Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/556

 532 J A C J A C called the Horned Screamer, was at one time thought to be allied to this Family, but is now, by almost common consent, relegated to the neighbourhood of the Geese (A natidee), though forming a separate Family. (A. N.) JACINTH, a name given to the reddish-brown variety of zircon, known also as Hyacinth. The hyacinthus of ancient writers appears to have been our sapphire, or blue corundum, while the jacinth or hyacinth of modern mineralogists may have been the ancient lyncurium. The true jacinth is a silicate of zirconium, crystallizing in the dimetric or tetragonal system, and exhibiting strong double refraction. Its hardness is denoted by 7 5 ; that is to say, it is harder than quartz but not so hard as topaz. The most distinctive feature of the stone, serving to distinguish it from other minerals with which it is likely to be con founded such as garnet, topaz, and cairngorm is its high specific gravity ; this varies, however, in different varieties of zircon from 4 05 to 475. On ignition, most zircons increase in density without loss of weight ; but Professor Church has shown that the jacinth of Mudgee, when heated, remains practically unchanged in density, though it loses colour. It is only when the native silicate of zirconium pre sents a red colour that it is known as jacinth or hyacinth, those varieties which are of yellow brown and green colours being distinguished, if transparent, by the name of jargoon, while the dull-coloured varieties, more or less opaque, are termed simply zircon. The lustre of the zircon when polished is of the peculiarly brilliant character designated adamantine, and indeed some of the pale jargoons are often sold as inferior diamonds. The Singalese variety, found chiefly at Matura, has been termed &quot;Matura diamond.&quot; The true jacinth, or red zircon, is an extremely rare stone. Fine examples, however, have been found of late years as pebbles among the auriferous detritus at Mudgee in New South Wales. Small crystals occur in the river-sands of Expailly, Puy-en-Velay, France, but these are too small to be cut as ornamental stones. Most of the gems termed jacinth or hyacinth by jewellers belong to the deep orange-brown variety of garnet known to mineralogists as essonite or cinnamon stone : the lower specific gravity of the garnet serves to distinguish the false from the true jacinth. It is probable that many of the antique camei and intagli reputed to be jacinths are merely hyacinthine garnets. JACKAL (Canis aureus), a carnivorous mammal belong ing to the dog family (Canidx), and believed by many naturalists to be one of the species from which certain of the semi-domesticated dogs of Asia and North Africa have been derived. It is dog-like in external appearance, and there is, according to Geoffrey Saint Hilaire, no constant dif ference between its structure and that of the small canine races. It resembles them in dentition, in the roundness of its eye pupils, in its period of gestation, and to a large extent also in its habits, while like the dog it is subject to hydrophobia. It grows to a height of 15 inches at the shoulders, and to a length of about 2 feet, exclusive of its bushy fox-like tail. Its fur is of a greyish-yellow colour, darker on the back and lighter coloured beneath. An excrescence consisting of a horny cone, half an inch in length, and concealed by a tuft of hair, is, according to Emerson Tennent, sometimes found on the head of the jackal. The Singhalese aver that it is only found on the leader of the pack, and they esteem it as an invaluable talisman. Jackals, of which there are several well-marked varieties, are widely distributed throughout southern Asia and the north of Africa. They are nocturnal animals, concealing themselves until dusk in woody jungles and other natural lurking places, thereafter sallying forth in packs, which sometimes number two hundred individuals, and visiting farmyards, villages, and towns in search of food. This consists for the most part of the smaller mammals and poultry, although their association in packs enables them also to hunt down antelopes and sheep. When unable to obtain living prey, they feed upon carrion and refuse of all kinds, and are thus useful in removing putres- cent matter from the streets of Eastern towns. They are also fond of grapes and other fruits, and are thus the pests of the vineyard as well as the poultry-yard. The cry of the jackal has been described as even more appalling than that of the hyaena, a shriek from one member of a pack being the signal for a general chorus of screams, which is kept up during the greater part of the night. In India these animals are occasionally hunted with foxhounds Jackal. and greyhounds, and from their extreme cunning and pluck they are said to afford excellent sport. When brought to bay, they frequently turn upon their assailants and inflict severe wounds with their teeth ; at other times they have been known to feign death as a means of escape. Jackals are readily tamed; and domesticated individuals are said, when called by their masters, to wag their tails, crouch, and throw themselves on the ground, and otherwise behave in a dog-like fashion. The jackal, like the fox, has a peculiarly offensive odour, due to the secretion of a gland at the base of the tail, but in domesticated specimens this odour is much fainter than in the wild forms. JACKDAW, or simply DAW (Old Low German, Daha ; Dutch, Kaauw], the prefix being doubtless imitative of the bird s cry, as indeed is probably the substantive name 1 one of the smallest species of the genus Corvus (Cnow, vol. vi. p. 617), and a very well known inhabitant of Europe, the C. monedula of ornithologists. In some of its habits it much resembles its congener the ROOK (q.v.), with which it constantly associates during a great part of the year ; but, while the Rook only exceptionally places its nest elsewhere than on the boughs of trees and open to the sky, the Daw almost invariably chooses holes, whether in rocks, hollow trees, rabbit-burrows, or buildings. Nearly every church-tower and castle, ruined or not, is more or less numerously occupied by Daws, and if they are not 1 See Professor Skeat s Etymol. Dictionary, pp. 153, 304.