798 



ROOF 



In milder and rainifr climates, roofs sloping from 

 a central ridge are the ordinary form.' (jreat Creek 



Fig. 1. 



tmildings were covered with marble slabs, carefully 

 grooveoT together ; in (iininum Creek and Italian 

 buildings roofing tiles are used. In tin- rainy 

 climate north of the Alps Bteeper roofs are needed 

 to throw off rain and snow. 



Fig. 2. 



Roofs well constructed nerve to bind the walls 

 together and strengthen the building ; if too heavy 

 they crush the walls. The actual covering of the 

 roof and its supports are therefore made as light as 

 possible, and the strength concentrated in 'prin- 

 cipals' or 'trusses.' Fig. 1 represent* a king-post 

 roof ( A being the king-post ), and fig. 2 a queen- 

 post roof ( B, 15 being the queen-post* ). The latter 

 IB used for wider spans, and leaves the centre clear 

 for attics. Early Christian basilicas (and prob- 

 ably the Roman 'basilicas ) had such roofs. In the 

 early Gothic style the king-post was carved and 

 the tie-beam moulded. The Decorated style intro- 

 duced an arch or a scries of cants (fig. 3). As the 

 style progressed curved braces were placed under 

 the tie-beam, to support it ; these were carved, and 

 rested on elegant corbels, the spandrels between 



;he braces and the wall being filled with tracery. 

 In the Perpendicular style the central part of the 

 tie-beam U cut away, and the lieautiful hamiiier- 

 beam roofs of the [>eriod become usual (see fig. 4). 

 The roof of Westminster Hall is one of the finest 



ROOK 



example* of this kind of roof. These HJM-II timber- 

 riMifs are much used in Kngland lioth in churches 

 and halls, Inn aluoad cliielly in the latter, a- the 

 church riMifs were more frequently vaulted. In 



Fig. 4. 



modern times, when great spans have to lie roofed 

 over, combinations similar to those used in lattice 

 bridges (see BRIDGE, Vol. II. p. 411) are required. 

 Iron has been introduced, and by means of it, spaces 

 of almost any width ran be roofed over. See also 

 CEILING, MANSARD ROOF, FAN-TRACER v, \c. 



Rook (Corrns frmiili <fii.t i. a species of Crow, 

 common in Britain and in many parts of Europe 

 and Asia, especially in northern and central regions. 

 In late autumn there is a migration from the Con- 

 tinent to the eastern shores of Britain, and a return 

 in early spring. Some of the characters <>f the 

 rook have been contrasted with those of other 

 species of Corvus in the article CROW. The plum 

 is bluish black; the forehead, cheeks, and throat 

 are bare ; the bill, legs, and feet are black. White 

 and piebald spots sometimes occur. The rook 

 doea not breed till it is about two years old. 

 The nest, built of twigs with a lining of grass 

 and roots, is almost always on a lofty tree. The 

 noi-v cawing of the builders in March is one. of the 

 familiar signs of departing winter. The eggs (three 

 to five) are bluish green with olive-brown mark- 

 ings. As to food, the rook is almost omnivorous, 

 but it depends in great part on insects and grubs. 

 Unlike the crow, tne rook is characteristically a 

 social bird, feeding in great flocks, nesting in rook- 

 eries, and some! inies combining to beat off a common 

 foe. Confident perhaps in their numciie.il strength, 

 and reliant on their habit of posting sentinels, 

 rooks are by no menus shy, for they sometimes 

 ne-i in the trees of a town garden, and. though 

 much afraid of a gun, soon grow accustomed to 

 scarecrows and noise. They are very wide-awake 

 birds, exhibiting no small degree of that acuti 

 which is often displayed by gregarious birds and 

 lieasts. They show sagacity in ch-Kising fit trees 

 on which to nest, in posting sentinels who warn 

 tl thers when danger threaten-, and in distin- 

 guishing real from fictitious sources of alarm. 

 Though quarrelling and mutual nibliery 

 common during the nest-building, there is no 

 doubt that looks have a sort of social feeling, 

 which manifests itself sometimes in the punishment 

 which they inflict on an oll'ending member. The 

 same rooks seem to take possession of their old 

 nests year after year, repairing the damage done 

 by the winter storms. The male rook feeds the 



