nearly white is the light which it gives out. So well is this known that in almost all forms of civilized speech there are terms corresponding to our "red-hot," "white-hot," &c. | As another instance, suppose a powerful electric current is made to pass through a stout iron wire. The wire becomes gradually hotter, up to a certain point, at which the loss by radiation and convection just balances the gain of heat by electric resistance. And as it becomes hotter the amount of its radiation increases, till at a definite temperature it becomes just visible in the dark by red rays of low refrangibility. As it becomes still hotter the whole radiation increases; the red rays formerly given off become more luminous, and are joined by others of higher refrangibility. This process goes on, the whole amount of radiation still increasing, each kind of visible light becoming more intense, and new rays of light of higher refrangibility coming in, until the whole becomes white, i.e., gives off all the more efficient kinds of visible light in much the same relative proportion as that in which they exist in sunlight. When the circuit is broken, exactly the same phenomena occur in the reverse order, the various kinds of light disappearing later as their refrangibility is less. But the radiation continues, growing weaker every instant, even after the whole is dark. This simple observation irresistibly points to the conclusion that the so-called "radiant heat" is precisely the same phenomenon as "light," only the invisible rays are still less refrangible than the lowest red, and that our sense of sight is confined to rays of a certain definite range of refrangibility, while the sense of touch comes in where sight fails us. Sir W. Herschel in 1798, by placing the bulb of a thermometer in the solar spectrum formed by a flint-glass prism, found that the highest temperature was in the dark region outside the lowest visible red,-a result amply verified at the time by others, though warmly contested by Leslie.

5 This striking conclusion is not without close analogies in connexion with the other senses, especially that of hearing. Thus it has long been known that the "range of hearing" differs considerably in different individuals, some, for instance, being painfully affected by the chirp of a cricket, which is inaudible to others whose general bearing is quite as good. Extremely low notes, on the other hand, of whose existence we have ample dynamical

6. We may now rapidly run over the principal facts characteristic of the behaviour of visible rays (see LIGHT), and point out how far each has been found to characterize that of so-called "radiant heat" under similar conditions. (a) Rectilinear propagation: an opaque screen which is placed so as to intercept the sun's light intercepts its heat also, whether it be close to the observer, at a few miles from him (as a cloud or a mountain), or 240,000 miles off (as the moon in a total eclipse). (b) Speed of propagation: this must be of the same order of magnitude, at least, for both phenomena, i.e., 186,000 miles or so per second; for the sun's heat ceases to be percep. tible the moment an eclipse becomes total, and is perceived again the instant the edge of the sun's disk is visible. (c) Reflexion: the law must be exactly the same, for the heat-producing rays from a star are concentrated by Lord Rosse's great reflector along with its light. (d) Refraction: when a lens is not achromatic its principal focus for red rays is farther off than that for blue rays; that for dark heat is still farther off. Herschel's determination of the warmest region of the spectrum (§ 4 above) is another case in point. (e) Oblique radiation: an illuminated or a self-luminous surface appears equally bright however it is inclined to the line of sight. The radiation of heat from a hot blackened surface (through an aperture which it appears to fill) is sensibly the same however it be inclined (Leslie, Fourier, Melloni). (f) Intensity: when there is no absorption by the way the intensity of the light received from a luminous point-source is inversely as the square of the distance. The same is true of dark heat. But this is not a new analogy; it is a mere consequence of (a) rectilinear propagation, (g) Selective absorption : light which has been sifted by passing through one plate of blue glass passes in much greater percentage through a second plate of the same glass, and in still greater percentage through a third. The same is true of radiant heat, even when the experiment is made with uncoloured glass; for clear glass absorbs certain colours of dark heat more than others (De Laroche, Melloni). () Interference bands, whether produced by two mirrors or by gratings, characterize dark heat as well as light; only they indicate longer waves (Fizeau and Foucault). (i) Polarization and double refraction: with special apparatus, such as plates of mica split by heat into numerous parallel films, the polarization of dark heat is easily established. two of these bundles are so placed as to intercept the heat, an unsplit film of mica interposed between them allows the heat to pass, or arrests it, as it is made to rotate in its own plane (Forbes). () By proper chemical adjustments photographs of a region of the solar spectrum beyond the visible red have been obtained (Abney). We might mention more, but those given above, when considered together, are conclusive. In fact (b) or (i) alone would almost settle the question.

When

7. But there is a superior as well as an inferior limit of visible rays. Light whose period of vibration is too small to produce any impression on the optic nerve can be degraded by fluorescence (see LIGHT) into visible rays, and can also be detected by its energetic action on various photographic chemicals. In fact photographic portraits can be taken in a room which appears absolutely dark to the keenest eyesight. By one or other of these processes the solar spectrum with its dark lines and the electric arc with its bright lines have been delineated to many times the length of their visible ranges. The electric arc especially gives (in either of these ways) a spectrum of extraordinary length; for we can examine it, as we can not examine sunlight, before it has suffered any sensible absorption.

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