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Rh There have, from time to time, been made experiments of a similar nature, notably by Tennyson, but rhyme has retained its sway as an essential ornament of all English poetry which is not in blank verse. There have been not a few poems composed, principally in the nineteenth century, in rhyme less hexameters, and even the elegiac couplet has been attempted. The experiments of Longfellow, Clough, Kingsley and others demand respectful notice, but it is more than doubtful whether any one of these, even the mellifluous Andromeda of the last-named writer, is really in harmony with the national prosody.

In Germany a very determined attack on rhyme was made early in the seventeenth century, particularly by a group of aesthetic critics in the Swiss universities. They attacked rhyme as an artless species of sing-song, which deadened and destroyed the true movement of melody in the rhythm. The argument of this group of critics had a deep influence in German practice, and led to the composition of a vast number of works in unrhymed measures, in few of which, however, is now found a music which justifies the experiment. Lessing recalled the German poets to a sense of the beauty and value of rhyme, but the popularity of Klopstock and his imitators continued to exercise a great influence. Goethe and Schiller, without abandoning rhyme altogether, permitted themselves a great liberty in the employment of unrhymed measures and in imitation of classic metres. This was carried to still greater lengths by Platen and Heine, the rhymeless rhythm of the last of whom was imitated in English verse by Matthew Arnold and others, not without an occasional measure of success. In France, on the other hand, the empire of rhyme has always been triumphant, and in French literature the idea of rhymeless verse can scarcely be said to exist. There the rime pleine or riche, in which not merely the sound but the emphasis is perfectly identical, is insisted upon, and a poet who rhymed as Mrs Browning did, or made “ flying ” an equivalent in sound to “ Zion,” would be deemed illiterate.

In French, two species of rhyme are accepted, the feminine and the masculine. Feminine rhymes are those which end in a mute e, masculine those which do not so end. The Alexandrine, which is the classical metre in French, is built up on what are known as rimes croisées, that is to say a couplet of masculine rhymes followed by a couplet of feminine, and that again by masculine. This rule is unknown to the medieval poetry of France.

In Italian literature the excessive abundance and facility of rhyme has led to a rebellion against its use, which is much more reasonable than that of the Germans, whose strenuous language seems to call for an emphatic uniformity of sound. But it was the influence of German aesthetics which forced upon the notice of Leopardi the possibility of introducing rhymeless lyrical measures into Italian verse, an innovation which he carried out with remarkable hardihood and success. The rhymeless odes of Carducci are also worthy of admiration, and may be compared by the student with those of Heine and of Matthew Arnold respectively. Nevertheless, in Italian also, the ear demands the pleasure of the full reiterated sound, and the experiments of the eminent poets who have rejected it have claimed respect rather than sympathy or imitation. At the close of the 19th century, particularly in France, where the rules of rhyme had been most rigid, an eliort to modify and minimise these restraints was widely made. There is no doubt that the laws of rhyme, like other artificial regulations, may be too severe, but there is no evidence that the natural beauty which pure rhyme introduces into poetry is losing its hold on the human ear or is in any real danger of being superseded by accent or rhythm.

See Joseph B. Mayer, A Handbook of Modern English Metre (Cambridge, 1903); J. Minor, Neuhochdeutsche Metrik (Strassburg, 1893); J. B. Schutze, Versuch einer Theorie des Reimes nach Inhalt und Form (Magdeburg, 1802).

 RHYMNEY, an urban district in the western parliamentary division of Monmouthshire, England, on the borders of Glamorganshire, 22 m. N. by W. of Cardiff, on the Rhymney, the London & North-Western, and the Brecon & Merthyr railways. Pop. (1901), 7015. The Rhymney river, in the upper valley of which this town lies, forms almost throughout its course, to the estuary of the Severn near Cardiff, the boundary between England and Wales (Monmouthshire and Glamorganshire). In its upper part the valley, like others adjacent and parallel to it, is populous with mining townships, and the town of Rhymney owes its importance to the neighbouring coal-mines and to its iron and steel works, which employ nearly the whole population. The works of the Rhymney Iron Company, including blast furnaces and rolling mills, are among the largest of the kind in England.

 RHYOLITE (Gr. ῥεῖν, to flow, because of the frequency with which they exhibit fluxion structures), the group name of a type of volcanic rock, occurring mostly as lava flows, and characterized by a highly acid composition. They are the most siliceous of all lavas, and, with the exception of the dacites, are the only lavas which contain free primary quartz. In chemical composition they very closely resemble the granites which are the corresponding rocks of plutonic or deep-seated origin; their minerals also present many points of similarity to those of granite though they are by no means entirely the same. Quartz, orthoclase and plagioclase felspars, and biotite are the commonest ingredients of both rocks, but the quartz of rhyolites is full of glass enclosures and the potash felspar is pellucid sanidine, while the quartz of granite contains dust-like fluid cavities of very minute size and its potash felspar is of the turbid variety which is properly called orthoclase. The granites also are holocrystalline, while in the rhyolites there are usually porphyritic crystals floating in a fine ground-mass. Rhyolites have also been called liparites because many of the lavas of the Lipari Islands are excellent examples of this group. Above all rocks they have a disposition to assume vitreous forms, as when fused they crystallize with great difficulty. Hence it has long baffled experimenters to produce rhyolite synthetically by fusion; it is stated that these difficulties have now been overcome, but geologists believe that the presence of steam and other gases in the natural state expedites crystallization. In crucibles these cannot be retained at the temperatures employed; when the rocks are melted the gases escape and on cooling a pure glass is formed. The vitreous forms of rhyolite are known as, and  (qq.v.).

The minerals of the first generation, or phenocrysts, of rhyolite are generally orthoclase, oligoclase, quartz, biotite, augite or hornblende. The felspars are usually glassy clear, small but of well-developed crystalline form: the potash felspar is sanidine, usually Carlsbad twinned; the soda-lime felspar is a most always oligoclase, with characteristic polysynthetic structure. Both of these may be corroded and irregular in their outlines; their cleavage and twinning then distinguish them readily from quartz. Glass enclosures, sometimes rectangular with small immobile bubbles, are frequent. The quartz occurs as blebs or sub-rounded grains, which are corroded double hexagonal pyramids. Its glass enclosures are many and nearly always rounded or elliptical in section. No proper cleavage is seen in the quartz, though arcuate (conchoidal) fractures may often be noticed; they may have been produced by strain on cooling. Phenocrysts of micropegmatite are known in some rhyolites; they may have the shape of felspar or of quartz crystals; in the former case Carlsbad twinning is by no means uncommon, but in other cases hour-glass structure is very conspicuous. Biotite is always deep brown or greenish brown, in small hexagonal tablets, generally blackened at their edges by magmatic corrosion. Muscovite is not known in rhyolites. Hornblende may be green or brown; in the quartz-pantellarites it sometimes takes the form of strongly pleochroic brown cossyrite. Like biotite it is eumorphic but often corroded in a marked degree. Augite, which is equally common or more common than the other ferro-magnesian minerals, is always green; its crystals are small and perfectly shaped, and corrosion phenomena are very rarely seen in it. Zircon, apatite and magnetite are always present in rhyolites, their crystals being often beautifully perfect though never large. Olivine is never a normal ingredient, but occurs in the hollow spherulites or lithophysae of some rhyolites with garnet, tridymite, topaz and other minerals which indicate pneumatolytic action. Among the less common accessory minerals of the rhyolites are cordierite in crystals which resemble hexagonal prisms but break up under polarized light into six radiating sectors owing to complicated twinning: they weather to green aggregates of chlorite and Muscovite (pinite); garnet, sphene and orthite may also be met with in rhyolites.

The ground-mass of rhyolitic rocks is of three distinct types which are stages in crystalline development, viz. the vitreous, the felsitic or cryptocrystalline, and the microcrystalline. Hence some authorities have proposed to subdivide the group