remote. The former are therefore retarded by the latter, while the latter are accelerated by the former. There is thus one particle which will be accelerated and retarded to an equal amount, and which will therefore move as if it were a simple pendulum unconnected with the rest of the body. The point in the body occupied by this particle is called the centre of oscillation.

As all the particles of the body are rigidly connected, they all vibrate in the same time. Hence it follows that the time of vibration of the rigid body will be the same as that of a simple pendulum, called the equivalent or isochronous simple pendu. lum, whose length is equal to the distance between the centres of suspension and oscillation.

The determination of the centre of oscillation of a body requires the aid of the calculus. It may be stated, however, that it is always farther from the axis of suspension than the centre of inertia, and is always in the line joining the centres of suspension and oscillation. Let A be the centre of suspension, B the centre of inertia, and C the centre of oscillation, and let AB be equal to h, and be the radius of gyration of the body about an axis through B parallel to the fixed axis, then it is easily shown that

A

B

Fig. 3. From this there follows the important proposition that the centres of oscillation and suspension are convertible, a proposition which was taken advantage of by Kater for the practical determination of the force of gravity at any station.

CENTRE OF PERCUSSION.-If a body receive a blow which makes it begin to rotate about a fixed axis without causing any pressure on the axis, the point in which the direction of the blow intersects the plane in which the fixed axis and the centre of inertia lie is called the centre of percussion. That such a point must exist is easily shown by suspending a straight rod by a long string attached to one end, and striking it with a hammer in different points. If the rod is struck near the top the foot will move in one direction, and if the blow be applied near the foot the top will move in the opposite direction. It is thus evident that there must be some point which does not move at all at the instant of the blow. If a line through this point be regarded as an axis of rotation, the point at which the body was struck is the centre of percussion, since no pressure is roduced on the axis. It is easily proved by means of higher mathematics that the centre of percussion with respect to any axis is the same point as the centre of oscillation.

From what has been said it is obvious that in order that no jar may be felt on the hand a cricket ball must be lit in the centre of percussion of the bat with respect to an axis through the hand.

There are, it may be mentioned, many positions which the axis may have in which there will be no centre of percussion. For example, there is no centre of percussion when the axis is a principal axis through the centre of inertia.

CENTRE OF PRESSURE.-When a plane surface is immersed in a fluid at rest, and held in any position, the pressures at different points of the surface are perpendicular to the surface. These pressures may therefore be looked upon as constituting a system of parallel forces whose resultant is the whole pressure. The point at which this resultant acts is called the centre of pressure, and may be defined as the point at which the direction of the single force which is equivalent to the fluid pressures on the plane surface meets the surface. The resultant action of fluids on a curved surface is not always reducible to a single force. The defini

67

tion given above is, therefore, limited to plane surfaces. In the case of a heavy fluid it is clear that the centre of pressure of a horizontal area corresponds with the centre of gravity. When, however, the plane is inclined at any angle to the surface of the fluid, the pressure is not the same at all points, being greater as the depth increases; since in the same liquid the pressure varies with the depth. In general, the centre of pressure will be below the centre of gravity. The determination of the centre of pressure requires the use of the integral calculus, but special cases may be treated by ordinary algebra. In the case of a parallelogram, one edge of which is in the surface of the fluid, the centre of pressure is at a distance of one-third up the middle line from the base. In the case of a triangle, having one side in the surface of the fluid, the centre of pressure is at the middle point of the median corresponding to the vertex immersed; while in the case of a triangle, with its apex in the surface, and the base horizontal, the centre of pressure is on the median corresponding to the vertex and at a distance of three-fourths of the median from the vertex.

CENTRE OF BUOYANCY.-The pressures which act on every point of a surface immersed in a fluid can be resolved into horizontal and vertical components. The former balance one another. The resultant pressure must therefore be vertical; and, as the pressure increases with the depth, it is clear that the upward pressures must be greater than the downward. Hence the resultant pressure on an immersed body must be a force acting vertically upwards. Now it is easily shown that the magnitude of this pressure is equal to the weight of the fluid displaced. The point in the displaced fluid at which the resultant vertical pressure may be supposed to act is called the centre of buoyancy, or centre of displacement. Hence, we see that when a body floats in a fluid, it is kept at rest by two forces, the weight of the body acting downwards through its centre of gravity, and the weight of the fluid acting vertically upwards through its centre of gravity, or centre of buoyancy. The relative positions of the centre of gravity and the centre of buoyancy have an important bearing on the safety of ships at sea. If the centre of buoyancy be above the centre of gravity, the equilibrium is stable; in other words, if the ship is displaced, it will tend to return to its original position. If, on the other hand, the centre of buoyancy be below the centre of gravity, the equilibrium will generally be unstable, although a body may float in stable equilibrium even if the centre of buoyancy be below the centre of gravity, as is explained in the article HYDROSTATICS.

CENTRAL FORCES.-Central forces are forces whose action is to cause a moving body to tend towards a fixed point called the centre of force. By Newton's first law of motion we know that

every body continues in its state of rest or of uniform motion in a straight line, except in so far as it is compelled by forces to change that state.' From this we learn that, if the speed of a body changes, or if the line of motion be not straight, whether the speed be unaltered or not, some force must be acting. In the latter case the forces acting are called central forces. The doctrine of central forces considers the paths which bodies will describe round centres of force, and the varying velocity with which they will pass along these paths. It investigates the law of the force in order that a given curve may be described, and many other problems which can only be solved by mathematical methods. Gravity affords the simplest illustration of a central force. If a stone be slung from a string, gravity deflects it from the rectilinear path which it would otherwise pursue, and makes it move in a

curve called a parabola. Again, the moon is held in her orbit round the earth by the action of gravity, which is constantly preventing her from going off in the line of the tangent to her path at any instant.

In connection with this subject we have to make some remarks on what is called centrifugal force. We have seen that force must always be applied to make a body move in a curved path. Such a force is called a centrifugal force, the old erroneous notion being that bodies have a tendency to fly outwards from the centre about which they are revolving. The use of the term will, however, cause no inconvenience, provided we interpret it merely as indicating that, to keep a body moving in a curve instead of in its natural straight line, a force directed towards the centre of curvature is always required.

As a

Many familiar illustrations of the action of the so-called centrifugal force will occur to the reader. A ball fastened to the end of a string, and whirled round, will, if the motion is sufficiently rapid, et last break the string, and fly off in a tangential path. This is due to the fact that the cohesion of the particles of the string are no longer able to supply the force necessary to keep the ball moving in its circular path. For a similar reason a flywheel or a grindstone bursts when it is made to rotate too rapidly. It is found that at a curve on a railway it is the outer of the two rails which is most worn. This is due to the fact that the outer rail has to supply the force necessary to keep the trains moving in curved paths. A glass of water may be whirled so rapidly that, even when the mouth is downwards, the excess of the centrifugal force over the weight of the water is sufficient to prevent the water from falling out. The centrifugal force increases with the velocity. matter of fact, it can be shown that when a body moves in a circle of radius r, with velocity v, its centrifugal force is By means of this formula it can be proved that about th of its weight is required merely to keep a body on the earth's surface at the equator. By this amount the weight of a body is diminished. Now 289 is equal to 17o. Hence it follows that if the earth were to rotate seventeen times as fast as it does now, the attraction of gravitation would only just be able at the equator to keep bodies from flying off its surface. If the rotating body be plastic, it will swell out in all directions perpendicular to the axis of rotation, and assume the form of an oblate spheroid. For the same reason the earth itself has assumed the form of an oblate spheroid, a result which is seen on a greater scale in the case of Jupiter and Saturn on account of their larger size and more rapid rotation.

mv.

r

CEPHALASPIS

Centurion (Lat. centurio, from centum, 'a hundred'), a Roman officer commanding a century or company of foot-soldiers. There were sixty centurions in a Legion (q.v.).

Ceorl, a word which occurs frequently in the laws before the Norman Conquest under somewhat varying senses, but substantially meaning an ordinary freeman not of noble birth. His position gradually sank in social status until it hardly differed from that of the serf, save that the ceorl had the right of choosing his own master in accordance with the law of Athelstan, which required every landless man to find himself a lord. He still remained law-worthy,' and paid his wer-gild of two hundred shillings; but part of his freedom had disappeared, and ultimately his condition developed into the complete villenage characteristic of feudalism. On the other hand, ceorls who possessed land often contrived to force their way into a higher social class, that of the thegns, a kind of nobility of service who may be roughly put as equivalent to the knights of the period after the Conquest. A ceorl with 5 hides (600 acres) of land was 'thegnworthy.' The name ceorl does not occur in Domesday-the very degradation of the meaning of the word churl in modern usage is but a part of the historical degradation of the social class which it denoted.

Centre-board. See YACHT, Vol. X. p. 770. Centrifugal and Centri'petal are terms used in Botany to designate two different kinds of leaf development or inflorescence, the former term being applied when the development proceeds from the apex towards the base of the axis or leaf, and the latter when it is from the base upwards towards the apex. See LEAF, INFLORESCENCE. Centrifugal Force. See CENTRE. Centripetal Force. See CENTRE. Centum'viri (‘a hundred men'), a college of justice in ancient Rome, which had jurisdiction in civil cases. It has been supposed that the body was originally made up of three delegates from each of the thirty-five tribes. There were 180 members in the time of Augustus, and under the emperors it increased in importance, as it became the only scene left for the display of judicial eloquence and of legal knowledge.

The central

Ceos (sometimes called by the Italianised name of Zea or Tzia), one of the Cyclades, in the Ægean It is 13 miles Sea, 14 miles off the Attic coast. long, 8 broad, and 39 sq. m. in area. and culminating point is Mount Elias, 1863 feet high. It is fairly fertile, raising fruit, wine, honey, and valonia. The population is 4311, of whom 4295 In ancient belong to the capital, Zea or Ceos. times Ceos was noted as the birthplace of the poets Simonides and Bacchylides, and the physician Erasistratus; and the Cean laws were famous for

their excellence.

Cephalaspis, a genus of fossil Ganoid fishes, of which six species have been described, two belonging to the Upper Silurian, and four to the Devonian measures. The head was protected by a large ganoid plate, sculptured externally with circular radiating markings. The shield was produced into a horn at each posterior corner, and bore a median and posterior dorsal spine. Agassiz gave the name cephalaspis ('buckler-headed') from this extraordinary covering, which has very much the appearance of, and was formerly supposed to be, the cephalic shield of an Asaphus or Trilobite. The body was covered with rhomboidal enamelled scales, and furnished with dorsal and pectoral fins : it terminated in a large unsymmetrical tail. In a graphic description of this fossil in his Old Red Sandstone, Miller thus sketches the general appearance of the animal: Has the reader ever seen a saddler's cutting-knife-a tool with a crescentshaped blade, and the handle fixed transversely in the centre of its concave side? In general outline, the cephalaspis resembles this tool; the crescentshaped blade representing the head, the transverse cartilaginous, retaining the notochord through life. handle the body.' The endo-skeleton was mainly The flexible body, assisted by the large tail and the fins, would give the cephalaspis the power of moving rapidly through the water. Being a predaceous fish, it must have been a formidable enemy to its associates in the Paleozoic seas, for, besides its power of rapid motion, the sharp margin of its shield probably did the work of a vigorously hurled javelin, as in the sword-fish. Pteraspis, Asterolepis (20 to 30 feet in length), Scaphaspis, Auchenaspis, and a number of other genera, are united in the same family as Cephalaspis. See Ray Lankester, A Monograph of the Fishes of the Old Red Sand

CEPHALODISCUS

stone in Britain, part i. Cephalaspida' (Lond. 1868-70); R. H. Traquair, The Ganoids of the British Carboniferous System (Palæont. Society, Lond. 1877).

Cephalodiscus, one of the most curious and interesting organisms dredged by the Challenger expedition. It was found in the Strait of Magellan, was first supposed to be a compound Ascidian, was monographed (1887) by Professor M'Intosh as one of the Polyzoa (section Aspidophora), but is regarded by Mr Harmer as closely allied to that marvellous vertebrate-like worm, Balanoglossus (q.v.). The organisms form a spreading seaweed-like brownish colony, measuring in some cases 9 inches by 6, and including a great number of little individuals, protected by a membranous, flexible investment or house. Each individual resembles Balanoglossus (and also in part backboned animals) in many important points, such as (a) the presence of gill-slits; (b) the existence of a notochord as a dorsal outgrowth from the gut, growing forwards into the anterior region or proboscis; and (c) the possession of a dorsal central nervous system, most richly developed in the middle region (or collar), but extending on to the proboscis. As another apparent connecting link between invertebrates and vertebrates, Cephalodiscus is of the greatest zoological interest. See zoology of the voyage of

Cephalodiscus.

H.M.S. Challenger, Part lxii.; Report on Cephalodiscus, by Professor W. C. M'Intosh and Mr S. F. Harmer.

Cephalonia (anc. Cephallenia; Homeric Same), the largest of the seven Ionian Islands (q.v.), lies opposite the entrance of the Gulf of Lepanto or Corinth. It is irregular in shape, with a maximum length of 30 miles, and an area of 302 sq. m.; pop. 80,178. The surface is mountainous, in one point attaining 5310 feet; the soil for the most part thin, and water scarce. The inhabitants, however, have planted vineyards wherever the grape will grow, and currants and olive-oil are also produced for export. The capital is Argostoli (q.v.).

Cephalo poda (Gr., 'head-footed'), the highest class of molluscs, and in some respects the highest invertebrates. They are usually large animals, exclusively marine, with well-developed headregion, but (as the quaint name suggests) with the 'foot' or ventral surface grown round the mouth, and split up into arms, which (with one exception) bear suckers. Another part of the foot is

mantle-cavity. While the ancient forms lived in shells, the Pearly Nautilus alone remains in this state, the shell being in all other cases internal and degenerate. The eyes are peculiarly large, and their ferocious aspect has earned for many common forms the title of 'devil-fish.' The mouth in the midst of the arms' is equipped with parrot-like teeth, and with a rasping ribbon on the tongue. The central nervous system, with its closely associated ganglia, is surrounded by a protective cartilaginous sheath, analogous, though in no way homologous, with a vertebrate brain-box. The sexes are separate. The structure and life of these animals is discussed under the more familiar title CUTTLEFISH; only the general characters, classification, and distribution are here noticed.

Classification.-The Cephalopoda include two distinct orders, one represented by the Pearly Nautilus, the other by all the other living forms, which are again divided into Octopoda and Decapoda, according to the number of the arms.'

Distribution. Most species occur in warm and temperate seas, but those found in the colder waters seem much more prolific. The Tetrabranchiata are the older forms, and begin in the Silurian, whereas the Dibranchiata first appear in Triassic times. The Ammonites (q.v.) are the most familiar representatives of the former, the Belemnites (q.v.) of the latter.

AMMONITES; also CALAMARY, OCTOPUS, SEPIA; Owen, See especially CUTTLEFISH, NAUTILUS, BELEMNITES, Memoir of the Pearly Nautilus (1832); Férussac and D'Orbigny, Histoire naturelle des Céphalopodes (2 vols. Paris, 1835-48); Hoyle, Challenger Report on Cephalopoda.

Cephaloptera, a name formerly used for a genus of rays. See RAY.

Cephissus, one of the two rivers which water the Athenian plain. It rises on the western slope of Mount Pentelicus and the southern side of Mount Parnes, and flows past Athens on the west into the Saronic Gulf near Phalerum.

Cepola. See BANDFISH.

Ceram' (SERANG), the largest island of the southern Moluccas, lies NE. of Amboyna, to which Dutch residency it belongs, and is divided into Great and Little Ceram by the Isthmus of Taruno. Area, 6605 sq. m.; pop. 195,000. The island is one of the least explored in the archipelago, and comparatively little is known of the interior, which is, moreover, but scantily populated, the great mass of the people, mostly native Alfuros and immigrant Malays, inhabiting the coast villages. Much of the island is very fertile. A mountain-chain runs through the country, reaching in Nusa Keli some 11,000 feet. The chief exports are sago, iron, timber, earthenware, birds of Paradise, dried fish, edible nests, &c.

Ceramics (Gr. keramos, potter's clay'), a term used to designate the department of plastic art which comprises all objects made of clay, such as vases, cups, bassi-rilievi, cornices, and the like. See POTTERY.

Cerastes, or HORNED VIPER, a genus of serpents of the family Viperidæ, distinguished by a broad depressed heart-shaped head, the scales of which are similar to those of the back, and particularly remarkable for the development of one of the scales of each eyelid into a spine or horn, often of considerable length. The tail is very distinct

Horned Viper (Cerastes vulgaris).

from the body. This genus is exclusively African, and very venomous. There is probably only one species, Cerastes ægyptiacus or cornutus, the Horned Viper of the north of Africa, called Cerastes by the ancients, the name being derived from the Greek keras, a horn.' It was correctly described by the traveller Bruce, but his description was for some time regarded with incredulity.

Cerate (Lat. cera, wax'), a compound of wax with other oily and medicinal substances in such proportions as to have the consistence of an ointment (see OINTMENTS). Simple cerate is made by melting together 6 parts of olive-oil, 3 of white wax, and 1 of spermaceti.

Ceratites, a genus of Ammonites (q.v.) peculiar to, and characteristic of, the Trias.

Cerat'odus, the Queensland mud-fish, one of

the remarkable sub-class of double breathers or Dipnoi. The name was originally used for the fossil possessors of certain tooth-plates found in the

Ceratodus.

Triassic and Jurassic strata, and to this genus the Queensland survivor, which has similar dental arrangements, was referred when discovered in 1870. Barra munda is the local name. The fish may occasionally attain a length of six feet, has a later

CEREALIA

ally compressed body with large scales, and possesses very unfish-like limbs with a central jointed axis and lateral pieces. It lives in muddy water often containing much decaying vegetable matter. In this medium it does not find the gill-respiration sufficient, and comes to the surface to take gulps of air into the swimming-bladder, which functions as a lung. It eats leaves and other parts of plants. At nights Ceratodus sometimes leaves the water, and moves along the river-bank. The expulsion of air from its air-bladder or lung is supposed to account for a grunting noise then often heard. In the dry season it buries itself in the mud.

Limb of Ceratodus.

The flesh is much esteemed, and compared with salmon. This interesting animal is discussed, in its more technical relations, along with its neighbour genera-Lepidosiren and Protopterus-under the title MUD-FISHES.

Ceratonia. See CAROB.

Cerberus, in Greek Mythology, the many. headed dog-according to Hesiod, the offspring of Typhaon and Echidna-who guarded the portal of the infernal regions. Later writers describe him as only three-headed, with the tail and mane composed of serpents, though the poets sometimes encumber him with a hundred heads. Orpheus charmed him by the magic of his lyre, and Hercules overcame him by strength and dragged him to the upper

world.

Cerca'ria, the technical name applied to an suckered flat parasitic worms (the Distomes embryonic form of many flukes. In all the twodivision of Trematodes) the development is indirect or circuitous.

which, instead of growing into adults, produce The eggs develop into embryos, asexually one or more sets of intermediate forms. The final form, produced more or less directly from the embryo, is called a cercaria, and grows up into the adult fluke. It differs from the adult in having only rudiments of reproductive organs, in possessing eye-spots, and in being (except in one genus) equipped with a very movable tail. It is (1) born within some host, such as a water-snail; (2) leaves this and swims freely in the water; (3) becomes sluggish, and enters a second host, or fixes itself on some foreign body. In this state it loses its tail and encapsules itself, and does not experience any further change till (4) it or its host is eaten by a vertebrate, within which the cercaria becomes an adult and sexual fluke. From the latter the embryos which eventually enter the first-mentioned host arise. Sometimes the life-history is simpler, but in all cases the cercaria is the form produced (generally indirectly) by the original embryo, and developing into the adult. See FLUKE.

Cercis. See JUDAS' TREE.

Cercopithe'cus (Gr., ' tail-ape '), a genus of monkeys. See MONKEY.

Cere (in natural history). See BILL.

Cerea'lia, or CEREAL GRASSES, so named from Ceres (q.v.), are the plants which produce grain or corn; in strictness, all the species of grasses (Gramineae) cultivated for the sake of their seed as an article of food. They are also called Corn-plants or Bread-plants; but in this wide

CEREBRATION

popular sense the term cereal ceases to have any botanical limits, and includes plants of wholly distinct orders, notably Buckwheat (natural order, Polygonacea), and Quinoa (Chenopodiacee), &c.; even the Lotus of the Nile, the Victoria regia, and other species of water-lilies might thus be added to the list.

The cereals proper do not belong to any particular tribe of the great order of grasses, but the employ. ment of particular species as bread-plants seems to have been determined chiefly by the superior size of the seed, or by the facility of procuring it in sufficient quantity, and of freeing it from its unedible envelopes. The most extensively cultivated grains are Wheat (Triticum), Barley (Hordeum), Rye (Secale), Oats (Avena), Rice (Oryza), Maize or Indian Corn (Zea), different kinds of Millet (Setaria, Panicum, Paspalum, Pennisetum, and Penicillaria), and Durra or Guinea Corn (Sorghum or Andropogon). These have all been cultivated from time immemorial, and there is great uncertainty as to the number of species to which the many existing varieties belong; their original forms and native countries often cannot confidently be determined. Barley, oats, and rye are the grains of the coldest regions, the cultivation of the former two extending even within the arctic circle. Wheat is next to these, and in the warmer regions of the temperate zone its cultivation is associated with that of maize and rice, which are extensively culti vated within the tropics. The millets belong to warm climates, and durra is tropical or sub-tropical. Rice is the food of a greater number of the human race than any other kind of grain. See CORN, BARLEY, MAIZE, MILLET, RICE, WHEAT, and other separate articles.

Cerebration, UNCONSCIOUS. There can be no doubt that molecular changes in the cerebrum accompany all our conscious mental processes. The doctrine of unconscious cerebration as stated by Carpenter, Laycock, and others, holds that similar changes may go on in the cerebrum without any consciousness on our part, until the fully elaborated mental result is presented. It is an every-day experience that after one has been in vain trying to recall some name or incident, it will suddenly flash into the mind when one is thinking of some entirely different subject. According to Carpenter the cere brum put in action by our consciousness has gone on working automatically but unconsciously, until the processes accompanying the mental operation of remembering the name or incident have been completed. This is the physiological statement corresponding to the psychological doctrine that the mind may undergo modifications without being conscious of the process until the new combination 1s presented to consciousness. See CONSCIOUSNESS, BRAIN, PSYCHOLOGY, PERSONALITY.

Cerebro-spinal Fluid is a clear, almost colourless, slightly alkaline fluid, closely resembling lymph in its composition, but containing less albumen. It is contained partly within the ventricular system of the brain, and in part in the loose connective tissue (subarachnoid meshwork), which lies between the Arachnoid and Pia Mater (q.v.), being continued from this latter situation along the lymphatic sheaths, which closely invest all the blood-vessels in the substance of the brain and spinal cord. The spaces which contain it comrounicate with the lymphatics of the head and of the nerves, and with the venous sinuses in the dura mater. Its main function, besides that of removing waste products, is to equalise the pressure within the skull. As the blood pressure increases that of the cerebro-spinal fluid diminishes, and vice cers. As the brain atrophies it is replaced by a proportionate increase in the fluid. In some dis

eases, such as acute and chronic Hydrocephalus (q.v.), it is greatly increased, and then it becomes a cause of atrophy of the brain. Its value as a water-cushion in diminishing the violence of shock from external injury has been already referred to at BRAIN. Cerebro-spinal means pertaining to the brain and spinal cord together, to the cerebrospinal system. For Cerebro-spinal Meningitis, see MENINGITIS.

Cerebrum. See BRAIN.

Ceremonies, MASTER OF THE, an officer at ambassadors and dignitaries. The same name came court, instituted by James I. for the reception of to be used for the supreme authority on etiquette at public assemblies at Bath and elsewhere; Beau Nash (q.v.) being the most memorable.

Cereopsis (Gr., 'wax-face'), a genus of birds of the family Anatidae, to which the New Holland goose (C. nove hollandia) belongs. This bird has been known since the southern shores of Australia were first visited by navigators. There, and on the adjacent islands, they were found in great abundance; and so little were they acquainted with the danger to be apprehended from man, that the earlier navigators easily supplied themselves with fresh provisions by knocking them down with sticks. The flight is slow and heavy, and the bird is naturally becoming less abundant. The cere (see BILL) is remarkably large, whence the name.

Ceres, the Roman name of the great Greek goddess Demeter, the protectress of agriculture and the fruits of the earth. Her worship was borrowed by the Romans from Sicily. Her first temple in Rome was vowed by the dictator A. Postumius Albinus (496 B.C.), to avert a famine with which the city was threatened. A great festival, with games, the Cerealia, was instituted in her honour, and her worship acquired great importance in the in her temple for the inspection of the tribunes The decrees of the senate were deposited city. of the people. See DEMETER.

Ceres, one of the Planetoids (q.v.), and the first of them that was discovered. It was first seen by Piazzi at Palermo, January 1, 1801, and is sometimes visible to the naked eye, looking like a star between the seventh and eighth magnitudes.

Cereus, a large genus of Cactaceae (q.v.), containing many of the most imposing forms of the order, both as respects vegetation and flowering. C. giganteus reaches a height of 60 feet, often unbranched, its tall pillars giving an extraordinary character to the landscape of New Mexico, while the allied C. peruvianus (36 feet) takes its place in Peru. Others have thin snake-like branches (C. flagelliformis), while the short obconical C. senilis is covered with long silky hairs. Many have splendid flowers, and of these C. speciosissimus with scarlet or purplish flowers is often cultivated, while C. grandiflorus is the well-known night-flowering cactus. The fruits are often much esteemed. For illustration, see CACTUS.

Cerignola, a town of Italy, 22 miles SE. of Foggia by rail, with manufactures of linen, and a trade in almonds and cotton. The Spaniards' decisive victory over the French here in 1503 established Spain's supremacy in Naples. Pop. 22,659.

Ceri'go, the southernmost of the seven Ionian Islands (q.v.), now officially known again by its old Greek name of Cythera, is separated from the coast of Morea by a narrow strait. Area, 107 sq. m.; pop. (1879) 13,259. It is mostly barren and mountainous in some parts; but corn, wine, and olives and fruits are raised. Capsali is the capital. In ancient times the island was sacred to Venus, as the land that received the goddess when she arose from the sea.