ROOD 



the positive electrode or anode 

 and if these emanations, or so- 

 called cathode rays, strike upon 

 matter, then, in addition to induc- 

 ing phosphorescence and raising 

 the temperature, they give rise to 

 the production of another kind of 

 rays which differ from the cathode 

 rays and from ordinary light rays 

 in very many particulars. These 

 rays were first found by Professor 

 Rontgen in 1893 and announced in 

 1895. Many experiments have 



Early Gothic hih pitched Roof 



Principal 



lie Beam ' 



Georgian Hipped Roof 



Purli, 



Boot Diagrams illustrating types 01 

 sloping roof construction 



cince been conducted with them, 

 and their power of penetrating 

 many kinds of ordinary matter to 

 a differential extent has proved of 

 great value in diagnostic surgery 

 by affording means of taking X- 

 ray photographs or skiagrams. 

 Their nature is, however, not yet 

 completely cleared up, because 

 they do not seem to answer the 

 tests which reconcile other forms 

 of light with the theory of wave 

 motion. See X-Bays. 



6693 



Rood (A.S. rod, cross). Old 

 name for a cross or crucifix. It i? 

 specially used for the great crucifix 

 which in English churches, from 

 the 14th century to the reign of 

 Elizabeth, generally stood on the 

 rood-screen dividing the chancel 

 from the nave. At the foot were 

 often figures of the Virgin and S. 

 John the Evangelist. In somo 

 churches a gallery, from which 

 parts of the service were recited 

 ran along the top of the screen 

 This was called the rood-loft 01 

 lube" ; and a staircase in the 

 masonry of one of the piers, called 

 the rood-stairs, still seen in many 

 churches, gave access to it. Modern 

 roods occasionally replace those 

 destroyed at the Reformation. 

 See Doom ; Holyrood. 



Rood. Unit of land or super- 

 ficial measure, equal to one-fourth 

 of an acre. It is divided into 40 

 rods, or 1,210 sq. yds. The name 

 is cognate with rod, and probably 

 originally denoted the wand first 

 used in measuring land. 



Roof. Part of a building which, 

 being nearest to the sky, protects 

 the interior from sun and rain. In 

 the hot, nearly rainless countries 

 of the East the prevalent type of 

 roof is flat. Where heavy rainfall 

 or snowfall may occur it is sloped, 

 the angle of the slope varying 

 with, and often being character- 

 istic of, the particular style of 

 architecture employed. The aver- 

 age slope of an ancient Greek roof 

 was not more than 16 degrees, that 

 of Roman, Romanesque, and Re- 

 naissance styles was some six de- 

 grees steeper, while the Gothic 

 pitch sometimes reached as much 

 as 60 degrees. 



Among sloping roofs one may 

 note especially the high-pitched 

 " cradle " roof of timber, fre- 

 quently used for important build- 

 ings in the Middle Ages, which was 

 structurally a triangle inscribed by 

 a series of semi-circular arches. To 

 this class of open timber roof be- 

 longs, also, the beautiful hammer- 

 beam roof of the Perpendicular 

 period (q.v.). The curb roof, of 

 which the Mansard roof and the 

 French roof are varieties, is one 

 in which the line of the slope is 

 bent on two or four sides. The 

 gabled roof is a ridge roof ending 

 in a gable (q.v.) ; the hipped roof, 

 characteristic of Georgian archi- 

 tecture, is one in which the inward 

 slope from wall-plate to ridge is at 

 the same angle on the four sides ; 

 an M roof is composed of two 

 parallel ridges separated by a valley 

 or gutter ; a lean-to roof is a 

 single slope such as that covering 

 the aisle of a church. 



In connexion with roof construc- 

 tion, the chief problem facing the 



ROOK 



Rood. Cross above chancel rail in 

 Westminster Cathedral, London 



medieval builders was to prevent 

 the downward and outward thrust 

 of the roof from exercising too 

 much pressure on the walls. This 

 they accomplished by the counter- 

 thrust of the flying buttress and by 

 strengthening the framework of 

 the roof itself by a solid tie-beam, 

 extending from wall to wall, and 

 by trusses, at the same time using 

 as light a material as possible for 

 the roof covering. Tiles have been 

 the favourite weathering materials 

 from classic times. Lead and 

 copper have been used in Franco 

 and Great Britain, and in the 

 U.S.A. the roofs are often pro- 

 tected by tin plates. Roofs of very 

 large span, e.g. rly. stations, are 

 commonly constructed of iron or 

 steel and glazed to admit light. 

 Cottages are often roofed with 

 thatch, or with stone or slate in 

 certain districts. See Architec- 

 ture ; Building ; Mansaid. 



Rook (Corvus frugilegus). Com- 

 mon bird of the crow family. The 

 plumage is black with purple re- 

 flections, and _ , . ., 



the length of ' 

 the bird is 18 

 ins. 1 1 i s 

 readily distin- 

 guished from 

 the crow by 

 the bare whit- 

 i s h patch of 

 skin surround- 

 ing the base of 

 the beak. It is 

 common in 

 Great Britain, 

 and nests in large colonies in the 

 tops of high trees, preferably near 

 human dwellings. 



About March the old nests, which 

 are made of sticks and lined with 

 grass, are repaired or new ones 

 built. Five or six eggs are laid, 



Rook. Gregarious 



bird of the crow 



family 



W.S. Berridge, F.Z.S. 



