Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/877

R o R P 843 in which these feathers persist, the Rook may be readily known from the black form of CROW (vol. vi. p. 618) by the rich purple gloss of its black plumage, especially on the head and neck, the feathers of which are soft and not pointed. In a general way the appearance and manners of the Rook are so well known, to most inhabitants of the British Islands especially, that it is needless here to dwell upon them, and particularly its habit of forming com- munities in the breeding-season, which it possesses in a measure beyond that of any other land bird of the northern hemisphere. Yet each of these communities, or rookeries, seems to have some custom intrinsically its own, the details of which want of space forbids any attempt to set before the reader. In a general way the least-known part of the Rook's mode of life are facts relating to its migration and geographical distribution. Though the great majority of Rooks in Britain are sedentary or only change their abode to a very limited extent, it is now certain that a very considerable number visit this country in or towards autumn, not necessarily to abide here, but merely to pass onward, like most other kinds of birds, to winter further southwards ; and, at the same season or even a little earlier, it cannot be doubted that a large proportion of the young of the year emigrate in the .same direction. As a species the Rook on the European continent only resides during the whole year through- out the middle tract of its ordinary range. Further to the northward, as in Sweden and northern Russia, it is a regular summer- immigrant, while further to the southward, as in southern France, Spain, and most parts of Italy, it is, on the contrary, a regular winter-immigrant. The same is found to be the case in Asia, where it extends eastward as far as the upper Irtish and the Ob. It breeds through- out Turkestan, in the cold weather visiting Afghanistan, Cashmere, and the Punjab, and Sir Oliver St John found a rookery of considerable size at Casbin in Persia. In Palestine and in Lower Egypt it is only a winter-visitant, and Canon Tristram noticed that it congregates in great numbers about the mosque of Omar in Jerusalem. 1 There are several moot points in the natural history of the Rook which it is impossible here to do more than mention. One is the cause of the curious shedding on reaching maturity of the feathers of its face, and another the burning question whether Rooks are on the whole beneficial or detrimental to agriculture. In England the former opinion seems to be generally entertained, but in Scotland the latter has long been popular. The absence of suffi- cient observations made by persons at once competent and without bias compels the naturalist to withhold his judgment on the matter, but the absence of such observations is eminently discreditable to the numerous Agricultural Societies of the United Kingdom. (A. x. ) ROOKE, SIR GEORGE {(1650-1709), naval commander, was born near Canterbury in 1650. Entering the navy as a volunteer, he became post-captain in 1680, and vice- admiral in 1692. In May of this year he greatly dis- tinguished himself in a night attack on the French fleet off Cape La Hogue, when he succeeded in burning six of their ships. Shortly afterwards he received the honour of knighthood and a reward of 1000. In 1702 he com- manded the expedition against Cadiz, and on the passage home captured the Plate fleet off Vigo. Along with Sir Cloudesley Shovel he took part in the capture of Gibraltar, 21st July 1704. On 13th August of the same year he attacked the French fleet off Malaga, the battle being drawn. On account of the dissatisfaction expressed indirectly at the result of the contest, he retired from tlie service in February 1705. He died 24th January 1709. See The Life and Glorious Actions of Sir George Eooke, 1707. 1 It is right to mention that the Canon considers the Rook of Palestine entitled to specific distinction as Corvus agricola (Proc. Zool. Society, 1864, p. 444 ; Ibis, 1866, pp. 68, 69). In like manner the Rook of China has been described as forming a distinct species, under the name of C. pastinator (Proc. ZooL Society, 1845, p. 1), from having the feathers of its face only partially deciduous. ROPE. All varieties of cordage having a circumference of an inch or more are known by the general name of rope. Twisted cordages of smaller dimensions are called cords, twines, and lines, and when the dimensions are still smaller the article becomes thread or doubled yarn. All these varieties of cordage are composed of at least two, and in most cases of very many separate yarns, which are textile fibres drawn out and twisted into a uniform compact line. From thread and fine twine upwards the whole art of manufacture is simply that of twisting together fibres and yarns, but the comparative heaviness and coarse- ness of the materials operated on in rope-making render necessary the adoption of strong machinery and modified processes which clearly define this manufacture as a distinct calling. The modern trade of rope-making is again divided into two branches dealing respectively with certain vegetable fibres and with metallic wire. Silk cords and hair lines and ropes do not come within the scope of rope-making proper. Vegetable fibres fit for rope-making are numerous, but ordinarily not many are employed. Speaking generally, for the prime requisites of strength, suppleness, flexi- bility, and durability, none can'compete with the common HEMP (q.v.), which consequently is the staple of the rope- maker. MANILA HEMP (q.v.) is a fibre of the most remarkable tenacity, of unapproached value for heavy cordage, but too stiff and woody for small cords and twines. After these in utility come sisal hemp of South America (Agave sisalana), phormium hemp of New Zealand (Phormium tenax, see vol. xviii. p. 812), and the sunn hemp of the East Indies (Crotalaria juncea, see vol. xi. p. 647) all fibres of great strength, and largely used by rope- makers. Among fibres more rarely seen in rope-works are Jubbulpore hemp (Crotalaria tenuifolia), bowstring hemp (Sanseviera zeylanica), and other "hemps" of the East Indies, and plantain fibre (Musa paradisica) and agave fibre (Agave americana) of America. Ropes and twine of cotton are extensively made, especially for driving-bands for machinery. JUTE (q.v.) is now in considerable use by rope-makers, on account of its cheapness, but it is very deficient in strength and durability. COIR (see vol. vi. p. 917) is also largely employed, and many other fibres are used, principally in the localities of their production. A rope is composed of a certain number of " strands," the strand being itself made up of many "yarns." Three strands laid or twisted together form a "hawser- laid" rope, and three such hawsers similarly laid make a " cable-laid rope " or " cable. " A " shroud-laid " rope consists of four strands laid around a central strand or core. The prepared fibre is twisted or spun to the right hand to form yarn ; the required number of yarns receive a left hand twist to make a strand ; three strands twisted to the right make a hawser ; and three hawsers twisted to the left yield a cable. Thus the twist in each successive operation is in a different direction from the preceding, and this alternation of direction serves to some extent to preserve the parallelism of the fibres. The primary object of twisting fibres together in a rope is that by mutual friction they may be held together when a strain is applied to the whole. Hard twisting has the further advantage of compacting the fibres and pre- venting the penetration of moisture when the ropes are exposed to water. The proper degree of twist is a matter of considerable importance, as all twisting injuri- ously affects the strength of the individual fibres, and indeed it is possible to twist a cord so hard that it will break under the action. The degree of twist given to ropes is generally such that the rope is from three- fourths to two-thirds the length of the yarn composing it, and the lighter the twist the greater in proportion is