Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/335

Rh R E D R E D 317 to within 200 fathoms of the surface in a channel that has a much smaller average depth and is only 13^ miles wide. As no rivers discharge into it and little rain falls, it must be viewed as a purely evaporational area, and as such it is of extreme scientific interest. It reproduces and exaggerates all the special physical conditions of the Mediterranean ; but on account of the extremely, trying nature of the climate it has not been so thoroughly investigated. The average amount of evaporation at Aden is variously estimated at from Q- 25 to 0'75 inch per day, or from 8 to 23 feet per year ; in the Red Sea generally it must be at least equal to the smaller figure, and probably exceeds it. As the level of the Red Sea is not sub- ject to any permanent change it is evident that water must flow in through the Strait of Bab-el-Mandcb the slight current through the Suez Canal need not be considered to replace loss by evapora- tion. If there were no return current it is estimated that the Red Sea would become a mass of solid salt in one or two thousand years. Although the salinity of the water is higher than that of the water of the ocean it does not appear to be on the increase. The density of Red Sea water at 60 Fahr. is about 1'030, corre- sponding to 4'0 per cent, of total salts, while that of average ocean water is 1'026, which corresponds to 3'5 per cent, of salts. _ In order to account for the constancy of salinity in the Red Sea it is necessary to assume the existence of strong undercurrents of salt water passing out of the sea, beneath the opposite entering current of fresher water. These undercurrents have not yet been ob- served, but there are indirect proofs of their existence. During the hottest months (July to September), when there is most eva- poration, the prevalence of northerly winds drives the water out of the Red Sea as a rapid surface-drift ; the south-west monsoon is blowing in the Indian Ocean at the same time, and the general level in the Red Sea is from 2 to 3 feet higher than during the cooler months, when evaporation is less, and when the north-east monsoon forces water into the funnel-shaped Gulf of Aden, and thence through the Strait of Bab-el-Mandeb. This is held by Dr W. B. Carpenter to be a proof of the existence of an undercurrent, for the north-east wind forms a head of water at the strait, which to equalize pressure over the area produces an under-return-current, and this greatly accelerates the flow of the regular undercurrent of the Red Sea, and so lowers the general level. In summer the outflow of dense salt water is slower, and this more than neutralizes the effect of the outward surface-drift, which to some extent reduces the volume of the entering fresher water at that season. In the Red Sea there is a constant and regular sub-surface circulation of water due solely to evaporation ; the surface-drifts caused by wind, although they form rapid currents and render navigation dangerous at times, are minor agents in the system and modify it only to a slight extent. The Red Sea and the Persian Gulf serve as concen- tration areas for maintaining the salinity of the deep water in the Indian Ocean, in opposition to the currents of comparatively fresh water flowing northwards from the Antarctic Ocean. Deposits. In a sea so nearly landlocked and so narrow the deposits which cover the bottom are naturally of the order classed as terrigenous. The large quantity of sand blown into the sea, the immense abundance of corals and other calcareous organisms in the water, and the entire absence of rivers with their suspended sediments produce deposits more nearly resembling in some of their characteristics those of the open ocean than those of inland seas. But the sand and ooze from the bottom of the Red Sea have not yet been thoroughly examined. Fauna. Animal life in all its forms is extremely abundant in the Red Sea, which, however, cannot be said to have been any more completely surveyed from a biological than from a physical point of view, although several eminent zoologists have studied special types. Great numbers of new species have been discovered by each investigator, and it has been ascertained that the Red Sea fauna differs considerably from that of the Mediterranean, not more than twenty species being common, it is stated, to both, thus indicating that the separation of the two seas must have taken place at a remote epoch, which appears from geological evi- dence to be the Eocene period. It exhibits affinities with the fauna of the Pacific, particularly with that of the coast of Japan. Corals are more plentiful and more active in the Red Sea than in almost any other piece of water of its size, a result probably due equally to the high temperature, the great salinity of the water, and the abundance of food. (H. E. M.) REDSHANK, the usual name of a bird the Scolopcu calidris of Linnaeus and Totanus calidris of modern authors so called in English from the colour of the bare part of its legs, which, being also long, are conspicuous as it flies over its marshy haunts or runs nimbly beside the waters it affects. In suitable localities it is abundant throughout the greater part of Europe and Asia, from Iceland to China, mostly retiring to the southward for the winter, though a considerable number remain during that season along the coasts and estuaries of some of the more northern countries. Before the great changes effected by drainage in England it was a common species in many districts, but at the present day there are very few to which it can resort for the purpose of reproduction. In such of them as remain, its lively actions, both on the ground and in the air, as well as its loud notes render the Redshank, during the breeding-season, one of the most observable inhabitants of what without its presence would often be a desolate spot, and invest it with a charm for the lover of wild nature. At other times the cries of this bird may be thought too shrill, but in spring the love-notes of the male form what may fairly be called a song, the constantly repeated refrain of which hero, leero, hero (for so it may be syllabled) rings musically around, as with many gesticulations he hovers in attendance on the flight of his mate ; or, with a slight change to a different key, engages with a rival ; or again, half angrily and half piteously complains of a human intruder on his chosen ground. The body of the Redshank is almost as big as a Snipe's, but its longer neck, wings, and legs make it appear a much larger bird. Above, the general colour is greyish -drab, freckled with black, except the lower part of the back and a conspicuous band on each wing, which are white, while the flight-quills are black, thus producing a very harmonious effect. In the breeding-season the back and breast are mottled with dark brown, but in winter the latter is white. The nest is generally concealed in a tuft of rushes or grass, a little removed from the wettest parts of the swamp whence the bird gets its sustenance, and contains four eggs, usually of a rather warmly tinted brown with blackish spots or blotches; but no brief description can be given that would point out their differences from the eggs of other birds, more or less akin, among which, those of the LAPWING (vol. xiv. p. 308) especially, they are taken and find a ready sale. The name Redshank, prefixed by some epithet as Black, Dusky, or Spotted, has also been applied to a larger but allied species t&Totamis fuscus of ornithologists. This is a much less common bird, and in Great Britain as well as the greater part of Europe it only occurs on its passage to or from its breeding-grounds, which are usually found south of the Arctic Circle, and differ much from those of its congeners the spot chosen for the nest being nearly always in the midst of forests and, though not in the thickest part of them, often with trees on all sides, generally where a fire has cleared the undergrowth, and mostly at some distance from water. This peculiar habit was first ascertained by Wolley in Lapland in 1853 and the following year. The breeding-dress this bird assumes is also very remarkable, and seems (as is suggested) to have some correlation with the burnt and blackened surface interspersed with white stones or tufts of lichen on which its nest is made for the head, neck, shoulders, and lower parts are of a deep black, con- trasting vividly with the pure white of the back and rurnp, while the legs become of an intense crimson. At other times of the year the plumage is very similar to that of the common Redshank, and the legs are of the same light orange-red. (A. N.) REDSTART, a bird well known in Great Britain, in many parts of which it is called Firetail a name of al- most the same meaning, since " start " is from the Anglo- Saxon steort, a tail. 1 This beautiful bird, the Rutidlla phoenicurus of most ornithologists, returns to England about the middle or towards the end of April, and at once takes up its abode in gardens, orchards, and about old buildings, when its curious habit of flirting at nearly every change of position its brightly-coloured tail, together with the pure white forehead, the black throat, and bright bay breast of the cock, renders him conspicuous, even if attention be not drawn by his lively and pleasing though short and intermittent song. The hen is much more plainly attired ; but the characteristic colouring and action of the tail per- 1 On this point the articles " Stark -naked " and "Start" in Prof. Skeat's Etymological Dictionary may be usefully consulted ; but the connexion between these words would be still more evident had this bird's habit of quickly moving its tail been known to the learned author.