RONDO 



ROOF 



797 



Rondo ( Ital. ), the most obvious and elementary 

 form in music, in which the first subject, clearly 

 marked out, followed by a second, more or less 

 definite, recurs again in its original key. In later 

 developments the repetition may take place twice, 

 thrice, or even four times, sometimes in part only, 

 or in modified form, the intervening sections being 

 varied in different ways. A large proportion of 

 songs and instrumental pieces are in this form ; 

 and the final movement of a sonata, symphony, or 

 concerto is frequently a rondo. 



Rondont, till 1872 a post-village of New York, 

 with a pop. of 10,000 ; now part of Kingston (q.v.) 



Ronge, JOHANN. See GERMAN CATHOLICS. 



Ronsard, PIERRE DE, French poet, born at the 

 Chateau de la Poissonniere in Vendome, September 

 11, 1524, served the Dauphin and the Due d'Orleans, 

 and accompanied James V. with his bride, Marie 

 de Lorraine, to Scotland, where he stayed three 

 years. Becoming deaf, he abandoned arms for 

 letters, and at the College Coqueret studied with 

 Du Bellay and other members of the famous 

 Pltiade. His Odes (1550) excited violent opposi- 

 tion from the older national school. In 1552 ap- 

 peared his Amours and the fifth book of his Odes, 

 his Hymn* in 1555, in 1560 (Euvres Completes, and 

 in 1572, just after the St Bartholomew massacre, 

 La Franqiade, a fragment of an epic. Charles IX. 

 heaped favours upon the lucky poet, who spent his 

 later years in lettered ease at the Abbey of Croix- 

 Val in Vendome. He died at his priory of St 

 Cosme at Tours, December 27, 1585. 



See editions by Blanchemain (1857-67) and Marty - 

 Laveaux (1887-91); Sainte-Beuve's (Euvres Choisies de 

 Rmuard ( 1828 ) ; and studies by Scheffler ( 1874 ), Chalan- 

 don (1875), Bizos (1891), and Fieri (1896). 



Rontgen, WILHELM KONRAD VON, physicist, 

 born -27th March 1845 at Lennep in Rhenish Prus- 

 sia, studied at Zurich, and became professor at 

 Strasburjj, Giessen, and ( 1885) at Wiirzburg. He 

 has contributed to science on specific heat in gases, 

 elasticity, compressibility, capillarity, the absorp- 

 tion of heat in steam and gases, and especially the 

 X-rayH, usually called after him. 



RONTGEN RAYS, a peculiar kind of radiation dis- 

 covered in 1895 by Professor Rontgen, and produced, 

 under suitable conditions, by electric discharge in 

 VACUUM TUBES ( q.v. ). They pass, with compara- 

 tively little absorption, through wood, flesh, paper, 

 and other optically opaque substances, but are 

 strongly absorbed by such substances as metals, 

 bone, and glass. In a general way the ' transpar- 

 ency" of matter to these peculiar rays decreases 

 as the density increases. Their presence is de- 

 tected by their power of producing luminescence in 

 certain fluorescent substances, such as the platino- 

 cyanide of barium, sodium, or potassium (PHOS- 

 PHORESCENCE). A screen covered with a layer of 

 these fluorescing crystals becomes brightly lumi- 

 nescent in the neighbourhood of a vacuum tube 

 which is giving out Tlontgen rays. When a slab of 

 wood or vulcanite is interposed between the vacuum 

 tube and the screen, the screen still continues to 

 glow. An arm interposed casts upon the screen a 

 shadow in which the dark central bony structure 

 can be clearly distinguished from the lighter flesh 

 shadows. These shadow-pictures may also be photo- 

 graphed on a sensitive photographic film or plate, 

 and a permanent record secured an application of 

 immense service to surgery. 



It should be noted that there is nothing really 

 extraordinary in optically opaque matter being 

 transparent to other kinds of rays. A similar 

 group of phenomena is met with in the opacity of 

 class and the transparency (or diathermancy) of 

 rock-salt to the dark heat-rays, although optically 

 both are transparent. Moreover, in their power of 



exciting fluorescent substances and in affecting the 

 photographic plate the Rontgen rays may be com- 

 pared to the actinic or ultra-violet rays. They 

 have also the property of discharging electrified 

 bodies, a property possessed under certain condi- 

 tions by violet light. But in almost all other 

 respects the Rontgen rays differ markedly from the 

 recognised forms of ether radiation. They cannot 

 be reflected or refracted ; they suffer no diffraction ; 

 they have not yet been polarised. 



As to their nature, many views have been ad- 

 vanced. The hypothesis which appears to be most 

 satisfactory is that enunciated by Sir George Stokes, 

 who regards the Rontgen rays as a succession of 

 impulses communicated to the ether in an irregular 

 or fitful manner. He gives reasons for believing 

 that the behaviour of ordinary rays of radiant 

 energy, when refracted, reflected, or diffracted, de- 

 pends upon the fact that they are composed of 

 trains of waves periodically associated. However 

 this may be and the question is one of extreme 

 difficulty there is no doubt that, in the impacts 

 of rapidly moving particles on the glass walls of 

 the vacuum tube, we have conditions favourable 

 for the production of the impulses imagined by 

 Stokes. There is strong evidence that such a bom- 

 bardment is going on. For a particular condition 

 of vacuum in a Crookes tube, there appears to be 

 projected from the negative electrode a bright beam 

 of rays, the so-called kathode rays. At a some- 

 what higher vacuum these rays cease to be visible 

 as a stream of Crookes' ' radiant matter ;' but their 

 presence is indicated by the phosphorescence pro- 

 duced on the glass walls. By suitable contrivances 

 the kathode rays can be focussed on a definite part 

 of the containing glass wall ; and it is there that 

 Rontgen rays are produced in quantity. 



In 1894 Philipp von Lenard (an Austrian pupil 

 of Hertz, and from 1896 professor at Heidelberg), 

 following out a suggestion by Hertz, observed what 

 seemed to be a passing of the kathode rays through 

 a thin piece of aluminium which formed part of the 

 containing wall of the vacuum tube. These Lenard 

 rays, in their phosphorescing effects and in their sen- 

 sitiveness to an approaching magnet, have an un- 

 doubted resemblance to the kathode rays. There is 

 no evidence, however, that the kathode rays have 

 really passed through the metal disc. It is possible 

 that their bombardment of the disc on the one side 

 may produce electrical changes capable of starting 

 similar rays on the other. This is the explanation 

 given by Professor J. J. Thomson, whose measure- 

 ment of the speed of the kathode rays quite dis- 

 proves the contention (based largely on Lenard's 

 observation ) that the kathode rays are ether vibra- 

 tions. This speed was found to be about one or 

 two hundred miles per second that is, about 

 ToWth the speed of light. It was when studying 

 the properties of the kathode and Lenard rays, 

 which, seem to differ only in their mode of produc- 

 tion, that Rontgen discovered what he himself called 

 the X-rays. A large and increasing literature is 

 now devoted to the discussion of their properties 

 and applications. 



Rood (a form of the word rod) is used of the 

 Cross of Christ, the Holy Rood, and of crosses and 

 crucifixes generally, but especially the great cruci- 

 fix which in mediaeval churches stood on the rood- 

 screen (see SCREEN). As a measure of surface, a 

 rood is the fourth part of an acre, and contains 40 

 square poles or perches, or 1210 square yards. The 

 square rod or rood used in estimating mason-work 

 is equal to 272J square feet. 



Roof. In warm countries, such as India, flat roofs, 

 covered with cement, are usual. Those of Palestine, 

 Egypt, and Assyria also were flat, and were composed 

 of wooden beams covered with thick layers of earth. 



