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Rh sleepers (which are of iron) are very portable, and skilled labour is not required to lay or to take them up; the making of a “turn-out” is easy, by taking out a 15 ft. section of the way and substituting a section with points and crossings. The safe load per wheel varies between 12 cwt. on a 10 in. 16 &#x2114; wheel and 40 cwt. on an 18 in. 56 &#x2114; wheel. The rolling stock is constructed either for farm produce or heavy minerals, the latter holding 10 to 27 cub. ft. For timber, 4 or 5 ft. bogies can be used. A useful wagon for agricultural transport on a 24 in. gauge line is 16 ft. long by 5 ft. wide; it weighs 72 cwt. and costs £30. A portable line of this kind will have 20 &#x2114; steel rails and 2112 steel sleepers—4 ft. 6 in. long—to a mile, laid 2 ft. 6 in. apart centre to centre. The total cost per mile of such a line, including all bolts, nuts, fish-plates and fastenings, ready for laying, delivered in the United Kingdom, is under, £500 a mile.

See Evans Austin, The Light Railways Act 1896, which contains the rules of the Board of Trade; W. H. Cole, Light Railways at Home and Abroad; Lieut.-Col. Addison, Report to the Board of Trade (1894) on Light Railways in Belgium.

 RAIMBACH, ABRAHAM (1776–1843), English line-engraver, a Swiss by descent, was born in London in 1776. Educated at Archbishop Tenison’s Library School, he was an apprentice to J. Hall the engraver from 1789 to 1796. For nine years part of his working-time was devoted to the study of drawing in the Royal Academy and to executing occasional engravings for the booksellers, whilst his leisure hours were employed in painting portraits in miniature. Having formed an intimacy with Sir David Wilkie, Raimbach in 1812 began to engrave some of that master’s best pictures. At his death, in 1843, he held a gold medal awarded to him for his “Village Politicians” at the Paris Exhibition of 1814. He was elected corresponding member of the Institute of France in 1835.

 RAIMUND, FERDINAND (1790–1836), Austrian actor and dramatist, was born on the 1st of June 1790, in Vienna. In 18121. he acted at the Josefstädter Theater, and in 1817 at the Leopoldstädter Theater. In 1823 he produced his first play, Der Barometermacher auf der Zauberinsel, which was followed by Der Diamant des Geislerkönigs (1824) and the still popular Bauer als Millionär. The last-mentioned play, which appeared in 1826, Der Alpenkönig und der Menschenfeind (1828) and Der Verschwender (1833) are Raimund’s masterpieces. He committed suicide on the 5th of September 1836, owing to the fear that he had been bitten by a mad dog. Raimund was a master of the Viennese Posse or farce; his rich humour is seen to best advantage in his realistic portraits of his fellow-citizens.

 RAIN (O.E. regn; the word is common to Teutonic languages, cf. Ger. Regen, Swed. and Dan. regn; it has been connected with Lat. rigare, to wet, Gr. ), the water vapour of the atmosphere when condensed into drops large enough to be precipitated upon the earth. Hence the term is extended to signify the fall of such drops in a shower, and in the plural, “the rains,” it signifies the rainy seasons in India and elsewhere where under normal climatic conditions such seasons are clearly distinguished from the dry. A rain-band is “a dark band in the solar spectrum, caused by the presence of water-vapour in the atmosphere” (New Engl. Dict.); a rain-gauge is an instrument used to measure the amount of rainfall (see, where the whole subject of precipitation is fully treated).

 RAINBOW, formerly known as the iris, the coloured rings seen in the heavens when the light from the sun or moon shines on falling rain; on a smaller scale they may be observed when sunshine falls on the spray of a waterfall or fountain. The bows assume the form of concentric circular arcs, having their common centre on the line joining the eye of the observer to the sun. Generally only one bow is clearly seen; this is known as the primary rainbow; it has an angular radius of about 41°, and exhibits a fine display of the colours of the spectrum, being red on the outside and violet on the inside. Sometimes an outer bow, the secondary rainbow, is observed; this is much fainter than the primary bow, and it exhibits the same play of colours, with the important distinction that the order is reversed, the red being inside and the violet outside. Its angular radius is about 57°. It is also to be noticed that the space between the two bows is considerably darker than the rest of the sky. In addition to these prominent features, there are sometimes to be seen a number of coloured bands, situated at or near the summits of the bows, close to the inner edge of the primary and the outer edge of the secondary bow; these are known as the spurious, supernumerary or complementary rainbows.

The formation of the rainbow in the heavens after or during a shower must have attracted the attention of man in remote antiquity. The earliest references are to be found in the various accounts of the Deluge. In the Biblical narrative (Gen. ix. 12–17) the bow is introduced as a sign of the covenant between God and man, a figure without a parallel in the other accounts. Among the Greeks and Romans various speculations as to the cause of the bow were indulged in; Aristotle, in his Meteors, erroneously ascribes it to the reflection of the sun’s rays by the rain; Seneca adopted the same view. The introduction of the idea that the phenomenon was caused by refraction is to be assigned to Vitellio. The same conception was utilized by Theodoric of Vriberg, a Dominican, who wrote at some time between 1304 and 1311 a tract entitled De radialibus impressionibus, in which he showed how the primary bow is formed by two refractions and one internal reflection; i.e. the light enters the drop and is refracted; the refracted ray is then reflected at the opposite surface of the drop, and leaves the drop at the same side at which it enters, being again refracted. It is difficult to determine the influence which the writings of Theodoric had on his successors; his works were apparently unknown until they were discovered by G. B. Venturi at Basel, partly in the city library and partly in the library of the Dominican monastery. A full account, together with other early contributions to the science of light, is given in Venturi’s Commentari sopra la storia de la Teoria del Ottica (Bologna, 1814). John Fleischer (sometimes incorrectly named Fletcher), of Breslau, propounded the same view in a pamphlet, De iridibus doctrina Aristotelis et Vitellonis (1574); the same explanation was given by Franciscus Maurolycus in his Photismi de lumine et umbra (1575).

The most valuable of all the earlier contributions to the scientific explanation of rainbows is undoubtedly a treatise by Marco Antonio de Dominis (1566–1624), archbishop of Spalatro. This work, De radiis visūs et lucis in vitris perspectivis et iride, published at Venice in 1611 by J. Bartolus, although written some twenty years previously, contains a chapter entitled “Vera iridis tota gene ratio explicatur,” in which it is shown how the primary bow is formed by two refractions and one reflection, and the secondary bow by two refractions and two reflections. Descartes strengthened these views, both by experiments and geometrical investigations, in his Meteors (Leiden, 1637). He employed the law of refraction (discovered by W. Snellius) to calculate the radii of the bows, and his theoretical angles were in agreement with those observed. His methods, however, were not free from tentative assumptions, and were considerably improved by Edmund Halley (Phil. Trans., 1700, 714). Descartes, however, could advance no satisfactory explanation of the chromatic displays; this was effected by Sir Isaac Newton, who, having explained how white light is composed of rays possessing all degrees of refrangibility, was enabled to demonstrate that the order of the colours was in perfect accord with the requirements of theory (see Newton’sOpticks, book i. part 2, prop. 9).

The geometrical theory, which formed the basis of the investigations of Descartes and Newton, afforded no explanation of the supernurnerary bows, and about a century elapsed before an explanation was forthcoming. This was given by Thomas Young, who, in the Bakerian lecture delivered before the Royal Society on the 24th of November 1803, applied his principle 